Rectal microbiota associated with C. trachomatis and N. gonorrhoeae infections in MSM

In this study, we assessed the bacterial composition of the rectal microbiota associated with Chlamydia trachomatis (CT) and/or Neisseria gonorrhoeae (NG) infections in a cohort of men having sex with other men (MSM).Patients eligible for the study were selected from a group of MSM, attending the STI Outpatients Clinic of S. Orsola-Malpighi Hospital in Bologna (Italy) and reporting unsafe rectal intercourse. CT/NG rectal infections were detected by a real-time commercial NAAT and the rectal microbiota composition was analyzed from rectal swabs, by means of the amplification and sequencing of hypervariable V3-V4 regions of the 16S rRNA gene.A total of 125 rectal swabs were available for the analysis and 4 groups of patients were compared: negative subjects (n=53), patients with CT (n=37) or NG rectal infection (n=17) and patients with contemporary positivity for CT/NG (n=18).The rectal microbiota of all subgroups was dominated by Prevotellaceae (19-24%) Enterobacteriaceae (7-16%) and Ruminococcaceae (7-9%) families. In particular, we found that the rectal environment of all the MSM enrolled, irrespective of the subgroup analyzed, was rich in Prevotella (19-24%) and Escherichia (4-11%). An interesting shift in the bacterial composition between patients with sexually transmitted rectal infections and controls was noticed: infected patients were, globally, characterized by a depletion of Escherichia species, associated with an increase of various bacterial genera, including mainly anaerobes, as Peptoniphilus, Peptostreptococcus and Parvimonas.Getting insight into the CT group, significant differences in the microbial rectal profiles were detected on the basis of infecting serovars, and, at a lesser extent, on the basis of HIV-positivity. Considering the strong association between HIV and lymphogranuloma venereum infection found in our setting, further investigations are needed to evaluate their contribution to the dynamics of the rectal microbiota. Finally, we confirmed that HIV-positive patients are characterized by a lower bacterial richness than HIV-negative subjects.Information about the composition of the rectal microbiota in CT and NG infections could shed light on the pathogenesis of these conditions and could contribute to the onset of new strategies for their control.