AcinetobacterAcinetobacterShyam Kumar MishraShyam Kumar Mishra

Assistant Professor,Assistant Professor,

Institute of Medicine,Institute of Medicine,

Tribhuvan UniversityTribhuvan University

NepalNepal

• Family- MoraxellaceaeFamily- Moraxellaceae

• Genus- AcinetobacterGenus- Acinetobacter

Historical PerspectiveHistorical Perspective

• Beijerinck (1911) – Beijerinck (1911) – Micrococcus Micrococcus calcoaceticuscalcoaceticus (soil)………..( (soil)………..(Herella Herella vaginicola, Mima polymorphavaginicola, Mima polymorpha)……….)……….

• Original definition (1954) – nonmotile, gram-Original definition (1954) – nonmotile, gram-negative, oxidase- positive and oxidase-negative, oxidase- positive and oxidase-negative saprophytes without pigmentationnegative saprophytes without pigmentation

• 1971 – Oxidase negative only1971 – Oxidase negative only

EtymologyEtymologyGr. Gr. aa, not; , not; Gr. Gr. kineôkineô, to set in motion, move; , to set in motion, move; acinetusacinetus, unable to move; , unable to move; bacterbacter, a rod; , a rod; Acinetobacter, nonmotile rod., nonmotile rod.

baumannii, of Baumann (named in honor of Paul and , of Baumann (named in honor of Paul and Linda Baumann)Linda Baumann)

L. L. calxcalx - -ciscis, limestone, chalk; , limestone, chalk; L. L. acidumacidum aceticumaceticum, acetic acid; , acetic acid; calcoaceticus, pertaining to calcium acetate, which , pertaining to calcium acetate, which was used by Beijerinck in the enrichment medium was used by Beijerinck in the enrichment medium from which he isolated the organism. from which he isolated the organism.

Genus definitionGenus definition

• Short, stout gram-negative coccobacilliShort, stout gram-negative coccobacilli• Strictly aerobicStrictly aerobic• non-motilenon-motile• Catalase-positive, oxidase-negativeCatalase-positive, oxidase-negative• Frequently capsulateFrequently capsulate• Nitrates are reduced only rarelyNitrates are reduced only rarely• Saprophytes; parasites and occasional pathogens of Saprophytes; parasites and occasional pathogens of

man and other animalsman and other animals• Good growth on nutrient media at 20-30Good growth on nutrient media at 20-3000CC• G+C content 39-47 mol%G+C content 39-47 mol%

HabitatsHabitats

• Ubiquitous, free-living saprophytes Ubiquitous, free-living saprophytes found in soil, water, foods and the found in soil, water, foods and the clinical environmentclinical environment

• Dry or moist inanimate surfaces and as Dry or moist inanimate surfaces and as commensals on the skin of man and commensals on the skin of man and animalsanimals

MorphologyMorphology

• Short, plump, gram-negative bacilliShort, plump, gram-negative bacilli

• 1.0-1.5 1.0-1.5 m x 1.5-2.5 m x 1.5-2.5 m (log phase)m (log phase)

• 0.6-0.8 0.6-0.8 m x 1- 1.5 m x 1- 1.5 m (coccoid in stationary phase)m (coccoid in stationary phase)

• May retain crystal violet (Gram’s stain)May retain crystal violet (Gram’s stain)

• No flagella; however, may show twitching motilityNo flagella; however, may show twitching motility

• FimbriateFimbriate

• Most strains are capsulateMost strains are capsulate

Cultural characteristicsCultural characteristics• Most clinical isolates (37Most clinical isolates (3700C) and many environmental isolates at C) and many environmental isolates at

lower temp.lower temp.

