Healthy Patients & Effect of Antibiotics

Each year, antimicrobial resistance causes over two million infections and 23,000 deaths in the US alone, representing a critical global public health issue. Some of the most feared multidrug resistant organisms (MDROs) include Clostridium difficile, carbapenem-resistant Enterobacteriaceae (CRE), extended spectrum beta-lactamase producing Enterobacteriaceae (ESBL), MDRO Acinetobacter, and MDRO Pseudomonas aeruginosa; there are few antimicrobials effective against these MDROs, and available antimicrobials often have rate-limiting toxicities. The major risk factor for MDRO colonization and subsequent MDRO infections is exposure to antimicrobials. The use of antimicrobials has been associated with an altered and often less diverse composition of the fecal microbiome, and expansion of the resistome. A "healthy" microbiome provides "colonization resistance" against potentially pathogenic bacteria; antimicrobials disrupt this protective community, providing selective pressure that favors MDRO colonization, persistence, and transmission to others. Methods to proactively prevent MDRO colonization, rather than reliance on reactive approaches to this problem, are urgently needed. Antimicrobial stewardship is a key component of MDRO prevention efforts; however, there is no method to determine which antimicrobials cause the greatest degree of microbiome disruption. A better understanding of exactly how antimicrobials alter the microbiome is necessary to optimally guide future MDRO prevention efforts and antimicrobial stewardship. The development of microbiome disruption indices (MDIs) would help characterize the risk associated with specific antimicrobials, and can be used during antimicrobial development, patient monitoring while on antimicrobials, and to facilitate infection prevention efforts to contain MDRO spread. Additionally, MDIs can be used as an alert when microbiome disruptions reach a critical level and MDRO colonization is imminent. At that point, interventions to restore the microbiome could be implemented. Community-acquired pneumonia (CAP) is one of the leading causes of death in the United States, with an estimated \>900,000 cases each year in adults age 65 and older. Large amounts of antimicrobials are used in treating patients with CAP because the disease is relatively common. A better understanding of the effect of CAP antimicrobial treatment on the microbiome could result in improved treatment options for patients with CAP and protect CAP patients from colonization or infection with MDROs.