Lecture 7: Gram negative bacteria -The Enterics Flashcards
1) Classify the enterics based on biochemical and antigenic classification 2) Pathogenesis of the enterics 3) Diseases caused by the members of family Enterobacteriaceae 4) Diseases caused by the members of the family Vibrionaceae 5) Deiseases caused by the members of family Pseudo monadaceae
The Enterics
- Gram (+) or (-)
- Main groups (4)
Gram (-) bacteria that are part of normal intestinal flora or cause gastrointestinal disease
- Main groups
1) Enterobacteriaceae -E.coli, Klebsiella, Shigella, Salmonella
2) Vibrionaceae -Vibrio
3) Bacteriodaceae -Bacteroides
4) Pseudomonadaceae -Pseudomonas
* Hospital acq’d
Biochemical Classification
- 4 processes
- Major***
1) The Ability to Ferment Lactose***
- Most of the Enterobacteriaceae are lactose fermentors, while Salmonella, Shigella, & Pseudomonas aeruginosa are not
2) Production of H2S
- ability to hydrolyze urea, liquefy gelatin, and decarboxylate specific AAs
3) EMB (Eosin Methylene Blue) Agar
- Methylene blue inhibits gram(+) bacteria and lactose fermentors become deep purple to black in this media
- E.coli shows metallic green sheen on this media
4) MacConkey Agar
- Bile salts in the medium inhibit gram(+) bacteria and lactose fermentors develop a pink-purple coloration
Antigenic Classification
-____major surface antigens
Enterics have 3 major surface antigens
1) O antigen - most external component of LPS, differs from organism to organism
2) K antigen - capsule (kapsule) that covers the O antigen
3) H antigen - makes up the subunits of the bacterial flagella, so only the bacteria that are motile will possess this antigen
Pathogenesis
-2 types of disease
1) Diarrhea, with or without systemic invasion
- Different clinical manifestations depending on depth of intestinal invasion
a) No Cell Invasion -bind to intestinal epithelial cells but do not enter the cell, release of exotoxins
- Enterotoxigenic E.coli & V.cholerae
b) Invasion of Intestinal epithelial cells -virulence factors enable bacteria to bind and invade the cells. Toxins are then released that destroy the cells
e. g Enteroinvasive E.coli, Shigella, and Salmonella enteritidis
c) Invasion of the lymph nodes and blood stream -along with abdominal pain and diarrhea containing WBC and RBC, this invasion results in systemic symptoms of fever, headache, & WBC cound elevation (e.g. Salmonella typhi, Yersinia enterocolitica & Campylobacter jejuni)
2) Various other infections -nosocomial gram (-) including UTI, pneumonia, bacteremia, and sepsis (e.g. E.coli, Klebsiella pneumoniae, Proteus mirabilis)
Family Enterobacteriaceae
Escherichia coli
- normal resident of colon w/o disease
- acquires virulence by conjugation w/plasmid exchange, lysogenic conversion by temperate bacteriophages & direct transposon mediated DNA insertion
- NON-pathogenic E.Coli+Virulence factors=Disease
Family Enterobacteriaceae
-Virulence factors
- Mucosal adherence w/pili and ability to invade intestinal epithelial cells
- Exotoxin production by heat-labile(LT) & stable (ST) and shiga-like toxin
- Endotoxin
Escherichia coli
- Diseases
- > Diarrhea
may affect infants, children, or adults
1) Enterotoxigenic E.coli (ETEC)
- causes traveller’s diarrhea
- has pili that bind to intestinal epithelial cells where it releases heat labile (LT) exotoxin
- osmotic pull of the ions causes water and electrolyte loss
2) Enterohemorrhagic E.coli (EHEC)
- secrete shiga-like toxin or verotoxin
- inhibit protein synthesis by inhibiting the 60S ribosome resulting in intestinal epithelial cell death
- diarrhea is bloody, called hemorrhagic colitis, no fever, no pus, secretes shiga-like toxin
- hemolytic uremic syndrome (HUS) with anemia, thrombocytopenia and renal failure (uremia) associated with a strain of EHEC called E.coli 0157:H7, source- infected meat
3) Enteroinvasive E.coli (EIEC)
- same as caused by Shigella
- main virulence factor encoded in a plasmid shared by Shigella and E.coli
- produces small amts of shiga-like toxin
- host tries to get rid of invading bacteria resulting in immune-mediated inflammatory rxn w/fever
- WBC invade intestinal wall and diarrhea is bloody with WBC like shigellosis
Escherichia coli
- Diseases
- >UTIs
- pili helps E.coli to travel up the urethra and infect the bladder (cystitis) and sometimes move up to infect the kidney (pyelonephritis)
- most common cause of UTI in women and hospitalized patients with catheters in urethra
- TX: Trimethoprine & Nitrofurantoin
Escherichia coli
- Diseases
- > Other
1) E.coli Meningitis
- common cause of neonatal meningitis (group B streptococcus is 1st). During the first month of life, neonate is very susceptible
2) E.coli Sepsis
- most common cause of gram(-) sepsis
- usually occurs in debilitated hospital patients
- septic shock due to Lipid A component of LPS
3) E.coli pneumonia
- common cause of hospital acq’d pneumonia
Klebsiella pnuemoniae
- capsule?
