Resistance of bacterial strains to dry conditions: use of anhydrous silica gel in a desiccation model system

168

In order to determine desiccation tolerances of bacterial strains, the survival of 58 diarrheagenic strains (18 salmonellae, 35 Shiga toxin-producing Escherichia coli [STEC], and 5 shigellae) and of 15 nonpathogenic E. coli strains was determined after drying at 35°C for 24 h in paper disks. At an inoculum level of 10 7 CFU/disk, most of the salmonellae (14/18) and the STEC strains (31/35) survived with a population of 10 3 to 10 4 CFU/disk, whereas all of the shigellae (5/5) and the majority of the nonpathogenic E. coli strains (9/15) did not survive (the population was decreased to less than the detection limit of 10 2 CFU/disk). After 22 to 24 months of subsequent storage at 4°C, all of the selected salmonellae (4/4) and most of the selected STEC strains (12/15) survived, keeping the original populations (10 3 to 10 4 CFU/disk). In contrast to the case for storage at 4°C, all of 15 selected strains (5 strains each of Salmonella spp., STEC O157, and STEC O26) died after 35 to 70 days of storage at 25°C and 35°C. The survival rates of all of these 15 strains in paper disks after the 24 h of drying were substantially increased (10 to 79 times) by the presence of sucrose (12% to 36%). All of these 15 desiccated strains in paper disks survived after exposure to 70°C for 5 h. The populations of these 15 strains inoculated in dried foods containing sucrose and/or fat (e.g., chocolate) were 100 times higher than those in the dried paper disks after drying for 24 h at 25°C.A nationwide outbreak of gastroenteritis due to consumption of dried squid chips (water activity, 0.5 to 0.6) contaminated with Salmonella enterica serovars Oranienburg and Chester occurred in Japan in 1999, in which a total of 1,634 cases were reported from all over the country (46/47 prefectures) (25). Even though this outbreak was the first one caused by contaminated dry foods in Japan, a number of outbreaks of gastroenteritis caused by dry foods such as dried milk, chocolate, potato chips, and almonds contaminated mainly by salmonellae have been reported in the United States and Europe since the 1960s (5,12,16,18). Since the middle of the 1990s, outbreaks of Shiga toxin-producing Escherichia coli (STEC) O157 infections have also been reported to be associated with dry foods such as deer jerky and salami in the United States (8,14,19,24). Many outbreaks of gastroenteritis associated with dry foods contaminated with salmonellae and STEC strains have been reported all over the world, even though the bacterial growth was inhibited by low water activity (a w ) in these dry foods. Accordingly, we tried to investigate the ability of these desiccated strains to survive under dried conditions, using salmonellae and STEC O157, O26, and O111 strains in paper disks with a w s of 0.5 to 0.6 and in selected dry foods. In order to study the effect of bacterial environments on the survival of bacteria during a process of being made "desiccated" bacteria and of storage conditions on the survival of desiccated bacteria produced after 24 h of drying, we examined t...

Section: Discussionmentioning

confidence: 45%

Ability of Shiga Toxin-Producing Escherichia coli and Salmonella spp. To Survive in a Desiccation Model System and in Dry Foods

Hiramatsu

Matsumoto

Sakae

et al. 2005

168

“…We have presented the first genome-wide study of the transcriptional response of a grampositive bacterium to desiccation. In studies that have compared the survival of gram-positive and gram-negative bacteria during air drying, the gram-positive species have consistently proven themselves better adapted to dry conditions (20,42,44). In particular, actinomycetes have long been considered dry-soil specialists, since their proportion within a bacterial community increases in arid regions (27).…”

Section: Discussionmentioning

confidence: 99%

Global Response to Desiccation Stress in the Soil Actinomycete Rhodococcus jostii RHA1

