Bacterial Physiology

Dr Shireen RafiqMBBS, M.Phil, Ph.D

Growth cycle

• Bacteria reproduce by BINARY FISSION• Exponential growth---logarithmic growth

Definitions

• Aerobic bacteria• Adequate amount of oxygen enhances

metabolism and growth• Oxygen generates two toxic metabolites

hydrogen peroxide and superoxide ----bacteria require enzyme superoxide dimutase and catalase----catalyses the reaction

Obligate Aerobes

• Require oxygen to grow----as ATP generating system is dependent on oxygen as the hydrogen acceptor

• E.g. Mycobacterium tuberculosis

Facultative anaerobes

• Utilize oxygen if present to generate energy by respiration

• Can use fermentation pathway to synthesize ATP in the absence of sufficient oxygen

Obligate Anaerobes

• Can not grow in the presence of oxygen • Lack superoxide dismutase or catalaze or both

Obligate Aerobes

• They require oxygen to grow----ATP generating system is dependent on oxygen as hydrogen acceptor

• E.g. Mycobacterium tuberculosis

Bacterial Culture Media

Microbiological Culture Media• Culture media are mixtures of

nutrients for growth of micro organism outside their natural habitat.

• They supply the organism with sources of energy and elements allowing its optimum growth.

Culture and MediumCulture is the term given to microorganisms that are

cultivated in the lab for the purpose of identifying and studying them

Medium is combination of ingredients that will support the growth and cultivation of microorganisms by providing all the essential nutrients required for the growth (that is, multiplication) in order to cultivate these microorganisms in large numbers to study them.

Microbiological Culture Media

• A- Water• B- Nitrogen-containing compounds• C- Energy sources• D- Accessory growth factors• E- Solidifying agents• F- pH Indicators• G- Reducing agents• H- Selective agents

Classification of Culture media• Based on the consistency:

Liquid -- Peptone water, Nutrient broth Semisolid -- Nutrient agar stabs Solid -- Blood agar, Serum agar

• Based on Oxygen requirement:

-- Aerobic medium -- Anaerobic media

Aerobic media

Simple media- consists of only basic necessities

Liquid media - Peptone water(1% peptone +0.5%Nacl + 100 ml water)

- Nutrient broth ( peptone water + 1% meat extractSolid media

- Nutrient agar (nutrient broth + 2% Agar)

Use: To grow non-fastidious microorganisms

Aerobic Media

• Simple media• Complex media

- Enriched media - Differential media - Enrichment media - Selective media - Sugar media - Transport media

Basic Media Contain the essential

requirements for the growth of most micro organisms

Example: 1. Nutrient Broth / Agar 2. Nutrient Gelatin 3. Peptone Water 4. Sabouraud’s Dextrose Broth/

Agar

Enriched Media• Contain nutrients (growth factors) required to support the

growth of a wide variety of organisms, including some of the more fastidious ones.

• These factors are usually body fluids . Example: 1. Blood Agar 2. Chocolate Agar (streptococcus pneumoniae) 3. Loeffler’s Serum (Corynebacteria , shows proteolytic activity) 4. Dorset’s egg medium (Mycobacteria)

Selective Media

• These media contain a substance that 1. inhibits the growth of some micro organism 2. while allowing the growth of others

• i.e. they select for certain microbes.

Example: 1. Lowenstein-Jensen

(Mycobacterium tuberculosis)

Selective and Differential Media

• These are both selective & differential.Example: 1. Mannitol Salt Agar (MSA) 2. Eosin Methylene Blue Agar (EMB) 3. Deoxycholate Citrate Agar (DCA) 4. Thiosulfate Citrate Bile Salts Medium (TCBS) 5. Triple Sugar Iron Agar (TSI) 6. Bismuth Sulfite Agar (BS)

Transport media

• Stuart’s medium contain reducing agents to prevent oxidation.

• Charcoal to neutralize certain bacterial inhibitors to Gonococci,

• Amies transport media• Cary blair media

Blood culture media

• - Brain-heart infusion medium - In general

• - Mac Conkey’s Biphasic medium - Glucose broth - Streptococci- Bile broth - Salmonella- Casteneda Biphasic M - Brucella