1. Antimicrobials CHAPTER 14 Dr. Dipa Brahmbhatt VMD MpH dbrahmbhatt@vettechinstitute.edu

2. Basic Terminology An antimicrobial is a chemical substance that has the capacity, in diluted solutions – To kill (biocidal activity) OR Attack something that micoorganism have but patient doesn’t – Inhibit the growth (biostatic activity) of microbes Attack both have but microorganism needs more of it Antimicrobials can be classified as: – Antibiotics – Antifungals – Antivirals – Antiprotozoals – Antiparasitics – Ch 15 Staphylococcus

3. Pathogenic Microorganisms Cause a wide variety of infections and illness in different organs or body systems May be classified as local or systemic – A localized infection may involve skin or an internal organ and may progress into a systemic infection – A systemic infection involves the whole animal and is more serious than a local infection

4. Pathogenic Microorganisms Enter the body through: Integumentary – Break through skin or mucous membrane Respiratory system – Inhaling contaminated droplets GI tract – Ingestion contaminated food and water Genitourinary – Contaminated vaginal secretions, semen or urine

5. Antimicrobials Prokaryotic – Fewer organelle & smaller than Euk. – Cell wall +/- capsule – Cell/ plasma membrane – Nucleoid – Cytoplasm – Ribosomes – +/-: pili, plasmids, flagellum – Few have endospore Eukaryotic – Cell / plasma membrane – Nucleus – Nucleolus – Cytoplasm – Mitochondria – Golgi apparatus – Endoplasmic reticulum – Ribosomes – Vacuoles – Lysosomes

6. Boundary/ semi-permeable Controls cellular activity Genetic material Nucleolus Produces RNA that Forms ribosomes Semi-fluid medium with organelles Energy producers Chemical processor of the cell Has ribosomes Syn. proteins No ribosome Syn. Lipids and some carbohydrates Site of protein synthesis Small, membrane bound Organelles with food, water or metabolic waste Digestive system of the cell

7. Not membrane bound Smaller than Eukaryotic Barrier against phagocytosis Hairlike protein extensions Attach/communicate with Other cells DNA outside chromosome Replicate independently Pass info via pilus Mobility FEW BACTERIA HAVE ABILITY TO PRODUCE ENDOSPORES Persists in variable environment

8. Antibiotics spectrum of action Antibiotics work only on bacteria and are described by their spectrum of action (range of bacteria for which the agent is effective) either – Narrow-spectrum antibiotics work only on either gram-positive or gram-negative bacteria (not both) both – Broad-spectrum antibiotics work on both gram-positive and gram- negative bacteria (but not necessarily all) bactericidalbacteriostatic Antibiotics can be classified as bactericidal or bacteriostatic kill – Bactericidals kill the bacteria inhibit the growth – Bacteriostatics inhibit the growth or replication of bacteria

9. Gram stain Procedure Staphlylococcus sp. Streptococcus sp. Salmonella sp. Proteus sp.

10. Antimicrobials The goal of antimicrobial treatment is to render the microbe helpless (either by killing them or inhibiting their replication) and not to hurt the animal being treated Antibiotic treatment is accomplished by making sure that the infecting bacteria are susceptible to the antibiotic, that the antibiotic reaches the infection site and that the animal can tolerate the drug

11. Agar Diffusion Test A.k.a. Kirby-Bauer antibiotic sensitivity testing Used to determine if a particular antibiotic is effective against a particular bacterium. Antibiotic-impregnated disks placed onto agar plates containing bacteria being tested. After incubation at proper temperature for the proper time, zones of inhibition (clear zones) are measured and compared to a standardized chart to determine R. – R = resistant (antibiotic does not work); I = intermediate (antibiotic may work); S = sensitive (antibiotic will work)

13. Broth Dilution Method Minimum Inhibitory Concentration (MIC): Lowest conc. Of Antibiotic that visually inhibits growth of bacteria

14. EFFECTIVE ANTIBIOTIC Bacteria sensitive to antibiotic Proper dose of Ab. Get’s into infection site at high enough doses

