Streptococcus + Staphylococcus

Question 1

intracellular pathogens

Answer 1

able to survive and proliferate within host cells

Question 2

obligate intracellular

Answer 2

require host cell to survive and proliferate

may have extracellular phase for transmission only

cells: macrophages, platelets, PMNs, epithelial cells

Question 3

facultative intracellular

Answer 3

can survive and proliferate within and outside of host cells

cells: macrophages

Question 4

extracellular pathogens

Answer 4

entire life cycle is extracellular only

may be phagocytosed within PMNs but are not replicating

Question 5

beta hemolytic

Answer 5

causes complete clearing of RBCs on agar

Question 6

catalase positive

Answer 6

causes bubbling of hydrogen peroxide

(H2O2 –> H2O + O2)

Question 7

what strains of streptococcus are more pathogenic

Answer 7

beta hemolytic strains

Question 8

are beta hemolytic strains of strep susceptible to beta lactams

Answer 8

yes, reliably

Question 9

what characteristics are shared by strep and staph

Answer 9

• gram positive cocci
• beta hemolytic
• common commensal bacteria on mucous membranes
• opportunistic
• causes purulent inflammation

Question 10

what cell type is most responsive to strep and staph

Answer 10

neutrophils

Question 11

should antimicrobials be used in strangles

Answer 11

not in most cases

Question 12

necrotizing fasciitis

Answer 12

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

Question 13

what strains of staphylococcus are more pathogenic

Answer 13

coagulase positive strains

Question 14

coagulase positive strains

Answer 14

able to clot rabbit blood

• staph aureus (LA)
• staph pseudintermedius (SA)
• staph hyicus (pigs)

Question 15

are coagulase negative strains given names

Answer 15

not given specific names because less pathogenic and often commensal

Question 16

methicillin resistance (MRS)

Answer 16

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)

Question 17

how is methicillin resistance determined on a susceptibility test

Answer 17

oxacillin resistance

Question 18

why are MICs not usually reported for methicillin resistant drugs

Answer 18

to avoid confusion - no concentration of drug will overcome PBP resistance mechanism

Question 19

MRSA vs MRSP

Answer 19

MRSA: methicillin resistant staph aureus (common in large animals and humans)

MRSP: methicillin resistant staph pseudintermedius (common in small animals)

Question 20

biofilms

Answer 20

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

Question 21

where are biofilms most commonly formed

Answer 21

formed on a nidus such as a catheter, bone, or surgical implants

must remove the nidus to clear the infection

Question 22

how do biofilms develop

Answer 22

1. bacteria attaches to nidus
2. forms a small community
3. community grows surrounded by an extracellular matrix
4. bacteria able to escape from biofilm to proliferate