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Questions and Answers
Which organism is the most commonly isolated non-fermenting bacilli in clinical specimens?
Which organism is the most commonly isolated non-fermenting bacilli in clinical specimens?
- Pseudomonas aeruginosa (correct)
- Escherichia coli
- Stenotrophomonas maltophilia
- Acinetobacter baumanii
What characteristic is true for all non-fermenting bacilli?
What characteristic is true for all non-fermenting bacilli?
- They are all Gram-positive.
- They ferment glucose.
- They grow on MacConkey agar. (correct)
- They are all anaerobic.
Which of the following features is commonly associated with Pseudomonas aeruginosa?
Which of the following features is commonly associated with Pseudomonas aeruginosa?
- It does not have flagella.
- It is oxidase positive. (correct)
- It is anaerobic.
- It ferments lactose.
How is Pseudomonas aeruginosa mainly acquired in the environment?
How is Pseudomonas aeruginosa mainly acquired in the environment?
What is a common characteristic of Acinetobacter baumanii?
What is a common characteristic of Acinetobacter baumanii?
What is the primary function of the repeating polymer of mannuronic and glucuronic acid in Pseudomonas aeruginosa?
What is the primary function of the repeating polymer of mannuronic and glucuronic acid in Pseudomonas aeruginosa?
Which characteristic is true about the motility of Pseudomonas aeruginosa?
Which characteristic is true about the motility of Pseudomonas aeruginosa?
Which of the following antibiotics is Pseudomonas aeruginosa typically resistant to?
Which of the following antibiotics is Pseudomonas aeruginosa typically resistant to?
What is an indicator of multi-drug resistant Pseudomonas aeruginosa (MDRP)?
What is an indicator of multi-drug resistant Pseudomonas aeruginosa (MDRP)?
In which of the following conditions is Pseudomonas aeruginosa most frequently isolated?
In which of the following conditions is Pseudomonas aeruginosa most frequently isolated?
What type of test results indicate that Pseudomonas aeruginosa does not ferment carbohydrates?
What type of test results indicate that Pseudomonas aeruginosa does not ferment carbohydrates?
Which treatment approach is essential for managing severe infections caused by Pseudomonas aeruginosa?
Which treatment approach is essential for managing severe infections caused by Pseudomonas aeruginosa?
Pseudomonas aeruginosa is particularly noted for its ability to:
Pseudomonas aeruginosa is particularly noted for its ability to:
Which populations are at high risk for infections caused by Pseudomonas aeruginosa?
Which populations are at high risk for infections caused by Pseudomonas aeruginosa?
What is the leading cause of nosocomial respiratory tract infections?
What is the leading cause of nosocomial respiratory tract infections?
Which virulence factor of Pseudomonas aeruginosa is associated with adhesion?
Which virulence factor of Pseudomonas aeruginosa is associated with adhesion?
Which of the following infections is NOT commonly associated with Pseudomonas aeruginosa?
Which of the following infections is NOT commonly associated with Pseudomonas aeruginosa?
What type of bacteria is Pseudomonas aeruginosa based on its cellular morphology?
What type of bacteria is Pseudomonas aeruginosa based on its cellular morphology?
What is a characteristic trait of Pseudomonas aeruginosa colonies on Blood Agar Plate (BAP)?
What is a characteristic trait of Pseudomonas aeruginosa colonies on Blood Agar Plate (BAP)?
What is a common pigment produced by Pseudomonas aeruginosa?
What is a common pigment produced by Pseudomonas aeruginosa?
Which characteristic is associated with the mucoid strain of Pseudomonas aeruginosa?
Which characteristic is associated with the mucoid strain of Pseudomonas aeruginosa?
Which infections are commonly associated with Acinetobacter baumannii in immunocompromised patients?
Which infections are commonly associated with Acinetobacter baumannii in immunocompromised patients?
What is a key characteristic of Acinetobacter baumannii's cellular morphology?
What is a key characteristic of Acinetobacter baumannii's cellular morphology?
Which of the following growth characteristics is true for Acinetobacter baumannii on MAC?
Which of the following growth characteristics is true for Acinetobacter baumannii on MAC?
What is Acinetobacter baumannii's resistance to many antimicrobials attributed to?
What is Acinetobacter baumannii's resistance to many antimicrobials attributed to?
What can cause false staining with Acinetobacter baumannii?
What can cause false staining with Acinetobacter baumannii?
What is the typical catalase test result for Acinetobacter baumannii?
What is the typical catalase test result for Acinetobacter baumannii?
Which of the following is true regarding the mortality rate associated with infections caused by Acinetobacter baumannii?
Which of the following is true regarding the mortality rate associated with infections caused by Acinetobacter baumannii?
What is the lysine decarboxylase test result for Acinetobacter baumannii?
What is the lysine decarboxylase test result for Acinetobacter baumannii?
What type of infections is Stenotrophomonas maltophilia primarily associated with in hospitalized patients?
What type of infections is Stenotrophomonas maltophilia primarily associated with in hospitalized patients?
Which of the following treatments is inherently ineffective against Stenotrophomonas maltophilia?
Which of the following treatments is inherently ineffective against Stenotrophomonas maltophilia?
Which characteristic is true regarding the colonial morphology of Stenotrophomonas maltophilia on BAP?
