Causes of Bacterial Resistance to Antibiotics

Minimising the Development of Antimicrobial Resistance

Aug 25, 2009 Lindsay Napier

Minimising the risk of development of bacterial resistance to antibiotics is important to ensure the continued ability of physicians to treat serious infections.

Bacteria are particularly skilled at adapting to survive in hostile circumstances, such as when targeted with antimicrobial agents. Resistance is a big issue in the treatment of infections worldwide, with resistant organisms, the most well-known being methicillin-resistant Staphylococcus aureus (MRSA), appearing shortly after the introduction of each new antibiotic. Consequently, infections caused by drug resistant organisms are hard to treat.

By understanding what drives bacteria to develop resistance, we may be able to limit its impact on the treatment of infections. Some of the factors that may increase the risk of bacterial resistance are discussed below.

Previous Exposure to Antibiotics

Resistance is more likely to occur if bacteria have been exposed to a particular antibiotic before. For example, if an antibiotic was prescribed at too low a dose, or for too short a duration to be effective, more bacteria are likely to survive. These survivors will continue to grow, resulting in an infection that is made up almost entirely of resistant organisms (1).

Overuse of Antibiotics

It has been recognised that overuse of antibiotics is strongly associated with the development of resistance. Widespread use means that more patients, and more strains of bacteria, are likely to have been exposed to an antibiotic. Consequently, Clinical guidelines recommend that these ‘antibiotics of last resort’ against resistant strains are used only when appropriate (2).

Broad Spectrum Antibiotics

Broad spectrum antibiotics are those that are effective against a wide range of bacteria. Sometime this is useful, for instance in the treatment of animal bite wounds or certain other skin infections that often contain a mix of infecting organisms. However, use of broad spectrum antibiotics for single-strain infections may increase the risk of tolerance in subsequent use for an infection caused by a different susceptible strain (3).

Use of Similar Antibiotics

An infection that has failed treatment with one antibiotic may not respond with an antibiotic that works in a similar way. For example, many strains that are tolerant of the anti-MRSA antibiotic vancomycin are also resistant to teicoplanin, which are both members of the glycopeptide class of antibiotics. As a result, the term 'glycopeptide resistance' has been coined (4).

Reducing the Risk of Resistance

To reduce risk of resistance, clinical guidelines generally recommend that antibiotics are used only when needed, and that they are used appropriately according to the type and severity of infection. This means that antibiotics should be chosen that are active against the infecting pathogen, and that empiric treatment (when you don't know what is the infecting organism) should be based on the most likely infecting pathogen (2).

These recommendations will go some way to ensure that patients are not needlessly exposed to antimicrobial agents, thereby increasing the chance that these agents will be effective if they are needed in the future.

References

1. Tacconelli E et al. J Antimicrob Chemother 2008; 61:26-38.
2. Gemmell CG et al. J Antimicrob Chemother 2006; 57:589-608.
3. Peterson LR. Clin Microbiol Infect 2005; 11(Suppl 5):4-16.
4. Linares J. Clin Microbiol Infect 2001; 7(Suppl 4):8-15.

The copyright of the article Causes of Bacterial Resistance to Antibiotics in General Medicine is owned by Lindsay Napier. Permission to republish Causes of Bacterial Resistance to Antibiotics in print or online must be granted by the author in writing.

Methicillin-Resistance Staphylococcus Aureus

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