Growth And Nutrition Of Bacteria.ppt 4n126k

Growth and nutrition of bacteria

Nutrition • Process by which chemical substances ( nutrients) are acquired from the surrounding environment and used in cellular activities such as metabolism and growth

Bacterial growth • Mode of division of bacteria-Binary fission • Optimal growth of bacteria - Suitable environment & nutrition • Minimal nutrientsC,H,N,O,Inorganic salts • Bacteria of medical importance derive nutrition from organic material

Essential nutrients • Macronutrients-Required in relatively large quantities and play principal role in cell structure and metabolism • Micronutrients-Also called trace elements.Needed in small quantities for enzyme and pigment structure and function

Classification of bacteria • Autotrophs - Synthesise their essential metabolites from atmospheric CO2 & N2. Free living: Non parasitic; found in soil and water • Photoautotrophs - Derive energy from sunlight

Classification of bacteria ….. • Chemoautotrophs – Use inorganic compounds for oxidation • Heterotrophs - Cannot synthesise their own metabolites.Require preformed organic compounds. Most are pathogenic and parasitic.Evolved with animal body environment where there is a ready and easy source of complex nutrients

Nutritional requirements of bacteria • Essential- C,N,O,H for carbohydrate,lipid,protein & nucleic acid • P & S –Elemental or complex form • H & O- available in water • C & N-From environment.(C needed in assimilable form) • Carbohydrate- Principal source of carbon.Degraded by oxidation or fermentation.

Nutritional requirements ….. • Nucleoprotein,Nucleic acids-Ammonium salt ; from environment or deamination of aminoacid • Salts-K,Mg,Fe,P,& S • Minimal quantity-Ca,Mn • Trace-Co,Zn,chlorine,copper,nickel • Sulphur & phosphorous-Part of coenzymes & cysteinyl & methionyl side chains of proteins • Bacteria use sulphur & reduce it to H2S

Nutritional requirements…. • Organic growth factorsThiamine, riboflavine, nicotinic acid, pyridoxin, folic acid, vitamin B12 • Essential –Exogenous supply required; Mutation in bacteria can result in failure of intake • Accessory- “X” & “V” factors in H.influenzae.X is haemin & V is NAD

Oxygen requirement of bacteria • Aerobic-Grow well in normal atmospheric oxygen.Have enzymes needed to process toxic oxygen products • Obligate aerobe-Cannot live without oxygen Eg. fungi, protozoa, bacillus sp • Microaerophilic - Require small amount of oxygen.live in soil,water or tissues & not exposed to atmosphere Eg. Treponema, Actinomyces

Anaerobic bacteria • Anaerobe-do not grow in the presence of oxygen.have no enzymes to neutralise toxic oxygen products • Obligate anaerobe-Killed in the presence of oxygen.Require special media for growth Eg. Clostridia, Bacteroides

• Facultative anaerobe-Aerobic but capable of growing in the absence of oxygen. Have oxidative & fermentative capabilities. Eg. enteric bacilli, Staphylococcus

Oxygen and bacteria • Aerotolerant-Do not utilise oxygen but survive in it’s presence.Have mechanisms to break down peroxidases & superoxides. Eg. Lactobacilli, Peptostreptococci • Capnophiles - Grow at higher atmospheric CO2 tension.(10%). Need CO2 incubator or candle jar. Eg. Gonococci, Pneumococci

Moisture and dessication • Moisture is an absolute necessity for bacteria • Sensitivity to drying varies with different species • Highly sensitiveG.C , T.pallidum • Resistant to dryingM.tb, S. aureus

Osmotic pressure • Cell wall renders stability to variations in osmotic pressure • 0.5% sodium chloride suspension renders stability • Rupture occurs due to cell wall rupture in hyperosmotic states

Hydrogen ion concentration • Bacteria require physiological pH(7.2-7.4) • Acidophils -Acidic pH eg. Lactobacilli (3) • Basophils - Alkaline ph (9) eg.V.cholera • pH of growth medium keeps changing depending upon the utilisation of nutrients • An optimal pH will last only for a short time in fermentative bacteria

