Molecular Characterization of β-Lactam Resistant Streptococcus pneumoniae

Streptococcus pneumoniae (S. pneumoniae) is a commensal bacterium that normally colonizes the human nasopharyngeal cavity. Once disseminated, it can cause several diseases, ranging from non-invasive infections such as acute otitis media and sinusitis through to invasive infections with higher mortality. Antibiotic resistance among S. pneumoniae has increased dramatically and penicillin-resistant strains have spread worldwide with pneumococcus also being resistant to other types of antibiotics like erythromycin, tetracycline, and chloram-phenicol. The aim of the present study was to study the susceptibility of the isolated strains to β-lactam and other antibiotics from different classes and to determine the prevalence of β-lactam resistance genes among S. pneumoniae clinical isolates.

From a total of 178 sputum samples, isolates identified by standard microbiological method as S. pneu-moniae were subjected to antibiotic susceptibility tests to β-lactam and non β-lactam antimicrobial agents by disk diffusion method. Biofilm formation was detected by microtitration plate and the resistance genotype was also determined using multiplex PCR technique with primers designed for PBP genes.

Out of 178 sputum samples, sixty isolates were recovered as Streptococcus pneumoniae. Most of isolates were multidrug-resistant (MDR) possessing a high (> 0.2) multiple antibiotic resistance index (MAR) value. Biofilm formation ability of isolates were strong, moderate, weak, and none, accounting for 21.67%, 45%, 25%, and 8.33% biofilm formers, respectively, and it was found that pbp1a, pbp2b, and pbp2x were present in 33 (55%), 25 (41.7%), and 45 (75%) of isolates, respectively.

Streptococcus pneumoniae clinical isolates have an alteration in PBP resistance genes in response to β-lactam therapy which subsequently lead to increased MDR phenomena among these clinically important pathogens. These findings necessitate continuous monitoring of antimicrobial resistance to guide the empirical treatment of pneumococcal disease, as well as to encourage reflections to support public immunizations strategies.