LeBlanc

Gonçalves

Mohn

2008

122

Rhodococcus jostii RHA1 is a soil-residing actinomycete with many favorable metabolic capabilities that make it an ideal candidate for the bioremediation of contaminated soils. Arguably the most basic requirement for life is water, yet some nonsporulating bacteria, like RHA1, can survive lengthy droughts. Here we report the first transcriptomic analysis of a gram-positive bacterium during desiccation. Filtered RHA1 cells incubated at either low relative humidity (20%), as an air-drying treatment, or high relative humidity (100%), as a control, were transcriptionally profiled over a comprehensive time series. Also, the morphology of RHA1 cells was characterized by cryofixation scanning electron microscopy during each treatment. Desiccation resulted in a transcriptional response of approximately 8 times more differentially regulated genes than in the control (819 versus 106 genes, respectively). Genes that were differentially expressed during only the desiccation treatment primarily had expression profiles that were maximally up-regulated upon complete drying of the cells. The microarray expression ratios for some of the highly up-regulated genes were verified by reverse transcriptase quantitative PCR. These genes included dps1, encoding an oxidative stress protection protein which has not previously been directly associated with desiccation, and the two genes encoding sigma factors SigF1 and SigF3, possibly involved in the regulatory response to desiccation. RHA1 cells also induced the biosynthetic pathway for the compatible solute ectoine. These desiccation-specific responses represent the best candidates for important mechanisms of desiccation resistance in RHA1.Fluctuation in water availability is a fundamental stress challenging soil-residing microorganisms, and desiccation tolerance is a key adaptation of many such organisms. The structural integrity and proper functioning of many proteins and other cellular macromolecules depend upon interactions with water molecules. The mechanisms by which microorganisms adapt to water limitation have been best studied in cyanobacteria. Many cyanobacteria mitigate water loss by synthesizing extracellular polysaccharides (EPS) to create a barrier between themselves and the dry environment (31). The second main strategy employed by cyanobacteria for retaining water during air drying is to increase their intracellular solute concentrations to equilibrate them with those of their increasingly hypertonic surroundings (41). The molecules either imported or synthesized for this purpose are referred to as compatible solutes because, even at high concentrations, they permit cellular machinery to function (32). In a microarray study of a desiccated cyanobacterial species, Anabaena sp. strain PCC7120, the importance of compatible solute production as a major water stress response was identified (21). Other, concurrent responses included the up-regulation of genes associated with protein stabilization (heat shock and chaperone proteins) and with countering oxidative threats (probable...

“…Salmonella, known for its survival in dried conditions (10,11), can live in liquid egg remaining in a product line. We thought the high frequency of Salmonella detection in the liquid egg samples was due to contamination of the product line.…”

Section: Discussionmentioning

confidence: 99%

Detection of Salmonella enterica in Naturally Contaminated Liquid Eggs by Loop-Mediated Isothermal Amplification, and Characterization of Salmonella Isolates

Ohtsuka¹,

Yanagawa²,

Takatori

et al. 2005

137

Loop-mediated isothermal amplification (LAMP) assay was effective in detecting Salmonella enterica in naturally contaminated liquid egg samples. Salmonella was detected in 110 samples taken from four eggbreaking plants. The egg samples were pre-enriched in buffered peptone water (BPW) at 37°C for 20 h. The selective enrichment was done in Rappaport-Vassiliadis or tetrathionate broth and plated onto xylose lysine deoxycholate agar and brilliant green agar, modified. In addition, the PCR assay was used to detect Salmonella after pre-enrichment in BPW at 37°C for 20 h. The culture method and PCR assay were compared to the LAMP assay, which was also performed after pre-enrichment in BPW. PCR failed to detect Salmonella in 10% of 110 samples, whereas the culture method and LAMP assay successfully identified Salmonella in all samples. However, the LAMP assay was found to be much more rapid than the culture method and as sensitive in detecting Salmonella from liquid eggs. In all of the egg-breaking plants studied, Salmonella was isolated on most tested days. The positive samples showed that more than 75% of the Salmonella strains had identical genetic patterns when analyzed by pulsed-field gel electrophoresis. This suggests that the same Salmonella strains having survived long periods of time in the plants were contaminating the production line. The LAMP assay is rapid, specific, and sensitive for Salmonella detection in liquid eggs and is able to monitor Salmonella contamination in egg-handling plants more reliably.