Resistance to essential oils affects survival of Salmonella enterica serovars in growing and harvested basil

Abstract

The number of outbreaks of food-borne illness associated with consumption of fresh products has increased. A recent and noteworthy outbreak occurred in 2007. Basil contaminated with Salmonella enterica serovar Senftenberg was the source of this outbreak. Since basil produces high levels of antibacterial compounds the aim of this study was to investigate if the emerging outbreak reflects ecological changes that occurred as a result of development of resistance to ingredients of the basil oil. We irrigated basil plants with contaminated water containing two Salmonella serovars, Typhimurium and Senftenberg, and showed that Salmonella can survive on the basil plants for at least 100 days. S. Senftenberg counts in the phyllosphere were significantly higher than S. Typhimurium, moreover, S. Senftenberg was able to grow on stored harvested basil leaves. Susceptibility experiments demonstrated that S. Senftenberg is more resistant to basil oil and to its antimicrobial constituents: linalool, estragole and eugenol. This may indicate that S. Senftenberg had adapted to the basil environment by developing resistance to the basil oil. The emergence of resistant pathogens has a significant potential to change the ecology, and opens the way for pathogens to survive in new niches in the environment such as basil and other plants.

Survival of Salmonella and Escherichia coli O157:H7 on Strawberries, Basil, and Other Leafy Greens during Storage

“…Foodborne outbreaks occurred with strawberries and basil after transport and storage, suggesting survival of E. coli 0157:H7 or Salmonella on both commodities, even in adverse environ ments. Although survival of these pathogens has been studied on leafy greens, such as spinach (45,54), escarole (1,54), and especially, on fresh-cut iceberg or romaine lettuce (11,20,22,58,61), and growth models are available for iceberg lettuce (37,47) to predict growth of E. coli under temperature abuse, limited information is available about the survival of E. coli 0157:H7 and Salmonella on basil leaves during storage (29,35). Moreover, no information about the survival of Salmonella or E. coli 0157:H7 on basil leaves during storage at 15°C is available, which is the recom mended temperature to maintain quality during storage.…”

Adaptation of Salmonella enterica Serovar Senftenberg to Linalool and Its Association with Antibiotic Resistance and Environmental Persistence

“…Salmonella enterica serovar Senftenberg ATCC 07885, a clinical isolate from the 2007 outbreak linked to basil, was used in this study (30,62). S. Senftenberg was grown at 37°C in Luria-Bertani (LB) broth and agar (Difco), which was supplemented with 50 g/ml kanamycin (Kan) when necessary.…”

“…The antibacterial activities of basil oil, its major components (eugenol, linalool, and estragole), and different antibiotics against the S. Senftenberg wild type and the LASS strain were measured by a paper disk diffusion assay (30). Briefly, overnight cultures were diluted 1:100 in fresh LB medium and then grown to an optical density at 600 nm (OD 600 ) of 0.4 (approximately 10 7 CFU/ml).…”

“…We have previously shown that the wild-type S. Senftenberg strain survives on soil, as does S. Typhimurium, but survives better on basil plants pre-and postharvest and is less sensitive to basil oil and to linalool than S. Typhimurium (30). Here, the selective pressure of linalool on the same S. Senftenberg strain further increased the linalool resistance of the resultant LASS strain and did not significantly affect its growth in broth or on agar medium, nor did it affect its persistence on the phyllosphere of growing basil plants; furthermore, it improved its survival on harvested basil during refrigerated storage.…”

“…Salmonella enterica serovar Senftenberg was identified to be the cause of this outbreak (29). Investigation of a clinical isolate from this outbreak revealed that S. Senftenberg possessed an increased resistance to basil oil and each of its major compounds, which correlated with better survival on basil plants pre-and postharvest (30). The inhibition zone of linalool against S. Senftenberg, for instance, was 12.5 mm, whereas it was 21.0 mm against S. Typhimurium (30).…”