Salmonellosis and Colibacillosis in Poultry: Bacterial Foodborne Pathogens
By Dr. Zubair Khalid, DVM, MS, PhD ·
Key Takeaways
- Salmonellosis and colibacillosis are economically significant bacterial diseases in poultry, caused by Salmonella spp. and avian pathogenic Escherichia coli (APEC) respectively. Transmission occurs via fecal-oral routes, contaminated feed/water, and vertically through eggs, with migratory birds posing a risk for multidrug-resistant (MDR) strains.
- Clinical signs of salmonellosis range from acute septicemia and diarrhea in young chicks (S. Pullorum, S. Gallinarum) to subclinical intestinal carriage in adults, while colibacillosis manifests as omphalitis, respiratory disease, and polyserositis.
- Definitive diagnosis involves bacterial isolation and identification using selective enrichment and plating media (e.g., tetrathionate broth, XLD agar for Salmonella; MacConkey agar for E. coli), followed by biochemical tests, serotyping, and antimicrobial susceptibility testing. Molecular methods like PCR and whole-genome sequencing are crucial for detailed characterization.
- Treatment is challenged by widespread antimicrobial resistance; however, fluoroquinolones, aminoglycosides, and beta-lactams are used, guided by susceptibility testing. Alternative strategies include bacteriophage therapy, probiotics, and plant-based antimicrobials.
- Control relies on stringent biosecurity measures, effective cleaning and disinfection, rodent/wild bird control, and vaccination programs. Hatchery sanitation and competitive exclusion products are also vital for reducing pathogen load.
- Poultry meat and eggs are significant vehicles for foodborne transmission of Salmonella and APEC to humans, necessitating proper handling and thorough cooking to an internal temperature of 74°C to prevent illness. Antimicrobial resistance in these pathogens is a critical One Health concern.
Etiology
Salmonellosis and colibacillosis represent two of the most economically significant bacterial disease complexes in commercial poultry production worldwide. Salmonellosis is caused by motile, Gram-negative, facultatively anaerobic bacilli belonging to the genus Salmonella within the family Enterobacteriaceae [<a href="#ref-1">1</a>, <a href="#ref-2">2</a>]. More than 2,500 serovars have been described, with host-restricted serovars such as Salmonella Gallinarum and Salmonella Pullorum causing systemic disease in poultry, while broad-host-range serovars including Salmonella Enteritidis and Salmonella Typhimurium are frequently associated with subclinical intestinal carriage and foodborne transmission [<a href="#ref-3">3</a>, <a href="#ref-4">4</a>]. Colibacillosis is caused by avian pathogenic Escherichia coli (APEC), a subset of extraintestinal pathogenic E. coli (ExPEC) that possess specific virulence factors enabling colonization of the respiratory tract, air sacs, pericardium, and internal organs [<a href="#ref-5">5</a>, <a href="#ref-6">6</a>]. APEC strains are classified by serogroup (O78, O2, O1, O161 being common) and carry virulence-associated genes encoding fimbriae, toxins, iron acquisition systems, and protectins [<a href="#ref-6">6</a>, <a href="#ref-7">7</a>].
