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Questions and Answers
What is a defining characteristic of non-fermenting gram-negative rods (GNR)?
What is a defining characteristic of non-fermenting gram-negative rods (GNR)?
Which biochemical test is NOT commonly used for identifying non-fermenting gram-negative rods?
Which biochemical test is NOT commonly used for identifying non-fermenting gram-negative rods?
What type of environment do non-fermenting GNR prefer?
What type of environment do non-fermenting GNR prefer?
What unique metabolic characteristic do non-fermenting gram-negative rods exhibit?
What unique metabolic characteristic do non-fermenting gram-negative rods exhibit?
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Which of the following is a common characteristic of Pseudomonas species?
Which of the following is a common characteristic of Pseudomonas species?
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What type of growth pattern is expected for non-fermenting gram-negative rods on MacConkey agar?
What type of growth pattern is expected for non-fermenting gram-negative rods on MacConkey agar?
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What does an alkaline slant and no change in the deep butt reaction of TSI and KIA indicate?
What does an alkaline slant and no change in the deep butt reaction of TSI and KIA indicate?
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Which of the following statements about Pseudomonas aeruginosa is false?
Which of the following statements about Pseudomonas aeruginosa is false?
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What characteristic feature of Pseudomonas aeruginosa colonies is often associated with a sweet, fruity odor?
What characteristic feature of Pseudomonas aeruginosa colonies is often associated with a sweet, fruity odor?
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What is the typical coloration of Pseudomonas aeruginosa under UV light due to its pigmentation?
What is the typical coloration of Pseudomonas aeruginosa under UV light due to its pigmentation?
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Which of the following pathways can Pseudomonas aeruginosa use for respiration when oxygen is absent?
Which of the following pathways can Pseudomonas aeruginosa use for respiration when oxygen is absent?
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Which enzyme produced by Pseudomonas aeruginosa helps in breaking down host physical barriers during infection?
Which enzyme produced by Pseudomonas aeruginosa helps in breaking down host physical barriers during infection?
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What distinguishes the mucoid colonies of Pseudomonas aeruginosa from its other colony types?
What distinguishes the mucoid colonies of Pseudomonas aeruginosa from its other colony types?
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Which of the following is a common biochemical characteristic of Pseudomonas aeruginosa?
Which of the following is a common biochemical characteristic of Pseudomonas aeruginosa?
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What factor contributes to the opportunistic pathogenicity of Pseudomonas aeruginosa in hospital settings?
What factor contributes to the opportunistic pathogenicity of Pseudomonas aeruginosa in hospital settings?
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During an infection, which stage involves the local invasion by Pseudomonas aeruginosa following colonization?
During an infection, which stage involves the local invasion by Pseudomonas aeruginosa following colonization?
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What type of consistency do larger, smoother colonies of Pseudomonas aeruginosa typically exhibit?
What type of consistency do larger, smoother colonies of Pseudomonas aeruginosa typically exhibit?
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What role do the pigments pyocyanin and pyoverdin play in identifying Pseudomonas aeruginosa?
What role do the pigments pyocyanin and pyoverdin play in identifying Pseudomonas aeruginosa?
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What is the primary reason for the presence of S. maltophilia in urine?
What is the primary reason for the presence of S. maltophilia in urine?
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Which antibiotic combination is usually required for treating S. maltophilia infections?
Which antibiotic combination is usually required for treating S. maltophilia infections?
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What characteristic differentiates B. cepacia from S. maltophilia?
What characteristic differentiates B. cepacia from S. maltophilia?
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Which media is specifically mentioned for selecting and differentiating the Burkholderia cepacia complex?
Which media is specifically mentioned for selecting and differentiating the Burkholderia cepacia complex?
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What is the most significant environmental habitat for Burkholderia cepacia?
What is the most significant environmental habitat for Burkholderia cepacia?
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What type of hemolysis is associated with the colonies of Burkholderia cepacia on sheep's blood agar?
What type of hemolysis is associated with the colonies of Burkholderia cepacia on sheep's blood agar?
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What method is recommended for susceptibility testing for S. maltophilia?
