Molecular epidemiological survey of Streptococcus agalactiae in neonatal nosocomial infection

Abstract

Objective The present study aimed to investigate the molecular characterizations and virulence factors mediating adhesion of S. agalactiae. Methods All the 6 GBS strains from maternity ward, 4 isolated from the blood of neonates and 2 isolated from the vaginal secretions of their mothers, were performed antimicrobial susceptibility tests through disk diffusion method, and analyzed by multilocus sequence typing (MLST) and pulse field gel electrophoresis typing(PFGE) to determine the relationship between the strains and whether it was nosocomial infection or not. The S. agalactiae isolates were subjected to capsular genotyping by PCR. Determinants of adherence factors were also detected by PCR and sequencing, including surface proteins and pilus-like structures. Results The results of antimicrobial susceptibility tests of 7 /13/37/66 are the same, while 142 and 158 are the same but different from the other 4 strains. The MLST results indicate that 7 /13/37/66 are of the same sequence type ST-12, while 142 and 158 are ST-19. PFGE results have further proved that 7/13/37/66 are of the same clone type, and 142 and 158 were another clone type. The strains of 7/13/37/66 are serotype Ib, and contain bac, bca, and alp2/3 genes, while 142 and 158 are serotype III and contain e gene. All the six strains contain PI-1 and PI-2a genes. Conclusions There are not only vertical but also horizontal transmissions in the 4 cases, which may be a nosocomial infection event. Six strains all contained primary adhesion factor of S. agalactiae: surface proteins and pilus-like structures, which indicates that all the 6 strains has a strong toxicity in adhesion and spread. The hospitals should reinforce the prenatal examination of S. agalactiae and control the nosocomial infection.(Chin J Lab Med, 2018, 41: 352-355) Key words: Bacteremia; Streptococcus agalactiae; Virulence factors; Infant, newborn; Molecular epidemiology