The team’s methodology combined classical bacteriology with molecular confirmation, a dual approach that proved essential for accuracy. Of the 400 nasal swabs, 49 samples yielded colonies consistent with P. multocida on culture and biochemical screening, suggesting a presumptive prevalence of 12.25 percent. However, when the researchers applied polymerase chain reaction assays targeting species-specific genes, only 29 of those isolates were molecularly confirmed, yielding a PCR-confirmed prevalence of 7.25 percent. The discrepancy between the two methods underscores a persistent challenge in field microbiology: phenotypic identification can overestimate true prevalence because closely related commensal bacteria may mimic the colony morphology and biochemical profile of P. multocida, while PCR specificity comes at the cost of occasional sensitivity losses in samples with low bacterial DNA loads or inhibitory compounds.

Perhaps the most consequential molecular finding was capsular typing. Every PCR-positive isolate belonged to capsular type B, the serogroup associated with serotype B:2, one of the two strains—alongside E:2—responsible for devastating hemorrhagic septicemia outbreaks across Asia. Hemorrhagic septicemia is among the most lethal bacterial diseases of cattle and buffaloes in the region, producing fever, edema, respiratory distress, and rapid death. Because recovered and subclinically infected animals can harbor the organism in the lymphatic tissues of the upper respiratory tract and intermittently shed it in nasal secretions, the identification of type B organisms in nasal carriers carries significant epidemiological weight. Carrier animals act as a reservoir from which the bacterium can spread to susceptible herdmates and even to other indigenous species through aerosols, secretions, and direct contact.

The geographic distribution of positive samples varied considerably across the study sites, hinting at the influence of local husbandry and hygiene practices. Zakiganj recorded the highest detection rates, with 19.64 percent culture positivity and 14.29 percent molecular confirmation, followed closely by Fenchuganj. At the other extreme, no PCR-positive samples were recovered from Companiganj despite a small number of culture-positive swabs there, and Golapganj showed the lowest confirmed prevalence at 1.89 percent. The researchers did not find a statistically significant association between study area and infection status, but the spatial heterogeneity they observed aligns with the idea that management intensity, biosecurity, and animal movement patterns shape local reservoirs of infection in resource-limited farming systems.

Animal-level risk factors told a clearer story. Buffaloes aged between one and three years carried significantly higher odds of infection than calves under one year of age, with an odds ratio of 3.94. The researchers attribute this pattern to the confluence of immunological and management stressors that young adult animals face: weaning, increased movement and mixing with other animals, the onset of draught work or fattening regimens, and dietary and environmental changes that can suppress immune defenses. Meanwhile, calves may retain protection from maternally derived antibodies acquired through colostrum in areas where dams have been vaccinated or exposed, and older adults in endemic regions may have developed acquired immunity that reduces detectable carriage. Sex showed no significant effect, with males at 8.79 percent and females at 5.96 percent prevalence, suggesting that biological sex is far less determinative than age, stress, and management context.

The single strongest predictor of nasal carriage was clinical status. Buffaloes presenting with respiratory symptoms were 8.88 times more likely to test positive for P. multocida than apparently healthy animals, with a prevalence of 18.48 percent among symptomatic animals compared with just 2.49 percent among healthy ones. This association, highly significant statistically, reinforces the pathophysiological role of P. multocida as both a primary and an opportunistic respiratory pathogen. Under conditions of stress—poor nutrition, transport, adverse weather, or concurrent infections—the bacterium proliferates in the upper respiratory tract and can descend into the lower airways, initiating pneumonia or the systemic catastrophe of hemorrhagic septicemia. Once clinical signs appear, treatment is often ineffective, which is why the carrier state identified in this study represents such a critical intervention point.

The antimicrobial susceptibility results are where the study delivers its most alarming message. Among the 29 confirmed isolates, resistance to ampicillin reached 96.55 percent, oxytetracycline 93.10 percent, and penicillin-G 89.65 percent—three drugs that constitute the backbone of empirical treatment in many Bangladeshi livestock systems. Resistance to streptomycin, sulfamethoxazole-trimethoprim, gentamicin, and chloramphenicol also exceeded 50 percent. Only cefixime, a third-generation cephalosporin to which 93.10 percent of isolates remained susceptible, and azithromycin, with 68.96 percent susceptibility, retained meaningful activity. The researchers link the resistance patterns to decades of indiscriminate antibiotic use in a country where veterinary oversight is limited, informal animal health providers are widespread, and farmers frequently administer drugs without susceptibility testing, imposing relentless selective pressure on bacterial populations.

