Background: This study determined macrolide resistance genotypes in clinical isolates of Streptococcus\r\npneumoniae from multiple medical centers in Lebanon and assessed the serotype distribution in relation to these\r\nmechanism(s) of resistance and the source of isolate recovery.\r\nMethods: Forty four macrolide resistant and 21 macrolide susceptible S. pneumoniae clinical isolates were tested\r\nfor antimicrobial susceptibility according to CLSI guidelines (2008) and underwent molecular characterization.\r\nSerotyping of these isolates was performed by Multiplex PCR-based serotype deduction using CDC protocols. PCR\r\namplification of macrolide resistant erm (encoding methylase) and mef (encoding macrolide efflux pump protein)\r\ngenes was carried out.\r\nResults: Among 44 isolates resistant to erythromycin, 35 were resistant to penicillin and 18 to ceftriaxone.\r\nExamination of 44 macrolide resistant isolates by PCR showed that 16 isolates harbored the erm(B) gene, 8 isolates\r\nharbored the mef gene, and 14 isolates harbored both the erm(B) and mef genes. There was no amplification by\r\nPCR of the erm(B) or mef genes in 6 isolates. Seven different capsular serotypes 2, 9V/9A,12F, 14,19A, 19F, and 23,\r\nwere detected by multiplex PCR serotype deduction in 35 of 44 macrolide resistant isolates, with 19F being the\r\nmost prevalent serotype. With the exception of serotype 2, all serotypes were invasive. Isolates belonging to the\r\ninvasive serotypes 14 and 19F harbored both erm(B) and mef genes. Nine of the 44 macrolide resistant isolates\r\nwere non-serotypable by our protocols.\r\nConclusion: Macrolide resistance in S. pneumoniae in Lebanon is mainly through target site modification but is also\r\nmediated through efflux pumps, with serotype 19F having dual resistance and being the most prevalent and invasive.
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