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Jordan University of Science and Technology Faculty of Veterinary Medicine Department of Pathology and PUBLIC Health Prof Akram Al Abboodi. E. coli O157:H7 Characteristics, Pathogenicity, Spread and Control. E. coli. Gram-negative rod, facultative anaerobe

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Jordan University of Science and TechnologyFaculty of Veterinary MedicineDepartment of Pathology and PUBLIC Health Prof Akram Al Abboodi

e coli
E. coli

Gram-negative rod, facultative anaerobe

Normal flora of the mouth and intestine

Protects the intestinal tract from bacterial infection

Assists in digestion

Produces small amounts of vitamins B12 and K

Colonizes newborns GI tract within hours after birth

E. coli 0157:H7 on the other hand produces toxins that cause severe damage to the lining of the intestine, and produce illness in humans.

many strains


Antibody – antigen rxn

Many strains
  • O antigen
    • Somatic (on LPS)
    • 174 antigens
  • H antigen
    • Flagella
    • 57 antigens
  • K antigen
    • Capsule and or fimbria antigen
    • 80 antigens
  • There are more than 700 different serotypes of E. coli
  • Distinguished by different surface proteins and polysaccharides
e coli that cause human gastrointestinal illness
E. coli that cause human gastrointestinal illness
  • Shiga toxin-producing (STEC), also called Enterohemorrhagic (EHEC)
    • E. coli O157 serogroup
    • Non-O157 serogroups
  • Enteropathogenic (EPEC)
  • Enterotoxigenic (ETEC)
  • Enteroinvasive (EIEC)
  • Other types, less well characterized

E coli O157

Pathogenic E. coli are classified according to

virulence factors(aea,hly,stxs) Intimin,Hemolysin,,Shiga toxin

mechanisms of diseases(adhering)

clinical signs(HUS)Hemolytic-uremic syndrome

presence of O and H antigens (174 O, 57H)


The Shiga toxin-producing E. coli(STEC) pathotype refers to those strains of E. coli that are capable to produce one class of cytotoxins called Shiga toxin.

Shiga toxin-producing E. coli (Sub set) that cause hemorrhagic colitis and hemolytic uremic syndrome are commonly knows as enterohemorrhagic E. coli (EHEC).


The STEC are also named verotoxin producing E. coli (VTEC). The name Shiga toxin (Stx), derived from similarity to a cytotoxin produced by Shigella dysenteriae serotype 1.

verotoxin (VT), means they are cytotoxic to Vero cells.


Shiga toxin-producing E. coli (STEC) serotypes commonly isolated from beef cattle or their products.

Therefore beef cattle or it is products can cause severe gastrointestinal disease in humans, such as hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS).






  • SOURCES of E coli
  • Primary habitat:
  • large intestine, recto-anal junction?
  • warm, constant
  • nutrient rich
  • vigorous growth
  • Secondary habitat:
  • water, soil, sediment
  • cool, fluctuating
  • nutrient limiting
  • survival





Has HACCP led to a reduction in human incidence?


An estimated 73,000 cases occur annually in the United States. That number is probably many times multiplied due to poor reporting in less industrialized countries.

example of a case study
Example of a case study

In February 2004, the Okinawa Prefectural Chabu Health Center and the Okinawa Prefectural Institute of Health and Environment reported multiple cases of E. coli 0157:H7 in a single family possibly after eating contaminated meat bought at a U.S. military commissary in Okinawa.

Positive ID of E. coli 0157:H7 was made on 02/17/2004, after OCHC gathered samples of the frozen meat and analyzed it by means of pulse field gel electrophoresis (PFGE),

. The samples were sent to Pulse Net USA for comparison to U.S. isolates, and matched E. coli 0757:H7.

To exclude the possibility of contamination after opening of the meat packages, the U.S. Naval Hospital, Okinawa, Jp. Obtained unopened packages, leftovers, and the samples of human isolates, and compared all the samples.


Example of a case study

Outbreak of Shiga toxin-producing E. coli O157 associated with consumption of watercress, United Kingdom, August to September 2013N Launders ()1, L Byrne1, N Adams1, K Glen1, C Jenkins2, D Tubin-Delic3, M Locking4, C Williams5, D Morgan1,

An increase in the number of cases of Shiga toxin-producing Escherichia coli O157 PT 2 stx2 infection was reported in the United Kingdom on 9 September 2013.

Of the 19 cases, 13 were interviewed, of which 10 reported consuming watercress purchased from one retailer. The retailer recalled pre-packed bagged salads containing watercress on 12 September.

The descriptive epidemiology was supported by a case–case study performed after control measures were implemented.