Correlation analysis of the resistance profiles revealed patterns that point to shared underlying mechanisms. Penicillin-G and ampicillin resistance were strongly and positively correlated, consistent with class-wide β-lactam resistance driven by β-lactamase production or altered penicillin-binding proteins. Gentamicin resistance correlated strongly with oxytetracycline resistance, and ampicillin resistance likewise tracked with tetracycline resistance, a pattern the authors interpret as evidence of co-selection: tetracycline and aminoglycoside resistance determinants are commonly carried together on mobile genetic elements such as plasmids and transposons, so selection pressure from one drug class can maintain resistance to another. The lone notable negative correlation, between cefixime and gentamicin, fits the observation that cephalosporins, rarely used in veterinary medicine, have escaped the co-resistance cascade that has eroded the utility of older drugs.

The study’s limitations are acknowledged by its authors. Molecular characterization was confined to species confirmation and capsular typing; more granular tools such as virulence gene profiling, multi-locus sequence typing, and whole-genome sequencing were not applied, and resistance was assessed phenotypically rather than by identifying the specific genes or mobile elements involved. Even so, the practical implications are immediate. The findings argue for routine susceptibility testing before treatment, targeted vaccination programs, improved biosecurity and husbandry to reduce stress in high-risk young adult animals, and strengthened national antimicrobial stewardship. Because cefixime and azithromycin remain effective but are considered critically important antimicrocrobials for human medicine, the authors caution that their use in animals must be judicious to preserve that efficacy.

For Bangladesh, where buffaloes supply milk, meat, and draught power to rural communities operating with limited veterinary infrastructure, the study provides the first systematic molecular characterization of nasal P. multocida carriage in the species. It demonstrates that the reservoir for hemorrhagic septicemia extends beyond visibly sick animals into the herds themselves, and that the bacteria circulating in that reservoir have accumulated resistance to the drugs farmers reach for first. Integrating molecular diagnostics with antimicrobial resistance monitoring, the researchers conclude, will be essential to controlling pasteurellosis and preventing resistant strains from spreading further through buffalo production systems—and, by extension, through the food animal populations on which millions of livelihoods depend.

Subject of Research: Prevalence and antimicrobial resistance of Pasteurella multocida carried in the nasal cavity of buffaloes in Bangladesh

Article Title: Prevalence, Molecular Identification, and Antimicrobial Resistance Traits of Pasteurella multocida Isolated From Nasal Swabs of Buffaloes in Bangladesh

Article References: Ghosh, P. K., Rahman, A., Roy, M., Sakib, M. A. N., Tuha, M. M.-E.-A., Ali, M., Chowdhury, M. S. R., Uddin, M. B., Rahman, M. M., & Hossain, M. M. (2026). Prevalence, Molecular Identification, and Antimicrobial Resistance Traits of Pasteurella multocida Isolated From Nasal Swabs of Buffaloes in Bangladesh. MicrobiologyOpen, 15(5), Article e70432. https://doi.org/10.1002/mbo3.70432

Image Credits: AI Generated

DOI: 10.1002/mbo3.70432

Keywords: Pasteurella multocida, buffalo, Bangladesh, hemorrhagic septicemia, antimicrobial resistance, nasal swabs, capsular type B, PCR, respiratory disease, livestock, multidrug resistance, veterinary microbiology

Urinary tract infections are among the most frequently diagnosed infectious diseases in dogs, and uropathogenic E. coli, commonly abbreviated UPEC, causes the majority of these infections in both humans and animals. UPEC belongs to the broader family of extraintestinal pathogenic E. coli, or ExPEC, a group of strains that also includes avian pathogenic and sepsis-associated subpathotypes. What distinguishes UPEC is a toolkit of virulence factors that allows the bacterium to colonise and proliferate on the epithelial cells lining the bladder. Chief among these are fimbrial adhesins, particularly Type 1 fimbriae, extracellular protein appendages that anchor the bacteria to bladder cells and initiate infection.

The defining feature of the isolates in this study was their haemolytic activity, the ability to lyse red blood cells on sheep blood agar. That trait is driven by alpha-haemolysin, encoded by the hlyCABD operon. Alpha-haemolysin is a pore-forming toxin that inserts itself into target cell membranes, creating transmembrane pores whose dimensions and conductance properties have been fully characterised through decades of biochemical and structural work. The loss of membrane integrity causes the target cell to burst. In human medicine, roughly half of all UPEC strains carry the hlyA gene, but that proportion climbs with disease severity, reaching up to 78 percent in cases of pyelonephritis, a serious infection of the kidney. Previous work in companion animals has also linked hlyA genes to urinary infections in dogs and cats.

The Vienna team collected isolates from 32 dogs and 19 cats, most of which presented with cystitis, haematuria or dysuria. After recultivating the bacteria on 5 percent sheep blood agar, the researchers extracted DNA and deployed a custom-made DNA microarray platform to screen for a wide panel of virulence-associated genes. They also phylotyped the isolates using the quadruplex Clermont assignment method, determined clonal groups through two-locus CH-clonotyping based on the fumC and fimH sequences, and performed antimicrobial susceptibility testing by agar disc diffusion against fourteen antibiotic agents, following Clinical and Laboratory Standards Institute protocols.

