APBI - M2 L4

Pharmacology

• study of drugs and chemicals on living systems

  • basis of treatments

Therapeutic treatments

• those that’re applied after a problem has occurred; reactive treatments

• Chemicals applied in preventive manner

•  usually directed against bacterial and/or parasitic diseases brought about by stress

  • main application = form of application (metabolic products of microorganisms) designed to inhibit or kill competing bacteria

  • some broad spectrum and active against many bacteria others not so much and only inhibit few species

 Drugs don’t often eliminate infectious organism

Keep applying antibiotics even if fish look better

Antibiotics

• substances that kill or inhibit bacterial growth

  • may be natural products of microorganisms (bacterial, fungi), semi-modifications, or fully synthetic compounds

  • competitive factors

• don’t kill viruses

Resistance development in face of selection pressures

• bacterial capacity to adapt to external changes using these mechanisms

  • developing resistance lets resistant orgs to proliferate in prevailing conditions

Inherent/intrinsic resistance

species not normally susceptible to particular drug

• could be due to inability of antibacterial agent to enter bacterial and reach target site

• or lack of affinity between antibacterial and its target (site of action)

• or absence of target in the cell

Acquired resistance

• when bacterial species normally susceptible to particular drug but certain strains express drug resistance

  • after resistance develops, antibiotic not able to cure or treat disease caused by infective agent

  • low level resistance might be detected by slight increase in minimal inhibitory concentration (MIC) for antibiotic from usual value (not necessary of clinical significance)

  • higher degree of resistance characterized by MIC that exceeds concentrations of drug safely attainable in patients tissues

Plasmid acquisition

2 basic mechanisms for development of antibiotic resistance in microbes

• accounts for enzymes that inactivate the antibiotic, or titration, by over-production of target enzyme

• resistance genes carried on R plasmids

• plasmids replicate independently of bacteria's genomic DNA; circular

• inheritance of resistance from plasmid = exogenous inheritance since resistance genes on R plasmids have diff base comp from corresponding genes in host

Chromosomal mutant

2 basic mechanisms for development of antibiotic resistance in microbes

• resistance acquired by mutation results in altering of target site most of time

• changing protein's structure by chromosomal mutation → changes conformation of target site → antibiotic doesn't bind

• might also result in decreased permeability to antibiotic

• mutations allow resistance to one antibiotic / closely related antibiotics cuz structure of specific protein = altered

Conjugation

• how plasmids are transmitted between bacteria

  • one way transfer of genetic info

  • not species-specific

  • many diff species of bacteria share similar resistance methods

Transposons

• discrete genetic units that translocate from one bacterial genome to another

  • incapable of autonomous replication; unlike plasmids

  • have special sequences @ terminals → can integrate into other strands of DNA (transposition)

• Plasmids can obtain new resistance genes by this

 

Gene cassettes

• plasmids can also acquire resistance genes from these

  • they encode specific resistance gene

  • integrons have to provide receptor site for them + enzyme that catalyzes mobility of gene

 

Prophylactic treatments

designed to prevent disease outbreaks through vaccination, biosecurity, and management practices

• use is usually discouraged due to resistance concerns

• prop vaccination + improved husbandry = essential prevention tactics

Multivalent vaccines

• one vaccine can provide protection against number of diff pathogens

  • many contain compounds called adjuvants or immunomodulators

  • compounds supposed to start body's production of protective molecs and might help fish defend fish itself against other pathogens that vaccine not specifically designed to combat

Killed vaccines

• vaccines where chemicals, or heat, used to kill but not destroy pathogen; commonly called bacterins

  • most on market today = bacterins made from cultures of disease agents grown under specific conditions then killed

  • leaves external structure intact so that they stimulate immune system to produce protective antibodies and maintain memory of agent

  • doesn't cause disease and can't replicate

Attenuated vaccines

• v effective; pathogen alive and viable, weakened, can't cause disease

  • it will infect fish and reproduce sufficiently enough to stimulate immune system

  • concern: it could revert to virulent state so pause on development for fish cultures

Sub-unit and DNA vaccines

• expose fish to parts of the pathogen that incite immune response 

  • made by growing infectious organism → ID-ing external surface responsible for stimulating protective immune response → using genetic engineering to produce another org that has same external structure on its surface

  • that engineered org can be used to make a bacterin

  • can apply the DNA that codes for the imp antigens

Immersion treatments

• strong concentration of chemotherapeutant used for short period of time

• fish suspended in aerated container of solution

• exposure varies with treatment but don't generally last more than few minutes

• duration short, but make sure container with therapeutics is aerated

• they need more oxygen when stressed; and container is probably at lower conc than enclosure they just came out of

• make sure water is same temp

• water for anaesthetic and treatment baths should come from same enclosure as fish you're treating

 

Spraying

• exposed skin, mucus, potentially gills sprayed w/ vaccine

  • somewhat stressful for fish

Rapid flush

• strong conc of chemical flushed through treatment system

• treatment duration = length of time it takes to completely replace water in trough, tank, incubator

• entire chemical added at once; moves through unit as water is exchanged

 

Bath method

• is longer than dip or rapid flush

  • required amount of chemical added and remains for prescribed length of time

  • ensure chemical is adequately mixed in treatment unit

• prolonged + indefinite variety

• should be observed continuously during treatment

• if distress seen, untreated water should be added quickly and chemical flushed out

• use aerators in tanks during treatment to maintain adequate oxygen supply

Prolonged variety

type of bath method; where chemical is rapidly flushed from system after specific timeframe

Indefinite variety

type of bath method; chemical allowed to dissipate or disintegrate naturally

Chloramine-T

• useful surface anti-parasitic and antibacterial treatment usually as bath treatment @ 10-20 mg/L between 1 hr - 3 days

  • dose depends on use, pH and water hardness

  • shouldn't be used as high dose dip treatment

    • chemical action will cause serious damage to fish

  • may also be dangerous to person

    • wear mask and goggles when handling to prevent injury to skin or eyes

Injections

• Not really viable unless small numbers of valuable fish or broodstock

 

• Fish have to be anaesthetized fully minimize handling stress + ease of injection

  • fish weighed and vol of required drug then calculated and injected either intramuscular or intra-peritoneal (into body cavity)

  • dorsal sinus injection was also a common method in the past; needle isn't inserted long enough for treatment to permeate, so most follows needle out of fish

Intraperitoneal Injection (IP)

used in fish particularly farmed salmonids

• Peritoneal cavity = easy access to deposit medications and vaccines

  • this way rapid uptake of compounds into systemic circulation of fish

• Oil added to IP-injected vaccines to delay antigen release

•  safe and fast process

Dorsal sinus injections (DS)

drugs placed connective tissue lined sinus between back muscles of fish

• Technique og developed to deliver erythromycin to broodstock cuz antibiotic caused muscle necrosis and absorbed too rapidly is intramuscularly injected

•  hit exact midline and proper depth; if needle not left in for short period following injection, much of injected compound often follows needle as drawn out

Intramuscular injections (IM)

Not commonly used method of injection

• Several sites that can be injected:

  • midway between dorsal fin and lateral line (midline dorsal site)

  • musculature of peduncle or flank (towards tail)

  • pectoral fin muscles

• Not practical w/ small fish; lacks muscle