FOOD MICROBIOLOGY MEDI 2371. Prepared BY PROF. MOHAMMAD EID SHUBAIR. Definition. Food Microbiology is the study of microorganisms that inhabit, make or contaminate food.
PROF. MOHAMMAD EID SHUBAIR
Food Microbiology is the study of microorganisms that inhabit, make or contaminate food.
Many microorganisms are used to make food e.g the bacteria which converts liquid milk into yogurt or cheese, yeast for making bread, through fermentation.
Other microorganisms or the toxins they produce cause spoilage of food.
Safety of food must be ensured to protect human health.
Food preservation is being used to avoid health hazards.
Preservation methods include drying, cooking, smoking, salting, sugaring, low temperature storage and radiation.
Historical Development of Food Microbiology
Louis Pasteur(1860) showed that fermentation of lactic acid and alcohol from sugar was the result of growth of specific bacteria and yeast.
Theodor Schwan (1837) named the organism involved in sugar fermentation as Saccharomyces( sugar fungus).
Emil Chirstianhansen (1883) used pure culture of yeasts to ferment sugars.
Harry Russell (1895) showed that gaseous swelling with bad odors in canned peas was due to growth of heat-resistant bacteria(spores).
Tyndall(1876) observed that bacteria in decomposing substances were always traceable to air, substances or containers.
Bacillus coagulanswas first isolated from coagulated milk by B.W. Hammer(1915).
In 1902 the term psychrophile was first used by Schmidt-Nielsen for organisms that grow at 0C.
In 1857 milk was incriminated as a transmitter of typhoid fever by W. Taylor
In 1888 gaertner first isolated Salmonella enteritidis from meat that had caused 57 cases of food poisoning.
In 1894 T. Denys was the first to associate Staphylococci in food poisoning.
In 1896 Van Ermengen first discovered Clostridium botulinum.
In 1937 paralytic shellfish poisoning was recognized.
In 1939 gastroenteritis caused by Yersiniaenterocolitica was first recognized by Schleifstein and Coleman
In 1951 Vibrioparahaemolyticus was shown to be an agent of food poisoning.
In 1960 the production of aflatoxin by Aspergillusflavus was first reported.
In 1986 Bovine spongiform encephalopathy was first diagnosed in cattle in U.K.
In 1810 preservation of food by canning was developed by Appert in France.
Fish and Fruits were first canned in 1840.
In 1842 H- Benjamin in U.K. introduced freezing foods by immersion in an ice and salt brine.
In 1878 the first successful cargo of frozen meat went from Australia to England.
In 1890 pasteurization of milk began in USA.
In 1907, Metchnikoff isolated one of yogurt bacteria (Lactobacillus bulgaricus).\
In 1943, Procter in USA employed ionizing radiation to preserve hamburger meat.
Hepatitis A and Hepatitis E Viruses
Human Caliciviruses(Noroviruses and Sapporo Viruses)
These bacteria have a rapid growth rate, ability to grow under a wide range of temperature, aerobiosis, pH, water activity, and utilization of food nutrients
They better survive adverse conditions such as survival of spores at high temperatures.
1- Lactic Acid Bacteria
These bacteria produce large quantities of lactic acid from carbohydrates, species from genera Lactococcus, Leuconostoc, Pediococcus, Lactobacillus, and Streptococcus thermophilus.
They are bacteria that produce acetic acid , such as Acetobacteraceti
3- Propionic Acid Bacteria
They produce propionic acid and are used in dairy fermentation e.gPropionibacteriumfreudenreichii
They are the bacteria that produce butyric acid in relatively large amounts, Clostridium butyricum is included in this group.
5- Proteolytic Bacteria
They are bacteria that can hydrolyze proteins because they produce extracellular proteinases, they include species in the genera Micrococcus, Staphylococcus, Bacillus, Clostridium, Pseudomonas, Alteromonas, Flavobacterium, Alcaligenes, some Enterobacteriaceae and Brevibacterium.
They hydrolyze triglycerides as they produce lipases. Species in genera Micrococcus, Staphylococcus, Pseudomonas, Alteromonas and Flavobacterium are included in this group.
7- Saccharolytic bacteria
They hydrolyze complex carbohydrates, Species in the genera Bacillus, Clostridium, Pseudomonas, and Enterobacter are included in this group.