15. How Do Antibiotics Work? Antibiotics work by a variety of mechanisms: – Inhibition of cell wall synthesis Bacteria have cell walls & animals don’t Bactericidal: growing and dividing not in developed bacteria – Damage to the cell membrane Alters membrane permeability Bactericidal/static Loss of cellular substances causes lysis of cell

16. How Do Antibiotics Work? – Inhibition of protein synthesis In ribosomes – RNA copy (of DNA), t RNA (AA’s) – Disrupts linkage of AA’s – Bactericidal/static – Interference with metabolism Block enzymes / essential nutrients – Can’t divide and cell death Bacteriostatic – Impairment of nucleic acids Intefere with nucleic acid production – Can’t divide/ function properly Bactericidal

18. cidal static

19. Considerations when using antibiotics Antibiotic resistance – Means that the bacteria survive and continue to multiply after administration of the antibiotic – Occurs when bacteria change in some way that reduces or eliminates the effectiveness of the agent used to cure or prevent the infection – Causes Drug not properly used (used for viral infection) Not admin. For proper length of time Not at proper dosage

20. Considerations when using antibiotics Antibiotic resistance dvlps. through Natural/Intrinsic resistance Ab. Acts on enz. Systems or biological processes not used by microorganism Acquired resistance: sensitive before Bacterial mutation – E.g. bacteria produce beta-lactamase, inactivates penicillin Bacteria acquiring genes that code for resistance – Plasmids Other means – Cross –resistance e.g. between Ab’s. with same actions: penicillins & cepalosporins – Noscomial infections (sick patients and close contact) – Handwashing

22. Considerations when using antibiotics An antibiotic residue is the presence of a chemical or its metabolites in animal tissue or food products Residue is not usually degraded by cooking/ pasteurization – Antibiotic residues can cause allergic reactions in people or can produce resistant bacteria that can be transferred to people who consume these products – Withdrawal times for antibiotics are aimed at eliminating antibiotic residues in food-producing animals

23. Considerations when using antibiotics The FDA approves all drugs marketed for use in animals in the United States The FDA also establishes tolerances for drug residues to insure food safety The FDA also establishes withdrawal times and withholding periods – Times after drug treatment when milk and eggs are not to be used for food, and also when animals are not to be slaughtered for their meat – FARAD: Food Animal Residue Avoidance Databank

24. Classes of Antibiotics Cell wall agents Protein synthesis agents Antimetabolites Nucleic acid agents Miscellaneous agents

25. Cell Wall Agents Penicillins (mold) Penicillins (mold) beta-lactam – Have beta-lactam structure that interferes with bacterial cell wall synthesis – Identified by the –cillin ending in the drug name – Spectrum of activity depends on the type of penicillin

26. Cell Wall Agents Natural Penicillins Natural Penicillins – Penicillin G and V are narrow-spectrum gram-positive antibiotics (Staphylococcus sp. & Streptococcous sp.) Penicillin G is given parenterally (inactivated by stomach acid) – Only sodium or potassium salt of Pen-G can be admin. IV, IM: peak levels 20 mins – Refrigerated: 14 days – Procaine & Benzathine (suspensions): increase duration – PPG: 24 hr. duration – Benzathine PG: 5 days – SE: Anorexia, V/D (orally), hypersensitivity

27. Cell Wall Agents Natural Penicillin (cont …) Penicillin V is given orally – Give PCN on empty stomach (except amoxicillin) – Penicillin V potassium: preferred better absorbed in GI and stable in stomach acid – Broader-spectrum penicillins are semi-synthetic Slowly excreted from kidneys Examples include amoxicillin, ampicillin, carbenicillin, ticarcillin, and methicillin

28. Cell Wall Agents Beta-lactamase resistant penicillins More resistant to beta-lactamase / penicillinase(an enzyme produced by some bacteria that destroys the beta-lactam structure of penicillin) Examples include methicillin, oxacillin, dicloxacillin, cloxacillin, and floxacillin – Potentiated penicillins are chemically combined with another drug to enhance the effects of both amoxicillin and clavulanic acid An example is a drug containing amoxicillin and clavulanic acid (which binds to beta-lactamase to prevent the beta-lactam ring from being destroyed) E.g. Clavamox and Augmentin

