Enteric Bacilli Flashcards
Module 2
What are characteristics of the order?
1) non-spore forming, facultatively anaerobic, gram-negative rods
2) ferment glucose
3) reduce nitrates to nitrites
4) do not produce cytochrome oxidase
5) slang name “enterics”
What is the natural habitat of enteric bacilli?
ubiquitous in nature; most are present in the intestinal tract of animals and humans as commensal flora
Where do we see them outside of their natural habitat?
may produce serious extraintestinal opportunistic infections (E. coli causing fatal meningitis in the newborn)
What toxins do these organisms produce?
endotoxins, exotoxins, and enterotoxins
What can these endotoxins do?
LPS in the outer membrane can cause hypotension, shock, fever, intravascular coagulation, and death
What are LPS macromolecules composed of?
lipid A (endotoxin portion), core polysaccharide, and O antigens
what can the enterotoxins do?
causes diarrhea or vomiting; they are exotoxins that act on the intestinal tract
What potent exotoxin does Shigella dysenteriae produce?
shiga toxin; causes hemorrhages and leads to bloody diarrhea
What are flagellar or “H” antigens?
protein in nature and heat-labile; associated with motility
What are capsular or “K” antigens?
capsules are surface polysaccharides and also heat-labile
What are somatic or “O” antigens?
associated with the “body” of the bacterial cell, they are the polysaccharide side chain of the LPS in the outer membrane; heat-stable
What are the primary pathogens of the enteric bacilli group?
Salmonella, Shigella, shiga toxin producing E. coli (STEC), and Yersinia
What does Salmonella typhi cause?
typhoid fever; prolonged fever, bacteremia, reticuloendothelial system involvement (liver and speen), dissemination to multiple organs
What do other groups of Salmonella cause?
acute gastroenteritis or food poisoning; vomiting and diarrhea; can also cause nontyphoidal bacteremia and less virulent enteric fevers
Where do we tend to find Salmonella?
we find it colonizing chickens, in soft cheeses, ground beef and often it’s a common outcome of poor sewage
What are the characteristics of Shigella?
it is closely related to E. coli, NOT a normal flora of GI tract, humans are the only known reservoir, it is a fragile organism, and it takes very little to infect someone
How can Shigella be transmitted?
likely by direct fecal-oral contact; can be carried by flies, food, or water in areas of crowding / poor sanitation
What does Shigella cause?
all four species of Shigella cause dysentery, but the effects of it differ for each
What are symptoms of Shigella?
fever, chills, abdominal cramps, and watery diarrhea followed by bloody stools containing mucus and numerous leukocytes
What does Shiga Toxin-Producing E. coli (STEC) produce and what does it do?
it produces a toxin identical to S. dysenteriae, causes a range from mild diarrhea to hemorrhagic colitis (severe abdominal pain, bloody diarrhea), sometimes vomiting and usually no fever
What STEC serotype is commonly associated with severe disease in the US?
E. coli O157:H7
What syndrome can STEC cause?
it can cause hemolytic uremic syndrome (HUS) which causes renal failure and low platelets, can be a complication especially in young children
What species of Yersinia are we most concerned about?
Yersinia pestis
What are the two forms of Yersinia pestis?
caused the plague; occurs in bubonic or pneumonic form, pneumonic develops secondary to bubonic when the bloodstream and respiratory tract are invaded
How is Yersinia pestis spread?
it is transmitted to humans by the bite of rodent fleas, domestic dogs and cats can become infected with it, the pneumonic plague can spread person to person causing epidemics
What is the most commonly isolated Yersinia species?
Yersinia enterocolitica
Where is Y. enterocolitica found?
various wild and domestic animals including swine, dogs, and cats
What is the most common infection from Y. enterocolitica?
acute enteritis
What is the other relevant species of Yersinia?
Yersinia pseudotuberculosis
Where do we see Yersinia pseudotuberculosis?
it is a pathogen primarily of rodents especially guinea pigs, human infections are rare but associated with close contact with infected animals / their feces
How does Yersinia tuberculosis present in humans?
it is rare but presents as septicemia accompanied by mesenteric lymphadenitis (similar presentation to appendicitis)
Where do we find Escherichia coli?
it is the primary facultative inhabitant of the large intestine, it is the most commonly isolated opportunistic pathogen causing urinary tract and wound infections, pneumonia, meningitis and septicemia
What are the implications for Escherichia coli?
some serotypes and toxin-producing strains are highly virulent primary pathogens, it is the primary cause of “traveler’s diarrhea”
How do we test for Enterobacterales?
we take a specimen; then culture, use antigen detection (for some stool pathogens and their toxins), or molecular detection (like PCR)
How do Enterobacterales appear?
rods that are pink or red in appearance, presence of white blood cells resembling ‘blobs’, happy and plump
