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In this paper, a model of stochastic competition between plasmid-bearing and plasmid-free organisms in a chemostat is investigated. First, we show that there is a unique global positive solution for the stochastic system. Second, by employing stochastic Lyapunov functions, Itô formula, strong law of large number and some other important inequalities, stochastic characteristics of the stochastic competition chemostat model are studied such as the stochastic asymptotic behaviors of the system. Finally, some numerical simulations are given.

Poultry and its products are often referred to as reservoirs of Salmonella to infect humans. Salmonella serovars were determined from samples of terminated eggs (early-terminated eggs, EEs, and late-terminated eggs, LEs) on farms YA (layers), YB (native hybrid broilers, NHCs), and YF (NHCs); one-day-old chicks (OCs) on farm YB; and shoe covers (SCs) on farms YB, YC (broilers), YD (broilers), YE (NHCs), and YF using multiplex PCR and agglutination methods. One hundred isolates were examined for susceptibility to 13 antimicrobials and profiles of pulsotypes and plasmids. Nine serovars were identified as serogroup B Agona and Schwarzengrund, serogroup C1 Montevideo and Mbandaka, serogroup C2 Albany, Kentucky and Newport, serogroup E Weltevreden, and serogroup G Kedougou. Different from those in 2003, Albany, Kentucky, Montevideo, and Mbandaka were the predominant serovars that differed in chromosomal and plasmid variations and antibiogram profiles. Albany and Kentucky isolates had higher resistance levels to the antimicrobials than the Montevideo and Mbandaka isolates. The antibiogram differences among the serovars may be related to the presence of antibiotic resistance genes in Salmonella genomic island 1-F (SGI1-F) and plasmids in Albany isolates. Albany and Kentucky exhibited the largest chromosomal and plasmid variations, respectively. The main serovars associated with embryogenesis termination were Mbandaka and Montevideo in EEs and LEs, Newport in NHCs, and Kedougou in LEs from layers. Furthermore, Montevideo and Agona were the only serovars detected in OCs, and Albany and Kentucky were the main serovars on SCs. Farm management also affected the Salmonella prevalence and predominant serovars.

The development of DNA vaccines and plasmid vectors for gene therapy in recent years is based on the capacity of mammalian cells and tissues to take up exogenous DNA spontaneously. Naked DNA uptake is a universal property of mammalian cells, having been demonstrated in several different mammalian cell lines, primary cells in culture, solid tumours as well as in normal tissues (e.g. skeletal muscle and liver) in vivo. While mechanisms of uptake of exogenous DNA by bacteria are understood in some detail, almost nothing is known about this process in mammalian cells. It is unlikely that the extremely poor efficiency of naked plasmid entry into mammalian cells and tissues can be overcome until eukaryotic mechanisms are elucidated. We review the current state of knowledge of naked plasmid entry into mammalian cells, and present preliminary evidence for saturable plasmid binding sites on the plasma membrane of C2C12 myoblasts followed by time-dependent translocation of internalized plasmid into the nuclear compartment. Myoblasts can be engineered for insulin secretion via plasmid-mediated gene transfer. Thus, muscle and myoblast implants may be a suitable platform for developing genetic treatment of systemic metabolic disorders.