Epidemiology
The epidemiology of these pathogens is complex and multifactorial. Salmonella spp. and APEC are transmitted horizontally via the fecal-oral route, through contaminated feed, water, litter, and fomites, and vertically through transovarian transmission in the case of Salmonella Enteritidis and certain APEC serogroups [<a href="#ref-1">1</a>, <a href="#ref-8">8</a>]. Migratory birds serve as a risk factor for introducing multidrug-resistant (MDR) Salmonella and E. coli into broiler farms and surrounding environments [<a href="#ref-8">8</a>]. Prevalence studies from diverse geographic regions demonstrate the global burden. In Jiangxi Province, China, bacterial pathogens isolated from poultry between 2020 and 2022 showed high prevalence of E. coli and Salmonella with significant antimicrobial resistance profiles [<a href="#ref-9">9</a>]. A subsequent study from the same region (2023-2024) confirmed persistent resistance patterns [<a href="#ref-10">10</a>]. In Wakiso District, Uganda, broiler farms exhibited substantial prevalence of Salmonella and pathogenic E. coli with resistance to multiple antimicrobial classes [<a href="#ref-11">11</a>]. In South Korea, extended-spectrum beta-lactamase (ESBL)-producing Salmonella Typhimurium isolates from food animals demonstrated increasing resistance trends over an 11-year period [<a href="#ref-12">12</a>]. European surveillance of third-generation cephalosporin-resistant E. coli and Salmonella from food-producing animals revealed widespread dissemination of resistance determinants [<a href="#ref-13">13</a>]. In Egypt, MDR bacterial agents were implicated in duck enteritis, with the first record of Salmonella enterica subspecies arizonae [<a href="#ref-14">14</a>], and omphalitis in broiler flocks was associated with E. coli, Salmonella spp., and Staphylococcus aureus [<a href="#ref-15">15</a>]. In Ethiopia, conventional poultry farms harbored antimicrobial-resistant Salmonella and E. coli isolates [<a href="#ref-16">16</a>]. The question "does chicken have e coli or salmonella" is clinically relevant, as both pathogens are commonly isolated from poultry intestinal tracts and carcasses [<a href="#ref-2">2</a>, <a href="#ref-11">11</a>]. The concept of a "chicken without salmonella" is a goal of pre-harvest food safety interventions, though complete elimination remains challenging due to environmental reservoirs and vertical transmission [<a href="#ref-2">2</a>, <a href="#ref-17">17</a>]. "Raw chicken breast bacteria" frequently include both Salmonella and E. coli, and "chicken bacteria news" regularly reports on outbreaks linked to these pathogens [<a href="#ref-2">2</a>]. "Undercooked chicken e coli" is a common consumer concern, as inadequate thermal processing fails to inactivate these bacteria [<a href="#ref-2">2</a>].
Clinical Signs
Clinical manifestations vary by pathogen serovar, host age, immune status, and concurrent infections. In salmonellosis, Salmonella Pullorum causes pullorum disease in young chicks, characterized by acute septicemia, white diarrhea, pasted vents, anorexia, and high mortality [<a href="#ref-18">18</a>]. Salmonella Gallinarum causes fowl typhoid in older birds, presenting with depression, anorexia, diarrhea, decreased egg production, and mortality [<a href="#ref-6">6</a>]. Paratyphoid infections (e.g., Salmonella Enteritidis, Typhimurium) are often subclinical in adult birds but can cause diarrhea, decreased feed intake, and reduced growth in young chicks [<a href="#ref-19">19</a>, <a href="#ref-20">20</a>]. In colibacillosis, APEC infections present as a spectrum of disease including yolk sac infection (omphalitis) in neonates, respiratory disease (airsacculitis), pericarditis, perihepatitis, peritonitis, salpingitis, and cellulitis [<a href="#ref-5">5</a>, <a href="#ref-7">7</a>, <a href="#ref-18">18</a>]. Early chick mortality studies in Kashmir, India, identified E. coli and Salmonella as primary etiological agents in broiler chicks [<a href="#ref-18">18</a>]. Experimental leg disorders in poultry have been linked to MDR and multivirulent avian bacterial pathogens including APEC [<a href="#ref-7">7</a>].
Pathology
Gross pathological findings in salmonellosis include caseous cecal cores, hepatomegaly, splenomegaly, necrotic foci in the liver and spleen, and hemorrhagic enteritis [<a href="#ref-6">6</a>, <a href="#ref-18">18</a>]. In pullorum disease, necrotic foci in the myocardium, liver, and ceca are characteristic. Histologically, there is multifocal necrosis, heterophilic and mononuclear infiltration, and bacterial emboli in parenchymatous organs [<a href="#ref-18">18</a>]. In colibacillosis, fibrinous polyserositis is the hallmark lesion, with fibrinous exudate covering the pericardium (pericarditis), liver capsule (perihepatitis), and air sacs (airsacculitis) [<a href="#ref-5">5</a>, <a href="#ref-7">7</a>]. Omphalitis presents as unabsorbed yolk sacs with thickened, discolored walls and caseous exudate [<a href="#ref-15">15</a>, <a href="#ref-18">18</a>]. Histopathological examination reveals fibrin deposition, heterophil infiltration, and Gram-negative bacilli within lesions [<a href="#ref-18">18</a>].
