Role of Streptococcus intermedius phosphoglucosamine mutase in bacterial growth, cell morphology, and resistance to polymorphonuclear leukocyte killing.

Streptococcus intermedius is a member of the anginosus group of streptococci, an oral commensal bacterium found in infected root canals, and the causative agent of deep-seated abscesses. This organism has slow clearance when phagocytosed within neutrophils. Here, we investigated the role of its phosphoglucosamine mutase (GlmM), an enzyme associated with peptidoglycan synthesis, in bacterial growth, cell morphology, and resistance to polymorphonuclear leukocyte killing. The glmM -deletion (Δ glmM) mutant and the plasmid-borne complementation (Δ glmM / glmM) strain of S. intermedius were generated. The wild type, the Δ glmM mutant, and the Δ glmM / glmM strain were phagocytosed with human polymorphonuclear leukocytes (PMNs), and bacterial viability in PMNs was determined by LIVE/DEAD staining. Additionally, bacterial growth and cell morphology were also compared. The survival rate of the Δ glmM mutant was significant lower than that of the wild type. Although the difference in the survival rate of the Δ glmM / glmM strain compared to that of the wild type or the Δ glmM mutant was not significant, the rate appeared to be restored to the middle level. Compared to the wild type and the Δ glmM / glmM strain, the Δ glmM mutant showed reduced growth potential, a significant increase in the number of bacterial chains, and heterogeneous bacteria. GlmM is one of the factors responsible for the stable resistance of S. intermedius to clearance by PMNs. • Survival rate of the glmM mutant was lower than Streptococcus intermedius wild type. • Growth reduction, bacterial chain elongation, cell heterogeneity found in glmM mutant. • GlmM is a factor for the stable resistance of S. intermedius to PMN killing. [ABSTRACT FROM AUTHOR]