M6- Staphylococcus

Question 1

Describe staphylococcus species.

Answer 1

• Gram +ve
• Non-motile
• Irregular grape like clusters
• aerobe + facultative anearobe
• Catalase +ve (usually)
• Oxidase -ve
• Coagulase +ve or -ve
• Tolerate 15% NaCl

Question 2

what shape is coccus?

Answer 2

round

Question 3

what is facultative anaerobe?

Answer 3

grow anaerobically

Question 4

who carries S.epidermis?

Answer 4

Found in everyones skin and mucosal membranes and only cause problems in immunocompromised individuals (cannula, burns, catheter)

Question 5

what is a nosocomial infection?

Answer 5

hospital acquired infection

Question 6

who carries S.aureus?

Answer 6

3 different states:

• permanent carrier
• never carry it
• transient carrier

Question 7

Describe transmission of staphylococci.

Answer 7

-Contact:
direct- hand , skin, mucous
Indirect- instruments

-Air-borne- shedding of cocci from infected site into atmosphere

Question 8

Describe entry (opportunistic).

Answer 8

• Hair follicles and sebaceous glands
• damaged/diseased skin
• broken skin
• catheters/implants

Question 9

Describe pathogenicity of S. aureus.

Answer 9

•  Superficial lesions 
–  Boil to abscesses
•  Systemic
–  life-threatening
•  Toxinoses
–  Toxic Shock (only females)
–  Scalded Skin Syndrome

Question 10

Name some virulence factors of staphylococcus aureus.

Answer 10

• fibrinogen binding protein -adhesin
• Leukocidin -kills leukocytes
• TSST-1 -shock, rash, desquamation

Question 11

what does fibronogeon promote?

Answer 11

clot formation

Question 12

Evasion of host defences.

Answer 12

• protein A
• proteases
• superantigens
• lipases.
• coagulase
• capsule

Question 13

what is toxinoses.

Answer 13

single component or toxin that causes damage to the host (true poison )

Question 14

what are super antigens?

Answer 14

• binds outside super variable cleft

- antigen is not processed by PMN, binds directly to MHCII complex i.e outside conventional binding groove

Question 15

what do super antigens cause?

Answer 15

Massive release of cytokines and inappropriate immune response

Question 16

what does protein A bind?

Answer 16

binds Fc portion of IgG antibodies

Question 17

when is protein A produced?

Answer 17

during exponential growth

Question 18

what do proteases do?

Answer 18

– Cleave antibodies, defensins, Platelet Microbiocidal
Proteins (PMPs)
– destruction of host tissue

Question 19

what do lipase,phospholipases, esterase do?

Answer 19

– combat surfactants produced to disrupt bacterial membrane
– post-exponentially expressed scavenging enzymes

Question 20

what is PVL?

Answer 20

panton - valentine leukocidin

• severe skin infections (sepsis, necrotising fascitis)
• linked to necrotising pneumonia (MRSA)

Question 21

Describe features of necrotising pneumonia.

Answer 21

-rapid progression : 
acute respiratory disease, deterioration in pulmonary function , multi-organ failure despite antibiotic therapy 
-young 
-community acquired 
-more than 75% mortality

Question 22

Describe coagulase.

Answer 22

• Coagulase forms Staphylothrombin promotes conversion of fibrinogen to fibrin and clotting
• Coagulase may also assist deposition of fibrin on surface and prevent phagocytes recognising them

Question 23

Describe capsule.

Answer 23

– 90% clinical isolates produce capsular polysaccharides

– 2 types Mucoid & Microcapsule

Question 24

What is the antibiotic treatment .

Answer 24

50-80% resistant (ß-lactamase +ve)
• Flucloxacillin (meticillin) β-lactamase resistant
• Penicillin
• Erythromycin

Question 25

summary slide.

Answer 25

• S. aureus & S. epidermidis
• S. aureus
– major pathogen, variety of diseases
• Wide number of virulence associated proteins – virulence factors
• Different strains carry different virulence factors.
• Virulence factors;
– enable colonisation/adhesion,
– evasion of host defenses, & damage to the host.
• Antibiotic treatment/therapy, MRSA & resistance.

Question 26

Describe how S.aureus can affect patients?

Answer 26

–  20%-(60%) colonisation (carriage)
–  anterior nares & perineum
–  nosocomial & community
–  nasal strain can protect
–  MRSA