Chapter 255

Pseudomonas and Burkholderia species are nonlactose fermenting gram-negative bacilli that were previously classified in the same genus. The name Burkholderia was proposed in 1992 for 7 species that were previously classified as Pseudomonas.1 Both genuses consist of nutritionally diverse water- and soil-borne organisms; because they have related biochemical characteristics, Burkholderia may be misidentified as Pseudomonas or other nonfermenting gram-negative bacilli.

The most clinically important Pseudomonas species is P aeruginosa. It is an opportunistic pathogen that rarely causes disease in normal hosts, but it may cause serious infections in patients with underlying conditions, including neutropenia, immunodeficiency, and cystic fibrosis, and in hospitalized patients with wounds, burns, or indwelling catheters. Many former pseudomonads including Burkholderia cepacia,2Sphingomonas paucimobilis,3 and Stenotrophomonas maltophilia4 are also pathogenic in specific human hosts. Both P fluorescens and P putida have been reported as the cause of catheter-associated infections in cancer patients and in outbreaks of pseudobacteremia, and P oryzihabitans has been increasingly identified as an agent of catheter-associated infections in patients who are immunocompromised.5 Other pseudomonads occasionally seen in human disease include P stutzeri and P luteola.

The B cepacia-complex (composed of 9 named species, eTable 255.1)2 is the most important group of organisms in the Burkholderia species, causing infections in patients with cystic fibrosis and chronic granulomatous disease. Burkholderia pseudomallei is the etiologic agent of melioidosis, a common pediatric infection in Southeast Asia. Other Burkholderia species that occasionally cause human disease are B mallei, the etiologic agent of glanders, a rare zoonosis seen in the Far East, and B gladioli, an occasional cause of cystic fibrosis infection.6

eTable 255.1. Burkholderia Cepacia Complex Species

### Epidemiology

Pseudomonas aeruginosa is found widely in the natural environment, including in soil and water, and is also endemic in most hospital environments. The epidemiology of P aeruginosa transmission is not well understood. Acquisition of environmental strains has been documented, as has person-to-person transmission in the setting of cystic fibrosis. The latter is suggested by studies of risk factors for colonization of young children7 and is further supported by evidence of direct person-to-person transmission of antibiotic-resistant P aeruginosa strains in studies from Germany,8 the United Kingdom,9,10 and Australia.11 However, common environmental sources cannot be excluded.

Burkholderia species are primarily plant and animal pathogens and are generally avirulent in healthy humans. Their distribution in nature appears to be somewhat more limited than pseudomonads, and they are less easily isolated from sources in the hospital environment. However, B cepacia-complex, in particular, has a unique ...

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