Species identification by groESL genes and analysis of antibiotic resistance determinants in viridans group streptococci
Date Issued
2005
Date
2005
Author(s)
Fu, Huey-Ling
DOI
zh-TW
Abstract
Viridans group streptococci (VGS) are a group of heterogeneous gram positive facultative anaerobic cocci. They are usually considered to be commensals of the human oral cavity, but in recent years it has become clear that members of these species can be responsible for many infections, such as endocarditis, meningitis, purulent infections etc. VGS can also cause infection or death in immunocompromised patients. Furthermore, the clinical pathogenic and treatment may differ between species, thus, a correct identification for VGS to individual species level seems to be an important and meaningful work.
Members of VGS can be divided into five major clusters according to their 16S rRNA sequences, which are highly conserved among bacteria and usually considered as gold standard. The five clusters include anginosus group, mitis group, sanguinis group, mutans group and salivarius group. Species identification of VGS has been difficult by conventional or automated systems. Differentiation between species by 16S rRNA gene is also not satisfactory due to their high similarity, therefore, some confusion may occur especially for anginosus group and mitis group.
Our previous studies showed the groESL (cpn10/60 ) gene sequences were useful in differentiation of several bacterial species. The identities of the groES gene sequences among the VGS species for limited strains were about 62.1 to 95.1%, and the groEL gene sequences were 77.2 to 95.2%. Thus, we tested more clinical isolated using the same strategy to evaluate the clinical application for species identification. The tested isolates include anginosus, mitis, and sanguinis groups. We performed PCR and nucleotide sequencing, group-specific PCR, PCR- RFLP, multiplex PCR and compared the results with 16S rDNA identification. Our data revealed that the groESL genes can provide an additional parameter for species identification of VGS, particularly when 16S rRNA sequences share high degrees of similarity, otherwise, if more sufficient information can be available from Databank, the groESL gene is potentially useful in the differentiation of closely related species.
Furthermore, the incidence of penicillin resistance in VGS has been increasing in recent years, and the major mechanism was known as modification of the PBPs. PBPs are made up of an N-terminal hydrophobic region, a central penicillin-binding domain, and a C-terminal domain, the active site of transpeptidase activity is formed by three conserved amino acid motifs, SXXK, SXN, and KTG.
It has been reported that amino acid alternations in or flanking conserved motifs are associated with low-affinity variants of the PBPs, specifically decreased affinity of PBP1a, 2x, and 2b with β-lactams. These three PBPs are considered to be the key targets for β-lactams and were therefore chosen for examination in this study by using PCR-nucleotide sequencing, TA-cloning and PCR-RFLP methods. In this study, we found some possible significant amino acid alternations in penicillin-intermediate or resistant strains in both mitis and sanguinis groups. The amino acid alternations were in or near the active binding sites of PBP 1a, 2b and 2x, thus, possibly correlated with penicillin resistance.
Subjects
草綠色鏈球菌
groESL基因
青黴素
viridans group streptococci
groESL genes
penicillin
Type
other
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