29. Table 14-2

30. Cell Wall Agents Cephalosporins (fungus derivative) Cephalosporins (fungus derivative) – Are semi-synthetic, broad-spectrum Have the beta-lactam ring (like penicillins) Can be identified by the ceph- or cef- prefix in the drug name Tx: Respiratory, skeletal, genitourinary, skin, soft tissue Peri-operatively SE: v/d (give w/food), phlebitis, myositis, nephrotoxic four generations – Are classified into four generations In general, as the number of the generation increases, the spectrum of activity broadens (but becomes less effective against gram- positive bacteria)

31. Cell Wall Agents 1 st generation Greatest cidal/static gram – and some against gram + Can be inactivated by beta-lactamase No blood-brain barrier – 2 nd generation Broader spectrum of activity gram – compared to 1 st No BBB – 3 rd gen. Better gram – Resistant to some beta-lactamase – 4 th gen. Like 3 rd and Pseudomonas aeruginosa and Enterobacteriaceae More active against gram + than 3rd Cefpodoxime: Daily Cefovecin: 14 days Cefpodoxime: Daily Cefovecin: 14 days

32. Convenia® (cefovecin sodium) Convenia® (cefovecin sodium) – First antibiotic that provides an assured course of treatment by providing up to 14 days of treatment in a single injection, eliminating missed doses associated with daily oral antibiotic administration – Labeled specifically for secondary superficial pyoderma, abscesses, and wounds (S. intermedius, S. canis ) in dogs and abscesses and wounds (P. multocida) in cats. – Must be reconstituted, refrigerated, and used within 28 days of reconstitution – Second dose may be necessary in 14 days.

34. Cell Wall Agents Bacitracin Bacitracin – Disrupts the bacterial cell wall via polypeptide chain – Effective against gram-positive bacteria – Used topically (skin, mucous membranes, eyes) and as a feed additive – SE: Nephrotoxic Vancomycin Vancomycin – Bacteriocidal; effective against many gram-positive bacteria; used for resistant infections (to penicillin/cephalo.) – Useful in treatment of Staphylococcus aureus & Clostridium difficile (humans) – SE: Nephro/Oto toxicity, pain IV injection

35. Cell Membrane Agents Polymyxin B (plasma membrane, polypeptide) Polymyxin B (plasma membrane, polypeptide) – Works by attacking the cell membrane of bacteria (remember that animal cells have cell membranes too) – Is a narrow-spectrum, gram - antibiotic Not absorbed when taken orally or applied topically Used as an ointment or wet dressing – Often combined with neomycin and bacitracin = triple ABX ointment

36. Protein Synthesis Agents Aminoglycosides (Streptomyces microbes) Aminoglycosides (Streptomyces microbes) – Interfere with the production of protein in bacterial cells – Are a specialized group of antibiotics with a broad spectrum of activity, used for gram-negative bacteria (septicemia, ocular, otic) – Are not absorbed well from the GI tract, so are given parenterally – May be recognized by –micin or –mycin ending in drug name (but are not the only group to use these suffixes) – Side effects are nephrotoxicity and ototoxicity – Examples include gentamicin, neomycin, amikacin, tobramycin, and dihydrostreptomycin – NOT approved for use in food-producing animals. – Vancomycin & Erythromycin ARE NOT aminoglycosides

37. Protein Synthesis Agents Tetracyclines Tetracyclines – Are a group of bacteriostatic antibiotics with a broad spectrum of activity, including rickettsial agents (Mycoplasma, Chlamydia) Treats Lyme disease, Ehrlichia, Hemobartonella, leptospirosis, – Can bind to calcium (affecting muscle contraction) and be deposited in growing bones and teeth (yellow), or bind components of antacids and other mineral-containing compounds – Are recognized by –cycline ending in drug name – Short acting water soluble: tetracycline, oxytetracycline, chlortetracycline, – Long acting lipid soluble: doxycycline, and minocycline – Oral and parenteral forms – Don’t give to young, pregnant or with dairy products, antacids, kaolin, pectin, bismuth – SE: ORAL: v/d, renal damage; PARENTERALLY: anaphylaxis, hypotension, shock

