Flashcards in Staphylococci and Related Gram + cocci Deck (45)
What are the two major groups in the family microccaceae?
What are the 5 KEY characteristics of staph?
1) Gram + (clusters)
4) catalase positive
5) facultative anaerobes
What is the main way to determine staph from strep?
+ = staph
- = strep
What are the 4 main types of staph to know?
Where is staph aureus normally found?
perineum, axillae, vagina
What are 5 factors that predispose one to staph aureus infection?
1) defects in leukocyte chemotaxis
2) defects in opsonization by antibodies
3) defects in intracellular killing of bacteria following phagocytosis
4) skin injuries
5) presence of foreign bodies
True or false: the usual site of infection is that where the organism is part of the normal flora
(skin, nose + throat, GI tract, urethra, vagina)
any skin disease that is pyogenic (pus forming)
What is a furuncle?
skin disease caused by infection of hair follicles resulting in localized accumulation of pus and dead tissue
What is a carbuncle?
abscesses larger than boils (with one or more openings)
What are 3 toxin-mediated infections from staph aureus?
1) scalded skin syndrome
2) toxic shock syndrome
3) food poisoning
What are 4 components that interfere with phagocytosis? (AKA VIRULENCE FACTORS)
2) protein A
3) panton-valentine leukocidin (PVL)
How do capsules interfere with phagocytosis?
prevent ingestion of organisms by PMNs
How does Protein A act as a virulence factor?
binds to Fc region of IgG interfering with opsonization and ingestion of organism by PMNs
What is PVL and what does it do?
enzyme that alters cation permeability of rabbit and human leukocytes resulting in white cell destruction
How does Coagulase work?
binds to prothrombin catalyzing fibronogen to fibrin which then coats cells (with fibrin) rendering them resistant to opsonization and phagocytosis
Which type of staph aureus is more infectious, PVL+ or PVL-?
What are the 4 hemolysins in staph aureus?
alpha, beta, gamma, delta
What are the hallmarks of alpha hemolysin?
lyses RBCs, dermonecrotic on SubQ injection, leukocyte toxicity
What are the hallmarks of beta hemolysin?
produces hot-cold lysis
What are hallmarks of delta hemolysin?
acts as surfactant to disrupt cell membrane (forms channels that result in leakage of cellular contents)
can cause enterocolitis in neonates
What are the hallmarks of gamma hemolysin?
can cause lysis in a variety of cells
What toxins are responsible for staphylococcal scalded skin syndrome?
exfoliatins (aka epidermolytic toxins)
works by dissolving mucopolysaccharide matrix of epidermis causing separation of skin layers
What are enterotoxins?
heat-stable molecules responsible for clinical features of staphylococcal food poisoning, probably most common cause of food poisoning in U.S.
What 3 enzymes are produced by staph aureus?
1) Fibrinolysins - break down fibrin clots and facilitate spread of infection
2) Hyaluronidase - hydrolyze intercellular matrix of acid mucopolysacch to spread organisms to adjacent tissues
3) Phospholipase C - makes tissues more susceptible to damage by complement
What are examples of some superantigens associated with staph aureus?
toxic shock (TSST-1)
streptococcal pyrogenic exotoxins (SPE)
What 3 biological characteristics are shared by staph aureus supertoxins?
enhance lethal effects
all induce polyclonal T-cell proliferation
What virulence factor is used to identify staph aureus?
if it clots it is staph aureus
What is the alternative coagulase test?
agglutination = positive
What is the most common coagulase NEGATIVE staph?
What particular infections are associated with staph epidermidis?
infections of indwelling devices (makes extracellular slime that makes biofilm - need to remove entire device)
What is the cause of acute urinary tract infection in young women?
What are 2 HUGE identifiers of staph saprophyticus?
1. Coagulase NEGATIVE
2. Resistant to novobiocin
(should be furozolidone susceptible)
What is the only staph species that is both PYR and Ornithine positive?
Which staph colonizes the human inguinal area?
True or false: the majority of MRSA infections occur in hospitals?
What are common community acquired MRSA sources?
MPSM (men play sports men)
What is the significance of the mecA gene?
confers methicillin resistance
What does mecA gene encode?
altered penicillin binding protein 2a (PBP2a)
which has decreased binding affinity for beta lactam antibiotics and allows PG synthesis in the presence of betal lactam antibiotics
True or false: mecA gene is born on chromosomes
FALSE; carried on a mobile element (has to be acquired) called SCCmec
When should MRSA come up in differential?
skin and soft tissue infections (SSTIs)
True or false: infected patients contaminate hospital environment better than colonized patients (with MRSA)
FALSE; same frequency
True or false: MRSA testing in patients has DECREASED bacteremia in ICUs
What is the most effective method of detecting MRSA in patients?
real time PCR