ABSTRACT
Salmonella enterica is increasingly linked to disease outbreaks associated with consumption of low-water-activity (low-aw) foods. Persistence of the pathogen in these foods was attributed to its ability to implement desiccation resistance mechanisms. Published knowledge about methods that disrupt desiccation resistance in S. enterica is lacking. We hypothesize that strong membrane-active compounds disrupt the desiccation resistance that S. enterica may acquire in low-aw foods or environments. The newly discovered antimicrobial lipopeptide paenibacterin was the membrane-active agent investigated in this study. Strains of S. enterica serovars Tennessee and Eimsbuettel, with a history of association with low-moisture foods, were investigated. The viability of these strains did not decrease significantly during dehydration and subsequent storage in the dehydrated state. Considering that the paenibacterin MIC against S. enterica strains was 8 μg/ml, concentrations of 4 to 16 μg/ml paenibacterin were tested. Within this range, desiccation-adapted S. Eimsbuettel was much more tolerant to the antimicrobial agent than the desiccation-adapted S. Tennessee. Pretreatment with 8 μg/ml paenibacterin increased inactivation of S. enterica during desiccation. The use of paenibacterin at 16 μg/ml or higher concentrations resulted in leakage of intracellular potassium ions from desiccation-adapted cells. Paenibacterin significantly decreased the biosynthesis of the intracellular osmoprotectant solute, trehalose, in a concentration-dependent manner. Treatment with 64 μg/ml paenibacterin increased the permeability of the cytoplasmic membranes of desiccation-adapted cells. Transcription of the desiccation-related genes proV, STM1494, kdpA, and otsB in response to paenibacterin treatment was investigated using reverse transcription-quantitative PCR. Transcription of some of these genes was downregulated in a concentration- and strain-dependent manner.
IMPORTANCE Salmonella enterica adapts effectively and persists for a long time in low-aw foods or environments through resistance mechanisms to desiccation stress. Desiccation-resistant cells compromise food safety and constitute a serious health hazard. Strategies to combat desiccation resistance in S. enterica are needed to sensitize the pathogen to lethal processes used in food preservation. The study proved that the membrane-active lipopeptide paenibacterin disrupts the resistance in desiccation-adapted S. enterica, as measured by phenotypic, biochemical, and genetic analyses. This study highlighted the role of the lipopeptide paenibacterin in disrupting mechanisms employed by S. enterica to resist desiccation. This knowledge may lead to the design of novel control measures to improve the safety of low-aw foods. |
