Medical Microbiology A Tutorial

Medical Microbiology A Tutorial Q1) What is bronchoalveolar lavage fluid? How is it obtained? What is its value as a diagnostic specimen? Bronchoalveolar lavage is a diagnostic procedure of washing a sample of cells and secretions from the alveolar and bronchial airspaces. It is performed by installing commercial sterile 0.9% saline solution for intravenous use via a channel of a fiberoptic bronchoscope, which has been wedged into a bronchus with a matching diameter. The fluid is then immediately withdrawn. The instilled fluid fills the airspaces distal to the tip of bronchoscope, replacing the air. A portion of the installed volume remains to be absorbed or expectorated after the procedure. After withdrawal, the fluid should be kept on ice until it is further processed. A major clinical limitation for the utility of bronchoalveolar lavage is the large range of normal values for each parameter, which makes BALF insensitive in detecting disease. Furthermore, abnormalities in BALF are rarely specific for any of the interstitial lung diseases. There is large interindividual variation which may not be related to the disease, and the airspace cells and secretions may not reflect interstitial processes. The removal of BALF may preferentially select, activate or injure some cells, and the composition of the epithelial lining fluid (ELF) may change during the bronchoalveolar lavage. (Davis 1994). Q2) Which organisms can be positive on an acid-fast stain? Corynebacterineae, Mycobacterium and Nocardia. Q3) Given his medical history, which organism is this likely to be? How does the finding that the patient is HIV positive affect this decision? Mycobacterium tuberculosis.

4) Which factors in his medical history do you think are important in his contracting this infection with acid-fast bacteria?

5) What is a PPD test? What is its value in this patient? What additional tests would you order with a PPD test? Purified Protein Derivative (PPD) test is also known as Mantoux test. This test is used as a diagnostic test for tuberculosis.