Micro-organisms in Foods Flashcards
Micro-organisms, in relation to food, can have one of these 3 roles:
⦁ Pathogenic micro-organisms can cause infections or intoxications
⦁ Saprophytic micro-organism play a role in biodegradation and cause food spoilage
⦁ Cultured micro-organisms like probiotic bacteria are used in food processing.
cause food-borne infections or intoxication, and include bacteria, viruses, parasites and moulds.
Pathogenic micro-organisms
The main factors that contribute to occurrence of foodborne diseases are:
⦁ The use of raw food and ingredients from unsafe sources
⦁ Inadequate cooking or heat processing
⦁ Allowing several hours to pass between preparation and eating of food
⦁ Inadequate reheating
⦁ Improper hot holding, meaning below 65°C
⦁ Food handling by infected persons or carriers of infection
⦁ Inadequate cleaning of equipment and utensils
are the most important microorganisms to the food processor.
Bacteria
three basic shapes:
spherical, straight rods, and spiral rods
Some rod-shaped bacteria are capable of existing in two forms
dormant spores and active vegetative cells
Is a common cause of diarrhea humans as well as some animal species. The transmission can be by direct contact between humans and infected animals or their feces. More commonly, it is transmitted by the consumption of contaminated food or water, t person-to-person spread.
⦁ Campylobacter jejuni
There are more than 2000 serotypes of salmonella spp, of which only a few cause Salmonella gasteroenteritis in humans. Animals are the main reservoir, and transmission occurs by ingestion of contaminated products. Foods especially at risk are poultry, meat, eggs and milk.
⦁ Non-typhi salmonellosis
Cause typhoid fever and paratyphoid fever respectively. Since the reservoir for both these bacteria are usually humans, transmission occurs mainly through person-to-person contact or contamination of food by food handlers.
⦁ Salmonella typhi and paratyphi
The source of this infection are humans. The bacteria are often found in smaller amounts in the nose and on the skin of clinically healthy people.
⦁ Staphylococcus aureus
There are several serotypes, some of which are harmless to humans whereas others can cause gastroenteritis. Enterotoxigenic E.coli is the most common cause of traveller’s diarrhea. The source is humans, and transmission usually occurs through contaminated food and water.
⦁ Escherichia coli
This bacterium is highly associated with food stored for long periods of time in the fridge because it is ubiquitous, and has the ability to grow slowly, even at low temperatures. Can be fatal in immunocompromised, where it can cause septicemia and meningitis.
⦁ Listeria monocytogenes
The source is humans and primates. Because it has low infectious dose, the main mode of transmission is person-to-person contact. It can also be transmitted through infected food and water. The symptoms of shigellosis are fever and watery diarrhea. The infection can also manifest as a dysenteric syndrome which includes fever, abdominal cramps and tenesmus, and frewuent, small volume, bloody stools containing mucous.
⦁ Shigella
The source of this infection is humans. The main mode of transmission is through contaminated water and food, or person-to-person spread in overcrowded, unhygienic situations. It causes severe watery diarrhea, which can reach up to 20 liters per day.
⦁ Vibrio Cholerae 01
Its source is the intestinal tract of fish, birds, and mammals. It is also widely distributed in nature. The bacterium is a spore producing anaerobe, with a highly potent heat labile toxin that affects the nervous system.
⦁ Clostridium Botulinum
Many parasites, such as the helminths, have a complex lifecycle involving more than one host. The major route of transmission for these parasites to humans is by the route of food. The consumption of undercooked pork or beef, or the consumption of raw salads washed in contaminated water seems to be the trend.
⦁ Parasites
also called pig and beef tapeworms. Their cysts,, present in the muscle of the animal are ingested and the adult worm develops in the gut. The ova may develop into larvae that may invade other tissues, such as the brain, forming cysticercosis and severe neurological disorders as a consequence.
⦁ Taenia solium and T. saginata
is found in undercooked pork. The larvae can invade tissues and cause a febrile illness.
⦁ Trichinella spiralis
This infection can be foodborne, waterborne or spread by interpersonal contact. It causes acute or subacute diarrhea, with malabsorption, fatty stools, and abdominal pain and bloating.
⦁ Giardia lambila
The transmission is mainly food- or waterborne. The cysts pose a major problem since they are highly resistant to chemical disinfectants, including chlorination. The infection is usually asymptomatic, but may appear as either a persistent mild diarrhea or a fulminant dysentery.
⦁ Entamoeba histolytica
are the smallest and simplest microorganisms.
viruses
are the major causes of gastroenteritis
⦁ Rotaviruses and Norwalk virus
outbreaks are mainly caused by asymptomatic carriers which handle food.
