Effect of short-course antibiotics on the antimicrobial resistance profile of colonizing gut bacteria in the ICU

Background: The need for early antibiotics in the intensive care unit (ICU) is often balanced against the goal of antibiotic stewardship. We sought to determine how short-course antibiotics in the ICU affect the antimicrobial resistance phenotype and genotype of colonizing gut bacteria. Results: Deep rectal swabs were performed on 48 adults at the time of ICU admission and 72 hours later, including patients who did and did not receive antibiotics. To determine resistance phenotype, rectal swabs were cultured for MRSA and VRE; in addition, Gram-negative isolates were cultured against relevant antibiotics. To determine resistance genotype, quantitative PCR was performed for 87 established resistance genes. Within-individual changes in antimicrobial resistance were calculated based on culture and qPCR results and correlated with exposure to relevant antibiotics (e.g., β-lactam exposure and changes in β-lactam resistance). Of 48 ICU patients, 41 (85%) received antibiotics. Overall, there was no increase in the antimicrobial resistance profile of colonizing gut bacteria during the 72 hour study period. There was also no increase in antimicrobial resistance after stratification by receipt of antibiotics (i.e., no increase in β-lactam, vancomycin, or macrolide resistance regardless of whether patients received those same antibiotics). This was true for both culture and PCR. Antimicrobial resistance pattern at ICU admission strongly predicted resistance pattern after 72 hours. Conclusions. Short-course ICU antibiotics made little difference in the antimicrobial resistance pattern of colonizing gut bacteria over 72 hours in the ICU. This provides improved understanding of the dynamics of antimicrobial resistance in the ICU and some reassurance that short-course antibiotics may not adversely impact the stewardship goal of reducing antimicrobial resistance.