Bacteria and temperature • Psychrophilic-Grow below 20˚C.Usually soil & water saprophytes • Mesophilic-Grow below 25˚& 40˚C.Most are pathogenic bacteria • Thermophilic-Grow below 55˚C & 80˚C. Eg. B.stearothermophilus

Light and bacteria • Most bacteria except phototrophs prefer to grow in dark • Some produce pigment when grown in sunlight / darkness. Eg. Mycobacteria

Bacterial metabolism • Metabolism-Series of changes of a substance inside a cell. Absorption to elimination • Catabolism-Breakdown of macromolecules into simpler products. Eg. ADP to ATP Enzyme dependent pathways (TCA etc) • Anabolism-Basic building of cellular structures in monomers & polymers. Energy dependent process

Oxidation(aerobic respiration) • Removal of electron or H ion from substrate • Conversion of ADP to ATP (oxidative phosphorylation) • Executed by enzymes through metabolic pathways • Hydrogen acceptor is oxygen • Hydrogen donors are inorganic substances • Enzyme of cell wall- cytochrome oxidase • Glucose oxidised to CO2 and water • H2O2 byproduct broken down by catalase & peroxidase

Fermentation (Anaerobic respiration ) • Process of substrate phosphorylation • Hydrogen acceptor is an organic ion like nitrate, sulphate or carbonate • Glucose 6 phosphate + NAD = NADH+phosphate • Glucose converted into lactic acid, ethanol and water

Effect of one bacteria on another • Symbiosis - S.aureus & H. influenzae • AntagonismPseudomonas and Gonococci • Colicins - Secretory substances that inhibit the growth of other species of bacteria

Nutrition uptake by bacteria • Most bacteria are capable of synthesizing macromolecules Eg. amino acids, purines • Small molecules diffuse across cell membrane • Nutrients in higher concentration in cells need energy dependent process for diffusion • Macromolecules(sugars) diffuse slowly

OF test and OR potential • Hugh leifson test-Differentiates fermenters and oxidisers • OR potential( Redox potential)-Measures the reducing capacity of a system.Potential difference between a given system and a hydrogen electrode.Assessed by dyes like methylene blue, litmus, resazurin • Anaerobes require low redox potential

Bacterial growth • No obligatory life cycle • Divide by binary fission when there is adequate nutrition and conducive environment • Generation time/doubling time/replication time is the time required to complete one cell cycle

How fast do organisms grow? • • • • • • •

Most viruses Escherichia coli Staphylococcus aureus Mycobacterium tuberculosis Mycobacterium leprae Treponema pallidum Plasmodium falciparum

< 1 hour 30 mts 30 mts 24 hrs 10 to 30 days 30 hrs 8 hrs

Bacterial growth curve • • •

Lag phase • Phase of adaptation • Cause for missed bacteria in sampling

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Log phase Phase of rapid growth. Short duration with utilisation of nutrients. Best bacterial morphology & typical biochemical characters. Can be prolonged by continuous supply of nutrients as with chemostat & turbidostat

Bacterial growth curve • • • •

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Stationary phase Decline in growth rate Increase in death rate Growth and cell division imbalanced Excretion of organic acids and biochemical products Total count static Decline in viable count

• • • • •

Decline phase Phase of death Depletion of water Accumulation of toxic end products Decline in total count of organisms Can be slowed down by refrigeration

Application of growth curve • Implication in microbial growth,infection,food microbiology and cultural technology • Microbes in exponential phase are more susceptible to antibiotics,heat and disinfectants • Microbes in exponential phase are far more virulent and viable • Bacterial morphology,motility,biochemical characters and antigen demonstration best done in growth phase

Measurement of bacterial growth • Mass of cellular material Dry weight, packed cell volume, nitrogen content, turbidity as measured by calorimeter or spectrophotometer • Cell numbers Total cell number by coulter counter Viable count by sub culture and counting the colonies

Products of bacterial growth • Toxins Exotoxins and endotoxins

• Extracellular enzymes • Tissue degrading enzymes - Collagenase, coagulase, haemolysin etc

• Ig A protease • Pigments Localized and diffuse