Linear Thanatin Is an Effective Antimicrobial Peptide against Colistin-Resistant <i>Escherichia coli in Vitro</i>

Abstract

Colistin has been regarded as the last line antibiotic for treatment of infections caused by multidrug resistant gram-negative bacteria. Therefore, the increasing emergence of colistin resistance among gram-negative bacteria represents a serious problem. The objective of this study was to characterize the effectiveness of the chemically synthesized thanatin in linear form against colistin-resistant E. coli isolated from a pig farm in China. Agar diffusion assay and broth microdilution test were employed to analyze the susceptibility of colistin-sensitive E. coli (ATCC25922) and colistin-resistant E. coli (SHP45) to linear thanatin (L-thanatin). Combinatory effect of linear thanatin and colistin against E. coli was also determined by fractional inhibition concentration index (FICI) analysis. The results showed that L-thanatin at a concentration of 1 mg/ml produced larger inhibition zone on agar against ATCC25922 than SHP45. In the quantitative microdilution test, L-thanatin had the same MIC of 3.2 µg/ml for ATCC25922 and SHP45. Based on the FICI analysis, additive effect was obtained with 1.56 µg/ml of L-thanatin and 0.125 µg/ml of colistin for ATCC25922; but with 1.56 µg/ml of L-thanatin and 0.25 µg/ml of colistin or with 2 µg/ml of colistin and 0.39 µg/ml of L-thanatin for SHP45. These data proved that L-thanatin is an effective antimicrobial peptide against colistin-resistant E. coli.

Complementary Activities of Host Defence Peptides and Antibiotics in Combating Antimicrobial Resistant Bacteria

“…A linear analog of thanatin from Podisus maculiventris was additive in combination with colistin against E. coli [59]. Coprisin from Scarabaeus satyrus acts synergistically in combination with GP and PC classes against E. coli, E. faecium, S. aureus, Streptococcus mutans, and P. aeruginosa but is only additive in combination with CP class antibiotics against E. coli, S. aureus, and S. mutans [60].…”