A 21-year-old college student complained of malaise, low-grade fever, and a harsh cough, but not of muscle aches and pains. An x-ray revealed a diffuse interstitial pneumonia in the left lobes of the lung. The WBC count was normal. The student has been ill for a week. The following laboratory data were available within 2 days: cold agglutinins--negative; complement fixation (M. pneumoniae)--1:64; viral culture--pending, but negative to date; bacterial culture of sputum on blood agar and MacConkey's agar--normal oral flora. In order to confirm the diagnosis, which of the following procedures could be ordered to achieve a specific and sensitive diagnosis?
Mycoplasma pneumoniae causes a respiratory infection known as primary atypical pneumonia or walking pneumonia. Although disease caused by M. pneumoniae can be contracted year-round, thousands of cases occur during the winter months in all age groups. The disease, if untreated, will persist for 2 weeks or longer. Rare but serious side effects include cardiomyopathies and central nervous system complications. Infection with M. pneumoniae may be treated with either erythromycin or tetracycline. The organism lacks a cell wall and so is resistant to the penicillin and the cephalosporin groups of antibiotics Until recently, diagnostic tests have been of limited value. Up to 50% of cases may not show cold agglutinins, an insensitive and nonspecific acute-phase reactant. However, if cold agglutinins are present, a quick diagnosis can be made if signs and symptoms are characteristic. Complement fixation tests that measure an antibody to a glycolipid antigen of M. pneumoniae are useful but not routinely performed in most laboratories. Also, cross-reactions may occur. Culture of M. pneumoniae, while not technically difficult, may take up to 2 weeks before visible growth is observed. A DNA probe is available. It is an 125I probe for the 16S ribosomal RNA of M. pneumoniae. Evaluations in a number of laboratories indicate that compared with culture it is highly sensitive and specific. Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition
Culture of the sputum on charcoal yeast extract
A repeat cold agglutinin test
A DNA probe to the 16S ribosomal RNA of an organism lacking a cell wall
A repeat CF test in 5 days
Bacteriology