Extended Incubation Protocols for Slow-Growing Bacteria

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-27

Quick Answer

Incubation timelines for slow-growing bacteria typically extend from 7 to 28 days depending on the organism, specimen source, and culture system in use.
Select media and incubation conditions based on the suspected pathogen, then monitor cultures at defined intervals to detect growth before overgrowth or desiccation occurs.
Extended incubation requires strict moisture control and biosafety containment because slow-growing pathogens such as Brucella and Francisella present aerosol hazards.

Extended Incubation in Diagnostic Microbiology

Extended incubation protocols address a core problem in diagnostic microbiology: many clinically significant bacteria grow slowly or fail to grow under standard 24 to 48 hour incubation periods. Organisms such as Brucella species, Francisella tularensis, Mycobacterium species, and certain anaerobes require longer observation windows before a culture can be reported as negative. The laboratory professional must balance the need for prolonged observation against the risks of media desiccation, overgrowth by faster organisms, and the biosafety hazards posed by working with these pathogens.

This article provides a practical framework for designing, executing, and interpreting extended incubation protocols. It covers the scientific basis for prolonged culture, media selection, environmental controls, observation schedules, quality assurance, and the safety measures required when handling slow-growing pathogens. The guidance is intended for biology students, researchers, laboratory professionals, and life-science practitioners who need a defensible approach to recovering these organisms.

At a Glance

The table below summarizes common slow-growing bacteria, their typical incubation windows, and the media and conditions that support their recovery. These values represent general laboratory practice and should be adjusted based on the specific organism, specimen type, and the requirements of the laboratory's quality system.

Organism	Typical Incubation Window	Recommended Media	Key Observation Notes
Brucella species	7 to 21 days	Blood culture bottles, Brucella agar, trypticase soy agar with blood	Growth may be very faint, blind subculture at 7 and 14 days is common
Francisella tularensis	7 to 14 days	Cysteine-enriched media such as chocolate agar with IsoVitaleX or Thayer-Martin	Requires cysteine for growth, colonies are small and slow to appear
Mycobacterium species	2 to 8 weeks	Lowenstein-Jensen, Middlebrook 7H10 or 7H11 agar	Growth rate varies by species, some require CO2 enrichment
Anaerobic bacteria	5 to 14 days	Brucella blood agar with hemin and vitamin K, or other anaerobe media	Incubate in an anaerobic environment, check for desiccation
Legionella species	5 to 10 days	Buffered charcoal yeast extract agar	Requires L-cysteine and iron, growth appears as small colonies

Core Principles of Extended Incubation

Why Some Bacteria Grow Slowly

Bacteria grow at different rates based on their metabolic pathways, nutrient requirements, and environmental tolerances. Slow-growing organisms often have long generation times, meaning the time between cell divisions is extended. For example, Mycobacterium tuberculosis has a generation time of approximately 15 to 20 hours, whereas Escherichia coli can divide every 20 minutes under optimal conditions. This difference explains why mycobacterial cultures require weeks of incubation while routine enteric cultures are complete in 24 hours.

Other organisms grow slowly because they require specific nutrients that are not present in standard media. Francisella tularensis requires cysteine and iron for growth, and Legionella species require L-cysteine and iron as well. When these nutrients are absent or present in insufficient amounts, the organism grows poorly or not at all. The laboratory must select media that meet these nutritional needs.

The Role of Media in Extended Incubation

Media selection is the first decision in an extended incubation protocol. The medium must support the target organism while suppressing or limiting the growth of contaminants and normal flora. For slow-growing pathogens, the medium must also remain stable over the incubation period. Some media lose moisture, change pH, or degrade over time, which can affect the recovery of the target organism.

The American Type Culture Collection provides authenticated strains and detailed information about the growth requirements of many organisms. Using authenticated reference strains is important for validating media and incubation conditions before they are used for clinical or research specimens. The American Society for Microbiology also provides educational resources on laboratory practice and media selection.

The Balance Between Recovery and Overgrowth

Extended incubation creates a tension between the need to recover slow-growing organisms and the risk of overgrowth by faster-growing bacteria. In specimens that contain mixed flora, such as respiratory or wound specimens, the fast-growing organisms can cover the plate and obscure the slow-growing target. This is a common reason why extended incubation is not appropriate for all specimens.

