Chitosan Films for Microfluidic Studies of Single Bacteria and Perspectives for Antibiotic Susceptibility Testing.

Single-cell microfluidics is a powerful method to study bacteria and determine their susceptibility to antibiotic treatment. Glass treatment by adhesive molecules is a potential solution to immobilize bacterial cells and perform microscopy, but traditional cationic polymers such as polylysine deeply affect bacterial physiology. In this work, we chemically characterized a class of chitosan polymers for their biocompatibility when adsorbed to glass. Chitosan chains of known length and composition allowed growth of Escherichia coli cells without any deleterious effects on cell physiology. Combined with a machine learning approach, this method could measure the antibiotic susceptibility of a diversity of clinical strains in less than 1 h and with higher accuracy than current methods. Finally, chitosan polymers also supported growth of Klebsiella pneumoniae, another bacterial pathogen of clinical significance.IMPORTANCE Current microfluidic techniques are powerful to study bacteria and determine their response to antibiotic treatment, but they are currently limited by their complex manipulation. Chitosan films are fully biocompatible and could thus be a viable replacement for existing commercial devices that currently use polylysine. Thus, the low cost of chitosan slides and their simple implementation make them highly versatile for research as well as clinical use.

Genipin-crosslinked O-carboxymethyl chitosan-gum Arabic coacervate as a pH-sensitive delivery system and microstructure characterization.

The possibility of genipin-crosslinked O-carboxymethyl chitosan-gum Arabic coacervate as a pH-sensitive delivery vehicle was investigated. O-carboxymethyl chitosan-gum Arabic coacervates separated in pH 3.0, 4.5, and 6.0 were crosslinked by genipin for different durations and the crosslinked products were subjected to crosslinking degree, swelling behavior, bovine serum albumin release profile, and microstructure characterization. Genipin-crosslinking greatly improved the stability of the coacervates against the simulated gastric solution and created certain pH-sensitivity. The coacervates displayed higher swelling ratios in the simulated gastric solution than in the simulated intestine and colon solutions; meanwhile, the coacervates prepared in pH 4.5 and 6.0 swelled more severely than the complex separated in pH 3.0. Nevertheless, the bovine serum albumin release in the simulated gastric solution from the microcapsules prepared in pH 6.0 was much lower than those prepared in pH 4.5 and 3.0, whose cumulative release percentages in the three simulated solutions were 17.14%, 55.23%, and 79.79%, respectively, in crosslinking duration 2 h. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analysis revealed that genipin-crosslinking improved the regularity and compactness of coacervate structure, whereas confocal laser scanning microscopy observation indicated that O-carboxymethyl chitosan content was possibly the major reason for the different swelling and bovine serum albumin release behavior of the coacervates. It was concluded that the genipin-crosslinked O-carboxymethyl chitosan-gum Arabic coacervate was a potential intestine-targeted delivery system and its delivery performance could be tailored by varying the crosslinking degree and coacervation acidity.

Prenatal and developmental effect of high molecular weight chitosan (HMWCS) to mice.

High molecular weight chitosan (HMWCS) is effective at hemostasis and wound healing, and will be potentially used on injured internal organs. To study its prenatal and developmental effect in vivo, forty-four ICR pregnant mice per group were singly injected intraperitoneally at 0, 125, 500 or 2000 mg/kg body weight, respectively, on gestation day 6 (GD6). Clinical signs, reproductive capacity, fetus and infant developments, and histopathological changes were then observed. The results showed that the treatment of HMWCS could decrease body weights and food consumptions, and induce diarrhea, vaginal bleeding, and some other adverse effects in F0 mice. For the emaciation and threatened abortion of pregnant mice, the numbers of live fetuses and early resorption were reduced significantly in HMWCS groups. However, the developments of F1 and F2 mice were not affected, except for lower weights of the body and some organs. In addition, the NOAEL of HMWCS in maternal toxicity was considered to be less than 125 mg/kg, and the NOAEL in developmental toxicity was 125 mg/kg.

Inhibition of Listeria monocytogenes by a combination of chitosan and divergicin M35.

The antimicrobial activities of the class IIa bacteriocin divergicin M35 and several types of chitosan against Listeria monocytogenes were quantified by agar diffusion, critical micro-dilution, and viable count and observed by electron microscopy. Antimicrobial activity of chitosan depended on its molecular mass (MM) and the pH. Three chitosans with MM values of 2, 20, and 100 kDa and 87.4% degree of deacetylation (DDA) were chosen for further study, based on high anti-listerial activity at pH 4.5. Electron microscopy suggested that the mechanism of anti-listerial activity also varied with the MM. Low-MM chitosan appeared to inhibit L. monocytogenes by affecting cell permeability and growth, whereas medium- and high-MM chitosan may form a barrier on the cell surface that prevents entry of nutrients. The minimum inhibitory concentrations (MICs) of 2, 20, and 100 kDa chitosan and divergicin M35 against a divergicin-resistant strain of L. monocytogenes (LSD 535) were 2.5, 2.5, 0.625, and 0.25 mg/mL, respectively. The combination of any of these 3 chitosans and divergicin M35 appeared to have an additive effect against L. monocytogenes, as determined by fractional inhibitory concentration (FIC) index. This study provides useful data for the development of chitosan films incorporating divergicin M35 for inhibiting L. monocytogenes in foods.