Multiple-locus variable-number tandem repeat analysis for genotyping of erythromycin-resistant group B streptococci in Iran

Abstract

Background: Group B Streptococcus (GBS or S. agalactiae) is an important pathogen causing severe invasive diseases in neonates, pregnant women, and adults with underlying medical conditions.

Methods: To investigate the incidence of resistance to macrolide, lincosamide and streptogramin type B (MLS_B) antibiotics, macrolide and tetracycline resistance determinants and genetic relationships, a total of 146 clinical isolates of GBS were collected from Tehran, Iran. The genetic relationships between erythromycin-resistant strains were determined by multilocus variable tandem repeat analysis (MLVA).

Results: All isolates were susceptible to penicillin, vancomycin, linezolid, and quinupristin-dalfopristin, but were resistant to tetracycline (96.6%, 141/146), erythromycin (28.1%, 41/146) and clindamycin (16.4%, 24/146). Among the 41 erythromycin-resistant GBS (ERGBS), the most common antimicrobial resistance gene was tetM detected in 92.7% (38/41) of the isolates followed by ermTR and ermB found in 65.8% (27/41) and 29.3% (12/41) of isolates, respectively. Of the 41 ERGBS, 95% (39/41) exhibited the constitutive MLS_B phenotype, 2.4% (1/41) displayed inducible MLS_B and 2.4% (1/41) had M phenotype. The erm methylase genes were widely related to MLS_B phenotype isolates, while the mefA gene was associated with M phenotype. MLVA analysis performed on the 41 ERGBS revealed that 34 MLVA types (MTs). MLVA analysis showed that infections due to ERGBS have been caused by a variety of genotypes, suggesting that ERGBS were clonally unrelated and dissemination of these isolates was not due to a clonal outbreak.

Conclusion: Careful usage of macrolide antibiotics in therapy, continued surveillance of resistance rate and appropriate infection control measures can help to reduce spreading of resistance isolates.

Keywords: Erythromycin; GBS; MLVA; ermB; ermTR.

Fig. 1

The phenotypic and genotypic characteristics of 41 erythromycin-resistant GBS isolates included in the present study. Each MLVA type (MT) (n = 34) is presented. cMLSB: Constitutive macrolide–lincosamide–streptograminB resistance phenotype, iMLSB: Inducible MLSB, M- Phenotype: Macrolide resistance phenotype. I: Imam Khomeini hospital, B: Baqiyatallah hospital, P: Pars hospital.