Micro1- Aminoglycosides

• coag + organisms: most all encode a penicillinase (only potentiated penicillins will work against them)
• [GET OTHER ONE]

• radial immunodiffusion
• Zinc sulfate turbidity test

• blood cultures (b/c sepsis is what you're worried about here)
• surgical prep of venipuncture site b/c culture is susceptible to skin surface contamination

E. coli

• Strep zooepidemicus
• E coli
• Actinobacillus spp
• Salmonella enterica

• collect blood culture and send out
• initiate empirical therapy- IV antibiotics (3rd gen ceph- ceftiofur, ceftazidime; dual therapy with aminoglycoside indicated)
• aggressive supportive care
• adjust antibiotics based on blood culture results

• cidal against aerobic and facultative gram -
• some gram +, especially staphs
• Gram -: Enterobacteriacae, Pseudomonas
• Gram +: Staph, Enterococci (only when combined with a beta-lactam)
• NO COVERAGE FOR ANAEROBES

• [ALL PARENTERAL or topical]
• Gentamicin
• Amikacin
• Tobramycin (rarely used b/c too expensive)
• Neomycin (not used much anymore)- exception- administered orally for hepatic encephalopathy in dogs
• Streptomycin (not used much anymore)

• oral absorption
• Neomycin is given orally for dogs with hepatic encephalopathy because we want the drug to stay in the GI tract

• Proteus
• Enterbacter
• these bugs produce NH3; we want to kill these microbes in cases of hepatic encephalopathy--> give oral neomycin

O2-dependent entry into bacterial cell wall (ie. not effective against anaerobes; also, facultatives don't die if there is no O2 present)--> binds to 30S ribosome, causing misreading of mRNA--> protein synthesis is disrupted--> cell membrane is damaged--> drug uptake increases

• poor lipid solubility
• distribution to ECF (low Vd)
• no intracellular accumulation
• does not cross BBB
• entirely eliminated by kidneys

• dose high, dose infrequently
• maximum Cmax:MIC, minimum trough level

concentration- dependent (Cmax: MIC≥ 10); bactericidal

• continued kill despite dropping MIC (even though conc-dependent)
• Higher Cmax--> more post-antibiotic effect
• this allows us to dose SID (or even longer)

• temporary decline in drug uptake (kinda of like saturation with the drug)
• therefore, we have to wait long enough between doses for bacteria to become susceptible again (about 16+ hours)

acidic; abscesses, necrotic debris (not good for these cases)

• Ototoxic: cochlear, vestibular
• Nephrotoxic: tubular necrosis
• b/c they're so positively charged, they line up on the brush border of these types of cells--> with normal turnover of the cell membrane, all of this drug is getting endocytosed into the cell--> eventually, these things coalesce, rupture, and kill the cell

• decreased GFR d/t dehydration, renal dz
• given concurrently with other nephrotoxic drugs, such as NSAIDs (d/t constriction of afferent arteriole)

• take a blood sample and measure serum aminoglycoside level (at 24hour mark- look for 24-hr trough level) to determine exactly how often to re-dose
• Goal is to:
• maximize Cmax (to maximize PAE)
• minimize trough

• take blood samples to measure 24-hr trough level
• look for urinary casts (cellular or granular)
• BUN is not acceptable (this is a late indicator of big time damage)

Neomycin> Gentamicin>>> Amikacin> Tobramycin

Gentamicin> Neomycin> Amikacin= Tobramycin

Neomycin> Amikacin= Gentamicin> Tobramycin

• decrease presynaptic Ca uptake--> decreased Ach release
• this can lead to respiratory arrest
• risk factors for this include: low blood Ca, Mg
• Neomycin> Amikacin> Gentamicin> Tobramycin

• Plasmid-encoded enzymes in Gram + and Gram -
• Not all enzymes inactivate all drugs- this is why susceptibility testing is extremely important

• Salmonella enterica
• Clostridium difficile
• Clostridium perfringens
• Lawsonia intracellularis
• Neorickettsia risticii

• Foal heat diarrhea (6 days after birth)
• Salmonella enterica
• C. difficile Type C (Type A is always cultured...not significant)
• C. perf

• fecal culture with enrichment- 5 negative sequential cultures
• real-time PCR- fast, but no susceptibility data

• culture
• toxin type isolate by PCR

• Culture
• ELISA on feces for toxin

• obligate intracellular organism (ie. YOU CANNOT CULTURE IT)
• PCR on feces or serology IFA

• obligate intracellular (cannot culture!!!!!)
• PCR on feces or serology IFA
• common in Ohio!!!! spring and summer- moreso in adult horses
• Treated with Tetracycline

• Salmon poisoning- Neorickettsia helminthoeca
• not common in this part of the country (seen out west)
• Treated with tetracycline