![]() Psychrotrophic bacteria spoil the foods kept in a refrigerator. They are also called facultative psychrophiles. Psychrotrophs: The minimum growth temperature of psychrotrophs is 0☌-7☌, the optimum is 20-30☌, and the maximum is 35☌.E.g., Pseudomonas, Vibrio, Alcaligenes, Bacillus, Arthrobacter, Moritella, Photobacterium, and Shewanella. Psychrophiles: The minimum growth temperature of psychrophiles is 0☌, the optimum is 15☌, and the maximum is 20☌.Temperature requirement for bacterial growth E.g., Bacillus alcalophilus, Natronobacterium Classification of bacteria on the basis of temperature requirementsīased on the temperature requirement for growth, bacteria are classified into five types: psychrophiles, psychrotrophs, mesophiles, thermophiles, and hyperthermophiles. Alkalophiles: These bacteria grow at high pH with a pH optimum of 8.0 to 11.5.Neutrophiles: These bacteria grow at neutral pH with a pH optimum of 5.5 to 8.0.E.g., Sulfolobus, Picrophilus, Ferroplasma, Cyanidium caldarium Acidophiles: These bacteria grow at low pH with the pH optimum of pH 0 to 5.5.Classification of bacteria on the basis of pH Requirementsīased on the pH requirement, bacteria are classified into acidophiles, neutrophiles, and alkalophiles. , Treponema pallidum, Streptococcus pneumoniae, Helicobacter pylori, Campylobacter, Streptococcus pyogenes, and Borrelia burgdorferi. Microaerophilic bacteria: They cannot tolerate the atmospheric air but require oxygen at a low level of about 2-10% for growth.coli, Klebsiella, Salmonella, Shigella, Proteus, Vibrio cholerae etc. If oxygen is present, they may use it for energy production. Facultatively anaerobic bacteria: These bacteria do not require oxygen for growth, nor is oxygen inhibitory.E.g.: Gram-positive ( Clostridium, Propionibacterium, Bifidobacterium), Gram-negative: ( Bacteroids, Fusobacterium) Bacteria that cannot tolerate low oxygen levels are called strict or obligate anaerobes.E.g., Lactobacillus, Streptococcus pyogenes, etc. Bacteria that can tolerate low oxygen levels are called non-stringent or aerotolerant anaerobes.Anaerobic bacteria (anaerobes): Anaerobic bacteria cannot grow in atmospheric air.E.g., Bacillus spp., Pseudomonas, Micrococcus, Staphylococcus spp. Aerobic bacteria (aerobes): Aerobic bacteria can grow when incubated in atmospheric air containing 21% oxygen.Gram-negative curved rods: Campylobacter, Helicobacter, Vibrio Classification of bacteria on the basis of oxygen requirementsīased on the oxygen requirement, bacteria are classified into four types: aerobes, facultative anaerobes, anaerobes, and microaerophiles.Gram-negative rods (Enterics): Escherichia, Enterobacter, Serratia, Klebsiella, Salmonella, Shigella, Proteus.Gram negative coccobacilli: Haemophilus, Bordetella, Legionella, Brucella, Francisella, Pasteurella, Yersinia.Filamentous: Actinomyces, Nocardia Gram-Negative Bacteria.Non-filamentous: Corynebacterium, Listeria. ![]() Gram-positive cocci: Streptococcus, Staphylococcus.Free-living bacteria are further subdivided according to shape and staining reactions into a variety of gram-positive and gram-negative rods with different oxygen requirements and other attributes (spore-forming, capsule forming, flagella, etc.). Rigid, thick-walled cells: Most of the free-living bacteria (Gram-positive, Gram-negative, and acid-fast) and obligate intracellular parasites such as Rickettsiaīacteria with rigid, thick walls can be subdivided into free-living bacteria and non-free-living bacteria (obligate intracellular parasites).Flexible, thin-walled cells (spirochetes): Treponema, Borrelia, Leptospira.On the basis of cell wall characteristics, bacteria are of three types, those with rigid cell walls (most of the bacteria), those with flexible, thin walls (the spirochetes), and those without cell walls (the mycoplasma). The nature of the cell wall (i.e., is it rigid, flexible, or absent?) is the primary criterion used in the classification of bacteria. Classification of bacteria on the basis of capsule Classification of bacteria on the basis of the cell wall and staining reaction.Classification of bacteria on the basis of flagella.Classification of bacteria on the basis of shape and arrangement.Classification of bacteria on the basis of nutritional requirements.Classification of bacteria on the basis of salt and tolerance.Classification of bacteria on the basis of temperature requirements.Classification of bacteria on the basis of pH Requirements.Classification of bacteria on the basis of oxygen requirements.Classification of bacteria on the basis of the cell wall and staining reaction.
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