Bacteriological Media:Cultivation of Microbes
Dr. Md. Abdullah YusufAssistant Professor of Microbiology
National Institute of Neurosciences & HospitalDhaka, Bangladesh
Email: [email protected]
Learning Objectives
• Definition of culture/cultivation and media• Types of culture• Types of microbes as per ability of culture• Basic equipment and logistic arrangement for
bacterial culture• Indication of culture• Classification, type and use of bacteriological
media
Definition
• Cultivation– Process of allowing bacteria to multiply in
artificial food providing optimum environment
• Culture Medium/media– Artificial food for bacteria for in vitro growth
Types of Culture
• Inanimate– Using nutritional ingredients but no living cells
or tissues– Used for culture of bacteria and fungus
• Animate– Using nutritional ingredients and metabolic
substrate for living cells or tissues to multiply (Tissue/Cell Culture)
– Used for in vitro multiplication of virus, rickettsia, chlamydia
Types of Bacteria as per ability to Culture
• Some bacteria can multiply easily– ordinary
• some with difficulties– fastidious
• some cannot– uncultivable
Conti….
• Fastidious– Neisseria gonorrhoea– Neisseria meningitides – Haemophilus influenzae
• Uncultivable– Mycobacterium leprae– Treponema pallidum
Culture technique
Materials Needed for Culture
• Specimen• Sterile Cotton Swab • Bacteriological Wire Loop • Suitable Culture Media• Incubator
• Aerobic• CO2/Anaerobic
Indication of Culture
• Isolation- diagnosis • Identification- diagnosis• Antimicrobial susceptibility- treatment• Genomic study- characterization• Progressive research- up to date information
Culture Media
ClassificationA. On the basis of consistency• Liquid• Solid• Semi-solid (gel)
Conti…
B. On the basis of nutritional ingredients– Simple or basal– Enriched– Selective– Indicator – Differential
Classification-contd
C. On the basis of use– Primary– Subculture– Transport– preservative
Important points
• Liquid media is also called broth• Solid media– Liquid media + solidifying agent in appropriate
concentration (5-10%)• Semisolid media– liquid media + solidifying agents at low
concentration (study bacterial motility)
Solidifying agents
• Agar agar (sea weeds)– melt at high temperature (55-600 C)– solidified at low temperature (40-450 C)
• Egg whole• Gelatin• Potatoes• Tomato powder• Serum
According to ingredients• Simple/basal– contain basic nutrient support
• Enriched– contain growth enhancing substances. e.g.- blood,
serum, haemoglobin• Selective– inhibitory substance that do not inhibit one
group/species, but inhibit all other• Semi-selective– if allow growth of one family-many members
• Highly selective– allow only one species of a particular genus
According to Ingredients (contd.)
• Indicator– contain chemical substance that changes it’s
colour with change of pH– indicate particular property of a genus of
bacteria• Differential– substance with change of colour (black colour
due metalic tellurium) or phenomenon (haemolysis) observed due to growth of a particular bacteria
According to Use
• Primary– first inoculation then transfer or not
• Subculture– subsequent inoculation from primary media
• Transport– Dissolve or mix clinical specimens or bacteria– allow little growth but no inhibition– transported from one location to another
• Preservative– dehydrated media containing metabolically inactive
bacteria – kept for prolonged period (lyophilized skimmed milk)
Subculture
How a medium can be made selective?
• Adding inhibitory substance– bile salt in MacConckey agar
• Adding antibiotic– Campybap for Campylobacter
• Adding alkali/ Changing pH– Sodium bi carbonate in alkaline peptone water
• Removing oxygen– by reducing chemicals or mechanically for
anaerobic bacteria• Changing temperature– thermophiles grow at high temperature
Advantages of solid media over liquid media
• Discrete growth as separate unit (colony)– hazy or opaque appearance in liquid
• Clear colony morphology• Easy to pick-up for subculture• Sensitivity test or further identification tests
Differential media
Haemolysis in blood agar
Blood agar
Thank You
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