# How to Verify ATCC Strain Authenticity Without Molecular Methods Verifying an ATCC strain without molecular methods means confirming, with culture-based and biochemical tests alone, that a vial from the American Type Culture Collection (ATCC) contains a viable, pure culture whose observable properties match the documented identity of that catalog strain. The workflow delivers three concrete outcomes. It detects nonviable, contaminated, or mislabeled lots before they enter service. It confirms species-level identity against the lot-specific product data sheet. It establishes a phenotypic fingerprint, meaning the recorded colony morphology, key biochemical reactions, and antimicrobial susceptibility pattern, that you can compare against every future working stock. Use this procedure when your laboratory receives a new lot of a quality control (QC) organism, when a frozen working stock is revived after storage, when an accreditation audit requires documented traceability of reference cultures, and whenever nucleic acid methods such as 16S rRNA sequencing or whole-genome sequencing are unavailable or unnecessary for the decision at hand. Selection and management of suitable seed strains according to standard principles is a critical factor in producing high-quality biological products [1], and the same principle governs the diagnostic bench. Your QC strains anchor daily antimicrobial susceptibility testing (AST), identification panels, and media performance checks. An unverified QC strain quietly invalidates everything downstream of it, which is why incoming verification is a core element of microbiology quality control. Hands-on time totals about 3 to 5 hours spread across one week. Elapsed time runs 3 to 7 days for typical aerobic bacteria and up to 2 weeks for slow growers, anaerobes, or organisms with special atmosphere requirements. Most of the elapsed time is incubation, not labor. ## Why Strain-Level Identity Matters Species-level identity and strain-level identity are different questions. A biochemical panel can tell you that a culture is *Escherichia coli*. It cannot, by itself, tell you that the culture is *E. coli* ATCC 25922 rather than any other *E. coli*. That distinction matters because biological behavior is strain-specific. The Malaysian Society of Gastroenterology and Hepatology built its probiotic recommendations explicitly on strain-specific evidence, and its position statement names quality control during manufacturing as a core selection criterion for any probiotic product [2]. A laboratory that works with defined strains inherits the same obligation. Molecular laboratories answer the strain question with genome-level analysis. Complete, gap-free genome assemblies of live and inactivated veterinary vaccine seed strains were generated precisely so that analysts could confirm, at the strain level, whether manufacturers use the same seed strains over time [1] [3]. Those datasets set the benchmark. The workflow in this article is the accepted alternative for laboratories without access to sequencing, and it is also the routine gate every laboratory runs before any deeper characterization is justified. The need for incoming verification is not theoretical. In a quality study of 63 commercial lots of *Brucella abortus* vaccine strains S19 and RB51 obtained from multiple manufacturers, most lots matched the reference strains, but batches from individual manufacturers carried genotypes distinct from the reference at a single variable locus called Bruce07, differing by one repeat unit [4]. A lot that differs from its reference can move through a supply chain unnoticed unless someone checks the material on arrival. Phenotypic verification is that check. ## The Principle of Phenotypic Verification No single culture test proves a strain's identity. The workflow instead builds agreement among independent lines of evidence, and a verdict passes only when all of them converge: 1. **Documentation.** The catalog number, lot number, and product data sheet define the acceptance criteria. 2. **Viability and purity.** The culture grows within the stated window and shows a single colony type. 3. **Morphology.** Colony appearance and the Gram stain reaction match the documented description. 4. **Species identity.** A standardized biochemical panel identifies the organism to species with high confidence. 5. **Strain-level anchor.