Evaluation of antisera used for detecting enterotoxigenic Escherichia coli in Sao Paulo

The usefulness of antisera in detecting enterotoxigenic Escherichia coli (ETEC) strains in Sao Paulo was evaluated. Polyvalent antisera detected 49% of ETEC isolates and were more effective in identifying E. coli that produced heat-labile and heat-stable enterotoxins and in strains that produced only heat-stable enterotoxin. ETEC strains not detected by the antisera belonged to different serogroups not isolated in Sao Paulo before; 34% of these strains had undetermined O antigens, and most of them produced only heat-labile toxin. A variation of serogroups over time was especially observed among strains that produced heat-stable toxin. The importance of H-antigen determinations in the effectiveness of ETEC diagnosis by serological methods became evident, as non-ETEC strains were also detected by polyvalent antisera, but their serotypes were different from those of ETEC strains. Although antisera can be used to identify O:H types of ETEC strains with accuracy, serotyping cannot be recommended for routine diagnosis. However, such a procedure may be useful for studying outbreaks of ETEC diarrhea if the involved serotypes are already known.