Detection of Shigella and enteroinvasive Escherichia coli by PCR in the stools of patients with dysentery in Thailand.

The rate of detection of Shigella and enteroinvasive Escherichia coli (EIEC) using a PCR technique was compared with the rate detected by standard microbiological methods (bacteriology plus hybridization of E. coli colonies with a 17 kb EIEC probe) among patients with dysentery before and after antibiotic therapy. The PCR amplified DNA sequences encoding IpaH, a multiple copy sequence located on the chromosome and the invasion plasmid. Shigella or EIEC were detected using the IpaH PCR system among 72 (61%) of 119 patients with dysentery on the first day they were seen at hospital, compared to 50 (42%) using standard microbiological methods (p = 0.006). After three days of antibiotic therapy, IpaH sequences were detected in stools from 38 percent of patients, compared to 10 percent using standard microbiology (p < 0.001). After seven days of therapy, the rates were 26 percent vs. 8 percent respectively (p < 0.001). The IpaH PCR system appeared to be specific for Shigella or EIEC based on low rates of positive reactions among non-diarrhoea controls, and a strong correlation between persistently positive reactions and antibiotic resistance of bacterial isolates. IpaH sequences were detected in 10 (8%) of 119 drinking water samples from homes of patients with disease; none of these specimens were positive for Shigella or EIEC by standard microbiology. In conclusion, PCR amplification of IpaH sequences and detection of target DNA with a non-radioactive probe increased the rates of identification of Shigella and EIEC by 45% in initial clinical specimens and by nearly 300% in specimens obtained from patients receiving antibiotic therapy.