University of Guyana BIO 2107 Lecture 4: Microbes and the Food Industry PDF

UNIVERSITY OF GUYANA FACULTY OF NATURAL SCIENCES DEPARTMENT OF BIOLOGY BIO 2107 THE BIOLOGY OF MICROORGANISMS LECTURE 4 MICROBES AND THE FOOD INDUSTRY: FOOD SPOILAGE AND POISONING Dr. Sabrina Dookie 27th September, 20...

UNIVERSITY OF GUYANA FACULTY OF NATURAL SCIENCES DEPARTMENT OF BIOLOGY BIO 2107 THE BIOLOGY OF MICROORGANISMS LECTURE 4 MICROBES AND THE FOOD INDUSTRY: FOOD SPOILAGE AND POISONING Dr. Sabrina Dookie 27th September, 2024  Food Spoilage Food spoilage is any change in the appearance, smell, or taste of a food product that makes it unacceptable to the consumer, whether or not the change is due to microbial growth. With respect to spoilage, a food or food product falls into one of three categories: (1)Perishable foods include many fresh food items such as meats and many fruits and vegetables; (2)Semi-perishable foods include foods such as potatoes, some apples, and nuts; (3) Non-perishable foods include items such as sugar and flour. Non-perishable foods have low moisture levels and can generally be stored for long periods without spoilage. Perishable and semi-perishable foods, by contrast, typically have higher moisture levels and hence these foods must be stored under conditions that inhibit microbial growth. Fresh foods are typically spoiled by a wide variety of bacteria and fungi: The chemical properties of foods are characterised by their moisture level, the nutrients they contain and their acidity or alkalinity. Each susceptible food is typically spoiled by a specific group of microorganisms. The time required for a microbial population to reach a significant level in a given food product depends on both the size of the initial inoculum and the rate of growth during the exponential phase. Hence, an unconsumed portion of a food product that is palatable and eaten one day can be badly spoiled the next. The type of food spoilage and the microbial composition of the spoilage community are functions of both the food product and the storage temperature. Food spoilage microorganisms are often psychrotolerant, meaning that although they grow best at temperatures above 20°C, they can also grow at refrigeration temperatures (3–5°C).  Food Preservation Food storage and preservation methods are designed to slow or stop the growth of microorganisms that spoil food or that can cause foodborne disease. The major methods of food preservation include altering the temperature, acidity, or moisture level of the food, or treating it with radiation or chemicals that prevent microbial growth.  Examples of Food Preservation Techniques Examples include, but are not limited to: 1. Canning, refrigeration, and pasteurization. 2. Osmotic pressure: foods can be made drier by either physically removing the water or by adding solutes, such as salt or sugar. 3. Desiccation (removal of water through freeze drying) 4. The addition of small amounts of antimicrobial chemicals such as nitrites and sulphites (eg. dried fruit, sausages and wine). 5. The use of aseptic packaging. 6. The use of radiation (eg. to kill insects (disinfestation), reduce sprouting, and reduce the numbers of specific bacterial pathogens). 7. High-pressure preservation (eg. pascalization)  Fermentation Many common foods and beverages are preserved through the metabolic activities of microorganisms; these are fermented foods. The fermentation process yields large amounts of preservative chemicals. The major bacteria important in the fermented foods industry are organic acid–producing bacteria such as the lactic acid bacteria (in fermented milks), the acetic acid bacteria (in pickling), and the propionic acid bacteria (in certain cheeses). The yeast Saccharomyces cerevisiae produces alcohol as the preservative in the production of alcoholic beverages. The high level of organic acids or alcohol generated from these fermentations prevents the growth of both spoilage organisms and pathogens in the fermented food product. B Yeast. Various Saccharomyces species are used in alcohol fermentations. S. cerevisiae is the common baker’s yeast. To make sourdough bread, species of Lactobacillus are used. C Nonfermented pickles are cucumbers marinated in vinegar (5– 8% acetic acid). D a mould.  