- MRSA Is Putting Resistance in the News
- Humans Live with Many Pathogens
- Antibiotics Block Growth and Kill Pathogens
- Broad-Spectrum Antibiotics Also Perturb Our Microbiomes
- Antibiotic Resistance Protects Pathogens
- Antibiotic Resistance Is Widespread
- Antibiotic Resistance Is Divided into Three Types
- The Development of New Antibiotics Is Slowing
- Vaccines Block Disease
Antibiotic Resistance Is Widespread
The seriousness of antibiotic resistance depends on perspective. For most diseases, we still have at least one effective drug. If we instantly stopped all resistance from increasing, our healthcare system could continue to perform well. But clinical scientists see resistance increasing and call the situation "dire."13 For some pathogens, such as MRSA and Acinetobacter, physicians are forced to turn to antibiotics abandoned decades ago due to their toxic side effects. Our collective task is to develop attitudes and policies that enable all of us to use antibiotics without causing resistance to increase.
We estimate the extent of the resistance problem by surveillance studies. As pointed out, physicians collect microbial samples from patients and send the samples to clinical laboratories for testing (more than 2 billion per year in the United States14). Pathogens are cultured, and their susceptibility to specific antibiotics is determined (described in Chapter 2, "Working with Pathogens"). Surveillance workers then collect the data and calculate the percentage of the cultures that are resistant. (MIC breakpoints are used as the criterion for resistance.) This percentage, called the prevalence of resistance, indicates whether a particular antibiotic treatment is likely to fail due to pre-existing resistance. Surveillance also reveals trends when samples are obtained over several years from a similar patient population. Seeing the prevalence of resistance increase gives health planners advance warning that a change in treatment regimen is required.
Often, the prevalence of resistance is low for many years, and then it increases rapidly (see Figure 1-2). The challenge is to identify resistance problems while prevalence is still low. Then public health measures, such as increasing dose or halting the spread of the pathogen, may stop the increase. Many examples exist in which local outbreaks of resistance have been controlled. However, on a global level no antibiotic has returned to heavy use when resistance became widespread. Instead, the antibiotic is replaced with a more potent derivative.
Figure 1-2 Change in prevalence of methicillin resistance in S. aureusin Great Britain.
Data replotted from Johnson, A.P. "Antibiotic Resistance Among Clinically Important Gram-Positive Bacteria in the UK." Journal of Hospital Infection (1998) 40:17-26.
A partial list of major resistance problems is shown in Box 1-3. This list should be considered as a status report that needs to be continually updated, because pathogens are acquiring resistance to more and more antibiotics. It is also important to point out that resistance is generally a local or regional problem. For example, the prevalence of multidrug resistant (MDR) tuberculosis is particularly high in portions of Eastern Europe and South Africa, but in the United States it is rare.