Enteric Bacteria

Question 1

The Enterobacteriaceae

Answer 1

Major Foodborne:

• Shigella
• E. coli
• Salmonella

Minor Foodborne:

• Y. enterocolitica
• Y. pseudotuberculosis

ICU Bugs:

• Klebsiella/Enterobacter/Serratia
• Proteus/Providencia/Morganella

Question 2

Defining characteristics of Enterobacteriaceae

Answer 2

• gram (-)
• non-sporulating
• straight rods
• facultative aerobes
• catalase (+)
• oxidase (-)
• glucose fermenters

Question 3

Acquired gut virulence factors

Answer 3

-promiscuous to new DNA-
-pili for adhesions
-Type 3 Secretion Systems
1-Adhesion 2. Subversion of gut macrophage

Question 4

Enterobacteriaceae antibiotic resistance

Answer 4

• 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

Question 5

Classification of E. coli gastroenteritises

Answer 5

• 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

Question 6

Shigella bacterium

Answer 6

• 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

Question 7

Salmonella Bacteriology

Answer 7

• 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

Question 8

Salmonella pathogies

Answer 8

• M cell attempts immunological sampling but bacterium survives
• some salmonella spp proliferate in DCs, ride to distant sites in body -> typhoid fevers

Question 9

Virulence factors of Salmonella

Answer 9

• 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

Question 10

Enteric and Typhoid fevers

Answer 10

• 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

Question 11

Hemolytic-Uremic Syndrome (HUS)

Answer 11

• 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

Question 12

Reactive Arthritis

Answer 12

• 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

Question 13

Non-Foodborne Enterobacteriaceae

Answer 13

• 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

Question 14

Klebsiella

Answer 14

• 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

Question 15

Klebsiella/Enterobacter/Serratia Group Pathogenesis

Answer 15

• 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

Question 16

Klebsiella/Enterobacter/Serratia Group Diagnosis

Answer 16

• begin with culture and gram stain to implicate group and enable Ab resistance testing
• K. pneumoniae polysaccharide capsule gives mucoid appearance on agar
• more specific biochemical lab tests availible, often needed
• antiobiotics as indicated begin with aminoglycoside and cephalosporin