Food Bourne Diseases Foodborne illnesses resemble waterborne illnesses in being common source diseases. These diseases usually arise from IMPROPER HANDLING AND PREPARATION OF FOOD. Foodborne diseases are of two types, and some foodborne diseases fall into both categories: Food poisoning, also called food intoxication, results from ingestion of foods containing pre-formed microbial toxins. The microorganisms that produce the toxins do not have to grow in the host and may not even be alive at the time the contaminated food is consumed; ingestion and activity of the toxin are what causes the illness. Food infection occurs from the ingestion of food containing sufficient numbers of viable pathogens to cause colonisation and growth of the pathogen in the host, ultimately resulting in disease. Four of these—norovirus, Salmonella, C. perfringens, and Campylobacter— account for nearly 90% of all foodborne illness, with norovirus being the most common culprit (60%).  Factors leading to food poisoning preparation of food too far in inadequate thawing. advance; consuming raw food; storage at ambient temperature; improper warm holding (i.e. holding inadequate cooling; ‘hot’ food below 63ºC); inadequate reheating; infected food handlers; under cooking; contaminated processed food; poor hygiene.  Food Poisoning Staphylococcal Food Poisoning Cause: Bacteria - Staphylococcus aureus (gram– positive), can grow aerobically or anaerobically in many common foods and produces a suite of enterotoxins. Sources: Humans: nose, mouth and skin (a frequent cause of pus-forming wounds). Untreated milk, poultry, eggs etc. Treatment: Rest, drinking plenty of fluids, and using antinausea drugs are the best Signs and symptoms: prescription for a rapid recovery. Onset 1 – 6 hours. Severe vomiting, abdominal pain, diarrhoea, weakness and lower-than-normal Prevention: proper sanitation and temperature. This usually lasts 6 – 24 hours. hygiene in food production, preparation, and storage.  Food Poisoning Clostridial Food Poisoning Bacteria - Clostridium perfringens (gram-positive) Sources Commonly associated with improperly heated or reheated gravy, poultry, or meats. Prevention: cooked foods not be Clostridium perfringens forms spores that release enterotoxins. contaminated with raw foods and all Usually associated with ‘gas gangrene’ (myonecrosis) foods be properly heated during cooking and home canning. Signs and symptoms The perfringens enterotoxin is heat- Onset 12-18 hours. Abdominal pain, diarrhoea and nausea. labile and thus any toxin that may This usually lasts 12 – 48 hours. have formed in a food product is destroyed by proper Sometimes written off as ‘stomach flu’ or 24-hour flu.’ heating (75°C).  Food Poisoning Clostridial Food Poisoning Bacteria - Clostridium botulinum (gram-positive) Sources Consumption of exotoxin found in fish and meat, dust, soil and vegetables. Inadequately processed canned meat, vegetables and fish (faulty canning -anaerobic bacteria that can grow in canned foods). Spores can also enter an open wound. Prevention of foodborne botulism Signs and symptoms thus requires careful attention to canning and related food Onset 12-36 hours. Voice change, double vision, drooping eyelids, preservation practices. severe constipation. Botulinum toxin is a neurotoxin that affects autonomic nerves that control key body functions such as respiration Avoid feeding honey/corn syrup to and heartbeat; the typical result is flaccid paralysis. infants under 1 year. Death within a week or a slow recovery over months. Treatment for Avoid eating foods from cans that botulism is by administration of botulinum antitoxin if the diagnosis is are bulging. early.  Food Infection Food infection is not the same thing as food poisoning. Food infection results from the ingestion of food containing sufficient numbers of viable pathogens to allow the growth of the pathogen and disease in the host. In food infection, microorganisms multiply in intestinal tracts and cause disease. There are two types of food infection i.e. invasive type and enterotoxigenic type. ▪ In the enterotoxigenic type of food infection, microorganisms produce enterotoxin in the intestinal tract that causes disease (vibrio cholera) [PRODUCES ENTEROTOXINS - toxins that would be contained inside a bacterial cell and therefore are released whenever the cell deteriorates]. ▪ In the invasive type of food infection microorganisms cause disease by invading through the intestinal tract (Shigella and E. coli) [PRODUCES EXOTOXINS – by live bacterial cells into their surroundings].  