– is the science of classification, identification, and nomenclature. – For classification purposes, organisms are usually organized into subspecies, species, genera, families, and higher orders.

– Classification is the orderly arrangement of into groups. • Bacteria are single celled microbes. • The cell structure is simpler than that of other organisms as there is no nucleus or membrane bound organelles. • Some bacteria have an extra circle of genetic material called a plasmid. • The plasmid often contains genes that give the bacterium some advantage over other bacteria. – For example it may contain a gene that makes the bacterium resistant to a certain antibiotic. mode of nutrition optimum Formation temperature of spore requirement

optimal pH flagella Classification for growth of Bacteria salt gram concentratio staining n

gaseous morphology requirement 1. Phototrops: 3. Autotrops: •gain energy from light • uses carbondioxide as sole source of carbon to •divided into two groups on the basis of source of prepare its own food. electron. • Autotrops are divide into two types on the basis •Photolithotrops: gain energy from light and uses of energy utilized to assimilate carbondioxide reduced inorganic compounds such as H2S as electron source. Eg. okenii • Photoautotrops: they utilized light to •Photoorganotrops: gain energy from light and uses assimilate CO2. They are further divided into organic compounds such as succinate as electron two group on the basis of electron sources. Ie. source. Photolithotropic autotrops and Photoorganotropic autotrops 2. Chemotrops: • Chemoautotrops: they utilize chemical energy •gain energy from chemical compounds for assimilation of CO2 •They cannot carry out 4. Heterotrops: •divided into two groups on the basis of source of electron. • uses organic compound as carbon source •Chemolithotrops: they gain energy from oxidation • They lack the ability to fix CO2 of chemical compound and reduces inorganic compounds such as NH3 as electron source. • Most of the human pathogenic bacteria are Eg. Nitrosomonas heterotropic in nature •Chemoorganotrops: they gain energy from • Some heterotrops are simple, because they have chemical compounds and uses organic compound simple nutritional requirement. such as glucose and amino acids as source of • some bacteria that require special nutrients for electron. eg. Pseudomonas pseudoflava their growth; known as fastidious heterotrops.

1. Psychrophiles: 4. Thermophiles: • can grow at 0°C or below •Those bacteria that can best grow above 45C. • but the optimum temperature of growth is •Thermophiles capable of growing in mesophilic 15 °C or below and range are called facultative thermophiles. • maximum temperature is 20°C •True thermophiles are called as Stenothermophiles, they are obligate • Psychrophiles have polyunsaturated thermophiles, fattyacids in their cell membrane which •Thermophils contains saturated fattyacids in gives fluid nature to the cell membrane their cell membrane so their cell membrane even at lower temperature. does not become too fluid even at higher • Examples: Vibrio psychroerythrus, vibrio temperature. marinus, Polaromonas vaculata, •Examples: Streptococcus thermophiles, Bacillus Psychroflexus stearothermophilus, Thermus aquaticus, 2. Psychrotrops (facultative psychrophiles): 5. Hypethermophiles: • Those bacteria that can grow even at 0°C but •Those bacteria that have optimum optimum temperature for growth is (20-30)°C temperature of growth above 80C. 3. Mesophiles: •Mostly Archeobacteria are hyperthermophiles. • Those bacteria that can grow best between (25-40)C •Monolayer cell membrane of Archeobacteria is but optimum temperature for growth is 37C more resistant to heat and they adopt to grow • Most of the human pathogens are mesophilic in in higher remperature. nature •Examples: Thermodesulfobacterium, Aquifex, • Examples: coli, Salmonella, Klebsiella, Staphulococci Pyrolobus fumari, Thermotoga

1. Acidophiles: • Those bacteria that grow best at acidic pH • The cytoplasm of these bacteria are acidic in nature. • Some acidopiles are thermophilic in nature, such bacteria are called Thermoacidophiles. • Examples: Thiobacillus thioxidans, Thiobacillus, ferroxidans, Thermoplasma, Sulfolobus 2. Alkaliphiles: • Those bacteria that grow best at alkaline pH • Example: vibrio cholerae: oprimum ph of growth is 8.2 3. Neutriphiles: • Those bacteria that grow best at neutral pH (6.5-7.5) • Most of the bacteria grow at neutral pH • Example: E. coli

1. Halophiles: • Those bacteria that require high concentration of NaCl for growth. • Cell membrane of halophilic bacteria is made up of glycoprotein with high content of negatively (-Ve) charged glutamic acid and aspartic acids. So high concentration of Na+ ion concentration is required to shield the –ve charge. • Example: Archeobacteria, Halobacterium, Halococcus 2. Halotolerant: • Most of the bacteria do not require NaCl but can tolerate low concentration of NaCl in growth media are called halotolerant

