Enteric Bacteria and Coliforms- Felton Flashcards
What are the basic types of enteric bacteria?
- Either inhabits the gut as endogenous flora or infects the gut and causes disease there.
- Vast majority = obligate anaerobes (both G+/-)
- Also facultative species (mostly G-)
What are the basic characteristics of Enterobacteriaceae (Aka fecal coliforms)?
- Gram negative facultative rods.
- Non-spore forming.
- Can be grown on ordinary microbiological culture media.
- Ferment glucose.
- Oxidase negative.
- Reduce nitrate to nitrite.
- Have pili.
- Have LPS (endotoxin)
- Capable of causing infection anywhere in the body.
- Responsible for most of the nosocomial (hospital-acquired) infections.
- Most are commensals.
- The genera w/n these families are: Escherichia, Shigella, Salmonella, Klebsiella, Enterobacter, Serratia, Proteus, Yersinia, and many others.
How are Enterobacteriaceae classified?
-Classification based on antigenic structure:
1. O antigens: somatic antigen in the outer membrane. Component of LPS.
•Assigned numbers like O44 or O157 and used in antigenic typing.
2. Flagellar antigens (H antigens)
•Composed of protein subunits called flagellin.
•Heat labile.
•Can undergo antigenic variation: switching H antigen types.
3. Capsular antigens (K or Vi antigens)
•Typically consist of polysaccharides.
•Partially heat stable.
•Can sometimes inhibit the O antigen.
•Examples:
oVi antigen of Salmonella typhi.
oK1 antigen of E. coli.
What are the 3 parts of LPS? What can LPS activate?
Composed of 3 parts: 1. Lipid A = toxic active part. 2. R core = short non-repeating oligosaccharide. •Pretty conserved amongst bacteria. 3. O antigen = repeating polysaccharide. •Variable amongst bacteria. •Smooth bacteria = full-length O antigen •Rough = lost O antigen but have R core.
oHeat stable and toxic
oCan activate clotting pathway, complement pathway and interact w/ cells of the immune system like macrophages and B-cells to release cytokines and lymphokines.
oActivation of clotting cascade could cause disseminated intravascular coagulation (DIC).
Which genera infects: 1. CNS? 2. Lower Respiratory tract? 3. Blood stream? 4. GIT? 5. Urinary tract? 6. Bones?
- Escherichia
- Klebsiella, Enterobacter, Escherichia
- Escherichia, Klebsiella, Enterobacter, Salmonella
- Salmonella, Shigella, Yersinia, Escherichia
- Escherichia, Proteus, Providencia, Klebsiella
- Salmonella
What are the characteristics of Escherichia (example E. coli)?
•Found in intestinal tract of humans and animals.
•Motile
•Ferment lactose.
•Medias to see E. coli lactose fermentation:
oEMB media = Metallic green sheen (lactose positive)
oMacConkey = Purple color with halo (precipitating bile) = (lactose positive)
•Have ~4300 genes.
•Most commonly caused by endogenous gut flora.
•Many different types: 170 O antigens, 56 H antigens and 100 K antigens.
•Antibiotics are rarely used in these diseases. Can sometimes make the symptoms worse. Fluid and electrolyte replacement are main treatments.
What are the extraintestinal diseases associated with Escherichia?
- UTI:
oE. coli is the most common cause ~80% of all cases.
oOriginate from endogenous bowel flora.
oUsually possess pili, hemolysin and the ability to resist complement-mediated killing. - Bacteremia/Sepsis:
oE. coli is the most common cause and is usually associated w/ UTI. - Neonatal meningitis:
oE. coli and group B strep are the most common causes.
oUsually contain K1 capsular antigen. - Abdominal abscess:
oWhen colon contents escape from the bowel lumen into the peritoneum through a perforated diverticulum or other bowel perforation they can cause an abdominal abscess or peritonitis. These are typically mixed infections involving both facultative and anaerobic bacteria, and E. coli is frequently involved.
What are the types intestinal infections associated with Escherichia?
