666 - Effects of Antibiotic Exposure on Stool Antibiotic Resistance in Very Low Birth Weight Infants

Publication Number: 1643.666

Shaina K. Lodhi, Loma Linda University Children's Hospital, Loma Linda, CA, United States; Diana H. Taft, UF - Food Science and Human Nutrition Department, Gainesville, FL, United States; David A. Mills, University of California, Davis, Davis, CA, United States; Mark A. Underwood, UC Davis, Spokane, WA, United States; Raylene M. Phillips, Loma Linda University Children's Hospital, Loma Linda, CA, United States

Background: Neonates carry antibiotic resistance (AR) genes in their stool. Preterm infants are frequently exposed to antibiotics, which can affect their stool microbiome and alter AR gene enrichment.

Objective: To quantify specific stool AR genes in VLBW premature infants and to assess if antibiotic exposure affects enrichment of these AR genes.

Design/Methods: Infants ≤32 weeks' gestation and ≤1500 g at birth were enrolled in the study. Stool samples were analyzed at 5 timepoints: first stool after enrollment, stool near the end of antibiotic exposure, and stool samples at 1, 2, and 4 weeks after the end of antibiotic exposure. We used qPCR to identify specific AR genes: mecA, vanB1, blaTEM, and blaSHV2. Mean threshold cycle (Ct) values < 35 were considered positive. Lower Ct values indicate higher amounts of gene present. Repeated measures ANOVA and generalized linear models were used for analysis.

Results: Fifty-one infants were enrolled over 6 months, of which 46 met the inclusion criteria. Four infants were not exposed to any antibiotics. MecA was detected in 88%, vanB1 in 92%, blaTEM in 95%, and blaSHV2 in 95% of stool samples.

In infants exposed to penicillins (n=28), there was a decrease in mean Ct value of mecA from 24.66 ±1.28 in the first stool sample to 17.18 ±1.08 within 1 week of stopping antibiotics (p < 0.001). Subsequently, there was increase of mecA from 17.18 ±1.08 to 21.78 ±0.74 in the last stool sample (p=0.002). In infants exposed to vancomycin (n=13), mean Ct value of vanB1 decreased from 31.5 ±1.14 in first stool sample to 26.41 ±0.99 in stool sample within 2 weeks of stopping antibiotics (p=0.008), then did not significantly change to 27.21 ±1.05 at last stool sample (p=0.377). Interestingly, in infants not exposed to vancomycin (n=22) mean Ct value of vanB1 also decreased from 30.74 ±0.68 in first stool sample to 27.24 ±0.62 within 2 weeks of stopping antibiotics (p=0.002), then increased to 29.46 ±0.55 at last stool sample (p=0.013). Mean Ct value of blaSHV2 decreased with increasing day of life in all neonates (p < 0.001). No significant trends noted with blaTEM. Duration of antibiotic exposure did not appear to have significant effect on AR gene enrichment.

Conclusion(s): A high prevalence of AR genes was found in preterm infants' stool. In preterm infants exposed to penicillins, there was an initial increase in mecA gene enrichment, followed by a gradual decrease. Enrichment of vanB1 was noted in all infants, however infants not exposed to vancomycin had decreasing enrichment at the endpoint of this study. There was an overall increase in blaSHV2 enrichment in all infants over time.

Mean of mecA Ct value by Week of Life
MecA (antibiotic resistance gene) is enriched after penicillin exposure, enrichment slowly decreases in the following weeks.

Mean of mecA Ct value by Time Point
MecA (antibiotic resistance gene) is enriched after penicillin exposure, enrichment slowly decreases in the following weeks.

Mean of vanB1 Ct value by Time Point
VanB1 (antibiotic resistance gene) is enriched after vancomycin exposure and enrichment persists until study endpoint. In infants unexposed to vancomycin, initial vanB1 enrichment is also noted to a smaller degree but it decreases by study endpoint.