Chemical Defence in a Millipede: Evaluation and Characterization of Antimicrobial Activity of the Defensive Secretion from Pachyiulus hungaricus (Karsch, 1881) (Diplopoda, Julida, Julidae).

Slaviša Stanković,Bojan Mitić,Tatjana Stević,Ivica Dimkić,Ivana Sofrenić,Ljubodrag Vujisić,Vladimir Tomić,Zvezdana Jovanović,Sofija Pavković-Lučić

doi:10.1371/journal.pone.0167249

Abstract

The chemical defence of the millipede Pachyiulus hungaricus is reported in the present paper, in which a chemical characterization is given and antimicrobial activity is determined. In total, independently of sex, 44 compounds were identified. All compounds belong to two groups: quinones and pentyl and hexyl esters of long-chain fatty acids. The relative abundances of quinones and non-quinones were 94.7% vs. 5.3% (males) and 87.3% vs. 12.7% (females), respectively. The two dominant quinones in both sexes were 2-methyl-1,4,-benzoquinone and 2-methoxy-3-methyl-1,4-benzoquinone. Antibacterial and antifungal activity of the defensive secretion was evaluated in vitro against seven bacterial strains and eight fungal species. With the aid of a dilution technique, the antimicrobial potential of the secretion and high sensitivity of all tested strains were confirmed. The lowest minimum concentrations of these compounds (0.20–0.25 mg/mL) were sufficient for inhibition of Aeromonas hydrophila, Listeria monocytogenes and Methicillin resistant Staphylococcus aureus (MRSA). The growth of eight tested fungal species was inhibited by slightly lower concentrations of the secretion, with Fusarium equiseti as the most sensitive fungus and Aspergillus flavus as the most resistant. Values of MIC and MFC in the employed microdilution assay ranged from 0.10 to above 0.35 mg/mL. The given extract contains antimicrobial components potentially useful as therapeutic agents in the pharmaceutical and agricultural industries.

Highlights

Millipedes are the third most diverse class of terrestrial arthropods, with about 12 000 formally described species [1]
To provide additional information about the defence sequester of the julids, we here give a chemical characterization of the defensive fluids of P. hungaricus and report for the first time the effects of a secretion extract obtained from one member of the order Julida on some pathogenic organisms
The results indicate that fungi were more sensitive to the tested extract than were bacteria, which required higher concentrations for inhibition of growth

Summary

Introduction

Millipedes are the third most diverse class of terrestrial arthropods, with about 12 000 formally described species [1]. One of the most conspicuous features of the numerous members of the class Diplopoda is the presence of a pair of exocrine defence glands in the body somites. These glands produce a variety of volatile compounds provisionally grouped into alkaloids, quinones, phenols and cyanogenic compounds [2,3,4,5,6,7,8]. To provide additional information about the defence sequester of the julids, we here give a chemical characterization of the defensive fluids of P. hungaricus and report for the first time the effects of a secretion extract obtained from one member of the order Julida on some pathogenic organisms. The present study was aimed at investigating the in vitro antimicrobial activity of defensive secretions on some important bacterial and fungal strains

Methods

Results

Conclusion