Isolation of ESKAPE bacteria in healthy cattle, antibiotic resistance, and potential zoonotic risk

INTRODUCTION The inappropriate and unnecessary use of antibiotics and the limited availability of new antimicrobial agents have contributed to the increase in antimicrobial resistance. Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter species are included into the ESKAPE group, bacteria known to be the most significant causes of nosocomial infections. Particularly problematic and representative of multidrug-resistant bacteria are the ESKAPE pathogens, the name of which is due to the fact that they 'escape' the effects of antibiotics and can therefore pose a global threat to human health. As the role of healthy or otherwise asymptomatic animals as carriers of ESKAPE bacteria is poorly investigated, we tested the presence of ESKAPE isolates in healthy cattle and assessed their resistance to some antimicrobials. MATERIALS AND METHODS A prospective epidemiological study was conducted on dairy farms in the Marche and Campania regions. A total of 180 different samples were taken: eye, nasal, ear and oral swabs, milk, and faeces from healthy cattle. Standard cultures were performed in aerobiosis on nutrient and selective agar media and all the different colonies obtained were identified by MALDI-TOF MS. The susceptibility of ESKAPE isolates to a panel of 30 antibiotics belonging to different classes was assessed using the Kirby-Bauer and E-test methods (EUCAST, 2023). As suggested by Magiorakos et al. (2012), MDR was defined as acquired non-susceptibility to at least one agent in three or more antimicrobial categories, XDR to at least one agent in all but two or fewer antimicrobial categories, and PDR as non-susceptibility to all agents in all antimicrobial categories. RESULTS AND CONCLUSIONS Enterococcus faecium (n=17), Staphylococcus aureus (n=5), Klebsiella pneumoniae ssp. pneumoniae and Klebsiella pneumoniae ssp. ozaenae (n=15), Acinetobacter baumannii (n=7), Pseudomonas aeruginosa (n=7), and Enterobacter cloacae (n=12) were isolated. ESKAPE bacteria were susceptible to carbapenems, except for P. aeruginosa strains, polymyxins, sulphonamides, aminoglycosides, glycopeptides (vancomycin and teicoplanin), and S. aureus to β-lactams. No PDR strains were recorded, whereas 43 MDR (68.2%, n=63) and 18 XDR (28.6%) were observed. The nose and mouth of healthy cattle represent the anatomical sites of highest zoonotic risk (RR=28.55; AR=0.93) for transmission of A. baumannii, K. pneumoniae, and E. cloacae. The preliminary data obtained enable the acquisition of epidemiological information on the spread of ESKAPE pathogens from the healthy cattle population and to stimulate all international organisations involved in the One Health approach so that there is increased surveillance of antimicrobial resistance also in healthy animals to avoid the transmission of ESKAPE bacteria.