HIGH LEVEL OF SHIGA TOXIN-PRODUCING ESCHERICHIA COLI AND OCCURRENCE OF STX-NEGATIVE E-COLI O157 FROM RAW MEATS: CHARACTERIZATION OF VIRULENCE PROFILE AND GENETIC RELATEDNESS

摘要

Raw meats, especially beef, are particularly prone to Shiga toxin producing Escherichia coli (STEC)/enterohemorrhagicE. coli (EHEC) contamination. However, data regarding their quantity in raw meats are seldom reported in Thailand. Among four common meat types, beef possessed highest value of stx(1)-producing E. coli (STEC1) contamination in February 2015 [> 1,100 most probable number (MPN)/g] and stx(2)-producing E. coli (STEC2) highest MPN/g (460) in March of the same year. STEC2 was found, for the first time, in shrimp samples in March and April, 2015 with MPN/g value of 6.6 and 9.3, respectively. EHEC at 3 MPN/g was detected in only one (2%) beef sample. Even though stx-negative E. coli O157 from beef has rarely been reported in Thailand, isolation of E. coli O157 using immunomagnetic separation method revealed that four strains (PSVX-1, PSVX-2, PSVX-3, and PSVX-4) from three (8%) beef samples were shown to be stx-negative E. coli O157. These strains were members of phylogenetic group A and were multi-drug resistant. Genetic relatedness as determined by polytrinucleotide (GTG)(5)-PCR and BOX-PCR showed identical DNA profiles of PSVX-2 and PSVX-4, which by BOX-PCR were 90% to a clinical isolate, O157 strain PSU120, from Hat-Yai Hospital in 2014. The presence of these environment stx-negative E. coli O157 strains with the ability to acquire additional virulence properties could pose a potential public health problem particularly in this region of Thailand.