micro lecture 13

Question 1

list 9 facts about Gastrointestinal gram-negative rods

Answer 1

GI tract commensals of humans and other animals

Also in soil and water

Often very sensitive to drying

Facultative anaerobes

Lipopolysaccharide (LPS)
Antigenic
Potential endotoxin

Diverse taxonomy

Only a fraction of the total organisms within the GI tract

Can cause diseases in the GI tract, within the body or both

Faecal contamination is the route of transmission (faecal-oral)

Question 2

list facts about Escherichia coli (E. coli)

Answer 2

Originally Bacterium coli (for colon) and renamed in honour of Theodor Escherich

Normal flora in colon of humans and other animals

Pathogenic within and outside GI tract

Fimbriae / pili adhere to mucosal surfaces

Motile or non-motile

Ferment lactose (Lac+)

Question 3

list the three structural antigen of Escherichia coli (E. coli)

Answer 3

O antigens: On cell wall

H antigens: Flagellae

K antigens: Capsule / mucoid layer

Question 4

Escherichia coli (E. coli) G+ OR G-

Answer 4

G-

Question 5

is Escherichia coli - intestinal disease transmitted by faecal/oral route

Answer 5

yes

Question 6

describe Enterotoxigenic (ETEC) as an intestinal-pathogenic type of Escherichia coli - (intestinal disease) with differing pathogenic mechanisms

Answer 6

Travellers diarrhoea – most common cause

Transmission: food / water, human waste, person-to-person

Colonise small intestine

Two enterotoxins (toxin produced affecting the intestines)

Hypersecretion of chloride and water

Inhibition of sodium reabsorption

Gut becomes full of fluid – watery diarrhoea

Question 7

describe Enteropathogenic (EPEC) as an intestinal-pathogenic type of Escherichia coli - (intestinal disease) with differing pathogenic mechanisms

Answer 7

Diarrhoea in infants (poor sanitation)

Newborns infected during birth

Attach to small intestine

Shiga-like (named after Kiyoshi Shiga) toxins

Destruction of microvilli, development of lesions
Watery diarrhoea (chronic)

Question 8

describe Enterohaemorrhagic (EHEC) as an intestinal-pathogenic type of Escherichia coli - (intestinal disease) with differing pathogenic mechanisms

Answer 8

Most notorious strain O157:H7

Binds to cells in large intestine

Verotoxins in large amounts

These affect host cell protein synthesis

Severe copious bloody diarrhoea (haemorrhagic colitis)

may progress to haemolytic uraemic syndrome (HUS):
Fever, acute renal failure, anaemia
Common in children 5-10yrs
(still under 10% of cases)

Question 9

should you avoid antibiotics for Enterohaemorrhagic (EHEC) E.coli?

Answer 9

yes

Question 10

describe Enteroinvasive (EIEC) ​as an intestinal-pathogenic type of Escherichia coli - (intestinal disease) with differing pathogenic mechanism

Answer 10

No toxins but cause direct mucosal damage due to invasive infection

Dysentery-like syndrome

Fever and bloody stools

Question 11

list things to avoid and treatment for Escherichia coli enteritis (E.coli)

Answer 11

Care in selection, preparation and consumption of food and water

Maintain fluid and electrolyte balance

Antibiotics can shorten duration
(probably avoid if enterohaemorrhagic)

Resistance is widespread and readily spread

Question 12

what is the source of Escherichia coli extra-intestinal disease

Answer 12

Urinary tract infections (UTIs)
*Most common cause
  -Cystitis, pyelonephritis
  -Women most at risk (anatomy)
   Virulence
*Fimbriae (adhesion), haemolysin, resistance to  
 immune system activity (capsule)

Question 13

what is the clinical significance of Escherichia coli extra-intestinal disease

Answer 13

*Neonatal meningitis
-Major cause within first month of life
-K1 antigen – major virulence factor (capsule that
evades immune system)

• Nosocomial infections
  
  • Sepsis / bacteraemia

Question 14

what are the treatment for Escherichia coli extra-intestinal disease

Answer 14

Antibiotics often required (except EHEC / STEC ?)

β-lactams: (penicillin V+G, NO!  Amox)
broader penicillins (and β−lactamase inhibitors) better

cephalosporins: use 2nd generation and upwards

ESBL strains: carbapenems effective (but, …)

nitrofurantoin, ciprofloxacin, trimethoprim +/- sulphamethoxazole, fosfomycin, …

Resistance possible (and increasing) to “all” agents

Question 15

list fact about salmonella

Answer 15

Widely distributed in nature

Do not ferment lactose (Lac-)

Typhi – exclusively human pathogen

Others – other animals and foods

Epidemics in crowded situations

Invade epithelial cells of the small intestine

Disease may become systemic

Intracellular, survive in phagocytes

Question 16

another word for salmonellosis

Answer 16

Gastroenteritis

Question 17

state facts about Gastroenteritis (salmonellosis)

Answer 17

Serotype: typically non-typhi

Localised

Nausea, vomiting, non-bloody diarrhoea

Develops within 48hrs

Fever and abdominal cramping

Self-limiting, generally … but:
1.2 million illnesses and 450 deaths occur due to non-typhoidal Salmonella annually in the USA

Question 18

another term for Typhoid fever

Answer 18

enteric fever

Question 19

state facts about Typhoid fever (enteric fever)

Answer 19

Serotype: typhi

Incubation period 5-21 days

Severe, life-threatening, systemic illness

Fever and abdominal symptoms

Also: headache, chills, sweats, weakness,
sore throat, cough, myalgia

In the USA, estimated approx 5,700 cases annually. Mortality rate 15%

Question 20

what are the treatments and prevention for Salmonella

Answer 20

Treatment and prevention
  -Gastroenteritis (non-typhi strain)
  -Antibiotics may not be useful
   (can prolong convalescence)
  -Use supportive treatment alone ? 

Enteric fever
fluoroquinolones, β-lactams, macrolides

Prevention
proper sewage disposal, correct food handling