title: Differing mechanisms of surviving phagosomal stress among group B Streptococcus strains of varying genotypes.
abstract: Group B Streptococcus (GBS), a leading cause of neonatal sepsis and meningitis, asymptomatically colonizes up to 30% of women and can persistently colonize even after antibiotic treatment. Previous studies have shown that GBS resides inside macrophages, but the mechanism by which it survives remains unknown. Here, we examined the ability of 4 GBS strains to survive inside macrophages and then focused on 2 strains belonging to sequence type (ST)-17 and ST-12, to examine persistence in the presence of antibiotics. A multiple stress medium was also developed using several stressors found in the phagosome to assess the ability of 30 GBS strains to withstand phagosomal stress. The ST-17 strain was more readily phagocytosed and survived intracellularly longer than the ST-12 strain, but the ST-12 strain was tolerant to ampicillin unlike the ST-17 strain. Exposure to sub-inhibitory concentrations of ampicillin and erythromycin increased the level of phagocytosis of the ST-17 strain, but had no effect on the ST-12 strain. In addition, blocking acidification of the phagosome decreased the survival of the ST-17 strain indicating a pH-dependent survival mechanism for the ST-17 strain. Congruent with the macrophage experiments, the ST-17 strain had a higher survival rate in the multiple stress medium than the ST-12 strain, and overall, serotype III isolates survived significantly better than other serotypes. These results indicate that diverse GBS strains may use differing mechanisms to persist and that serotype III strains are better able to survive specific stressors inside the phagosome relative to other serotypes.
authors: a Department of Microbiology and Molecular Genetics , Michigan State University , East Lansing , MI , USA.
authors: Michelle L
authors: ML
authors: Korir
authors: a Department of Microbiology and Molecular Genetics , Michigan State University , East Lansing , MI , USA.
authors: Clare
authors: C
authors: Laut
authors: b Department of Medicine , Vanderbilt University , Nashville , TN , USA.
authors: Lisa M
authors: LM
authors: Rogers
authors: a Department of Microbiology and Molecular Genetics , Michigan State University , East Lansing , MI , USA.
authors: Jessica A
authors: JA
authors: Plemmons
authors: b Department of Medicine , Vanderbilt University , Nashville , TN , USA.
authors: David M
authors: 0000-0003-4587-6121
authors: DM
authors: Aronoff
authors: a Department of Microbiology and Molecular Genetics , Michigan State University , East Lansing , MI , USA.
authors: Shannon D
authors: SD
authors: Manning
mesh_terms: D000328:Adult; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D005838:Genotype; D006801:Humans; D008264:Macrophages / Q000187:drug effects / Q000382:microbiology*; D010587:Phagocytosis; D010588:Phagosomes / Q000187:drug effects / Q000382:microbiology*; D065288:Serogroup; D012703:Serotyping; D013290:Streptococcal Infections / Q000382:microbiology; D013292:Streptococcus agalactiae / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity*; D013312:Stress, Physiological; D000074084:THP-1 Cells; D037521:Virulence Factors / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D037521:Virulence Factors
keywords: Group B Streptococcus; Streptococcus agalactiae; intracellular survival; macrophages; phagocytosis