What method is recommended for susceptibility testing for S. maltophilia?
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Which characteristic is unique to Pseudomonas stutzeri compared to Acinetobacter species?
Which characteristic is unique to Pseudomonas stutzeri compared to Acinetobacter species?
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What is the primary method of classification for Acinetobacter species?
What is the primary method of classification for Acinetobacter species?
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Which of the following statements about Acinetobacter baumannii is false?
Which of the following statements about Acinetobacter baumannii is false?
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Which antibiotic is not typically used to treat Pseudomonas stutzeri infections?
Which antibiotic is not typically used to treat Pseudomonas stutzeri infections?
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Which of the following features does Pseudomonas putida exhibit?
Which of the following features does Pseudomonas putida exhibit?
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What color do colonies of Pseudomonas stutzeri exhibit when grown on blood agar plates?
What color do colonies of Pseudomonas stutzeri exhibit when grown on blood agar plates?
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Which statement about Acinetobacter's ecological distribution is true?
Which statement about Acinetobacter's ecological distribution is true?
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What is the optimum growth temperature for Pseudomonas putida?
What is the optimum growth temperature for Pseudomonas putida?
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Which organism is identified as a rare opportunistic pathogen that acts as a soil denitrifier?
Which organism is identified as a rare opportunistic pathogen that acts as a soil denitrifier?
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What is a primary method through which Acinetobacter baumannii is acquired during hospital stays?
What is a primary method through which Acinetobacter baumannii is acquired during hospital stays?
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What is a key characteristic of A.baumanii that contributes to its virulence?
What is a key characteristic of A.baumanii that contributes to its virulence?
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In which environment is A.baumanii most commonly found?
In which environment is A.baumanii most commonly found?
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Which of the following treatments is typically effective against most strains of A.baumanii?
Which of the following treatments is typically effective against most strains of A.baumanii?
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What is a significant feature of Stenotrophomonas maltophilia in clinical settings?
What is a significant feature of Stenotrophomonas maltophilia in clinical settings?
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Which feature is associated with the clinical significance of Stenotrophomonas maltophilia?
Which feature is associated with the clinical significance of Stenotrophomonas maltophilia?
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What is true regarding the transmission of A.baumanii?
What is true regarding the transmission of A.baumanii?
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Which characteristic is NOT associated with A.baumanii's antibiotic resistance?
Which characteristic is NOT associated with A.baumanii's antibiotic resistance?
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What helps Stenotrophomonas maltophilia exhibit a brownish discoloration on McConkey agar?
What helps Stenotrophomonas maltophilia exhibit a brownish discoloration on McConkey agar?
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Which of the following is NOT a common characteristic of A.baumanii?
Which of the following is NOT a common characteristic of A.baumanii?
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What does the TSI result of K/NC indicate for A.baumanii?
What does the TSI result of K/NC indicate for A.baumanii?
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Study Notes
Non-Fermenting GNR
- Prefer wet environments like sinks, respiratory equipment, and vases.
- Usually not part of healthy human microbiota.
- Considered opportunistic pathogens, colonizing and infecting immunocompromised individuals.
- Often found in hospitalized patients, potentially becoming nosocomial pathogens.
- Aerobic, gram-negative rods.
- Do not use carbohydrates as an energy source, primarily through non-fermentation metabolic pathways.
- Most are obligate aerobes, growing poorly in anaerobic conditions.
- Oxidizers and non-fermenters.
- Asaccharolytic; do not degrade carbohydrates.
- Typically show abundant growth on sheep BAP and CAP within 24-48 hours.
Clues for Isolating a Non-Fermenter (NF)
- The organism does not ferment carbohydrates.
- Shows an alkaline slant/no change on deep butt reaction in TSI and KIA.
- Requires oxygen for carbohydrate metabolism if carbohydrates are utilized.
- Fails to ferment carbohydrates.
Pseudomonas aeruginosa
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Gram-negative rod that may be encapsulated.
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Motile via a single polar flagellum.
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Non-spore forming.
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Often associated with a "polysaccharide capsule".
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Aerobic; requires oxygen for metabolism.
