Resistant Infections

Question 1

MRSA resistance is mediated by which gene?

Answer 1

(The MecA gene)

Question 2

What protein is encoded for by the MecA gene that has a low binding affinity for beta-lactam antibiotics?

Answer 2

(PBP 2a)

Question 3

(T/F) Any Staph aureus with the MecA gene is resistant to ALL beta-lactam antibiotics, even when paired with a beta-lactamase inhibitor.

Answer 3

(T)

Question 4

What are the two main risk factors for MRSA infections?

Answer 4

(Prior adm of antimicrobial drugs (specifically beta-lactams, fluoroquinolones, and 3rd generation cephalosporins) and IV catheterization)

Question 5

Why are MRSA infections not associated with an increased risk of mortality in veterinary medicine species?

Answer 5

(Because the common sites of infection (ear and skin) are not vital and still fairly easy to treat (with topicals))

Question 6

What is the basis for treatment of MRSA infections in veterinary medicine species?

Answer 6

(Treatment should be based on culture and susceptibility, there is no routine medication that is used for treatment of MRSA, especially bc some 1st tier antibiotics can be used to tx it but you need to know based on c+s)

Question 7

Extended-spectrum beta-lactamases (ESBLs) are gram positive/negative (choose) bacteria.

Answer 7

(Negative)

Question 8

(T/F) Extended-spectrum beta-lactamases can not be treated with any penicillins, even those with a beta-lactamase inhibitor.

Answer 8

(F, some still can be inhibited by beta-lactamase inhibitors, but only if you can get a high enough concentration such as clavamox in the urine (so your infection needs to be in the urine))

Question 9

(T/F) If you culture Enterococcus along with E. coli in the UTI of a cat with clinical signs, you need to treat both the Enterococcus and the E. coli.

Answer 9

(F, treat the E. coli and the Enterococcus will go away; if it were a pure, heavy growth of Enterococcus that is another story (would tx with ampicillin or vancomycin (scary) if clinical signs))

Question 10

Why is rifampin often combined with other drugs?

Answer 10

(Because resistance to it develops quickly (i.e. in the middle of tx) so other drugs are used in combo to prevent that from happening, short tx intervals also prevent that)

Question 11

(T/F) Rifampin can be used to treat gram negative, gram positive, and intracellular bacteria.

Answer 11

(T)

Question 12

What are the most common veterinary uses of rifampin?

Answer 12

(MRSP pyoderma in dogs and cats (10 day course) and R. equi in foals (usually combo’d with a macrolide)

Question 13

Rifampin causes hemolytic anemia and hepatotoxicity in foals when combined with what drug?

Answer 13

(Doxycycline)

Question 14

(T/F) Carbapenems are beta-lactam antibiotics.

Answer 14

(T)

Question 15

Why are carbapenems useless against MRSA infections?

Answer 15

(MRSA are resistant to ALL beta-lactams, guess what carbapenems are (beta-lactams); also useless against Enterococci)

Question 16

What drug must be given with imipenem to prevent the formation of renal tubular dipeptidase which causes nephrotoxicity?

Answer 16

(Cilastatin; also increases urine concentration of the active drug)

Question 17

Why is meropenem a better choice for use in small animals (if you have to use it)?

Answer 17

(It is easily administered SC (imipenem is painful given IM or SC), less likely to be nephrotoxic when compared to imipenem, and there is a generic option so cheaper)

Question 18

(T/F) Vancomycin has zero activity against gram positives.

Answer 18

(F, zero activity against gram negatives, it is used for tx of gram positive aerobes (MRSA, Enterococcus) and anaerobes (Clostridium))

Question 19

(T/F) Linezolid has ~100% oral bioavailability in dogs, has good intra and extracellular penetration, has a spectrum of gram-positive aerobes (Enterococci, streps, staphs), and is bactericidal.

Answer 19

(F, all true except bactericidal, linezolid is a protein synthesis inhibitor so it can only be bacteriostatic)

Question 20

Nitrofuran is bactericidal and gets gram negative and gram positive aerobes (such as E. coli and staphs), but that is all if the infection is where in the body?

Answer 20

(The urine)

Question 21

What is the spectrum for fosfomycin?

Answer 21

(Gram positive aerobes, gram negative aerobes, and some gram positive anaerobes)

Question 22

There is no evidence for use of fosfomycin in treatment of infections anywhere but where in dogs?

Answer 22

(Urinary tract)