S1B5 - Pseudomonads Flashcards
What 2 compounds does Pseudomonas aeruginosa produce that is responsible for its pigmented appearance? What odor does this organism have when grown on media?
P. aeruginosa synthesizes pyoverdin and pyocyanin, which functions to generate reactive oxygen species to kill competing microbes. Together, they give P. aeurginosa its characteristic sweet “grape-like’“odor.
What media can enhance pigment production when growing Pseudomonas aeruginosa?
Diagnosis of P. aeruginosa infection is made with growth on culture. Blue-green pigment production is enhanced on special media such as King’s A and B.
Where is Pseudomonas aeruginosa commonly found?
P. aeruginosa is widespread in moist areas of the environment and is a part of normal gut flora in a small percentage of normal healthy people.
Describe the gram stain, morphology, oxidase positive/negative, and lactose fermentation of Pseudomonas aeruginosa ?
Pseudomonas aeruginosa is a non-lactose fermenting oxidase-positive gram-negative bacillus.
Which antibiotics have anti-pseudomonal activity?
Treatment includes a number of antibiotics active against P. aeruginosa:
- Piperacillin-tazobactam
- Ticarcillin-clavulanate
- Aminoglycosides (amikacin, tobramycin, and gentamicin)
- Ceftazidime (3rd gen) and cefepime (4th gen)
- Carbapenems (except ertapenem)
- Certain fluoroquinolones (ciprofloxacin and levofloxacin)
- Polymyxin B
What are the infections caused by Pseudomonas aeruginosa (A mnemonic may be helpful here)?
P. aeruginosa is an opportunistic pathogen that can cause infections that can be remembered with the mnemonic PSEUDO MESH:
- Pneumonia (especially in Cystic Fibrosis and intubated patients)
- Sepsis
- External otitis
- UTI
- Diabetic/IV drug Osteomyelitis
- Malignant otitis externa in diabetes
- Ecthyma gangrenosum (rapidly progressive, necrotic cutaneous lesion) in immunocompromised patients
- Skin infections in burn patients and those with extensive wounds
- Hot tub folliculitis
Is Pseudomonas aeruginosa motile or non-motile?
P. aeruginosa is motile.
Which bacteria has a characteristic sweet odour?
P. aeruginosa synthesizes pyoverdin and pyocyanin, which functions to generate reactive oxygen species to kill competing microbes. Together, they give P. aeurginosa its characteristic sweet “grape-like’“odor.
How is Pseudomonas aeruginosa transmitted? What populations of patients are often susceptible to Pseudomonas aeruginosa infection?
Transmission of P. aeruginosa occurs via contact spread and often occurs in immunocompromised patients such as burn patients and individuals in nosocomial settings (chronically ill patients and elderly patients in nursing homes).
What toxins does Pseudomonas aeruginosa produce? What are their function?
Pseudomonas aeruginosa synthesizes exotoxin A, which inhibits host protein production by ADP-ribosylation of EF2. In addition, P. aeruginosa contains endotoxin from LPS.
A child wearing tennis shoes gets a puncture wound, and eventually results in osteomyelitis. What organism is high on your differential?
P. aeruginosa osteomyelitis and septic arthritis can result secondary to a nail puncture wound to the foot. This is usually seen in children wearing rubber footwear (e.g., tennis shoes) as the inner sole is thought to create a moist environment hospitable to the organism.
Is pseudomonas aeruginosa aerobic or anaerobic?
Pseudomonas aeruginosa is aerobic.
Gram negative obligate aerobic bacilli: Gram negative rods Cause BBovine Farmers Lots of Painful whooping cough.
- Coxiella burnetti
- B. pertussis
- Bruciella sp.
- Francisella tularensis
- Legionella pneumophila
- Pseudomonas aeruginosa
Is pseudomonas aeruginosa catalase positive or negative?
Pseudomonas aeruginosa is catalase positive
Catalase positive bacteria: Cats Need PLACESS to hide
- Nocardia
- Pseudomonas
- Listeria
- Aspergillus
- Candida
- E. coli
- Staphylococci
- Serratia
Is pseudomonas aeruginosa oxidase positive or negative?
