Authors: Kenneth M Bischoff Kelly A SkinnerNemec Timothy D Leathers
Publish Date: 2007/08/28
Volume: 34, Issue: 11, Pages: 739-744
Abstract
Bacterial contamination of commercial fermentation cultures is a common and costly problem to the fuel ethanol industry Antimicrobials such as virginiamycin VIR and penicillin PEN are frequently used to control contamination but there are little data available on the susceptibility of bacterial contaminants to these agents A survey of bacterial contaminants from a wetmill ethanol plant with no history of using antibiotics and a drygrind facility that periodically doses with VIR found that the majority of contaminants were species of Lactobacillus Thirtyseven isolates of Lactobacillus species from the wetmill and 42 isolates from the drygrind facility were tested for antimicrobial susceptibility using broth dilution and agar dilution methods In general the Lactobacillus isolates from the drygrind plant had higher minimum inhibitory concentrations MICs for the tested agents than the isolates from the wetmill facility The MIC90 for VIR was 4 μg/ml for the drygrind isolates versus 025 μg/ml for the wetmill isolates and for PEN the MIC90’s were 8 and 2 μg/ml for the drygrind and wetmill isolates respectively Sixteen Lactobacillus isolates from the drygrind plant but none from the wetmill possessed vatE a gene that encodes a streptogramin acetyltransferase associated with resistance to virginiamycin Despite decreased susceptibility to virginiamycin most drygrind isolates had MICs lower than the maximal recommended application rate of 6 ppm
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