** At least one trait that varies between strains, most practically the AST zone pattern, matches the expected pattern. The strain-level anchor deserves a definition. This article calls the recorded baseline the **golden profile**, meaning the colony morphology, biochemical profile code, and zone sizes captured at first verified receipt. Every later revival is compared against it. A related term used throughout is **passage**, defined as one transfer of the organism to fresh medium. Passage count is the quiet variable that erodes authenticity over time, so the workflow logs it from day one. A **seed strain** is the well-characterized parent stock from which all working cultures descend. Your verified revival becomes the seed. Everything else in the laboratory grows from it under a passage cap. ## Materials and Reagents | Item | Preparation or working concentration | Purpose | |--|--|--| | Tryptic soy agar (TSA) | Commercial dehydrated base, 40 g/L, autoclaved and poured per label | Revival plating, purity checks, colony morphology | | TSA with 5% sheep blood | Add 5 mL sterile defibrinated sheep blood per 100 mL cooled, molten TSA | Fastidious organisms, hemolysis reading | | Tryptic soy broth (TSB) | Commercial dehydrated base, 30 g/L per label | Revival of lyophilized and frozen pellets, cryopreservation base | | Mueller-Hinton agar | Commercial premix, poured to a uniform 4 mm depth, pH 7.2 to 7.4 | AST fingerprint | | Antimicrobial disks | Ampicillin 10 µg, ciprofloxacin 5 µg, gentamicin 10 µg, tetracycline 30 µg (select 4 to 6 drugs with published QC ranges for your strain) | Strain-level fingerprint | | Gram stain kit | Crystal violet, Gram iodine, 95% ethanol or acetone-alcohol decolorizer, safranin counterstain | Cell morphology and Gram reaction | | Hydrogen peroxide, 3% | Fresh, room temperature | Catalase test | | Oxidase reagent, 1% | 1 g tetramethyl-p-phenylenediamine dihydrochloride per 100 mL distilled water, prepared fresh the day of use | Oxidase test | | Rabbit plasma with EDTA | Reconstituted per vial, held at 2 to 8°C | Coagulase test for staphylococci | | Identification panels | API 20E, API 20 NE, API STAPH, or Vitek 2 cards, inoculated in sterile 0.85% sodium chloride at 0.5 McFarland | Species-level identification | | McFarland 0.5 standard | Barium sulfate turbidity reference, roughly 1 to 2 × 10⁸ colony-forming units per mL | Inoculum standardization | | Sterile 0.85% sodium chloride | Physiological saline | Inoculum preparation | | Nitrocefin disks | Commercial beta-lactamase detection disks | Beta-lactamase phenotype where the data sheet specifies it | | Typing antisera | *Salmonella* O and H antisera, *Streptococcus* Lancefield grouping kits, as applicable to your strain | Serotype anchor | | Sterile glycerol | 15 to 20% final concentration in TSB | Cryopreservation of the working seed | | Anaerobic jar or chamber | Fresh gas pack, room-temperature catalyst, anaerobic indicator | Revival of anaerobes | **Safety.** Handle every [bacterial culture](/blog/guides/bacterial-culture) under standard [Biosafety Level](/knowledge/diagnostics/emerging-tech/biosafety-levels-1-4-a-comparative-framework-for-diagnostic-laboratory-design) 2 (BSL-2) practices, including gloves, laboratory coat, and eye protection, and decontaminate all waste by autoclaving at 121°C before disposal. Oxidase reagent and nitrocefin are skin irritants, so wear gloves when handling them. Hydrogen peroxide is a mild irritant, and water baths are a burn and contamination hazard, which the revival step below addresses. ## How to Verify ATCC Strain Authenticity Without Molecular Methods Step by Step ![Four phases from day 1 growth in broth through day 2 isolation and Gram stain, days 3 to 4 panel and AST, and banking the seed.](/article-images/illustrations/verify-atcc-strain-authenticity-without-molecular-methods-verification-week.webp) 1. **Read the documentation before you open anything.** Check the catalog number, lot number, and product data sheet. Note the recommended medium, temperature, atmosphere, and expected growth window. Enter the lot into the strain log and attach the data sheet. Reason: the data sheet is your acceptance criteria document, and the lot number anchors traceability under your [laboratory quality management system](/knowledge/diagnostics/emerging-tech/laboratory-quality-management-systems-a-practical-implementation-framework-for-diagnostic-labora). 2. **Inspect the shipping condition.** Confirm the cold pack is still cold, the vial is intact, the label is legible, and no seal is breached. Photograph the vial and packing. Reason: transit stress produces atypical first-subculture behavior that can be mistaken for a bad lot. 3. **Revive exactly as the data sheet directs.** For a lyophilized pellet, hydrate with the stated volume of the recommended broth (commonly 0.5 to 1.0 mL), transfer the entire suspension to 5 to 6 mL of broth, and incubate at the stated temperature and atmosphere. For a frozen vial, thaw quickly in a 35 to 37°C water or bead bath and transfer to broth. Reason: the single most common cause of apparent nonviability is deviating from the specified medium, temperature, or atmosphere. **Safety.** Keep vials sealed above the water line or use a bead bath to prevent water intrusion and burns. 4. **Streak for isolation as soon as growth appears.** Turbidity, a pellicle, or sediment counts as growth. Streak onto TSA or blood agar and incubate 18 to 24 hours at the specified conditions, or 48 to 72 hours for slow growers. Reason: every later test must come from a pure subculture, and the isolation plate is where contamination shows itself. 