Two categories of diarrheal diseases:
- Secretory diarrhea: high volume of watery stools, little or no fever, and absence of blood in stools.
- Dysentery: low volume of stools containing blood, mucus, and sometimes pus, high fever, and straining and painful defecation.
What are the types of diarrheagenic E. coli?
- Enterotoxigenic E. coli (ETEC)
- Enteropathogenic E. coli (EPEC)
- Enteroaggregative E. coli (EAggEC)
- Enteroinvasive E. coli (EIEC)
- Enterohemorrhagic E. coli (EHEC)
Describe Enterotoxigenic E. coli (ETEC).
- Gastroenteritis caused by ETEC is due to two exotoxins: a heat-labile toxin and a heat-stable toxin.
- The heat-labile toxin activates adenylate cyclase, resulting in hypersecretion of fluids and electrolytes into the lumen of the small intestine.
- Similar to that of the Vibrio cholerae enterotoxin.
- The heat-stable toxin activates guanylate cyclase, and it too stimulates fluid secretion.
- ETEC are an important cause of traveler’s diarrhea.
- Due to eating fruit w/o washing or bad water supply. This infection of the small intestine has a 1-2 day incubation period and persists for ~3-4 days. Symptoms are mild, with watery, non-bloody diarrhea, cramps, nausea, and vomiting most commonly experienced.
Describe Enteropathogenic E. coli (EPEC).
- Cause childhood diarrhea, particularly in developing countries.
- Usually in institutional outbreaks of diarrhea, especially in nurseries.
- The site of infection is the small intestine, where they adhere to the mucosal epithelium in a focal pattern (“localized adherence”), forming piled-up three-dimensional microcolonies. They produce characteristic “attaching and effacing lesions” on the mucosa of the small intestine with destruction of microvilli and “intimate” attachment to cell membrane at sites of “pedestal” formation.
- Symptoms include fever, nausea, vomiting, and non-bloody stools. Sometimes referred to as Enteroadherent E. coli (EAEC). Can be life-threatening.
Describe Enteroaggregative E. coli (EAggEC).
- Also sometimes referred to as Enteroadherent E. coli (EAEC).
- Affects small intestine, causing persistent diarrhea in infants. Low grade fever, sometimes bloody stools.
- Adhere to gut epithelial cells in an aggregative manner, with formation of single-layered two-dimensional arrays of bacterial cells resembling “stacked bricks” lying flat on the epithelial surface. Another pattern of adherence that is seen is called diffuse adherence, and these strains are referred to as diffusely adherent E. coli (DAEC).
Describe Enteroinvasive E. coli (EIEC).
•These strains are able to invade and destroy the epithelium of the large intestine, producing a disease similar to bacillary dysentery (shigellosis), with a high incidence of fever and bloody diarrhea. Rare in the US.
Describe Enterohemorrhagic E. coli (EHEC)
- These E. coli produce a cytotoxin called verotoxin, and are not invasive.
- Usually cause mild diarrhea but can cause hemorrhagic colitis, with severe abdominal pain, and bloody diarrhea with little or no fever (rare though).
- Outbreaks of EHEC hemorrhagic colitis transmitted in undercooked ground beef in fast food restaurants often involve strains of antigenic type O157:H7. An uncommon, but serious, complication of infection with EHEC stains is hemolytic-uremic syndrome (HUS) in infants and young children. HUS is also verotoxin-mediated; bacteria are not found in the blood stream but the toxin is. EHEC usually comes from GI tract of animals.
What are the basic characteristics of Klebsiella?
•Non-motile.
•Encapsulated.
•Lactose-fermenting.
•Have a capsule that gives it a mucoid (gooey) appearance on colonies and increased virulence.
•Example:Klebsiella pneumoniae:
oAssociated w/ community-acquired lobar pneumonia.
oUsually an opportunistic pathogen (affects alcoholics etc.)
oAlso causes wound, soft tissue and UT infections.
oHave currant jelly sputum (compared to rusty color seen in pneumococcus)
