Compiled from lecture notes, this is a condense but detailed and extensive summary of all the module content (and more), containing an overview of all the content in a logical order, easy to search and use for revision.
Staphylococcus aureus
• Forms cocci which grow in clusters (grape-like)
• Commensal – found in nose, vagina, and colon
• Produces catalase and coagulase (differentiate from S. epidermidis)
• Range of diseases
o Skin and soft tissue infections (SSTI)
o Impetigo
o Toxic shock syndrome (TSS)
o Septicaemia
o Osteomyelitis
• Large, approx. 2um
• Facultative aerobe
• Highly resistant strains – methicillin-resistant (MRSA) and penicillin-G
• Foodborne or healthcare acquired (HCAI)
• Lab diagnosis
o Clinical specimens – swabs from lesion, pus or nasal
o Forms yellow colonies on nutrient agar
o Yellow colonies on mannitol salt agar
o Alpha and beta haemolysis on blood agar
o Positive Gram stain (purple)
o Catalase positive
o Coagulase positive
o Molecular - not needed unless outbreak for epidemiology
▪ PCR for 16s mecA gene in MRSA strains
• Virulence factors
o Enzymes
▪ Coagulase – prevent plasma clots and coat bacterial cells to evade phagocytes
▪ Hyaluronidase – breaks down hyaluronic acid in host’s skin to allow entry to blood
and spread (septicaemia)
▪ DNAse – nucleases which break down host DNA
▪ Lipase – break downs oils on skin for better colonisation
▪ Beta-lactamases (penicillinases) – resistance to beta-lactam antibiotics
▪ Staphylokinase – digests fibrin by converting plasminogen to plasmin which digests
fibrin clots
o Toxins
▪ Enterotoxins
• Food poisoning symptoms
• 7 serotypes of cytolysins – A, B, C, D, E, G
• Alpha toxin (SEA) – alpha hemolysin, pore forming, chromosomal gene
• Beta toxin (SEB) – sphingomyelinase damages host plasma membrane,
plasmid gene
• Delta toxin (SED) – cytotoxic peptide toxin
▪ Superantigens
• Toxic shock syndrome toxin-1
o Septic shock
o Expressed systemically
o Some non-menstrual cases (usually caused by tampon)
▪ Exotoxins – leucocidin acts on polymorphonuclear leukocytes
, o Immunoevasion
▪ Polysaccharide capsule (glycocalyx)
• Surface proteins
o Protein A binds IgG molecules – disrupts opsonisation and
phagocytosis
o Some promote bacterial binding to host epithelial and endothelial
surfaces
o Adhesins bind to fibronectin and laminin so bacterial cells aren’t
moved on
o Clumping factors bind to fibrogen/fibrin
• Prophylaxis
o Stop transmission/colonisation
▪ Drain infected areas
▪ Clean infected areas using anti-bacterials
▪ Autoclave contaminated bedding/clothes
• Treatment – antibiotics
o Semi-synthetic penicillin – flucloxacillin, dicloxacillin
o Cephalosporins
o Clindamycin
o Lincomycin
o Erythromycin
o MRSA
▪ Treated with vancomycin or teicoplanin
▪ Nosocomial strains treated with combination of oral antimicrobials – usually
rifampicin and fusidic acid)
o New antibiotics – linezolid, quinupristin/dalfoprisitin
o Surface infection treated with oral administration
o Systemic infection treated with IV administration
Staphylococcus epidermidis
• Form cocci which grown in clusters (grape-like)
• Commensals found in nose, vagina, and colon
• Does NOT produce catalase and coagulase (used to differentiate from S. aureus)
• Large, approx. 2um
• Facultative anaerobe
• Highly resistant – amoxicillin, methicillin
• Healthcare acquired infections – catheters, biofilms, UTIs
• Lab diagnosis
o White colonies in culture
o Gamma-haemolysis on blood agar
o Catalase negative
o Coagulase negative
o Molecular tests – not needed unless outbreak for epidemiology
• Virulence factors
o Toxins
▪ Exfoliatin toxins (ETA, ETB)
• Scaled skin syndrome
• Causes separation from epidermis
o Exotoxins – leucocidin acts on polymorphonuclear leukocytes
o Immunoevasion
