Evaluation of Antimicrobial Activity by Marine Nocardiopsis dassonvillei against Foodborne Listeria monocytogenes and Shiga Toxin-Producing Escherichia coli

Abstract

The emergence of multidrug-resistant pathogens creates public health challenges, prompting a continuous search for effective novel antimicrobials. This study aimed to isolate marine actinomycetes from South Africa, evaluate their in vitro antimicrobial activity against Listeria monocytogenes and Shiga toxin-producing Escherichia coli, and characterize their mechanisms of action. Marine actinomycetes were isolated and identified by 16S rRNA sequencing. Gas chromatography–mass spectrometry (GC–MS) was used to identify the chemical constituents of bioactive actinomycetes’ secondary metabolites. Antibacterial activity of the secondary metabolites was assessed by the broth microdilution method, and their mode of actions were predicted using computational docking. While five strains showed antibacterial activity during primary screening, only Nocardiopsis dassonvillei strain SOD(B)ST2SA2 exhibited activity during secondary screening for antibacterial activity. GC–MS identified five major bioactive compounds: 1-octadecene, diethyl phthalate, pentadecanoic acid, 6-octadecenoic acid, and trifluoroacetoxy hexadecane. SOD(B)ST2SA2′s extract demonstrated minimum inhibitory concentration and minimum bactericidal concentration, ranging from 0.78–25 mg/mL and 3.13 to > 25 mg/mL, respectively. Diethyl phthalate displayed the lowest bacterial protein-binding energies (kcal/mol): −7.2, dihydrofolate reductase; −6.0, DNA gyrase B; and −5.8, D-alanine:D-alanine ligase. Thus, marine N. dassonvillei SOD(B)ST2SA2 is a potentially good source of antibacterial compounds that can be used to control STEC and Listeria monocytogenes.

A Mini-Review of Anti-Listerial Compounds from Marine Actinobacteria (1990–2023)

“…In contrast, the bacterial strains are generally susceptible to penicillins, except for oxacillin [48]. However, some of the strains eventually become antimicrobial resistant, mainly through horizontal gene transfer, gene mutation, and biofilm formation [52,[82][83][84][85]. The acquired antimicrobial resistance may involve various mechanisms [52].…”

“…Sp1 was evaluated for its anti-Listerial activity by the agar well diffusion method (Table 4) [150]. Ngema et al [85] employed the 96-well microdilution and in silico molecular docking methods to examine the anti-Listerial potential of Nocardiopsis dassonvillei SOD(B)ST2SA2 ′ s crude extract (Table 4). Such preliminary screening assays are a yet-to-be-tapped potential source of new anti-Listerial compounds, provided they are processed further.…”