Gram negatives I Flashcards
What are some characteristics of G- rods?
Most are enterobacteriaceae
Resistant to Penicillin and Vancomycin
Inhabitants of normal GI flora
Ceftriaxone and Ciprofloaxin normally treatment of choice
What are the characteristics of the enterobacteriaceae family?
Gram negative rods with LPS in the cell wall
Serological typing: O antigen, K antigen (capsule), H antigen
All ferment glucose and oxidase negative
Lactose fermentation varies
What are some characteristics of Klebsiella?
Non-motile, capsular intestinal flora
Resistant to many antibiotics
Infects immunocompromised people (nosocomial), and aspiration of GI contents
What is Klebsilla pneumonia?
Occurs in alcoholics or diabetics, often after aspiration
Classically results in red “currant jelly” sputum
Can also cause lung abscesses
Rare cause of UTIs
What are the E. coli diseases?
Watery diarrhea
Bloody diarrhea (dysentery)
UTI/pyelonephritis
Neonatal meningitis
Septicemia
Describe Enterotoxigenic E. coli (ETEC).
Plasmid-mediated strain
Produce heat labile (LT) and heat stable (ST) enterotoxins
Causes watery diarrhea in infants and traveler’s diarrhea
No inflammation and no fever
Describe Enteropathogenic E. coli (EPEC).
No toxin, no inflammation, no fever
Blunt microvilli, preventing absorption
Causes infantile diarrhea, similar to ETEC
Common in underdeveloped countries
Describe Enterohemorrhagic E. coli (EHEC).
Does not ferment sorbitol
Does not invade host cells
Produces Shiga-like toxin (aka verotoxin)
Usually from undercooked beef
Pediatric diarrhea, copious bloody discharge hemorrhagic colitis, intense inflammation and hemolytic uremia
What are the effects of Shiga-like toxin?
Endothelium swells, detaches, vessel lumens narrow
Fibrin-platelets aggregation in microvasculature, ischemia and small vessel damage
Hemolysis
What is hemolytic uremic syndrome (HUS)?
Occurs in about 10% of EHEC cases, common in children
Triad: hemolytic anemia, thrombocytopenia, acute renal failure (uremia)
HUS + fever, mental status change = TTP
Describe Eneroinvasive E. coli (EIEC).
Invasive, enters M cells
Does not produce shiga toxin
Dysentery-like diarrhea, severe inflammation, fever
Very large plasmid
What are the treatments for E. coli?
Most E.coli diarrhea is self-limited
Hydration
Antibiotics are rarely used because they may increase toxin release
What are the characteristics of gram negative sepsis?
Fever, tachycardia, hypotension
Driven by endotoxin (LPS, Lipid A)
Common presentation: Elderly patient, UTI, + blood culture
What diseases are caused by Salmonella spp.?
Gastroenteritis
Typhoid fever
Bacteremia
Localized infections in other sites
What are the symptoms of Typhoid fever?
Fever, headache, malaise, and anorexia
Skin rash with rose-colored spots also possible
How does typhoid fever spread through the body?
Starts in the small intestine through Peyer’s patches, then spreads to the phagocytes of the lvier, gallbladder, and spleen - causing bacteremia
Survives in the phagosomes in phagocytic cells
Can remain in gallbladder
Describe enterocolitis.
Caused by non-typhoid Salmonella
Invasion of epithelia and subepithelial tissue of the small and large intestines
PMN response limits the infection to the gut and the adjacent mesenteric lymph node
Gastric acid important host defense
What is septicemia?
Occurs on only about 5-10% of Salmonella infections
Underlying chronic disease: sickle cell or cancer
Bacteremia results in seeding of many organs, with osteomeylitits, pneumonia and meningitis as the most common sequelae
What is the treatment for gastroenteritis?
Fluids, electrolytes
Antibiotics not helpful due to resistance
What is the treatment for typhoid fever?
Ceftriaxone, Flurorquinolones
Typhoid vaccine available for travelers to high risk areas
What are some characteristics of Shigella?
Invades mucosal cells (M cells in Peyer’s patches)
Spreads cell to cell, not through blood
Nonmotile
Produces shigella toxin, but non-toxin strain can cause disease as well
What is the virulence mechanism in Shigella?
Targets M cells in Peyer’s Patches
S. dysenteriae strains produce Shiga toxin
What is Reiter’s Syndrome?
Arthritis, conjunctivitis and urethritis appear after the intestinal infections by one of the intestinal pathogens
Cause is unclear, most patients are male
What is the treatment for Shigella?
Fluids, electrolytes
Antibiotics improve symptoma
Ceftriaxone and cirprofloxacin
What is Proteus?
Rare cause of UTIs
Swarm phenotype: Long flagella, Bullseye on agar plate
Produce urease
Associated with struvite kidney stones
What is enterobacter?
Rare cause of nosocomial UTIs
Resistant to many antibiotics, most beta-lacams
Treated with Carbabpenems
What are Cirtobacter and Serratia?
Not dominant pathogens for any condition
Resistant to many antibiotics
Cirtobacter - GN sepsis
Serratia - distinctive red colonies, hospital outbreaks, sometimes osteomeylitis
