Anti-MRSA Activity of Actinomycin X2 and Collismycin A Produced by Streptomyces globisporus WA5-2-37 From the Intestinal Tract of American Cockroach (Periplaneta americana)

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is recognized as one of the serious pathogen that causes acquired infections worldwide. Its emerging need to discover novel, safe and potent anti-MRSA drugs. In this study, primary screening by anti-MRSA activity assay found one strain WA5-2-37 isolated from the intestinal tract of Periplaneta americana, exhibited great activity against MRSA ATCC 43300. The strain WA5-2-37 produced actinomycin X₂ and collismycin A which showed strong inhibition of MRSA with minimum inhibitory concentration (MIC) values of 0.25 and 8 μg/mL. The structures of the pure compounds were elucidated by analysis of mass spectrometry (MS), ¹H and ¹³C nuclear magnetic resonance (NMR). The strain WA5-2-37 was considered as Streptomyces globisporus on the basis of morphological characteristics, genotypic data, and phylogenetic analysis. This is the first reported naturally occurring strain of S. globisporus isolated from the intestinal tract of P. americana, whereas it has almost been found from plants, marine, and soil previously. Moreover, S. globisporus has not been reported to produce any anti-MRSA substances previously, such as actinomycin X₂ and collismycin A. In conclusion, the insect-derived strain of S. globisporus WA5-2-37 was considered of great potential as a new strain of producing actinomycin X₂, collismycin A or other anti-MRSA compounds.

Keywords: Periplaneta americana; Streptomyces globisporus; actinomycin X2; collismycin A; methicillin-resistant Staphylococcus aureus.

FIGURE 1

The anti-MRSA activity, morphological characteristics of strain WA5-2-37. (A) The anti-MRSA activity of WA5-2-37, 1–3 refers to sample, positive control and blank control. The concentrations of sample and positive control were both 100 μg/mL and the experiment was performed in triplicate. (B) Culture on Gause’s synthetic agar no. 1. (C) Observation of the culture under optical microscopy following Gram staining (100×). (D) Observation of the culture by scanning electron microscopy (5,000×).

FIGURE 2

The phylogenetic tree of strain WA5-2-37. Maximum-likelihood phylogenetic tree based on 16S rDNA gene sequences showing the positions of strain WA5-2-37, the type strains of other Streptomyces and representatives of some other related taxa. Only bootstrap values (expressed as percentages of 1,000 replications) greater than 50% are shown at branching points. Bar, 0.02 substitutions per nucleotide position.

FIGURE 3

Structure identification of the purified compound 1. (A) Molecular structure of the compound. (B) Mass spectrometry. (C) Proton (¹H) nuclear magnetic resonance. (D) Carbon (¹³C) nuclear magnetic resonance spectrum of the compound 1 in DMOS-6d.

FIGURE 4

Structure identification of the purified compound 2. (A) Molecular structure of the compound. (B) Mass spectrometry. (C) Proton (¹H) nuclear magnetic resonance. (D) Carbon (¹³C) nuclear magnetic resonance spectrum of the compound 2 in DMOS-6d.

FIGURE 5

Scanning electron microscopy (SEM) images of pure compounds treated and untreated MRSA (50,000×). (A) Untreated MRSA. (B) Actinomycin X₂ treated MRSA. (C) Collismycin A treated MRSA.