Test: Culture Media and Methods, Identification of Bacteria by Conventional - NEET PG MCQ

CLED agar (Cysteine lactose electrolyte-deficient agar) is akin to MacConkey agar and serves to differentiate between LF and NLF.

• It is utilised as an alternative to the combination of blood agar and MacConkey agar for processing urine specimens.
• Advantages compared to MacConkey agar include:
  • It is less inhibitory than MacConkey agar.
  • It supports the growth of gram-positive bacteria (with the exception of β hemolytic Streptococcus) and Candida.
• As for its benefits over blood agar:
  • It can inhibit the swarming of Proteus.

• Thayer-Martin media: Selective media for Gonorrhea
• Chocolate agar: Enriched media
• Lowenstein-Jensen Medium: Selective media for Mycobacterium tuberculosis
• Muller-Hinton agar: Used for antibiotic susceptibility testing
• Mac Conkey’s agar: Differential media that distinguishes between LF (pink colonies) and NLF (colourless colonies).

TSI is a popular composite medium, which indicated whether bacteria ferments glucose only, or lactose and sucrose also, with/without gas formation, besides indicating H₂S production as well.

Deoxycholate citrate agar (DCA) and Xylose lysine deoxycholate (XLD) are selective media for Shigella.

Typically, a concentration of 2% agar is employed for the preparation of solid media.

Roberson's cooked meat broth serves as a medium for the cultivation of anaerobic organisms.

Enriched media includes additional nutritional components such as blood, serum, and egg to facilitate the growth of fastidious organisms. Examples include:

• Blood agar
• Chocolate agar
• Loeffler’s serum slope

• Nutrient broth, Peptone water, and Nutrient Agar serve as the foundational media.
• These are utilised to create solid media, although they lack nutritive value.
• Chocolate medium is considered an enriched medium.
• The incorporation of selective substances into a solid medium is referred to as a selective medium.

Smith Noguchi’s medium: Utilised for nonpathogenic Treponemes. Pathogenic Treponemes are unable to be cultivated in artificial culture medium.

Agar concentration commonly employed:

• In solid media: 2%
• In semisolid media: 0.5-1%
• To prevent swarming: 6%

The polymerase chain reaction (PCR) is a biochemical technique used in molecular biology to replicate a single or a small number of copies of a DNA fragment, producing thousands to millions of copies of a specific DNA sequence.

Reverse transcriptase exhibits RNA-dependent DNA polymerase activity. It utilises the genomic RNA as a template to:

• Initially synthesise single-stranded DNA through the reverse transcription of genomic RNA,
• And subsequently produce double-stranded DNA.

HIV and various other retroviruses contain reverse transcriptase.

Taq Polymerase is a DNA Polymerase that replicates the target gene into millions of copies without denaturing. It is one of the essential components of PCR, along with other necessities such as primers, nucleotides, and Mg²⁺ ions.

Agarose gel electrophoresis is employed to isolate DNA based on its charge or size. It is typically conducted to observe the amplified DNA following PCR, but it can also serve as a preparative technique before employing other methods such as:

• mass spectrometry
• RFLP
• PCR
• cloning
• DNA sequencing
• Southern blotting

for further analysis. Please note that it is merely a technique for visualising DNA after it has been separated by size.

Northern blotting is employed for the identification of RNA. Southern blotting is utilised for the identification of DNA. Western blotting is used for the identification of protein.

The heat-stable DNA polymerase enzyme employed in PCR is obtained from the organism Thermus aquaticus.

DNA hybridisation is referred to as the Southern blot. RNA hybridisation is known as the Northern blot.