Gram negative rod

Question 1

Gram negative, aerobe, facultative anaerobic, Catalase positive, oxidase negative, sugar fermenter, most strains are motile as they have flagella

Answer 1

E.coli

Question 2

LPS consists of outer somatic O polysaccharide and lipid A, Capsule K, and Flagella H

Answer 2

E.coli

Question 3

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

Answer 3

E.coli

Question 4

How to differentiate E.coli and Shigella/Salmonella on MacConkey Agar?

Answer 4

E.coli produce bright pink colonies due to lactose fermentation
Shigella and Salmonella produce colorless colonies due to non-lactose fermentation

Question 5

What is the observation of E.coli on blood agar?

Answer 5

No haemolysis

Question 6

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

Answer 6

E.coli

Question 7

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

Answer 7

Virulence factors of E.coli

Question 8

Gram negative, non-motile, non-lactose fermenter, catalase positive, oxidase negative, disease spread person to person by faecal-oral route

Answer 8

Shigella

Question 9

Endotoxins - invasion, multiplication, and resistance to phagocytosis by tissue macrophages
Intestinal adherence factor - colonization
Shiga toxin - disrupts protein synthesis and produces endothelial damage

Answer 9

Virulence factors of Shigella

Question 10

Gastroenteritis (shigellosis)
Bacillary dysentery (bloody diarrhea)

Answer 10

Shigella

Question 11

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

Answer 11

Salmonella

Question 12

What are the species of Salmonella?

Answer 12

Salmonella typhi
Salmonella paratyphi A
Salmonella paratyphi B
Salmonella enterica

Question 13

What disease does S.typhi give?

Answer 13

Enteric fever

Question 14

What disease does S.paratyphi B give?

Answer 14

Enteric fever: typhoid or paratyphoid fever

Question 15

What disease does S.enterica give?

Answer 15

Gastroenteritis (diarrhea, abdominal cramps, fever)

Question 16

How to differentiate Salmonella and Shigella on XLD agar?

Answer 16

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

Question 17

What is the colour of the colonies of E.coli on XLD agar?

Answer 17

Yellow colonies which indicate the bacteria ferment lactose and produce acid.

Question 18

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

Answer 18

Virulence factors of Salmonella spp.

Question 19

How is Salmonella transmitted?

Answer 19

5F, Food, Fluid, Faeces, Flies, and Fingers.

Question 20

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

Answer 20

Klebsiella

Question 21

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

Answer 21

Virulence factors of Klebsiella pneumoniae

Question 22

Lobar pneumoniae
UTI
Bacteremia and sepsis

Answer 22

Klebsiella pneumoniae