AFB Drug Susceptibility Test

AFB denotes Acid-fast bacteria, also called acid-fast bacilli. These are a group of bacteria sharing the property of acid fastness, that is the physical ability to resist decolorization by acids during staining procedures. This unique feature serves as a distinguishing ability in classifying and detecting acid-fast bacteria like Mycobacteria.

Tuberculosis or TB, caused by the bacterium Mycobacterium tuberculosis (MTB) is one of the diseases with a high fatality rate. Susceptibility testing is important due to the emergence of drug resistance in the bacterium. The AFB drug susceptibility test is used to determine the sensitivity of AFB culture to different types of antibiotics to determine whether the bacteria are sensitive or resistant to antibiotics.

https://www.apollodiagnostics.in/test/afb-antibiotic-susceptibility-test

https://www.ncbi.nlm.nih.gov/books/NBK537121/

In AFB Drug susceptibility (13 drugs) test, susceptibility of the acid-fast bacilli (Mycobacterium tuberculosis) is tested against 13 drugs (First-line drugs- Streptomycin, Isoniazid, Rifampicin, Ethambutol, and Pyrazinamide as well as Second-line drugs- Kanamycin, Ethionamide, Para-aminosalicylic acid, Ofloxacin Moxifloxacin, Amikacin, Clofazimine, and Capreomycin) used for TB treatment. This test is useful in providing effective treatment for individuals suffering from TB.

Why get tested with AFB Drug Susceptibility (13 Drugs)?
AFB Drug Susceptibility (13 Drugs) test is performed to detect drug-resistant Tuberculosis. This test can identify the sensitivity of MTB against 13 drugs (First-line drugs- Streptomycin, Isoniazid, Rifampicin, Ethambutol, and Pyrazinamide as well as Second-line drugs- Kanamycin, Ethionamide, Para-aminosalicylic acid, Ofloxacin Moxifloxacin, Amikacin, Clofazimine, and Capreomycin) used for TB treatment.

What is a drug susceptibility test?
Drug susceptibility test (DST) or Antibiotic susceptibility testing (AST) is a widely-used technique for evaluating antibiotic resistance and determining the most effective antibiotic for treatment. This is achieved by observing the effect of a particular antibiotic on microbial growth. The treatment can be directed as per the knowledge of the microbe and its sensitivity to the drug.

https://medlineplus.gov/lab-tests/antibiotic-sensitivity-test/

https://tbfacts.org/drug-susceptibility/

What sample is required and what preparation is needed for this test?
A pure culture obtained from body fluids, sputum, bronchial alveolar lavage, cerebrospinal fluid (CSF), pus, tissue, biopsies, lymph nodes, abscess, urine is used for performing this test. There is no special preparation required before getting this test.

What are the types of drug-resistant TB?
Drug-resistant tuberculosis infection, caused by drug-resistant Mycobacterium tuberculosis (MTB) bacterium is divided into the following categories

• Multidrug-resistant or MDR-TB: MDR-TB is the TB infection caused by MTB that is resistant to the most potent drugs used in TB treatment – isoniazid and rifampin.
• Extensively drug-resistant or XDR-TB: XDR-TB is the TB infection caused by MTB that is resistant to most commonly used drugs used in TB treatment like isoniazid and rifampin, plus any fluoroquinolone as well as at least one of the three injectable second-line drugs (amikacin, kanamycin, and capreomycin).

https://www.cdc.gov/tb/topic/drtb/default.htm

Against which drugs is the susceptibility of Mycobacterium tuberculosis analysed using this test?
AFB Drug Susceptibility (13 Drugs) test analyses the sensitivity of MTB against 13 most effective antibiotics used for TB treatment.

• First-line drugs
  • Streptomycin
  • Isoniazid
  • Rifampicin
  • Ethambutol
  • Pyrazinamide
• Second-line drugs
  • Kanamycin
  • Ethionamide
  • Para-aminosalicylic acid
  • Ofloxacin
  • Moxifloxacin
  • Amikacin
  • Clofazimine
  • Capreomycin

What are the causes of drug resistance in TB bacteria?

• Misuse or mismanagement of TB drug
• Incomplete treatment course
• Wrong treatment (drug dose or period)
• Unavailability of proper drugs
• Poor drug quality

https://www.cdc.gov/tb/topic/drtb/default.htm