Some Antibacterial Agents Used with Koi

Some Antibacterial Agents Used with Koi

(oz refers to weight unless otherwise specified)

(Note: many chemicals have been used at one time or another to combat bacterial disease in koi. We have attempted to summarize some of these in a manner helpful to the KHA. In the case of prescription antibiotics, we refer the KHA to a veterinarian or veterinary reference such as Advanced Koi Care by Nicolas Saint-Erne or Koi Health and Disease by Erik Johnson for dosages.)

Antibiotics

Aminoglycosides – they are used against gram negative, aerobic bacteria. . In addition to gram-negative pathogens, aminoglycosides can be effective against some gram-positive organisms, such as Staphylococcus aureus, some mycobacteria, some mycoplasma strains, and some spirochetes. They are sometimes administered concurrently with other antibacterials for a possible synergistic effect. They are very poorly absorbed from the gut, so they are usually injected. Toxicity can be a problem with class of antibiotics so special care must be taken in their use. Often, systemic use is limited to the treatment of serious gram-negative infections resistant to less toxic medications.

Amikacin: by prescription only, refer to veterinarian or veterinary reference for dosage. A semi-synthetic aminoglyside derived from kanamycin. It has the least bacterial resistance and broadest spectrum of activity of any in this group because it resists some aminoglycoside inactivating enzymes. An alternative to gentimicin when toxicity or bacterial resistance is a concern.

Gentimicin: by prescription only, refer to veterinarian or veterinary reference for dosage. May be lethal if injected intraperitoneally. May be injected intramuscularly when less toxic alternatives are ineffective. Gentimicin is also effective against some gram positive bacteria.

Kanamycin: is fed 10 to 20 mg/kg bodyweight/day for 10 days. If fish are consuming 2-3% of body weight in feed per day, the drug would be added to the feed at 660 mg/kg food. It can also be administered as a continuous bath at 5-10 mg/L every three days for three treatments or 750 mg/L for 2 hrs daily. In use for a long time, bacterial resistance is common with this drug.

Neomycin: is fed at 20 mg/kg bodyweigh four times a day for 10 days. If fish are consuming 2-3% of bodyweight in feed per day, the drug would be added to the feed at 3.3 g/kg food. One of the oldest and most toxic aminoglycosides. Like all the whole group, neomycin is poorly absorbed from the gut, so it tends to be effective only against enteric pathogens. On the other hand, it is potentially more toxic than amikacin or gentamicin and injection should be avoided.

Potentiated Neomycin (Tricide-Neo, Neocide 3): used as a well aerated dip for up to 10 minutes or as a spray (fish out of water) for 1 to 2 minutes. Treat every day or every other day for three treatments. Recommended for treatment of bacterial ulcers in koi. In this case “potentiated” means an ingredient is added to weaken the bacteria’s cell wall and allow the antibiotic to enter the bacteria more freely. The use as a dip gets around the poor absorbtion by the gut of neomycin and the danger of toxicity when injected.

Cephalosporins - are beta-lactam antibiotics that produce their bactericidal effect by inhibition of cell wall synthesis. They are less toxic than the aminoglycosides. They are grouped into “generations” that correspond with their general effectiveness against different types of bacteria.

Cefotetan: by prescription only, refer to veterinarian or veterinary reference for dosage. A second generation cephalosporin that is generally effective against gram negative bacteria, but notably Pseudomonas tend to be resistant.

Naxcel (ceftiofur): by prescription only, refer to veterinarian or veterinary reference for dosage. A “new” generation cephalosporin with activity against gram positive bacteria, including Streptococci, as well as gram negative, but not Pseudomonas.

Rocephin (ceftriaxone): by prescription only, refer to veterinarian or veterinary reference for dosage. A third generation cephalosporin that is generally effective against gram negative bacteria, but again Pseudomonas tend to be resistant. Other third generation cephalosporins (ceftazidime and cefoperoazone) are effective against Pseudomonas.

Chloromycetin (chloremphenicol): by prescription only, refer to veterinarian or veterinary reference for dosage. Usually acts as a bacteriostat (stops growth) rather than a baceriocide (kills). Broad spectrum antibiotic against gram positive and negative, aerobic and anaerobic bacteria.

Nuflor/Aquaflor (florfenicol): injectable by prescription only, refer to veterinarian or veterinary reference for dosage. Feed premix available over the counter (Aquaflor) for furunculosis. Fed at 10mg/kg bodyweight for 10 days. Florfenicol is a broad-spectrum, primarily bacteriostatic, antibiotic with a range of activity similar to that of chloramphenicol, including many gram-negative and gram-positive organisms.

Fluroquinolones

Baytril (enrofloxacin): by prescription only, refer to veterinarian or veterinary reference for dosage. Effective against most gram negative bacteria including both Aeromonas and Pseudomonas. Generally well tolerated.

Monobactams

Azactam (aztreonam): by prescription only, refer to veterinarian or veterinary reference for dosage. A synthetic bactericidal antibiotic based on beta-lactam structure that inhibits cell wall synthesis in bacteria. Aztreonam's spectrum of activity resembles that of an aminoglycoside. It is active against most aerobic gram-negative organisms and inactive against gram positive organisms and anaerobic bacteria. In potential mixed organism infections involving gram positive or anaerobic bacteria, an additional antibacterial agent must be included in the therapy. Notably, it is active against many gentamicin resistant strains. However, some Pseudomonas are resistant to Azactam. Typically, it is used to treat septicemia.

