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 nutrients-C,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 factors-Thiamine, 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 sensitive- G.C , T.pallidum

• Resistant to drying-M.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

• Antagonism-Pseudomonas 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 < 1 hour

• Escherichia coli 30 mts

• Staphylococcus aureus 30 mts

• Mycobacterium tuberculosis 24 hrs

• Mycobacterium leprae 10 to 30 days

• Treponema pallidum 30 hrs

• Plasmodium falciparum 8 hrs

Bacterial growth curve

Lag phase

• Phase of adaptation

• Cause for missed bacteria in sampling

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

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