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Oxidase and catalase positive.
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Simple nutritional requirements; non-fastidious.
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Optimum growth temperature is 37°C, able to grow at 42°C.
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Resistant to salts, dyes, weak antiseptics, and many antibiotics.
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Common inhabitant of soil, water, and the gastrointestinal tract. Includes species like P. fluorescens, P. putida, and P. stutzeri.
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Can grow in the absence of oxygen if nitrate is available as a respiratory electron acceptor.
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Rarely part of human microbiota.
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Often a beta-hemolytic opportunistic pathogen, with rough spreading, ground glass colonies. The colonies have serrated or jagged edges.
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May display metallic sheen and blue-green, red, or brown pigmentation.
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Often associated with a sweet fruity odor (similar to grapes or tacos).
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Mucoid colony consistency is attributed to alginate slime production; pigments (pyoverdin/fluorescein – yellow under UV light, pyocyanin – blue pigment).
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Grows well on most lab media; oxidizes glucose, fructose, and xylose but not lactose or sucrose.
Pseudomonas aeruginosa ID
- Grows at 42°C.
- Deaminates acetamide.
- Reduces nitrate.
- Decarboxylates arginine.
Pseudomonas aeruginosa Infection
- Requires a break in the body's defenses.
- Has a natural resistance to many antibiotics from bacteria and fungi.
- Invasive and toxigenic.
- Infections consist of three stages: (1) bacterial attachment and colonization, (2) local invasion, (3) dissemination via blood and systemic disease.
- Often found in hospitalized individuals.
- Ability to invade tissues due to toxins and enzymes breaking down physical barriers, damaging host cells, and evading host defenses.
- Extracellular proteases (elastase, alkaline protease), cytotoxins and hemolysins (phospholipase, lecithinase).
- The blue pigment can impair upper respiratory cilia's ability to clear mucus and debris, damaging lung epithelium by inhibiting catalase activity.
- Causing apoptosis of white blood cells.
Pseudomonas aeruginosa Virulence Factors
- LPS (endotoxin), Exoenzyme S, Exotoxin A.
- Associated with respiratory infections, prevalent in ICU patients and those receiving broad-spectrum antibiotics.
- Individuals with cystic fibrosis often have a unique mucoid strain that is difficult to eradicate.
- Associated with bacteraemia and septicemia.
- Cause of endocarditis in intravenous drug users and those with prosthetic heart valves.
- Well known cause of swimmer's ear, bacterial keratitis (often due to poor contact lens hygiene), and chronic osteomyelitis (in bones).
- UTI/infection caused by catheterization, instrumentation or surgical procedures.
- Cause of necrotizing enterocolitis in infants and skin/soft tissue infections (burn wounds, pyoderma, dermatitis, folliculitis).
Pseudomonas Prevention and Treatment
- Observe proper isolation procedures, aseptic techniques.
- Carefully clean respirators, catheters, and other instruments.
- Treatments include anti-pseudomonal beta-lactams, fluoroquinolones, and aminoglycosides, alongside carbapenems (imipenem).
- Current standard often involves a combination of anti-pseudomonal beta-lactam and an aminoglycoside.
Pseudomonas fluorescens and P. putida
- Often described together.
- Motile, aerobic, ox/+. Oxidase positive.
- Gram-negative bacilli.
- Produces pyoverdin or fluorescein, but not pyocyanin.
- Environmental organism often found in soil, water, plants, including contaminated milk.
- Rarely isolated from clinical specimens due to poor growth at 35°C.
- Optimum growth temperature is 25-30°C.
- Typical colonies on BAP appear wet, gray, and non-lactose fermenting (NLF) on McConkey.
- Can grow at 4°C and hydrolyze gelatin.
A. baumannii
- Ubiquitous in various environments.
- Associated with ventilators, humidifiers, catheters.
- Found in soil, water, and food products.
- About 25% of adults carry A. baumannii on their skin, 7% in their pharynx.
A. baumannii Identifying characteristics
- Strictly aerobic gram-negative coccobacilli.
- Oxidase negative, catalase positive, and non-motile.
- Can appear gram-positive in blood smears.
