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CHAPTER 21: Acinetobacter , Stenotrophomonas ,and Similar Organisms

  all oxidase-negative and grow on MacConkey agarexcept for CDC group NO-1 

  either oxidize or do not utilize glucose   Although NO-1 is oxidase-negative and does not

usually grow on MacConkey agar, it is included herebecause it must be distinguished from theasaccharolytic Acinetobacter spp. 

EPIDEMIOLOGY

  inhabit environmental niches   Acinetobacter spp. and S. maltophilia being

widely distributed in nature and hospital

environments.  relatively high prevalence of Acinetobacter spp.

and S. maltophilia in hospitals frequently resultsin colonization of the skin and respiratory

tract of patients 

PATHOGENESIS AND SPECTRUM OF DISEASE

(**all organisms that will be discussed are opportunisticpathogens for which no definitive virulence factors areknown.)

Acinetobacter spp. and S. maltophi l ia : relatively commoncolonizers of hospitalized patients

  clinical significance when found in patient specimenscan be difficult to establish

  organisms are more frequently isolated as colonizersthan as infecting agents**infection does occur, it usually involves debilitatedpatients, such as those in burn or intensive care units,

who have undergone medical instrumentation and/orhave received multiple antimicrobial agents.  Infections caused by Acinetobacter spp. and S.

maltophilia usually involve the respiratory orgenitourinary tract, bacteremia, and, occasionally,wound infections, but infections involving severalother body sites have been described   Community-acquired infections with theseorganisms can occur, but the vast majority ofinfections are nosocomial.

LABORATORY DIAGNOSIS

SPECIMEN COLLECTION AND TRANSPORT(**No special considerations are required for

specimen collection and transport of the organismsdiscussed in this chapter)

DIRECT DETECTION METHODS

(**no specific procedures for the direct detection of theseorganisms in clinical material.)

   Acinetobacter spp. are plump coccobacilli thattend to resist alcohol decolorization; they may bemistaken for Neisseria spp.  Bordetella spp. are coccobacilli or short rods

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  S. maltophilia, P. oryzihabitans, and P. luteolaareshort to medium size straight rods.

  CDC group NO-1 are coccoid to medium-size bacilli.

CULTIVATIONMedia of Choice

  Also grow in 5% sheep blood and chocolate agars.   also grow well in the broth of blood culture systems 

and in common nutrient broths such asthioglycollate 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 orambient air for a minimum of 24 hours.

  MacConkey agar  should be incubated only inambient air .

COLONIAL APPEARANCE

APPROACH TO IDENTIFICATION

Acinetobacter spp. and S. maltop hi l ia- reliably identifiedby the API 20E system (bioMérieux Inc., St. Louis, Mo)

**most reliably identified using conventional biochemical andphysiologic characteristics

Comments Regarding Specific Organisms   There are 25 geno species or genomo species in the

genus Acinetobacter  Each genospecies comprises a distinct DNA

hybridization group and is given a numericdesignation, which has replaced previous speciesnames.

genus is also divided into two groups:  contains the saccharolytic (glucose-oxidizing) species

  contains the asaccharolytic (non –glucose-utilizing)species

  Most glucose-oxidizing, nonhemolyticstrains werepreviously identified as A.baumanii  

  Most non –glucose-utilizing, nonhemolyticstrains were designated as A. lwoffi. 

  The majority of beta-hemolytic organisms werepreviously called A. haemolyticus 

  Nitrate-reducing strains of asaccharolytic Acinetobacter spp. are difficult to differentiate from

CDC group NO-1 **Acinetobacter transformationtest provides the most dependable criterion for thispurpose, but this test is not commonly performed inclinical microbiology laboratories.

  S. maltophi l ia  - can produce biochemical profiles similar to those ofBurkholderia cepacia, but a negative oxidase testmost often rules out the latter- oxidizes maltose faster than glucose (hence thespecies name, maltophilia, ( “maltose loving”) - produces a brown pigment on heart infusion agar  that contains tyrosine.

ANTIMICROBIAL SUSCEPTIBILITY TESTING ANDTHERAPY:Acinetobacter spp. and S. malto phi l ia- exhibitresistance to a wide array of antimicrobial agents,making the selection of agents for optimal therapydifficultS. maltop hi l ia- primary drug of choice:trimethoprim-sulfamethoxazole

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PREVENTION:

**organisms are ubiquitous in nature- there are norecommended vaccination or prophylaxis protocols.

  Hospital-acquired infections are best controlled byfollowing appropriate sterile techniques andinfection control guidelines and by implementingeffective protocols for the sterilization anddecontamination of medical supplies.