5. **Record colony morphology.** Describe size, edge, elevation, texture, opacity, and pigment. On blood agar, record hemolysis as beta (complete clearing), alpha (green partial clearing), or gamma (none). Compare with the data sheet and your golden profile. Reason: morphology is the fastest mismatch detector you have. 6. **Gram stain an 18 to 24 hour culture.** Record the Gram reaction, cell shape, and arrangement. Reason: the stain confirms the fundamental identity gate and exposes mixed cultures that look uniform on the plate. **Safety.** Heat-fix or methanol-fix smears before staining so organisms stay on the slide. 7. **Run the rapid presumptive tests.** Catalase: emulsify a colony in a drop of 3% hydrogen peroxide on a slide, where immediate effervescence is positive. Oxidase: place a drop of fresh 1% reagent on filter paper, smear a colony with a plastic loop or wooden stick, and read a purple color within 30 seconds as positive. Coagulase for staphylococci: mix a colony into reconstituted rabbit plasma and read clotting at 4 hours, then at 24 hours if still liquid. Reason: these tests gate the choice of identification panel and confirm basic physiology in minutes. 8. **Run the species-level identification panel from a pure, young culture.** Standardize to 0.5 McFarland in 0.85% saline, inoculate the matching panel (API 20E for Enterobacterales, API 20 NE for nonfermenting Gram-negatives, API STAPH for staphylococci, or the corresponding Vitek 2 card), and incubate per the manufacturer, commonly 18 to 24 hours at 35 to 37°C with some reactions read at 48 hours. Record the numeric profile and the identification percentage. Reason: inoculum density and reading time are the two controllable variables behind most false mismatches. 9. **Build the AST fingerprint.** Prepare a 0.5 McFarland suspension, swab it onto dried Mueller-Hinton agar in three directions, apply disks within 15 minutes, incubate 16 to 18 hours at 35°C in ambient air (CO₂ only when the organism requires it), and measure zones to the nearest whole millimeter. Compare each zone with the published QC range for that strain and drug. For example, the Clinical and Laboratory Standards Institute lists 28 to 36 mm for a 5 µg ciprofloxacin disk on *E. coli* ATCC 25922. Also compare with your golden profile. Reason: the susceptibility pattern is the most practical strain-level anchor available without sequencing, and the QC ranges simultaneously validate your technique. 10. **Add serotype or signature traits where they exist.** Slide agglutination with *Salmonella* O and H antisera, Lancefield grouping for streptococci, nitrocefin beta-lactamase testing where documented, pigment expression at the specified temperature, and motility in semi-solid medium at 25°C for *Listeria*. Reason: each independent anchor that agrees raises confidence and narrows the space for error. 11. **Apply the pass rule.** Verification passes only when documentation, purity, colony and cell morphology, species-level identification, and the AST fingerprint all agree with the data sheet and the golden profile. Any single mismatch quarantines the lot pending investigation. Reason: convergent evidence prevents one weak or drifted test from driving a wrong conclusion. 12. **Bank the verified culture.** From the first revival, prepare cryovials of a dense broth suspension in TSB with 15 to 20% sterile glycerol and freeze at -70 to -80°C. Label each vial with the strain, lot, date, and passage number 1. Reason: the bank preserves the verified identity and caps future passages. 13. **Close the record.** Enter every result, medium lot, operator, incubator, and deviation into the [laboratory information management system](/knowledge/bioinformatics/lims-explained-lab-information-management-systems) (LIMS). Reason: accreditation standards such as ISO/IEC 17025 expect documented traceability of reference materials, and the record is what turns a bench exercise into a quality system asset. ## Controls - **Parallel viability control.** Revive a known-good QC strain, such as *E. coli* ATCC 25922, alongside the incoming lot on day 1. If the control grows and the new lot does not, the lot is suspect. If neither grows, look at technique, medium, or incubator performance. - **Sterility control.** Incubate one uninoculated plate and one uninoculated broth from each medium lot alongside the session. Growth in a sterility control invalidates the purity judgment for that session. - **Reagent controls.** Run catalase positive with *S. aureus* ATCC 25923 and negative with *Enterococcus faecalis* ATCC 29212, oxidase positive with *P. aeruginosa* ATCC 27853 and negative with *E. coli* ATCC 25922, and coagulase positive with *S. aureus* and negative with a coagulase-negative staphylococcus. Run these the day you run the tests, because oxidase reagent loses potency within hours once prepared. - **AST session control.