Antimicrobial Resistance and Extended-Spectrum Beta-Lactamase Genes in Enterobacterales, Pseudomonas and Acinetobacter Isolates from the Uterus of Healthy Mares

bla SED-1 beta-lactamase-producing Citrobacter sedlakii isolated from horses and genomic comparison with human-derived isolates

AIMS

We aim to detect beta-lactamase-producing Citrobacter sedlakii from horses and compare the genomic characteristics with isolates from humans.

METHODS AND RESULT

We characterized phenotypically and genotypically nine C. sedlakii isolates from the feces of horses and then compared them to human-derived isolates using whole genome sequencing and phylogenomic methods. Seven isolates (7/9) were ampicillin-resistant, while at least one isolate was resistant to ceftriaxone, gentamicin, meropenem, and streptomycin. All nine isolates were carriers of the chromosomal-mediated blaSED-1  beta-lactamase gene, which confers resistance to ampicillin. One isolate was positive for the mcr-9 gene that confers resistance to colistin, and another isolate had the aac(6')-lid gene that confers resistance to aminoglycosides. Seven isolates (7/9) were carriers of genes that confer metal resistance to copper, silver, and arsenic. Phylogenetically, two horse-derived isolates clustered together with two human-derived isolates from the NDARO database.

CONCLUSION

The results from our study provide insight into the antimicrobial susceptibility of C. sedlakii in horses, which was previously lacking, and the specific beta-lactamase gene mediating resistance.

Metagenomic characterization of the equine endometrial microbiome during anestrus

The equine uterus is highly interrogated during estrus prior to breeding and establishing pregnancy. Many studies in mares have been performed during estrus under the influence of high estrogen concentrations, including the equine estrual microbiome. To date, it is unknown how the uterine microbiome of the mare is influenced by cyclicity; while, the equine vaginal microbiome is stable throughout the estrous cycle. We hypothesized that differences would exist between the equine endometrial microbiome of mares in estrus and anestrus. The aim of this study was two-fold: to characterize the resident endometrial microbiome of healthy mares during anestrus and to compare this with estrus. Double-guarded endometrial swabs were taken from healthy mares during estrus (n = 16) and in the following non-breeding season during anestrus (n = 8). Microbial population was identified using 16S rRNA sequencing. Our results suggest that the equine uterine microbiome in estrus has a low diversity and low richness, while during anestrus, a higher diversity and higher richness were seen compared to estrus. Despite this difference, both the estrus and anestrus endometrial microbiome were dominated by Proteobacteria, Firmicutes, and Bacteroidota. The composition of the microbial community between anestrus and estrus was significantly different. This may be explained by the difference in the composition of the endometrial immune milieu based on the stage of the cycle. Further research investigating the function of the equine endometrial microbiome and dynamics changes within the uterine environment is required.

Frequency of potentially pathogenic bacterial and fungal isolates among 28,887 endometrial samples from mares, with an emphasis on multi-drug resistant bacteria in Germany (2018-2022)

Antimicrobial-resistant bacteria pose a serious threat to the wellbeing of animals and humans. In equine reproduction, endometritis caused by facultative microbial pathogens is a condition, which is usually treated with antibiotics. Data from Germany on prevalence of facultative pathogenic microorganisms cultured in samples from the equine uterus and the frequency of multi-drug resistant (MDR) bacteria is lacking. The aim of the study was to provide representative numbers for both. Microbiological culture results (n = 28,887) of endometrial samples submitted to a large veterinary diagnostic laboratory from 2018-2022 were analyzed. An average of 25.9 % of the culture results showed growth of facultative pathogenic bacteria. The dominant isolated bacteria were β-hemolytic streptococci (79.7 %) followed by Escherichia (E.) coli variatio haemolytica (5.2 %). E. coli were cultured in 4.3 % of the samples and occurred more often than Klebsiella pneumoniae (3.9 %), Candida species (2.9 %), Pseudomonas aeruginosa (2.0 %), and Staphylococcus aureus (1.5 %). Antibiotic susceptibility testing revealed sensitivity of β-hemolytic streptococci towards penicillins in almost 100 % of the cultured samples (99.5 %). E. coli-isolates were sensitive to gentamicin in 96.2 % of the cases. The frequency of multidrug-resistant extended spectrum beta-lactamase (ESBL)-positive bacteria and methicillin-resistant Staphylococcus aureus (MRSA) was 3.1 % of all positive culture results. The number of ESBL-positive isolates (n = 159) and MRSA was stable from 2018-2022. In conclusion, the situation regarding occurrence of MDR bacteria in Germany is favorable, but should further be monitored.