Antimicrobial resistance - what vet techs need to know
DIEPPE, NB – In the last 20 years, there has been an emergence of resistant tuberculosis, methicillin resistant staphylococci, and increasingly resistant E. coli, salmonella, and clostridium. Antimicrobial resistance, defined as “the ability of a microorganism to withstand the effect of a normally active concentration of an antimicrobial agent”, prolongs hospital stays, increases morbidity, affects animal welfare by prolonging suffering, and increases the cost of therapy and production, explained Sandra McConkey, DVM, PhD, Dipl. ACVP, speaking at the Eastern Veterinary Technicians Association Conference.
How does antimicrobial resistance work?
Antimicrobials select for resistance when they kill susceptible organisms, leaving behind resistant organisms. Resistance can occur to any antimicrobial agent, usually by any one of several different mechanisms. It can occur when an organism acquires a gene that produces enzymes that inactivate a drug, or a gene that alters the binding site of a drug thereby decreasing the drug’s affinity or totally preventing a drug from binding. Organisms may also develop drug transporters that can transport one or more drugs out of the organism; reduce permeability to a drug so that there is less drug uptake; or they may acquire the ability to bypass or repair damage from antimicrobials.
Acquired resistance can be slow or rapid in onset. Bacteria under stress due to the presence of antimicrobials or detergents, and bacteria already resistant to one antimicrobial, are more prone to developing resistance to additional antimicrobials because their DNA is predisposed to mutating and may have compromised DNA repair mechanisms. Acquired resistance due to chromosomal mutations is often a slow stepwise process with succeeding generations progressively showing more resistance. Acquired resistance due to the transfer of one or more resistance genes on a plasmid is rapid and can occur between different bacterial species.
Multidrug resistance
Multidrug resistance describes an organism that is resistant to two or more classes of antimicrobials that it is usually considered sensitive to. Common examples are methicillin resistant Staphylococcus aureus or pseudintermedius. Pseudomonas, E. coli, and Salmonella spp. are also capable of developing resistance to many antimicrobials; there are now Salmonella spp. that may carry resistance to nine antimicrobials.
Can we monitor resistance?
Monitoring is difficult. The clinical signs may resolve because the number of bacteria has decreased but there may still be resistant bacteria remaining. Dr. McConkey said that the best method for monitoring the development of resistance is to measure MICs over a period of time, but this is not economically viable.
Factors affecting resistance
Antimicrobial resistance is increasing due to overuse in both humans and animals, and organizations worldwide are now working to address this problem. This has resulted in the ban of ceftiofur injections in chicken hatcheries and the recent announcement that much of the use of antimicrobials as growth promotants in Canada will be phased out.
A considerable amount of antimicrobial resistance in human medicine is due to the overuse of antimicrobials by human doctors but some is due to overuse in veterinary medicine. Resistant organisms can transfer from animals to people indirectly by ingestion of food or water-borne bacteria or exposure to contaminated environments. Direct transmission occurs following exposure to animal carriers. Veterinarians and veterinary staff are at an increased risk for direct transmission.
The most important factor is repeated exposure to sub-optimal concentrations, which can occur even with appropriate therapy. Sufficient drug dosages to treat pathologic organisms in one location can result in low antimicrobial concentrations elsewhere in the body, predisposing to resistance within commensals. Other factors that can lead to suboptimal concentrations are insufficient efficacy of a drug, poor owner or producer compliance, and the host immune system’s ability to decrease the number of bacteria.
What can vet techs do to minimize antimicrobial resistance?
When antimicrobials are required, decide what to use by logic rather than repeatedly simply reaching for the same drug.
-Work with clients to avoid the need for antimicrobials (integrated disease control programs, animal isolation programs)
-Support the judicious use of antimicrobials. When possible, ensure the organism has been identified first to narrow the antibiotic spectrum
-Develop and support clinic protocols. Record and justify deviations from protocols. Monitor the sensitivity
-Minimize prophylactic and perioperative use
-Reduce hospital stays, improve decontamination procedures in hospital, improve staff hygiene, and decrease use of invasive devices such as catheters
-Support the use of the lowest tier of antimicrobial agents possible, and first-line therapies for initial treatment if possible
Goals of antimicrobial therapy
The goal is to treat with an appropriate antimicrobial agent at a dose that is sufficient to kill or suppress bacterial growth at the site of infection so that the patient’s immune system can contend with the infection.
The selection of an antimicrobial for a specific case is guided by a combination of rational assessment of advantages/disadvantages of an antimicrobial, culture and sensitivity, personal experience or preference, and traditional practices in veterinary medicine.
Antimicrobials should only be used for bacterial infections, contaminated and infected surgeries, and prophylactically when appropriate. Dr. McConkey stressed that using antimicrobials “just in case” or for trivial infections leads to antimicrobial resistance and exposes the patient to unnecessary risks.
Ideally, it is important to establish the diagnosis before therapy. For infectious diseases of unknown cause, pathogens with irregular microbial sensitivity, severe infections, a history of previous treatment failure in individual(s), or if there are other animals at risk, the causative agent should be isolated and identified.
How an antimicrobial should be selected
1. Decide if an antimicrobial is truly needed.
2. Determine if the antimicrobial can be selected empirically (based on experience and the literature) or rationally (based on a culture and sensitivity).
3. Determine why an antimicrobial is being used. Is it for prophylaxis or an infection that is already present?
4. What is the likely organism?
5. What antimicrobials are effective against the presumed or identified bacteria?
6. Where is the infection located and what antimicrobials can reach it?
7. Is a bactericidal antimicrobial necessary?
8. Consider the risk vs. benefit.
9. Chronic vs. acute disease: How long will you treat?
10. So you need IV treatment? Oral treatment? Are appropriate formulations available for how you wish to treat?
11. Economic factors/regulatory factors?
12. Is a combination of antibiotics required?
13. Consider patient factors:
Is the drug approved for use in that species?
Do you know the dose in that species?
Age-related contraindications?
Sex: Teratogenicity?
Breed: Any breed-specific susceptibility to toxicities?
Body characteristics?
Use: Food animal, racing animal, etc.?
Concurrent disease?
Immune status: Do you need a bactericidal drug?
Are there concurrent medications that may cause interactions?
14. Consider client factors, e.g., large vs. small animal clients, economic factors, can the dosage schedule be met, owner’s opinion, risk to owner of specific antibiotics.
What can veterinary practitioners do to help prevent antimicrobial resistance?
What can veterinary practitioners do to help prevent antimicrobial resistance?Veterinary associations worldwide are being proactive in the battle against antimicrobial resistance. The CVMA has been at the forefront of these initiatives, releasing production animal prudent use guidelines for antimicrobials in 2008. This year, the CVMA released a popular app, free to its members, for prudent use guidelines for urinary tract infections in companion animals. This is to be followed by an app with guidelines for treating pyoderma.CVT
