Multidrug resistance of bacterial pathogens in canine pyometra

To characterise multidrug antimicrobial resistance and pathogenicity profiles of bacteria isolated from different anatomical sites in bitches with pyometra, emphasising their clinical relevance for diagnosis and therapeutic decision-making in small animal practice.

Bacteria were obtained from the faeces, urine, uterus and vagina of 23 dogs diagnosed with pyometra undergoing ovariohysterectomy. Antimicrobial resistance profiles were analysed for all identified isolates, together with phylogenetic classification of Escherichia coli and detection of virulence factor-encoding genes.

Bacterial isolates obtained from faecal, urinary, uterine and vaginal samples showed predominantly positive growth for Escherichia coli, followed by Staphylococcus spp., Klebsiella pneumoniae and Proteus spp. Among these isolates recovered from each anatomical site, multidrug-resistant bacteria - defined as resistance to three or more classes of antimicrobials - were identified across all bacterial genera, with frequencies of 37.7% among faecal isolates, 16.7% among urinary isolates, 44.5% among uterine isolates and 100% among vaginal isolates, except for Enterobacter spp. Among dogs positive for Escherichia coli (11/23), phylogroups A/C (30.9%) were the most prevalent, followed by D/E (16.9%), B2 (15.5%), B1 (12.7%), A (12.7%), C (8.5%) and U (2.8%). In 90% (10/11) of cases, Escherichia coli isolates recovered from faecal, vaginal and/or uterine samples belonged to the same clonal family, suggesting faecal contamination. Overall, 77.4% of Escherichia coli isolates of uterine origin were classified as resistant or multidrug-resistant, and 83.9% harboured one or more virulence factor-encoding genes (hlyA, uspA, papC and predominantly fimH). Phylogroup B2 was the only group in which all assessed virulence factors were simultaneously detected.

The presence of multidrug-resistant bacteria across all genera isolated in cases of canine pyometra underscores the clinical importance of antimicrobial susceptibility testing. Furthermore, the recovery of genetically related Escherichia coli isolates from intestinal and reproductive tract samples supports the intestinal microbiota as a relevant source of infection in affected bitches.