In VitroandIn VivoSynergistic Effects of Cryptdin 2 and Ampicillin against Salmonella

Abstract

In view of the emergence of multidrug-resistant Salmonella strains, there is a need for therapeutic alternatives. To reduce the dose of antibiotic required in order to decrease the associated side effects, the present study was aimed at evaluating the synergism between cryptdin 2 (a Paneth cell antimicrobial peptide) and ampicillin (Amp) against Salmonella enterica serovar Typhimurium. The synergy was evaluated in terms of the fractional bactericidal concentration (FBC) index, time-kill assay results (in vitro), macrophage functions, i.e., intracellular killing, lipid peroxidation, superoxide dismutase activity, and generation of nitrite (ex vivo), and decreases in CFU of salmonellae in livers, spleens, and small intestines of infected mice treated with cryptdin 2 and/or Amp (in vivo). In vitro synergism between the two agents was observed on the basis of the FBC index and time-kill assays. When the agents were used in combination, ex vivo studies revealed an enhanced effect on macrophage functions, particularly exhibiting a synergetic effect in terms of SOD levels. In vivo synergy was indicated by larger log unit decreases in all target organs of mice treated with the combination than those for the drugs used alone. These results point toward the possible use of cryptdin 2 as an adjunct to ampicillin and may help in developing alternate strategies to combat Salmonella infections.

Strategies employed in the design and optimization of synthetic antimicrobial peptide amphiphiles with enhanced therapeutic potentials

“…The synergistic combination of an AMP with small molecule antibiotics [33,53,[144][145][146][147] or different AMPs [148][149][150][151] has considerable advantages to enhance antimicrobial potencies, reduce cost and toxicities due to consequential dose reduction and to prevent development of drug resistance. Although there is currently a lack of detailed mechanistic studies on the enhanced efficacies of synergistic combinations, one common mode of action proposed is that the formation of pores in microbial membranes by the AMP permits an increased entry of the accompanying antibiotic into the cytosol or nucleus where they concomitantly exert their antimicrobial effects via dissimilar mechanisms such as the inhibition of DNA synthesis, protein synthesis or cell wall synthesis, hence effectively reducing the dosage of each therapeutic agent required for antimicrobial activities.…”

Efficacy of Cryptdin-2 as an Adjunct to Antibiotics from Various Generations Against Salmonella

“…The minimum bactericidal concentrations (MBCs) of all the agents against serovar Typhimurium were determined by macro and micro broth dilution assay methods as described by us earlier [17]. In brief, various antimicrobial agents (cryptdin-2 and antibiotics) were added to the bacterial suspension containing *10 7 CFU/ml of log phase cells of the bacterial strain.…”

“…To evaluate synergy, the fractional inhibitory concentration (FIC) index was determined by checkerboard microtitre test, using an 8-by-8 well configuration at 64 different combinations as described earlier [15,17]. Briefly, twofold serial dilutions of cryptdin-2 and each antibiotic were prepared, with concentrations ranging from 0.016 to 2 times the MBC.…”

“…Earlier, the combinations of AMPs and conventional drugs have been successfully employed to overcome antibiotic resistance in selected cases [13][14][15]. Recently, we demonstrated that cryptdin-2 possesses a strong in vivo therapeutic potential against murine salmonellosis and it can be used as a possible adjunct to ampicillin for superior treatment of salmonellosis [16,17]. However, possibility of using this peptide as an adjunct to the currently recommended conventional antibiotics (in the present scenario) remains to be explored.…”

Activity of Tigecycline in Combination with Colistin, Meropenem, Rifampin, or Gentamicin against KPC-Producing Enterobacteriaceae in a Murine Thigh Infection Model

“…All statistical analyses were performed using Minitab software (version 13.31). A combination was considered to be synergistic when resulting in a higher reduction of CFU yielded from treated mice than with each of the drugs alone; antagonism was considered when monotherapy caused a higher log CFU reduction than the combination (26). CFU reductions of Ͼ3 ⌬log were considered to indicate bactericidal levels of activity (10).…”