Week 6 - Catalase Positive and Negative GPC

Question 1

Staphylococcus Genus

Answer 1

GPC
Catalase positive
Oxidase negative
Non-motile
Non-spore forming
Most facultative anaerobes
Fermentative

Question 2

Staphylococcus aureus

Answer 2

Most virulent staph
Creamy colonies
Coagulase positive
Significant cause of nosocomial infection
Makes up normal flora at:
- Nostrils
- Nasopharynx
- Skin etc.

Question 3

How can you tell that a Staphylococcus species is Staph aureus?

Answer 3

GPC
Catalase Pos
Oxidase Neg
Coagulase Pos = Staph aureus

Question 4

Examples of Staph aureus Infections

Answer 4

Wound infections
Meningitis
Pulmonary infections
Food poisoning
Septic arthritis

Question 5

Staphylococcus aureus - Virulence Factors

Answer 5

Capsule
Protein A
Enzymes
- Catalase
- Coagulase
- Fibrinolysins
- Hyaluronidase
Haemolysins
- Toxic to a variety of host cells
Toxins
- Epidermolytic toxins (causes scalded skin syndrome)
- Enterotoxins

Question 6

Coagulase Test

Answer 6

Coagulase an enzyme which reacts with fibrinogen

If organism positive, clumping occurs

Question 7

What are the two forms of Coagulase?

Answer 7

Bound (outside of cell wall) - detected by slide test

Free (secreted by living cell) - detected by tube test

Question 8

Staphylococcus Epidermidis

Answer 8

Most common coagulase negative staph
Makes up 90% of skin flora
Almost all infections are of nosocomial origin
Produces a biofilm so able to grow on artificial surfaces
Grey to white colonies
Not usually haemolytic

Question 9

Staphylococcus Saprophyticus

Answer 9

UTI’s
Coagulase negative
Novobiocin resistant
Usually very bright white glossy colonies

Question 10

Staphylococcus Saprophyticus - Virulence Factors

Answer 10

Adherence to epithelial cells
- specificity for urethral and periurethral cells
Urease production
- contributes to bladder tissue invasion
Produce slime layer in presence of urine and urease
- therefore sticky in urinary system and not flushed out

Question 11

Streptococci and Enterococci

Answer 11

GPC
Usually in pairs and chains
Catalase negative 
Facultative anaerobes
Fermentative

Question 12

Types of Haemolysis

Answer 12

Alpha - partial lysis of RBC
Beta - completely clear zone around colonies
Gamma - no lysis

Question 13

Lancefield Groups

Answer 13

Based on cell wall carb C antigens
A, B, C, F, G antigens are cell wall polysaccharides
D anitgen in group D enterococci and streptococci are lipoteichoic acids

Question 14

Streptococcus pyogenes

Answer 14

Catalase Neg
Beta haemolysis
Bacitracin susceptible
Inhabits skin and mucous membrane of the Upper Respiratory Tract
Causes:
- Tonsillitis
- Impetigo
- Erysipelas

Question 15

Tonsilitis

Answer 15

Caused by S.pyogenes
Abrupt onset of fever, sore throat, headache
Suppurative complications (pus forming):
- sinusitis, abscess
Non-suppurative complications
- acute and chronic rheumatic fever
- glomerular nephritis

Question 16

Streptococcus pyogenes - Virulence Factors

Answer 16

M proteins - help with adherence to epithelial cells, resistant to phagocytosis
Haemolysin O and S - both toxic to various host cells
Strep Pyrogenic Exotoxins - Cause toxic shock syndrome
Enzyme production - DNases, hyaluronidase
Hyaluronic acid capsule - resists phagocytosis

Question 17

Streptococcus Agalactiae

Answer 17

Normal flora in URT, GIT, Genital tract
Neonatal Disease
- neonate acquires organism in uterus before delivery 
- causes pneumonia, septicaemia
Resistant to Bacitracin

Question 18

Streptococcus agalactiae - Virulence Factors

Answer 18

Capsules
Enzymes - hyaluronidase
Beta haemolysin - toxic to lung endo cells
Lipoteichoic acid - adherence

Question 19

How to see if a Beta-haemolytic substance is Strep Pyogenes or not

Answer 19

If it is bacitracin susceptible then it is Strep pyogenes

Question 20

Enterococcus

Answer 20

Normal gut flora
Group D antigen positive
Usually grey
Non-haemolytic
Bile tolerant and aesculin positive

Question 21

Enterococcus Infections

Answer 21

UTI
Meningitis
Septicaemia

Question 22

Streptococcus Pneumoniae

Answer 22

GP diplococci
Two colony types
- mucoid (smooth) and draughtsman (rough)
Alpha haemolytic
Fastidious - requires BA or CHOC

Question 23

Streptococcus Pnuemoniae - Virulence Factors

Answer 23

Capusle
Alpha haemolysin
Enzymes - hyaluronidase, neuraminidase
Increasing resistance to penicillin

Question 24

What does MRSA stand for?

Answer 24

Methicillin resistant Staphylococcus aureus

Question 25

What is the name for Group A and Group B Streptococci?

Answer 25

A - Streptococcus pyogenes

B - Streptococcus agalactiae

Question 26

With Staphylococcus Epidermidis what clinical relevance should be substantiated before ID and reporting?

Answer 26

Purity of growth
Quantity of growth
Site of infection
Clinical Hx

Question 27

Viridians Streptococci

Answer 27

NF of the mouth, GIT and Urogenital tract
Causes:
- endocarditis (esp. sub-acute) e.g. septicemia
Virulence factors
- hydrolytic enzymes (leads to plaque build up)
- capsule

Question 28

Rheumatic Fever and Glomerular Nephritis

Answer 28

Rheumatic
- 1-5 weeks post pharyngitis infection only
- sudden onset of fever and joint pain
- cardiac murmurs, heart failure
Glomerular Nephritis
- post URT infection/scarlet fever/ skin infection
- onset 10 days after pharyngitis
- onset 3-6 weeks after skin infection
- weakness, anorexia, hypertension