Enterobacteriae Flashcards
What is the significance of agglutinin titres in the context of typhoid?
Agglutinins appear by the end of the first week, with titres increasing until the third or fourth week, after which they decline gradually.
Significant titres: 1/100 or more for ‘O’ agglutinins and 1/200 or more for H agglutinins.
What antibodies are present in individuals immunized with the TAB vaccine?
Antibodies to S. typhi, S. paratyphi ‘A’, and ‘B’.
In case of infection, antibodies will be seen only against the infecting species.
What is the Vi polysaccharide vaccine and its administration details?
It contains purified Vi capsular polysaccharide from Ty2 strain, given as a single dose by subcutaneous or intramuscular route, with re-vaccination every 3 years for individuals ≥ 2 years of age.
It can be co-administered with other vaccines, e.g., yellow fever and hepatitis A.
What are the characteristics of the Ty 21a Oral vaccine?
It is an orally administered live attenuated vaccine containing > 10º viable organisms of live attenuated Ty 21a strain, administered on days 1, 3, and 5, with a recommendation to repeat every 3 years for endemic areas and yearly for travelers from non-endemic to endemic countries.
The Ty 21a strain lacks the enzyme UDP-galactose-4-epimerase (Gal E mutant).
What is the drug of choice (DOC) for treating typhoid cases?
Ceftriaxone.
Ciprofloxacin should be used if the strain is sensitive to ciprofloxacin.
What is the treatment for typhoid carriers?
Ampicillin or amoxicillin for 6 weeks.
Describe the characteristics of Proteus bacteria.
Gram negative, motile, non-capsulated, pleomorphic bacilli that appear in various forms (coccobacilli, bacillary, filamentous) and are non-lactose fermenters.
Includes Proteus vulgaris, Proteus mirabilis, Morganella, and Providencia.
Which bacteria are urease positive?
Proteus vulgaris, Proteus mirabilis, and Morganella.
Providencia is the exception, as it is urease negative.
What does a positive result in the PPA test indicate?
It indicates urease positivity and H2S production, used for P. mirabilis and P. vulgaris.
What are the indole test results for P. vulgaris and P. mirabilis?
Positive for P. vulgaris, negative for P. mirabilis.
What characteristic odor do Proteus cultures produce?
Characteristic putrid ‘fishy’ or ‘seminal’ odor.
What is the mechanism of action of the active fragment A in the plasmid-coded toxin?
Causes ADP ribosylation of G protein, upregulates adenylate cyclase, leading to cyclic AMP production and resulting in water and electrolytes secretion, causing diarrhea.
What does Fragment B of the plasmid-coded toxin bind to?
Binds to GM1 ganglioside receptors on intestinal epithelium.
What is the mechanism of action of the heat-stable toxin (ST) produced by Enterotoxigenic E. coli?
Binds to guanylate cyclase, leading to cyclic GMP production and diarrhea.
What is Verocytotoxin also known as?
Shiga-like toxin.
What is the mechanism of action of Shiga-like toxin?
Fragment B binds to globotriosyl ceramide (Gb3) receptor on intestinal cells; Fragment A inhibits protein synthesis.
How is Shiga-like toxin coded?
Bacteriophage coded.
What are the two types of surface antigens in E. coli?
- O antigen (somatic lipopolysaccharide)
- K antigen (capsular antigen/envelope antigen)
What is the role of the O antigen in E. coli?
Has endotoxic activity, protects bacteria from phagocytosis and bactericidal effects of complement.
What is the function of the K antigen in E. coli?
Affords protection against phagocytosis and antibacterial factors in normal serum.
What is the significance of fimbriae in uropathogenic E. coli?
Plasmid coded, important in urinary tract infections (UTI); no role in gastroenteritis.
What disease is caused by Enterotoxigenic E. coli (ETEC)?
Traveler’s diarrhea and infant diarrhea in developing countries.
What is the site of action for Enteropathogenic E. coli?
Small intestine.
What type of diarrhea is caused by Enteropathogenic E. coli?
Watery diarrhea in infants and children, with non-bloody stools.
