Purulent and bacteraemic infections Flashcards
Purulent Infections
- what are they
- 3 main culprits
-Purulent = pus forming
Main culprits;
- Staphylococci
- Streptococci
- Corynebacteria and others
Staphylococcus
- what are they
- what they cause (and due to what)
- commersals of skin and mucous membranes
- also important pathogens
- are opportunists
- cause suppurative (pus forming) inflammation due to the production of leukotoxins
- can lead to septicaemia (potentially fatal whole body inflammation)
- Also can cause food poisoning, toxic shock
Isolation & identification of Straphylococcus
- gram & morphology
- what it can tolerate
-3 features
-Gram positive cocci in clusters
-tolerates high salt concentration (mannitol salt agar useful)
-also grow readily on blood agar
Identification;
-pigmented
-haemolytic
-catalase positive (hydrogen peroxide into gas bubbles)
Staphylococcus aureus (“Golden Staph”)
Staphylococcus albus (“white Staph”)
-features
S. aureus
- not necessarily golden (can be white or grey)
- are a coagulase positive species
- carried on skin and nose by many, can be pathogenic
S. albus
- now called S. epidermidis
- coagulase negative
- skin commensals/opportunists
- less pathogenic, but can form biofilms in catheters, joints etc & may be resistant to antibiotics
Properties of Pathogenic Straphylococcus species
- Often resistant to penicillins
- mecA gene causes changes in penicillin binding proteins in peptidoglycan layer (transmissible - horizontally)
- Produce range of tissue-damaging enzymes
- produce leukotoxins - pus
- strains vary greatly - some can be highly aggressive
- Vaccines generally not available due to strain differences
Staph aureus -> major human pathogen
- Localised skin infections it can cause
- MRSA
- what is it
- reservoir
- where can it come from & what can it cause
Causes various localised skin infections;
-impetigo
-boils (infected hair follicle)
-furunculosis (recurring crops of boils in an area)
-Staph scalded skin syndrome (SSSS) - skin blisters and sheds
MRSA (Methicillin resistant S. aureus)
-reservoir in pigs, horses, dogs
-nosocomial (from hospitals) , also emerging in community, transmitted by contact
-toxic shock syndrome
-food poisoning
Streptococci
- where found
- what they are
- what they usually cause
- Widespread - skin, nose, throat
- Commensals/opportunists (many species/strains of varying pathogenic potential
- usually localised purulent lesions - but can spread in bloodstream
Streptococci vs Staphococci
Strept - Staph
Chains - clusters
small colonies on plates - large colonies
enriched media - basal media
catalase negative - catalase positive
Enterococcus
- problem with them
- Avoparcin in pigs
- 2 e.g.
- not very virulent, but highly resistant to antimicrobials & readily become bacteraemic from the gut
- Vancomycin resistant enterococci (VRE) in hospitals = major problem
- Avoparcin (antibiotic/growth promoter) banned from vet use because of fears of inducing cross-resistance w/ vancomycin in enterococci in poultry and pigs
- then fear of subsequent spread to humans
e.g. E. faecium & E. faecalis
Lancefield Grouping of Pathogenic Streptococci
- What is it, what is it based on
- Types & Species
- Virulence factors of different strains (6)
-based on antigenicity of cell wall polysaccharides
-further typing uses M proteins
Types: based on antisera to surface proteins
Species: Based on biochemical reactivity etc. within groups
Virulence factors of different strains;
-Haemolysins
-Sreptokinase
-Hyaluronidase
-DNases
-Erthyrogenic toxin
-Capsules
Streptococcal haemolysis (3 types)
alpha = partial beta = complete haemolysis gamma = no haemolysis
Human Diseases associated with groups a and b of streptococcus
-e.g. of bacterial species
Group A - e.g. Strep pyogenes -Tonsilitis -Erysipelas -scarlet fever -septicaemia -rheumatic fever -Glomerulonephritis (inflammation of kidney) -Necrotising faciitis Group B - e.g. strep agalactiae - neonatal bacteraemia strep mutans - tooth decay
Streptococcus pneumoniae
- what organ they affect
- Difficulties in vaccination
- resistance
- what it is also involved in
“the pneumococcus” -> infects lungs
- No groups but over 90 capsular serotypes (therefore polyvalent vaccines)
- hard to do
- multi drug resistant strains emerging
- middle ear infection
- sinuses
- lungs
- joints/meninges
Corynebacterium
- features
- Clinical disease
- animal forms
- C. ulcerans
- C. diptheriae
-Pleomorphic
-gram positive rods and opportunists
-stain irregularly
-many species
Clinical disease
-Occasional infection w/ “animal coryneforms (e.g. C. equi in AIDS patient)
-C. ulcerans: pharangitis
-C. diptheriae: localised pharangitis, generalised toxaemia (tho not all strains are toxaemic - can carry w/out disease - esp so in developing countries)
Erysipelothrix
-features
- E. rhusiopathiae
- where it multiples in cells
- 2 sources
- Small, gram positive rods
- resistant
- facultative intracellular pathogens (need to invade cell)
- Have rough filamentous forms (allows adhesion)
E. rhusiopathiae
-multiples in and kills neutrophils -> bacteraemia
Sources: soil, carriers
