Streptococcus + Staphylococcus Flashcards
intracellular pathogens
able to survive and proliferate within host cells
obligate intracellular
require host cell to survive and proliferate
may have extracellular phase for transmission only
cells: macrophages, platelets, PMNs, epithelial cells
facultative intracellular
can survive and proliferate within and outside of host cells
cells: macrophages
extracellular pathogens
entire life cycle is extracellular only
may be phagocytosed within PMNs but are not replicating
beta hemolytic
causes complete clearing of RBCs on agar
catalase positive
causes bubbling of hydrogen peroxide
(H2O2 –> H2O + O2)
what strains of streptococcus are more pathogenic
beta hemolytic strains
are beta hemolytic strains of strep susceptible to beta lactams
yes, reliably
what characteristics are shared by strep and staph
- gram positive cocci
- beta hemolytic
- common commensal bacteria on mucous membranes
- opportunistic
- causes purulent inflammation
what cell type is most responsive to strep and staph
neutrophils
should antimicrobials be used in strangles
not in most cases
necrotizing fasciitis
rapidly spreading necrotic cellulitis leading to toxic shock syndrome
most severe disease caused by strep Canis - can cause death within 12 hours
associated with prior enrofloxacin treatment
what strains of staphylococcus are more pathogenic
coagulase positive strains
coagulase positive strains
able to clot rabbit blood
- staph aureus (LA)
- staph pseudintermedius (SA)
- staph hyicus (pigs)
are coagulase negative strains given names
not given specific names because less pathogenic and often commensal
methicillin resistance (MRS)
staphylococcus that have altered penicillin binding protein (PBP2) that prevents binding of all beta lactam drugs
NOT the same as beta lactamase resistance mechanism but some staph can have both resistance mechanisms (mec A gene for altered PBP2 and beta lactamase production)
how is methicillin resistance determined on a susceptibility test
oxacillin resistance
why are MICs not usually reported for methicillin resistant drugs
to avoid confusion - no concentration of drug will overcome PBP resistance mechanism
MRSA vs MRSP
MRSA: methicillin resistant staph aureus (common in large animals and humans)
MRSP: methicillin resistant staph pseudintermedius (common in small animals)
biofilms
community of bacteria attached to a surface or to each other and embedded in an extracellular polymeric substance
allows the bacteria to evade antibiotics and host immune response
where are biofilms most commonly formed
formed on a nidus such as a catheter, bone, or surgical implants
must remove the nidus to clear the infection
how do biofilms develop
- bacteria attaches to nidus
- forms a small community
- community grows surrounded by an extracellular matrix
- bacteria able to escape from biofilm to proliferate
