We report the potential of carbon nanodots (CNDs) as a molecular scaffold for enhancing the antimicrobial activities of small dendritic poly(amidoamines) (PAMAM). Carbon nanodots prepared from sago starch are readily functionalized with PAMAM by using N-ethyl-N'-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). Electron microscopy images of these polyaminated CNDs show that they are approximately 30-60nm in diameter. Infrared and fluorescence spectroscopy analyses of the water-soluble material established the presence of the polyamidoaminated moiety and the intrinsic fluorescence of the nanodots. The polyaminated nanodots (CND-PAM1 and CND-PAM2) exhibit in vitro antimicrobial properties, not only to non-multidrug resistant bacteria but also to the corresponding Gram-negative multidrug bacteria. Their minimum inhibitory concentration (MIC) ranges from 8 to 64μg/mL, which is much lower than that of PAMAM G1 or the non-active PAMAM G0 and CNDs. Additionally, they show synergistic effect in combination with tetracycline or colistin. These preliminary results imply that CNDs can serve as a promising scaffold for facilitating the rational design of antimicrobial materials for combating the ever-increasing threat of antibiotic resistance. Moreover, their fluorescence could be pertinent to unraveling their mode of action for imaging or diagnostic applications.
Enterovirus 71 (EV-71) infections are generally manifested as mild hand, foot and mouth disease, but have been reported to cause severe neurological complications with high mortality rates. Treatment options remain limited due to the lack of antivirals. Octaguanidinium-conjugated morpholino oligomers (vivo-MOs) are single-stranded DNA-like antisense agents that can readily penetrate cells and reduce gene expression by steric blocking of complementary RNA sequences. In this study, inhibitory effects of three vivo-MOs that are complementary to the EV-71 internal ribosome entry site (IRES) and the RNA-dependent RNA polymerase (RdRP) were tested in RD cells. Vivo-MO-1 and vivo-MO-2 targeting the EV-71 IRES showed significant viral plaque reductions of 2.5 and 3.5 log10PFU/ml, respectively. Both vivo-MOs reduced viral RNA copies and viral capsid expression in RD cells in a dose-dependent manner. In contrast, vivo-MO-3 targeting the EV-71 RdRP exhibited less antiviral activity. Both vivo-MO-1 and 2 remained active when administered either 4h before or within 6h after EV-71 infection. Vivo-MO-2 exhibited antiviral activities against poliovirus (PV) and coxsackievirus A16 but vivo-MO-1 showed no antiviral activities against PV. Both the IRES-targeting vivo-MO-1 and vivo-MO-2 inhibit EV-71 RNA translation. Resistant mutants arose after serial passages in the presence of vivo-MO-1, but none were isolated against vivo-MO-2. A single T to C substitution at nucleotide position 533 was sufficient to confer resistance to vivo-MO-1. Our findings suggest that IRES-targeting vivo-MOs are good antiviral candidates for treating early EV-71 infection, and vivo-MO-2 is a more favorable candidate with broader antiviral spectrum against enteroviruses and are refractory to antiviral resistance.