Haemophilus influenzae is a Gram-negative, non-spore-forming bacterium associated with community diseases such as otitis and sinusitis, especially in children. It is classified into serogroups “a” through “f,” with type b being the most prevalent in the pre-vaccine period. Streptococcus pneumoniae, in turn, is a Gram-positive, also non-spore-forming bacterium that causes community infections in children and older adults. It has more than 100 serotypes, whose distribution varies by geographic region. Both microorganisms can cause invasive disease such as septicemia, and they are two of the three main causes of meningitis, alongside Neisseria meningitidis. They colonize the upper respiratory tract, their only natural reservoir, and this colonization is a key factor for both invasive and non-invasive infections. In many cases, colonization is asymptomatic, making it difficult to identify carriers and compromising prevention strategies such as vaccination. In addition, these carriers can act as reservoirs and disseminators of antimicrobial-resistant strains. This ongoing study investigates the presence of asymptomatic carriers of S. pneumoniae and H. influenzae among young adults in the metropolitan region of Rio de Janeiro. The objective is to characterize obtained isolates regarding antimicrobial susceptibility, serotyping/serogrouping, genotyping, and possible identification of multidrug-resistant (MDR) strains.

A total of 306 volunteers, aged 18 to 30 years, were included, with collection of oropharyngeal mucosa samples. Samples were processed within up to 5 hours and colonies were isolated based on their morphotinctorial characteristics. Identification was performed by PCR (ply gene for pneumococcus and p6 for H. influenzae) and 16S gene sequencing. Techniques used included antibiogram, MLST (Multilocus Sequence Typing), and PCR for serotyping.

A total of 314 isolates were obtained, of which 12 were H. influenzae and 11 were S. pneumoniae, in addition to other microorganisms. Although some strains showed resistance to antibiotics, none were classified as multidrug-resistant. MLST indicated the possible presence of new alleles and sequence types.

The results reinforce the importance of continuous monitoring of these pathogens, since new variants may compromise the effectiveness of prevention strategies and contribute to increased infection cases, even in vaccinated populations.