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J Med Entomol. 2018 Feb 28;55(2):436-439. doi: 10.1093/jme/tjx225.

Prevalence of Shiga-toxigenic Escherichia coli in House Flies (Diptera: Muscidae) in an Urban Environment.

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Department of Entomology, Kansas State University, Manhattan, KS.
Department of Biology, Pittsburg State University, Pittsburg, KS.
Department of Diagnostic Medicine and Pathobiology, Kansas State University, Manhattan, KS.


House flies (Musca domestica L. [Diptera: Muscidae]) can act as a mechanical vector for food-borne pathogens including Shiga toxin-producing Escherichia coli (Migula; Enterobacteriales: Enterobacteriaceae) (STEC) in and around cattle feedlots. The present study assessed the prevalence of STEC in house flies from a restaurant area of a town in northeastern Kansas. Two hundred twenty-four house flies were collected over 10 wk, surface sterilized, individually homogenized, and cultured by a multifaceted approach of direct plating on selective media and an enrichment broth, followed by the immunomagnetic separation. Bacterial isolates were screened for eight serogroups of E. coli: O103, O104, O26, O111, O45, O145, O121, and O157 using multiplex polymerase chain reaction (PCR). Furthermore, O-serogroup-positive isolates were tested for virulence genes stx1, stx2, eae, and ehxA by PCR. The majority (91.5%) of flies carried enteric bacteria, and the mean value of enteric concentration on the modified Possé agar was 6.7 ± 1.1 × 106 colony forming units per fly. Thirty-nine of the 224 flies (17.4%) were positive for one or more E. coli serogroup of interest; with the majority O103 (10.7%), followed by O26 (3.1%), O121 (1.3%), O45 (1.3%), and O104 (0.9%). However, none of the serogroup-positive isolates carried any of the virulence genes tested. Results of our study show that house flies in the urban environment do not carry STEC. Nevertheless, detection of E. coli O-serogroups with the potential to acquire virulence traits indicates that house flies in an urban environment represent a public health risk.


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