Gram Positive Cocci

Question 1

Staphylococcus

Answer 1

Cells in clusters
Adapted to skin - normal flora
Hardy - easily spread
Aerobic metabolism - Catalase positive

Question 2

Staphylococcus aureus

Answer 2

Yellow colour
Produces coagulase - clots plasma
Inhabit anterior nares
carried by 1/3 of people
most common human pathogen

Question 3

Staphylococcal virulence factors

Answer 3

Coagulase
Protein A - binds Ig
α-, β- , δ- and γ- toxins - RBC lysis
Leukocidin - leukocyte

Question 4

Staphylococcus aureus toxins

Answer 4

Heamocydin & Leukocydin - Lyse RBC, damage membranes, kill neutrophils
Super antigen toxins: Link MHC to TCR Vβ non - specifically activate many T-cells with overproduction of cytokines

Toxic Shock Syndrome Toxin

Enterotoxins - SAg with second enterotoxic domain - produces food poisoning

Question 5

Staphylococcus aureus - disease

Answer 5

Abcesses
Wound Infections
Osteomyelitis
Septicemia
Toxic Shock Syndrome

Question 6

Endocarditis

Answer 6

Staph and Strep both cause endocarditis.

Viridans Strep, Group D strep and Enterococcus faceless all cause subacute endocarditis.

Question 7

Staphylococcus aureus - antibiotic resistance

Answer 7

Penicillin introduced 1945
Penicillin resistant plasmids omnipresent by 1955
Development of ‘Anti-staph’ penicillins
MRSA - resistant to all β-lactams
Vancomycin for MRSA
VRSA appeared, rare. Genes transferred form enterococci

Question 8

Staphylococcus epidermidis & other coagulase-negative staphylococci

Answer 8

Natural habitat - Skin
Fewer virulance - factor genes
Wound infections, catheter infections, etc.

Question 9

Streptococcus Identification

Answer 9

Heamolysis

Cell-wall antigen

Question 10

Types of Haemolysis

Answer 10

β-Haemolysis - Complete haemolysis
α-Haemolysis - Red-cell damage, Hb turns green/brown (H2O2)
γ-haemolysis - No haemolysis

Question 11

Cell Wall Antigen Extraction: Strep

Answer 11

Antigen extracted with weak acid;
pH neutralised;
Reacts with specific antisera

Question 12

Group A Streptococci

Answer 12

S. Pyogenes
pyrogenic superantigen exotoxin causes scarlet fever
streptococal pharyngitis (strep throat)
M-protein - filamentous protein adhesion
Antibodies to some M protein cross-reacts to heart valve tissue
Dx/Rx important to prevent rheumatic fever

Question 13

Group B Streptococci

Answer 13

Natural habitat: female reproductive system
septicemia/meningitis in newborns
culture and treatment of women before delivery

Question 14

Group D Streptococci

Answer 14

subacute bacterial endocarditis

Question 15

α-Haemolytic streptococci

Answer 15

Many species
Natural habitat: oral and intestinal mucosa
Oral flora may cause bacterial endocarditis especially on damaged or prosthetic valves
Streptococcuss mutans causes dental caries
Major pathogen: streptococcus pneumoniae