Antimicrobial susceptibility of Lactobacillus species isolated from commercial ethanol plants

Authors: Bischoff, Kenneth; SKINNER-NEMEC, KELLY - ARGONNE LAB; Leathers, Timothy

Submitted to: Journal of Industrial Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2007
Publication Date: 10/1/2007
Citation: Bischoff, K.M., Skinner-Nemec, K.A., Leathers, T.D. 2007. Antimicrobial susceptibility of Lactobacillus species isolated from commercial ethanol plants. Journal of Industrial Microbiology and Biotechnology. 34(11):739-744.

Interpretive Summary: Bacterial contamination of commercial fermentation cultures is a common and costly problem to the fuel ethanol industry. Antibiotics, such as virginiamycin or penicillin, may be used to control contamination but there is little information available on antibiotic resistance among bacterial contaminants. In the present study, bacteria were isolated from a wet-mill and from a dry-grind ethanol plant, and tested for resistance to antibiotics. The dry-grind plant had a history of using antibiotics while the wet-mill did not. In general, a higher concentration of antibiotics was required to inhibit growth of isolates from the dry-grind plant than isolates from the wet-mill, but most isolates were still inhibited with the recommended dose of virginiamycin. This information will be of interest to ethanol producers and researchers attempting to design effective intervention strategies to control bacterial contamination in commercial fermentation cultures.

Technical 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 wet-mill ethanol plant with no history of using antibiotics and a dry-grind facility that periodically doses with VIR found that the majority of contaminants were species of Lactobacillus. Thirty-seven isolates of Lactobacillus species from the wet-mill and forty-two isolates from the dry-grind facility were tested for antimicrobial susceptibility using broth dilution and agar dilution methods. In general, the Lactobacillus isolates from the dry-grind plant had higher MICs for the tested agents than the isolates from the wet-mill facility. The MIC90 for VIR was 4 ug/ml for the dry-grind isolates versus 0.25 ug/ml for the wet-mill isolates; and for PEN, the MIC90s were >8 ug/ml and 2 ug/ml for the dry-grind and wet-mill isolates, respectively. Sixteen Lactobacillus isolates from the dry-grind plant but none from the wet-mill possessed vatE, a gene that encodes a streptogramin acetyltransferase associated with resistance to virginiamycin. Despite decreased susceptibility to virginiamycin, most dry-grind isolates had MICs lower than the maximal recommended application rate of 6 ppm.