Sixty-nine Staphylococcus aureus isolates from two epidemiologically unrelated sources were typed by pulsed-field gel electrophoresis after SmaI digestion of chromosomal DNA (genome typing), and the results were compared with those obtained by other typing methods: phage typing with the international set of phages, capsular serotyping with monoclonal antibodies against capsular polysaccharides type 5 and 8, and zymotyping by polyacrylamide agarose electrophoresis for esterase polymorphism. A good correlation of S. aureus types was found by these four typing methods. Differentiation increased in the order capsular typing < zymotyping < phage typing < genome typing, yielding 2, 10, 20, and 26 different S. aureus types, respectively. Five of the 26 genome types were further divided into several subtypes revealing clonal relationships. When 36 French S. aureus isolates were compared with 33 German S. aureus isolates, 3 strains representing clonal populations were identical in both groups. S. aureus isolates from patients with cystic fibrosis were also typed at the beginning and the end of a 4-week summer camp for these patients. The results suggested a possible strain transmission during the summer camp. We conclude that genome typing by pulsed-field gel electrophoresis is a powerful tool not only for strain identification but also for the resolution of the clonal relationships of S. aureus strains.
The electrophoretic polymorphism of esterases was compared with that of other enzymes in Escherichia coli populations by investigating allozyme distribution of four esterases (A, B, C and I) within both the subspecific groups I, I1 and I11 and the new groups A, B1, B2, C, D and E, which have been distinguished by electrophoretic analysis of 11 and 35 enzymes respectively in the 72 reference strains of the ECOR collection. Electrophoretic distribution of esterases was distinct for each of the three subspecific groups as indicated by distributions of allozymes and electrophoretic types (distinctive combination of allozyme for the four esterases). Esterase polymorphisms of the three subspecific groups appeared to have similar features to those of three previously studied natural populations of strains obtained from human and animal gastrointestinal tracts and extra-intestinal infections in humans. Multiple correspondence analyses using data obtained from the four esterases and the 11 other enzymes also distinguished the groups A, Bl, B2, C, D and E. All strains of group B2 showed the B2 electrophoretic pattern of esterase B, which appeared to be a marker of a distinct cluster of strains frequently implicated in extra-intestinal infections.
We determined the carboxylesterase B electrophoretic profiles of 74 blood isolates of Escherichia coli from patients with urosepsis. Most strains (64%) exhibited the B2 electrophoretic pattern. P fimbrial and hemolysin genetic determinants were present and expressed significantly more often among strains with the B2 than with the B1 electrophoretic pattern. In contrast, aerobactin determinants were significantly more prevalent and more commonly expressed among the B1 strains; this difference was attributable to the presence of plasmid-encoded aerobactin in one-third of the B1 strains (P = 0.02, B1 versus B2). The prevalence and extent of antimicrobial resistance was significantly greater among the B1 strains, and the B1 electrophoretic pattern was more often found in isolates from patients with urinary tract abnormalities. We conclude that the carboxylesterase B electrophoretic pattern differentiates two groups of E. coli isolates from patients with urosepsis: strains with the B1 electrophoretic pattern are associated with urologicaHly impaired hosts, characteristically lack P fimbrial and hemolysin determinants, and often carry a plasmid-encoded aerobactin system (possibly on multiple antimicrobial resistance plasmids), whereas B2 strains more commonly invade noncompromised hosts, express P fimbriae and hemolysin, carry chromosomal aerobactin determinants, and lack antimicrobial resistance.
One hundred and ninety one strains of Escherichia coli isolated from extra-intestinal infections and 85 strains isolated from the stools of healthy human beings were compared for electrophoretic mobility and isoelectric point of carboxylesterase B, and for production of a-haemolysin and the presence of mannose resistant haemagglutinin. Fast and slow electrophoretic mobilities were distinguished among the strains. The frequency of strains showing slow mobilities was considerably higher when they originated from extra-intestinal infections (40 %) than when they were obtained from the stools of healthy individuals (7%). In a two-dimensional electrophoretic profile, the fast and slow mobility variants of carboxylesterase B were resolved into two patterns, B, and B2, respectively. The frequency of pathogenic strains that concomitantly produced a-haemolysin and mannose resistant haemagglutinin was 48.7 % for strains of pattern B2 but only 243% for strains of pattern B1. Thus, the electrophoretic pattern B2of carboxylesterase B appears to be a molecular marker for a group of highly pathogenic E. coli strains which are frequently implicated in extra-intestinal infections.
Summary. Methicillin-sensitive and methicillin-resistant strains of Staphylococcus aureus from diverse geographic origins were analysed by polyacrylamide-agarose gel electrophoresis for esterase polymorphism. Three kinds of esterase bands, designated A, B and C, were defined by their ranges of activity toward five synthetic substrates and their resistance to di-isopropyl fluorophosphate. There were five allozymes of esterase A, four of esterase B and four of esterase C. Eighteen distinct combinations of allozymes (zymotypes) were distinguished amongst 105 strains analysed. Two major zymotypes were represented by 35 and 19 strains respectively, whereas other zymotypes were represented by one or, at most, seven strains. The coefficient of genetic diversity was lower for methicillin-resistant strains than for methicillinsensitive strains. Most of the methicillin-resistant strains are represented by the two major zymotypes which differed from each other by the electrophoretic behaviour of the three esterases. These results indicate that, on the basis of esterase electrophoretic polymorphism, methicillin resistance is expressed in genetically different strains.
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