[Selective screening of enterohemorrhagic Escherichia coli depending on hemolysis on Beutin's washed sheep blood agar plates].

Recently, Beutin et al have studied hemolysin production in a large number of serologically diverse verotoxin (VT) producing Escherichia coli (VTEC) strains and found a close association between hemolysin production and VT production. This study was to examine whether hemolysin production on sheep blood agar can be used as an epidemiological marker for microbiological screening of enterohemorrhagic Escherichia coli (EHEC). In comparison of hemolysis on washed blood agar plates prepared in our laboratory and commercially available blood agar, all VT producing strains exhibited a typical hemolytic phenotype on the former, on the other hand, VT non-producers were less hemolytic on the former than the latter. On the washed blood agar, 11 VT1 producing strains belonging to 4 different serotypes, 1 strain of VT2 producer, 5 VT1&2 producers belonging to 2 different serotypes, all the 17 strains of VTEC were positive for hemolysis. The 85 VT non-producing strains belonging to 18 different serotypes isolated from faecal specimens from patients with diarrhea were tested, 10 strains (12%) belonging to 4 different serotypes (O6, 18, 26, UT: untypable) produced hemolysin. Two-hundred four (10%) of the 2,036 strains isolated from faecal specimens from 507 healthy persons exhibited typical hemolysis. As a result of identification of these 204 hemolytic strains, 148 strains of E. coli 13 strains of Citrobacter and 10 strains of other enterobacteria, and 13 strains of Pseudomonas, 12 strains of Aeromonas, 5 strains of Proteus and 3 strains of Vibrio were detected. 148 hemolytic strains of E. coli were carried out O-serotyping with commercially available pathogenic E. coli antisera, 57 strains (39%) were classified into 11 different serotypes, but 91 strains were not typable. Most frequent serotype was O18 (24 strains), next O6 (18 strains), and other 8 different serotypes (O25, 26, 28ac, 29, 55, 146, 152, 159) were less than 2 strain respectively.