▪ Polysaccharide capsule (glycocalyx)
,BHCS3003 revision
• Surface proteins
o Protein A binds IgG molecules – disrupts opsonisation and
phagocytosis
o Some promote bacterial binding to host epithelial and endothelial
surfaces
o Adhesins bind to fibronectin and laminin so bacterial cells aren’t
moved on
o Clumping factors bind to fibrogen/fibrin
• Prophylaxis
o Stop transmission/colonisation
▪ Drain infected areas
▪ Clean infected areas using anti-bacterials
▪ Autoclave contaminated bedding/clothes
• Treatment – antibiotics
o Semi-synthetic penicillin – flucloxacillin, dicloxacillin
o Cephalosporins
o Clindamycin
o Lincomycin
o Erythromycin
o New antibiotics – linezolid, quinupristin/dalfoprisitin
o Surface infection treated with oral administration
o Systemic infection treated with IV administration
Streptococci pyogenes
• Cocci that form chains
• Small, 0.6-1um
• Ferment carbohydrates
• Lancefield group A
• Aerotolerant
• Causes a range of diseases
o Sore throat (Strept throat)
o Skin infections
o Rheumatic fever
o Post Strept glomerulonephritis (PSGN)
• If stringy and sticky when colony is picked up off agar = mucoid colonies produced by an
encapsulated cell
• Lab diagnosis
o Clinical specimens – swabs from lesions, pus, nasal; blood, sputum
o Positive Gram stain (purple)
o Oxidase negative
o Catalase negative
o Beta haemolysis
o Forms white colonies in culture
o Bacitracin sensitive (differentiates from S. agalactiae which is also beta-haemolytic)
o Molecular tests – not needed unless outbreak for epidemiology
• Antigenic structure
o Capsule composed on hyaluronic acid
o Complex polysaccharides in cell wall
▪ L-rhamnose and N-acetyl-D-glucosamine
o T-antigens
o Two major classes of proteins – T and M-antigen pilli
, ▪ M proteins – ‘hairy’ extensions
• Specific adherence by lipoteichoic acid
• Trigger immune response
• Form biofilm (white patches on throat seen in strep throat, allow survival out
of host)
• Highly immunogenic
• Lysogenic
o All S. pyogenes strains carry one or more bacteriophage within genome
o Lysogenised bacteriophage encodes various Strept enzymes and toxins
• Virulence factors
o Enzymes
▪ C5a peptidase – destroys C5a signals used by host in recruitment and activation
phagocytosis (complement system)
▪ Hyaluronidase – breaks down hyaluronic acid for spread through host (how does it
not break down bacteria capsule)
▪ Nucleases – four antigenic types facilitate liquidation of pus
▪ Proteases – phosphatases
▪ Streptokinase – lyse blood clots using fibrinolysin
o Toxins
▪ Streptolysin O
• Oxygen labile cytolysin for beta haemolysis
• Toxin to leukocytes
• Strongly immunogenic
▪ Streptolysin A
• Oxygen stable cytolysis for beta haemolysis
• Non-immunogenic
▪ Pyrogenic exotoxins (erythrogenic)
• Superantigens in lysogenised strains
• Causes pyrogenic (fever) properties in hypothalamus and causes rash of
scarlet fever
• Strept toxic shock syndrome typified by multisystem involvement (renal and
respiratory failure, rash, diarrhoea)
o Immunoevasion
▪ Hyaluronic capsule
• Anti-phagocytic
• Non-antigenic – chemically similar to host for evasion
• Prevents opsonised phagocytes
▪ Surface proteins
• Adhesins – fibronectin binding protein, lipoteichoic acids
• M-protein
o Anti-phagocytic
o Anti-complement
o Cytotoxic to neutrophils
o Acute glomerulonephritis follows Strept infection of pharynx
• Treatment depends on Lancefield group – antibiotics
o Penicillin VK, amoxicillin, penicillin G
o Erythromycin, clarithromycin, azithromycin
Streptococci agalactiae
• Cocci that form chains
• Lancefield group B
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller AH1984. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $15.18. You're not tied to anything after your purchase.