Which characteristic is true regarding the colonial morphology of Stenotrophomonas maltophilia on BAP?
What is the cellular morphology of Stenotrophomonas maltophilia?
What is the cellular morphology of Stenotrophomonas maltophilia?
Which test result would be expected for Stenotrophomonas maltophilia?
Which test result would be expected for Stenotrophomonas maltophilia?
Why is susceptibility testing a must when treating Stenotrophomonas maltophilia?
Why is susceptibility testing a must when treating Stenotrophomonas maltophilia?
What odor is commonly associated with Stenotrophomonas maltophilia colonies?
What odor is commonly associated with Stenotrophomonas maltophilia colonies?
Which test result would be negative for Stenotrophomonas maltophilia?
Which test result would be negative for Stenotrophomonas maltophilia?
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Study Notes
Non-Fermenting Bacilli (NFB)
- Common NFBs include Pseudomonas aeruginosa, Acinetobacter baumanii, and Stenotrophomonas maltophilia.
- All are Gram-negative bacilli and grow on MacConkey agar.
- All are oxidase and catalase positive.
- All are resistant to a wide range of antimicrobials.
Pseudomonas aeruginosa
- Most common NFB.
- Ubiquitous in the environment, including water, soil, and plants.
- Opportunistic pathogen, often infecting immunocompromised patients, burn victims, and those with medical devices.
- Commonly causes nosocomial (hospital-acquired) infections.
- Can cause a variety of infections, including pneumonia, wound infections, bacteremia, and UTI's.
- Produces pigments including pyocyanin, pyorubin, pyomelanin, and pyoverdin.
- Mucoid strains, often associated with cystic fibrosis, produce alginate, which forms a biofilm.
- Susceptibility testing is crucial due to the organism's inherent resistance to many antibiotics.
Acinetobacter baumanii
- Second most common NFB.
- Ubiquitous in the environment and hospitals.
- Opportunistic pathogen, often infecting immunocompromised patients.
- Can cause a variety of infections, including pneumonia, bacteremia, meningitis, and UTI's.
- Highly resistant to antibiotics, including carbapenems, with multi-drug resistant strains (MDRA) emerging.
- Often appears coccobacillary.
- Produces a purplish tinge on MacConkey agar.
- Growth on blood agar is smooth, opaque, raised, and creamy.
Stenotrophomonas maltophilia
- Third most common NFB.
- Not normal flora but a colonizer in hospitalized patients.
- Opportunistic pathogen, often infecting immunocompromised patients.
- Can cause a variety of infections, including endocarditis, wound infections, bacteremia, and meningitis.
- Inherently resistant to many antibiotics, including cephalosporins, penicillins, carbapenems, and aminoglycosides.
- Trimethoprim-sulfamethoxazole (SXT) is often the drug of choice for treatment.
- Colonies produce a strong ammonia smell.
- On MacConkey agar, colonies appear non-lactose fermenting with a bluish tinge.
- On blood agar, colonies are large, smooth, glistening, with uneven edges and lavender-green to light purple pigment.
Pseudomonas aeruginosa – Key Virulence Factors
- Lipopolysaccharide: Antiphagocytic activity, cytotoxicity.
- Pili: Adhesion.
- Flagella: Motility, adhesion.
- Type III secretion system: Cytotoxic activity.
- Phospholipases: Cytotoxicity.
- Proteases: Cytotoxicity, proteolytic activity.
- Exotoxin A: Cytotoxicity.
- Capsule: Antiphagocytic activity.
- Deoxyribonuclease (DNase): Breaks down DNA.
- Elastase: Cytotoxicity, proteolytic activity.
- Lecithinase: Cytotoxicity, proteolytic activity
- Hemolysins: Cytotoxicity.
Pseudomonas aeruginosa – Identification
- Motile with polar flagellum.
- Oxidase positive.
- Catalase positive.
- Nitrate positive, usually beyond nitrite to nitrogen gas..
- Arginine Dihydrolase (ADH) positive.
- Citrate positive.
- Oxidizer of carbohydrates on OF test, non-fermenter.
- TSI Alk/Alk, or K/K.
- Growth at 42°C positive.
Acinetobacter baumanii – Identification
- Oxidase negative.
- Catalase positive.
- Nonmotile.
- TSI K/NC or NC/NC.
- Glucose OF: +/-
- Lysine Decarboxylase negative.
Stenotrophomonas maltophilia – Identification
- Oxidase negative.
- Catalase positive.
- Motility positive.
- Dnase positive.
- Esculin positive.
- Gelatinase positive.
- Lysine Decarboxylase positive.
Comparison of NFB
| Organism | Cellular Morphology | Colonial Morphology (MAC) | Colonial Morphology (BAP) | Oxidase | Motility | TSI | OF |
|---|---|---|---|---|---|---|---|
| P. aeruginosa | Slender GNB | NLF (May have pigment) | Metallic sheen, fruity odor | Positive | Positive | K/K | Oxidizer |
| A. baumanii | Small GNB (can be coccid) | NLF (May have purplish tinge) | NH, small, wet | Negative | Negative | K/K | Oxidizer |
| S. maltophilia | GNB | NLF (May have bluish tinge) | NH, small, wet, ammonia odor | Negative | Positive | K/K | Oxidizer |
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