Prevalence, Antimicrobial Susceptibility and Macrolide Molecular Study in Vaginal Group B Streptococcus: A Five-Year Study among Pregnant Women Attending Antenatal Clinics in a Tertiary Care Hospital in Tunisia

Abstract

Background: Group B Streptococcus (GBS) is an important perinatal pathogen. It is considered as a leading cause of stillbirth and early onset neonatal infections. The epidemiology of maternal GBS colonization is poorly understood in Tunisia. We investigated genital GBS carriage prevalence and its associated risk factors in pregnant women. Antibiotic susceptibility was evaluated for isolated strains; macrolide gene resistance and capsular serotyping were also performed.Methods: A retrospective study conducted during 4 years at Aziza Othmana hospital of Tunis, Tunisia in pregnant women. Sampling was performed by vaginal swab. GBS was isolated by culture on selective medium; capsular serotyping was performed by rapid agglutination on Latex (PastorexStrepto B, Biorad®).Antibiotic susceptibility was performed according to the recommendations of the Antibiogram Committee of the French Society of Microbiology. Macrolide resistance was studied by a multiplex PCR assay.Results: A total of 3839 pregnant women was enrolled in the study; mean age was 31 ± 5 years A carriage GBS prevalence was estimated to 12.7% (486/3869). It was significantly associated to primiparity, third gestational trimester, altered vaginal flora and Candida co-infection. No significant association wasobserved with gestational diabetes, membranes premature rupture and premature delivery threat. The most frequent serotypes were serotype III (33.3%), II (12.8%) and I (5.1%). All GBS strains were sensitive to beta-lactams and glycopeptides; only one strain was resistant to pristinamycin and another had high level resistance to gentamycin. Tetracycline resistance was observed in 96.1% of cases. Resistance to macrolides and lincosamides was detected in 37% and 32.4% respectively. A constitutive macrolide-lincosamidestreptogramin B (MLS(B)) phenotype was observed in 73.5% of cases, the inducible type MLS(B) in 14.8% of cases and the M phenotype in 11.7% of cases. Erm(B), erm(TR) and mef (A) genes were found in 79.4%, 15.3% and 12.9% of erythromycin resistant strains. Conclusion:Vaginal GBS screening and intrapartum antibiotic prophylaxis are the most effective way to reduce early neonatal bacterial infections. Beta-lactams remain the antibiotics of choice. When allergy is diagnosed, antibiotic susceptibility is compulsory to choose an alternative such as clindamycine.