Microbial Culture Media types and examples.pptx

thorough examination of the various types and instances of Microbial Culture Media

1. Microbial Culture Media Submitted by Abhijit padhi

2. Introduction The media is a source of nutrients to support the growth of the micro-organisms in-vitro. The media helps in the growth and counting of microbial cells, selection of microorganisms, and survival of microorganisms. The culture medium can be liquid or gel. Common ingredients of culture media Peptone- source of carbon and nitrogen. Beef extract- source of amino acid, vitamins, minerals. Yeast extract- source of vitamin, carbon, nitrogen. Distilled water Agar- solidifying agent.

3. Preparation of cultured media Weigh the amount of ingredients powder on weighing machine. Dissolve the ingredients in distilled water. Adjust PH of the medium if needed. Add agar and boiled it to dissolve. Pour the media into flask. Autoclave the media when ingredients fully dissolve. Sterilization is done in autoclave to prevent from contamination, at 121ºC for 15 min at 15lbs. After the autoclave place the media flask in laminar air flow. Sterilize the laminar air flow with 70% alcohol. A bit cools down the media and pours into sterile Petri-plates for solidification. Then sample is ready to spread(spreader) / streak (Inoculation loop) on the medium for identification or isolation of microbes. Sealed the Petri plates with paraffin, label them. Keep them inverted in incubator at 37ºC for 24hrs. Observe the result next day colonies formation is visible on the media.

4. Defined media  and  complex media  are two broad classes of culture media used in microbiology.  Defined media  are prepared by adding precise amounts of highly purified inorganic or organic chemicals to distilled water. Therefore, the exact composition of a defined medium is known.   Complex media  are prepared using digests of microbial, animal, or plant products. Casein (milk protein), beef (beef extract), soybeans (tryptic soy broth), yeast cells (yeast extract), or any other highly nutritious yet impure substances are used to prepare complex media; thus, the exact composition of the medium is not known. For culturing many microorganisms, this information is not essential either. Culture media contains nutrients and physical growth parameters necessary for microbial growth. If a culture medium meets a bacterial cell’s growth requirements, then that cell will multiply to sufficient numbers to allow visualization by the unaided eye. Bacterial culture media can be classified based on  composition, consistency, and purpose. All microorganisms cannot grow in a single culture medium; many can’t grow in any known culture medium. Organisms that cannot grow in the artificial culture medium are obligate parasites. Mycobacterium leprae, Rickettsia, Chlamydia trachomatis, and Treponema pallidum are obligate intracellular parasites.

5. Types of media

6. 1. Solid Medium It contain agar at a concentration of 1.5-2.0% or some other primarily inert solidifying agent. Solid medium has a physical structure and allows bacteria to grow in physically informative or useful ways (e.g., as colonies or in streaks). MacConkey agar, chocolate agar, nutrient agar, blood agar, etc., are some examples of solid culture media. Uses of solid culture media For isolating bacteria from various types of specimen For determining the colony characteristics of the isolate (such as colony morphology, hemolysis, pigment production, etc. For performing antimicrobial susceptibility testing using the Kirby Bauer disc diffusion method

7. 2. Semisolid Medium This type of culture media are prepared with agar at 0.5% or less concentrations. Semisolid medium has a soft custard-like consistency and is helpful for the cultivation of microaerophilic bacteria or for determining bacterial motility. Motility test medium, Stuart’s and Amies transport media, etc., are semisolid media. 3. Liquid (Broth) Medium These media contain specific amounts of nutrients but don’t have a trace of gelling agents such as gelatin or agar. Commonly used liquid media in the lab are; nutrient broth, glucose broth, brain-heart infusion (BHI) broth, alkaline peptone water (APW), tryptic soy broth (TSB), and selenite F broth. Broth medium serves various purposes such as propagation of many organisms, fermentation studies, and various other tests. Uses of liquid culture media To grow bacteria for motility testing To grow bacteria for inoculum production for antibiogram testing To revive bacteria from lyophilized or stock culture To study metabolism, toxin, and enzyme production To enrich and/or transport clinical material

8. 1. Basal media This medium is straightforward since it promotes the growth of several microbes. It is a common laboratory media that contains both carbon and nitrogen. This medium, which is used for sub-culturing, permits the development of non-fastidious bacteria in the absence of an enrichment source. This medium is non-selective. Staphylococcus  and  Enterobacteriaceae  grow in this media. Examples of Basal media Nutrient Agar,  Peptone water .

9. 2. Enriched media Other materials, such as blood, eggs, or serum, must be added to this medium. Although other, picky bacteria cannot thrive in an enriched medium because they need nutrients like vitamins and chemicals that promote growth, they can grow in it. Example of Enriched media Blood agar, Chocolate agar, LSS, Monsor’s taurocholate,  Lowenstein Jensen media . Blood agar identifies hemolytic bacteria, chocolate media for  N. gonorrhea .

