Quick Review Cards for Medical Laboratory Science

Laboratory Identification of Mycobacteria Clinical Microbiology Review 207

Lab safety

Specimens requiring

digestion/decontamination

Specimens not requiring

digestion/decontamination

Digestion/decontamination

methods

Staining

Media

Mycobacterium tuberculosistransmitted by inhalation of aerosols. Low infective dose. Separate room,

if possible, with non-recirculating ventilation system & negative air pressure. BS-2 practices. Use of

BSC for all procedures that might generate aerosols. Electric incinerators instead of flames to sterilize

wire loops. Slide-warming trays instead of flames to fix slides. Tuberculocidal disinfectants to clean

equipment & BSC, e.g., 1:10 dilution of household bleach made fresh daily. UV light in BSC (only when

not in use). Annual testing of employees for exposure, e.g., Mantoux skin test with PPD.

Sputum & other specimens with normal flora such as gastric lavage, urine, feces.

Tissue or body fluids collected aseptically.

Sodium hydroxide (NaOH), N-acetyl-L-cysteine (NALC)/NaOH, benzalkonium chloride, oxalic acid.

NaOH is digestant & decontaminating agent. NALC is liquefying agent.

Cell walls have high lipid content (mycolic acids). Difficult to stain. Resist decolorization by acid

alcohol (acid-fast). Gram stain poorly. Use carbolfuchsin or fluorochrome acid-fast stains.

Agar-based (Middlebrook 7H10 & 7H11), egg-based (Löwenstein-Jensen, Petragani, American

Thoracic Society), liquid (Middlebrook 7H9). Combination of a solid-based medium & a liquid-based

medium recommended for primary isolation.

continued...

PPD = purified protein derivative