Pseudomonas aeruginosa is oxidase positive.
An oxidase test is used to determine if bacteria produce certain cytochrome c oxidases to help differentiate bacteria.
A patient presents with a corneal ulcer under a soft contact lens. Infection by what bacteria is high on your differential?
P. aeruginosa - Eye infections
- Corneal ulcer under a soft contact lens
- Infection after trauma to cornea (e.g., abrasion from contact lens).
- Acute irritation, rapid corneal perforation, may cause vision loss.
The pictures and descriptions below are identifiers of what bacteria?
Pseudomonas aeruginosa
What is 1st line therapy for diarrhea secondary to Vibrio cholera?
Treatment includes oral rehydration therapy (glucose and Na), which uses the Na-glucose co-transporters in the small intestine.
How does the amount of inoculum needed to be infected by V. cholerae compare to other organisms such as Shigella and Salmonella?
Large inoculums are necessary to overcome gastric acid defense: V. cholerae requires 108 – 1010 organisms, Shigella requires 101 organisms, and Salmonella requires 105 – 108 organisms.
What type of toxin does V. cholerae produce? Describe the mechanism whereby this toxin causes diarrhea?
V. cholerae produces cholera toxin, an AB5 exotoxin that ADP-ribosylates and activates Gs. This increases cAMP, which opens CFTRs to increase Cl secretion in crypt cells and subsequently allows less Na absorption by villous cells. The osmotic loss of water to lumen leads to voluminous watery diarrhea (30L/day) with visible flakes of mucus and epithelial cells (“rice water” stool). This may eventually lead to hypovolemic shock and death.
NOTE: CFTR (Cystic Fibrosis Transmembrane conductance Regulator) is an ABC (ATP-binding cassette) transporter encoded on chromosome 7 that is implicated in the pathogenesis of cystic fibrosis.
What growth media is used to grow V. cholerae, and how do the colonies appear?
V. cholerae grows flat yellow colonies on TCBS (Thiosulfate Citrate Bile Salts Sucrose) agar.
In patients suffering from diarrhea secondary to Vibrio cholera, blood cultures and tests looking for fecal leukocytes are almost always negative. Why?
V. cholerae does not invade GI mucosa or blood, which means no fecal leukocytes or bacteremia.
What bacterial spp. are often associated with contaminated seafood?
Vibrio spp. often associated with contaminated seafood.
What does V. cholerae produce that allows the organism to bypass the mucous coat in the intestine?
Once ingested, V. cholerae produces mucinase to digest the protective mucous coat around intestinal cells and attaches to the proximal small intestine.
How is V. cholerae transmitted?
V. cholerae is transmitted via a fecal-oral route or from ingestion of contaminated water, food, and shellfish.
A man with HIV comes into the emergency room with signs of sepsis. On examination, there is signs of a open wound in his hand. His history is significant for recent exposure to shucking oysters on a recent trip to New England. What is the most likely organism responsible?
V. vulnificus is also associated with wound infections from contact with contaminated water or shellfish.
What is the clinical presentation of V. cholerae?
V. cholerae causes non-inflammatory or watery diarrhea sometimes described as “rice water.”
Is V. cholerae motile or non-motile?
V. cholerae is a motile organism.
Is V. cholerae oxidase positive or negative?
V. cholerae is oxidase-positive.
What is the morphology and gram stain of Vibrio cholerae?
Vibrio cholerae is a comma-shaped gram-negative bacillus. Pseudomonas aeruginosa, C. jejuni and H. pylori are also motile, oxidase-positive, gram-negative rods.
Below is a description of a diseased caused by what bug?
- GI infection:
- From self-limiting diarrhea to a mild cholera like illness.
- No blood or mucus except for severe cases.
Below is a description of what bug?
Characteristics & epidemiology:
- Free-living in fresh and/or brackish water.
- From contaminated water, undercooked oysters, shrimp, other seafood
Diseases:
- Opportunistic systemic diseases in I/C patients (hepatobiliary patients).
- Diarrheal disease and wound infections in healthy individuals.
Identification: Grow well on TCBS agar; not a halophile; (+)ve oxidase test
What are common reservoirs for C. jejuni?