Diagnostics
Definitive diagnosis relies on isolation and identification of the causative agent. For Salmonella, selective enrichment media (e.g., tetrathionate broth, Rappaport-Vassiliadis broth) followed by plating on selective agar (e.g., xylose lysine deoxycholate agar, brilliant green agar) are standard [<a href="#ref-3">3</a>, <a href="#ref-11">11</a>]. Biochemical confirmation using triple sugar iron agar, lysine iron agar, and urease tests is followed by serotyping using somatic (O) and flagellar (H) antisera [<a href="#ref-3">3</a>, <a href="#ref-12">12</a>]. For E. coli, samples are plated on MacConkey agar and eosin methylene blue agar, with lactose-fermenting colonies confirmed by biochemical tests (indole, methyl red, Voges-Proskauer, citrate) [<a href="#ref-11">11</a>, <a href="#ref-15">15</a>]. Molecular diagnostics include polymerase chain reaction (PCR) targeting serovar-specific genes (e.g., invA for Salmonella, fimH for E. coli) and virulence gene profiling [<a href="#ref-4">4</a>, <a href="#ref-6">6</a>]. Whole-genome sequencing (WGS) using high-throughput sequencers enables detailed characterization of antimicrobial resistance genes, plasmid replicons, and phylogenetic relationships [<a href="#ref-12">12</a>, <a href="#ref-13">13</a>]. Antimicrobial susceptibility testing by disk diffusion or broth microdilution following Clinical and Laboratory Standards Institute (CLSI) guidelines is essential for therapeutic guidance [<a href="#ref-10">10</a>, <a href="#ref-11">11</a>, <a href="#ref-16">16</a>]. Serological tests, including commercial ELISA kits for Salmonella antibody detection, are used for flock-level surveillance [<a href="#ref-2">2</a>].
Treatment
Therapeutic intervention is complicated by widespread antimicrobial resistance. In acute outbreaks, antimicrobial therapy guided by susceptibility testing is recommended. Commonly used agents include fluoroquinolones (enrofloxacin), aminoglycosides (gentamicin), and beta-lactams (amoxicillin, ceftiofur), though resistance is increasingly reported [<a href="#ref-1">1</a>, <a href="#ref-10">10</a>, <a href="#ref-11">11</a>, <a href="#ref-16">16</a>]. Combination therapy with cefotaxime, colistin, and fosfomycin has shown synergistic effects against resistant E. coli and Salmonella isolates in vitro [<a href="#ref-21">21</a>]. Alternative strategies are under active investigation. Bacteriophage therapy using lytic phages (e.g., vB_SalS_KY05 for Salmonella, vB_EcoS_PJ16 for APEC) has demonstrated efficacy in reducing pathogen loads without disrupting cecal microbiota [<a href="#ref-17">17</a>, <a href="#ref-22">22</a>]. Probiotic strains such as Enterococcus faecium and Saccharomyces cerevisiae fermentation products have shown protective effects against APEC and Salmonella infection in laying hens and broilers [<a href="#ref-5">5</a>, <a href="#ref-23">23</a>]. Plant-based antibiotic alternatives, including fenugreek-based formulations and fermented onion extracts, have been evaluated for their ability to mitigate mixed bacterial infections [<a href="#ref-19">19</a>, <a href="#ref-20">20</a>, <a href="#ref-24">24</a>]. Silver nanoparticles synthesized from Withania coagulans have demonstrated antibacterial activity against poultry pathogens [<a href="#ref-25">25</a>]. CpG oligodeoxynucleotides have been shown to upregulate heterophil bactericidal activities and enhance immunoprotection against Salmonella Typhimurium septicemia in neonatal broilers [<a href="#ref-26">26</a>]. Recombinant diffusible signal factor production inhibits Salmonella invasion and animal carriage [<a href="#ref-27">27</a>].