⦁ Viral hepatitis A
It is the change of look, consistency, flavor and odor of foods, and is caused by bacteria, moulds and yeasts.
food spoilage
Examples of action of bacteria involved in food spoilage:
1.Lactic acid formation
2.Lipolysis
3.Pigment formation
4.Gas formation
5.Slime or rope formation
Some strains produce mycotoxins under certain conditions
Moulds
Foods most at risk for moulds:
1.Grains and grain products
2.Peanuts, nuts and pulses
3.Fruits and vegetables
4.Milk and milk products - aflatoxin
Most commonly used microorganisms
yeast, bacteria, moulds, (YBM)
Fermented milk products:
Lactobacillus, Lactococcus, Bifidobacterium
are live food supplements used in yoghurt and other fermented milk products.
Probiotics
Mould in food production:
cheese, dry salami, soy sauce, sake
is an unwanted quality change in a foodstuff, such as staling, discoloration, the development of off-flavours and odours (e.g. rancidity), and thinning of sauces.
Chemical food spoilage
A series of continuous degradative changes occurring in a food item which may affect the product’s wholesomeness, result in a reduction of its quality, and/or alter its serviceability.
Food Deterioration
is a term that refers to freedom from pathogenic or otherwise harmful microorganisms.
Wholesomeness
is a term which we often hear in conjunction with deterioration. It is often used as a synonym for deterioration. However, it needs to make distinction between these two terms.
Spoilage
is food procured, packed, or held under unsanitary conditions that renders it injurious to the health of the consumer, or food or food containers having naturally occurring or added harmful substances, or food found to be filthy, putrid, decomposed, or produced from a diseased animal or an animal that died other than by slaughter.
Unwholesome
is any variation from the expected appearance, feel, smell, or taste characteristics of a product when it was initially produced or processed for resale
Off-condition
a term that refers to the degree of excellence or grade of a Product.
Quality
a term that refers to the usefulness of a food item. Reduced serviceability in a product may result in the use of additional processing methods to return the food item to its original state.
Serviceability
Major causes of food deterioration include:
1.Growth and activities of micro-organisms, mainly bacteria, yeasts and moulds;
2.Activities of natural food enzymes;
3.Insects, parasites and rodents;
4.Temperature, both heat and cold;
5.Moisture and dryness;
6.Air and in particular oxygen;
7.Light;
8.Time.
Human illnesses caused by foodborne microorganisms are popularly referred to as…
Food Poisoning
A few of this strains found in human feces are in themselves pathogenic, causing infection and disease.
Escherichia coli
commonly referred to as “staph,” is normally present on the skin, the mucous membranes, and in pimples and boils of human beings and other animals.
Staphylococcus aureus
is almost always caused by eating contaminated food or drink. Contamination originates from the intestinal tract of human beings or animals who harbor Salmonella organisms.
Salmonella
produces a rare but often fatal disease called botulism. It is caused by a neurotoxin produced during growth in the absence of air.
Costridium botulinum
is a spore-forming organism which, like botulinum, grows only in the absence of air.
Clostridium perfringens
is a spore-forming organism that grows in the presence of oxygen and is widely distributed in most raw foods. Since the spores survive boiling for several minutes, they remain viable in cooked foods in small numbers.
Bacillus cereus
is a non-spore forming, slightly curved rod, closely related to the organism that causes cholera. It is widely distributed and grows in brackfish waters, estuarine sediments, raw fish, and shellfish throughout the world.
Vibrio parahaemolyticus
This changed with food related outbreaks in Nova Scotia, Massachusetts, California and Texas.
Listeria
was first isolated from human diarrheal stools in 1971. Since, then it has continually gained recognition as a disease causing organism in humans.
Campylobacter jejuni
are harmful byproducts from molds that grow on foods and feeds. They have caused severe illness and death in animals for centuries.
Mycotoxins
refers to the growth of a population (or an increase in the number of cells), not to an increase in the size of the individual cell. Cell division leads to the growth of cells in the population.
microbial growth
Two Types of Asexual Reproduction in Microbes:
- Binary Fission - Bacterial reproduction occurs through fission, a primitive form of cell division that does not employ a spindle fiber apparatus.
2.) Budding - A few bacteria and some eukaryotes (including yeasts) may also replicate by budding, forming a bubble-like growth that enlarges and separates from the parent cell.
Requirements for Growth
Ph
Temperature
Food
Acidity
Osmotic pressure
Time
Oxygen
Moisture
