Date of Award

2005

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Dr. Tibor Pal

Second Advisor

Sebastian G.B. Amyes

Third Advisor

Dr. Pauline Jumaa

Abstract

Identification of Shiga Toxin-Producing Escherichia coli in the UAE

By

Khawla Hamad Mohd Al-Areef Al-Dhaheri

Abstract

Various patho-groups of Escherichia coli strains are important causes of diarrheal diseases worldwide. Among these strains Shiga toxin producing isolates are particularly important. They are carried by various animals and upon infection, in humans, they may cause serious bloody diarrhea, and in some cases even life threatening sequels as hemolytic uremic syndrome. However, these infections are often under-diagnosed due to the fact that pathogenic strains do not differ from their nonpathogenic counterparts in characters investigated by standard microbiological techniques. Consequently, they can only be identified by cumbersome virulence tests, immune assays recognizing virulence specific antigens, or molecular techniques (e.g. Polymerase Chain Reaction, PCR) targeting genes coding for virulence factors. This work reports on the first attempt to reveal the presence and to characterize Shiga toxin producing E. coli (STEC) strains recovered from humans with diarrhea and from healthy farm animals in the United Arab Emirates.

Fecal samples of 146 children and 106 adults with diarrhea were tested for intestinal parasites, for common enteric bacteria and, in case of specimens from infants, also for rotavirus. Furthermore, all samples were investigated for the presence of virulence-specific genes of various diarrhea causing E. coli groups, among others STEC, by PCR. Using the same PCR method, the fecal samples of 150 sheep, 150 goats and 162 camels were also tested for STEC. Once genes of Shiga toxins were detected in the DNA extract of the samples attempts were made to isolate the strains by testing 200 randomly selected colonies by PCR. Isolated strains were serotyped, their antibiotic sensitivity tested and typed by macrorestriction analysis and by ERIC-PCR to reveal the variety of clones present.

While various enteric pathogens, among them different pathotypes of E. coli, were frequently encountered in human samples, STEC specific sequences were found only in one specimen from an adult patient. Contrary to the low prevalence of STEC in human samples, the pathogen was frequently detected in specimens collected from farm animals. Stx positive strains were isolated from 16 (10.67%) of 150 sheep, 14 (9.3%) of 150 goats, and 1 (0.6%) of 162 camels. Animal STEC strains belonged to 8 different O, and 6 different H-types, the most frequently encountered ones being O76:HNT and ONT:H2. The most frequent genotype found was stx1+, stx2+, ehxA-, eae-. None of the strains carried the eae gene and only four of them (members of a single clone) harbored the gene of enterohemolysin (ehxA). With the exception of tetracycline and chloramphenicol strains were not resistant to the antibiotics tested. Based on serotyping and molecular typing results the isolates represented several independent clones suggesting that the transfer of STEC to the local herds had not been a single event, but that they are well established in the UAE.

In summary, our findings showed that STEC is present in the UAE in farm animals and in humans. For the first time we also shown that camels can be carriers of stx positive strains. Consequently, they should also be expected as sources of human infections in this country. To meet the challenge presented by these pathogens requires an extensive use of molecular methods in local microbiological laboratories.

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