1. Obligate aerobes: 4. Microaerophiles: • Those bacteria that require oxygen and cannot grow in the absence of O2. • Those bacteria that do not require O2 for growth but can tolerate low concentration of O2. • These bacteria carryout only oxidative type of metabolism. • At atmospheric level of Oxygen growth of these bacteria is inhibited. • Examples; Mycobacterium, Bacillus • These bacteria only have oxidative type of metabolism 2. Facultative anaerobes: • Example: Campylobacter • Those bacteria that do not require O2 but can use 5. Obligate anaerobes: it if available. • Those bacteria that can grow only in absence of • Growth of these bacteria become batter in Oxygen. presence of O2 • Oxygen is harmful to obligate anaerobes • These bacteria carryout both oxidative and • These bacteria have only fermentative type of fermentative type of metabolism metabolism • Examples: coli, Klebsiella, Salmonella • Examples: Peptococcus, Peptostreptococcus, Slostridium, methanococcus 3. Aerotolerant anaerobes; 6. Capnophiles: • Those bacteria do not require O2 for growth but can tolerate the presence of O2. • Those bacteria that require carbondioxide for growth. • Growth of these bacteria is not affected by the • They are CO2 loving organism presence of O2. • Most of the microaerophiles are capnophilic in nature. • These bacteria have only fermentative type of • Example: Campylobacter, Helicobacter pylori, Brucella metabolism. abortus • Example: lactobacillus

F] Classification of bacteria on the basis of Morphology

1. Coccus: 3. Mycoplasma • These bacteria are spherical or oval in shape • On the basis of arrangement, cocci are further • They are cell wall lacking bacteria classified as- • Also known as PPLO (Pleuropneumonia like • i) Diplococcus: coccus in pair. Eg, Neissseria organism) gonorrhoae, Pneumococcus • Mycoplasma pneumoniae • ii) Streptococcus: coccus in chain. Eg. Streptococcus salivarius 4. Spirochaetes: • iii) Staphylococcus: coccus in bunch. Eg. Staphylococcus aureus • They are spiral shaped bacteria • iv) Tetrad: coccus in group of four. • Spirochaetes • v) Sarcina: cocus in cubical arrangement of cell. Eg. Sporosarcina 5. Rickettsiae and Chlamydiae; 2. Bacilli: • They are obligate intracellular parasites resemble more closely to viruses than • These are rod shaped bacteria bacteria • On the basis of arrangement, bacilli are further classified as- 6. Actinomycetes • i) Coccobacilli: Eg. Brucella • They have filamentous or branching • ii) Streptobacilli: chain of rod shape bacteria: Eg. Bacillus subtilis, structure • iii) Comma shaped: Eg. Vibrio cholarae • They resemble more closely to Fungi than • iv) Chinese letter shaped: Corynebacterium bacteria dephtherae • Example: Streptomyces

• classification is based on differences in their cell walls and outer membranes. It groups bacteria into Gram- positive and Gram-negative bacteria – 1. • cell wall of these bacteria is composed of peptidoglycan layer only. • Eg. Staphylococcus, Streptococcus, micrococcus – 2. GRAM NEGATIVE BACTERIA: • cell wall of these bacteria is composed of Peptidoglycan and outer membrane. • Eg. E. coli, Salmonella

Classification of bacteria on the basis of flagella • 1. end of cell. – bacteria having single – eg. Aquaspirillium flagella in one end of cell. • 4. – eg. Vibrio cholera, – bacteria having flagella all Pseudomonas aerogenosa over the cell surface. • 2. – Eg. E.coli, Salmonella, – bacteria having bundle of Klebsiella flagella in one end of cell. • 5. – eg. Pseudomanas – bacteria without flagella. fluroscence – Eg. Shigell • 3

– bacteria having single or cluster of flagella at both

I] Classification of bacteria on the basis of Spore • 1. Spore forming bacteria: – Those bacteria that produce spore during unfavorable condition. – These are further divided into two group • i) – Spore produced within the bacterial cell. – Bacillus, Clostridium, Sporosarcina etc • ii) – Spore produced outside the cell – Methylosinus • 2. Non sporing bacteria: – those bacteria which do not produce spore. – Eg. E. coli, Salmonella

(A) Schematic representation of the bacterial spore. (B) Spore stain of C. tetani (fuchsin-methylene blue stain). (C) Size, morphology, and location of bacterial spores.