TYPES OF CULTURE MEDIA-II

TYPES OF CULTURE MEDIA-II


Mueller Hinton Agar (MHA)

  • Mueller and Hinton developed Mueller Hinton Agar (MHA) in 1941 for the isolation of pathogenic Neisseriaspecies
  • Five percent sheep blood and nicotinamide adenine dinucleotide may also be added when susceptibility testing is done on Streptococcus species, This type is also commonly used for susceptibility testing of Campylobacter.
  • It is a non-selective, non-differential medium. This means that almost all organisms plated on here will grow.
  • It contains starch. Starch is known to absorb toxins released from bacteria, so that they cannot interfere with the antibiotics. It also mediates the rate of diffusion of the antibiotics through the agar.
  • It is a loose agar. This allows for better diffusion of the antibiotics than most other plates. A better diffusion leads to a truer zone of inhibition.
  • MHA shows acceptable batch-to-batch reproducibility for susceptibility testing.
  • MHA is low in sulfonamide, trimethoprim, and tetracycline inhibitors (i.e. concentration of inhibitors thymidine and thymine is low in MHA).
  • Both the para-aminobenzoic acid (PABA) and thymine/thymidine content in Mueller Hinton Agar are reduced to a minimum, thus markedly reducing the inactivation of sulfonamides and trimethoprim when the media is used for testing the susceptibility of bacterial isolates to these antimicrobics.

Uses of MHA

  1. The major use of Mueller Hinton Agar is for antimicrobial susceptibility testing. It has become the standard medium for the Bauer Kirby method and its performance is specified by the NCCLS.
  2. It can be used to cultivate Neisseria
  3. It is specified in FDA Bacteriological Analytical Manual for food testing, and procedures commonly performed on aerobic and facultative anaerobic bacteria

Löffler’s medium

  • Friedrich Loeffler devised a culture medium containing horse serum, meat infusion, and dextrose for use in the cultivation of corynebacteria and for differentiating them from other organisms.
  • Buck, in 1949, described a modified Loeffler’s medium for cultivating Corynebacterium diphtheriae.
  • The primary value of Loeffler medium is in the growth and morphological characterization of members of the genus Corynebacterium. This formulation enhances the formation of metachromatic granules within the cells of the organisms.
  • Due to its serum content, Loeffler medium can be used for the determination of proteolytic activities of microorganisms.
  • The gray-white surface of the medium provides an excellent background for the detection and observation of colonial pigmentation.
  • If all extraneous moisture is removed aseptically from the slants and the upper part of the slant is heated until the slant ruptures, this medium can be used for the detection of ascospores.

Lowenstein Jensen Medium (LJ Medium)

  • LJ Medium is a selective medium that is commonly used for the cultivation and isolation of Mycobacterium, specifically Mycobacterium tuberculosis from clinical specimens. LJ medium was originally formulated by Lowenstein who incorporated congo red and malachite green to inhibit unwanted bacteria.
  • The present formulation comprises of a glycerated egg-based medium and is based upon Jensen’s modification. Jensen modified Lowenstein’s medium by altering the citrate and phosphate contents, eliminating the congo red dye and by increasing the malachite green concentration.
  • Gruft further modified L. J. Medium with the addition of penicillin, nalidixic acid and ribonucleic acid (RNA) to increase selectivity. This medium supports the growth of a wide variety of Mycobacteria and can also be used for niacin testing
  • It is used for the diagnosis of Mycobacterial infections. It is used for testing antibiotic susceptibility of isolates. It is also used for differentiating different species of mycobacterium (by colony morphology, growth rate, biochemical characteristics and microscopy)

Exam Important

  • Mueller and Hinton developed Mueller Hinton Agar (MHA) in 1941 for the isolation of pathogenic Neisseriaspecies
  • Löffler’s medium Used  in the cultivation of corynebacteria and for differentiating them from other organisms.
  • LJ Medium is a selective medium that is commonly used for the cultivation and isolation of Mycobacterium, specifically Mycobacterium tuberculosis from clinical specimens

 

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