• Grow well on ordinary solid mediaGrow well on ordinary solid media

• Nutrient agar – Smooth, mucoid, greyish white colonies, 2-3 mm in Nutrient agar – Smooth, mucoid, greyish white colonies, 2-3 mm in diameterdiameter

• MacConkey agar – Non-lactose fermentingMacConkey agar – Non-lactose fermenting

• Blood agar– usu. Non-hemolyticBlood agar– usu. Non-hemolytic

• May show surface spreading associated with twitching motilityMay show surface spreading associated with twitching motility

• Nutrient broth – uniform turbidity Nutrient broth – uniform turbidity

ClassificationClassification

• Previously……….A. calcoaceticusPreviously……….A. calcoaceticus• var var anitratusanitratus• var var lwoffiilwoffii

• At least 33 Genomic species of which few have been given At least 33 Genomic species of which few have been given formal species name, e.g.,formal species name, e.g.,

• A. calcoaceticus• A. baumanniiA. baumannii• A. pittiiA. pittii• A. nosocomialisA. nosocomialis• A. haemolyticusA. haemolyticus• A. juniiA. junii• A. johnsoniiA. johnsonii• A. lwoffii• A. radioresistensA. radioresistens

•Acinetobacter Acinetobacter calcoaceticus calcoaceticus baumanniibaumannii complexcomplex

PathogenicityPathogenicity

• Polysaccharide capsulePolysaccharide capsule

• Adhesion to human epithelial cells Adhesion to human epithelial cells (fimbriae, capsule)(fimbriae, capsule)

• LipasesLipases

• LipopolysaccharideLipopolysaccharide

• SiderophoresSiderophores

Risk factorsRisk factors

• Hospitilization Hospitilization • Significant co-morbidity Significant co-morbidity • Mechanical ventilation Mechanical ventilation • Cardiorespiratory failure Cardiorespiratory failure • Previous infection Previous infection • Antimicrobial therapy Antimicrobial therapy • CVP lines CVP lines • Urinary catheters Urinary catheters

Factors leading to the emergence and transmission of multidrug-resistant (MDR) Acinetobacter species.

Eliopoulos G M et al. Clin Infect Dis. 2008;46:1254-1263

© 2008 by the Infectious Diseases Society of America

Factors leading to the emergence and transmission of multidrug-resistant (MDR) Acinetobacter species.

• Acb Acb complex has been associated with complex has been associated with various nosocomial infections including:various nosocomial infections including:• pneumonia (esp. ventilator-associated) (esp. ventilator-associated)• septicaemia (true (true AcinetobacterAcinetobacter bacteremia bacteremia

should be distinguished from pseudobacteremia). should be distinguished from pseudobacteremia). • meningitis (esp. post trauma or surgery) (esp. post trauma or surgery) • wound infections (in association with an indwelling (in association with an indwelling

venous catheter) venous catheter) • UTIs

IraqibacterIraqibacter

Antibiotic resistanceAntibiotic resistance

• Most strains are resistant to ampicillin, first-Most strains are resistant to ampicillin, first-generation cephalosporins, chloramphenicolgeneration cephalosporins, chloramphenicol

• Resistance mechanisms that are expressed frequently in nosocomial strains include • β-lactamases, • alterations in cell-wall channels (porins), • efflux pumps

• A. baumannii can become resistant to quinolones through mutations in the genes gyrA and parC

• Resistant to aminoglycosides by expressing aminoglycoside-modifying enzymes.

• “Resistance island” containing 45 resistance genes within the acinetobacter genome

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Laboratory isolation and Laboratory isolation and identificationidentification

• Selective mediaSelective media• Herellea agarHerellea agar• Leeds acinetobacter mediumLeeds acinetobacter medium

• Unique browning effect on blood agar in Unique browning effect on blood agar in presence of D-Glucose by glucose presence of D-Glucose by glucose oxidising strainsoxidising strains

• TSI – Alk/No changeTSI – Alk/No change

• SIM – HSIM – H22S Negative, Indole Negative, S Negative, Indole Negative,

Motility- Non-motileMotility- Non-motile

• Simmon’s Citrate – Citrate UtilizedSimmon’s Citrate – Citrate Utilized

• Carbohydrate breakdown - OxidativeCarbohydrate breakdown - Oxidative

Typing methodsTyping methods

• BiotypingBiotyping

• Phage-typingPhage-typing

• SerotypingSerotyping

• Bacteriocin typingBacteriocin typing

• Molecular fingerprintingMolecular fingerprinting

• Plasmid profilingPlasmid profiling

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