Common Foodborne Pathogens - V

Bacillus cereus sp. Risk Profile

Bacillus cereus and other bacillus species are gram-positive, facultatively anaerobic, endospore-forming, large rods. The identification and differentiation of serotypes further required biochemical tests to differentiate and confirm the presence of B. cereus, given characteristics are fairly common in B. mycoides, B. pseudomycoides, B. thuringiensis, and B. anthracis. Thus, differentiation depends on several factors specific to each organism such as determination of motility where most B. cereus strains are motile and the presence of toxin crystals distinguishes the B. thuringiensis. B. anthracis is usually non-hemolytic while B. cereus and others are beta-hemolytic. The rhizoid growth is characteristic of B. cereus var. mycoides and B. weihenstephanensis is a psychrotrophic strain that can grow at refrigerated temperatures.

Production of enterotoxin is associated with the vomiting form of B. cereus food poisoning. The same effect can also be caused by B. weihenstephanensis or other bacilli groups, which suggests that the plasmid carrying the emetic toxin can undergo lateral transfer, conferring the same properties to otherwise non-pathogenic strains. B. cereus is widespread in the environment and majorly on soil and vegetation.

 

The maximum temperature recorded is 48°C and the minimum growth temperature is 4°C where the optimal growth temperature is between 28°C to 35°C, and tolerance to pH ranges from 4.9 to 9.3, and the salt tolerates at 7.5%.

 

Sources

A wide range of foods such as meats, milk, vegetables, and fish, have been associated with diarrheal-type food poisoning. Vomiting-type food poisoning has been largely associated with rice products and other starchy foods such as potato, pasta, and cheese products. Besides, food mixtures such as sauces, puddings, soups, casseroles, pastries, and salads, are also been frequently linked with B. cereus food-poisoning outbreaks.

Disease

B. cereus food poisoning is a common term for the infection associated with the B. cereus family of human pathogens. There are two recognized types of infections that are caused by two distinct toxins, where diarrhea is caused by a large-molecular-weight protein, and vomiting is associated with cereulide (an ionophoric low molecular-weight dodecadepsipeptide). The cereulide is one of toughest to beat as its stability against pH and resistance to heat as well as proteases, where this non-antigenic peptide is stable after heating at 121°C for 30 minutes, cooling at 4°C for 60 days, and at a pH range of 2 to 11.

Mortality:

The mortality is a rare occurrence, but the emetic enterotoxin of B. cereus has been implicated in liver failure and death and a newly identified cytotoxin isolated from a B. cereus strain can cause a severe outbreak and deaths.

Infective dose:

The presence of large numbers of B. cereus usually more than 106 organisms/g in a portion of food is an indication of active growth and proliferation of the organism, where most often the number associated with human infection is 105 to 108 organisms/g. The pathogenicity arose from preformed toxin which is a potential human health hazard.

 

Onset:

Diarrheal stains: 6 to 15 hours after consumption of contaminated food.

Vomiting/emetic stains: 0.5 to 6 hours after consumption of contaminated foods.

 

Complications:

B. cereus foodborne infections that are caused by diarrheal or vomiting toxins producing stains generally considered mild and self-limiting, but more severe and fatal forms of the infection have been reported. Further, B. cereus can cause severe systemic and pyogenic infections such as gangrene, septic meningitis, cellulitis, panophthalmitis, lung abscesses, infant death, and endocarditis, and, in cows, bovine mastitis.

 

Symptoms:

Food poisoning of diarrheal stains can cause symptoms such as watery diarrhea, abdominal cramps, and pain where nausea may accompany diarrhea, but vomiting is a rare occurrence. Emetic stains usually cause symptoms of nausea and vomiting.

 

Duration of symptoms:

The symptoms usually subside after 24 hours of onset.

 

Route of entry:

Consumption of food contaminated with enterotoxigenic B. cereus or with the emetic toxin.

 

Pathway:

Cereulide is implicated to be toxic to mitochondria which acts as a potassium ionophore, where a serotonin5-HT3 receptor-mediated mechanism is associated with the emetic syndrome. Dermonecrotic and vascular permeability activities and fluid accumulation are observed in two diarrheal enterotoxins which are composed of multi-component proteins and the third type of enterotoxin is a member of the β-barrel toxin family that is similar to the β-toxin of Clostridium perfringens.

 

Frequency

There are thousands of cases around the world annually, but most of them are underreported or misdiagnosed due to the symptomatic similarities to Staphylococcus aureus intoxication with B. cereus vomiting type and Clostridium perfringens food poisoning with B. cereus diarrheal type. The United States has an annual average of over 60,000 for the B. cereus infections where foods that were associated with outbreaks included beef, turkey, rice, beans, and vegetables.

 

Diagnosis

Confirmation of as the pathogenic agent in a foodborne outbreak requires, either B. cereus diagnosis is carried out through isolation of B. cereus from suspect foods or isolation of large numbers of a B. cereus serotype or isolation of strains of the same serotype from the suspected food and feces or vomitus of the patient known to cause foodborne infection. Then determination of their enterotoxigenicity using serological tests for diarrheal toxin or biological tests for diarrheal and emetic stains. On the other hand, rapid-onset time to symptoms in the emetic form of the disease, coupled with some food evidence, is often sufficient to diagnose this type of food poisoning.

 

Target Populations

All humans are believed to be susceptible to B. cereus food poisoning.

 

Food Analysis

Several methods are used for the recovery, enumeration, and confirmation of B. cereus in foods, where a serological method has been developed for detecting the putative enterotoxin of B. cereus diarrheal type isolates from suspect food sources and the vomiting-type toxin can be detected through animal models or, possibly, by cell culture.

Reference:

FDA Bad Bug Book, Foodborne Pathogenic Microorganisms and Natural Toxins. Second Edition. 2013

Preventive Controls for Human Foods. 2016

www.cdc.gov