Gram negative rod Flashcards
Gram negative, aerobe, facultative anaerobic, Catalase positive, oxidase negative, sugar fermenter, most strains are motile as they have flagella
E.coli
LPS consists of outer somatic O polysaccharide and lipid A, Capsule K, and Flagella H
E.coli
MacConkey Agar
- Pink colonies as they produce acid that lowers the pH value which means they are lactose-fermenting bacteria
- Clear zones surrounding the colonies indicate bile salt precipitation
E.coli
How to differentiate E.coli and Shigella/Salmonella on MacConkey Agar?
E.coli produce bright pink colonies due to lactose fermentation
Shigella and Salmonella produce colorless colonies due to non-lactose fermentation
What is the observation of E.coli on blood agar?
No haemolysis
Directly invades the intestinal mucosa or produces toxins to cause intestinal infections (Gastroenteritis)
Directly invades the urinary tract causing UTIs or cause intra-abdominal infections
Enter the bloodstream and cause septicemia, meningitis, and other systemic manifestations
Neonatal meningitis due to poor hygiene from the mother and pass it onto neonates
E.coli
Adhesins - prevent the bacteria from being eliminated
Hemolysins - important in the pathogenesis of disease
Enterotoxins
Shiga toxins - damages the lining of the intestinal wall, causing bloody diarrhea
Heat stable toxin (ST) - causes increased secretion of fluids
Heat labile toxin (LT) - watery diarrhea due to hypersecretion of fluid into the lumen of gut
Virulence factors of E.coli
Gram negative, non-motile, non-lactose fermenter, catalase positive, oxidase negative, disease spread person to person by faecal-oral route
Shigella
Endotoxins - invasion, multiplication, and resistance to phagocytosis by tissue macrophages
Intestinal adherence factor - colonization
Shiga toxin - disrupts protein synthesis and produces endothelial damage
Virulence factors of Shigella
Gastroenteritis (shigellosis)
Bacillary dysentery (bloody diarrhea)
Shigella
Gram negative, facultative anaerobes, oxidase negative, fermenter (produce acid and hydrogen sulphide gas from mannose and glucose), most infections are by eating contaminated food products
Salmonella
What are the species of Salmonella?
Salmonella typhi
Salmonella paratyphi A
Salmonella paratyphi B
Salmonella enterica
What disease does S.typhi give?
Enteric fever
What disease does S.paratyphi B give?
Enteric fever: typhoid or paratyphoid fever
What disease does S.enterica give?
Gastroenteritis (diarrhea, abdominal cramps, fever)
How to differentiate Salmonella and Shigella on XLD agar?
Salmonella only ferments xylose. As xylose exhausted, Salmonella will utilise lysine which gives rise to amines, producing pink colonies. Salmonella also reduces hydrogen sulphide, thus, producing pink colonies with black center.
Shigella does not utilise any of the sugars and remain pink in colour.
Pink colonies = alkaline
Yellow = acidic
Black at center = reduces hydrogen sulphide
What is the colour of the colonies of E.coli on XLD agar?
Yellow colonies which indicate the bacteria ferment lactose and produce acid.
Endotoxin
Type III secretion systems - secretion of virulence factors into host cells
Fimbriae - mediate binding to M cells present in Peyer patches of the small intestine
ATR gene - protects from stomach acids and the acid pH of the phagosome
Catalase - protects the bacteria from intracellular killing in macrophages
Superoxide dismutase - protects the bacteria from intracellular killing in macrophages
Virulence factors of Salmonella spp.
How is Salmonella transmitted?
5F, Food, Fluid, Faeces, Flies, and Fingers.
Gram negative, rod shaped, non-motile bacteria, a prominent polysaccharide capsule, thicker and shorter facultative anaerobes, lactose-fermenting, large mucoid red/pink colonies on MacConkey agar
Klebsiella
Capsule - prevents the bacteria from phagocytosis
Multiple adhesins - help the bacteria to adhere to host cells, which is crucial to initiate the disease process
LPS - prevents membrane damage and death of bacteria
Virulence factors of Klebsiella pneumoniae
Lobar pneumoniae
UTI
Bacteremia and sepsis
Klebsiella pneumoniae