The genetic picture that emerged was strikingly uniform. Fifty of the 51 isolates belonged to phylogenetic group B2, the lineage most commonly associated with extraintestinal pathogenic E. coli in both humans and animals; only a single isolate fell into group B1. Every single isolate carried both fimH, the adhesion gene regarded as a major UPEC virulence marker, and hlyA, the haemolysin gene. Nearly all isolates, 50 of 51, also carried cnf1, a toxin-encoding gene that codes for cytotoxic necrotising factor 1. Additional virulence factors appeared frequently but not universally: pic, which encodes a serine protease, was found in 15 isolates, while papC, part of the P-fimbriae apparatus, and iucD, an aerobactin synthesis gene found only in virulent strains, each appeared in 11 isolates, always occurring together.

The authors note that while the predominance of phylogroup B2 was expected, the complete conservation of the cnf1 and hlyA linkage within this geographic cohort offers novel insight into the regional clonal stability of UPEC in Austrian companion animals. Clonotyping differentiated 34 distinct CH clonotypes, with CH103-9 the most prevalent, accounting for seven isolates. Several other clonotypes appeared in pairs, suggesting limited clonal relatedness among the sampled animals. Notably, most of the detected clonotypes correspond to clonal complexes previously reported in UPEC studies elsewhere, including CC73, CC12, CC127, CC141 and CC372, the last of which has been primarily associated with dogs rather than humans.

Antimicrobial resistance proved to be rare. Forty-five of the 51 isolates, or about 88 percent, were susceptible to every antibiotic tested, a reassuring result for clinicians managing urinary infections in pets. Resistance, where it occurred, was well explained by the genotype. Detected resistance genes including blaTEM, blaOXA-2, sul1, sul2, dfrA1, dfrA5, tet(A), aac(3′)-IVa and catA matched the phenotypic findings, and four isolates displayed multidrug-resistant profiles.

One isolate, however, stood out as a cause for vigilance. This strain carried an extended-spectrum beta-lactamase phenotype and was resistant to beta-lactams, ciprofloxacin, tetracycline, gentamicin and fosfomycin. Sequencing of the quinolone resistance-determining regions revealed classic amino acid substitutions in gyrA and parC that explain the fluoroquinolone resistance. Genotypically, the isolate proved to belong to phylogroup B2, serogroup O25b, sequence type ST131 and clonotype CH40-30, and it carried both blaCTX-M-15 and blaOXA-2. The B2-O25b-ST131 clone is recognised as a major human-associated high-risk pandemic pathogen responsible for a wide range of infections worldwide. Its sporadic detection in Austrian animals, from wildlife, canine prostate tissue, porcine intestinal samples and most recently a faecal sample, had been documented before, but this is a noteworthy addition from a companion animal with a urinary infection.

The study has limitations the authors acknowledge candidly. By restricting the analysis to haemolytic isolates, the work introduces selection bias, and the virulence and resistance potential of non-haemolytic strains causing urinary infections remains to be investigated. The virulence gene panel, while extensive, was finite, and the researchers suggest that whole-genome sequencing of a larger strain collection would provide an even more comprehensive characterisation. The low number of resistant isolates also limits broader epidemiological conclusions about antimicrobial resistance in canine and feline urinary infections.

Nevertheless, the clinical message is broadly positive. The data indicate that a significant proportion of E. coli urinary tract infections in companion animals can still be successfully managed with existing antibiotic therapies. At the same time, the virulence potential of these strains poses a relevant concern for both public and animal health, and the risk of human infection or colonisation from pet-associated isolates has yet to be fully determined. The existence of multidrug-resistant strains in pets with zoonotic potential, exemplified by the ST131 finding, underscores, in the authors’ view, the critical need for a continuous One Health approach to monitor and control the virulence and antimicrobial resistance of E. coli at the interface between animals and people.

Subject of Research: Characterisation of haemolytic uropathogenic Escherichia coli isolated from dogs and cats with urinary tract infections

Article Title: Characterisation of Haemolytic Uropathogenic Escherichia coli Isolated From Dogs and Cats

Article References: Büttner, S., Spergser, J., Makarova, O., Szostak, M. P., Rosel, A. C., Ruppitsch, W., Schäfer‐Somi, S., Müller, E., Braun, S. D., Monecke, S., Ehricht, R., Künzel, F., & Loncaric, I. (2026). Characterisation of Haemolytic Uropathogenic Escherichia coli Isolated From Dogs and Cats. Veterinary Medicine and Science, 12(5), Article e71200. https://doi.org/10.1002/vms3.71200

Image Credits: AI Generated

DOI: 10.1002/vms3.71200

Keywords: uropathogenic E. coli, dogs, cats, urinary tract infections, alpha-haemolysin, virulence genes, phylogroup B2, ST131, antimicrobial resistance, ESBL, One Health, veterinary microbiology