Nitrofurans

Nitrofurazone: a nitrofuran that is likely carcinogenic and genotoxic. Use prohibited in food fish in most countries. While it is available over the counter, we do not recommend its use for the reasons stated above. The antibiotic is administered as a bath at 20 mg/L for 1 hour or 10 mg/L for 6hours. Sensitive to light.

Quinolones – these antibiotics work by preventing DNA replication in bacteria. Bacterial resistance is a problem with this group.

Nalidixic Acid: a broad spectrum antibiotic that is fed at 660 mg/kg food/day for 10 days or administered as a bath at 5-13 mg/L may be used for 24 h followed by water change. Behavior of fish during treatment should be monitored. May be repeated.

Oxolinic Acid: a broad spectrum antibiotic that is fed at 330 mg/kg food/day for 10 days or administered as a bath at 1 mg/L for 24 hours or as a bath at 25 mg/L for 30 min.

Sulfonamides

Romet-30 (sulfadimethoxine-ormetoprim): an antibiotic used to treat Aeromonas infection. Treatment can be 50 mg/kg IM or as a feed additive at a rate of 2.5g /kg feed/day for 5 days. A broad-spectrum antimicrobial inhibiting both gram positive and gram negative bacteria. Considered ineffective against most obligate anaerobes. This drug has been used for a long time, so bacterial resistance is a problem.

Tetracyclines - broad spectrum antibiotics with activity against gram positive and gram negative bacteria, including some anaerobes.

Minocycline: has been used to treat gram-positive bacterial infections in koi. Oral treatment at 2 mg/kg. A semisynthetic derivitive of tetracycline.

Terramycin (oxytetracycline): used to treat Aeromonas and Pseudomonas. It is used as a feed additive at a rate of 50-75 mg/kg body weight/day for 10 days. If fish are consuming 2-3% of body weight in feed per day, the drug would be added to the feed at 2.5g /kg feed.

Disinfectant Treatments

Copper sulfate: an external treatment used to treat fungus and fish parasites such as Ich. Dosages vary with the total alkalinity of the water. Do not use if total alkalinity is less than 20 ppm. A preliminary bioassay must be performed if alkalinity (ppm ALK) is less than 50 ppm. Powder measurements relative to ppm ALK are as follows: 20-49 ppm ALK = 0.034-0.07 oz/1000gal (0.25-0.5 mg/L); 50-99 ppm ALK = 0.07-0.1 oz/1000gal (0.5-0.75 mg/L); 100-149 ppm ALK = 0.1-0.13 oz/1000gal (0.75-1mg/L); 150-200 ppm ALK = 0.13-0.27 oz/1000gal (1-2 mg/L).

Formalin: may be used as a 25 ppm (~10 ml/100 gallons) continuous bath or a short term 50 ppm treatement for two hours followed by a 25 ppm continuous. Formalin removes oxygen from the water, thus should not be used if DO is low, unless aeration is employed. Monitor the 2-hour prolonged treatment unattended, and flush formalin from water if fish begin to stress.

Potassium Permanganate: an external treatment used to control bacterial (Columnaris, Aeromonas) and parasitic (Ich) infections. Treatment concentrations at 2 ppm are as follows: 0.027 oz/100gal (2 mg/L). Concentrations higher than this can be toxic to fish if the organic content of the water is low. If the water color changes from red to yellow-brown in less than 4 hours, the KMnO4 has broken down too quickly and you should treat with an additional 2 ppm. Avoid contact with skin and eyes.

Sodium Chloride: an external treatment for fungus (high concentrations) and as an osmoregulatory enhancer (low concentrations). A 10-30min treatment (10,000-30,000 ppm or 1 to 3%) is administered as 13.4-40.2 oz/10gal (10-30 g/L). An indefinite treatment (200-500 ppm) is administered as 0.27-0.67 oz/10gal (200-500 mg/L.

Chloramine-T: used to treat bacterial gill disease (Pseudomonas) as a 1-hour bath at 10 mg/L.

Anesthetics

Clove oil: this anaesthetic is not soluble in water so it must be administered in either a 9:1 concentration of ethanol to clove oil or emulsified in water by vigorous shaking. The lowest effective doses, which vary by the size of the fish, range from 0.5-1 oz/100gal (40-80 mg/L). This anesthetic, while widely used, is not as thoroughly researched as MS-222.

MS-222 (tricaine methanesulfonate): is the most common anaesthetic used today. Effective doses, which vary by the size of the fish range from 0.7-2 oz/100gal (50-150 mg/L).

Equipment disinfectant

Benzalkonium chloride: is used at 100 to 250 mg/L to disinfect equipment.

Chlorine: HTH (calcium hypochlorite,65% chlorine) or liquid bleach (Chlorox) is an effective equipment/tank disinfectant and sanitizer when used at 200 mg/L free chlorine. Fish must be removed before the treatment. To achieve 200mg/L with HTH use 0.41 oz/10gal (309 mg powder/L). To achieve 200 mg/L with liquid bleach use 0.5 fluid oz/gal. Traces of residual chlorine must be flushed from equipment before re-entering fish.