Global Transcriptional Analysis of Spontaneous Sakacin P-Resistant Mutant Strains of Listeria monocytogenes during Growth on Different Sugars

Subclass IIa bacteriocins have strong antilisterial activity and can control the growth of Listeria monocytogenes in food. However, L. monocytogenes may develop resistance towards such bacteriocins. In this follow-up study, the transcriptomes of a high level (L502-1) and a low level (L502-6) spontaneous sakacin P-resistant mutant strain of L. monocytogenes were compared to the wild-type (L502). The growth of the resistant strains was reduced on mannose but not affected on cellobiose and the transcriptomics was performed during growth on these sugars. The mannose phosphotransferase system (PTS) encoded by the mptACD operon (mpt) is known for transporting mannose and also act as a receptor to class IIa bacteriocins. The mpt was repressed in L502-1 and this is in accordance with abolition of the bacteriocin receptor with resistance to class IIa bacteriocins. In contrast, the mpt was induced in L502-6. Despite the induction of the mpt, L502-6 showed 1,000 times more resistance phenotype and reduced growth on mannose suggesting the mannose-PTS may not be functional in L502-6. The microarray data suggests the presence of other transcriptional responses that may be linked to the sakacin P resistance phenotype particularly in L502-6. Most of commonly regulated genes encode proteins involved in transport and energy metabolism. The resistant strains displayed shift in general carbon catabolite control possibly mediated by the mpt. Our data suggest that the resistant strains may have a reduced virulence potential. Growth sugar- and mutant-specific responses were also revealed. The two resistant strains also displayed difference in stability of the sakacin P resistance phenotype, growth in the presence of both the lytic bacteriophage P100 and activated charcoal. Taken together, the present study showed that a single time exposure to the class IIa bacteriocin sakacin P may elicit contrasting phenotypic and transcriptome responses in L. monocytogenes possibly through regulation of the mpt

Deletion of sigma54 (rpoN) alters the rate of autolysis and biofilm formation in Enterococcus faecalis

Transcription initiation is a critical step in bacterial gene regulation and is often controlled by transcription regulators. The alternate sigma factor (sigma54) is one such regulator that facilitates activator-dependent transcription initiation and thus modulates the expression of a variety of genes involved in metabolism and pathogenesis in bacteria. This study describes the role of sigma54 in the nosocomial pathogen Enterococcus faecalis. Biofilm formation is one of the important pathogenic mechanisms of E. faecalis, as it elevates the organism’s potential to cause surgical site and urinary tract infections. Lysis of bacterial cells within the population contributes to biofilm formation by providing extracellular DNA (eDNA) as a key component of the biofilm matrix. Deletion of rpoN rendered E. faecalis resistant to autolysis, which in turn impaired eDNA release. Despite the significant reduction in eDNA levels compared to the parental strain, the rpoN mutant formed more robust biofilms as observed using laser scanning confocal microscopy and Comstat analysis, indicating and emphasizing the presence of other matrix components. Initial adherence to a polystyrene surface was also enhanced in the mutant. Proteinase K treatment at early stages of biofilm development significantly reduced the accumulation of biofilm by the rpoN mutant. In conclusion, our data indicate that other factors in addition to eDNA might contribute to the overall composition of the enterococcal biofilm and that the regulatory role of sigma54 governs the nature and composition of the biofilm matrix

Who plays what? participation profiles in chance versus skill-based gambling

To determine whether gambling participation falls into skill and chance-based categories and, if so, to determine the socio-demographic characteristics associated with these different categories. A cross-sectional analysis of all respondents to the 2005 Northern Territory Gambling Prevalence Survey who gambled in the 12 months prior to the survey. Factor analysis was employed to determine whether a chance versus skill-based dichotomy described the structure of gambling participation. Gambler preference groups were constructed using the median of rotated factor scores. Multinomial logit regression was then used to determine independent associations between explanatory variables and categories of gambler preferences. The skill and chance-based dichotomy did describe player preferences for the sample of adult gamblers in the Northern Territory, Australia. Gender, age, household income, household structure and the geographic location (access to gambling opportunities) of respondents were all associated with different degrees of participation in skill and chance based gambling activities. Notably, respondents 35 years and over were significantly over-represented in the low-skill/high-chance participation group, and under-represented in the high-skill/low-chance group. It is clear that the term gambling is a confounding rubric that hides differences both in the type of activity and the socio-demographic profiles of participants. An examination of the latter raises important questions about the role of chance in later life, as well as the role of self-determination in gambling for other groups, particularly younger men