- Purplish hue on MacConkey resembles lactose-fermenting bacteria, not A baumannii.
- Optimal growth at pH 5.5-6.0, temperature 30-35°C.
- A. baumannii is saccharolytic; A. iwoffi is assaccharolytic.
A. baumannii Clinical Significance
- Hospitalized patients may become easily colonized.
- Is an opportunistic pathogen, second to P. aeruginosa in isolation frequency.
- Associated with UTI, pneumonia, tracheobronchitis, endocarditis, septicemia, meningitis, cellulitis, trauma, burns and the introduction of foreign bodies.
- Reported in eye infections.
- A. iwoffi is less virulent, isolation indicates colonization (rather than infection).
Identifying characteristics of Acinetobacter
- Strictly aerobic, gram-negative coccobacilli.
- Oxidase negative, catalase positive, non-motile.
- Can appear as gram-positive cocci in smears of blood cultures.
- Purplish hue on MacConkey agar may resemble lactose-fermenting bacteria.
- pH 5.5 - 6.0, temperature 30-35°C are preferred.
- A. baumannii is saccharolytic, A. iwoffi is assaccharolytic.
- Produces a K/NC reaction.
- Majority of beta-hemolytic organisms are called Acinetobacter haemolyticus.
Acinetobacter Clinical Significance
- Able to form biofilms on inanimate objects.
- Presence of pili allows organisms to adhere to epithelial cells.
- Can produce proteins that can cause cell death.
- Possesses LPS (part of its cell wall).
- Often resistant to disinfectants.
- Can survive in moist and dry surfaces; best known for its multidrug resistance.
- Has the ability to acquire resistance to many classes of antibiotics, including newer beta-lactams; presence of resistance plasmids is a significant virulence feature.
- Named “gram-negative MRSA”.
- Reservoir sites include digestive tract, skin, mucous membranes of ICU patients.
- Transmission occurs from contact with healthcare workers and environmental reservoirs.
- A. baumannii infections are rare outside hospitals.
Stenotrophomonas maltophilia
- Motile, gram-negative, oxidase-negative rod.
- Commonly found in soil, plants and water, as well as nosocomial pathogens.
- Previously included in Pseudomonas and then Xanthomonas, now a unique genus.
- Appears as non-distinct, straight, or slightly curved rods in singles or pairs.
- BAP colonies are non-hemolytic, large, smooth and shiny; can be gray-white or have a slightly yellow pigment and a distinct ammonia-like odor.
- NLF on McConkey.
- Colonies may exhibit a lavender-green/brownish discoloration of agar in areas of heavy growth.
- Oxidase negative; strong rapid oxidation of maltose.
- Weaker oxidation of glucose, and lysine decarboxylase.
- DNAse positive.
- TSI: K/NC.
Stenotrophomonas maltophilia Clinical Significance
- Important nosocomial pathogen in debilitated and immunocompromised individuals.
- Produces proteases and elastases and has LPS; part of its cell wall.
- Difficult to distinguish between colonization and infection; its presence is a marker of deterioration.
- Commonly found in medical devices, such as IV/CV and urinary catheters, causing pneumonia.
- Cystic fibrosis patients can be colonized by S. maltophilia, along with other fermenters.
- Urine presence is usually due to colonization of the urinary tract, urinary catheter or manipulation.
- Can be present in wounds. Absence of WBCs suggests it's only a colonizer.
Burkholderia cepacia Complex
- Complex of 9 subspecies not easily differentiated.
- Very significant, motile, gram-negative bacilli; often associated with cystic fibrosis patients.
- Previously classified as Pseudomonas.
- Inhabits soil and water, not part of healthy human microbiota.
- Commonly known as a plant pathogen, not a significant pathogen in healthy individuals.
- Found in hospital environments: tap water, disinfectants, soaps, and lotions.
- Grows on sheep's BAP and CAP.
- NLF, but after 4–7 days, may become pink or red due to lactose oxidation.
Burkholderia cepacia Identifying characteristics
- Able to grow on sheep's BAP, CAP and McConkey.