The laboratory must decide which specimens are appropriate for extended incubation based on the clinical question. For example, a blood culture from a patient with suspected brucellosis should be held for an extended period, but a routine wound culture should not. The decision is based on the clinical presentation, the specimen type, and the organisms that are suspected.

Practical Workflow for Extended Incubation

Step 1: Determine the Suspected Organism

The first step is to identify the organism or group of organisms that the culture is intended to recover. This decision is based on the clinical presentation, the specimen type, and the patient history. For example, a patient with a history of unpasteurized dairy consumption and a fever of unknown origin may be suspected of having brucellosis. The laboratory would then select media and incubation conditions that support the growth of Brucella species.

The World Health Organization provides context on the public health importance of certain pathogens, including those that require extended incubation. The WHO also emphasizes the importance of accurate identification for antimicrobial stewardship, which is relevant when the laboratory is working with slow-growing organisms.

Step 2: Select the Appropriate Media

The media must support the growth of the target organism and be appropriate for the specimen type. For Brucella species, the laboratory may use blood culture bottles or solid media such as Brucella agar or trypticase soy agar with blood. For Francisella tularensis, the laboratory must use a medium that contains cysteine, such as chocolate agar with IsochickenX or Thulin-Martin agar.

The U.S. Food and Drug Administration publishes the Bacteriological Analytical Manual, which provides detailed methods for the isolation and identification of foodborne pathogens. While this manual is focused on food microbiology, the principles of media selection and incubation apply to other specimen types.

Step 3: Inoculate and Incubate

The specimen is inoculated onto the selected media and placed in the appropriate incubation environment. The temperature, atmosphere, and duration of incubation are determined by the target organism. Most slow-growing bacteria are incubated at 35 to 37 degrees Celsius, but some require lower temperatures or specific atmospheric conditions.

The incubation environment must be monitored to prevent desiccation. Plates can be placed in a humidified incubator or sealed in a plastic bag to reduce moisture loss. The laboratory should also check the plates at regular intervals to ensure that the media has not dried out.

Step 4: Observe and Subculture

The plates are examined at regular intervals during the incubation period. The frequency of observation depends on the organism and the protocol. For Brucella species, the laboratory may examine the plates every 2 to 3 days for up to 21 days. For Mycobacterium species, the laboratory may examine the plates weekly for up to 8 weeks.

If the plates show no growth at the end of the incubation period, the culture is reported as negative. If growth is observed, the organism is identified using standard methods. The laboratory may also subculture the organism to fresh media to obtain a pure culture for identification and susceptibility testing.

Step 5: Report and Document

The laboratory reports the results of the culture, including the organism identified and the time to growth. This information is important for the clinician, as it can help guide treatment decisions. The laboratory also documents the incubation period, the media used, and the observation schedule in the laboratory records.

Media-Specific Recommendations

Blood Culture Bottles

Blood culture bottles are often used for the recovery of slow-growing organisms from blood specimens. The bottles contain a liquid medium that supports the growth of a wide range of organisms. The laboratory can use an automated blood culture system that monitors the bottles for growth, or it can use a manual system that requires periodic subculture.

For Brucella species, the blood culture bottles are incubated for up to 21 days. The laboratory may perform a blind subculture at 7 and 14 days to check for growth that is not detected by the automated system. The subculture is performed onto solid media, which is then incubated for an additional period.

Solid Media

Solid media are used for the isolation of slow-growing organisms from specimens that are not blood. The media is selected based on the target organism and the specimen type. For Francisella tularensis, the laboratory uses a cysteine-enriched medium such as chocolate with Isochicken or Thulin agar. The plates are incubated at 35 to 37 degrees Celsius with CO2 for up to 14 days.

The plates must be examined at regular intervals to detect growth. The colonies of Francisella tularensis are small and may be difficult to see. The laboratory should use a magnifying lens or a stereomicroscope to examine the plates.

Mycobacterial Culture

Mycobacterial culture requires a longer incubation period than most other bacteria. The laboratory uses specialized media such as Lowenstein-Jensen or Middlebrook 7H10 or 7H11 agar. The cultures are incubated at 35 to 37 degrees Celsius with CO2 for up to 8 weeks.

The laboratory examines the cultures weekly for growth. The colonies of mycobacteria are slow to appear and may be small. The laboratory must also be aware of the risk of contamination, as the long incubation period provides ample time for environmental organisms to grow.

