Epidemiological studies on Escherichia coli O157:H7 in Egyptian sheep

What is it about?

In the present work, the epidemiological role of apparently healthy sheep in transmission of Escherichia coli O157:H7 in different seasons was investigated. Fecal samples (convenience sampling) of apparently healthy farmed sheep (three farms, n = 70) and from 15 wandering flocks fed on city wastes (n = 80) in the Giza governorate were examined. The samples were collected in spring under mild weather conditions and during hot summer to be compared. Out of the 150 animals, 13 (8.7 %) were E. coli O157 shedders. The 13 ovine sorbitol-negative E. coli O157 were characterized by different PCR sets. The eae gene was detected in 11 isolate (85 %), stx1 in 3 isolates (23 %), stx2 in 8 isolates (62 %), and finally the hlyA in 11 isolate (85 %). Among the 13 isolates, 2 strains (15 %) were positive for eae, stx1, stx2, and hlyA as gene combination, one isolate (8 %) for eae, stx1, and hlyA, 5 isolates (38 %) for eae, stx2, and hlyA, 1 isolate (8 %) for eae and stx2, 2 isolates (15 %) contained eae and hlyA, 1 isolate (8 %) contained hlyA only, and finally, 1 isolate (8 %) did not contain any of these genes. None of the isolates showed the gene combination eae stx1, stx1 hlyA, or stx2 hlyA. The results indicated significant association of unfavorable weather and management conditions on O157:H7 shedding while the age or sex did not play any role in this process. zoonotic importance of ecolio157:h7

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Why is it important?

The continuous evolution of new pathogenic strains of Escherichia coli through the acquisition of virulence genes carried on mobile genetic represents a great challenge for the agro-ecosystems and public health (El-Sayed 2000; Etcheverria and Padola 2013). One of the major emerged E. coli strains in the last few decades is the E. coli O157:H7 which is a serious food-borne pathogen responsible for great economic loses in the food industry worldwide. The pathogenicity of E. coli O157 is associated with a number of virulence factors, including two bacteriophage encoded cytotoxins called Shiga toxin 1 and 2 (stx1 and stx2) and their variants in addition to the outer membrane protein (intimin) which is encoded by the eaeA gene (Ayaz et al. 2014). The gastrointestinal tract of ruminants constitutes the main natural reservoir of E. coli O157:H7; however, infection in animals is typically asymptomatic (Nguyen and Sperandio 2012). The utilization of Sorbitol MacConkey agar medium (SMAC) is a simple, economic, rapid, and a reliable tool which permits the recognition of E. coli O157:H7 in stool cultures with a sensitivity of 100 %, a specificity of 85 %, and an accuracy of 86 % (March and Ratnam 1986). On the other hand, both commercial latex sets (Oxoid, Pro-Lab and Remel O157 latex reagents) are used as good alternatives to standard serologic methods for detecting E. coli O157:H7 (Sowers et al. 1996). The used kit (Oxoid, UK) in this study had a sensitivity and specificity of 100 % compared with the CDC reference antiserum (Sowers et al. 1996). In sheep, the number of epidemiological studies carried out on STEC strains is limited (Blanco et al. 2003; Rey et al. 2003; Martins et al. 2015). In Egypt, STEC was isolated from cattle (El-Sayed 2000), buffaloes and chicken (El-Jakee et al. 2012), humans (Selim et al. 2013) but not from camels (El-Sayed et al. 2008). The sheep in Egypt are usually offered poor ration such as the organic wastes and grass. Usually, they are kept with goats outdoors at the borders of large cities as wandering flocks which makes them exposed to heat stress and dryness conditions. These two factors are known to negatively affect the colonization of STEC in the gastrointestinal tract (GIT) and decrease its survival chances (El-Sayed et al. 2008). Therefore, the effect of diet and housing system on STEC isolation was investigated in the present work. In addition, and to our knowledge, there is no epidemiological or genotypical study on sorbitol-negative E. coli O157 in feces of healthy sheep in Egypt. The aim of the present work was to (1) investigate the presence of E. coli O157 in the feces of apparently healthy sheep; (2) detect the influence of different factors such as management, environment, sex, and age on the shedding and survival of E. coli O157; and finally, (3) molecular characterization of E. coli O157 in Egyptian sheep.

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