Sphingomonas paucimobilis and Similar Organisms
1. Identify cultivation methods and colonial characteristics for Sphingomonas paucimobilis and similar organisms.
2. State the initial clues that alert the CL to the presence of this group of organisms for clinical laboratorians.
3. Select identification approaches for this group of organisms.
4. Identify susceptibility testing methods appropriate for this group of organisms.
Epidemiology, Spectrum of Disease, and Antimicrobial Therapy
As demonstrated in Table 27-1, these organisms are rarely or only occasionally isolated from human materials and have limited roles as agents of infection. Because they are infrequently encountered in the clinical setting, little information is available on their epidemiology, ability to cause human infections, and potential for antimicrobial resistance. For example, even though O-1 and O-2 organisms have been submitted to the Centers for Disease Control and Prevention (CDC) after being isolated from clinical materials such as blood, cerebrospinal fluid (CSF), wounds, and pleural fluid, their natural habitat is unknown. The genus Sphingobacterium is ubiquitous in nature, and Sphingomonas spp. are known for their waterborne nature. Some of these groups are present in hospital settings, such as hospital water supplies. When the organisms discussed in this chapter are encountered in clinical specimens, their clinical significance and potential as contaminants should be considered; human infections have been documented, so care must be taken to determine whether these organisms are infectious agents or contaminants.
TABLE 27-1
Epidemiology, Spectrum of Disease, and Antimicrobial Therapy
| Organism | Epidemiology | Disease Spectrum | Antimicrobial Therapy |
| Acidovorax facilis | A. facilis is found in soil and has been used as a soil additive to improve plant growth in areas of agriculture and horticulture. | Commonly found in soil. Rarely found in clinical material and not substantiated as a cause of human infections. | No guidelines; little is known about antimicrobial resistance potential. Disk diffusion testing cannot be performed. |
| CDC group IIc CDC group IIe CDC group IIh CDC group IIi |
CDC groups IIc, IIe, IIh, and IIi are found in soil, plants, foodstuffs, and water, including moist areas in hospitals. Not part of human flora. | Rarely found in clinical material and rarely substantiated as a cause of human infections; have been isolated from blood, eyes, and wounds. | No guidelines; little is known about antimicrobial resistance potential |
| CDC group O-1 CDC group O-2 CDC group O-3 |
Epidemiology is unknown. | Rarely found in clinical material and rarely implicated as a cause of human infections. CDC group O-3 has been isolated from bone, blood, lung, and lymph node tissue. | No guidelines; one report indicates susceptibility of CDC group O-3 to aminoglycosides, imipenem, trimethoprim-sulfamethoxazole, and chloramphenicol (however, the breakpoints used were based on those for the Enterobacteriaceae family). |
| Sphingobacterium mizutaii S. multivorum S. spiritivorum |
Sphingobacteria are ubiquitous in nature. | Rarely involved in human infections. S. mizutaii has been associated with blood, cerebrospinal fluid, and wound infections; S. multivorum with blood and wound infections; and S. spiritivorum with blood and urine infections. | Literature references report the following susceptibilities: S. mizutaii—erythromycin, trimethoprim-sulfamethoxazole, and pefloxacin. S. multivorum—amikacin, gentamicin, aztreonam, cefepime, cefotaxime, ceftazidime, meropenem, piperacillin, piperacillin/tazobactam, and chloramphenicol. S. spiritivorum—amikacin, gentamicin, aztreonam, cefepime, cefotaxime, chloramphenicol. |
| Sphingomonas paucimobilis S. parapaucimobilis |
S. paucimobilis inhabits environmental niches and is known especially as a waterborne organism that can exist in hospital water systems. Not part of human flora. Mode of transmission is uncertain but probably involves patient exposure to contaminated medical devices or solutions. | S. paucimobilis virulence factors are unknown. It has been implicated in community- and hospital-acquired infections, specifically in blood and urine infections. | No definitive guidelines; potentially active agents include trimethoprim-sulfamethoxazole, chloramphenicol, ciprofloxacin, and aminoglycosides; resistance to beta-lactams is known, but validated susceptibility testing methods do not exist. |
Laboratory Diagnosis
Specimen Collection and Transport
No special considerations are required for specimen collection and transport of the organisms discussed in this chapter. Refer to Table 5-1 for general information on specimen collection and transport.
Cultivation
Media of Choice
Colonial Appearance
Table 27-2 describes the colonial appearance and distinguishing characteristics (e.g., pigment) of each organism on 5% sheep blood agar. When these organisms do grow on MacConkey agar, they appear as lactose nonfermenters.
TABLE 27-2
Colonial Appearance and Characteristics
| Organism | Medium | Appearance |
| Acidovorax facilis | BA | No distinctive appearance |
| CDC group IIc | BA | No distinctive appearance but colonies sticky |
| CDC group IIe | BA | No distinctive appearance |
| CDC group IIh | BA | No distinctive appearance |
| CDC group IIi | BA | No distinctive appearance |
| CDC group O-1, O-2, O-3 | BA | Yellow pigment present in O-1 and O-2 but not in O-3 |
| Sphingobacterium spp. | BA | Yellow pigment present in S. mizutaii |
| Sphingomonas paucimobilis S. parapaucimobilis |
BA | Small, circular, smooth, convex; bright yellow growth pigment |
BA, 5% sheep blood agar.
Approach to Identification
The ability of many commercial identification systems to identify accurately the organisms discussed in this chapter may be limited or uncertain. Tables 27-3 through 27-6 show some biochemical tests that are helpful for presumptive differentiation among the various organisms in this group.
TABLE 27-3
Key Biochemical and Physiologic Characteristics
| Organism | Insoluble Pigment | Glucose Oxidized | Xylose Oxidized | Sucrose Oxidized | Esculin Hydrolysis | Motility |
| Acidovorax facilis | − | + | (+) | − | − | + |
| CDC group IIc | Tan or buff | + | − | + | + | nm |
| CDC group IIe | − | + | − | − | − | nm |
| CDC group IIh | − | + | − | − | + | nm |
| CDC group IIi | Yellow | + | + | + | + | nm |
| CDC group O-2 | Yellow to orange | v | − | + | v | v* |
| Sphingobacterium mizutaii | v† | + | (+) | + | + | nm |
| Sphingomonas spp.‡ | Yellow | + | + | + | + | +§ |
nm, Nonmotile; v, variable; +, >90% strains positive; −, >90% strains negative; (+), delayed.
*Only 20% are motile; motility is only apparent upon wet mount or flagellar staining.
