INFECTIONS DUE TO PSEUDOMONAS SPECIES AND RELATED ORGANISMS: INTRODUCTION

The pseudomonads are a heterogeneous group of gram-negative bacteria that have in common an inability to ferment lactose. Once classified in the genus Pseudomonas, the members of this group are now assigned to three medically important genera—Pseudomonas, Burkholderia, and Stenotrophomonas—whose biologic behaviors encompass both similarities and marked differences and whose genetic makeups differ in many respects. The pathogenicity of most pseudomonads is based on opportunism; the exceptions are the organisms that cause melioidosis (B. pseudomallei) and glanders (B. mallei).

P. aeruginosa, the major pathogen of the group, is mainly associated with infections in hospitalized patients and in patients with cystic fibrosis (CF; Chap. 253). Cytotoxic chemotherapy, mechanical ventilation, and broad-spectrum antibiotic therapy probably paved the way for increasing colonization and infection by P. aeruginosa. Since the implementation of these advances in medical therapy, most conditions predisposing to P. aeruginosa infections have involved host compromise and/or broad-spectrum antibiotic use. Other members of the genus Pseudomonas—P. putida, P. fluorescens, and P. stutzeri—infect humans infrequently.

The genus Burkholderia comprises >40 species, of which B. cepacia is most frequently encountered in Western countries. Like P. aeruginosa, B. cepacia is both a nosocomial pathogen and a cause of infection in CF. The other medically important members of this genus are B. pseudomallei and B. mallei, which, as mentioned above, cause melioidosis and glanders, respectively.

The genus Stenotrophomonas contains one species of medical significance, S. maltophilia (previously classified in the genera Pseudomonas and Xanthomonas). This organism is strictly an opportunist that “overgrows” in the setting of potent broad-spectrum antibiotic use.