P-027 - Minimum inhibitory concentrations of commercial copper pesticides are dependent on Salmonella serovar and preparation method

Monday, August 4, 2025

3:45 PM - 4:30 PM HST

Location: Exhibit Hall 3

Presenting Author(s)

EG

Ellen Louise Gabriel (she/her/hers)

Virginia Tech Department of Food Science & Technology
Blacksburg, Virginia, United States

Author(s)

DW

Daniel Weller

Virginia Tech
Blacksburg, Virginia, United States
CE

Cyril Etaka

Virginia Tech
Blacksburg, Virginia, United States
ZX

Zirui Xiong

USDA - ARS
Beltsville, Maryland, United States
AA

Adib Adnan

USDA - ARS
Beltsville, Maryland, United States
MS

Manan Sharma

USDA - ARS
Beltsville, Maryland, United States
SR

Steven Rideout

Professor / Extension Specialist
Virginia Tech
Blacksburg, Virginia, United States
LS

Laura Strawn

Associate Professor & Extension Specialist
Virginia Tech
Blacksburg, Virginia, United States

Abstract Text: Copper (Cu)-based pesticides play a vital role in controlling bacterial and fungal diseases in produce crops. This study aimed to quantify the minimum inhibitory concentration (MIC) of two commercial copper pesticides for eight Salmonella serovars. MIC assays with two Cu pesticides - copper octanoate (C₁₆H₃₀CuO₄) and cuprous oxide (Cu₂O) - were performed on eight rifampicin (R)-resistant Salmonella serovars. Two methods, dilution- and vortex-based, were compared for preparing C₁₆H₃₀CuO₄. Cu pesticides were either diluted in sterile DI water or added directly to Salmonella cultures (9.05±0.17 log CFU/mL). After incubation, aliquots from wells were streaked onto Tryptic Soy Agar-R, then incubated again. MIC was the lowest Cu concentration that inhibited growth across all eight replicates. Linear models were fit to determine if the MIC of C₁₆H₃₀CuO₄ differed significantly between preparation method, serovars, and Cu pesticides. For the dilution method, C₁₆H₃₀CuO₄ has a MIC of 0.86±0.00mg/mL Cu for all serovars tested, and Cu₂O MIC is 113.9±35.8mg/mL Cu, which ranged from 101.3-202.5mg/mL Cu, where S. Newport had the highest MIC. When the dilution method was used, the MIC for Cu₂O was 114.2mg/mL Cu (95% CI=83.1, 145.3), higher than for C₁₆H₃₀CuO₄. The MIC for C₁₆H₃₀CuO₄ was approximately 0.59mg/mL Cu (95% CI = -0.65, -0.53) lower for the vortex method, compared to the dilution method. These results highlight the variability in antimicrobial efficacy between Cu formulations and suggest that preparation method can influence MIC outcomes.