β-Lactam resistance in Streptococcus mitis isolated from saliva of healthy subjects

• Published in: Journal of infection and chemotherapy : official journal of the Japan Society of Chemotherapy Vol. 9; no. 4; pp. 321 - 327
• Main Authors: Nakayama, Ayako, Takao, Ayuko
• Format: Journal Article
• Language: English
• Published: Tokyo Elsevier Ltd 01.12.2003; Springer
• Subjects: Adult; Ampicillin - metabolism; Ampicillin - pharmacology; Anti-Bacterial Agents - pharmacology; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bactericidal effect; beta-Lactam Resistance; beta-Lactams - pharmacology; Biological and medical sciences; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cefaclor - pharmacology; Cefotaxime - pharmacology; Female; Hexosyltransferases - genetics; Hexosyltransferases - metabolism; Humans; Infectious diseases; Male; Medical sciences; Microbial Sensitivity Tests; Minimum inhibitory concentrations (MICs); Molecular Sequence Data; Muramoylpentapeptide Carboxypeptidase - genetics; Muramoylpentapeptide Carboxypeptidase - metabolism; Mutation; Penicillin-binding protein genes; Penicillin-Binding Proteins; Penicillin-binding proteins (PBPs); Peptidyl Transferases - genetics; Peptidyl Transferases - metabolism; Saliva - microbiology; Sequence Analysis, DNA; Streptococcus mitis; Streptococcus mitis - drug effects; Streptococcus mitis - genetics; β-Lactam-resistant streptococci; Penicillin-binding protein genes; Penicillin-binding proteins (PBPs); β-Lactam-resistant streptococci; Streptococcus mitis; Minimum inhibitory concentrations (MICs); Bactericidal effect; Human; Resistance; Streptococcaceae; Antibiotic; Healthy subject; β-Lactams; Bacteria; Micrococcales; Saliva
• ISSN: 1341-321X; 1437-7780
• DOI: 10.1007/s10156-003-0286-Y

The purpose of this study was to examine the percentage of β-lactam-resistant streptococcal carriers in healthy adults, and to investigate the relationships among minimum inhibitory concentrations (MICs) of β-lactams, alterations in the penicillin-binding protein genes (pbp genes), and the affinity of penicillin-binding proteins (PBPs) for ampicillin (ABPC) in Streptococcus mitis. We also compared numbers of surviving bacteria at various ABPC concentrations in both ABPC-susceptible and -resistant S. mitis strains. The percentages of subjects carrying ABPC- and cefaclor (CCL)-resistant streptococci were 52% (27 of 52 subjects) and 100%, respectively. S. mitis, including both antibiotic-susceptible and -resistant strains, were classified into five groups according to the pbp gene mutations that resulted in alterations of the deduced amino-acid sequence in the homology boxes of PBPs. All ABPC-resistant strains showed alterations in PBP1A, 2X, and 2B, while no or only PBP2X alterations were detected in the susceptible strains. These results suggest that the accumulation of pbp gene mutations is strongly related to the MIC of ABPC for S. mitis. In the resistant strains, the affinity of PBPs for ABPC was reduced in comparison with that in the susceptible strains, and the bactericidal effect of ABPC was also reduced. Therefore, we should be aware of conditions such as infective endocarditis that are caused by β-lactam-nonsusceptible streptococci in the normal oral flora.