Gram Positive Bacteria Flashcards
where are Staphylococcus found in humans?
Found all over the skin
Form part of the human microbiota – normal flora
how is staphylococcus transmitted?
Transmitted by direct contact, via fomites and medical instruments
OPPORTUNISTIC pathogens
Cause minor to life threatening diseases
Staphylococcus genus
Genus is:
Gram positive
Facultatively anaerobic prokaryote
Staphylococcus shape
Spherical cells-clustered like grapes- due to cell division occuring in successively different planes and daughter cells remain attached
Staphle - greek for bunch of grapes
Kokkos - berry
Staphylococcus tolerance
Salt tolerant – sweat
Tolerant to desiccation, radiation and 60 deg C-survival on environmental surfaces
Desiccation - the removal of moisture from something
Survive in dust
Produce catalase
Can different between straph and streph. As one produces catalase to neutralise
2 staphylococcus species commonly associated with disease in humans
Staphylococcus aureus -more virulent
Staphylococcus epidermidis (collective term for many species) -part of normal flora of human skin-opportunistic pathogen
Common ‘staph’ infections occur when physical barriers breached.
Physical barriers breached, by IV drip, surgery,
Staphylococcus aureus defences against phagocytosis x3
Protein A coated – binds IgG stems and inhibits complement cascade (triggered by ab mol bound to ag)
Bound coagulase on surface – forms fibrin clots – hides bacteria
Slime/capsules – polysaccharide – inhibit chemotaxis and endocytosis by leukocytes and facilitates attachment (to entry points, IV drips, catheters)
Staphylococcus epidermidis
Relies almost exclusively on slime
Opportunistic – attach to urinary catheters, intravascular catheters – form biofilms
enzymes produced by Staphylococcus aureus x5
Coagulase – fibrin threads
Hyaluronidase – breaks down hyaluronic acid – major matrix component of cells
Staphylokinase – dissolves fibrin threads
Lipases – digest lipids- allows growth on skin and in cutaneous oil glands
β lactamase – 90%
Staphylococcus toxins
Cytolytic toxins – coded by genes and disrupt cytoplasmic membranes of cells including leukocytes.
Exfoliative toxin – dissolve intercellular bridge proteins causing skin sloughing
Enterotoxins – cause vomiting associated with Staphylococcal food poisoning
disease caused by staphylococcus toxins
Toxic shock syndrome toxin - fever, rash, low bp and loss of skin (tampons)
Noninvasive Staphylococcus aureus infection
food poisoning
Cutaneous Staphylococcus aureus infection
localised pyogenic lesions, e.g. SSS, impetigo
Folliculitis Staphylococcus aureus infection
hair follicle infection with progressive stages
furuncle or boil - extension of hf to surrounding tissue
carbuncle – coalesce of furuncle – deep tissue infection – fever/chills(2nd line)
Bacteremia caused by Staphylococcus aureus infections
systemic blood infection, septic
Endocarditis caused by Staphylococcus aureus infections
life-threatening inflammation of the inner lining of your heart’s chambers and valves(endocardium).
Resulting after bacteremia circulating through heart
other systemic diseases caused by Staphylococcus aureus infections
Pneumonia and empyema
Osteomyelitis caused by Staphylococcus aureus infections
infection of bone after bad bone breakage, breaks the skin
Other important groups of gram positive bacteria x7
Streptococci – lead to scarlet fever Bacillus - aerobic spore producers Clostridium Listeria Corynebacteria Mycobacteria Propionibacteria
Streptococci morphology
cocci
0.5-1.2um in diameter
Found in pairs and chains
characterics of streptococci
Gram positive cocci
Catalase negative
Facultatively anaerobic
Differentiation between gram positive cocci
Serology – reactions of antibodies to specific bacterial antigens
Haemolysis
Cell arrangement
Physiological – biochemical tests
Haemolysis differentiation
Alpha – Strep.pneumoniae & viridans streptococci
Beta – mainly Lancefield groups – Strep.pyogenes, Strep.agalactiae
Gamma – non haemolytic - Enterococci