Macrolide- and tetracycline-resistance determinants of colonizing group B streptococcus in women in Egypt

Abstract

Group B streptococcus (GBS) is a commensal bacterium of the human gastrointestinal and genital tracts. It is a leading cause of neonatal sepsis and meningitis, and has also been recognized as an important pathogen in pregnant women and the elderly. We investigated mechanisms of macrolide and tetracycline resistance in GBS colonizing women in Egypt. A total of 100 isolates were screened using standard antibiotic susceptibility tests. A multiplex PCR assay was used to detect macrolide- and tetracycline-resistance determinants. All isolates were uniformly susceptible to penicillin G, ampicillin, cefotaxime, vancomycin and levofloxacin. The resistance rates to erythromycin, clindamycin, azithromycin, tetracycline and chloramphenicol were 17, 14, 16, 98 and 1 %, respectively. Among the erythromycin-resistant isolates, 82.4 % had constitutive macrolide–lincosamide–streptogramin B (cMLSB) resistance, 5.9 % had inducible MLSB (iMLSB) resistance and 11.8 % had M phenotype resistance. Among the cMLSB phenotypes, 64.3 % of isolates harboured the ermB gene and 35.7 % of isolates harboured none of the investigated macrolide-resistance genes. The single strain expressing the iMLSB phenotype possessed the ermA gene. Of the two strains with the M phenotype, only one possessed the mefA/E gene. Conversely, seven macrolide-sensitive strains (MIC <0.03 µg ml−1) were ermB positive and one macrolide-sensitive strain (MIC <0.03 µg ml−1) harboured mefA/E. Tetracycline resistance was predominantly due to tetM, which was detected alone (83.7 %) or in association with tetL (12.2 %), tetK (1 %) or tetO (1 %). One strain carried tetM associated with both tetL and tetK, and another strain carried tetO alone. The tetO strains were positive for the mefA/E gene, and the tetL and tetK carrier strains harboured the ermB gene. Susceptible strains harbouring but not expressing an antibiotic-resistance gene should be regarded as potentially resistant. These results emphasize the need to monitor the epidemiology of GBS antibiotic resistance in Egypt.