Beyond the target pathogen: ecological effects of antibiotics

Clostridium difficile Antibiotics can have ecological effects that impact the efficacy of other antimicrobial agents or facilitate the development of secondary infections. When antibiotics are administered, particularly when they are overused or misused, they change the environment and the biome, which in turn can lead to the selection or development of bacterial strains resistant to a wide range of antibiotic agents, extending beyond the particular antibiotic or antibiotic class initially administered. Certain antibiotic agents also change the normal bacterial flora or environment within the gastrointestinal tract, which in turn can promote the colonization and overgrowth of particular bacteria (e.g. Clostridium difficile), and increase the risk of gastrointestinal infections associated with these bacteria. Antibiotic usage can also have an impact on skin and mucosa colonization (such as for methicillin-resistant Staphylococcus aureus) with significantly increased risk of subsequent infections. These forms of ‘collateral damage’ associated with antibiotic use are important considerations when deciding how best to use antibiotics to prevent or treat infections in the hospital (and community) setting. This review looks at some of the ecological effects of antibiotics used in the hospital and their potential for collateral damage of the nosocomial environment. Collateral damage is becoming an increasing problem due to the increasing severity of illness in hospitalized patients and the increasing use of broad-spectrum antibiotics. The ultimate goal is to understand how to better use antibiotics to optimize their beneficial effects, while minimizing risk of collateral damage, in other words, to improve antibiotic stewardship within hospitals and other institutions.

Beyond the target pathogen: ecological effects of the hospital formulary. (2011) Curr Opin Infect Dis. 24 Suppl 1: S21-31
Antibiotic therapy has the potential for intended as well as unintended consequences due to ecological effects that extend beyond the target pathogen. This review examines some of the collateral damage and collateral benefit that may occur when using antibiotic therapy. Antibiotics excreted in the gastrointestinal tract cause alterations of the indigenous flora. Such disruptions may increase the risk of colonization and overgrowth of pathogenic bacteria, including resistant species, with the potential for serious infection for an individual patient as well as possible hospital-wide dissemination resulting in local outbreaks of infection. For example, Clostridium difficile infection (CDI), and particularly associated diarrhea and colitis, is a potentially serious and growing problem in hospitals worldwide, and is associated with disruption of gut flora through use of broad-spectrum antibiotics, especially those with antianaerobic activity. Infection control measures and improved antibiotic stewardship are key measures for CDI prevention. Another example is the risk of intestinal colonization and overgrowth with resistant bacteria, which is heightened in surgical patients requiring antimicrobial therapy for intraabdominal infections. Results from two Optimizing Intra-Abdominal Surgery with Invanz studies (OASIS-I and OASIS-II) suggested emergence of resistant Enterobacteriaceae was less likely in these patients treated with ertapenem than in those treated with ceftriaxone/metronidazole or piperacillin/tazobactam. Finally, recent studies have reported that increased use of a nonpseudomonal carbapenem such as ertapenem does not reduce the susceptibility of Pseudomonas aeruginosa to pseudomonal carbapenems, for example, imipenem or meropenem. In fact, data from one study showed increased ertapenem/decreased imipenem use was associated with improved susceptibility of P. aeruginosa to imipenem, probably due to decreased selective pressure for resistant species. Improper antibiotic use can be associated with detrimental effects related to the ecological impacts of these drugs. Improved antibiotic stewardship and appropriate infection control measures are key to minimization of the collateral damage associated with antibiotic therapy and may even have collateral benefits.

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