Predatory bacteria constitute a heterogeneous group of prokaryotes able to lyse and feed on the cellular constituents of other bacteria in conditions of nutrient scarcity. In this study, we describe the isolation of Actinobacteria predator of other bacteria from the marine water of the Moroccan Atlantic coast. Only 4 Actinobacteria isolates showing strong predation capability against native or multidrug-resistant Gram-positive or Gram-negative bacteria were identified among 142 isolated potential predatory bacteria. These actinobacterial predators were shown to belong to the Streptomyces genus and to inhibit the growth of various native or multidrug-resistant micro-organisms, including Micrococcus luteus, Staphylococcus aureus (native and methicillin-resistant), and Escherichia coli (native and ampicillin-resistant). Even if no clear correlation could be established between the antibacterial activities of the selected predator Actinobacteria and their predatory activity, we cannot exclude that some specific bio-active secondary metabolites were produced in this context and contributed to the killing and lysis of the bacteria. Indeed, the co-cultivation of Actinobacteria with other bacteria is known to lead to the production of compounds that are not produced in monoculture. Furthermore, the production of specific antibiotics is linked to the composition of the growth media that, in our co-culture conditions, exclusively consisted of the components of the prey living cells. Interestingly, our strategy led to the isolation of bacteria with interesting inhibitory activity against methicillin-resistant S. aureus (MRSA) as well as against Gram-negative bacteria.

Atriplex semibaccata R.Br. is a perennial halophyte that has received much attention for studies of revegetation of marginal lands in arid and semi-arid environments. It was, recently, demonstrated that there are no risks in terms of contamination of essential oil (EO) from growing plant on such land. Interest in exploring the antibacterial and antioxidant potential of A. semibaccata EO has consequently been renewed. The objective of this study was to investigate the chemical composition, as well as the antioxidant and antibacterial activities of A. semibaccata EO. The antibacterial activity was evaluated against native (drug-sensitive) and multidrug-resistant (MDR) bacteria by testing the EO alone and in combination with conventional antibiotics. The chemical composition of EO was analyzed by gas chromatography/mass spectrometry, 52 chemical compounds were identified, and 2-Methoxy-4-vinyl phenol (48.9%), benzaldehyde (6.7%), and benzyl alcohol (6.3%) were found to be the main constituents of EO. Furthermore, the antioxidant activity was evaluated using a 2,2-diphenyl-1-picrylhydrazyl reducing–scavenging test. The EO from this species possessed high antioxidant activity (938.65 μg TE/g EO). The antibacterial test demonstrated an inhibitory effect on six native and MDR bacterial strains. We found that Staphylococcus aureus (Gram+), Klebsiella pneumoniae (Gram−), and Escherichia coli (Gram−) were more sensitive than MDR strains, with an inhibition zone ranging from 11.16 mm to 12 mm. Moreover, the minimum inhibitory concentration ranged from 3.12 mg/mL to 6.25 mg/mL. The combination of gentamicin and EO revealed a high synergistic effect. The effect on S. aureus and K. pneumoniae showed lower fractional inhibitory concentration indices of 0.39 and 0.27, respectively. The results also revealed that A. semibaccata EO contained compounds with antibacterial potential against MDR bacteria, with antioxidant properties, and with a moderate synergistic effect in combination with gentamicin. The EO from A. semibaccata could be considered a new and potential source of natural antioxidant and antibacterial agents. These findings make A. semibaccata an excellent choice for the revegetation of marginal lands with the subsequent use of biomass for the production of EO with significant potential in the control of microbial infection.

In this study, the chemical composition, antioxidant potential and antimicrobial interactions with a conventional antibiotic of essential oil (EO) isolated from Andryala pinnatifida subsp. mogadorensis aerial parts were assessed. Twenty eight compounds were identified. Farnesene (14.92%), Decanal (9.51%) and Tetradecanoic acid (7.44%) were the main compounds. The antibacterial potential was evaluated against two bacterial strains identified as resistant to antibiotics: Methicillin-resistant Staphylococcus aureus and Escherichia coli, as well as two sensitive bacterial strains: S. aureus and E. coli. The results obtained reveal that no bacterial strain tested was resistant to the studied EO, with MIC values in the range of (1.56-3.12) mg/mL. However, the combination of the studied EO with gentamicin showed a complete synergism against S. aureus. Furthermore, EO was screened for its antioxidant activity using three methods. IC₅₀ values were 4.34 ± 0.06 mg/mL, 1.16 ± 0.1 mg/mL and 1.94 ± 0.09 mg/mL, respectively, for DPPH, Ferric reducing and β-carotene/linoleic acid assays. The data indicate that the essential oil of this Moroccan endemic plant proved to be an important source of antioxidant and antibacterial products and may be used for the treatment of pathogenic bacteria and could be also implicated in food industries as preservative of foodstuffs.

In the original publication, there was a mistake in Figure 1b as published