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
Erysipeloid in humans
- what it causes
- where commonly found (what type of workers)
- features of bacteria (Hint; it is caused by Erysipelothrix)
- what it is resistant to
- Raised purple skin lesion (e.g. crayfish handlers)
- Often found in butchers, fishmonger and abbatoir workers
- Gram positive bacillus
- catalase negative
- Intrinsically Vancomycin resistant
Listeriosis
- Symptoms
- Common sources
Symptoms; -high fever -severe headaches -nausea -abdominal pain -diarrhea Common sources; -Washing salad w/ unclean water -uncooked fish -cheese -processed meats
Listeria monocytogenes
- features of disease/bacteria
- where it multiplies
- ideal temperatures
- where found
- why is it an important foodborne zoonosis?
- what can it cause
-Sporadic disease
-Reduced host resistance
-multiplies in macrophages (intracellular pathogen)
-High case fatality
-‘Cold enrichment”
Found in soil, faecs, silage etc.
*in humans, is an important foodborne zoonosis esp. in pregnant individuals
Can cause;
-abortions, high mortality and epidemics/endemic
Bacillus -features
-why are they significant medically?
- Bacillus cereus
- features
- what mainly involved in?
- illness & what specifically causes it
- Large Gram positive Rods
- Spore formers
- Very Resistant (antibiotically & environmentally)
Bacillus cereus
- no bacteraemia
- occasionally bovine mastitis
- Human food poisoning (esp. in reheated rice)
- nausea, vomiting, diahorrea
- toxin is in spore coat (is what causes illness)
Anthrax
- Pulmonary, Gastrointestinal and Cutaneous symptoms
- name for skin lesions
- Pulmonary: Flu-like symptoms, pneumonia, severe respiratory collapse
- Gastrointestinal: Vomiting blood, severe diarrhea, loss of appetite, acute inflammation of GI tract
- Cutaneous: Boil-like skin lesions, painless necrotic ulcer w/ black centre (ESCHAR)
Anthrax Letters (9/11/01)
- Letters addressed to certain senators had anthrax in them
- was the Ames strain that had 2 virulence plasmids;
- anthrax toxin, polyglutamic acid capsule - Vollum strain is more dangerous
Bacillus antrhracis
- how it grows
- vaccine
- Use in war/terrorism
- What it is a clone of (difference between them)
- spores (features and how reactivated)
- grows in chains (rods)
- notifiable: humans and animals
- Pasteur’s vaccine 1881 = 5 dose series
- Has been used in germ warfare & bio-terrisim
- is a virulent clone of B. cereus (just has an extra plasmid!)
- spores can survive for centuries
- are reactivated when inhaled, ingested or come in contact with skin
- soil borne spores present globally
3 features that make anthrax dangerous
- Where found in Australia -> what is most susceptible
- what infection causes
- Endospores: prolonged survival
- Capsule: hard for them to be engulfed or for antibodies to bind to them
- Produce powerful toxins (all 3 needed to produce anthrax toxin)
- oedema factor
- protective factor
- lethal factor
- all three cause tissue degradation, swelling, bleeding and death
- is an anthrax belt in central NSW - spores in soil
- Ruminants most susceptible as they may inhale/ingest spores
- spores germinate, local lesion
- lymphatics - spleen - spill out: causes septicaemia/toxaemia – peracute death
- Ruminants most susceptible as they may inhale/ingest spores
