Non-enteric Gram Negative Bacilli Flashcards
Pseudomonas aeruginosa
Inhabits soil and water; contact with healthy humans is widespread but usually insignificant. Opportunistic pathogen. Produce pigments, pyocyanin and pyoverdin, giving them a characteristic blue-green and yellow-green color on agar media
Pseudomonas aeruginosa.
The media is clear, but P. aeruginosa has made it blue/green via release of its pigments pyocyanin and pyoverdin.
Medical equipment that requires a wet, bodytemperature environment, such as dialysis tubing and respiratory therapy equipment, is susceptible to contamination by _____.
Medical equipment that requires a wet, bodytemperature environment, such as dialysis tubing and respiratory therapy equipment, is susceptible to contamination by Pseudomonas aeruginosa.
Gross Disease caused by Pseudomonas aeruginosa
Causes only minor infections in people who have intact host defenses.
Body sites with medical instruments are vulnerable to infection with this organism. Aspiration of P. aeruginosa into the respiratory tract in an intubated patient can lead to serious pneumonia. Neutropenic patients are vulnerable to bacteremia and severe softtissue infections with P. aeruginosa. P. aeruginosa if a common cause of burn infections. P. aeruginosa colonizes and infects the lungs of patients with cystic fibrosis
Mechanism of P. aeruginosa-induced disease
Flagella and pili mediate motility and adherence to epithelial cells. P. aeruginosa forms biofilm when growing in the host, particularly in the lung of patients with cystic fibrosis. The polysaccharide alginate can also act as an adhesin that offers protection. Alginate is one of the major components of the biofilm in isolates from the lungs of cystic fibrosis patients. Injury of host cells and tissues by these bacterial factors may also lead to increased attachment and colonization
It secretes an exotoxin A, elastase, and LasA. It also uses a type III secretion system to deliver ExoS, ExoT and ExoU.
Exotoxin A
an AB toxin that ADP-ribosyles host elongation factor 2, which is required for protein synthesis.
Elastase and LasA
Extracellular proteases that can degrade elastin in host cells.
ExoS, ExoT, and ExoU
P. aeruginosa uses a type III secretion system to deliver ExoS, ExoT, and ExoU.
ExoS and ExoT ADP-ribosylate host cell target proteins, disrupting the cell cytoskeleton and leading to apoptosis.
ExoU is a phospholipase that causes lysis of host cells.
Treatment of P. aeruginosa infection
P. aeruginosa is inherently resistant to many commonly used antibiotics, including most penicillins, first and second generation cephalosporins and tetracyclines. This is the result of the limited permeability of the outer membrane and the presence of multidrug resistance efflux pumps.
Serious P. aeruginosa infections are sometimes treated with two antibiotics. Third and fourth generation cephalosporins, carbapenems, aminoglycosides, and fluoroquinolones are often effective.
Helicobacter pylori
A Gram-negative helical-shaped bacterium that selectively colonizes the human stomach. Present in ~50% of humans. Acquired during childhood via fecal–oral or oral–oral modes of transmission. Inhabits the human stomach for decades.
H. pylori-induced disease
Induces low-grade, persistent inflammation within the gastric mucosa. As a result, essentially all individuals infected with H. pylori develop superficial gastritis, which typically persists throughout their lifetime.
The majority of colonized persons remain asymptomatic with only chronic gastritis, approximately 10% of infected individuals develop gastric or duodenal ulcers. Inflammatory process is associated with loss of epithelial glands, termed atrophic gastritis.
Gastric cancer develops in approximately 1 to 3% of infected individuals, and gastric MALT lymphoma occurs in less than 0.1% of infected individuals
Series of events leading to H. pylori-induced cancer
How H. pylori manipulates the stomach in order to inhabit it
- Secretion of urease to generate amonia that neutralizes stomach acid.
- Flagella and spiral shape allow it to dig into the gastric mucous to protect itself from acid and peristalsis.
- H. pylori flagella and LPS are far less immunogenic than those of other invading pathogens. H. pylori express a repertoire of human antigens on LPS, and these antigens undergo phase variation
- Vacuolating cytotoxin, VacA, supresses T cell responses as well as inducing epithelial cell apoptosis
- CagA is delivered into host cells via T4SS where it interferes with junctional proteins and allows H. pylori to colonize deeper.
H. pylori diagram
Elimination of H. pylori leads to complete regression of stomach lymphomas in ____% of cases.
Elimination of H. pylori leads to complete regression of stomach lymphomas in more than 80% of cases.
Diagnosing H. pylori infection
Invasive methods involve obtaining gastric tissue biopsies by endoscopy and include rapid urease tests, histology, and microbial culture.
Noninvasive diagnostic tests include the urea breath tests and stool antigen tests.
Rapid urease test
Detects the presence of gastric urease, indicating H. pylori infection.
Method of choice when endoscopy is used.
Urea breath tests
Ingestion of radioactive carbon-labeled urea. If H. pylori is present, urea is metabolized to ammonia and carbon dioxide, and radioactive carbon dioxide is detected in breath samples.
HpSA (H. pylori stool antigen)
An enzymatic immunoassay
both sensitive and specific
Steiner stain of H. pylori
H. pylori stain black with silver and are therefore easily detectable in biopsy specimens.
“Successful eradication” of H. pylori is defined as
A negative test for the bacterium 4 or more weeks after completion of therapy.
Treatment of H. pylori infection
Limited by rapidly developing bacterial resistance to metronidazole, quinolones, and macrolides, by reduced efficacy of certain drugs, such as clarithromycin and amoxicillin, under acidic conditions; and by patient noncompliance owing to side effects or the burden of ingesting multiple medications for 10 to 14 days.
Antisecretory agents such as PPIs relieve ulcer symptoms and promote ulcer healing. In addition, the gastric pH is raised by these agents, which in turn increases the efficacy of antibiotics such as amoxicillin and clarithromycin. Therapy usually consists of a PPI and two antibiotics (usually clarithromycin and either amoxicillin or metronidazole) given for 10 to 14 days.
Recommended H. pylori treatment
Omerperazole, clarithromycin, and amoxicillin for 2 weeks.
Which type of cancer can often be successfully treated with antibiotics?
Gastric mucosa-associated lymphoid tissue (MALT) lymphoma