Options and Tradeoffs in Extended Incubation

Automated vs. Manual Systems

Automated blood culture systems offer the advantage of continuous monitoring and early detection of growth. These systems use a sensor that detects changes in the culture medium, such as a change in pH or the production of gas. The system alerts the laboratory when growth is detected, which can reduce the time to a positive result.

Manual systems require the laboratory to perform periodic subcultures and inspections. This is more labor-intensive but may be necessary for organisms that do not grow well in automated systems. The laboratory must weigh the cost of the automated system against the labor cost of the manual approach.

The Use of Enrichment Media

Enrichment media can be used to increase the recovery of slow-growing organisms. These media contain additional nutrients that support the growth of the target organism. For example, the addition of cysteine to a medium can support the growth of Francisella tularensis. The laboratory must ensure that the enrichment does not also support the growth of contaminants.

The Risk of Overgrowth

The risk of overgrowth is a significant limitation of extended incubation. In specimens with mixed flora, the faster-growing organisms can overgrow the plate and obscure the slow-growing target. The laboratory can reduce this risk by using selective media that suppresses the growth of the normal flora. However, selective media may also inhibit the growth of the target organism.

The laboratory must decide whether to use selective or nonselective media based on the specimen and the target organism. For specimens with a high likelihood of mixed flora, the laboratory may use a selective medium. For specimens that are expected to be sterile, the laboratory may use a nonselective medium.

Observations and Measurements

Time to Growth

The time to growth is an important measurement in extended incubation. The laboratory records the day on which growth is first observed. This information is used to determine the incubation period for the culture and to guide the interpretation of the results.

The time to growth can vary based on the organism, the media, and the incubation conditions. For example, Brucella species may grow in 3 to 5 days, but some strains may require up to 21 days. The laboratory must be aware of the expected time to growth for the target organism.

Colony Morphology

The colony morphology is used to identify the organism. The laboratory examines the colonies for size, shape, color, and texture. The colonies of Francisella tularensis are small, smooth, and grayish. The colonies of Brucella species are small, smooth, and translucent.

The laboratory must be careful when examining the colonies, as some slow-growing organisms are highly infectious. The examination should be performed in a biosafety cabinet to reduce the risk of exposure.

Subculture and Identification

When growth is detected, the laboratory subcultures the organism to obtain a pure culture. The pure culture is used for identification and susceptibility testing. The identification is based on the biochemical characteristics of the organism, such as the production of catalase, oxidase, or urease.

The laboratory may also use molecular methods for identification, such as PCR or sequencing. These methods can provide a more rapid and accurate identification than biochemical methods.

Quality Controls and Assurance

Positive and Negative Controls

The laboratory must include positive and negative controls in each batch of cultures. The positive control is a known organism that is expected to grow under the conditions. The negative control is a sterile medium that is expected to show no growth. The controls are used to verify that the media and the incubation conditions are appropriate.

The positive control should be a strain that is known to grow in the medium. The American Type Culture Collection provides authenticated strains that can be used for this purpose. The negative control should be a sterile medium that is incubated under the same conditions as the test cultures.

Media Quality

The quality of the media is critical for the recovery of slow-growing organisms. The laboratory must use media that is prepared correctly and stored under the appropriate conditions. The media should be checked for the pH, the color, and the presence of contamination before use.

The laboratory should also verify the performance of the media by testing it with a known organism. This is done by inoculating the media with a reference strain and observing the growth. The media is considered acceptable if the reference strain grows within the expected time.

The Role of the Laboratory

The laboratory must have a quality assurance program that includes the monitoring of the incubation conditions, the media quality, and the performance of the culture. The program should also include the documentation of the results and the corrective actions taken when the results are not acceptable.

The American Society for Microbiology provides professional resources on laboratory quality assurance and the best practices for the microbiology laboratory.

Common Failure Patterns in Extended Incubation

Desiccation of the Media

Desiccation is a common problem in extended incubation. The media can dry out during the incubation period, which prevents the growth of the target organism. The laboratory must monitor the moisture of the media and take steps to prevent desiccation, such as placing the plates in a humidified incubator or sealing them in a plastic bag.

