Staphylolococcus Aureus & E.coli

Question 1

What is MRSA?

Answer 1

Methicillin-Resistance Staphylococcus Aureus

Question 2

What are the characteristics of S. aureus?

Answer 2

It is a gram positive cocci, grape-like clusters (staphylo).
Yellow/gold (aureus) pigmented colonies, often B-haemolytic.

Question 3

What characterizes a gram positive bacteria?

Answer 3

A thick peptidoglycan layer in the cell wall.

Question 4

What building blocks is the gram positive cell membrane made of, and how is the cell wall built?

Answer 4

The cell wall is builded of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).

Peptidoglycan building blocks are made intracellularly. The building blocks are transported over the cell membrane.
Transglycolisation happens extracellularly: building blocks are attached to each other in chains.

Question 5

What is transpeptidation?

Answer 5

The peptidoglycan chains in the gram positive cell wall are cross binded. It is facilitated by transpeptidase - penicillin binding protein (PBP).
Penicillin and other betalactam antibiotics bind to PBPs and inhibit the building of peptidoglycan and thereby cell division.

Question 6

How is the S. aureus genome builded?

Answer 6

Consists of a single circular chromosome.
Can also contain one or more plasmids.
Ranges in size from 2.7-2.9 Mbp, encoding 2700-2900 proteins.

Question 7

What infections are caused by S. aureus?

Answer 7

1) Skin and soft tissue infections
2) Septic arthritis, osteomyelitis
3) Endocarditis
4) Prostheses infections
5) Mastitis = Breast infection
6) Sepsis

Question 8

What toxin mediated diseases are caused by S. aureus?

Answer 8

1) Staphylococcal food poisoning
2) Staphylococcal scalded skin syndrome
3) Toxic shock syndrome (tampon associated)

Question 9

What is Staphylococcal food poisoning?

Answer 9

The food is contaminated by a human carrier, like whipped cream, ice cream, processed meat.
The bacteria multiplies in the food and produce a toxin.
The food may be heated and kill the bacteria, but the toxin remain.

Question 10

What is a fundamental biological property of S. aureus?

Answer 10

A property of S. aureus is its ability to asymptomatically colonize healthy individuals.

Question 11

What is the primary mode of transmission of S. aureus?

Answer 11

The primary mode is by direct contact, usually skin-to-skin contact with a contaminated objects and surfaces might also have a role.

Question 12

What three methods are used for S. aureus genotyping?

Answer 12

1) Multi-locus sequence typing (MLST)
2) Pulsed-field gel electrophoresis
3) spa typing

Question 13

What is arginine catabolic mobile element (ACME)?

Answer 13

ACME is a 30.9 kb segment of DNA that seems to be unique to USA300. It contains two potential virulence factors; a cluster of arginine catabolism (arc) genes that encode an arginine deiminase pathway, and opp3 which encodes an oligopeptide permease.

Question 14

How is E.coli in humans?

Answer 14

It is the predominant aerobic bacterium in the gut.
It colonize the gut shortly after birth.
It is both a commensal and an opportunistic pathogen.
E.coli is a gram negative bacteria.

Question 15

What methods are used in detection of E.coli?

Answer 15

1) Chromogenic agar
2) MALDI-TOF MS
3) PCR/sequencing of virulence genes

Question 16

What classes are the pathogenic E.coli devided into?

Answer 16

1) Diarrhoeagenic E.coli
2) Extra-intestinal pathogenic E.coli (EXPEC)

Question 17

How is the virulence of E.coli emerging?

Answer 17

1) Acquisition of new gene(s), mainly through horizontal gene transfer
2) Inactivation of genes
3) Change in function caused by point mutations

Question 18

What is STEC?

Answer 18

STEC is Shiga Toxin-producing E.coli.
It cause disease ranging from watery diarrhoea to bloody diarrhoea and hemolytic uremic syndrome.
Stx1 and Stx2 are the known Shiga toxins.

Question 19

What is EPEC?

Answer 19

EPEC is Enteropathogenic E.coli.
It causes acute watery diarrhoea.
Attaching and effacing lesions in the intestines.

Question 20

What is ETEC?

Answer 20

ETEC is Enterotoxigenic E.coli.
It causes acute watery diarrhoea, afebrile, occasionally severe.
Heat-labile toxin and heat-stabile-toxin

Question 21

What diseases are caused by extra-intestinal pathogenic E.coli?

Answer 21

1) Urinary tract: urinary tract disease, pyelonephritis
2) Abdominal origin: biliary infections, infective peritonitis, pelvic inflammatory
3) Neonatal meningitis
4) Skin and soft tissue disease
5) Hospital aquired pneumoniae
6) Sepsis

Question 22

Name ExPEC virulence factors?

Answer 22

1) Adhesins
2) Iron acquisition systems
3) Protectins and invasins
4) Toxins

Question 23

What methods are used for typing of E.coli?

Answer 23

1) Serotyping
2) Multilocus enzyme electrophoresis (MLEE)
3) Multilocus sequence typing (MLST)
4) Pulsed field gel electrophoresis (PFGE)
5) Multilocus variable-number tandem repeats analysis (MLVA)
6) Whole genome sequencing

Question 24

What two pathovars of E.coli is classified as ExPEC?

Answer 24

1) Uropathogenic E.coli (UPEC)
2) Neonatal meningitis E.coli (NMEC)

Question 25

How is adhesion to host cells achieved by E.coli?

Answer 25

It is achieved by pili.

Question 26

What is a pathogenicity island (PAI)?

Answer 26

It is a large cluster of virulence genes which can be found on plasmids or integrated into the chromosome in pathogenic bacteria.
PAIs are usually flanked by mobile genetic elements.

Question 27

What is Shigella?

Answer 27

Shigella are highly infectious bacteria that cause bacillary dysentery and bloody diarrhoea. This pathovar differs from the other E.coli pathovars, because it includes obligate intracellular bacteria that have neither flagella nor adherence factors, Virulence is largely due to a 220 kb plasmid that encodes a T3SS on the Mxi-Spa locus that is required for invasion, cell survival and apoptosis of macrophages.