Highly synergistic activity of melittin with imipenem and colistin in biofilm inhibition against multidrug-resistant strong biofilm producer strains of Acinetobacter baumannii

Abstract

The rapid increase of drug resistance and failure of available antibiotics to treat biofilm-associated infections is of great health concern. Accordingly, our study aimed to evaluate the synergistic antibacterial, biofilm inhibitory, and biofilm removal activities of melittin in combination with colistin, imipenem, and ciprofloxacin against multidrug-resistant (MDR) strong biofilm producer Acinetobacter baumannii isolates. The kinetics of biofilm formation were evaluated for the isolates for 144 h. Minimum inhibitory concentrations (MICs), minimum bactericidal concentrations (MBCs), minimum biofilm inhibitory concentrations (MBICs), and biofilm removal activities for melittin and combinations with antibiotics were determined. Inhibition of biofilm-associated protein (bap) expression by melittin was evaluated with real-time polymerase chain reaction (PCR). Field emission scanning electron microscopy (FE-SEM) was used to visualize the effect of synergism on the inhibition of biofilm production. The geometric means of the fractional inhibitory concentration index (FICi) for melittin-colistin, melittin-imipenem, and melittin-ciprofloxacin combinations were calculated as 0.31, 0.24, and 0.94, respectively. Comparing the geometric means of the removal activity for melittin, colistin, imipenem, and combinations of them in both 6 and 24 h showed a significant difference between the groups (p-value < 0.05). Exposure to melittin induced a statistically significant downregulation of bap mRNA levels in all isolates at sub-MIC doses. Analysis of the FE-SEM results demonstrated that the synergism of melittin-colistin at 0.125-0.25 μg inhibited biofilm formation completely. In conclusion, our findings indicate that melittin possesses considerable potential for use in combination with colistin and imipenem to treat infections caused by MDR strong biofilm producer A. baumannii isolates.

Pan-Drug Resistant Acinetobacter baumannii, but Not Other Strains, Are Resistant to the Bee Venom Peptide Melittin

“…A recent survey reported the synergistic antibacterial, biofilm inhibition and biofilm removal activities of melittin in combination with several antibiotics against MDR, a strong biofilm producer A. baumannii strains from clinical isolates. Significant synergistic behaviors were observed combining melittin with colistin and imipenem [57], corroborating previous findings reported by Giacometti et al in 2003 [59].…”

“…Moreover, melittin has been reported to inhibit either biofilm formation or bacterial surface attachment in a time-dependent manner [31]. The peptide was also capable of inhibiting five-strong biofilm-producer strains of MDR A. baumannii and inhibiting their biofilm formations, alone or in combination with colistin and imipenem [57]. Noticeably, melittin lessened both biofilm biomass and the viability of biofilm-embedded Borrelia burgdorferi strain B31 at different concentrations in comparison to PBS-treated biofilms, which was further confirmed by SYBR Green I/(PI) assay and atomic force microscopy [60].…”

“…Among them, melittin from bee venom has been proven to have potent antibacterial activity [31]. There are multiple lines of evidence and several studies that confirm the antibacterial activity of melittin toward antibiotic-resistant bacteria [31,[53][54][55][56][57].…”

“…The co-administration of antibiotics with permeability enhancing compounds can enhance activity due to an increase of drug with permeability [67]. Several investigations have addressed possible synergistic effects between melittin and other anti-microbial agents, in particular, conventional antibiotics [55,57,59,68,69].…”

Molecular typing of multi-drug resistant Acinetobacter baumannii isolates from clinical and environmental specimens in three Iranian hospitals by pulsed field gel electrophoresis

“…The ability of A. baumannii isolates to produce biofilm was assessed by the microtiter plate method as previously described [35]. Briefly, biofilm formation was performed in triplicate from overnight cultures diluted in Tryptic soy broth (TSB) medium supplied with 1% glucose to an optical density (OD) of 0.01 at 600 nm and deposited in 96-well plates.…”