Salmonellosis Cause: is a gastrointestinal disease typically caused by ingesting food contaminated with Salmonella enterica/ Salmonella typhimurium (gram- negative). Sources Raw meat, poultry and eggs. Flies, people, sewage, contaminated water, and contaminated animals. Foods containing Salmonella but heated to at least 70°C are generally safe if consumed immediately, Signs and symptoms held at 50°C or above, or quickly refrigerated. Onset 6-48 hours. Headache, general aching of limbs, Any foods that become contaminated by an infected abdominal pain and diarrhoea, vomiting and enteric fevers food handler can support the growth of Salmonella if (including typhoid fever) the food is held for a long enough period, especially if it is not kept very warm or refrigerated. This usually lasts 1 – 7 days and rarely is fatal. Can cause Salmonella septicemia  Pathogenic Escherichia coli Causes: Shiga Toxin–Producing E. coli and enterotoxigenic E. coli (gram – negative bacillus). The most widely distributed STEC is E. coli O157:H7 (Figure 32.14b ) Sources (known to be a part of normal intestinal flora) Raw and undercooked meat and poultry. Unwashed vegetables, and contaminated water. Signs and symptoms Onset usually 3-4 days. Diarrhoea, which may contain blood, can lead to kidney failure or death.  Pathogenic Escherichia coli Prevention: The most effective way to prevent infection with pathogenic E. coli of any type is to wash raw foods vigorously and make sure that meat, especially ground beef, is cooked thoroughly, which means that it should appear grey or brown with clear juices and have attained a temperature of greater than 70°C. In general, proper food handling, water purification, and appropriate hygiene also prevent the spread of pathogenic E. coli. Travelers can avoid diarrhoea from pathogenic E. coli by drinking water only from properly sealed bottled water and avoiding any uncooked foods.  Campylobacter Cause: Several species of Campylobacter (gram-negative) are recognized, but C. jejuni and C. fetus (Figure 32.15) are the most commonly linked to human foodborne illnesses. Sources: Raw and undercooked poultry, unpasteurised milk, and contaminated water, contaminated produce. Signs and symptoms: Onset 2 – 5 days (can be longer). Fever, headache, diarrhoea (bloody), stomach cramps, and dizziness for a few hours, followed by abdominal pain. This usually lasts 2 – 7 days and can recur over a number of weeks.  Campylobacter Treatment and Prevention: Antibiotic treatment with the drug azithromycin is widely practiced if a confirmed diagnosis is made from culture or culture-independent evidence. In addition, severe cases of dehydration from a Campylobacter infection may require intravenous perfusion and hospitalization. Rigorous personal hygiene, especially by those in food preparation facilities, proper washing of uncooked poultry (and any kitchenware coming in contact with uncooked poultry), and thorough cooking of meat are the major means of preventing Campylobacter infections.  Listeriosis Cause: Listeria monocytogenes (gram positive), a gastrointestinal food infection that may lead to bacteremia (bacteria in the blood) and meningitis. L. monocytogenes is a gram-positive, nonsporulating coccobacillus (phylum Firmicutes) that is acid-, salt-, and cold tolerant and facultatively aerobic (Figure 32.16). Sources: Unpasteurized milk and dairy products, cook-chill foods, meat, poultry and salad vegetables. Common in persons with low immunity e.g. Pregnant women (mother→ fetus via placenta) Signs and symptoms: Onset 1-70 days. Ranges from mild, flu-like illness to meningitis, septicaemia (blood poisoning), and pneumonia. During pregnancy, it may lead to miscarriage or the birth of an infected baby.  Listeriosis Prevention and Treatment: Intravenous antibiotic treatment with penicillin, ampicillin, or trimethoprim plus sulfamethoxazole is used to treat invasive listeriosis. Recalling contaminated food and taking steps to limit L. monocytogenes contamination at the food-processing site. Because L. monocytogenes is susceptible to heat and radiation, raw food and food-handling equipment can be readily decontaminated. However, unless the finished food product is pasteurized or cooked, the risk of contamination cannot be eliminated because of the widespread distribution of the pathogen.  