Food & Dairy Microbiology (CC - 11) - PowerPoint Presentation

1. Food & Dairy Microbiology (CC - 11)Food Borne Diseases (Unit - 5)

2. Food – borne diseases are common-source diseases; a single contaminated food source at a food-processing plant or a restaurant, may affect a number of individualsFailure to adequately decontaminate & preserve food may allow the growth of pathogens, resulting in diseases with significant morbidity and mortalityFood poisoning / Food intoxicationIt results from ingestion of foods containing preformed microbial toxinsThe microorganisms that produced the toxins do not have to grow in the host and are often not alive at the time the contaminated food is consumedThe illness is due to ingestion & subsequent action of preformed bioactive toxin

3. These toxins are called enterotoxins as they disrupt the functioning of the intestinal mucosa Example – exotoxin of Clostridium botulinum and the superantigen toxins of Staphylococcus aureusFood infectionFood infections are active infections resulting from ingestion of pathogen-contaminated foodIn addition to the passive transfer of microbial toxins, food may contain sufficient numbers of viable pathogens to cause infection and disease in the hostExample – Salmonella food infection

4. Staphylococcal Food PoisoningCausative agent: Staphylococcus aureus It is a Gram –positive coccus and is resistant to heat, drying, radiationIt is found in the nasal passage & on the skin of humans & other mammalsFrom these sources it can readily enter foodIf the bacteria are allowed to incubate in certain foods, they produce heat-stable enterotoxins that render the food dangerousEven if the toxin -containing foods are reheated before eating, the toxin may remain active as it is heat-stable

5. Foods involved: contaminated custard & cream – filled baked goods, ice cream, pastries, poultry, meat and meat products, gravies, egg and meat salads, puddings, creamy salad dressings etc.The disease is caused by ingestion of improperly stored or cooked food or the food may be inoculated with the bacteria from an infected food handlerIf such foods are kept refrigerated after preparation, they usually remain safe, because S. aureus growth is significantly reduced at low temperaturesPathogenesis:It produces 6 different enterotoxins – A, B, C1, C2, D, EEnterotoxin A (a superantigen) is most frequently associated with Staphylococcal food poisoning

6. Superantigens work by stimulating large numbers of T cells, which in turn release intracellular mediators called cytokines & lymphokines, thereby activating a general inflammatory response in the intestine that results in gastroenteritis, including massive loss of fluids from the intestine S. aureus enterotoxin A is a small single peptide of 30,000 molecular weight that is encoded by a chromosomal geneSymptoms: Typical symptoms include severe abdominal pain, cramps, diarrhea, vomiting, nausea, occurs within 1-6 hours and usually resolving within 24-48 hours after onset

7. Diagnosis:Detection of either enterotoxin or S. aureus exonuclease are availableThese rapid tests are qualitative, confirming only the presence or absence of S. aureus above the detection limits of the assayBacterial plate count is performed for quantitative detection and to determine the extent of bacterial contaminationFor Staphylococcal growth, high-salt medium containing 7.5% sodium or lithium chloride is used. Among food contaminants, Staphylococci are the only bacteria that can tolerate such high levels of salt

8. Diagnosis is based on the symptoms or laboratory diagnosis of the bacteria from foodsTreatment:Severe cases may require treatment for dehydration with fluid and electrolyte restorationTreatment with antibiotics is not useful because the disease is caused by a preformed toxin, not an active infection

9. Prevention:Prevention & control involve avoidance of food contamination and control of personnel responsible for food preparation & distributionThe disease can be prevented by careful sanitation & hygiene measures both in production and food preparation steps and by storage of foods at low temperatures to inhibit bacterial growthFoods susceptible to colonization by S. aureus that kept for several hours above 40C should be discarded rather than eaten

10. Clostridial Food PoisoningCausative agent: Clostridium perfringens & Clostridium botulinumThey are obligately anaerobic, endospore-forming, Gram positive rod, found in soil and aquatic sedimentsThe most common source of infection is home-canned food that has not been heated sufficiently to kill contaminating endosporesCanning & cooking procedures kill living organisms but do not kill spores. Under appropriate anaerobic conditions, the spores germinate & toxin is produced during vegetative growthIf the food is then eaten without adequate cooking, the toxin remains active & the disease results