The outbreak strain was intimin (eae)positive and haemolysin (hylA) positive

serogroups of 23 non o157 stec outbreaks u s 1990 2007
Serogroups of 23 non-O157 STEC outbreaks, U.S., 1990-2007

Green shows most common serogroups of sporadic cases

persons with hus rarely had non o157 stec strains that produced only shiga toxin 1
Persons with HUS rarely had non-O157 STEC strains that produced only Shiga toxin 1

Isolates with clinical information submitted to CDC, 1983-2002

Overall, 61% of human non-O157 STEC produced only Shiga toxin 1

Brooks, JID 2005

Pyramid of Surveillance

Reported to health department & CDC

STEC isolated

Clinical lab tests for STEC

Specimen obtained

Person seeks care

Person becomes ill

Exposed to STEC


Being educated about foods that hold a certain risk to consumers is very important in preventing outbreaks of E.coli as well as other food borne pathogens.

  • Get off to a CLEAN start:

One of the best ways to prevent the spreading of and illness is hand washing. This needs to be done before and after food handling as well as when switching between different foods.

  • CHILL food and stop bacteria cold:

The danger zone for bacterial growth is between 40-140 degrees F. Chilling foods does not kill the bacteria it only stops growth. Cooking kills.

  • SEPARATE don’t cross contaminate:

Raw meat should be placed on the bottom shelf in the fridge so it cannot drip onto other foods. When shopping, storing or preparing food, raw meat should be placed away from ready to eat foods.

  • COOK safely:

Cooking meat to the safe temperature, 160 degrees F, kills E.coli. Hamburger can turn brown before it is at this safe temperature. The look, color, or feel of the meat is not a test for doneness, only trust the thermometer.

meat science 93 2013 463 468
Meat Science 93 (2013) 463–468

Prevalence and antimicrobial susceptibility of Escherichia coli O157:H7 on beef cattle slaughtered in Amman abattoirAkram R. Alaboudi ,Tareq M. Osaili, Majdi Rahahlahb Department of Pathology and Animal Health, Faculty of Veterinary Medicine, Jordan University of Science and Technology, Irbid, 22110, Jordan


Sources of Carcass Contamination

1- Hide

  • Cattle hides is an important source of microbial contamination of carcasses (McEvoy et al., 2000).
  • E.coli O157:H7 and non-O157:H7 STEC can get it is way from cattle hides to the carcass

(Barkocy-Gallagher et al., 2003, Nostosijevic et al 2008).



Many surveyed studies suggested that more than 20% of cattle shed VTEC in their feces and it might that these animals are the principle source of contamination (Elder et al. 2000; Smith et al. 2001).

The carcasses could be contaminated with VTEC when the gut contents or fecal materials get in contact with meat surfaces.

clinical lab testing for stec
Clinical lab testing for STEC
  • E. coli O157
    • Unusual feature: does not ferment sorbitol
      • streak stool specimen onto plate containing Sorbitol-MacConkey (SMAC) medium
        • select clear colonies (others are pink)
          • O157 strains agglutinate when O157 antisera is added
  • Non-O157 STEC
    • Lack unusual features, look like good E. coli

Inoculation of buffered washed onto selective medium

Chrom agar

CT-SMAC medium

Incubation at 37oC

for 18h-24h

Incubation at 37oC

for 24 hrs

five typical sorbitol- negative colonies

five typical colonies

Confirmation of pure colonies by indole formation , biochemical (MUG)

and serological with antiserum (O157,H7)

Identification by PCR;

Stx1, Stx2, Hly, eae ,O157,H7


Figure 3: Multiplex PCR for detection of virulent and toxigenic gene for E.coli O157:H7. Electrophoresis analysis (2% agarose gel) of PCR patterns for E.coli O157:H7 detection. Lane M= DNA ladder marker (Promega, USA). Lane 1 = positive control E.coli O157:H7 (ATCC # 43895). Lane 4, 6, 8, and 10 = positive result for (hly , Stx1, aea, Stx2,) with expected band size 166, 210, 397, 484 respectively. Lane 2, 3 = negative control. Lane 5, 7, and 9 No sample.



  • The 10% prevalence rate of E.coli O157: H7in hides comes in agreement with other studies reporting an E. coli O157 occurrence in hide that commonly varied from 4.5-56%

(Borhom et al., 2002, Tutenel et al. 2003b).



  • E. coli O157:H7 fecal prevalence was 8.3% and this again comes in agreement with many studies that found a fecal prevalence in cattle at slaughter or at the farm that ranges from 5 to 17%

(Laegreid et al., 1999; Bonardi et al., 2001; Chapman et al., 2001; Conedera et al., 2001; Meyer-Broseta et al., 2001; Paiba et al., 2002).


The Prevalence of E.coli O157:H7 in Dressed Beef Carcass

  • A 7.8% prevalence was higher than

0.2% reported In the U.S (FSIS, 1994).

