Rectal carriage of antimicrobial resistant Enterobacteriaceae among MSM using HIV pre-exposure prophylaxis (PrEP): A cross-sectional study in Italy

Background: Men who have sex with men (MSM) receiving HIV pre-exposure prophylaxis (PrEP) are often exposed to repeated antimicrobials due to a high burden of sexually transmitted infections (STIs). These factors may contribute to the selection of antimicrobial resistant bacteria within the intestinal microbiota. This study aimed to investigate the prevalence of antimicrobial resistance (AMR) among Enterobacteriaceae isolated from rectal swabs of MSM receiving PrEP and to assess possible associations with behavioral and PrEP-related variables. Methods: In this cross-sectional study, rectal swabs were collected from MSM receiving PrEP who had no gastrointestinal symptoms and were attending the Infectious Diseases Clinic of the 'IRCCS Azienda Ospedaliero-Universitaria di Bologna' (Italy) for routine STI screening. The same anorectal specimens were used for culture-based isolation, and antimicrobial susceptibility testing of Enterobacteriaceae. Behavioral and clinical data were collected through structured questionnaires. Results: A total of 126 Enterobacteriaceae isolates, predominantly Escherichia coli (n = 79; 63%) and Klebsiella spp. (n = 35; 28%), were recovered from 89 of the 92 subjects enrolled. Nearly three-quarters of participants reported antimicrobial use in the previous 12 months, and almost one quarter in the month preceding enrolment. Overall, 40% and 39% of participants reported Chlamydia trachomatis and Neisseria gonorrhoeae, respectively, within the previous two years. Considering all Enterobacteriaceae isolates, resistance to sulfamethoxazole/trimethoprim was the most frequent, followed by ciprofloxacin; resistance to third-generation cephalosporins ranged from 5% to 8%. Resistance to piperacillin/tazobactam was rare (2%), and no carbapenem-resistant isolates were detected. Although not statistically significant, participants reporting recent antibiotic use were more likely to harbor resistant strains across all antimicrobial classes. Conclusions: Repeated antimicrobial exposure for STI management may shape intestinal resistance patterns of Enterobacteriaceae among MSM receiving PrEP. Our findings support the need for continued AMR monitoring and targeted antimicrobial stewardship interventions in this population.