Effects of ampicillin, gentamicin, and cefotaxime on the release of Shiga toxins from Shiga toxin-producing Escherichia coli isolated during a diarrhea episode in Faisalabad, Pakistan.

The Shiga toxin-producing Escherichia coli (STEC) is an emerging foodborne pathogen. The proportion of cases attributed to STEC in an episode of diarrhea in the Faisalabad region of Pakistan was investigated. In addition, as increase in Shiga toxin (Stx) release after exposure to various antimicrobial agents is widely reported, we also elucidated the in vitro effects of three commonly used antibiotics (ampicillin, gentamicin, and cefotaxime) on Stx release. Isolation and detection of STEC was done using enzyme-linked immunosorbent assay and polymerase chain reaction, followed by phenotypic characterization. In vitro Stx release from isolated STEC was determined using enzyme-linked immunosorbent assay, and Stx-induced verocytotoxicity was quantified using cytotoxicity detection assay. STEC was detected in 5 (21.7%) of 23 patients. Exposure to minimum inhibitory concentration (MIC) of ampicillin, gentamicin, and cefotaxime resulted in a considerable decrease in toxin release and level of cytotoxicity in most of the STEC isolates when compared with control (without antibiotic exposure). Exposure to sub-MIC of ampicillin resulted in a relative increase in Stx release and cytotoxicity (p <or= 0.05) in three of the four isolates tested, whereas a decreasing trend was observed in isolates exposed to sub-MICs of gentamicin and cefotaxime. Sub-MIC of gentamicin resulted in largest decrease in Stx release and a similar trend was observed with cefotaxime to a lesser extent. In conclusion, these in vitro observations suggested that sub-MIC of ampicillin may stimulate Stx release and level of cytotoxicity and therefore should be avoided. Gentamicin did not show such effects and therefore may be considered for STEC antimicrobial therapy.