Antibiotics in Food Animals Flashcards
Fuselier material
What 3 major spp.of bacteria have known resistance to sulfonamides?
Pseudomonas
Bacteroides
Enterococcus
Microbes that rely on follic acid will have susceptibility to this antibiotic…
sulfonamides
General concept behind sulfonamide activity…
- In* bacteria that rely on FA:
- FA** precursor —> {reductions*} —>THFA {bioavailable form}
Potentiating Sulfas…
PABA & dihydrofolate reductase are blocked —> prevents production of THFA
—> bactericidal activity
Why would we not use systemic sulfas to treat mastitis?
it’s a weak acid; milk is a weak base…
—> there’s some collection; but not enough to be therapeutic
but it still will be detected in milk
generally, don’t use it, esp not on dairies!
What is the only sulfonamide that you can use on adult dairy cows?
Sulfadimethoxine
T or F:
Potentiated sulfas are used off label in calves & pigs.
True
What do Penems bind to that causes immediate cell death?
Penicillin-Binding Protein-1
What binding site do all beta-lactams target?
Penicillin Binding Proteins
{PBP}
Only _penems_ bind PBP-1
→ *immediate cell death
The others…*
{used in food animals: PBP-2, PBP-3}
cause cell membrane distortion so when the bacT goes to replicate, it can’t & it dies
…or it ruptures
T or F:
Penicillins always need more time than cephalosporins.
False!
Cephalosporins generally need more time than Penicillins.
What are the two main ways by which resistance or avoidance is achieved in the pathogen response to ß-lactams?
- ß-lactamase production
- altering the PBP to prevent binding
What class of antibiotics could we use for **G+** ***anaerobic*** bacT,
*select* **G-** bacT {*_Listeria*_}, & spirochetes {_*Leptospirosa_*}?Natural Penicillins
{Procaine Penicillin G}
In horses, the “shot gun approach” is penicillin & gentamicin, but we wouldn’t want that for calves because there’s an 18-month withdrawal period per injection of gentamicin. What did Dr. Fusilier tell us his favorite treatment for calf omphalophlebitis is? & Why?
Procaine Penicillin G & Ceftiofur
{strong G+ anaerobic; very good G- aerobic}
Bc it’s often a mixed infection…
What type of ß-lactams would we use to treat meningitis?
3rd Generation Cephalosporin
{i.e. Ceftiofur, Cefovecin (aka Convenia®)}
these 3rd gen.cephalosporins penetrate the CNS well
What’s Hexasol?
Combo: oxytetracycline & flunixine meglumine
What do tetracyclines work best for?
good for early stages of pink eye & foot rot,
also works really well against Anaplasma!
bind 30s ribosome;
minimal affinity for mammalian ribosomes;
inhibit protein synth.
T or F:
No gentamicin is labeled for pigs older than 5 days old.
true
so if you give it to a month-old pig—> zero tolerance
{stays in kidney tissue for a long time}
Gentamicin has an 18-month withdrawal period per injection in horses, but in piglets 3-5 days old, the withdrawal period is…?
40 days!
Aminoglycosides {Neomycin, gentamicin} are bactericidal; this means the ___________ is what matters, not the __________.
Concentration, not the duration
becasue of this, the dosing frequency is increased to keep it at the right concentration
primarily G- aerobic spectrum
What makes aminoglycosides dangerous from a toxicity standpoint?
They don’t differentiate b/t mammalian mitochondria & bacterial mitochondria
It just binds. This is also the reason we see phototoxicities & renal toxicities associated w.overuse of aminoglycosides.
What are the restrictions regarding gentamicin and cattle?
NOT labeled for use in cattle!!
buuuut,
current FARAD w.drawal times in cattle…
= 18 mo/single injection {meat}
& 5 days {milk}
…following IV, IM, or SQ dose
What are the restrictions regarding gentamicin in goats & sheep?
18 mo/single injection {meat}
& 10 days {milk}
What’s with food animals and chloramphenicol?
Chloramphenicol residues = lose license + go to jail
Florfenicol- took para-nitro group off — makes it safe
most important properties of florfenicol {3}
bacteriostatic {by nature}*
binds 50s ribosome
time-dependent
*some pathogens have very lo MIC for florfenicol - so at its max concentration,
it’s so suppressive that it kills them…
i.e. bacteriocidal against Fusobacterium, and Manheimia & Pasteurella at its Cmax.
In a case of BRD, keratoconjunctivitis, Histophilus somnei, or interdigital phlegmon {foot rot}, what antibiotic would we reach for?
Florfenicol
A beef cow has mastitis that you’re not gonna be able to bring in & give intra-mammary infusions every day, but you can catch it about every 3rd day. What do you want to treat it with?
Florfenicol
systemic florfenicol has high concentrations in mammary tissue
& does really well for typical mastitis cases in beef cattle
Florfenicol is not labeled for use in dairy cows, but extra-label use is permitted. What is the withdrawal period for florfenicol given IM in lactating dairy cattle?
60 days
If it was beef, it would be 28 days
What is Tylosin mainly used for today?
Liver abscesses
some places use it for Mycoplasma, too
What is the “parent compound” of the Macrolide class of antibiotics?
Erythromycin
Where do macrolides accumulate?
in lysosomes of neutrophils & macrophages
What are the Azalides?
newest development in the macrolide class;
have a higher positive charge—increasing affinity for intracellular sites
I.e. Azithromycin, Tulathromycin, Gamithromycin, & Tildipirosin
Aminoglycosides as well as tetracyclines act by binding the 30s ribosome. So how are they different?
Tetracyclines bind reversibly;
Aminoglycosides bind irreversibly
Does florfenicol concentrate better in healthy or diseased lung? What about macrolides??
Florfenicol:
better concentration in dz’d lungs
lipid soluble, concentrates in tear film, wide tissue distribution
Macrolides:
better concentration in healthy lungs
Why do we like Pulmotil®?
tilmicosin {macrolide}
has good absorption thru the gut
also 72hr T1/2=healthy lung tissue
What animals do we avoid using lincosamides?
Never use in fore-/hind-gut FERMENTORS…
BECAUSEthey have an affinity forG- organisms
—> Clostridial overgrowth —> diphtheric membranes
Which fluoroquinolones are approved for cattle?
enrofloxacin
&
danofloxacin
