Antibacterial and anti-biofilm activities of melittin and colistin, alone and in combination with antibiotics against Gram-negative bacteria

Abstract

In vitro antibacterial and anti-biofilm activities of antimicrobial cationic peptides (AMPs) - melittin and colistin - both alone and in combination with antibiotics were evaluated against clinical isolates of Gram-negative bacteria. Minimum inhibitory concentration (MIC) and fractional inhibitory concentration (FIC) index were determined by the microbroth dilution and chequerboard techniques, respectively. The time-kill curve (TKC) method was used for determining the bactericidal activities of AMPs alone and in combination. Measurements of anti-biofilm activities were performed spectrophotometrically for both inhibition of attachment and 24-hour biofilm formation at MIC or subMIC. According to MIC90 values, the most active agents against Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumoniae were colistin, imipenem and ciprofloxacin, respectively. In combination studies, synergistic effects were mostly seen with colistin-imipenem against E. coli and K. pneumoniae (50 and 54%, respectively), colistin-ciprofloxacin against P. aeruginosa (77%). In TKC studies, synergism was observed with almost all expected combinations, even more frequently than chequerboard method. All of the antimicrobial agents were able to inhibit attachment and 24-hour biofilm formation between 0-57% at 1/10 × MIC and 7-73% at 1 × or 1/10 × MIC, respectively. AMPs seem to be a good candidate for antimicrobial chemotherapy with their antibacterial and anti-biofilm activities as a single agent or in combination with antibiotics.

Analogs of the Frog-skin Antimicrobial Peptide Temporin 1Tb Exhibit a Wider Spectrum of Activity and a Stronger Antibiofilm Potential as Compared to the Parental Peptide

“…FIC index was calculated as follows: Σ (FIC A + FIC B ), where FIC A is the MIC of compound A in combination/MIC of compound A alone, and FIC B is the MIC of compound B in combination/MIC of compound B alone. Synergism was defined as a FIC index ≤ 0.5, indifference as a FIC index > 0.5 and antagonism as a FIC index > 4 (Katragkou et al, 2015; Dosler et al, 2016). …”

Hemin and bile pigments are the secondary structure regulators of intrinsically disordered antimicrobial peptides

“…Its maturated form shows multiple pharmacological actions including antibacterial, antiviral, anticancer, and antiinflammatory effects. [8][9][10][11][12] According to the primary sequence, the Nterminal part of melittin (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) consists mostly of hydrophobic/neutral residues, whereas the C-terminal (21)(22)(23)(24)(25)(26) is enriched in polar, basic side chains (Table 1). Melittin contains a lone proline residue that gives rise to a flexible hinge region at the middle of the molecule.…”

Ceragenins as Mimics of Endogenous Antimicrobial Peptides

“…Biofilms are microbial communities with altered phenotypes, relative to planktonic or free-growing microorganisms, that agglomerate through a extracellular polymeric matrix [73,74]. The impact of biofilms, both bacterial and fungal, are increasingly recognized as threats to public health due to the fact that biofilm formation is involved in more than 60% of bacterial infections, as well as being recognized as a causative agent in most medical device-related infections [75,76].…”