Molecular analysis of multiple isolates of the major serotypes of group B streptococci

Serotyping of clinical isolates is a widely used technique for epidemiologic study of group B streptococcal infections. However, serotyping cannot definitively determine epidemiologically related or unrelated isolates. We investigated the use of restriction endonuclease analysis (REA) with both conventional agarose gel electrophoresis (AGE) and pulsed-field gel electrophoresis (PFGE) in 50 isolates of the major serotypes of group B streptococci. Single digestion with HindIII and HaeIII and double digestion with HindIII and then EcoRI were used for conventional AGE, and digestion with SmaI was used for PFGE. The molecular profile of one strain was compared with those of the strains within the same serotype as well as with the profiles from strains of different serotypes. Among 10 type Ia, Ia/alpha, Ia/alpha+beta, and Ia/R1 isolates and depending on the restriction enzyme used, we found between five and six REA patterns by conventional AGE and seven by PFGE; among 4 type Ib/alpha+beta isolates we found 2 to 4 REA patterns by conventional AGE and 4 by PFGE; among 21 type II, II/alpha, II/beta, II/alpha+beta, and II/R4 isolates, we found 11 REA patterns by both AGE and PFGE; and among 14 type III, III/R1, and III/R4 isolates, we found from 7 to 12 different REA patterns by AGE and 10 by PFGE. In total, among 13 serotypes and one nontypeable strain, we found 29 to 31 REA patterns by conventional AGE and 33 by PFGE. A particular REA pattern within a serotype was different from the patterns found in the other serotypes, suggesting that REA analysis by using conventional AGE or PFGE is a sensitive method for analyzing genetic relatedness and diversity in group B streptococci and has potential value in molecular epidemiologic studies.

Characterization of methicillin-susceptible and methicillin-resistant Staphylococcus aureus isolates by molecular typing methods

Two groups of clinical Staphylococcus aureus isolates were examined by molecular typing methods. Detailed protocols for the technical procedures are described. By means of plasmid DNA profiles, plasmid DNA restriction enzyme digestion, as well as whole-cell DNA endonuclease digestions subjected to conventional agarose gel electrophoresis and pulsed-field gel electrophoresis, eight methicillin-susceptible S. aureus strains from three patients segregated into three different groups. Consecutive isolates from the same patient revealed identical fingerprints. Generally, good agreement between different molecular typing methods also was achieved in the investigation of 28 methicillin-resistant isolates. However, compared to whole-cell DNA restriction endonuclease analysis, plasmid DNA profiling (all but one strain had detectable plasmid DNA) showed a somewhat greater discriminatory ability. The techniques evaluated were reproducible and relatively easy to perform and provided valuable tools for studying the epidemiology of S. aureus in hospitals.

DNA fingerprints of Streptococcus pyogenes are M type specific

DNA from group A streptococci of various M and T types was cleaved with endonucleases to produce a DNA fingerprint. Comparison of DNA fingerprints proved to be a very useful tool for studying the epidemiology of isolates from various outbreaks of streptococcal disease. Patterns of DNA fragments from HindIII digests of samples of total DNA were conserved among strains of the same M serotype yet were easily distinguished from those of different M serotypes. Different M types were associated with specific restriction enzyme profiles. DNA fingerprints of strains of the same M type were stable enough to establish a clonal relationship between strains obtained from an isolated outbreak of disease or strains endogenous to people geographically isolated by continent. Strains of the same serotype from different continents had very similar, but distinguishable, restriction profiles. Those strains unable to be typed with standard typing sera were also amenable to comparison because they yielded unique fingerprints.