10. 3. Selective Media Principle:  Differential growth suppression Selective medium is designed to suppress some microorganisms’ growth while allowing others’ growth. Selective medium is an agar-based (solid) medium so that individual colonies may be isolated. Examples of selective media include Thayer Martin Agar  used to recover  Neisseria gonorrhoeae  contains antibiotics; vancomycin, colistin, and nystatin. Mannitol Salt Agar   and Salt Milk Agar used to recover  S.aureus  contains 10% NaCl. Potassium tellurite medium used to recover  C.diphtheriae  contains 0.04% potassium tellurite. MacConkey’s Agar  used for  Enterobacteriaceae  members, contains bile salt that inhibits most gram-positive bacteria. Pseudosel Agar (cetrimide agar)  used to recover  Pseudomonas aeruginosa  contains cetrimide (antiseptic agent). Crystal Violet Blood Agar used to recover  S. pyogenes  contains 0.0002% crystal violet. Lowenstein Jensen Medium  used to recover  M.tuberculosis  is made selective by incorporating malachite green. Wilson and  Blair’s Agar for recovering  S. typhi  is rendered selective by the addition of dye brilliant green. Selective media such as  TCBS Agar   for isolating Vibrio cholerae from fecal specimens have elevated pH (8.5-8.6), inhibiting most other bacteria.

11. 4. Enrichment Media The enrichment medium increases the relative concentration of specific microorganisms in the culture before plating on a solid selective medium. Unlike selective media, enrichment culture is typically used as a broth medium. Enrichment media are liquid media that also serves to inhibit commensals in the clinical specimen. Selenite F broth, tetrathionate broth,   and  alkaline peptone water (APW)  recover pathogens from fecal samples. Example of Enriched media Selenite F-broth does the isolation of Salmonella Typhi from a fecal sample. Selenium allows the growth of desired organisms and, detection levels increase for intestinal flora. .

12. 5. Differential/Indicator Media Certain media are designed to recognize different bacteria based on their colony color. Various approaches include incorporating dyes, metabolic substrates, etc., so those bacteria that utilize them appear as differently colored colonies. Such media are called differential media or indicator media. Differential media allow the growth of more than one microorganism of interest but with morphologically distinguishable colonies. Examples of differential media include: Mannitol salts agar (mannitol fermentation = yellow) Blood agar (various kinds of hemolysis i.e., α, β and γ hemolysis ) MacConkey agar (lactose fermenters, pink colonies whereas, non-lactose fermenter produces pale or colorless colonies. TCBS (Vibrio cholerae produces yellow colonies due to fermentation of sucrose)

13. 6. Transport Media Clinical specimens must be transported to the laboratory immediately after collection to prevent overgrowth of contaminating organisms or commensals and maintain the viability of the potential pathogens. This can be achieved by using transport media. Such media prevent drying (desiccation) of a specimen, maintain the pathogen to commensal ratio, and inhibit the overgrowth of unwanted bacteria. Some of these media (Stuart’s & Amie’s) are semi-solid. The addition of charcoal serves to neutralize inhibitory factors. Cary Blair transport medium and Venkatraman Ramakrishnan (VR) medium transport feces from suspected cholera patients. Sach’s buffered glycerol saline is used to transport feces from patients suspected of suffering from bacillary dysentery. Pike’s medium is used to transport streptococci from throat specimens.

14. 7. Storage media It maintains the longevity of bacterial culture.  Examples are-  cooked meat broth, NA egg saline.

15. 1. Aerobic media In this media, it is easy to cultivate microbes, on solid media, the growth occurs by keeping the culture in the incubator. It shows the growth; of non-fastidious microorganisms.  Examples of aerobic media are-   liquid media, solid media  Peptone water- 1%peptone + 0.5% Nacl +100ml water. Nutrient agar- nutrient broth +2% agar.

16. 2. Anaerobic media The media cultivates anaerobic bacteria at low oxygen, reducing oxidation-reduction potential. Anaerobic media contains extra nutrients like vitamin K, hemin, and oxygen that get reduced by a physical or chemical process. The addition of glucose (1%), thioglycollate (0.1%), ascorbic acid (0.1%), cysteine (0.05%), or iron fillings added to cause the medium to reduce. The medium is boiled in a water bath to force out dissolved oxygen and packed with sterile paraffin. Examples of Anaerobic media RCM (Robertson cooked meat) isolation for  Clostridium  sp. Thioglycolate broth – It has sodium glycolate that maintains low oxygen.

17. Application of culture media To culture microbes. To identify the cause of infection. To identify characteristics of microorganisms. To isolate pure culture. To store the culture stock. To observe biochemical reactions. To test microbial contamination in any sample. To check antimicrobial agents and preservatives effect. To observe microbe colony type, its color, shape, cause. To differentiate between different colonies. To create antigens for laboratory use. To estimate viable count. To test antibiotic sensitivity.

18. Limitations of culture media Risk of cross-contamination. High skill required for optimal results. Increased drying out of media can occur.

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