Week 6 - Catalase Positive and Negative GPC Flashcards
Staphylococcus Genus
GPC Catalase positive Oxidase negative Non-motile Non-spore forming Most facultative anaerobes Fermentative
Staphylococcus aureus
Most virulent staph Creamy colonies Coagulase positive Significant cause of nosocomial infection Makes up normal flora at: - Nostrils - Nasopharynx - Skin etc.
How can you tell that a Staphylococcus species is Staph aureus?
GPC
Catalase Pos
Oxidase Neg
Coagulase Pos = Staph aureus
Examples of Staph aureus Infections
Wound infections Meningitis Pulmonary infections Food poisoning Septic arthritis
Staphylococcus aureus - Virulence Factors
Capsule Protein A Enzymes - Catalase - Coagulase - Fibrinolysins - Hyaluronidase Haemolysins - Toxic to a variety of host cells Toxins - Epidermolytic toxins (causes scalded skin syndrome) - Enterotoxins
Coagulase Test
Coagulase an enzyme which reacts with fibrinogen
If organism positive, clumping occurs
What are the two forms of Coagulase?
Bound (outside of cell wall) - detected by slide test
Free (secreted by living cell) - detected by tube test
Staphylococcus Epidermidis
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
Staphylococcus Saprophyticus
UTI’s
Coagulase negative
Novobiocin resistant
Usually very bright white glossy colonies
Staphylococcus Saprophyticus - Virulence Factors
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
Streptococci and Enterococci
GPC Usually in pairs and chains Catalase negative Facultative anaerobes Fermentative
Types of Haemolysis
Alpha - partial lysis of RBC
Beta - completely clear zone around colonies
Gamma - no lysis
Lancefield Groups
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
Streptococcus pyogenes
Catalase Neg Beta haemolysis Bacitracin susceptible Inhabits skin and mucous membrane of the Upper Respiratory Tract Causes: - Tonsillitis - Impetigo - Erysipelas
Tonsilitis
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
Streptococcus pyogenes - Virulence Factors
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
Streptococcus Agalactiae
Normal flora in URT, GIT, Genital tract Neonatal Disease - neonate acquires organism in uterus before delivery - causes pneumonia, septicaemia Resistant to Bacitracin
Streptococcus agalactiae - Virulence Factors
Capsules
Enzymes - hyaluronidase
Beta haemolysin - toxic to lung endo cells
Lipoteichoic acid - adherence
How to see if a Beta-haemolytic substance is Strep Pyogenes or not
If it is bacitracin susceptible then it is Strep pyogenes
Enterococcus
Normal gut flora Group D antigen positive Usually grey Non-haemolytic Bile tolerant and aesculin positive
Enterococcus Infections
UTI
Meningitis
Septicaemia
Streptococcus Pneumoniae
GP diplococci Two colony types - mucoid (smooth) and draughtsman (rough) Alpha haemolytic Fastidious - requires BA or CHOC
Streptococcus Pnuemoniae - Virulence Factors
Capusle
Alpha haemolysin
Enzymes - hyaluronidase, neuraminidase
Increasing resistance to penicillin
What does MRSA stand for?
Methicillin resistant Staphylococcus aureus
