Question

Direct sensitivity test for gram negative organisms in mueller hinton agar

Answer 1

Legionella is easily cultured from sputum, transtracheal aspirates, pleural effusions, and bronchoscopic specimens. This gram-negative bacillus grows easily on supplemented buffered charcoal yeast extract or a modified Mueller-Hinton agar. The most sensitive tissue organismic stains are the silver impregnation stains, such as a Steiner, Warthin-Starry, or Dieterle (Fig. 10.14); the bacilli are difficult to see on Gram and Brown and Hopps bacterial stains. Direct fluorescent antibody tests are commonly used, can be applied to deparaffinized, formalin-fixed tissue slides, and can have a sensitivity of up to 80%. Urinary antigens remain the most useful test to detect L. pneumophila, with a sensitivity of 90%.