** Run your full disk set on your in-house QC strain in the same session. A control zone outside its published range invalidates the fingerprint reading for that session. - **Golden profile.** At first verified receipt, photograph the colonies, scan the panel profile code, and record every zone size. This baseline is what all later comparisons use. ## Expected Results and How to Read Them ![Decision tree showing that agreement passes the lot, while a single mismatch quarantines it for repeat testing, investigation, or rejection.](/article-images/illustrations/verify-atcc-strain-authenticity-without-molecular-methods-pass-rule-branches.webp) **Day 1.** Growth appears in broth within the stated window, often within 24 hours for common aerobic strains and over several days for slow growers. No growth at 48 hours triggers the troubleshooting table, not an immediate verdict. **Day 2.** The isolation plate shows a single colony type, and the description matches the data sheet. The Gram stain shows the expected reaction, shape, and arrangement. Rapid tests match expectations. **Days 3 to 4.** The identification panel returns the expected species with high confidence. For API strips, the typical excellent-identification band is an identification percentage of 99% or higher with no low-discrimination comment. Vitek 2 reports a high confidence value for the expected organism. **Day 3.** Every AST zone falls inside the published QC range for that strain and drug and matches the golden profile within a few millimeters. A worked example makes the reading concrete. *E. coli* ATCC 25922 on TSA at 24 hours gives gray, moist, circular, convex colonies with entire edges. The Gram stain shows Gram-negative rods. Catalase is positive, oxidase negative, indole positive, citrate negative, and the organism is motile. An API 20E profile identifying *E. coli* at 99% or higher, plus ciprofloxacin, gentamicin, ampicillin, and tetracycline zones inside the CLSI QC ranges, constitutes a pass. Read the verdict with a simple decision list: - **Everything agrees.** Verified. Bank the culture and log passage 1. - **Species matches, one AST zone out of range.** Repeat the AST session with fresh disks, a fresh suspension, and a passing control strain. A reproducible out-of-range zone means reject or investigate. - **Species matches, zones in range but shifted from the golden profile.** Treat as possible drift or substitution. Check the passage history and quarantine the stock. - **Species mismatch or mixed culture.** Reject the lot, document the finding, and reorder. - **No growth with a growing parallel control.** Suspect a dead or injured lot. Make one rescue subculture on enriched medium, then reject if still negative. ## Troubleshooting | Symptom | Likely cause | Fix | |--|--|--| | No growth in broth after 48 hours | Wrong medium, temperature, or atmosphere for the strain | Recheck the data sheet, add the specified enrichment or CO₂, extend observation to 7 days | | No growth while the parallel control grows | Dead or heat-injured lot from transit | One rescue subculture on enriched medium, then reject the lot if still negative | | Two colony types on the isolation plate | Contamination during revival or a breached vial | Restreak a single colony of the expected type, repeat verification, reject if contamination persists | | Gram variable or weak staining | Culture older than 24 hours or over-decolorization | Restain from a fresh 18 to 24 hour culture and shorten decolorizer exposure | | Panel reports low discrimination | Inoculum too light or too heavy, strip read too early | Repeat at 0.5 McFarland with full incubation, add the supplemental tests the manufacturer lists | | Oxidase negative in an expected positive strain | Reagent oxidized, metal loop used, colony taken from a high-sugar medium | Prepare fresh reagent, use a plastic loop or wooden stick, test from blood agar or TSA | | All AST zones too small | Inoculum too heavy, agar too deep, plates too wet, disks expired | Restandardize to 0.5 McFarland, confirm 4 mm agar depth, dry plates before swabbing, use fresh disks | | One drug out of range, others in range | Faulty disk lot or technique on that disk | Repeat with a fresh disk from another lot and a passing control strain | | Zones inside QC ranges but shifted from the golden profile | Passage drift or strain substitution | Repeat once, then check passage history and quarantine the stock if the shift reproduces | | Pigment absent | Incubated at the wrong temperature for pigment expression | Repeat on the medium and temperature named in the data sheet, since many pigments express best at 25 to 30°C | | Motility negative in an expected motile strain | Tested at 37°C in an organism motile only at lower temperature | Repeat in semi-solid medium at 25°C from a young culture | | Anaerobe grows poorly or not at all | Medium not reduced, catalyst exhausted | Use pre-reduced media, refresh the catalyst, confirm the indicator strip changes color | ## Variations **MALDI-TOF mass spectrometry.** Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry measures the mass spectrum of abundant ribosomal proteins, not [nucleic acids](/blog/guides/nucleic-acids), so most laboratories classify it as a non-molecular identification method. A fresh colony gives a species-level identification in minutes against the manufacturer's score thresholds. It carries the same ceiling as biochemical panels, species yes and strain no, so pair it with the AST fingerprint. If your laboratory has MALDI-TOF, use it as the rapid species gate in step 8 and keep the rest of the workflow unchanged. **Anaerobes.** Use pre-reduced or thioglycollate media, inoculate promptly, incubate 48 to 72 hours in an anaerobic jar with a fresh gas pack and catalyst, and use API 20A or an equivalent panel. Expect a longer elapsed time and handle the golden profile the same way. **Fastidious organisms.** *Haemophilus* species require chocolate agar for revival and Haemophilus test medium for AST. *Neisseria* species require GC agar with supplements. Pneumococci add optochin susceptibility and bile solubility as signature anchors. **Yeasts and fungi.** The germ tube test identifies *Candida albicans*, micromorphology on corn meal agar adds confirmatory detail, and carbohydrate assimilation panels give species-level resolution. The golden-profile logic for continuity is identical. **Probiotic and industrial strains.** Because probiotic effects are strain-specific and the Malaysian Society of Gastroenterology and Hepatology ties its recommendations to strain-level evidence and manufacturing quality control [2], laboratories handling probiotic reference strains should record the golden profile and AST fingerprint at first receipt and treat any later shift as a strain change. Phenotyping may not separate very closely related strains within a species, so the practical ceiling without sequencing is species identity plus fingerprint continuity. **Vaccine seed lots.** Complete genome assemblies are the current reference approach for confirming that vaccine manufacturers use the same seed strains over time [1] [3]. Where sequencing is unavailable, a documented phenotypic fingerprint with strict passage control is the accepted bench alternative. ## Storage and Stability - **Lyophilized ATCC vials.** Store as the data sheet directs, commonly at 2 to 8°C, dry, and protected from moisture. Viability holds for years under correct storage, but every revival still passes through the verification gate. - **Working seed bank.** Cryovials in TSB with 15 to 20% glycerol at -70 to -80°C. Avoid frost-free freezers, because temperature cycling degrades viability. Thaw an aliquot once and discard the remainder. - **Working plates and slants.** Keep no longer than 2 to 4 weeks at 2 to 8°C, then discard and return to the freezer bank. - **Passage cap.** A widely used laboratory rule caps working cultures at five passages from the verified seed, after which the line is retired and a new aliquot comes out of the freezer. The cap has empirical support. In a stability study of *B. abortus* vaccine strains S19 and RB51, ten serial in vitro passages of the reference strains produced no detectable change by multiple-locus variable-number tandem repeat analysis (MLVA16), a DNA-based typing method using 16 loci, which showed that controlled short passage lines are stable [4]. Uncontrolled long-term serial passage is a different matter, and that is why the cap exists. ## Practical Tips for Reliable Results - **Verify on arrival, not after a QC failure.** A failed QC run traces back much faster when the strain was verified the week it arrived. - **Photograph colonies on day 2** and store the images with the strain record. A written description plus a photo beats either alone. - **Standardize the reader.** Have a second technologist measure AST zones, since zone edge reading is the most variable manual step in the workflow. - **Calendar the passage cap.** Enter the retirement date in the LIMS the moment you log passage 1. - **Attach the ATCC data sheet to the strain record** as a PDF inside the strain entry, not in a shared folder where it drifts away from the lot. - **Choose the smallest drug set that gives a unique fingerprint.** Four to six well-chosen drugs with published QC ranges usually separate the common QC organisms from one another. - **Never top up a working plate from another plate.** Always go back to the freezer seed. This keeps the passage count honest. ## Common Mistakes and Limitations **Treating a species-level identification as strain authenticity.** An API strip that reads *E. coli* at 99% proves the species, not the strain. The AST fingerprint and golden profile carry the strain-level weight. **Skipping the purity check.