Survival and Growth of Wild-Type and rpoS-Deficient Salmonella Newport Strains in Soil Extracts Prepared with Heat-Treated Poultry Pellets

Manure runoff can transfer pathogens to farmlands or to water sources, leading to subsequent contamination of produce. Untreated biological soil amendments, like manure, can be contaminated with foodborne pathogens, such as Salmonella Newport, which may lead to transfer of the pathogen to fruits or vegetables. Studies have reported the occurrence and survival of Salmonella in manure or manure slurries. However, data on the survival and growth of Salmonella Newport is lacking in matrices simulating runoff. We quantified the survival and growth of wild-type (WT) Salmonella Newport and rpoS-deficient (Δ rpoS) strains in sterile and nonsterile soil extracts prepared with (amended) or without (unamended) heat-treated poultry pellets at 25°C. Salmonella Newport WT and Δ rpoS populations reached a maximum cell density of 6 to 8 log CFU/mL in 24 to 30 h in amended and unamended soil extracts and remained in stationary phase for up to 4 days. Salmonella Newport in amended soil extracts exhibited a decreased lag phase (λ , 2.87 ± 1.01 h) and greater maximum cell densities ( N_max, 6.84 ± 1.25 CFU/mL) compared with λ (20.10 ± 9.53 h) and N_max (5.22 ± 0.82 CFU/mL) in unamended soil extracts. In amended soil extract, the Δ rpoS strain had no measurable λ , similar growth rates (μ_max) compared with WT, and a lower N_max compared with the WT strain. Unamended, nonsterile soil extracts did not support the growth of Salmonella Newport WT and led to a decline in populations for the Δ rpoS strain. Salmonella Newport had lower cell densities in nonsterile soil extracts (5.94 ± 0.95 CFU/mL) than it did in sterile soil extracts (6.66 ± 1.50 CFU/mL), potentially indicating competition for nutrients between indigenous microbes and Salmonella Newport. The most favorable growth conditions were provided by amended sterile and nonsterile soil extracts, followed by sterile, unamended soil extracts for both Salmonella Newport strains. Salmonella Newport may grow to greater densities in amended extracts, providing a route for increased Salmonella levels in the growing environments of produce.

Reverse flow injection spectrophotometric determination of ciprofloxacin in pharmaceuticals using iron from soil as a green reagent

A novel reverse flow injection spectrophotometric method for the determination of ciprofloxacin was successfully combined with the on-line introduction of an iron solution extracted from soil as green reagent. The assay was optimized by a univariate method to select the optimum conditions for the highest absorbance and highest stability of the complex. Beer-Lambert's law (λ_max=440nm) is obeyed in the range 0.5-50μgmL^-1 with a correlation coefficient (r²) of 0.9976 and 0.9996 using soil as green reagent from Khon Kaen, Thailand and Vientiane, Laos, respectively. The average percentage recoveries were in the range of 98.55-102.14% and the precision was in the range of 0.80-1.73%. The limit of detection and the limit of quantitation were 0.20 and 0.69μgmL^-1, respectively, with a sampling rate of over 46samplesh^-1. The method was successfully applied to the determination of ciprofloxacin in commercial pharmaceutical formulations. The results were in good agreement with those obtained by the reference HPLC method using a t-test at 95% of confidence level for comparison. This method is suitable for laboratories looking for alternative analytical methods using green reagents.

New SigD-regulated genes identified in the rhizobacterium Bacillus amyloliquefaciens FZB42

The alternative sigma factor D is known to be involved in at least three biological processes in Bacilli: flagellin synthesis, methyl-accepting chemotaxis and autolysin synthesis. Although many Bacillus genes have been identified as SigD regulon, the list may be not be complete. With microarray-based systemic screening, we found a set of genes downregulated in the sigD knockout mutant of the plant growth-promoting rhizobacterium B. amyloliquefaciens subsp. plantarum FZB42. Eight genes (appA, blsA, dhaS, spoVG, yqgA, RBAM_004640, RBAM_018080 and ytk) were further confirmed by quantitative PCR and/or northern blot to be controlled by SigD at the transcriptional level. These genes are hitherto not reported to be controlled by SigD. Among them, four genes are of unknown function and two genes (RBAM_004640 and RBAM_018080), absent in the model strain B. subtilis 168, are unique to B. amyloliquefaciens stains. The eight genes are involved in sporulation, biofilm formation, metabolite transport and several other functions. These findings extend our knowledge of the regulatory network governed by SigD in Bacillus and will further help to decipher the roles of the genes.