- NLF, but after 4-7 days, may become pink or red due to lactose oxidation.
- BCSA, a medium, selects and differentiates organisms based on CV, polymyxin B, Gm, and Va.
- OFPBL is a selective and differential medium; colonies are yellow due to lactose oxidation.
- Commercial identification systems may have difficulty identifying B. cepacia; molecular methods are recommended instead.
- Weakly Oxi+, TSI: K/NC.
- Able to decarboxylate lysine.
- Can oxidize glucose, maltose, and lactose.
- B. cepacia is able to oxidize mannitol while S. maltophilia is DNAse positive; the negative arginine reaction of B. cepacia differentiates it from B. pseudomallei.
- B. gladioli is unable to oxidize maltose and lactose.
Burkholderia cepacia Clinical Significance
- Extremely pathogenic for those with cystic fibrosis.
- Possesses few virulence factors (LPS and adhesion to mucous) and resistance to multiple antibiotics.
- Studies show presence prior to lung transplant, often leading to post-transplant death.
Burkholderia cepacia Treatment and Prevention
- Requires isolation of the patient when hospitalized.
- Antibiotic therapy rarely eradicates the organism from the CF respiratory tract.
- Resistant to aminoglycosides; multiple antibiotics, including minocycline, meropenem, ceftazidime, fluoroquinolones, and chloramphenicol, are often necessary.
- Susceptible to TMP-SXT.
Burkholderia pseudomallei
- Oxidase positive, motile, aerobic, gram-negative bacilli; slightly curved.
- Grows on standard lab media (35°C in a CO2 atmosphere).
- Smooth, mucoid colony or a dry wrinkled colony; resembling P. stutzeri on BAP.
- Mucoid colonies are a characteristic.
- Produces a musty or earthy odor.
- Colonies appear pink on MacConkey due to lactose oxidation.
- Decarboxylates arginine, whereas P. stutzeri, B. cepacia, and B. gladioli do not.
- Resistant to colistin and Polymyxin B.
Burkholderia pseudomallei Clinical Significance
- Associated with rice paddy surface waters, via aerosolized transmission.
- Causes melioidosis; known as “Vietnamese time bomb”.
- The pathogen can survive in phagocytes and reactivate decades after initial infection in immunocompromised individuals.
- Reactivation often presents as multiple abscesses throughout the body and skin.
Alcaligenes faecalis
- Inhabits environments, not part of human microbiota.
- Found in hospitals (respiratory equipment, disinfectants).
- Oxidase positive, motile, gram-negative bacilli.
- Thin, spreading colonies with irregular edges on sheep BAP.
- Can create green discoloration of the agar; NLF on McConkey (Non-Lactose fermenting).
- Produces a characteristic "green apple" odor.
- Assaccharolytic; creates a strong alkaline reaction on OF medium (appears as a blue color).
Alcaligenes faecalis Clinical Significance
- Causes opportunistic infections in immunocompromised and those with underlying diseases.
- Can colonize cystic fibrosis patients who are intubated.
- Known to reduce nitrate to nitrite.
Achromobacter xylosoxidans
- Aerobic, motile, oxidase positive, gram-negative bacilli.
- Found in moist environments.
- Can oxidize glucose and xylose.
- Opportunistic pathogen causing bacteremia, meningitis, pneumonia, and peritonitis.
- Responsible for colonizing respiratory tracts of patients with cystic fibrosis (CF) and medical equipment/solutions.
Elizabethkingia meningoseptica (formerly Chryseobacterium meningosepticum)
- Found in soil, plants, water; not part of normal human flora.
- Survive in chlorinated water.
- Oxidase positive; non-motile, slightly filamentous/thread-like gram-negative bacilli.
- Can be found in hospital tools and devices, such as incubators, sinks, faucets, saline solutions, and respiratory equipment.
- Colonies are circular, smooth, glistening, pale yellow on BAP.
- May not grow well on MacConkey.
- Positive indole reaction using Ehrlich’s reagent.
- Commonly associated with meningitis and bacteremia in premature infants; also implicated in pneumonia, cellulitis, and abscesses in immunocompromised patients.
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