Objective. To prepare biocompatible ciprofloxacin-loaded carboxymethyl chitosan nanoparticles (CCC NPs) and evaluate their cell specificity as well as antibacterial activity against Escherichia coli in vitro. Methods. CCC NPs were prepared by ionic cross-linking method and optimized by using Box-Behnken response surface method (BBRSM). Zeta potential, drug encapsulation, and release of the obtained nanoparticles in vitro were thoroughly investigated. Minimum inhibitory concentration (MIC) and killing profiles of free or ciprofloxacin-loaded nanoparticles against Escherichia coli were documented. The cytotoicity of blank nanoparticles and cellular uptake of CCC NPs were also investigated. Results. The obtained particles were monodisperse nanospheres with an average hydrated diameter of 151 ± 5.67 nm and surface of charge −22.9 ± 2.21 mV. The MICs of free ciprofloxacin and CCC NPs were 0.16 and 0.08 μg/mL, respectively. Blank nanoparticles showed no obvious cell inhibition within 24 h, and noticeable phagocytosis effect was observed in the presence of CCC NPs. Conclusion. This study shows that CCC NPs have stronger antibacterial activity against Escherichia coli than the free ciprofloxacin because they can easily be uptaken by cells. The obtained CCC NPs have promising prospect in drug delivery field.

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A bstract This study aimed to evaluate the potential impacts of an introduced clam Mercenaria mercenaria on estuarine ecosystem, and implications for the niche competition with a native clam M eretrix meretrix . The biodeposition, respiration, and excretion rates of M. mercenaria were determined seasonally using a sediment trap and a closed respirator in fi eld. The biodeposition rates of M. mercenaria were 0.06-0.37 g/ ind./d, and the respiration rates were 0.31-14.66 mg/ind./d. The ammonia and phosphate excretion rates were 0.18-36.70 and 1.44-14.87 μg/ind./d, respectively. The hard clam M. mercenaria may discharge dry deposits up to 2.1×10 5 t, contribute 18.3 t ammonia and 9.0 t phosphate to culture ponds, and consume 7.9×10 3 t O 2 from ponds annually. It suggested that the hard clam M. mercenaria might play an important role in pelagic-benthic coupling in pond ecosystem through biodeposition and excretion. A comparison of the key physiological parameters of the introduced clam M. mercenaria and the native clam M eretrix meretrix suggested that M. mercenaria had a niche similar to that of M eretrix meretrix in Shuangtaizi estuary and might have a potential competition with M eretrix meretrix for habitat and food if M. mercenaria species escaped from the culture pond or artifi cially released in estuarine ecosystem.