الفهرس 
Escherichia coliOnly 14 pages are availabe for public view
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Abstract
Shiga-toxin producing E. coli (STEC) is a pathogen that causes diseases in humans, ranging from non-bloody diarrhea to severe illnesses as haemorrhagic colitis (HC) and haemolytic uraemic syndrome (HUS). Ruminants are regarded as the natural reservoir for Shiga toxin-producing Escherichia coli (STEC). Monitoring of ruminants and environmental samples (such as irrigation water and soil) is essential to evaluate the risk factor associated with STEC infection in humans.This study highlights the occurrence of different types of O157 STEC and non-O157 STEC in animals such as cattle, sheep, goat and calves; environmental samples as irrigation water, soil and food samples of plant and animal origins.
A total of 642 samples were investigated directly for Shiga-toxin encoded genes by Real Time PCR method using stx and eae specific probes. After enrichment of the samples isolation of STEC on selective media was carried out. Suspected colonies were tested for shiga-toxin by Real Time PCR.
Results indicated that out of the642 samples only 36 isolates were positive to one or more of the previously mentioned genes. Out of 120 fecal samples from different ruminants, 16.7% were positive for Shiga toxin. The highest percent of positive STEC samples was recorded in buffalos (30%) were positive, while cows (15%); sheep (20%); goats (10%) and calves (20%). These results indicated the high prevalence of STEC in buffalos than cows and sheep. Irrigation water samples showed (8.3%) positive STEC. All the drinking water samples (25 samples) were negative.
Investigation of food samples indicated that (8%) of minced beef samples; (10%) chicken fillets and (4%) processed meat (4 %) in raw milk were found to be contaminated with STEC. However STEC was not isolated from the plants during this study.
Serotyping of the isolates revealed that serotype O157 was the most predominant serotype in water samples, while other various serotypes and non-O157 such as O78, O55, O26, O1 and O126 were distributed in the rest of the isolates recovered from the other sources. It was noted that the presence of non-O157 was greater than O157 in fecal samples and Milk.
STEC were not isolated from human fecal samples and screening using real time PCR didn’t give any amplification for the stx1 or stx2 genes. However, eae gene was isolated from various samples suggesting the presence of a pathogenic E. coli other than STEC which may be enteropathogenic E. coli.
The German strain of the year 2011 (E. coli O104:H4-2011) was not isolated or detected in this study suggesting that this strain is not found in our environment and that the causative agent of the 2011 outbreak was not originated from Egypt.
Antibiotic susceptibility of STEC isolates indicated that all the isolates were resistant to penicilliG, vancomycin, while most of them were resistant to the tetracyclin. All isolates were sensitive to the imipenem, gentamycin and norofloxacin. Isolates recovered from animal fecal samples and food samples were the most resistant isolates, some were resistant to 6 antibiotics.
Twelve isolates were selected from different samples for studying the distribution of shiga-toxin subtypes; it was noticed that the most frequent subtype was stx2 type (c) followed by stx2 subtype (d), and the least to be recorded was Subtype (a). A combination of stx2 subtypes was recorded in some isolates.
Detection of β lactamase resistance genes (blaCTX, blaSHV and blaTEM) was also studied; this study confirms the prevalence of ESBL-producing bacteria of STEC group and demonstrates the spread of genes encoding ESBLs among STEC isolated from animals and/or the environment.
Silver nano-particles are useful for medical applications due to their strong antibacterial activity. In this study, silver nano-particles were synthesized using specific chemical method and it was characterized by UV-vis spectroscopy and transmission electron microscope (TEM). Spherical nano-silver proved to have potential against E. coli and STEC.