Overgrowth by Contaminants

Overgrowth by contaminants is another common problem. The contaminants can be introduced during the collection of the specimen or during the inoculation of the media. The contaminants can overgrow the plate and obscure the target organism. The laboratory must use aseptic technique to reduce the risk of contamination.

The Failure to Detect Growth

The failure to detect growth is a common problem in extended incubation. The growth of the slow-growing organism may be faint and difficult to see. The laboratory must use the appropriate methods to detect the growth, such as the use of a magnifying lens or a subculture.

The Failure to Identify the Organism

The failure to identify the organism is a problem that can occur when the growth is not sufficient for the identification. The laboratory may need to subculture the organism to obtain a fresh media for the identification. The laboratory may also need to use the molecular methods for the identification.

Biosafety and Risk Assessment

The Risk of Slow-Growing Pathogens

Many slow-growing bacteria are also highly pathogenic. Brucella species and Francisella tularensis are classified as select agents and are a risk to laboratory workers. The laboratory must follow the biosafety guidelines for the handling of these organisms.

The Biosafety in Microbiological and Biomedical Laboratories provides the guidelines for the safe handling of these organisms. The guidelines include the use of a biosafety cabinet, the use of personal protective equipment, and the decontamination of the work area.

The Use of a Biosafety Cabinet

The laboratory must use a biosafety cabinet for the handling of slow-growing pathogens. The cabinet provides a barrier between the laboratory worker and the organism. The cabinet should be certified and maintained according to the manufacturer's instructions.

The Decontamination of the Work Area

The laboratory must decontaminate the work area after the handling of the slow-growing pathogens. The decontamination is performed with a disinfectant that is effective against the organism. The laboratory must also decontaminate the waste and the equipment that is used in the culture.

The Risk of Aerosols

The slow-growing pathogens can be aerosolized during the handling of the culture. The laboratory must avoid the creation of aerosols, such as the use of a loop to the culture. The laboratory should also use the appropriate personal protective equipment, such as a mask and gloves.

The Role of the Laboratory in the Diagnosis of Slow-Growing Bacteria

The Clinical Significance

The laboratory plays a critical role in the diagnosis of slow-growing bacteria. The laboratory must be able to detect the organism and to identify it correctly. The laboratory must also be able to provide the information to the clinician in a timely manner.

The World Health Organization provides the context for the importance of the accurate identification of the organism for the antimicrobial stewardship. The accurate identification is also important for the public health surveillance of the slow-growing pathogens.

The Interpretation of the Culture

The interpretation of the culture is a complex process. The laboratory must consider the specimen type, the incubation period, and the growth of the organism. The laboratory must also consider the clinical context of the patient.

The laboratory must be able to distinguish between the growth of the target organism and the growth of the contaminants. The laboratory must also be able to determine the significance of the growth, such as whether the organism is a pathogen or a normal flora.

The Reporting of the Results

The laboratory must report the results of the culture in a clear and concise manner. The report should include the organism identified, the time to growth, and the susceptibility of the organism to the antimicrobial agents. The report should also include the interpretation of the culture.

The laboratory must also report the results to the public health authorities when the organism is a reportable disease. The report should be made in a timely manner to ensure the public health is protected.

The Future of Extended Incubation

The Use of Molecular Methods

The molecular methods are increasingly used for the detection of slow-growing bacteria. The methods can provide a rapid and accurate identification of the organism. The methods can also be used to detect the organism directly from the specimen, which can reduce the time to the diagnosis.

The molecular methods are not a replacement for the culture. The culture is still needed for the susceptibility testing and for the epidemiological typing of the organism. The laboratory must use the molecular methods in conjunction with the culture.

The Use of Automation

The automation is increasingly used in the microbiology laboratory. The automated systems can be used for the culture, the identification, and the susceptibility testing. The automation can reduce the labor cost and the time to the result.

The automation is not a replacement for the expertise of the laboratory professional. The laboratory professional is still required for the interpretation of the results and for the decision-making.

The Use of the Artificial Intelligence

The artificial intelligence is being developed for the interpretation of the culture. The artificial intelligence can be used to detect the growth of the organism and to identify the organism. The artificial intelligence can also be used to predict the susceptibility of the organism.

The use of the artificial intelligence is still in the early stages. The laboratory must be cautious in the use of the artificial intelligence and must validate the results.

