Lecture 4 Part 5: Enterobacteriaceae Flashcards
What is the largest family of clinically important bacteria?
Enterobacteriaceae
Are most species and subspecies of Enterobacteriaceae human pathogens?
No, most species and subspecies are not human pathogens
Name three places where Enterobacteriaceae can be found?
water, soil, and as endogenous flora
What are the three types of Enterobacteriaceae?
- Strictly pathogens
- Opportunistic
3, Commensals that acquire virulence genes or novel body niches
What are the medically important Enterobacteriaceae species?
Escherichia coli, Salmonella, Shigella, Yersinia, Klebsiella
What is the Gram stain and shape of Enterobacteriaceae?
Gram-negative rods
Are Enterobacteriaceae facultative anaerobes ?
yes
Do Enterobacteriaceae form spores?
No, they are non-spore forming
What are the oxidase and catalase characteristics of Enterobacteriaceae?
Enterobacteriaceae are oxidase-negative and catalase-positive, with no cytochrome oxidase activity
What shared antigen is present in all Enterobacteriaceae?
Enterobacterial common antigen
Are all Enterobacteriaceae motile?
No, only some Enterobacteriaceae are motile
What are the three structural components used to classify Enterobacteriaceae?
- O polysaccharide (LPS component)
- K antigens (capsule polysaccharides)
- H proteins (flagellar proteins)
What are the 5 key virulence factors of Enterobacteriaceae?
- Endotoxin – Lipid A component of LPS
- Capsule
- Antigenic Phase Variation – Allows differential expression of O antigens, K proteins, and H antigens
- Type III Secretion System – complex that facilitates transfer of virulence factors
- Iron-Chelating Proteins
What are the key clinical impacts of E. coli infections?
- Most common Gram(-) rod in sepsis
- Causes >80% of community-acquired UTIs
- Major contributor to gastroenteritis
- Usually results from opportunistic commensal activity
What are the six strains of E. coli that cause gastroenteritis?
- Enterotoxigenic (ETEC) – Traveler’s diarrhea
- Enteropathogenic (EPEC) – Infant diarrhea
- Enteroaggregative (EAEC) – Persistent diarrhea
- Enterohemorrhagic (EHEC) – Bloody diarrhea, HUS
- Enteroinvasive (EIEC) – Dysentery-like illness
- Diffusely Adherent (DAEC) – Pediatric diarrhea
What extraintestinal diseases does E. coli cause?
Bacteremia
Neonatal meningitis
Urinary tract infections (UTIs)
What type of diarrhea is caused by Enterotoxigenic E. coli (ETEC)?
traveler’s diarrhea
What are the two toxins produced by ETEC?
- Heat-stable toxin (STa): monomeric, binds guanylate cyclase leading to
increased cGMP and hypersecretion - Heat-labile toxin (LT-I):
* exotoxin
* B subunit binds surface glycoproteins
* A subunit binds adenylate cyclase leading to
increased cAMP and hypersecretion & decreased
absoprtion
Does Enteropathogenic E. coli (EPEC) produce toxins?
No, EPEC does not produce toxins
How does Enteropathogenic E. coli (EPEC) cause disease?
EPEC adheres to and invades host cells using bundle-forming pili (BFP) and the locus of enterocyte effacement (LEE)
What is the “locus of enterocyte effacement” (LEE) in EPEC?
The LEE is a pathogenicity island containing about 40 genes that mediate the attachment and destruction of cell surface.
How does Enteroaggregative E. coli (EAEC) adhere to host cells?
EAEC uses Aggregrative Adherence Fimbriae I (AAF I) to form a “stacked brick” arrangement on intestinal epithelial cells
What effect does EAEC have on mucus secretion and biofilm formation?
EAEC stimulates mucus secretion, leading to the formation of a thick biofilm
What 2 toxins does EAEC produce?
EAEC produces Enteroaggregative heat-stable toxin and a Plasmid-encoded toxin, both of which induce fluid secretion
What is the most common serotype of Enterohemorrhagic E. coli (EHEC)?
E. coli O157:H7 is the most common serotype of EHEC
True or False
EHEC Low inoculum for disease (< 100 bacteria)
True
How many bacteria are needed to cause EHEC infection?
Less than 100 bacteria can cause EHEC infection due to its low infectious dose
What are the clinical manifestations of EHEC infection?
EHEC causes mild to hemorrhagic colitis and can lead to Hemolytic Uremic Syndrome (HUS), characterized by:
Acute renal failure
Thrombocytopenia
CNS manifestations
What toxin does EHEC produce?
EHEC produces Shiga toxin (Stx-1 & Stx-2)
How many serotypes exist for Salmonella enterica?
there are more than 2500 unique serotypes of Salmonella enterica
What are the two most clinically relevant serotypes of Salmonella in humans?
- Salmonella typhi (S. enterica serovar Typhi)
- Salmonella paratyphi
How is Salmonella transmitted?
Salmonella is transmitted through ingestion of contaminated food (poultry, eggs, dairy) or direct fecal-oral routes
Can Salmonella cause chronic infections?
Yes, Salmonella can cause both transient and chronic infections
How does Salmonella invade?
Salmonella invades through M cells, replicates in endosomes, and can enter the blood or lymph via transcytosis
What are the two major pathogenicity islands of Salmonella that help with Migration & colonization efficiency?
- Pathogenicity Island I (SPI-1) – Encodes Salmonella-secreted invasion proteins (Ssps) for host cell invasion
- Pathogenicity Island II (SPI-2) – Encodes a Type III Secretion System (T3SS) for intracellular survival and systemic spread
Name the 4 clinical diseases caused by Salmonella
- Gastroenteritis – most common form
- Septicemia – more risk for young, elderly or immuno-
compromised - Enteric fever – Typhoid fever (initial bacteremia with
subsequent colonization of the gallbladder and reinfection of
the intestines) - Asymptomatic colonization
What is the most common clinical disease caused by Salmonella?
Gastroenteritis
Which individuals are at higher risk for Salmonella septicemia?
Young children, elderly, and immunocompromised individuals are at greater risk for septicemia
What is enteric fever, and how does it develop?
Typhoid fever is a systemic illness caused by Salmonella typhi. It begins with bacteremia, followed by colonization of the gallbladder, and leads to reinfection of the intestines
How is Shigella related to E. coli?
Shigella is a biochemical variant of Enteroinvasive E. coli (EIEC)
What are the 2 most clinically relevant Shigella species?
- S. sonnei (85% of US infections)
- S. dysenteriae (more severe)
What is the only reservoir for Shigella?
humans
How is Shigella transmitted?
Transmitted through fecal-oral routes
What disease does Shigella cause?
Causes Shigellosis (cramps, diarrhea, fever, bloody stools)
How does Shigella establish infection?
Shigella attaches, invades, and replicates in the cells lining the colon
How does Shigella spread between cells?
Replicate intracellularly & spread through cell-cell passage
using type III secretion system proteins
- Avoid immune detection & clearance
What is the key toxin produced by Shigella?
Shiga toxin (Stx) – an exotoxin that disrupts protein synthesis, leading to
intestinal epithelial damage
How does Shiga toxin work?
- B subunit binds glycolipid (Gb3) on host cell
- A subunit cleave the 28S rRNA preventing tRNA from
binding to the “A” site of the ribosome
How does Shiga toxin affect cells during gastroenteritis?
*Shiga toxin bindis to the membrane,
enters the cell and then, the Golgi
network.
*Interferes with the protein synthesis
