Food poisoning caused by Gram-negative microorganisms.

Various Gram-negative bacteria like Salmonella spp and Gram-positive bacteria like Vibrio parahemolyticus causes the severe type of food poisoning. These both causes the foodborne infection after egestion of a large number of viable cells up to 10⁵ to 10³ in contaminated food.

Food poisoning caused by Salmonella spp :

Salmonellosis may result from the ingestion of viable cells of Salmonella,which results in colonization (attachment) in the small and large intestine. Since Salmonella-induced enterocolitis and arises because of ingestion of food containing a large number of viable Salmonella. It is the foodborne infection rather than foodborne intoxication.

Organism:

Salmonella is Gram-negative, non-spore forming rods that ferment glucose usually with gas but do not ferment lactose and sucrose. Most of the isolated Salmonella are motile with peritrichous flagella. They are the member of Enterobacteriaceaeand its growth is most favorable in the temperature range of 5*C to 47*C with the optimum being 37*C. Salmonella is heat sensitive and rapidly destroyed at pasteurization temperature.The most important Salmonella spp causing food poisoning include Salmonella typhimurium, Salmonella enteritidis.

Food involved:

Human beings or other animals are directly or indirectly be the source of contamination of food with Salmonella. The organisms may come from the actual cases of disease or from the carrier. A large number of foods are involved in gastroenteritis caused by Salmonella.The food products like milk and milk products, poultry, eggs, etc. are primary vehicles, and organisms even survived in undercooked food and may cause cross contamination in other food those are consumed without further cooking. Eggs can be contaminated on the outside of the inside of the shell. If eggs are contaminated with Salmonella which is left at room temperature for long period of time bacteria get the chance to increase their number with penetration into internal food content.

Pathogenesis and disease:

The pathogenesis of the disease is described as follow:

Ingestion of>10⁵ viable cells of Salmonella

⇓

Invade (penetrate) intestinal mucosa uptake by phagocytic cells (macrophages) and m,multiply within the phagocytic cells.

⇓

Inflammatory response leads to releases of chemical mediators called Prostaglandins.

⇓

⇓

Septicemia

⇓

Prostaglandins increase cyclic AMP in the intestinal epithelium.

⇓

Sodium uptake is inhibited and Chlorine secretion is increased.

⇓

Diarrhoea

Individual differ in food poisoning and their susceptibility to Salmonella infection. Susceptibility to human may vary with the strain of organisms and a total number of organism ingested. Symptoms of gastroenteritis appear within 6-24 hours after ingestion of contaminated food. Initially, symptoms include nausea, vomiting which subside after few hours, these symptoms are followed by abdominal pain, diarrhea, sometimes fever, etc. In severe cases, evidence of disease may include watery, greenish-fowl smelling diarrhea, muscular weakness, and restlessness.

Usually, the symptoms persist up to 3 months, in the small percentage of the case (1-3%). An infected individual may continuously shed bacteria for over a year (chronic carrier- longterm). The bacteria sometimes can also enter the blood stream and causes the septic shock with pyogenic effect. This is most likely to happen in the immunocompromised individual but cases of the systemic disease may also be seen in healthy individuals.

Lab diagnosis:

Diagnosis is made by observation of clinical symptoms, history of recent food consumption and by the culture of organisms from stool specimen or may form blood sample (in systemic infection). Culture can be done using selective media as there are a number of selective media for Salmonella.

Prevention and treatment:

The following are measures of prevention of food poisoning caused bySalmonella :

1. Avoidance of contamination of food withSalmonella from sources such as diseased human beings and animals.
2. Destruction of organisms in food by proper heat treatment such as cooking and pasteurization are most effective measures to prevent contamination and food spoilage.
3. If heating is not possible their growth can be retarded by refrigeration or by use of chemical preservatives.

Treatment:

• For enterocolitis caused bySalmonellatreatment is not necessary as it is not necessary as it is a self-limiting disease.
• However, in severe cases (such as systemic), treatment can be done with antibiotics.

Food poisoning caused by Vibrio parahemolyticus:

Food poisoning caused by Vibrio parahemolyticusis one the most commonly occurring seafood poisoning and it mainly causes gastroenteritis. It is caused by ingestion of food contaminated with Vibrio parahemolyticus , so it is an example of food-borne infection rather than foodborne intoxication.

Organism:

Vibrio parahemolyticus is the causative agent of food poisoning which is Gram-negative, non-sporing forming motile organism. These are halophilic in nature and have the absolute requirement of salinity for multiplication and survive up to 0.5 to 10%. The growth temperature for this organism may vary from 10-44*C , with optimism being 35-39*C, the organism can survive in the pH range of 4-11.

Food involved:

Food involved in food poisoning caused byVibrio parahemolyticus includes raw food of marine origin such as saltwater fish, shellfish, oysters and many other.

Pathogenesis and diseases:

Its pathogenesis is described as :

1. The most virulent strain of Vibrio parahemolyticus produces key virulent factor called Thermostable Direct Haemolysin (TDH). TDH is a pore-forming toxin and causes the influx of ions in the certain cell, disrupting signal transduction and osmotic balance which result in cell death.
2. Consequently, fluid secretion causes the production of watery diarrhea. Vibrio parahemolyticus also produce the same cell associated virulent factor such as hemagglutinin pili, which are correlated with adherence and colonization of bacterium.
3. The incubation period may range from 3-76 hours and symptoms may last for up to 8days.

Symptoms:

• Typical symptoms include diarrhea, abdominal pain, nausea, vomiting, headache, fever, chills.
• The mortality rate is very low but infection is fatal in immunocompromised individuals.

Lab diagnosis:

Diagnosis can be done with:

• Detection of organisms in stool specimen or in food sample contaminated withVibrio parahemolyticus.
• Growth in usually encouraged in media containing 3-4% of salt, TCBS (Thiosulphate Citrate Bile Salt ) media is the selective medium for isolation ofVibrioSPECIES.

Prevention and treatment:

The following preventive measure can be followed like:

1. Cooking food thoroughly chilling food rapidly may prevent foodborne infection fromVibrio parahemolyticus.
2. Vibrio parahemolyticus food poisoning can also be avoided with a rejection of sea water for rinsing , washing purpose.
3. If heating is not possible their growth can be retarded by refrigeration or by use of chemical preservatives.

Treatment:

The preventive measure for foodborne infection caused byVibrio parahemolyticus is sufficient to avoid food poisoning and if any outbreak occurs usually no treatment can be done with chemotherapeutic agents such as Ciprofloxacin and Erythromycin, etc.

Reference:

1. Alexander, M. Introduction to Soil Microbiology. Academic Press, 1961.
2. Rangaswami, G and Bagyaraja PT. Agricultural Microbiology. 2nd. Prentice Hall of India, 1993.
3. RM, Atlas and R Bartha. Microbial Ecology : Fundamental and Applications. The Benjamin Cummins Publication Co. Inc., 1998.