Antibiotic Resistance in Dogs and Cats
Factors in the Development of Bacterial Drug Resistance
Aug 25, 2009
Antibiotic resistance is a major medical concern in both pets and people. With methicillin-resistant Staphylococcus aureus (MRSA) infections becoming more common, bacterial resistance to antibiotics and other antimicrobial drugs is receiving increasing amounts of attention.
There are many factors which may play a part in creating antibiotic resistance. These factors include:
- problems which are specific to the patient,
- problems inherent with the antibiotic itself, and
- the ability of some bacteria to develop a specific resistance to some types of antibiotics and antimicrobial drugs.
Patient Factors Which Play a Role in the Development of Antibiotic Resistance
The health of the individual patient may play a role in determining whether an antibiotic is likely to be effective. This is particularly true when antibiotics which are bacteriostatic are used to treat the patient. Bacteriostatic antibiotics act to halt the replication of bacteria but rely on host (patient) defenses to actually kill and rid the body of the bacterial infection. However, even bacteriocidal antibiotics (antibiotics which kill bacteria) can be affected by the patient's health status.
Patient health factors which may make bacterial antibiotic resistance more likely include:
- compromise of the immune system, such as that resulting from HIV
- immune suppressant therapy administered simultaneously with antibiotics
- damaged organs or tissues
- decreased blood supply reaching infected tissues or organs
- failure to remove inflammatory exudates (such as pus) from infected tissues before instituting antibiotic therapy
Antibiotic Drug Resistance Resulting from Inappropriate Antibiotic Choices
Resistance to antibiotics can also result from inappropriate choices when dealing with these drugs. Potential complicating factors include:
- an inadequate dosage or inadequate frequency of administration of the antibiotic
- discontinuing antibiotic therapy before complete resolution of the bacterial infection
- decreased bioavailability of the antibiotic, such as that which may occur when other drugs or food interfere with the absorption or metabolization of the antibiotic being administered
- choosing the wrong antibiotic, such as choosing an antibiotic which does not reach adequate levels in the tissue which is infected or choosing an antibiotic which is not effective against the organism present
Bacterial Defenses Which Cause Resistance to Antibiotics
Many types of bacteria possess defense mechanisms which may render them resistant to antibiotics and other antimicrobial drugs.
- Some bacteria may produce specific enzymes which are capable of rendering antibiotics ineffective, such as beta-lactamase.
- Other bacteria may produce a biofilm which coats and protects them against antibiotics, rendering the antibiotics useless.
- Genetic alterations within groups of bacteria may be passed to subsequent generations of bacteria and provide resistance to multiple antibiotics. This is particularly common in situations where there has been previous exposure to the antibiotics in question.
- Some bacteria possess a drug efflux pumping mechanism which reduces the amount of antibiotic which actually enters the bacteria, resulting in the antibiotic never reaching levels high enough to become effective. This mechanism is important in MRSA infections.
There are numerous mechanisms by which bacteria may become resistant to antibiotics and many factors which play a role in drug resistance. For these reasons, it is important for veterinarians to carefully consider not only which antibiotic is most appropriate for each individual patient but which dosage and dosage frequency is likely to produce the best results. Pet owners should follow directions carefully and complete the full course of antibiotics prescribed to help avoid bacterial resistance to antibiotics. Antibiotics should be used judiciously and only when needed.
Sources:
Molecular basis of azithromycin-resistant Pseudomonas aeruginosa biofilms. RJ Gillis, et al. Antimicrobial Agents and Chemotherapy. 2005 Sep;49(9):3858-67.
Epigallocatechin-gallate enhances the activity of tetracycline in staphylococci by inhibiting its efflux from bacterial cells. Roccaro A Sudano, et al. Antimicrobial Agents and Chemotherapy. 2004 Jun;48(6):1968-73.
Synergistic interaction between phenothiazines and antimicrobial agents against Burkholderia pseudomallei. YY Chan, et al. Antimicrobial Agents and Chemotherapy. 2007 Feb;51(2):623-30.
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