Acidovorax facilis.

A. facilis is a straight to slightly curved, gram-negative rod that occurs singly or in short chains. It is aerobic and has a single polar flagellum, which makes it motile. On nutrient agar, it forms unpigmented colonies, and 30°C is its optimum temperature. A. facilis is oxidase positive and urease variable (some grow on Christensen urea agar but lack urease activity). Key characteristics are shown in Table 27-3. A. facilis is commonly found in soil, and no evidence of pathogenicity in healthy humans has been identified. A role for A. facilis as an opportunistic pathogen has not been proven or rejected.

CDC groups IIc, IIe, IIh, IIi, O-1, O-2, and O-3.

CDC groups IIc, IIe, IIh, IIi, O-1, and O-2 are short, straight rods that may appear as “II-forms” (i.e., bacteria with thickened ends and thin centers). The phenotypic characteristics of CDC group IIc are most similar to those of CDC groups IIe and IIh, the major difference being that CDC group IIc produces acid from sucrose, hydrolyzes esculin, and usually reduces nitrate. Strains of CDC groups IIe and IIh are similar to Empedobacter brevis (see Chapter 26) in that they oxidize glucose and maltose and produce indole. CDC group IIi resembles S. multivorum but produces indole. S. parapaucimobilis resembles CDC group O-1 in that both are motile, esculin positive, and positive for hydrogen sulfide (H₂S) in lead acetate; however, S. parapaucimobilis oxidizes more carbohydrates (CDC O-1 is weakly positive in OF glucose and negative in OF xylose, maltose, and mannitol).

CDC groups O-1 and O-2 are similar in that they are motile, oxidase-positive, esculin-positive, gram-negative rods that grow with yellow pigment and do not grow on MacConkey agar. CDC groups O-1 and O-2 have been isolated from clinical sources; antimicrobial susceptibility testing on these organisms has not been reported. CDC group O-2 does not oxidize xylose, mannitol, or lactose; this can help distinguish it from the other yellow-pigmented organisms growing on blood agar discussed in this chapter.

CDC O-3 bacteria, which are predominantly curved rods, do not produce yellow pigment. They are motile by a single polar flagellum. They grow well on a Campylobacter-selective medium and may be misidentified as a Campylobacter sp. CDC group O-3 are aerobic, glucose-oxidizing organisms that utilize xylose, sucrose, and maltose. They do not grow on MacConkey agar. They are oxidase positive, hydrolyze esculin, and are negative for urease, indole, nitrate, and gelatin. Key characteristics of the CDC groups are shown in Tables 27-3 and 27-4. CDC O-3 has been reported as susceptible to aminoglycosides, imipenem, chloramphenicol, and trimethoprim-sulfamethoxazole and resistant to beta-lactam antimicrobials.

Sphingobacterium mizutaii.

S. mizutaii exhibits II-forms. It can produce a yellow pigment, and it does not grow on MacConkey agar. Although aflagellate and therefore frequently classified as nonmotile, it can be motile by gliding movement. It is able to grow in the presence of 40% bile; it also is oxidase positive, catalase positive, esculin positive, indole negative, and urease negative (although a report exists that 20% are positive for Christensen urease). Key characteristics are shown in Tables 27-3 and 27-5. Reported infections in humans have included septicemia (blood culture), meningitis (CSF specimen), and cellulitis (wound source). This bacterium has been reported to be susceptible to erythromycin, trimethoprim-sulfamethoxazole, and pefloxacin.

Sphingobacterium multivorum.

S. multivorum is yellow pigmented, oxidase positive, and esculin positive. It is OF glucose positive; it does not produce acid from mannitol, ethanol, or rhamnose; and it is Christensen urease positive. This bacterium grows on blood agar plate (BAP), Mueller-Hinton agar, Burkholderia cepacia–selective agar (BCSA), and MacConkey agar. Key characteristics are shown in Table 27-5. These organisms are ubiquitous in nature and rarely associated with serious infection; however, cases of septicemia and peritonitis have been reported. This bacterium is nonmotile and resistant to polymyxin B, characteristics that distinguish it from S. paucimobilis. Susceptibility to amikacin, gentamicin, aztreonam, cefepime, cefotaxime, ceftazidime, meropenem, piperacillin, and chloramphenicol has been reported in a small study of eight isolates.

Sphingobacterium spiritivorum.

