Significance of pre-incubation temperature and inoculum concentration on subsequent growth of Listeria monocytogenes at 14 degrees C

Investigation of the effects of oxidative stress-inducing factors on culturing and productivity of Bordetella pertussis

The stress response of Bordetella pertussis during fermentation was assessed by means of fluorescence-based techniques. During the manufacturing of vaccines, B. pertussis is subjected to stress during adaptation to a new environment and operating conditions in the bioreactor, which can have harmful consequences on growth and protein yield. In this study, stress was imposed by varying the percentage of dissolved oxygen (DO) and inoculum size, and by adding rotenone and hydrogen peroxide. In this study, fluorescence spectroscopy is used as a tool for measuring oxidative stress. High levels of DO during fed-batch operation had no detrimental effect on growth, but the specific productivity of pertactin (PRN) decreased. Cultures that were started with an inoculum size that was 10 times smaller than the control resulted in significantly less PRN as compared to controls where reduction was more significant in flasks as compared to bioreactors. A comparison of filtered to heat-sterilized media revealed that filtered media offered a protective effect against H₂ O₂ . Heat sterilization of the media might result in the destruction of components that offer protection against oxidative stress. Nonetheless, filter sterilization on its own would be insufficient for large-scale manufacturing. It should be emphasized that the effects of these stressors while investigating for other microorganisms have not been studied for B. pertussis.

Lag Phase Is a Dynamic, Organized, Adaptive, and Evolvable Period That Prepares Bacteria for Cell Division

Lag is a temporary period of nonreplication seen in bacteria that are introduced to new media. Despite latency being described by Müller in 1895, only recently have we gained insights into the cellular processes characterizing lag phase. This review covers literature to date on the transcriptomic, proteomic, metabolomic, physiological, biochemical, and evolutionary features of prokaryotic lag. Though lag is commonly described as a preparative phase that allows bacteria to harvest nutrients and adapt to new environments, the implications of recent studies indicate that a refinement of this view is well deserved. As shown, lag is a dynamic, organized, adaptive, and evolvable process that protects bacteria from threats, promotes reproductive fitness, and is broadly relevant to the study of bacterial evolution, host-pathogen interactions, antibiotic tolerance, environmental biology, molecular microbiology, and food safety.

Kinetics of single cells: observation and modeling of a stochastic process

The successive generation times for single cells of Escherichia coli K-12 were measured as described by A. Elfwing, Y. LeMarc, J. Baranyi, and A. Ballagi (Appl. Environ. Microbiol. 70:675-678, 2004), and the histograms they generated were used as empirical distributions to simulate growth of the population as the result of the multiplication of its single cells. This way, a stochastic birth model in which the underlying distributions were measured experimentally was simulated. To validate the model, analogous bacterial growth curves were generated by the use of different inoculum levels. The agreement with the simulation was very good, proving that the growth of the population can be predicted accurately if the distribution of the first few division times for the single cells within that population is known. Two questions were investigated by the simulation. (i) To what extent can we say that the distribution of the detection time, i.e., the time by which a single-cell-generated subpopulation reaches a detectable level, can be identified with that of the lag time of the original single cell? (ii) For low inocula, how does the inoculum size affect the lag time of the population?

Influence of the sigB gene on the cold stress survival and subsequent recovery of two Listeria monocytogenes serotypes

The influence of serotype and the role of the sigB gene of Listeria monocytogenes during the survival and recovery on different substrates were determined. Wild-type and sigB mutants of two serotypes of L. monocytogenes were inoculated into buffer and onto beef steaks, and incubated at 4 degrees C for 8 weeks during which samples were removed and Listeria numbers determined. Growth kinetics of stationary phase wild-type and sigB mutant cells were compared, without prechilling and after prechilling at 4 degrees C. The two serotypes had similar survival capabilities under the conditions examined, and the sigB gene was influential in survival of chill stress, but was dependent upon additional nutritional factors. Prechilling cells prior to growth extended the lag phase of both strains, and this lag phase extension was compounded by the absence of a functional sigB gene. In conclusion, the sigB gene is involved in the survival and recovery from chill stress by the two serotypes tested. Additional factors such as previous growth conditions, nutritional requirements and serotype susceptibility are also contributory. This study adds relevant information regarding the influence of the sigB gene, in conjunction with the historical growth conditions and serotype differences. Understanding the significance of these factors may be useful in creating improved recovery systems for the detection of L. monocytogenes from at-risk foods.

Growth pH does not affect the initial physiological state parameter (pO) of Listeria monocytogenes

It has proven difficult to develop adequate mathematical models for the lag phase (lambda) which characterizes the adaptation period prior to the initiation of exponential growth by microorganisms. This is due, in part, to our incomplete understanding of the nature of the initial physiological state of cells (defined as h0 or p0 depending on the model), and changes taking place during adaptation. The objectives of the present study were to characterize p0 using data from growth of Listeria monocytogenes in an automated turbidimetric instrument (Bioscreen), and to determine the influence of limiting growth pH. A model was developed for individual cells which combined a continuous adaptation phase (defined by p0) with a discrete step marking the transition to a continuous exponential growth phase (the CDC model). Parameters of the new model were: p0; the specific growth rate (mu); the initial cell number (N0); and the maximum cell density (Nmax). Progressive reduction of the growth pH in the Bioscreen to 4.7 decreased the p. It was noted that the regression lines for all trials at all pH values appeared to have a common x-intercept (20.086+/-1.092), and it was deduced that, when the Bioscreen detection limit (15.07 In cfu well(-1)) was subtracted, the resulting value represented the "true" value for the initial physiological state of the cells.

Significance of inoculum size in the lag time of Listeria monocytogenes

The lag time of Listeria monocytogenes growing under suboptimal conditions (low nutrient concentrations, pH 6, and 6.5 degrees C) was extended when the inoculum was severely stressed by starvation and the inoculum size was very small. Predictive microbiology should deal with bacterial stress and stochastic approaches to improve its value for the agro-food industry.