staphylococcus Flashcards
what si the most common and most important staph?
staphylococcus aureus
what is the metabolism of staph?
facultative anaerobes
is staph catalase positive or negative?
catalse positive
S. aureus grows in what environment
high salt conc
what does S. aureus ferment?
mannitol
-mannitol salt agar
describe the hemolysis of S. aureus
double zone hemolysis
what does coagulase do?
converts fibrinogen to fibrin
does s. aureus produce coagulase?
yes
what does CNS mean?
staph aureus coagulase negative
what staphylococcal diseases occur in humans
- skin/soft tissue infections
- food poisoning
- MRSA
what does MRSA stand for?
methicillin resistant staphylococcus aureus
is MRSA zoonotic?
yes
what does S aureus cause in cows?
mastitis
what does S. aureus cause in chickens and turkeys?
-skin and joint infections
what does s aureus cause in pigs
septicemia (rarely)
what does S. aureus cause in horses
dermatitis and celllitis
what does S. pseudointermedius cause in dogs
- pyoderma
- otits externa
what does S. hyicus cause in pigs
-exfoliative epidermitis (greasy pig disease
what are the best sites to take samples from for S aureus?
the nostrils
what is protein A
a surface protein that binds to Fc region of TgG molecules, which disrupts opsonization and phagocytosis
what are caspsular polysaccharides
- 11 serologically distinct capsule type in s aureus of humans and cattle
- interfere with host defense mechanisms by inhiiting attachment of antibiodies, induce the relase of cytokines
- mediate binding to epithelial and endothelial cells
what do peptidoglycan and lipoteichoic acid do?`
stimulate cytokine release
what do ahesins do
surface proteins that promote attachment to host proteins
- fibronectin-binding protein
- collagen-binding protein
what are teh exoenzymes
coagulase
lipase
hylauronidase
protease
what is coagulase
- exoenzyme
- converts fibrinogen to fibrin
what is lipase
- exoenzyme
- hydrolyzes lipid molecules that the host produces in response to infections
what is hyaluronidase
-digests hyaluronic acid present in connective tisure and promtoes spread of the infection
what is protease
=-exoenzyme
- obtain amino acids as nutrient
- cleave and inactivate antibodies, antimicrobial peptides (defensins)
- contribute to tissue proein destruction and enhance invasiveness
- best described enzyme is serine protease
what us toxic shock syndrome toxin
- exotoxin
- superantigen activity
do all strains of S. aureus produce exotoxins?
no
what do enterotoxins do?
- responsible for food borne infections
- nine types of enterotoxins and 9 enterotoxin-like toxins
- may have superantigen activity
- toxins are produces by bacteria in contaminated food
how do you get sick from enterotoxins
- they resist proteases, heat stable and not inactivated by cooking (the bacteria get killed from cooking but not the toxin)
- toxin is ingested with the food and in the stomach the toxin stimulates vagus nerve endings to induce vomiting and abdominal pain
what are exfoliative or epidermolytic toxins?
produces by S. aureus: ETA and ETB
-repsonisble for a variety of skin diseases in humans
what are hemolysins?
- protein toxins that lyse RBCs
- produced by S. saureus and S pseudointermedius
S aureus produces what 4 hemolysins?
-alpha, beta, gamma and delta hemolysins
what is alpha hemolysins
- membrane-damaging (pore-forming) toxin
- produced a zone of COMPLETE hemolysis surrounding the colony
- binding of thetoxin to platelets and monocutes results in the relase of cytokines triggering production of inflammatory mediators
- responsible for the symptom of septic shokc that occur during severe S aureus infcetions
what is beta hemolysins
- a sphingomyelinase, which damages membranes rich in sphingomyelin lipid
- responsible for INCOMPLETE hemolysis of ruminant erythrocytes
- aka hot-cold hemolysins, refrigeration enhances hemolysis
what is double zone hemolysis
alpha and beta hemolysins are responsible for double zone hemolysis
do all S aureus strains produce leukotoxin?
no
what is gamma hemolysin aka?
leukotoxin
what is significant abot leukotoxin?
pore-forming toxin and the genes are located on a prophage
what is delta hemolysin
- delta toxin is a small peptide
- direct/indirect effects on neutrphils, hence a pro-inflammatory toxin
what is beta-lactamase?
hydrolyzes beta lactam ring of penicillines and cephalosporins
what is penicillin-binding protein 2a
conferes resistance to penicillins and cephalosporins-class of antibiotics -carried by MRSA
what is the pathogenic mehcanism of S aureus
- pyogenic or supportive lesions
- injury to skin or immune suppression if a predisposing factor
- virulence factors to promote tissue colonization (protein A and ahesions)
- immune evasion (capsular polysaccharide, teichoic acid, protein A, catalse, coagulase),
- spread (hyaluronidase, lipase, protease)
- tissue destruction (toxins)
what is folluculitis?
infection of the hair follicle
what is furuncle
a boil, localized anscess surrounded by a zone of inflammation
what is a carbuncle
enlarged infected area
what staphylococcal diseases occur in humans?
- impetigo
- scaled skin syndrome
what is the route of infection for bovine mastitis?
though the teat
how can you diagnose bovine mastitis?
- double zone on blood agar
- biochemical tests
- increased somatic cell count because of increased leukocytes
how do you treat bovine mastitis
- intramammary administration of antibiotics (e.g. ceftiofur)
- dry cow therapy
what is dry cow therapy
administration of antibiotics a the beginning of the dry period is often used to treat or prevent staphylococcal mastitis
what are staphylocccal diseases in poultry
- dermatitis, osteomylelitis, arthritis, synovitis
- lameness due to infection
what is bumblefoot
localized lesion on the foot resulting from penetration by foreign object and subsequent infection by S. aureus and other bacteria
what is exudative dermatitis?
- caused by S. hyicus that produces exfoliative toxin
- organisms are normally present on the skin
- can penetrate the skin, however a breach of the epidermis is the most common predisposing factor
how do you treat exudative dermatitis?
- antibiotics in early stages are effective
- eg. ceftiofur
- severely infected animals do not repsond
what causes pyoderma in dogs?
S. pseudointermedius
what is pyoderma
- dermatitis and folliculitis
- lesions start as papular eruptions progressing into pustules and small intradermal abscesses
- deep skin lesions (furuncles) may rupture to become fistulous tracts with pus
are MRSA more virulent than other strains?
no, but they are more difficult to treat with standard antibiotics and thus more dangerous
what are MRSA resistant to ?
beta-lactam antibiotics and penicillins, and the cephalosporins
MRSA’s resistance is conferred by a gene called..
mecA
