Antibiotic resistance patterns of Pseudomonas spp. isolated from faecal wastes in the environment and contaminated surface water.

The Pseudomonas genus, which includes environmental and pathogenic species, is known to present antibiotic resistances, and can receive resistance genes from multi-resistant enteric bacteria released into the environment via faecal rejects. This study was aimed to investigate the resistome of Pseudomonas populations that have been in contact with these faecal bacteria. Thus, faecal discharges originating from human or cattle were sampled (from 12 points and two sampling campaigns) and 41 Pseudomonas species identified (316 isolates studied). The resistance phenotype to 25 antibiotics was determined in all isolates, and we propose a specific antibiotic resistance pattern for 14 species (from 2 to 9 resistances). None showed resistance to aminoglycosides, tetracycline, or polymyxins. Four species carried a very low number of resistances, with none to ß-lactams. Interestingly, we observed the absence of the transcriptional activator soxR gene in these four species. No plasmid transfer was highlighted by conjugation assays, and a few class 1 but no class 2 integrons were detected in strains that may have received resistance genes from Enterobacteria. These results imply that the contribution of the Pseudomonas genus to the resistome of an ecosystem first depends on the structure of the Pseudomonas populations, as they may have very different resistance profiles.

Comparative evaluation of the antimicrobial activity of 19 essential oils.

In our research on natural compounds efficient against human pathogen or opportunist microorganisms contracted by food or water, the antimicrobial activity of 19 essential oils (EOs) was investigated against 11 bacterial species (6 Gram positive, 5 Gram negative) and 7 fungal species (2 dermatophytes, 1 mould, 4 yeasts) using microdilution assays. Five essential oils were obtained from Tunisian plants (EOtun): Artemisia herba-alba Asso, Juniperus phoenicea L., Rosmarinus officinalis L., Ruta graveolens L. and Thymus vulgaris L., whereas others were commercial products (EOcom). Overall, T. vulgaris EOtun was the most efficient EO against both bacteria (Gram negative: MIC ≤ 0.34 mg/mL; Gram positive: MIC ≤ 0.70 mg/mL) and fungi (yeasts: MIC ≤ 0.55 mg/mL; mould: MIC = 0.30 mg/mL; dermatophytes: MIC ≤ 0.07 mg/mL). Two EOcom displayed both acceptable antibacterial and antifungal potency, although weaker than T. vulgaris EOtun activity: Origanum vulgare EOcom (bacteria: MIC ≤ 1.13 mg/mL, fungi: MIC ≤ 1.80 mg/mL), and Cymbopogon martinii var. motia EOcom (bacteria: MIC ≤ 1.00 mg/mL, fungi: MIC ≤ 0.80 mg/mL). Bacillus megaterium, Legionella pneumophila, Listeria monocytogenes and Trichophyton spp. were the most sensitive species to both EOcom and EOtun. This study demonstrated the noteworthy antimicrobial activity of two commercial EOs and points out the remarkable efficiency of T. vulgaris EOtun on all tested bacterial and fungal species, certainly associated with its high content in carvacrol (85 %). These three oils could thus represent promising candidates for applications in water and food protections.

Activity of Six Essential Oils Extracted from Tunisian Plants against Legionella pneumophila.

The aim of this study was to investigate the composition of six essential oils extracted from Tunisian plants, i.e., Artemisia herba-alba Asso, Citrus sinensis (L.) Osbeck, Juniperus phoenicea L., Rosmarinus officinalis L., Ruta graveolens L., and Thymus vulgaris L., and to evaluate their activity against Legionella pneumophila (microdilution assays). Eight Legionella pneumophila strains were studied, including the two well-known serogroup 1 Lens and Paris strains as controls and six environmental strains isolated from Tunisian spas belonging to serogroups 1, 4, 5, 6, and 8. The essential oils were generally active against L. pneumophila. The activities of the A. herba-alba, C. sinensis, and R. officinalis essential oils were strain-dependent, whereas those of the J. phoenicea and T. vulgaris oils, showing the highest anti-Legionella activities, with minimum inhibitory concentrations (MICs) lower than 0.03 and lower than or equal to 0.07 mg/ml, respectively, were independent of the strains' serogroup. Moreover, the microorganisms treated with T. vulgaris essential oil were shorter, swollen, and less electron-dense compared to the untreated controls. Isoborneol (20.91%), (1S)-α-pinene (18.30%) ß-phellandrene (8.08%), α-campholenal (7.91%), and α-phellandrene (7.58%) were the major components isolated from the J. phoenicea oil, while carvacrol (88.50%) was the main compound of the T. vulgaris oil, followed by p-cymene (7.86%). This study highlighted the potential interest of some essential oils extracted from Tunisian plants as biocides to prevent the Legionella risk.