Control
Control strategies encompass biosecurity, vaccination, and management practices. Biosecurity measures include all-in/all-out production, cleaning and disinfection of facilities, rodent and wild bird control, and monitoring of feed and water sources [<a href="#ref-1">1</a>, <a href="#ref-8">8</a>]. Hatchery sanitation using gas phase hydroxyl-radical processes has been shown to inactivate Salmonella and avian pathogens on eggs without compromising hatching performance [<a href="#ref-28">28</a>]. Vaccination against Salmonella includes live attenuated vaccines (e.g., Salmonella Gallinarum 9R) and killed bacterins [<a href="#ref-6">6</a>]. Recombinant vaccines expressing APEC type I fimbriae have been developed to provide protection against multiple serogroups [<a href="#ref-6">6</a>]. Competitive exclusion products containing defined bacterial cultures are used to reduce Salmonella colonization in chicks [<a href="#ref-2">2</a>]. Biofilm formation by probiotic bacteria on wood shavings has been explored as a strategy to control Salmonella and APEC in litter [<a href="#ref-29">29</a>]. The use of phage cocktails (e.g., SalmoFree) has been shown to improve health and productivity in laying hens [<a href="#ref-30">30</a>]. Commensal E. coli strains have been demonstrated to inhibit the growth and modulate the fitness, virulence, and antimicrobial resistance of Salmonella Heidelberg in vitro, suggesting potential for probiotic-based interventions [<a href="#ref-31">31</a>]. Horizontal gene transfer of tetracycline resistance from E. coli donors to Salmonella Heidelberg in chickens is impacted by the genetic context of donors, highlighting the need for careful selection of probiotic strains [<a href="#ref-32">32</a>]. Adhesion capacity of Salmonella Enteritidis and E. coli on polystyrene, stainless steel, and polyethylene surfaces underscores the importance of material selection in equipment design [<a href="#ref-33">33</a>]. Biofilm production among Enterobacteriaceae from poultry feces has been linked to multidrug resistance [<a href="#ref-34">34</a>]. Plasmid-mediated quinolone resistance in diarrheal E. coli from farmers and chickens in Tunisia and Nigeria demonstrates the interconnectedness of human and animal reservoirs [<a href="#ref-35">35</a>]. Small RNA (sRNA)-mediated regulation of Salmonella infection in the host represents an emerging area of research with potential for novel therapeutic targets [<a href="#ref-4">4</a>].
Food Safety Implications
Poultry meat and eggs are major vehicles for foodborne transmission of Salmonella and APEC to humans [<a href="#ref-2">2</a>]. The question "does chicken have e coli or salmonella" is answered affirmatively by prevalence data showing that a significant proportion of raw poultry carcasses harbor these pathogens [<a href="#ref-2">2</a>, <a href="#ref-11">11</a>]. "Raw chicken breast bacteria" are a primary concern for consumers and regulatory agencies. "Chicken bacteria news" frequently reports on recalls and outbreaks linked to Salmonella and E. coli in poultry products. "Undercooked chicken e coli" is a common cause of foodborne illness, as inadequate cooking fails to achieve the internal temperature required to inactivate these pathogens. The concept of a "chicken without salmonella" is the target of pre-harvest interventions including vaccination, competitive exclusion, and phage therapy [<a href="#ref-2">2</a>, <a href="#ref-17">17</a>, <a href="#ref-30">30</a>]. Post-harvest interventions include carcass decontamination with organic acids, chlorinated water, and novel antimicrobial treatments [<a href="#ref-28">28</a>]. Consumer education on proper handling, cooking (to an internal temperature of 74 degrees Celsius), and prevention of cross-contamination is essential [<a href="#ref-2">2</a>]. Antimicrobial resistance in foodborne Salmonella and E. coli from poultry is a One Health concern, as resistance determinants can transfer between animal and human pathogens [<a href="#ref-1">1</a>, <a href="#ref-13">13</a>, <a href="#ref-32">32</a>].
Diagnostic Workflow
The following Mermaid diagram illustrates a decision tree for the diagnostic approach to suspected salmonellosis or colibacillosis in poultry flocks.
flowchart TD
A["Clinical suspicion: diarrhea, mortality, respiratory signs"] --> B{"Post-mortem examination"}
B --> C["Gross lesions: fibrinous polyserositis, necrotic foci, enteritis"]
C --> D["Sample collection: liver, spleen, cecal tonsils, yolk sac, pericardial fluid"]
D --> E["Selective enrichment for Salmonella: tetrathionate broth"]
D --> F["Direct plating for E. coli: MacConkey agar"]
E --> G["Plating on selective agar: XLD, BGA"]
F --> H["Biochemical confirmation: TSI, LIA, urease, IMViC"]
G --> I["Serotyping: O and H antisera"]
H --> J["Serogrouping: O78, O2, O1, O161"]
I --> K["Antimicrobial susceptibility testing: disk diffusion, broth microdilution"]
J --> K
K --> L["Molecular characterization: PCR for invA, fimH, virulence genes"]
L --> M["WGS for resistance genes, plasmid typing, phylogeny"]
M --> N["Report: pathogen identification, resistance profile, epidemiological typing"]