Enteric Bacteria Flashcards
1
Q
The Enterobacteriaceae
A
Major Foodborne:
- Shigella
- E. coli
- Salmonella
Minor Foodborne:
- Y. enterocolitica
- Y. pseudotuberculosis
ICU Bugs:
- Klebsiella/Enterobacter/Serratia
- Proteus/Providencia/Morganella
2
Q
Defining characteristics of Enterobacteriaceae
A
- gram (-)
- non-sporulating
- straight rods
- facultative aerobes
- catalase (+)
- oxidase (-)
- glucose fermenters
3
Q
Acquired gut virulence factors
A
-promiscuous to new DNA-
-pili for adhesions
-Type 3 Secretion Systems
1-Adhesion 2. Subversion of gut macrophage
4
Q
Enterobacteriaceae antibiotic resistance
A
- antibiotic resistance testing must be performed for any Enterobacteriaceae infection that requires treatment
- a liquid culture of the patient isolate is spread on large agar plates
- disks of filter paper soaked in various antibiotics are placed on the plate prior to overnight incubation
- successful plating produces a solid lawn of bacteria interrupted by zones of clearing around the effective antibiotics
- measurements of the clear zones must be compared to a table to determine the most effective antibiotic
5
Q
Classification of E. coli gastroenteritises
A
- Enterotoxigenic E coli (ETEC) is a cause of traveler’s diarrhea
- Enteropathogenic E. coli (EPEC) is a cause of childhood diarrhea
- Enteroinvasive E. coli (EIEC) causes a Shigella-like dysentery
- Enterohemorrhagic E. coli (EHEC) causes hemorrhagic colitis and may progress to hemolytic-uremic syndrome (HUS)
- Enteroaggregative E. coli (EAggEC) is primarily associated with persistent diarrhea in children in developing countries
- Enteroadherent E. coli (EAEC) is a cause of childhood diarrhea and traveler’s diarrhea in Mexico and North Africa
6
Q
Shigella bacterium
A
- intestinal epithelium protected from invasion by mucus layer, tight junctions
- M cells of Peyer’s patch: immunological sampling
- entry of Shigella mediated by type III secretory system and other effector proteins and cytoskeletal rearrangements
- apoptosis of macrophage
- survival of bacteria
- initiation of inflammation
7
Q
Salmonella Bacteriology
A
- Gram (-) rods
- motile
- > 2500 serovars exist
- usually acquired from contaminated food
- enterocolitis
- enteric fevers (typhoid fever)
- inflammation and diarrhea, nausea and vomiting
- immune response restricts to gut, bacteremia is rare
- high infectious dose (100k bacteria)
- gastric acid is protective, antacids increase risk
- bacteria attach by fimbriae (pili) to cells lining the intestinal lumen
- salmonellae selectively attach to specialized epithelial cells (M cells) of the Peyer patches
8
Q
Salmonella pathogies
A
- M cell attempts immunological sampling but bacterium survives
- some salmonella spp proliferate in DCs, ride to distant sites in body -> typhoid fevers
9
Q
Virulence factors of Salmonella
A
- Ipf operon enhances adhesion to M cells
- type 3 secretion system injects M cell, enhances bacterial translocation
- SipB injected by Spi1 Type 3 sys causes macrophage apoptosis
- in S. typhi, Spi2 Type 3 sys remodels phagosomes for systemic spread
- Vi antigen: S typhi capsule for immune evasion
10
Q
Enteric and Typhoid fevers
A
- onset: fever, malaise, diffusion, abdominal pain, constipation (sometimes diarrhea)
- 3-4 week progression: dry cough, stupor, delerium, intestinal hemorrhage, bowel perforation, myocarditis, death (9-13%)
- necrosis of the infected Peyer patches causes hemorrhage/perforation
- other symptoms from toxemia
- survivors may have long-term neurological sequale or chronic carriage in gallbladder (reservoir)
- Typhoid Mary NYC c1905
11
Q
Hemolytic-Uremic Syndrome (HUS)
A
- shigella and enterohemorrhagic E coli both routinely cause fever, dehydration, severe headache, lethargy, diarrhea progresses from watery to bloody with mucus
- in a minority of cases (1-10%) bacteria escape the gut and shiga toxin is released into the bloodstream, causing HUS: fever, dehydration, hemolysis, thrombocytopenia, uremia requiring dialysis, 5-10% mortality
- blood smear shows schistocytes (distorted, fragmented red cells) probably generated as blood passes through many small thomboses (early DIC)
- predominantly peds
- antibiotic treatment of HUS is controversial: some antibiotics may worsen the outcome
12
Q
Reactive Arthritis
A
- autoimmune sequel in patients with HLA-B27
- triggered by infection with Shigella, Salmonella, Yersinia, Campylobacter, Chlamydia
- defined as conjunctivitis+urethritis+arthritis
- can also involve mouth, fingers, soles of feet
- treated with non-steroidal anti-inflammatories, usually resolves in 2-5 months
13
Q
Non-Foodborne Enterobacteriaceae
A
- usually normal flora gone bad
- usually opportunistic nosocomial infections, but some community-acquired diseases exist: Klebsiella pneumonia, Serratia endocarditis in IV drug users
- all common causes of catheter-associated UTIs
- “ICU Bugs”- opportunistic and extremely antibiotic resistant. Can easily become the last straw for a patient who was already seriously ill
14
Q
Klebsiella
A
- can be a primary pathogen, but usually with a predisposing condition like advanced age, chronic respiratory disease, diabetes, alcoholism
- large polysaccharide capsule defends against phagocytosis, complement
- adhesins adhere to gut cells, siderophores chelate iron
- particularly in men with predisposing conditions, causes lobar pneumonia with necrosis, inflammation, and hemorrhage thick bloody sputum “currant jelly sputum” In alcoholics, mortality may be 50% in alcoholics with bacteremia approaches 100% despite treatment
- less-lethal presentations include bronchitis, UTIs, wound infection, catheter infection
15
Q
Klebsiella/Enterobacter/Serratia Group Pathogenesis
A
- Klebsiella causes nosocomial outbreaks, among top 8 hospital-acquired infections, second only to E. coli as cause of Gram- sepsis
- K. oxytoca among top 4 pathogens in NICUs
- carbapenem-resistant K. pneumoniae is currently spreading among hospitals worldwide
