Resistance patterns and mechanism of group B Streptococcus isolated from infants with invasive disease

Abstract

Objective To investigate the antibiotics resistance rates and the resistance mechanisms of erythromycin and tetracycline among group B Streptococcus (GBS)-positive isolates cultured from infants with invasive infection, and to provide a reliable evidence for the prevention and treatment of infants with invasive GBS infection. Methods From January 2013 to June 2016, the GBS strains isolated from infants with invasive diseases of < 90 days from four teaching hospitals were collected to investigate the current antimicrobial resistance status and resistance genes of these strains. The GBS isolates were identified and the minimum inhibitory concentration (MIC) of the antibiotics was determined by VITEK-2 Compact automatic bacterial identification system. Genes associated with resistance to erythromycin (ermA, ermB, mefA) and tetracycline (tetK, tetL, tetM, tetO) were investigated using PCR amplification and DNA sequencing. Results Total of 93 non-duplicate colonizing GBS isolates were collected from infants with invasive GBS infection, among whom, 34 cases with early-onset infection and 59 cases with late-onset infection were diagnosed. All the isolates were susceptible to penicillins, cephalosporins, linezolid and vancomycin. The resistance of the isolates to levofloxacin, ofloxacin and azithromycin were 8.6 %, 2.2% and 1.1%, respectively. The resistance of isolates to erythromycin, clindamycin and tetracycline were significantly high, which were 60.2%, 78.5% and 93.5%, respectively. The most predominant phenotype was cMLSB (53.9%), followed by L phenotype (26.3%), iMLSB (15.8%) and M phenotype (3.9%). Among the resistance genes investigated, tetM (46%) and tetO (74.7%) were detected among tetracycline-resistant isolates and ermB (85.7%) and mefA (3.6%) were found among macrolide-resistant isolates. But ermA was not detected. Conclusions For neonates and young infants, empirical treatment with penicillins and ampicillin at birth for all high-risk neonates were recommended. Ribosomal modification by ermB gene play major role in erythromycin resistance of GBS, and the tetracycline resistance mediated by tetO and tetM genes were dominated. Key words: Infant; Group B Streptococcus; Antimicrobial sensitivity test; Resistance gene