** A mixed culture gives a chimeric biochemical profile that matches nothing, and the wasted panel is the cheap part of the loss. **Testing old cultures.** Biochemical panels and AST need 18 to 24 hour cultures unless the manufacturer says otherwise. Older cultures lose expression of key enzymes and give false negatives. **Eyeballing the inoculum.** A suspension that is one McFarland unit off shifts every zone and every panel reaction. Use the turbidity standard every time. **No golden profile at first receipt.** Without a baseline recorded at verified receipt, later comparisons have nothing to compare against. Capture it once and the problem never returns. **Silent passage creep.** Each quick subculture adds a passage. Without a logged count, the five-passage cap is fiction. **Trusting the vial label.** Labels detach and vials get mixed in storage boxes. The verification workflow exists precisely because labels are not evidence. **Reading AST on wet or deep plates.** Agar depth and surface moisture change zone diameters independently of the strain. Confirm 4 mm depth and dry plates before inoculation. The limitations are just as concrete. Phenotypic verification proves species identity and continuity with your own recorded baseline. It cannot detect within-species substitution or small genomic changes. The definitive strain-level check is genome-level analysis, and complete genome assemblies are the current benchmark for confirming seed strain identity across time [1] [3]. Closely related strains within a species can share biochemical profiles and even susceptibility patterns, which is why the workflow demands multiple anchors rather than one. Slow growers, anaerobes, and mycobacteria stretch elapsed time to weeks. In regulated or clinical settings, verification decisions and any rejection should be reviewed by the laboratory director or quality manager under the corrective action path of your quality system. ## Frequently Asked Questions ### Can phenotypic tests really confirm an ATCC strain is authentic? They confirm species identity and continuity with your recorded baseline, which is what most laboratory decisions require. They cannot prove strain-level identity the way genome sequencing can, so pair them with a golden profile and a strict passage cap. ### Is MALDI-TOF a molecular method? No. MALDI-TOF measures the mass spectrum of ribosomal proteins, not nucleic acids, so most laboratories treat it as a non-molecular identification tool that fits this workflow. ### How long does verification take? Expect 3 to 7 days elapsed for typical aerobic bacteria with about 3 to 5 hours of hands-on time, and up to 2 weeks for anaerobes, slow growers, or fastidious organisms. ### How many passages can I use before I must replace a QC strain? A widely used rule caps working cultures at five passages from the verified seed, after which you discard the line and start a new aliquot from the freezer bank. ### What is a golden profile and why do I need one? It is the recorded colony morphology, biochemical profile, and zone sizes captured at first verified receipt. Every later revival is compared against it, so without it you have no baseline. ### My biochemical panel gives a low-discrimination profile. What now? Repeat the panel with a correctly standardized 0.5 McFarland inoculum and the full incubation time, then add the supplemental tests the manufacturer lists or confirm with conventional tube media. ### Do I need to reverify every new lot and every revival? Yes. Each new lot gets the full workflow, and each revival from storage gets at minimum purity, morphology, and a rapid identification check before it enters service. ### What if the antimicrobial zones are inside the QC range but different from my golden profile? Repeat the session with fresh reagents and a passing control strain. A confirmed, reproducible shift is treated as a strain change, and the stock is quarantined and investigated. ## Further Reading - [Quality of Antimalarial Drugs in East Africa: A Systematic Review.](https://pubmed.ncbi.nlm.nih.gov/36277242/) - [Epidemiology and risk factors of Alzheimer's disease and related dementias in South and Southeast Asia: a systematic review and meta-analysis protocol.](https://pubmed.ncbi.nlm.nih.gov/40840983/) ## Sources 1. [High-quality genome assembly and annotation of live animal vaccine bacteria strains in South Korea.](https://pubmed.ncbi.nlm.nih.gov/40898044/) 2. [Use of probiotics in clinical practice with special reference to diarrheal diseases: A position statement of the Malaysian Society of Gastroenterology and Hepatology.](https://pubmed.ncbi.nlm.nih.gov/33490608/) 3. [High-quality genome assembly and annotation of inactivated animal vaccine bacteria strains in South Korea.](https://pubmed.ncbi.nlm.nih.gov/42576204/) 4. [Genetic stability of Brucella abortus S19 and RB51 vaccine strains by multiple locus variable number tandem repeat analysis (MLVA16).](https://pubmed.ncbi.nlm.nih.gov/23933375/)