Staphylococcus Flashcards
Staphylococcus
- gram positive, cocci, nomotile
- pairs; short chains;clusters
- facultative anaerobes; diversity
Indigenous bacteria
establish residence on surface tissue or alimentary tract; especially the anterior nares
-Staphylococci are part of the normal flora, problem in controlling infection
Coagulase
a biochemical test that differentiates S. aureus form other Staph contributes to the clotting of plasma (converts fibrinogen to fibrin)
S aureus is coagulase positive (major pathogen) and Staph epidermidis is coagulasenegative
Is staphylococcus catalase positive or negative
- staphylococcus is catalase positive
- streptococcus is catalase negative, this help distinguish between the two
catalsae
different gram positive bacteria do or don’t produce catalase under aerobic conditions
Protein A
- unique to staphylococcus aureus
- major protein component of cell wall that is covalently bound to peptidoglycan
- with IgG molecules bound in the “wrong” orientation (in relation to normal antibody function, the igG disrupts opsonization and phagocytossis
Toxins produced by S. aureus
different strains possess different toxins, producing unique diseases
- Hemolysins (a, b, g)
- Leukotoxins
- Enterotoxins (superantigens): toxic shock syndrome
- Exfoliative toxins
Hemolysins
- RBC membrane damaging proteins
- they contribute to pathogenicity by producing tissue damage after the establishment of a focus of infection
Leukotoxin
a two protein toxin, attacks Polymorphonuclear leukocytes (PMNs aa neutrophils) and macrophages
Enterotoxins
large family of Staphylococcus toxins, superantigens
-superantigens cause diarrhea and emesis (vomiting)
-intoxication of preformed enterotoxin, not an infection
-source of enterotoxin is from S. aureus contaminated foods (usually by food-handler)
-symptoms occur within 2-6 hours after ingestion and include cramping, nausea, vomiting, diarrhea with rapid recovery 6-8 hour
heat stable
-Includes Toxic Shock Syndrome
Enterotoxins and TSST bind to
Enterotoxins and TSST bind directly MHC class II and TCR independent of antigen stimulate about 20% of all T cells
What does massive cytokine production lead to
systemic toxicity of host/ suppression of the adaptive immune response
Name two superantigens
Staph enterotoxins (SE) and TSST are superantigens
Exfoliative toxins
2 forms, ETA/ETB proteases
-stimulate lysis of the intracellular attachment between cells of the epidermis
ex: Scalded Skin Syndrome (exclusively a peds illness)
Describe the epidemiology of Staphylococcus
Staphylococcus are normal component of human indigenous flora and are carries asymptomatically at several body sites, especially the anterior nares
Transmission of Staphylococcus
- direct contact by hands is the most important route of transmission
ex: hospital personnel with mild Staph lesion. air borne transmission is possible
Infection of Staph chaacteristics
- typically localized
- intact skin is a major barrier to infection (meaning that cuts make you susceptible)
- skin is the primary site of infection
What are the different infections Staph can cause (and where are they located? 5)
- Folliculitis-hair follicle
- Boil-subcutaneous tissue
- Impetigo-skin infection mixed infection (staph/strep) higly infectious
- Scalded skin syndrome-exfoliative toxins
- Pneumonia-compromised host (CF)
* influenza patients
* antibiotic therapy
* chemotherapy
* immunosuppressants
- other site of infection are osteomyelitis (bone) and arthritis
Treatment of Staphylococcus aureus infections
-No vaccine
-Therapy based treatment:
*drainage of wound
*removal of foreign objects
*antibiotic therapy
-but test for antibiotic sensitivity as there are multiple drugs resistant isolates
75% are methicillin resistant
10% are vancomycin resistant
MRSA
Methicillin Resistant Sthapylococcus aureus (MRSA)
-MR of SA is due to the selection of SA with mutation within the Penicillin Binding Proteins (PBP) that have low affinity for Penicillin
-Vancomycin is used to treat MRSA infections
How do you treat MRSA infections
Vancomycin
Vancomycin resistance in SA
- Staph aureus is resistant to intermediate, but clinically relevant levels of staph aureus. VIRSA
- VIRSA resistance is due to changes in the cell wall, NOT enterococcal mechanism
Community Acquired MRSA
transmitted more easily and cause more skin infections than Hospital Acquired MRSA
- HA-MRSA infection is easily transmitted in hospital infections
- CA-MRSA infection spreads through those living in close contact, such as military barracks, dormitories nd gyms
Staphylococcuus in the normal flora
- other staphylococcus pathogens (coagulase negative)
1. S. epidermidis
2. S. saprophyticus
S. epidermidids
- low virulence
- hospital acquired infection, contamination of surgical site binds to plastics (valves, catheter, prosthetic devices)
- treatment, problem multi-drug resistance so use an antibiogram (analysis of antibiotic sensitivyt locally)
S. saprophyticus
- responisble for urinary tract infections selectively binds to cells of the urinary tract (tropism)
- S. saprophyticus does NOT possess virulence factors found in S. aureus, such as coagulase, enterotoxins, exoenzymes, and extracellular matrix binding proteins
