[Show abstract][Hide abstract] ABSTRACT: Our objective was to characterize 46 unique, erythromycin-sensitive, and clindamycin-resistant Streptococcus agalactiae strains from S. Korea that displayed a novel phenotype in double-disk diffusion assay. We used polymerase chain reaction to determine presence of erythromycin and clindamycin resistance genes, disc diffusion assays to determine resistance phenotype, and microbroth dilution to determine minimal inhibitory concentration. We detected a novel phenotype in the double-disk diffusion assay for inducible resistance among 46 S. agalactiae strains that were both erythromycin sensitive and clindamycin resistant. Thirty-two strains with the novel phenotype tested positive for erm(B) by DNA-DNA hybridization; sequencing of the erm(B) gene revealed mutations in the ribosomal binding site region in the erm(B) open reading frame, which is consistent with a lack of erythromycin resistance phenotype. Although identified from patients at multiple hospitals, genotyping suggested that the strains are closely related. The new phenotype shows increased sensitivity to clindamycin in the presence of erythromycin.
Full-text · Article · Dec 2010 · Microbial drug resistance (Larchmont, N.Y.)
[Show abstract][Hide abstract] ABSTRACT: The prevalence of group B streptococcus (GBS) among pregnant women and disease burdens in neonates and adults are increasing in Korea. Colonizing isolates, collected by screening pregnant women (n=196), and clinical isolates collected from clinical patients throughout Korea (n=234), were serotyped and screened for antibiotic resistance. Serotype III (29.8%) and V (27.7%) predominated, followed by Ia (17.0%). Antibiotic resistance was higher among clinical than colonizing isolates for erythromycin (35.1% and 26.9%; P=0.10) and for clindamycin (49.4% and 42.1%; P=0.17). erm(B) occurred in 91.9% of erythromycin resistant isolates, and 84.0% of isolates resistant to clindamycin. Only five isolates (4.2%) resistant to erythromycin were susceptible to clindamycin; by contrast, and unique to Korea, 34% of isolates resistant to clindamycin were erythromycin susceptible. Among these 60 erythromycin-susceptible & clindamycin-resistant isolates, 88% was serotype III, and lnu(B) was found in 89% of strains. Four fifths of the serotype V isolates were resistant to both erythromycin and clindamycin. Further characterization of the genetic assembly of these resistance conferring genes, erm(B) and lnu(B), will be useful to establish the clonal lineages of multiple resistance genes carrying strains.
Full-text · Article · Jun 2010 · Journal of Korean medical science
[Show abstract][Hide abstract] ABSTRACT: Background: Group B Streptococcus (GBS), a leadingcause of neonatal mortality and morbidity in the United States, is increasingly resistant to the erythromycin and clindamycin therapies recommended for β-lactam sensitive patients. Phenotypic resistance can be constitutive or inducible, which is determined using a double disc diffusion assay. Methods: We tested 394 Korean GBS isolates collected in 2006-2007 and 896 GBS strains from two geographical regions in the USA collected in 1998-2002, for antibiotic susceptibility and prevalence of antibiotic resistance conferring genes, using high throughput DNA-DNA hybridization. Results: Resistance to clindamycin and erythromycin was 47 % and 31 % for Korean isolates, 19% and 24% for Wisconsin isolates, and 39% and 40% for Michigan isolates. For the majority of strains, phenotypic resistance correlated to the presence of ribosomal methylase genes ermAT, ermB, drug efflux gene mefA and lincosamide nucleotidyl transferase gene linB, either singly or in combination. However, one or more of the antibiotic genes was present in 6-11% of all strains phenotypically susceptible to erythromycin, clindamycin or both. Double disc diffusion assays of the 38 Korean GBS strains that were ermB and linB positive but phenotypically clindamycin resistant and erythromycin susceptible, revealed an unusual pattern: a channel of growth inhibition was observed between the erythromycin and clindamycin discs. Conclusion: To our knowledge this double disc diffusion pattern has not been reported previously. Studies to determine the mechanistic implication of this double disc diffusion pattern for erythromycin and clindamycin resistance are ongoing.