Other foodborne infectious diseases Bacteria Yersinia enterocolitica is an enteric bacterium commonly found in the intestines of domestic animals and causes foodborne infections from contaminated meat and dairy products. The most serious consequence of Y. enterocolitica infection is enteric (typhoid) fever, a severe, life-threatening infection. Y. enterocolitica can be isolated on the same selective, differential medium used to isolate Salmonella but is easily distinguished from this organism on plates.  Other foodborne infectious diseases Bacteria Bacillus cereus is responsible for a relatively small number of food poisoning cases. This endospore-producing bacterium produces two enterotoxins that cause different symptoms. In the emetic form, symptoms are primarily nausea and vomiting. In the diarrheal form, diarrhoea and gastrointestinal pain are observed. B. cereus grows in foods such as rice, pasta, meats, or sauces that are cooked and left at room temperature to cool slowly. When endospores of this bacterium germinate, the toxin is produced. Reheating may kill the B. cereus cells, but the toxin is heat-stable and may remain active. B. cereus is readily culturable and can be tentatively identified by a combination of microscopy and its typically large, grainy, and spreading colonies (Figure 32.18c, d).  Other foodborne infectious diseases Viruses Noroviral foodborne illnesses are characterized by diarrhoea, often accompanied by nausea and vomiting. Recovery from norovirus infections is typically spontaneous and rapid, usually within 24–48 hours (often nicknamed “the 24-hour bug”). Rotavirus, astrovirus, and hepatitis A make up the bulk of the remaining foodborne viral infections. These viruses inhabit the gut and are often transmitted in food or water contaminated with faeces. Hepatitis A virus (HAV) is an RNA virus that, like norovirus, is related to poliovirus, but replicates in liver cells. We considered hepatitis viruses transmitted primarily by blood but HAV is mainly a foodborne virus. HAV usually triggers mild, and in many cases subclinical, symptoms, but rare cases of severe liver disease from HAV can occur. The most significant food vehicles for HAV are fresh produce served without cooking, shellfish, usually oysters or clams harvested from water polluted by human faeces and then eaten raw.  Other foodborne infectious diseases Protists and Other Agents The major pathogens here include Giardia intestinalis, Cryptosporidium parvum, Cyclospora cayetanensis, and Toxoplasma gondii. G. intestinalis and C. parvum are spread in foods when contaminated water is used to wash, irrigate, or spray crops. Fresh foods such as fruits are often implicated as vehicles for these protists. Toxoplasma gondii is a protist spread primarily through cat faeces, but it can also be found in raw or undercooked meat, especially pork. The incidence of foodborne transmission of C. cayetanensis has remained low (fewer than 20 cases per year) in recent years, and fresh cilantro and related produce have been the major vehicles of this pathogen in the majority of outbreaks.  Other foodborne infectious diseases Protists and Other Agents At least one type of foodborne disease agent is neither cellular nor viral; these are the prions. Prions are proteins that adopt novel conformations, inhibiting normal protein function and causing degeneration of host neural tissues. Human prion diseases are characterized by neurological symptoms including depression, loss of motor coordination, and eventual dementia. A foodborne human prion disease called variant Creutzfeldt–Jakob disease (vCJD) has been linked to the consumption of meat products from cattle suffering from bovine spongiform encephalopathy (BSE), a disease caused by a prion.  Preventing food poisoning Always follow ‘use by’ dates. Store food correctly, either cold or hot, never warm. Separate raw and cooked food. Wash fruits and vegetables. Thoroughly cook food. Keep yourself and your workspace clean. Don’t cough or sneeze over food. Thoroughly wash and dry hands regularly. END OF LECTURE 4