The Professional Escalation Criteria

The laboratory should escalate the case when the culture is positive for a slow-growing pathogen. The laboratory should also escalate the case when the culture is negative but the clinical suspicion is high. The laboratory should also escalate the case when the organism is a select agent.

The escalation should be made to the clinical team and to the public health. The escalation should be made in a timely manner to ensure the patient is treated appropriately.

A Decision Framework for Selecting Extended Incubation Protocols

Choosing whether to extend incubation and for how long is not a single decision but a sequence of decisions that should be made before the specimen is processed. A structured decision framework helps the laboratory apply extended incubation consistently, avoid unnecessary work, and prevent the loss of clinically significant organisms. This section presents a practical framework that integrates specimen evaluation, risk assessment, media selection, and monitoring into a single workflow.

The Four Gate Decision Framework

The framework uses four gates. Each gate requires a yes or no answer based on information available at the time the specimen is received. If the answer at any gate is no, the laboratory follows the routine incubation protocol for that specimen type. If the answer is yes at all four gates, the specimen is placed on an extended incubation protocol.

Gate 1: Clinical Suspicion. Does the clinical presentation, patient history, or exposure history suggest an organism that requires extended incubation? Examples include a patient with undulant fever and a history of unpasteurized dairy consumption, a patient with a nonhealing ulcer and exposure to rabbits, or a patient with a chronic cough and a positive tuberculosis contact history. The clinical suspicion must be documented on the test request form or communicated directly to the laboratory. Without this information, the laboratory cannot justify the extended incubation period.

Gate 2: Specimen Suitability. Is the specimen type appropriate for extended incubation? Blood, bone marrow, sterile body fluids, and tissue biopsies are suitable for extended incubation because they are normally sterile or have low levels of normal flora. Respiratory specimens, wound swabs, and stool specimens are generally not suitable because they contain mixed flora that will overgrow the plate during the extended period. If the specimen is not suitable, the laboratory should contact the clinician to discuss alternative testing, such as serology or molecular methods.

Gate 3: Organism Risk Assessment. Does the suspected organism present a biosafety risk that requires special containment? Brucella species and Francisella tularensis are classified as select agents and require biosafety level 3 practices. The Biosafety in Microbiological and Biomedical Laboratories provides the risk assessment framework for these organisms. If the organism requires containment that the laboratory cannot provide, the specimen should be referred to a reference laboratory. The decision to refer must be made before the specimen is processed, not after growth is detected.

Gate 4: Laboratory Capacity. Does the laboratory have the resources to complete the extended incubation protocol? This includes the appropriate media, the incubation equipment, the staff time for the observation schedule, and the quality control materials. If the laboratory cannot complete the protocol, the specimen should be referred to a laboratory that can. The American Society for Microbiology provides professional guidance on laboratory capacity and the resources needed for extended culture.

Applying the Framework to Common Scenarios

The framework is best understood through its application to specific scenarios. The following examples show how the four gates are applied in practice.

Scenario 1: Blood culture from a patient with suspected brucellosis. Gate 1 is yes because the clinical presentation suggests brucellosis. Gate 2 is yes because blood is a sterile specimen. Gate 3 is yes because Brucella species require biosafety level 3 containment. Gate 4 depends on the laboratory. If the laboratory has the capacity, the blood culture is held for 21 days with blind subculture at 7 and 14 days. If the laboratory does not have the capacity, the specimen is referred to a reference laboratory.

Scenario 2: Sputum culture from a patient with suspected tuberculosis. Gate 1 is yes because the clinical presentation suggests tuberculosis. Gate 2 is no because sputum contains normal respiratory flora that will overgrow the plate during the extended period. The laboratory should not use the extended incubation protocol for this specimen. Instead, the laboratory should use a decontamination procedure and a selective medium for mycobacteria, which is a different protocol from the extended incubation described in this article.

**Scenario 3: Wound swab from a patient with a suspected Francisella infection.** Gate 1 is yes because the clinical presentation suggests tularemia. Gate 2 is no because the wound swab contains mixed flora. The laboratory should not use the extended incubation protocol for this specimen. The laboratory should inform the clinician that the specimen is not suitable for culture and recommend serology or molecular testing.

