Prevalence and molecular characterization of Escherichia coli O157:H7 and Shiga-toxin producing E. coli (STEC) in cattle related sources

Abstract

Shiga toxin producing E. coli are important food safety issue worldwide. They cause illness ranging from mild diarrhea to severe Hemorrhagic colitis (HC) and hemolytic Uremic Syndrome (HUS) (Brett, et. al 2003). Among the STEC, E. coli O157:H7 has been reported as the most predominant as it causes many outbreaks and sporadic cases of hemorrhagic Uremic Syndrome in U.S.A, U.K, Japan and Europe (C.D.C. 1982, Coombes et. al. 2011). It produces syndrome like bloody diarrhea, hemorrhagic colitis, hemolytic uremic syndrome and even cause death. Cattle are considered to be the natural reservoir of STEC and E. coli O157:H7 and isolated from their feces. People can be infected because of the consumption of contaminated water, undercooked meat, milk, vegetables and other product. Since Bangladesh is an agricultural country, there is a great chance of release of these pathogen and to contaminate water, meat, vegetables and other food staff. Our study was aimed to detect and isolate the STEC and E. coli O157:H7 from cattle related sources such as cow-dung, beef, goat meet, raw milk, cowshed soil and goat dropping and characterization of E. coli O157:H7 strains isolated from all these samples. The samples were collected from different meat shop and local market places in Dhaka city. The method followed was both cultural and molecular technic based. After following the procedure of preenrichment, the samples were plated on C.T SMAC. Then the presumptive isolates were cultured on EMB and MUG media and subjected to biochemical tests. Through serological tests and PCR amplification the pathogens were isolated and confirmed as E. coli O157:H7. The isolates those containing eaeA, stx-1 or stx-2 or both, rfbE and fliC genes were considered as E. coli O157:H7. 16S rRNA analysis and sequencing of the isolates were also done. Enterotoxicity, Hemolytic activity, Invasiveness and antibiogram were done to characterize the isolates. Total 33 samples of cow-dung were tested. Among them 14 samples (42.4%) were found STEC positive and 10 isolates from 6 samples (18% of total sample) were E. coli O157:H7. Out of 48 goat meat samples 09 isolates from 05 samples were identified as E. coli O157:H7 (10%) and 12 samples (25%) were identified as STEC. Likewise 10% beef was STEC positive of which only one (2%) was E. coli O157:H7. From 43 milk samples 04 samples were STEC positive which was 9% of total sample and no E. coli O157:H7 was found in milk samples. Out of 23 samples of goat dropping, 26% were STEC and only one sample was positive for E. coli O157:H7 (4%), from 22 samples of cowshed soil no STEC and E. coli O157H7 was found. All the E. coli O157:H7 isolates were found to be non-invasive, and also non-hemolytic. About 86% of the E. coli O157:H7 isolates were found as entero-toxin producing in Rabbitilial loop test because they had stx1 or stx2 or both genes. In case of antibiotic sensitivity 81% of isolated E. coli O157:H7 were sensitive to kanamycin and 68% were sensitive to streptomycin. On the other hand 100% isolates were resistant to novobiocin and 87% were resistant to ampicillin. From the above discussion it is alarming that there are huge sources of E. coli O157:H7 and other STEC which can contaminate inland water, meat, milk and vegetables. So, the findings emphasize the need for proper cattle handling, sanitation and meat processing in the market.