Antimicrobial polymers represent a very promising class of therapeutics with unique characteristics for fighting microbial infections. As the classic antibiotics exhibit an increasingly low capacity to effectively act on microorganisms, new solutions must be developed. The importance of this class of materials emerged from the uncontrolled use of antibiotics, which led to the advent of multidrug-resistant microbes, being nowadays one of the most serious public health problems. This review presents a critical discussion of the latest developments involving the use of different classes of antimicrobial polymers. The synthesis pathways used to afford macromolecules with antimicrobial properties, as well as the relationship between the structure and performance of these materials are discussed.

Large-scale industrial use of chromium(VI) has resulted in widespread contamination with carcinogenic chromium(VI). The abilities of microorganisms to survive in these environments and to detoxify chromate require the presence of specific resistance systems. Here we report identification of the transposon-located (TnOtChr) chromate resistance genes from the highly tolerant strain Ochrobactrum tritici 5bvl1 surviving chromate concentrations of >50 mM. The 7,189-bp-long TnOtChr of the mixed Tn21/Tn3 transposon subfamily contains a group of chrB, chrA, chrC, and chrF genes situated between divergently transcribed resolvase and transposase genes. The chrB and chrA genes, but not chrF or chrC, were essential for establishment of high resistance in chromium-sensitive O. tritici. The chr promoter was strongly induced by chromate or dichromate, but it was completely unresponsive to Cr(III), oxidants, sulfate, or other oxyanions. Plasmid reporter experiments identified ChrB as a chromate-sensing regulator of chr expression. Induction of the chr operon suppressed accumulation of cellular Cr through the activity of a chromate efflux pump encoded by chrA. Expression of chrB, chrC, or chrF in an Escherichia coli sodA sodB double mutant restored its aerobic growth in minimal medium and conferred resistance to superoxide-generating agents menadione and paraquat. Nitroblue tetrazolium staining on native gels showed that ChrC protein had superoxide dismutase activity. TnOtChr appears to represent a mobile genetic system for the distribution of the chromate-regulated resistance operon. The presence of three genes protecting against superoxide toxicity should provide an additional survival advantage to TnOtChr-containing cells in the environments with multiple redox-active contaminants.Chromium(VI) is one of the major environmental contaminants, which reflects its numerous high-volume industrial applications and poor environmental practices in the disposal of chromium-containing waste products (42). High solubility and tetrahedral conformation of the chromate anion promote its rapid transport across biological membranes (11), and once internalized by cells, Cr(VI) exhibits a variety of toxic, mutagenic, and carcinogenic effects (43). Formation of DNA damage is a major cause of toxic and mutagenic responses in both human and bacterial cells, as evidenced by their increased sensitivity to chromate in the absence of DNA repair (16, 36). Human and other mammalian cells lack any detectable extrusion of chromate, and DNA repair is their main cellular defense mechanism against chromate toxicity. Because bacterial cells are less proficient in repair of chromium-DNA adducts compared to human cells (35), their ability to survive in the environment with heavy chromate contamination required selection of alternative resistance mechanisms. Genes conferring resistance to chromate have been found in Pseudomonas spp. (7,27), Streptococcus lactis (13), and Cupriavidus metallidurans (28). Unlike other metal resistance systems that allow survival at...

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