Laboratory Diagnosis of Acinetobacter, Stenotrophomonas, and Similar Organisms
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p330-332
2025-07-20
544
Specimen Collection and Transport
No special considerations are required for specimen collection and transport of the organisms discussed in this chapter.
Specimen Processing
No special considerations are required for processing of the organisms discussed in this chapter.
Direct Detection Methods
Other than Gram stain of patient specimens, there are no specific procedures for the direct detection of these organisms in clinical material. Acinetobacter spp. are plump coccobacilli that tend to resist alcohol decolorization; they may be mistaken for Neisseria spp. The Bordetella spp. are coccobacilli or short rods. S. maltophilia, P. oryzihabitans, and P. luteola are short to medium-size straight rods. CDC group NO-1 are coccoid to medium-size bacilli.
Cultivation
Media of Choice
In addition to their ability to grow on MacConkey agar, all of the genera described in this chapter, except CDC group NO-1, grow well on 5% sheep blood and chocolate agars. These organisms also grow well in the broth of blood culture systems and in common nutrient broths, such as thioglycollate and brain-heart infusion. Incubation Conditions and Duration These organisms generally produce detectable growth on 5% sheep blood and chocolate agars when incubated at 35°C in carbon dioxide or ambient air for a minimum of 24 hours. MacConkey agar should be incubated only in ambient air.
Colonial Appearance
Table 1 describes the colonial appearance and other distinguishing characteristics (e.g., hemolysis and odor) of each genus when grown on 5% sheep blood and Mac Conkey agars.
Table1. Colonial Appearance and Characteristics
Approach to Identification
Acinetobacter spp. and S. maltophilia are reliably identified by the API 20E system (bioMérieux, St. Louis, Missouri), although other commercial systems may not perform as well. Automated identification systems typically identify the organisms in this chapter to the genus level. Additional testing may be required to speciate the organisms using conventional biochemical and physiologic characteristics, such as those outlined in Table 2.
Table2. Key Biochemical and Physiologic Characteristics
Molecular methods are invaluable for the speciation of Acinetobacter spp. Sequence-based methods, including amplification of the ribosomal RNA (rRNA) sequence, genomic fingerprinting, and restriction endonuclease analysis, have been used to identify Acinetobacter spp.
Comments Regarding Specific Organisms
The genus Acinetobacter has 21 genospecies or genomospecies. Each genospecies comprises a distinct DNA hybridization group and is given a numeric designation, which has replaced previous species names. Acinetobacter species are oxidase negative, catalase positive and nonmotile. The genus also is divided into two groups: the saccharolytic (glucose oxidizing) species and the asaccharolytic (non–glucose utilizing) species.
Most glucose-oxidizing, nonhemolytic strains were previously identified as Acinetobacter baumannii, and most non–glucose utilizing, nonhemolytic strains were designated as Acinetobacter lwoffi. The majority of beta hemolytic organisms previously were called Acinetobacter haemolyticus. Nitrate-reducing strains of asaccharolytic Acinetobacter spp. are difficult to differentiate from CDC group NO-1. The Acinetobacter transformation test provides the most dependable criterion for this purpose, but this test is not commonly performed in clinical microbiology laboratories.
S. maltophilia is an oxidase-negative, nonfermentative, gram-negative bacillus that can produce biochemical profiles similar to those of Burkholderia cepacia. A negative oxidase test result most often rules out the latter. S. maltophilia also oxidizes maltose faster than glucose (hence the species name, maltophilia, or “maltose loving”), and it produces a brown pigment on heart infusion agar that contains tyrosine.
Pseudomonas spp. (Chrysemonas and Flavimonas spp.) are gram-negative, nonfermentative, oxidase-negative, catalase-positive bacilli. The organisms characteristically produce rough colonies that are often yellow pigmented on sheep blood agar.
SERODIAGNOSIS
Serodiagnostic techniques are not generally used for the laboratory diagnosis of infections caused by the organ isms discussed in this chapter.
Fig1. Colony of Acinetobacter spp. on MacConkey agar. Note purple color.
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