VIRULENCE FACTORS OF ESCHERICHIA-COLI STRAINS ISOLATED FROM DIARRHEICCHILDREN - INFLUENCE OF STORAGE-CONDITIONS

The frequency of isolation of enterotoxigenic (ETEC), verotoxigenic (V TEC) and necrotizing Escherichia coli (NTEC) was determined in 167 chi ldren with diarrhea from a central area of Brazil. E.coli strains prod ucing verotoxin (VT), cytotoxic necrotizing factor (CNF) and thermolab ile enterotoxin (LT) were found in 3%, 3.6% and 7.2% of the cases, res pectively. The E.coli strains were also assayed for their ability to i nduce mannose resistant haemagglutination (MRHA) of human and bovine e rythrocytes. MRHA+ strains were observed in 42% of the cases and colon ization factor antigens I and II were identified in 32% of the MRHA+ c ases. After long term storage at room temperature, the stability of vi rulence factors produced by 28 selected isolates was evaluated. Produc tion of cytotoxins was maintained in 3 of the 5 VT+ and in 5 of the 6 CNF+ isolates. Expression of LT was maintained in 9 of the 12 LT+ isol ates. Of the 23 CFA+ strains, only 7 maintained the haemagglutination pattern. Expression of ST was detected in 4 strains and, besides those , 4 further ST+ strains were recognized by colony hybridization. The L T genotype was found in 11 of the selected isolates. In conclusion, by studying strains of E. coli isolated from children's diarrhea, NTEC s trains were identified for the first time in Brazil. This study also c onfirms the great importance of storage conditions for the detection o f virulence factors of ETEC and shows that VTEC and NTEC may lose its cytotoxin producing ability after prolonged storage at room temperatur e.