JAC Advance Access originally published online on September 11, 2008
Journal of Antimicrobial Chemotherapy 2008 62(6):1227-1233; doi:10.1093/jac/dkn388
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Original research |
Molecular characterization of erythromycin-resistant Streptococcus agalactiae strains
1 Université François-Rabelais de Tours, UFR de Médecine, EA 3854 ‘Bactéries et risque materno-fœtal’, Institut Fédératif de Recherche 136 ‘Agents Transmissibles et Infectiologie’, 37032 Tours Cedex, France 2 Service de Bactériologie et Hygiène Hospitalière, Hôpital Trousseau, CHU de Tours, 37044 Tours, France
Received 28 April 2008; returned 14 June 2008; revised 13 August 2008; accepted 19 August 2008
* Correspondence address. Service de Bactériologie-Hygiène, CHRU Trousseau, 37044 Tours cedex 9, France. Tel: +33-2-47-47-81-13; Fax: +33-2-47-47-85-30; E-mail: as.domelier{at}chu-tours.fr
Objectives: The aim of this study is to identify the molecular characteristics of erythromycin-resistant (Ermr) Streptococcus agalactiae strains and to correlate with the clinical origin of strains.
Methods: From 711 S. agalactiae strains, 119 Ermr strains (17%) were collected, serotyped and screened for macrolide resistance genes. The genetic relationship between strains was established by the PFGE analysis. Strains were tested for the group II intron GBSi1 downstream of the scpB gene, IS1548 in the hylB gene, four prophage DNA fragments and a lineage defined by multilocus sequence typing as ST-17.
Results: Erythromycin resistance involved 8% of serotype Ia, 15% of serotype Ib, 9% of serotype II, 16% of serotype III, 31% of serotype IV and 35% of serotype V. The prevalence of Ermr strains was higher among strains isolated from the gastric fluid of neonates (33%) than in those isolated from bacteraemia and meningitis during early-onset disease (EOD) or late-onset disease (7% and 11%) (P = 0.001). In serotype III, Ermr strains were more frequent in vaginal carriage (22%) and colonized neonates (18%) than in EOD (0%) (P = 0.03). The mef(A) gene was the most common in serotype Ia (55%), the erm(A) gene in serotype Ib (75%) and the erm(B) gene in the other serotypes (56% to 75%). All resistant strains with IS1548 also had the erm(B) gene. Ermr strains were not randomly distributed in the different PFGE genogroups, and 11% had the GBSi1 intron, 37% had at least one prophage DNA fragment and 7% belonged to ST-17.
Conclusions: Erythromycin resistance varied according to the clinical origin, serotype and molecular characteristics of S. agalactiae strains.
Keywords: group B streptococcus , macrolide , resistance genes , virulence , molecular markers , infectious diseases
Present address. The Methodist Hospital Research Institute Center for Molecular and Translational Human Infectious Disease Research, 6565 Fannin Street, SM8-060, Houston, TX 77030, USA.