IMPORTANT BACTERIAL GROUPS IN FOODS

VI. IMPORTANT BACTERIAL GROUPS IN FOODS
Among the microorganisms found in foods, bacteria constitute major important groups. This is not only because many different species can be present in foods, but also because of their rapid growth rate, ability to utilize food nutrients, and ability to grow under a wide range of temperatures, aerobiosis, pH, and water activity, as well as to better survive adverse situations, such as survival of spores at high
temperature. For convenience, bacteria important in foods have been arbitrarily divided into several groups on the basis of similarities in certain characteristics. This grouping does not have any taxonomic significance. Some of these groups and their importance in foods are listed here.
A. Lactic Acid Bacteria
They are bacteria that produce relatively large quantities of lactic acid from carbohydrates. Species mainly from genera Lactococcus, Leuconostoc, Pediococcus, Lactobacillus, and Streptococcus thermophilus are included in this group.
B. Acetic Acid Bacteria
They are bacteria that produce acetic acid, such as Acetobacter aceti.
C. Propionic Acid Bacteria
They are bacteria that produce propionic acid and are used in dairy fermentation. Species such as Propionibacterium freudenreichii are included in this group.
D. Butyric Acid Bacteria
They are bacteria that produce butyric acid in relatively large amounts. Some Clostridium spp. such as Clostridium butyricum are included in this group.


E. Proteolytic Bacteria
They are bacteria that can hydrolyze proteins because they produce extracellular proteinases. Species in genera Micrococcus, Staphylococcus, Bacillus, Clostridium, Pseudomonas, Alteromonas, Flavobacterium, Alcaligenes, some in Enterobacteriaceae, and Brevibacterium are included in this group.
F. Lipolytic Bacteria
They are bacteria that are able to hydrolyze triglycerides because they produce extracellular lipases. Species in genera Micrococcus, Staphylococcus, Pseudomonas, Alteromonas, and Flavobacterium are included in this group.
G. Saccharolytic Bacteria
They are bacteria that are able to hydrolyze complex carbohydrates. Species in genera Bacillus, Clostridium, Aeromonas, Pseudomonas, and Enterobacter are included in this group.

CHARACTERISTICS OF PREDOMINANT MICROORGANISMS IN FOOD

H. Thermophilic Bacteria
They are bacteria that are able to grow at 50°C and above. Species from genera Bacillus, Clostridium, Pediococcus, Streptococcus, and Lactobacillus are included in this group.

I. Psychrotrophic Bacteria
They are bacteria that are able to grow at refrigerated temperature (5°C). Some species from Pseudomonas, Alteromonas, Alcaligenes, Flavobacterium, Serratia, Bacillus, Clostridium, Lactobacillus, Leuconostoc, Carnobacterium, Brochothrix, Listeria, Yersinia, and Aeromonas are included in this group.
J. Thermoduric Bacteria
They are bacteria that are able to survive pasteurization temperature treatment. Some species from Micrococcus, Enterococcus, Lactobacillus, Pediococcus, Bacillus (spores), and Clostridium (spores) are included in this group.
K. Halotolerant Bacteria
They are bacteria that are able to survive high salt concentrations (10%). Some species from Bacillus, Micrococcus, Staphylococcus, Pediococcus, Vibrio, and Corynebacterium are included in this group.

L. Aciduric Bacteria
They are bacteria that are able to survive at low pH (<4.0). Some species from Lactobacillus, Pediococcus, Lactococcus, Enterococcus, and Streptococcus are included in this group.

M. Osmophilic Bacteria
They are bacteria that can grow at a relatively higher osmotic environment than that needed for other bacteria. Some species from genera Staphylococcus, Leuconostoc, and Lactobacillus are included in this group. They are much less osmophilic than yeasts and molds.

N. Gas-Producing Bacteria
They are bacteria that produce gas (CO2, H2, H2S) during metabolism of nutrients. Species from genera Leuconostoc, Lactobacillus, Propionibacterium, Escherichia, Enterobacter, Clostridium, and Desulfotomaculum are included in this group.

O. Slime Producers
They are bacteria that produce slime because they synthesise polysaccharides. Some species or strains from Xanthomonas, Leuconostoc, Alcaligenes, Enterobacter, Lactococcus, and Lactobacillus are included in this group.

P. Spore Formers
They are bacteria having the ability to produce spores. Species from Bacillus, Clostridium, and Desulfotomaculum are included in this group. They are further divided into aerobic sporeformers, anaerobic sporeformers, flat sour sporeformers, thermophilic sporeformers, and sulfide-producing sporeformers.

Q. Aerobes
They are bacteria that require oxygen for growth and multiplication. Species from Pseudomonas, Bacillus, and Flavobacterium are included in this group.

R. Anaerobes
They are bacteria that cannot grow in the presence of oxygen. Species from Clostridium are included in this group.

S. Facultative Anaerobes
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.


T. Coliforms
Species from Escherichia, Enterobacter, Citrobacter, and Klebsiella are included in this group. They are used as an index of sanitation.

U. Fecal Coliforms
Mainly Escherichia coli is included in this group. They are also used as an index of sanitation.

V. Enteric Pathogens
Pathogenic Salmonella, Shigella, Campylobacter, Yersinia, Escherichia, Vibrio, Listeria, hepatitis A, and others that can cause gastrointestinal infection are included in this group.

CHARACTERISTICS OF PREDOMINANT MICROORGANISMS IN FOOD
Because of the importance of these bacterial groups in food, many laboratory methods are designed to detect a specific group instead of a specific genus or species. Similarly, control methods are sometimes designed to destroy or prevent growth of a specific group.