Antimicrobial Susceptibilities and Distribution of Resistance Genes for β-Lactams in Streptococcus pneumoniae Isolated in Hamadan

BACKGROUND: β-lactams resistant Streptococcus pneumoniae are an emerging problem throughout the world. Several resistance mechanisms have been reported, including expression of drug-destroying enzymes such as β-lactamases, altered drug targets such as conformational changes in PBPs, decreased bacterial permeability, and increased drug efflux. OBJECTIVES: The present study aimed to determine the relationship between the results of polymerase chain reaction identification of the Pbp1a, Pbp2b and Pbp2x genes (penicillin-binding proteins) and susceptibilities of β-lactam antibiotics against S. pneumoniae. MATERIALS AND METHODS: Fifty five isolates of S. pneumoniae were obtained from clinical samples with antimicrobial tests. The susceptibilities of isolates to benzylpenicillin, imipenem, oxacillin, ceftazidime were determined. The resistance genotype was determined by the polymerase chain reaction with primers designed for the PBP genes. RESULTS: The number of S. pneumoniae isolates resistant to benzylpenicillin, imipenem, oxacillin and ceftazidime were 94.5%, 100%, 100%, and 21.8%, respectively. Analysis of mutation in the genes for pbp showed that 85% of isolates had mutations in pbp2x, pbp2b and pbp1a. Susceptibility to benzylpenicillin was decreased once the number of mutated pbp genes in S. pneumonia increased. According to the results of this study, S. pneumoniae isolates showed reduced susceptibility due to accumulation of resistance genes. CONCLUSIONS: We suggest that studies should be performed to evaluate changes in Minimum Inhibitory Concentration (MIC) values as well as genetic mutations in order to determine prevalence of S. pneumoniae resistance against antimicrobial agents.