Enterohemorrhagic Escherichia coli OH7 is a major foodborne pathogen causing severe disease in humans worldwide.
Healthy cattle are a reservoir of E. The abilities to cause human disease, colonize the bovine gastrointestinal tract, and survive in the environment require that E. Three major virulence factors of E. Among these virulence factors, the role of pO is least understood. This review provides a board overview of E. Escherichia coli E. This microorganism was first described by Theodor Escherich in Most E.
However, there are some strains that have evolved into pathogenic E.
These pathogenic E. Among them, enterohemorrhagic E. The outbreak surveillance data from CDC reported that E. However, large outbreaks and sporadic cases continue to occur. The annual cost of illness due to E. The high cost of illness requires additional efforts to control this pathogen.
To increase the selectivity for E. The serotypes O and H7 can be further confirmed by a commercially available latex agglutination assay.
The chromosomal size of E. This genome includes a 4. The remaining are specific to E.
Additionally, genome comparison of E. The majority of E. Virulence-associated genes between two sequenced E. Clearly, both the acquisition and loss of DNA have played an important role in the evolution of pathogenesis of E.
Several comparative and epidemiological studies indicate that E. Cattle are the major reservoir of E.
There are rare cases of diarrheal disease in young calves with this serotype. The proportion of cattle shedding at any one time varies. Sheep, goats, pigs, and turkeys have also been found to shed E.
Pathogenic E. coli 0157:H7 - Lucy Shapiro (Stanford)
A variety of molecular subtyping methods have been developed to improve the understanding of the epidemiology of E. Among them, the PFGE method was standardized by CDC and has been applied successfully to discriminate outbreak-associated, sporadic, or unrelated infections since [ 3 ]. Although the total case numbers of E. Human infection caused by E. Most cases initiate with non-bloody diarrhea and self-resolve without further complication.
However, some patients progress to bloody diarrhea or HC in 1—3 days. Children and the elderly are at increased risk of severe clinical symptoms such as HUS.
Several strategies for therapy have been studied including the use of antibiotics and vaccination. However, there is no specific treatment for E. Therefore, treatment is mainly supportive to limit the duration of symptoms and prevent systemic complications. Given this status, highly effective measures for prevention and control of E. In the United States, the most frequent route of transmission for E. However, it can also be spread directly from person to person, particularly in child day-care facilities, and from animal to person.
Escherichia Coli O157:H7
Infections have been documented from people visiting petting zoos, dairy farms, or camp grounds where cattle have previously grazed [ 28 , 31 ]. Recently, potential airborne transmission has been reported in a contaminated building having an animal exhibit [ 70 ]. The model of transmission of E. Healthy cattle are the major reservoirs of E. Contaminated bovine products and crops are predominant sources for human infections.
Cattle are the natural reservoir of E. Contaminated ground beef is the most common vehicle for E. Beef products may become contaminated during slaughter, and the process of grinding beef may transfer pathogens from the surface of the meat to the interior.
Therefore, if ground beef is incompletely cooked, the bacteria can survive. In addition, there are a variety of contaminated food vehicles other than ground beef that have been linked to E. The largest outbreak was traced to radish sprout contamination in Osaka, Japan, where 7, individuals were diagnosed with confirmed infections [ 45 ]. Epidemiological studies indicate that these food products seem to have been contaminated through bovine fecal materials.
Therefore, prevention of E. To control E. The low pH in the stomach pH 1. The ability to survive in the acidic environment of the stomach increases the chance of bacteria to colonize the intestines and cause infection. Acid resistance is associated with a lowering of the infectious dose of enteric pathogens [ 60 ].
The low infectious dose is one of the best known characteristics of E. A variety of studies have reported the AR of E.
These studies have determined three efficient AR systems. The first AR system requires the alternative sigma factor RpoS and glucose repression. The rpoS mutant of E.
E coli o157 h7 pdf
The second AR system requires the addition of arginine during exposure of acidic condition. The arginine decarboxylase adiA and the regulator of adiA cysB were reported in this second AR system. The third AR system requires glutamate for protection at low pH condition. Whereas only one of the two glutamate decarboxylases is neededfor protection at pH 2. Previous results revealed that glutamate-dependent AR is the most effective protection at pH 2.
Moreover, it was shown that alterations in the cell wall membrane or colonic acid production are associated with successful AR. Thus, E. Three distinct patterns of E.
First, animals can be transiently culture positive for short durations of a few days and are considered passive shedders and are likely not colonized at the RAJ mucosa. Second, cattle can be colonized and shed the bacteria for an average of 1 month and typically not longer than 2 months. Third, a few rare animals are colonized for a long duration and shed the bacteria from 3 to 12 months or longer.
Age, diet, and immunity of individual cattle could also potentially affect bacterial colonization.
Cray and Moon [ 14 ] reported that calves shed E. Reducing the level of carriage of E. The understanding of colonization factors of E. Composting manure is effective in destroying E. Barker et al. Thus, it can be an efficient transmission vehicle of E.
To survive in varied environments, E. For example, the exopolysaccharide EPS production of E. These environmental adaptations of E. In addition, the ability to survive outside the host reservoir increases the risk that the pathogen may contaminate crops and produce via bovine manure contamination, irrigation with contaminated water, or direct contact with infected animals [ 42 ].
Defining the virulence factors and mechanisms of E. The production of Stxs is considered essential but not solely responsible for disease. In addition, E. Each of these aspects is described below. Stx is a potent cytotoxin and is bacteriophage-encoded. Stx is expanded from a single transcriptional unit and causes damage to a variety of cell types [ 29 ].
Stx1 is identical to Stx from Shigella dysenteriae I, but for a single amino acid difference. Virulent isolates of E. Stx2 is known to be more toxic and is more often associated with HC or HUS in human infections than are Stx1 strains [ 6 , 50 ]. Stx has a conserved structure consisting of one enzymatically active A subunit A1 and five identical receptor-binding B subunits B5. The B5 subunit binds to the specific host receptors globotriaosylceramide Gb3 or globotetraosylceramide Gb4 [ 47 ].
After binding of Stx A1B5 to the host cell, the A subunit is internalized to the cytoplasm.