Common reservoirs include domestic animals such as poultry, cattle, and dogs.
In addition to C. jejuni, what are two other comma-shaped, oxidase positive, motile, and gram-negative bacilli?
Two other comma-shaped, oxidase positive, gram-negative bacilli, motile, besides C. jejuni, are Vibrio cholerae and Helicobacter pylori.
Which type of diarrhea does C. jejuni infection cause? What are the initial manifestations?
Patients typically present with inflammatory diarrhea (characterized by WBCs in stool) that is initially watery and ill-smelling that often precede bloody stools.
What are the treatment options for C. jejuni infections?
Treatments for C. jejuni include erythromycin or ciprofloxacin.
What is the morphology, gram staining, oxidase status, and urease presence of Campylobacter jejuni?
Campylobacter jejuni is a microaerophilic, comma-shaped, urease-negative, oxidase positive, motile, gram-negative bacillus.
What are two notable features about C. jejuni growth conditions?
C. jejuni is microaerophilic (grows best at lower oxygen than atmospheric) and grows best at 42°C.
What acute neuropathy does C. jejuni precede?
C. jejuni infection commonly precedes Guillain-Barre Syndrome (GBS), the most common acute peripheral neuropathy and the most common cause of acute flaccid paralysis.
How is C. jejuni transmitted? Where does it colonize?
C. jejuni is transmitted via a fecal-oral route or from ingestion of contaminated meat and can colonize the terminal ileum/colon.
Is H. pylori oxidase positive or negative?
H. pylori is oxidase-positive.
How is Helicobacter pylori infection treated?
Treatment includes triple therapy
- Proton pump inhibitor (PPI)
- Amoxicillin (metronidazole if penicillin allergy)
- Clarithromycin
or quadruple therapy for clarithromycin-resistant H. pylori
- PPI
- Bismuth therapy
- Metronidazole
- Tetracycline
Once ingested, where does H. pylori colonize? How is it able to survive inside the body?
Once in ingested, H. pylori colonizes the gastric antrum but does not invade. Production of ammonia via urease creates an alkaline environment that protects from gastric acid. Host inflammatory response leads to mucosal damage and loss of mucus-secreting cells, eventually causing gastritis. Hypersecretion of acid leads to a risk of duodenal ulcers.
How is Helicobacter pylori infection diagnosed?
Diagnosis is made with invasive techniques such as endoscopy, and with non-invasive techniques such as urease and stool antigen testing.
What is the typical manifestation of Helicobacter pylori infection?
Patients infected with H. pylori typically present with peptic ulcers in the stomach and duodenum.
What risk factors increase the susceptibility of Helicobacter pylori infection?
Prevalence of H. pylori infections increases in close living quarters, individuals of lower socioeconomic status, and areas of poor sanitation.
What is the morphology, gram staining, and oxygen requirement of Helicobacter pylori?
Helicobacter pylori is a microaerophilic, spiral or curved gram-negative bacillus.
How is H. pylori transmitted? How rare is infection with H. pylori?
Transmission is unknown, but likely fecal-oral, iatrogenic, and/or oral-oral. Many people are infected with H. pylori in childhood, with the majority of the population infected and asymptomatic by age 50.
What enzyme does H. pylori express that allows for its survival within stomach?
H. pylori is urease-positive.
The urea breath test can be used to diagnose or monitor treatment response for which infectious agent?
The urea breath test measures exhaled isotope-labeled carbon dioxide from ingestion of radiolabeled urea, indicating the presence of a urease-producing organism such as H. pylori.
What can cause a false negative urease test in a patient with Helicobacter pylori infection?
Individuals taking proton-pump inhibitors (PPIs) may have a false-negative urease test.
Histology of the stomach or duodenum infected with Helicobacter pylori can demonstrate what features?
Histology of gastric or duodenal biopsy can demonstrate gastritis, ulcers, or metaplasia.
What major diseases besides peptic ulcers can result from Helicobacter pylori infection?
Chronic untreated H. pylori infection is linked to gastric adenocarcinoma, primary B-cell lymphoma and MALT lymphoma.