The Decision Record

The laboratory must document the decision to use an extended incubation protocol. The record should include the date and time the specimen was received, the gate decisions, the media selected, the incubation conditions, and the observation schedule. The record should also include the name of the person who made the decision and the reason for the decision. This record is part of the laboratory quality system and is used for the review of the culture results.

The U.S. Food and Drug Administration publishes the Bacteriological Analytical Manual, which includes the documentation requirements for the culture methods. While the manual is focused on food microbiology, the principles of the documentation apply to the clinical laboratory.

The Monitoring Schedule

The monitoring schedule is the schedule of the observations that the laboratory performs during the extended incubation period. The schedule is determined by the organism and the media. The schedule should be written in the protocol and followed consistently.

For Brucella species, the laboratory may examine the plates every 2 to 3 days for up to 21 days. For Francisella tularensis, the laboratory may examine the plates every 2 to 3 days for up to 14 days. For Mycobacterium species, the laboratory may examine the plates weekly for up to 8 weeks. The schedule should be adjusted based on the growth rate of the organism and the condition of the media.

The laboratory should record the date and time of each observation and the result of the observation. The result should be recorded as no growth, growth suspected, or growth confirmed. If growth is suspected, the laboratory should perform a subculture to confirm the growth and to obtain a pure culture for identification.

The Moisture Monitoring Protocol

Desiccation is the most common cause of the failure of the extended incubation. The laboratory must monitor the moisture of the media at each observation. The moisture is assessed by the visual inspection of the media. The media should be moist and the surface should be smooth. If the media appears dry, cracked, or shrunken, the laboratory must take corrective action.

The corrective action depends on the stage of the incubation. If the desiccation is detected early in the incubation period, the laboratory may transfer the culture to a fresh plate. If the desiccation is detected late in the incubation period, the laboratory may report the culture as unsatisfactory and request a new specimen. The laboratory should not report a negative result from a desiccated culture.

The laboratory can reduce the risk of desiccation by using a humidified incubator, by sealing the plates in a plastic bag, or by using a plate that has a larger volume of media. The American Type Culture Collection provides the guidance on the storage and the handling of the culture media.

The Overgrowth Control

Overgrowth by the contaminants is the second most common cause of the failure of the extended incubation. The laboratory should monitor the plates for the growth of the contaminants at each observation. The contaminants are the organisms that are not the target organism. The contaminants can be introduced during the collection of the specimen or during the inoculation of the media.

The laboratory can reduce the risk of the overgrowth by using the selective media that suppresses the growth of the normal flora. The selective media should be chosen based on the target organism and the specimen type. For example, the laboratory may use a selective medium for the isolation of Brucella species from a specimen that contains the normal flora.

The laboratory must be aware that the selective media may also inhibit the growth of the target organism. The laboratory should use a nonselective medium in parallel with the selective medium to ensure that the target organism is not missed. The laboratory should also use the aseptic technique to reduce the risk of the contamination.

The Interpretation of the Results

The interpretation of the results of the extended culture is based on the growth of the target organism, the growth of the contaminants, and the clinical context. The laboratory must be able to distinguish between the growth of the target organism and the growth of the contaminants. The laboratory must also be able to determine the significance of the growth, such as whether the organism is a pathogen or a normal flora.

The laboratory must report the results of the extended culture in a clear and concise manner. The report should include the organism identified, the time to growth, and the susceptibility of the organism to the antimicrobial agents. The report should also include the interpretation of the culture.

The Clinical and Laboratory Standards Institute provides the standards for the antimicrobial susceptibility testing. The laboratory should follow the standards when the susceptibility testing is performed on the slow-growing organism.

The Escalation Criteria

The laboratory must have a clear escalation criteria for the extended incubation. The escalation criteria are used to determine when the laboratory should seek the advice of the clinical or the public health. The laboratory should escalate the case when the culture is positive for a slow-growing pathogen. The laboratory should also escalate the case when the culture is negative but the clinical suspicion is high. The laboratory should also escalate the case when the organism is a select agent.

The escalation should be made to the clinical team and to the public health. The escalation should be made in a timely manner to ensure the patient is treated appropriately. The World Health Organization provides the context for the importance of the accurate identification of the organism for the antimicrobial stewardship.

The Common Failure Patterns

The common failure patterns in the extended incubation are the desiccation of the media, the overgrowth by the contaminants, the failure to detect the growth, and the failure to identify the organism. The laboratory must be aware of these failure patterns and take the steps to prevent them.

