gram positive MDR pathogens

Question 1

features of staph. aureus

Answer 1

• g+, non-motile, non-spore forming
• beta haemolytic
• catalase positive

Question 2

diseases by staph

Answer 2

skin infections, food poisoning, Endocarditis (heart valve infections), bacteraemia, pneumonia, osteomyelitis (bone), implant infections

Question 3

virulence factors of staph

Answer 3

• capsule, adhesins (MSCRAMMs that recognise adhesive matrix molecules such as elastin and fibronectin)
• biofilm
• enzymes (DNAases, lipases)
• toxins: superantigens (TSST-1, toxic shock), enterotoxins, cytolytic toxin (alpha-toxin, beta toxin)

Question 4

genomic features of staph

Answer 4

2.8 Mbp
80% of pan-genome is accessory proteins
pan-genome is rich in mobile genetic elements

Question 5

MRSA

Answer 5

mecA gene that encodes alternative penicillin binding protein PBP2a -> methicilin resistance and most beta lactams

Question 6

methicillin

Answer 6

Methicillin is a partially synthetic penicillin that is resistant to beta-lactamase

Question 7

MecA transmission to other organisms

Answer 7

○ SCCmec
○ Mobile 21-60 Kb element
○ Multiple SCCmec types
○ Similar genetic structure, all contain:
§ MecA gene
§ Regulatory gene
§ Only other core elements include the mechanism for picking up and moving genes

Question 8

Enterococcus faecium features

Answer 8

g+, catalase negative, gamma-haemolytic, commensal

Question 9

genomics of e.faecium

Answer 9

2.85, 2/3 accessory proteins
- Pan-genome is heavily enriched for genes involved in carbohydrate transport and metabolism
○ Not mobile genetic elements

Question 10

virulence factors of E. faecium

Answer 10

GelE: gelatinase, hydrolyses compounds (gelatin, collagen), important to prevent complement activation
cyl: cytolysin that can lyse RBC, neutrophils, macrophages
MSCRAMMs that target silico
pili ( ○ PilA + PilF ~ clinical infections ○ PilB: contribute to adherence during UTI)

Question 11

E. faecium clades

Answer 11

HAIs associated with clade A, while clade B represents commensal bacteria
○ Altered cell wall and capsule
○ Lack of a CRISPR system
○ Unique phosphotransfer system
○ Prominent starvation tolerance
Overall better adapted to hospital environment

Question 12

how does e. faecium get genes

Answer 12

HGT (conjugation) not direct uptake (not naturally competent)

Question 13

e. faecium intrinsic resistance

Answer 13

intrinsic resistance to beta lactams PBP5
ampicillin can be used for treatment
poor penetration to aminoglycoside

Question 14

e. faecium vancomycin resistance

Answer 14

○ Change of the D-ala D-ala moiety to D-ala D-lac reduces vancomycin binding affinity by ~1000-fold

Question 15

e. faecium vancomycin resistance comes from?

Answer 15

soil bacterium Amycolatopsis orientalis

Question 16

Amycolatopsis orientalis

Answer 16

inducible expression of VanA (high resistance) or VanB (low resistance) upon exposure to vancomycin (which they can produce)
Phosphorylation cascade allows the rest of the operon to be expressed
○ vanH and vanA produces D-Ala-D-Lac
vanX cleaves D-Ala