The role of cell wall surface proteins and adherence of Streptococcus pneumoniae strains in host pathogen interaction

Abstract

Background: Trimethoprim/sulfamethoxazole or SXT, was previously used as a drug of choice for respiratory tract infections due to Haemophilus influenzae. However, its popularity declines due to increasing numbers of SXT-resistant strains. Trimethoprim resistance in H. influenzae is attributed to chromosomal mutations in dhfr genes encoding dihydrofolate reductase (DHFR) while sulfonamide resistance is either due to plasmid-mediated sul2, or insertion in the folP gene which encodes for dihydropteroate synthase (DHPS). To further understand the mechanism of SXTresistance in a collection of H. influenzae strains that were isolated in Malaysia, their dhfr and folP genes were sequenced and compared with similar genes in H. influenzae strain Rd KW20 and other H. influenzae strains.Methods & Materials: Antimicrobial susceptibility test and minimal inhibition concentration (MIC) against co-trimoxazole were performed on 34 strains obtained from 10 hospitals, in nine states of Malaysia. All resistant strains were subjected to PCR targeting for dhfr, folP, sul2 genes and plasmids. The amplified products were sequenced and multiple sequence alignment was performed against the DHFR and DHPS of H. influenzae strains in the Genebank.Results: From the total of 34 strains, nine isolates were resistant to SXT with MIC that ranged from 1 to >32 g/ml. Five of these strains each possessed plasmid which carried sul2 gene. Multiple alignment of the nucleotide sequence of dhfr showed that all the SXT-resistant strains had multiple point mutations resulting in 7% change in the protein sequence. An insert of 15-bp nucleic acid in folP was detected in four SXT-resistant strains which lacked plasmid that leads to four amino acids insertion into the gene. The insert was 100% identical to the insert of H. influenzae strain A12. Strains with intermediate resistance had only point mutations in the dhfr gene with no insert in the folP gene. Conclusion:Two mechanisms of SXT-resistance in H. influenzae were observed in the Malaysian strains. Trimethoprim resistance was mainly due to multiple point mutations, while presence of sul2 or DNA insertion in folP contributed to the sulfonamide resistance. Presence of the insert in folP gene is associated to the increase in the level of resistance.