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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