M6- Staphylococcus Flashcards
Describe staphylococcus species.
- Gram +ve
- Non-motile
- Irregular grape like clusters
- aerobe + facultative anearobe
- Catalase +ve (usually)
- Oxidase -ve
- Coagulase +ve or -ve
- Tolerate 15% NaCl
what shape is coccus?
round
what is facultative anaerobe?
grow anaerobically
who carries S.epidermis?
Found in everyones skin and mucosal membranes and only cause problems in immunocompromised individuals (cannula, burns, catheter)
what is a nosocomial infection?
hospital acquired infection
who carries S.aureus?
3 different states:
- permanent carrier
- never carry it
- transient carrier
Describe transmission of staphylococci.
-Contact:
direct- hand , skin, mucous
Indirect- instruments
-Air-borne- shedding of cocci from infected site into atmosphere
Describe entry (opportunistic).
- Hair follicles and sebaceous glands
- damaged/diseased skin
- broken skin
- catheters/implants
Describe pathogenicity of S. aureus.
• Superficial lesions – Boil to abscesses • Systemic – life-threatening • Toxinoses – Toxic Shock (only females) – Scalded Skin Syndrome
Name some virulence factors of staphylococcus aureus.
- fibrinogen binding protein -adhesin
- Leukocidin -kills leukocytes
- TSST-1 -shock, rash, desquamation
what does fibronogeon promote?
clot formation
Evasion of host defences.
- protein A
- proteases
- superantigens
- lipases.
- coagulase
- capsule
what is toxinoses.
single component or toxin that causes damage to the host (true poison )
what are super antigens?
- binds outside super variable cleft
- antigen is not processed by PMN, binds directly to MHCII complex i.e outside conventional binding groove
what do super antigens cause?
Massive release of cytokines and inappropriate immune response
what does protein A bind?
binds Fc portion of IgG antibodies
when is protein A produced?
during exponential growth
what do proteases do?
– Cleave antibodies, defensins, Platelet Microbiocidal
Proteins (PMPs)
– destruction of host tissue
what do lipase,phospholipases, esterase do?
– combat surfactants produced to disrupt bacterial membrane
– post-exponentially expressed scavenging enzymes
what is PVL?
panton - valentine leukocidin
- severe skin infections (sepsis, necrotising fascitis)
- linked to necrotising pneumonia (MRSA)
Describe features of necrotising pneumonia.
-rapid progression : acute respiratory disease, deterioration in pulmonary function , multi-organ failure despite antibiotic therapy -young -community acquired -more than 75% mortality
Describe coagulase.
- 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
Describe capsule.
– 90% clinical isolates produce capsular polysaccharides
– 2 types Mucoid & Microcapsule
What is the antibiotic treatment .
50-80% resistant (ß-lactamase +ve)
• Flucloxacillin (meticillin) β-lactamase resistant
• Penicillin
• Erythromycin
summary slide.
• 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.
Describe how S.aureus can affect patients?
– 20%-(60%) colonisation (carriage) – anterior nares & perineum – nosocomial & community – nasal strain can protect – MRSA
