| Abstrakt: |
The ability of Listeria monocytogenes to grow at refrigeration temperatures is critical for transmission of this foodborne pathogen. We evaluated the contributions of different transcriptional regulators and two-component regulatory systems to L. monocytogenes cold adaptation and cold growth. L. monocytogenes parent strain 10403S and selected isogenic null mutants in genes encoding four alternative δ factors (sigB, sigH, sigC, and sigL), two regulators of δB (rsbT and rsbV), two negative regulators (ctsR and hrcA), and 15 two-component response regulators were grown in brain heart infusion broth at 4°C with (i) a high-concentration starting inoculum (108 CFU/ml), (ii) a low-concentration starting inoculum (10² CFU/ml), and (iii) a high-concentration starting inoculum of cold-adapted cells. With a starting inoculum of 108 CFU/ml, null mutants in genes encoding selected alternative δ factors (ΔsigH, ΔsigC, and ΔsigL), a negative regulator (ΔctsR), regulators of δB (ΔrsbT and ΔrsbV), and selected two-component response regulators (ΔlisR, Δlmol172, and Δlmo1060) had significantly reduced growth (P < 0.05) compared with the parent strain after 12 days at 4°C. The growth defect for ΔsigL was limited and was not confirmed by optical density (OD600) measurement data. With a starting inoculum of 10² CFU/ml and after monitoring growth at 4°C over 84 days, only the ΔctsR strain had a consistent but limited growth defect; the other mutant strains had either no growth defects or limited growth defects apparent at only one or two of the nine sampling points evaluated during the 84-day growth period (ΔsigB, ΔsigC, and Δlmol172). With a 108 CFU/ml starting inoculum of cold-adapted cells, none of the mutant strains that had a growth defect when inoculation was performed with cells pregrown at 37°C had reduced growth as compared with the parent strain after 12 days at 4°C, suggesting a specific defect in the ability of these mutant strains to adapt to 4°C after growth at 37°C. Our data indicate (i) selected cr factors and two-component regulators may contribute to cold adaptation even though two-component regulatory systems, alternative cr factors, and the negative regulators CtsR and HrcA appear to have limited contributions to L. monocytogenes growth at 4°C in rich media, and (ii) inoculum concentration and pregrowth conditions affect the L. monocytogenes cold-growth phenotype. [ABSTRACT FROM AUTHOR] |