The desiccation of the media is prevented by the moisture control. The overgrowth by the contaminants is prevented by the aseptic technique and the selective media. The failure to detect the growth is prevented by the regular observation and the use of the magnifying lens. The failure to identify the organism is prevented by the subculture and the use of the molecular methods.

The laboratory must document the failure patterns and the corrective actions taken. The documentation is part of the quality assurance program and is used to improve the laboratory processes.

The Professional Escalation Criteria

The escalation should be made to the clinical team and to the public health. The escalation should be made in a timely manner to ensure the patient is treated appropriately. The Biosafety in Microbiological and Biomedical Laboratories provides the guidelines for the safe handling of the select agents.

Frequently Asked Questions

How long should a blood culture be incubated for Brucella species?

Blood cultures for Brucella species are typically incubated for up to 21 days. The laboratory may perform a blind subculture at 7 and 14 days to check for growth that is not detected by the automated system. The incubation period is extended because the organism grows slowly and may not be detected in the standard 5 day incubation.

What media is recommended for the isolation of Francisella tularensis?

The media for the isolation of Francisella tularensis must contain cysteine. The recommended media include chocolate with Isochicken or Thulin agar. The plates are incubated at 35 to 37 degrees Celsius with CO2 for up to 14 days. The growth is slow and the colonies are small.

How can I prevent the desiccation of the media during the extended incubation?

The desiccation of the media can be prevented by using a humidified incubator or by sealing the plates in a plastic bag. The laboratory should also monitor the moisture of the plates and take the corrective action when the media is dry.

What is the risk of the overgrowth of the contaminants in the extended culture?

The risk of the overgrowth of the contaminants is high in the extended culture. The laboratory must use the sterile technique to reduce the risk of the contamination. The laboratory may also use the selective media to suppress the growth of the contaminants.

How do I know if the culture is negative?

The culture is negative if there is no growth of the organism at the end of the incubation period. The laboratory must also consider the clinical context of the patient. The culture may be negative even if the patient is infected with the organism.

What is the role of the biosafety cabinet in the extended culture?

The biosafety cabinet is used to protect the laboratory worker from the slow-growing pathogens. The cabinet provides a barrier between the worker and the organism. The laboratory must use the cabinet for the handling of the slow-growing pathogens.

How do I report the results of the extended culture?

The laboratory must report the results of the culture in a clear and concise manner. The report should include the organism identified, the time to growth, and the susceptibility of the organism. The laboratory must also report the results to the public health when the organism is a reportable pathogen.

What is the role of the molecular methods in the extended culture?

The molecular methods can be used for the rapid and accurate identification of the slow-growing bacteria. The methods can also be used to detect the organism in the specimen. The molecular methods are not a substitute for the culture, but they can be used in conjunction with the culture.

Using the Evidence

Source	Best use in this topic	Important limitation
Biosafety in Microbiological and Biomedical Laboratories	official guidance	Check the linked page for current local requirements
Microbiology Resources	official guidance	Check the linked page for current local requirements
Antimicrobial Resistance	official guidance	Check the linked page for current local requirements

Related Diagnostic Guides

References and Further Reading

Biosafety in Microbiological and Biomedical Laboratories. CDC and NIH.
Microbiology Resources. American Society for Microbiology.
Antimicrobial Resistance. World Health Organization.
Bacteriological Analytical Manual. U.S. Food and Drug Administration.
Antimicrobial Susceptibility Testing. Clinical and Laboratory Standards Institute.
Culture Collections. American Type Culture Collection.
Laboratory Biosafety Manual. World Health Organization.
NCBI Literature Resources. National Center for Biotechnology Information.
An Adapted Optical Density-Based Microplate Assay for Characterizing Actinobacteriophage Infection.. Journal of visualized experiments : JoVE, 2023.
A New Culture Method for the Detection of Non-Tuberculous Mycobacteria in Water Samples from Heater-Cooler Units and Extracorporeal Membrane Oxygenation Machines.. International journal of environmental research and public health, 2022.
Bacteriophage T4 propagation in E.coli exposed to severe substrate limitation.. 2025.

This article is educational and does not replace validated laboratory procedures, institutional biosafety review, manufacturer instructions, or professional interpretation.