General Characteristics

The genera discussed in this chapter are considered together because most of them are usually oxidase-positive, non–glucose utilizers capable of growth on MacConkey agar. They are a diverse group of organisms. The organism’s specific morphologic and physiologic features are presented later in this chapter in the discussion of laboratory diagnosis.

Achromobacter species are gram-negative, nonsporulating, motile rods with 1 to 20 peritrichous flagella. They are strictly aerobic and nonfermentative. However, some strains are capable of anaerobic growth. The genus Alcaligenes is limited to the pathogenic type species A. faecalis, with two subspecies that are limited to environmental isolates: A. faecalis subsp. parafaecalis and A. faecalis subsp. phenolicus. Alcaligenes species are gram-negative, strict aerobic rods or coccobacilli that are oxidase and catalase positive. They are motile and have 1 to 12 peritrichous flagella. Comamonas spp. are typically environmental species that may be problematic opportunistic nosocomial pathogens. Comamonas and Delftia spp. are aerobic, non–spore forming, straight or slightly curved, gram-negative rods with one or more polar flagella. The genus Oligella comprises two asaccharolytic coccobacilli species, O. ureolytica and O. urethralis. O. ureolytica are motile by peritrichous flagella, and O. urethralis are nonmotile. Roseomonas spp. are coccoid, plump rods in pairs or short chains. They are typically motile by one or two polar flagella.

Epidemiology

The habitats of the species listed in Table 25-1 vary from soil and water environments to the upper respiratory tract of various mammals. Certain species have been exclusively found in humans, whereas the natural habitat for other organisms remains unknown.

The diversity of the organisms’ habitats is reflected in the various ways they are transmitted. For example, transmission of environmental isolates such as Achromobacter denitrificans frequently involves exposure of debilitated patients to contaminated fluids or medical solutions. In contrast, Bordetella bronchiseptica transmission primarily occurs by close contact with animals, whereas Bordetella holmesii has been detected only in human blood, and no niche or mode of transmission is known.

Pathogenesis and Spectrum of Disease

Identifiable virulence factors are not known for most of the organisms listed in Table 25-2. However, because infections usually involve exposure of compromised patients to contaminated materials, most of these species are probably of low virulence. Among the environmental organisms listed, Achromobacter spp. are most frequently associated with various infections, including bacteremia, meningitis, pneumonia, and peritonitis. They also have been implicated in outbreaks of nosocomial infections. Achromobacter piechaudii has been isolated from pharyngeal swabs, wounds, blood, and ear discharge. Achromobacter xylosoxidans increasingly has been recovered from patients with cystic fibrosis. However, it is unclear whether the organism is implicated in causing clinical disease in patients with cystic fibrosis or whether it simply colonizes the respiratory tract. A. denitrificans has been recovered from urine, prostrate secretions, the buccal cavity, pleural fluid, and eye secretions. A. faecalis has been isolated from a wide range of clinical specimens and has been identified in bacteremia, ocular infections, pancreatic abscesses, bone infections, urine, and ear discharge. Comamonas spp. have been identified in cases of endocarditis, meningitis, and catheter-associated bacteremia. They have also been recovered from sputum in patients with cystic fibrosis. Other organisms, such as O. urethralis and O. ureolytica have been isolated predominantly from the human urinary tract. Pseudomonas alcaligenes and Pseudomonas pseudoalcaligenes rarely have been identified in clinical samples.

No special considerations are required for collection and transport of the organisms discussed in this chapter. Refer to Table 5-1 for general information on specimen collection and transport.