11. Clostridium perfringens Food PoisoningIt is commonly found in soil & in the intestinal tract of many animals in small numbers and is therefore found in sewageFoods involved: cooked & reheated meats and meat productsThe disease results from the ingestion of a large dose of Clostridium perfringens (>108 cells) in contaminated cooked and uncooked food, especially meat, poultry and fishPathogenesis: Large numbers of C. perfringens can grow in meat dishes cooked in bulk & then left at 20-40 0C for short time periods

12. Spores germinate under anoxic conditions, such as in a sealed container, and grow quickly in the meatHowever the toxin is not yet presentAfter consumption of the contaminated food, the living C. perfringens begins to sporulate in the intestine, triggering production of the perfringens enterotoxinSymptoms: The enterotoxin alters the permeability of the intestinal epithelium, leading to diarrhea, intestinal cramps, usually with no fever or vomitingThe onset of perfringens food poisoning begins about 7-15 hours after consumption of the contaminated food, but usually resolves within 24 hours

13. Diagnosis: By isolation of C. perfringens from the gut or isolation of C. perfringens enterotoxin from feces by direct- ELISATreatment: C. perfringens food poisoning is self-limiting, treatment is not necessary, although antitoxin is availablePrevention: It requires measures to prevent contamination of raw & cooked foods and control of cooking and canning procedures to ensure proper heat treatment of all foods

14. Clostridium botulinum Food PoisoningBotulism is a severe food poisoningIt is often fatal & occurs following the consumption of food containing exotoxin produced by the bacteriumThis bacterium normally inhabits soil or water, but its spores may contaminate raw foods before harvest or slaughterIf the foods are properly processed so that the endospores are removed or killed, no problem arises; but if viable spores are present, they may initiate growth & toxin productionEven a small amount of the neurotoxin can be poisonous

15. Foods involved: Foods that are not cooked after processing - nonacid, home-canned vegetables such as corn, beans are often used without cooking when making cold saladsSmoked & fresh fish, vacuum packed in plastic, are often eaten without cookingUnder such conditions, the endospores germinate & the resulting cells produce toxinIf these foods are consumed, then ingestion of even a small amount will result in this severe & highly dangerous type of food poisoningPathogenesis: Botulinum toxin is a neurotoxin that causes flaccid paralysis, usually affecting the autonomic nerves that control body functions such as respiration & heart beat

16. This neurotoxin binds to the synapses of motor neuronsIt selectively cleaves the synaptic vesicle membrane protein synaptobrevin, thus preventing exocytosis and release of the neurotransmitter acetylcholineAs a consequence, muscles do not contract in response to motor neuron activity & flaccid paralysis resultsAt least, 7 distinct types of botulinum toxins are knownThe toxins are destroyed by high heat (80 0C for 10 min). Therefore, thoroughly cooked food, even if contaminated with toxin, may be harmlessSymptoms: Symptoms occur within 18-24 hours of toxin ingestion & include blurred vision, difficulty in swallowing and speaking, muscle weakness, nausea, vomitingWithout adequate treatment, 1/3rd of the patients may die within a few days of either respiratory paralysis or cardiac arrest

17. Infant BotulismIt occurs when spores of C. botulinum are ingested, often from raw honey or house dustIf the infant’s normal flora is not well developed or if the infant is undergoing antibiotic therapy, the spores may germinate & C. botulinum cells may grow & release toxinMost cases of infant botulism occur between the first week of life and 2 months of age; it is rare in children older than 6 months when the normal intestinal flora is more developedThe infant becomes constipated, generally weak and eats poorlyDeath may result from respiratory failure

18. Diagnosis: By hemagglutination test or inoculation of mice with the patient’s serum, stools, vomitus to prove toxigenicity or by finding toxin or C. botulinum cells in suspected food productsIn infant botulism, bacterial cell & toxin are often found in bowel contentsTreatment: Supportive care, mechanical ventilation & polyvalent antitoxinPrevention: Heating susceptible foods to destroy spores or boiling for 20 min to destroy the toxinsStrict adherence to safe food-processing practices by the food industryEducating public on safe home-preservation methods for foodsNot feeding honey to infants younger than 2 years of age