title: Inactivation ofSalmonellaspp. andListeriaspp. by Palmitic, Stearic, and Oleic Acid Sophorolipids and Thiamine Dilauryl Sulfate.
abstract: Food contaminated with human pathogens, such asSalmonellaspp. andListeria monocytogenes, frequently causes outbreaks of foodborne illness. Consumer concern over the use of synthesized antimicrobials to enhance microbial food safety has led to a search of natural alternatives. The objectives of this study were to evaluate the antimicrobial activity of various types of sophorolipids (SLs) and thiamine dilauryl sulfate (TDS) against pathogenicSalmonellaspp. andListeriaspp. Both free and lactonic forms of SLs were synthesized fromCandida bombicolausing palmitic, stearic, and oleic acids as co-feedstocks. TDS and purified SLs were used to treat cocktails ofSalmonellaspp. andListeriaspp. Results showed that lactonic SLs had higher antimicrobial activity than the free-acid form, and Gram-positiveListeriaspp. were more susceptible to SLs and TDS than Gram-negativeSalmonellaspp.Listeriapopulations were reduced from an initial concentration of 7.2 log CFU/mL to a non-detectible level within a 1 min treatment of 0.1% (w/v) lactonic SLs and TDS in the presence of 20% ethanol, which itself did not significantly reduce the populations. There were no significant differences in the antimicrobial efficacy among palmitic, stearic, and oleic acid-based SLs againstSalmonellaorListeriaspp. Ethanol was utilized to improve the antimicrobial activity of free-acid SLs against Gram-negative bacteria. In general, TDS was more effective than the SLs againstSalmonellaandListeriaspp. scanning electron microscopy and transmission electron microscopy images showed that SLs and TDS damagedListeriacell membranes and resulted in cell lysis. Overall, our results demonstrated that SLs and TDS in the presence of ethanol can be used to inactivate foodborne pathogens, especially Gram-positive bacteria.
authors.affiliation: Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences Beijing, China.
authors.forename: Xuejie
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Eastern Regional Research Center, United States Department of Agriculture - Agricultural Research Service Wyndmoor, PA, USA.
authors.forename: Richard
authors.initials: R
authors.lastname: Ashby
authors.affiliation: Eastern Regional Research Center, United States Department of Agriculture - Agricultural Research Service Wyndmoor, PA, USA.
authors.forename: Daniel K Y
authors.initials: DK
authors.lastname: Solaiman
authors.affiliation: Eastern Regional Research Center, United States Department of Agriculture - Agricultural Research Service Wyndmoor, PA, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Uknalis
authors.affiliation: Eastern Regional Research Center, United States Department of Agriculture - Agricultural Research Service Wyndmoor, PA, USA.
authors.forename: Xuetong
authors.initials: X
authors.lastname: Fan
keywords: Listeria monocytogenes; Salmonella; cell membrane; sophorolipids; thiamine dilauryl sulfate