Resistance Among Community-Associated Pathogens

Development and spread of resistance in community- associated bacteria (e.g., bacteria that cause respiratory tract infections, diarrheal diseases, and gonorrhea) have compromised many established therapeutic regimens for infectious diseases.

The increase in resistance has resulted from increased world travel in which people are exposed to novel microorganisms that they bring back to their home country; greater reliance on imported foods, such as fruits and vegetables, from international sources that may be contaminated; and dramatic increases in worldwide use of antimicrobial agents.

Among the organisms implicated in large outbreaks of disease in community settings are Shigella dysentariae strains that were resistant to all major drug classes, including the quinolones, multidrug-resistant strains of Salmonella typhi (the cause of typhoid fever) and other Salmonella species, and more recently, MRSA. The emergence of MRSA strains that predominantly have centered in the community, but now are spreading into health-care settings as well, complicates treatment and prevention strategies for this organism that for decades was know only as a nosocomial pathogen.

Gram-negative bacilli that are part of endogenous flora, such as E. coli and K. pneumoniae, are also associated with increasing prevalence of resistance to antimicrobial agents commonly used in community- acquired infections. The impact is especially notable in treatment for community-acquired urinary tract infections in women.

Another important community-acquired pathogen, S. pneumoniae, is a major cause of meningitis, sepsis, pneumonia, and ear infections in the United States and around the globe. Strains resistant to penicillin, tetracycline, chloramphenicol, and trimethoprim-sulfamethoxazole have now been isolated in the United States and in several areas of the world.

Other strains of pneumococci highly resistant to the extended-spectrum cephalosporins, the drugs of choice for treatment of penicillin-resistant strains, have emerged and appear to be spreading. This has significantly impaired the development of rational plans for treatment of meningitis caused by these strains.

Pneumococci can spread particularly well among children in day care centers, but pediatric strains of pneumococci are also now found with increasing frequency in adults. Thus, the availability of more effective pneumococcal vaccines that are immunogenic in younger children (especially those <2 years of age) may play a significant role in controlling the spread of these resistant pathogens.

Another community-acquired pathogen that continues to develop multidrug resistance is Neisseria gonorrhoeae, the agent of gonorrhea and a sexually transmitted pathogen that has been epidemic in the world for almost three decades. High-level plasmid-mediated penicillin resistance emerged in N. gonorrhoeae in 1976, when penicillin was the drug of choice for treating gonorrhea.

This was followed by the emergence of tetracycline resistance after doxycycline therapy replaced penicillin treatment. Recently, the CDC withdrew the recommendation of using fluoroquinolones for empiric treatment of gonorrhea in the United States because the levels of resistance to the fluoroquinolones were high enough that successful treatment could not be expected.

The emergence of resistance to the fluoroquinolones, which were highly effective oral drugs that were easy to administer, clearly threatens our ability to control this epidemic disease. Community-acquired infections due to the first cousin of the gonococcus, that is, Neisseria meningitidis, continue to occur both in developing countries, often as epidemics, and in developed countries, primarily as sporadic infections and localized outbreaks. Outbreaks of meningococci can be limited by vaccination campaigns, especially among those attending college and military training camps.