CASE 23
An 18-year-old woman presented with a worsening of her chronic cough for the past week. She had had a low-grade fever, as well as fatigue and shortness of breath. The cough was productive of greenish sputum that was thick and tenacious.
LABORATORY STUDIES
Imaging
A chest x-ray showed a small heart, hyperinflated lung fields, and patchy bilateral infiltrates.
Diagnostic Work-Up
Table 23-1 lists the likely causes of current illness (differential diagnosis). Investigational approach for a specific microbiologic diagnosis includes
TABLE 23-1 Differential Diagnosis and Rationale for Inclusion (consideration)
Rationale: The patient has chronic pneumonia. Whereas CF patients can get common respiratory pathogens, the organisms listed above are most commonly associated with chronic infection, due to their ability to persist in respiratory secretions and in the abnormal lung environment. In particular, colonization and infection with P. aeruginosa and B. cepacia are very common. S. aureus and H. influenzae are also important pathogens. Unusual organisms such as Aspergillus and mycobacteria are less common and are often difficult to treat.
MICROBIOLOGIC PROPERTIES
P. aeruginosa is a Gram-negative rod (Fig. 23-1A) in the family Pseudomonadaceae, which also includes Burkholderia and Stenotrophomonas. Pseudomonads are nonspore forming and actively motile by means of their single polar flagellum. These strictly aerobic bacteria are also nonfermentative and oxidase positive. The typical Pseudomonas bacteria in nature might be found in a biofilm, attached to some surface. The vast majority of strains are pigmented due to a water-soluble pigment, pyocyanin (“blue pus”). Colonies on routine blood agar plates have a characteristic fruity odor. P. aeruginosa isolates obtained from respiratory secretions of CF patients have a mucoid appearance (see Fig. 23-1B), which is attributed to its production of alginate capsule.
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