The importance of the study lies mainly in expanding knowledge of the phenomenon of antibiotic resistance in subjects using PrEP, studying for the first time in this population the resistance phenotype in commensal Enterobacterales of the gastrointestinal tract.

The data obtained from this study could pave the way for potential surveillance and awareness programs for the critical and conscious use of antimicrobials in PrEP subjects in order to mitigate the problem of antibiotic resistance, which currently represents a real global challenge.

ENTERO-PrEP is an observational, single-center, cross-sectional, tissue study. Patient enrollment will be performed at dedicated clinics for the monitoring and follow-up of PrEP subjects at the Infectious Diseases Unit of the IRCCS - University Hospital of Bologna.

In these clinics, on a quarterly basis, PrEP subjects undergo, as a normal diagnostic-assistance path, laboratory tests to exclude the presence of STIs, including the search for Chlamydia trachomatis and Neisseria gonorrhoeae in genital (urine) and extra-genital samples (pharyngeal swab and anorectal swab).

Each patient will be recruited only once during one of the normal monitoring visits scheduled for subjects using PReP.

The study aims to isolate commensal Enterobacterales strains from the gastrointestinal tract starting from the same anorectal swab sent for the detection of C. trachomatis and N. gonorrhoeae, without the need to perform any additional sampling compared to the normal care routine. For each isolated Enterobacterales strain, the sensitivity/resistance to antimicrobials (antibiogram) will subsequently be studied using broth micro-dilution. Bacterial isolation and antibiogram will be performed at the Microbiology Unit of the IRCCS - University Hospital of Bologna.

Subjects who consent to participate in the study will be asked to complete, directly during the outpatient visit, a questionnaire with information relating to personal and behavioral habits in order to identify risk factors that could favor the presence of antibiotic-resistant Enterobacterales.

Inclusion Criteria:

• age between 18 and 45 years
• HIV-negative subjects undergoing an anorectal swab for Chlamydia trachomatis and Neisseria gonorrhoeae using NAAT as a normal diagnostic-assistance procedure provided for subjects using PrEP

Exclusion Criteria:

• none

male and female subjects aged between 18 and 45 years who use PrEP and who go to the dedicated clinics of the Infectious Diseases Unit of the IRCCS - University Hospital of Bologna for normal check-ups/follow-ups Patients will be treated in accordance with their normal care process and the results of the study-specific laboratory analyses provided for by this protocol will in no way influence the diagnostic-therapeutic path of the patients.