  • Or 0.47% and 1.4% reported in the U.K (Richards et al., 1998; Chapman et al., 2001).
  • But closed to 12% in Italy(Bonardi et al., 2001).
distribution of e coli o157 h7 in hides feces and carcasses

The prevalence of E.coli O157:H7 on beef sample under study were 10%, 8.3%, and 7.8% for hides, feces and carcasses respectively.

  • These prevalence rates are closely related and nosignificant differences were observed between contamination level of carcasses, hides and feces. This seem to be quite logical as the main source of E.coli is the fecal material which found it is way to animal external surface in a way or another.
distribution of E.coli O157: H7 in hides, feces and carcasses

Contamination of carcasses with VTEC can occur when gut contents or fecal matter come into contact with meat surfaces.

  • These observations comes in close agreement with other findings in that a significant correlation do exist between the prevalence of E. coli O157 in feces and hides and carcass contamination

(Chapman et al 1994; Elder et al 2000; Bonardi et al 2001., Barkocy-Gallagher et al 2003).


Therefore the main sources of possible carcass contamination source in abattoir are both of hides or fecal content. However possible cross contamination from utensils and employers has not to be neglected.

  • This might be apparent from following observation recorded in this study, where in two cases the pathogenswere recovered from carcasses only, but not from hides or feces.

The distribution of E.coli O157:H7 among hides and carcasses depends mainly on level of hygienic precautions taken during slaughtering; hide removal evisceration and carcass dressing.

  • This could be shown when six animals revealed presence of E. coli O157 from intestinal contents but not from either hide or carcasses.

The apparently high 7.8% prevalence on carcasses surfaces reported in this study is most likely related to no good hygienicmeasures applied in studied abattoir .



  • Out of 47 toxigenic isolates, 30 (64%) isolates harboring Stx1; 6 (13%) Stx2; and 11(23%) reveled both toxin.
  • Different studies showed that Shiga toxins 2 producing strains of EHEC are more virulent than Stx1 or Stx1 and Stx2 producing EHEC (Donnenberg, 2002), and being more frequently associated with human disease complications (Boerling et al., 1999).
6 non toxigenic isolates

Non- pathogenic E.coli O 157:H7 strains (without toxins factors) have also been identified from feces or beef carcass by other researchers

(Cerqueira et al., 1999; Guyon et al., 2001; Rogerie et al., 2001; Genevieve et al., 2005).

susceptibility to antimicrobial agents

The minimum inhibitory concentration (MIC) values for 40 chosen E.coli O157:H7 isolates :

1- All isolates were susceptible to

(Gentamicin, Ampicillin, Tetracycline, Ciprofloxacin).

2- 50% of the isolates were resistant to three antibiotics (Erythromycin, Vancomycin and Neomycin).

3- 25% were multi resistant to four antibiotics

(Erythromycin, Vancomycin, Doxycycline ,Neomycin).

4- 5% resistant to five antibiotics

(Erythromycin, Vancomycin, Doxycycline, Neomycin , Streptomycin).

Susceptibility to antimicrobial agents

The results of present study indicated that E. coli O157:H7 were susceptible to gentamicin and ciprofloxacin, which come in agreement with local Jordanian isolates from sheep and goat(Tarawneh et al., 2008) and other studies in USA among E. coli O157:H7 isolates from humans, cattle, swine and food, where all E. coli O157:H7 isolates, regardless of the source of isolation were susceptible to gentamicin and ciprofloxacin

(Schroeder, 2001; Steve, 2005).


all E.coli O157:H7 tested were also susceptible to tetracycline which again comes in parallel with Dontorou et al.,2003, testing three isolates obtained from ewes’ milk, fresh sausages and swine intestines in Greece.


The uses of IMS showed increased sensitivity of the isolation method.

  • E.coli O157and E.coli O157:H7latex agglutination test are highly sensitive for confirmation of presumptively identification of E.coli O157:H7.

The results of this study may help in establishing a risk based analysis systems for E.coli and developing criteria for routine microbiological food standardization.


1- Further studies could follow to determine the prevalence of E. coli O157:H7 in other animal’s species from different farms and slaughterhouses

  • 2- A good hygienic practices or HACCP system should be applied equally at all levels along the food chain, especially in slaughterhouses to overcome the spread of E.coli O157:H7 among non carrier animals.
  • 3- It becomes necessary to add additional barriers or hurdles to control the presence of E.coli O157:H7 throughout the food chain.

3- Further studies are needed to determine other E.coli serotypes and shiga toxins subtypes.

  • 4- Implementation of a strict policy for use of antimicrobials is in need to control the emergence of antimicrobial resistant pathogens.
  • .
  • 6- Establish national record and documentation system for food borne outbreaks concerning E. coli O157:H7.