They are the bacteria that are able to grow at 50C and above. Species from genera Bacillus, Clostridium, Pediococcus, Streptococcus and Lactobacillus are included in this group.
They are the bacteria that are able to grow at refrigerated temperature. Some species from Pseudomonas, Alteromonas, listeria, Yersinia and Aeromonas are included in this group.
They are the bacteria that are able to survive Pasteurization temperature treatment. Some species from Micrococcus, enterococcus, Lactobacillus, Bacillus(spores), and Clostridium (spores) are included in this group.
11- Halotolerant Bacteria
Bacteria that are able to survive high salt concentration. Some species from Bacillus, Stahylococcus, Vibrio are included in this group.
They are the bacteria that can survive low pH. Some species from Lactobacillus, Lactococcus, Enterococcus, and Streptococcus are included in this group.
13- Osmophilic Bacteria
Bacteria that can grow at a relatively higher osmotic environment than that needed for other bacteria. Some species from genera Staphylococci, Leuconostic, and Lactobacillus are included in this group. They are much less osmotic than yeasts and molds.
They are bacteria that produce gas(CO2, H2, H2S) during metabolism of nutrients. Species from genera Leuconostic, Lactobacillus, Propionibacterium, Escherichia, Enterobacter, Clostridium and Desulfotomaculum are included in this group.
15- Slime Producers
They are the bacteria that produce slime because they synthesise polysaccharides. Examples include Xanthomonas, Leuconostic, Alcaligenes, Enterobacterand lactobacillus.
They are the bacteria that have the ability to produce spores. Species from Bacillus, Clostridium, and Desulfotomaculum are included in this group. They are further divided into:
Flat sour sporeformers
They are the bacteria that require oxygen for growth and multiplication. Examples include Pseudomonas, Bacillus, and Flavobacterium
They are the bacteria that cannot grow in the presence of oxygen. Species from Clostridium are included in this group.
They are bacteria that are able to grow in both the presence and absence of oxygen. Lactobacillus, Pediococcus, Leuconostoc. Enteric pathogens, and some species of Bacillus, Serratia and Coliforms are included in this group.
Species from Escherichia, Enterobacter, Cirtbacter and Klebsiella are included in this group. They are used as index of sanitation.
Mainly Escherichia coli is included in this group. They are also used as an index of sanitation.
22- Enteric Pathogens
Pathogenic Salmonella, Shigella, Campylobacter, Yersinia, Escherichia, Vibrio, Listeria, Hepatitis A, Rotavirus and others that can cause gastrointestinal infection are included in this group
An indicator organism or group of organisms is one whose numbers in a product reflect the success or failure of (good manufacturing practices). Coliform group of microorganisms and Escherichia coli are commonly used as indicator organisms.
An index organism is one whose presence implies the possible occurrence of a similar but pathogenic organism. E. coli is used as an index organism and its presence indicates possible presence of pathogenic enterobacteriaceae.g Salmonella sp.
1- Those which cause the disease by infection
2- Those which produce toxin in food
Those which cause infection must grow in food in large numbers and cause infection when consumed together with food. Common organisms in this category include Salmonella typhimurium, enteropathogenic E. coli, Vibrioparahaemolyticus and Yersiniaenterocolitica.
These are microorganisms which cause intoxication, they must grow in food in large numbers and produce enough toxin and when consumed together with food cause intoxication.
Common microorganisms in this category include Clostridium botulinum, Staphylococcus aureusand toxigenic fungi e.g. Aspergillusflavus.
These are the organisms whose presence in small numbers in food or water and when consumed can cause infection. In this case the food acts as a vector but not necessarily as a growth medium. Infectious organisms can be transmitted by various ways including man to man and are said to be contagious. Organisms in this group include; Vibriocholerae O1, Salmonella typhi, Shigellasonnei, Hepatitis A etc.
Spoilage organisms are the organisms whose growth in the food causes undesirable characteristics in that food. Any organism which is not intentionally added into food or intentionally allowed to grow in food so as to impart certain qualities in that food is considered a contaminant. Growth of the contaminant in that food will spoil the food making it unfit for human consumption. Some useful microorganisms e.g. lactic acid bacteria are considered as spoilage organisms when in alcohol but not in milk.