Anniris Rincon-Quintero

Objective: To investigate the urethral carriage rate of Haemophilus parainfluenzae isolated in men who have sex with men and to describe the clinical characteristics of carriers. We performed an analysis of the resistance determinants, virulence factors and the genetic phylogeny of the isolates. Methods: Clinical data were obtained from 234 patients attending the infectious diseases unit at the Álvaro Cunqueiro Hospital (Vigo, Spain) between 2021 and 2023. H. parainfluenzae isolated in urethral samples was subjected to antimicrobial susceptibility testing and whole-genome sequencing. Results: The urethral carriage rate was 25%. None of the risk factors studied (received antimicrobial therapy in the previous month, HIV status, Pre-Exposure Prophylaxis (PrEP) use and age) were related to a higher carriage rate. Neither multidrug-resistant (MDR), the presence of a capsule, nor virulence factors were useful to distinguish asymptomatic carriage from acute urethritis (urethral discharge, dysuria, irritation). Nearly half the isolates (48%) met the criteria for MDR. Furthermore, the bla _CTXM-15 gene was found in two isolates that were highly resistant to ceftriaxone (CRO). The other 22 CRO-resistant strains had low minimum inhibitory concentrations and showed alterations in the transpeptidase domain of penicillin-binding protein 3. Moreover, resistance to CRO was high (37%). Most of our urethral strains grouped into one cluster, and this difference was statistically significant when the phylogenetic analysis was performed with samples from different anatomical origins. Conclusions: The increase in H. parainfluenzae strains isolated in the urethra belonging to only one cluster is worrying. Moreover, the isolation of strains increasingly resistant to different groups of antimicrobials highlights the need for close monitoring of the evolution of resistance and the transmission of these resistant strains in the future. Larger studies should be planned to establish the epidemiological relevance of these difficult-to-treat MDR bacteria.

Streptococcus downii is a recently reported bacterial species of oral origin, with inhibitory capacity against Streptococcus mutans, Actinomyces naeslundii, Veillonella parvula and Aggregatibacter actinomycetemcomitans, which confers upon it the potential of being an oral probiotic. The aim of the present study was to identify the potential mechanisms by which S. downii exerts its inhibitory effect on S. mutans. To this end, the study assessed the consumption of glucose and proteins available in the culture medium, the modification of the pH, the production of short-chain fatty acids, the changes in the protein panel of the inhibition halo, the production of hydrogen peroxide and the effect of proteinase K. There were no differences in the glucose values or in the protein content of the medium, but there was a reduction in pH (with no effect on the growth of S. mutans). Significant increases were detected in the levels of lactic and formic acid (with no effect on the growth of S. mutans), as well as changes in the peptide panel (with no effect on the growth of S. mutans). The inhibitory effect was maintained in the presence of peroxidase but disappeared after adding proteinase K. Based on these results, it is suggested that the main mechanism of inhibition of S. downii against S. mutans is the production of bacteriocins.