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Mycobacteria (TB)

Mycobacteria

Introduction

Please include any details that show why Mycobacteria spp is suspected especially ‘atypicals’ as these samples may need to be handled differently especially with skin related infections.

Tuberculosis is caused by Mycobacterium tuberculosis complex; a group of acid fast bacilli (AFB). These bacteria are very slow growing and can take up to 8 weeks for the laboratory to isolate them. Once isolated, they are sent to the reference laboratory for full identification and antibiotic susceptibility testing.

This laboratory uses the BacT/Alert 3D Mycobacterial liquid culture system to isolate Mycobacteria spp. It uses a colorimetric sensor and reflected light to monitor the presence and production of Carbon dioxide (CO2). If micro-organisms are present in the test sample CO2 is produced which affects the gas-permeable sensor at the bottom of each bottle. The change in colour results in an increase in reflectance units which causes the system to alert us to a positive bottle. 

All samples are screened for the presence of AFB's using a fluorescence stain (auramine). These are reported promptly by the consultant microbiologists.

This method is suitable to enable growth of most types of atypical Mycobacteria but some have slightly different growth requirements; because of this it is vital that the laboratory is informed of any clinical details which may lead us to investigate further.

Sample types
Sputum
  • Ensure that at least 2 ml of sample is sent to us in a sterile universal. If additional tests are required such as routine culture, please send a separate sample where possible.

  • It is important to send 3 sputum samples on consecutive days; this will increase the chances of isolating any Mycobacteria spp that may be present.

  • For more information regarding alternative testing methods, treatment or epidemiology please the TB nurses in the Royal Derby hospital or the on-call consultant microbiologist.

  • When the cough is dry, physiotherapy, postural drainage or inhalation of nebulised saline before expectoration may be helpful.

 

 Broncho-alveolar washing/bronchial washings
  • Minimum sample size is preferably 5 ml.

 

 Gastric washings (for children)
  • Collect samples early in the morning (before breakfast) on 3 consecutive days.

  •  A minimum volume of 5 ml should be provided.

  • Aspirates should be promptly delivered to avoid acidic deterioration of organisms.

  • Results of direct microscopy on gastric washing can be misleading as acid-fast bacilli are normally present in the stomach.

 

Sterile Body Fluids (CSF, Pleural Fluids)
  • CSF- Collect aseptically as much CSF sample as possible into a sterile container. If a small volume is available after initial lumbar puncture and the findings of cell counts and protein suggest TB meningitis, a second procedure should be considered to obtain a larger volume to improve chances of achieving positive cultures.

  • Pleural Fluids - Ensure that at least 2 ml of sample is sent to us in a sterile universal. If additional tests are required such as routine culture, please send a separate sample where possible.

 

Tissue and Pus
  • Tissue - Send 1-4 small tissue pieces ideally 1cm3 in size.

  • Pus - A minimum volume of 2 ml should be provided.

 

 Urine Specimens
  • Collect in the entire 1st early morning produced on three consecutive days in a large early morning urine container.       

 

 Bone Marrow
  • Sample should be added directly to a sodium citrate bottle if liquid or a sterile universal if solid.


 (Modified Last By: AOM 21/01/2016)