Effects of amylose and amylopectin molecular structures on starch electrospinning.

The role of amylose content in electrospinning starch nanofibres is well understood, but that is not the case for the roles of the molecular structures of amylose and amylopectin. Here, correlations between starch molecular-structure parameters and electrospinnability evaluation indices (average droplet number, average bead number, and average fibre diameter) and dope properties (shear viscosity, conductivity, and surface tension) were examined. Starches with lower amounts of short amylopectin chains, higher amounts of either/or long amylopectin chains and/or lower degree of branching showed decreased viscosity of the electrospinning dopes, and resulted in a reduced average droplet number of electrospun fibre mats. The molecular sizes of amylose and whole starch, and the average degree of polymerization for amylose chains, all correlated with the shear viscosity and surface tension of dopes, and thus influenced the average fibre diameter. This expands the current understanding between amylopectin molecular structure and starch electrospinning, thereby assisting a better choice of starches for desired electrospinnability properties.

Characterization of Ciprofloxacin Resistance in Laboratory-Derived Mutants of Vibrio parahaemolyticus with qnr Gene.

Ciprofloxacin, a broad-spectrum fluoroquinolone, is a bactericidal antibiotic targeting DNA gyrase and DNA topoisomerase IV encoded by the gyrA and parC genes. Resistance to fluoroquinolones requires the accumulation of multiple mutations including those that alter target genes and increase drug efflux. To examine the development of fluoroquinolones resistance in Vibrio parahaemolyticus, ciprofloxacin induction and selection was used to obtain several resistant V. parahaemolyticus mutants, which showed decreased susceptibilities to quinolones, and increased or decreased susceptibility to other structurally unrelated antibiotics. Quinolone resistance-determining region mutations were characterized, and it was found that gyrA mutations occurred in some of the high-level resistant mutants although qnr was present in both wild-type susceptible and resistant mutant strains. The mutants showed increased qnr expression and exposure to sub-inhibitory concentrations of ciprofloxacin caused a further increase in qnr expression independently of the SOS system. Two mutants demonstrated increased expression of the VmeCD-VpoC pump gene that promotes quinolone efflux. In addition, some of the high-level resistance mutants significantly decreased bacterial fitness. These data suggested that multiple genes contributed to the enhanced ciprofloxacin resistance appeared in V. parahaemolyticus and that acquisition of ciprofloxacin resistance impaired bacterial fitness.