38. Protein Synthesis Agents Chloramphenicol Chloramphenicol – Is a broad-spectrum antibiotic that penetrates tissues and fluids well (including the eyes and CNS) – Has toxic side effects (bone marrow depression) that extremely limit use: Aplastic anemia – Use caution when handling this product (gloves) – Chloramphenicol is the only drug in this category – Also available in ophthalmic solution – Used for RMSF (among other conditions) – Banned from use in food-producing animals. – Not considered a first-line drug (cause of toxic SE)

39. Protein Synthesis Agents Florfenicol (Nuflor®) Florfenicol (Nuflor®) – Is a synthetic, broad-spectrum antibiotic – Injectable solution – Used to treat bovine respiratory disease and foot rot. – SE: include local tissue reaction (possible loss of tissue at slaughter), inappetence, decreased water consumption, and diarrhea – Florfenicol is the only drug in this category

40. Protein Synthesis Agents Macrolides Macrolides – Interfere with the production of protein in bacterial cells – Are broad-spectrum antibiotics that have a large molecular structure – Used to treat penicillin-resistant infections or in animals that have allergic reactions to penicillins – May cause stomach upset in animals Erythromycin (oral or ointment) Tylosin (used mainly in livestock - can cause fatal diarrhea in horses) Tilmicosin (used to treat bovine respiratory disease – single injection – 3 days)

41. Protein Synthesis Agents Lincosamides Lincosamides – Interfere with the production of protein in bacterial cells – Are narrow-spectrum, gram-positive antibiotics – Side effects include GI problems Veterinarians typically use erythromycin instead. – Examples include clindamycin, pirlimycin, and lincosamide

42. Antimetabolites Sulfonamides Sulfonamides – Are broad-spectrum antibiotics that inhibit the synthesis of folic acid (needed for the growth of many bacteria) – Some are designed to stay in the GI tract (enteric forms); some are absorbed by the GI tract and penetrate tissues (systemic forms) – Side effects include crystalluria, KCS (dry eye), and skin rashes – Precipitate in kidneys of animals that are dehydrated or have acidic urine; Adequate water intake = very important! – Bactericidal when potentiated with trimethoprim or ormetoprim – Examples include sulfadiazine/trimethoprim, sulfadimethoxine, and sulfadimethoxine/ormetoprim

43. Miscellaneous Agents Nitrofurans Nitrofurans – Are broad-spectrum antibiotics that include furazolidone, nitrofurazone, and nitrofurantoin – Used to treat wounds (topically) and urinary tract infections – Filtered unchanged through kidneys – Carcinogenic residues in animal tissues Nitroimiazoles Nitroimiazoles – Have antibacterial and antiprotozoal activity; work by disrupting DNA and nucleic acid synthesis – An example is metronidazole, which is considered by some the drug of choice for canine diarrhea

44. Nucleic Acid Agents Fluoroquinolones Fluoroquinolones – Are antibiotics with fluorine bound to the quinolone base, which increases the drug’s potency, spectrum of activity, and absorption – Are broad-spectrum antibiotics (gram + and gram -) – Can be recognized by –floxacin ending in drug name bubble-like cartilage lesions in growing dogs – Side effects include development of bubble-like cartilage lesions in growing dogs, and crystalluria – Quinolone-induced blindness in cats. – Indiscriminate use may result in bacterial resistance. – Examples include enrofloxacin, ciprofloxacin, orbifloxacin, difloxacin, marbofloxacin, and sarafloxacin

46. Metronidazole (Flagyl®) Metronidazole (Flagyl®) is drug of choice for canine diarrhea – Used to treat Giardia and Trichomonas infections – Also used for amoebiasis and anaerobic bacteria – Oral or intravascular administration – No approved veterinary form of metronidazole (used off-label) – Do not use in pregnant animals – Can cause neurologic signs (especially when given IV)

47. Miscellaneous Agents Rifampin Rifampin – Disrupts RNA synthesis – Is broad-spectrum; used in conjunction with other antibiotics (usually erythromycin) – May impart a reddish color to urine, tears, sweat, and saliva. Refer to Table 14-2 in your textbook for a review of antibiotics used in veterinary practice