S. spiritivorum is yellow pigmented and positive for oxidase and esculin. It does not grow on MacConkey agar but does grow on BAP, Mueller-Hinton agar, and BCSA. It produces acid in OF glucose and in mannitol, ethanol, and rhamnose. Like S. multivorum, this bacterium is ubiquitous in nature but rarely pathogenic for humans. It can be distinguished from S. paucimobilis by the fact that it is nonmotile and resistant to polymyxin B. Key characteristics are shown in Table 27-5. S. spiritivorum has been isolated environmentally from hospitals, most commonly from blood and urine. Susceptibility testing by Kirby-Bauer (KB) disk diffusion on 13 isolates showed susceptibility to amikacin, gentamicin, aztreonam, cefepime, cefotaxime, and chloramphenicol.

Sphingomonas paucimobilis.

S. paucimobilis is a medium-size, straight, gram-negative rod with a single polar flagellum; growth requires at least 48 hours’ incubation on sheep blood agar (Figure 27-1). Optimal growth occurs at 30°C in 5% CO₂ or ambient air; it does grow at 37°C but not at 42°C. It grows as a deep yellow colony on tryptic soy and blood agars. It is obligately aerobic, grows in broth (e.g., brain-heart infusion, thioglycollate, blood culture media), and does not grow on MacConkey agar (90% do not grow; 10% grow as lactose nonfermenters). S. paucimobilis oxidatively utilizes glucose, xylose, and sucrose. Biochemical test results of interest include the following: esculin hydrolysis positive; motile by wet mount or in motility medium when incubated at 18° to 22°C (nonmotile when incubated at 37°C); oxidase positive (90% to 94% positive); catalase positive; urease negative; and indole negative. S. paucimobilis is susceptible to polymyxin B, a trait that distinguishes it from Sphingobacterium spp. Key characteristics are shown in Table 27-6.

Antimicrobial susceptibility testing indicates that S. paucimobilis is susceptible to tetracycline, chloramphenicol, trimethoprim-sulfamethoxazole, and aminoglycosides. Susceptibility to vancomycin has been noted when the organism is grown on sheep blood agar with a vancomycin disk (30 µg). S. paucimobilis is ubiquitous in soil and water and has been isolated environmentally from swimming pools, hospital equipment, and water and laboratory supplies. It has been associated with human infections and found in a variety of clinical specimens, specifically, peritonitis associated with wound infections (chronic ambulatory peritoneal dialysis, leg ulcer, empyema, splenic abscess, brain abscess), blood cultures, and CSF, urine, vaginal, and cervical samples. Recent literature indicates that S. paucimobilis is usually regarded as having minor clinical significance; however, community-acquired infection, diabetes mellitus, and alcoholism have been identified as significant risk factors for primary bacteremia. A retrospective study suggests that the prevalence of S. paucimobilis infection in humans seems to have increased in recent times, and although it has low virulence, infection can lead to septic shock, particularly in immunocompromised patients. Another report indicates that although this bacterium has low mortality associated with infection, it frequently causes complications in hospitalized patients.

Sphingomonas parapaucimobilis.

S. parapaucimobilis is similar to S. paucimobilis in many ways. It is a medium-size, straight, gram-negative rod that grows with a deep yellow pigment. It is obligately aerobic, motile, and does not grow on MacConkey agar. S. parapaucimobilis can be distinguished from S. paucimobilis by several characteristics. S. parapaucimobilis is H₂S positive, as indicated by blackening of lead acetate paper suspended over Kligler iron agar (KIA); it is Simmons citrate positive (S. paucimobilis is negative); and it is negative for extracellular DNAse (S. paucimobilis is positive). Like S. paucimobilis, S. parapaucimobilis is acid in OF glucose, OF xylose, and OF maltose but negative in OF mannitol. It has been distinguished from Sphingobacterium spp. by its susceptibility to polymyxin B; however, S. parapaucimobilis is sometimes variable to polymyxin B. Key characteristics are shown in Table 27-6. Antimicrobial susceptibility testing indicates that S. parapaucimobilis displays variable resistance but is usually susceptible to tetracycline, chloramphenicol, sulfamethoxazole, aminoglycosides, third-generation cephalosporins, and fluoroquinolone. S. parapaucimobilis has been associated with human infections; specifically, it has been isolated from sputum, urine, and the vagina.