- motility?
- causes what?
- who is prone?
- encapsulated (prominent)
- non-motile (no H antigen)
- 2nd most common cause of hospital acq’d sepsis
- cause of UTI in hospitalized patients with Foley catheters
- Hospitalized and alcoholics are prone to a Kelbsiella pneumoniae pneumonia, characterized by a bloody sputum in 50% cases
- pneumonia is violent and destroys lung tissue, producing cavities
Shigella
- species
- motility?
- lactosee fermentation?
- H2S?
- hosts?
- susceptible pop?
- transmission?
- illness
4 species: dysenteriae, flexneri, boydii, and sonnei
- non-motile, no flagella
- no lactose fermentation
- no H2S
- Humans only host, strikes pre-school kids and populations in nursing homes
- transmission: fecal-oral
- similar to enteroinvasive E.coli invading intestinal epithelial cells and releasing shiga toxin
- illness begins with fever, abdominal pain, and diarrhea. colonoscopy reveals shallow ulcers in colon
- diarrhea may contain flecks of bright red blood and pus
Shiga Toxin
- found in?
- mech
found in Shigella, EHEC, and EIEC
- 1A and 5B subunits
- B subunits bind to microvillus in colon allowing the entry of the deadly A subunit
- A subunit inactivates the 60S ribosome, inhibiting protein synthesis and killing the intestinal epithelial cells
Salmonella
- lactose fermentation?
- motility?
- H2S?
- structure
- 3 groups
- how does it differ from other enterics?
- acquired how?
- exception
- Non-lactose fermenter
- Motile
- produces H2S
- has a Vi antigen, a polysaccharide capsule surrounding the O antigen, protecting it from antibody attack on the O antigen
- 3 groups: Salmonella typhi, S.choleraesuis and S.enteridis
- differs from other enterics as it lives in the GI tracts of animals and infects humans when there is contamination of food and water by animal feces.
- most commonly acquired from eating chicken and uncooked eggs
- S.typhi is exception, carried only be humans
Salmonella
- Diseases
- >Typhoid fever
Typhoid Fever -caused by Salmonella typhi, aka enteric fever
- after invading the intestinal epithelial cells, it invades the regional lymph nodes, finally seeding multiple organ systems
- bacteria are phagocytized by monocytes and can survive intracellularly
- *S.typhi is a facultative intracellular parasite
- Salmonellosis starts 1-3 wks afer exposure and includes fever, headache, and abdominal pain, either diffuse or localized to the right lower quadrant
- the spleen may enlarge, patient may develop diarrhea and rose spots on the abdomen
- Ciprofloxacin or ceftriaxone are appropriate therapy
Carrier State -some people recovering from typhoid fever become chronic carriers, harboring S.typhi in their gallbladders and excreting bacteria constantly
Salmonella
- Diseases
- > Sepsis
- systemic dissemination usually caused by Salmonella choleraesuis and does not involve the GI tract
- the immune system clears encapsulated bacteria by opsonizing them with antibodies and then macrophages and neutrophils in the spleen phagocytose the bacteria
- patients who have lost their spleens (asplenic) either from trauma or from sickle cell disease have difficulty in clearing encapsulated bacteria
- patients with sickle cell anemia are prone to Slamonella osteomyelitis (bone infection)
