Synergistic Inhibition of Methicillin-Resistant Staphylococcus aureus (MRSA) by Melaleuca alternifolia Chell (Tea Tree) and Eucalyptus globulus Labill. Essential Oils in Association with Oxacillin

The presence of antibiotic-resistant bacteria has become a major therapeutic priority. This trend indicates the need for alternative agents to antibiotics, such as natural compounds of plant origin. By assessing membrane permeability, we investigated the antimicrobial activity of Melaleuca alternifolia and Eucalyptus globulus essential oils (EOs) against three strains of methicillin-resistant Staphylococcus aureus (MRSA). Using the checkerboard method, the efficacy of single EOs, in association with each other or in combination with oxacillin, was quantified by calculating the fractional inhibitory concentrations (FIC Index). All EOs showed a reduction in bacterial load, an alteration of membrane permeability which leads to an increase in its function, resulting in the release of nucleic acids and proteins. The treatment with EO–oxacillin combinations and associated EO–EO resulted in a synergistic effect in most of the tests performed. EO–EO association showed a high activity in the alteration of the membrane, increasing the permeability to about 80% in all the MRSA strains treated. In conclusion, the combination of EOs and antibiotics represents a valid therapeutic support against MRSA bacteria, allowing for a decrease in the antibiotic concentration needed for therapeutic use

Influence of aquatic microorganisms on Legionella pneumophila survival

The ability of aquatic bacteria Pseudomonas fluorescens SSD (Ps-D) and Pseudomonas putida SSC (Ps-C) to support the persistence of Legionella pneumophila (Lp-1) in an artificial water microcosm was investigated for 42 day, at two different incubation temperatures. At 4 °C, individually suspended Lp-1 was no longer detectable just after 24 hours, while in co-cultures with Pseudomonas, Lp1 showed a better survival capability. At 30 °C, Lp-1 alone displayed high survival rates over the entire period of observation. When Lp-1 was inoculated with Ps-C and Ps-D, its count showed a marked decrease, followed by a gradual and costant decline

Study of two bacteriocins produced by Enterococcus casseliflavus and Ent. faecalis.

The antimicrobial activity of two plasmid-borne bacteriocins produced by Enterococcus casseliflavus IM 416K1 and Ent. faecalis IM 388C and their mating transferability were studied.Both bacteriocins showed antibacterial activity against taxonomically related micro-organisms and Listeria monocytogenes but differ for heat sensitivity, antimicrobial titre, molecular size and class of affiliation. The transferability by mating of the antibacterial properties from producers to Enterococcus faecalis JH2-2 revealed that the bacteriocin-phenotype was linked in both strains to genes located on a 34 MDa plasmid. This result was confirmed by loss of antibacterial activity and immunity after curing treatment.Restriction analysis has shown a different profile of the two conjugative plasmids. Enterocin 416K1 and Enterocin 388C could represent natural antilisterial agents to use in food technology.The transferability of the 34 MDa conjugative plasmids might be considered a possibility for the study of bacteriocins expression in bacterial hosts different from the native strains

Enterocin 416K1, an antilisterial bacteriocin produced by Enterococcus casseliflavus IM 416K1 isolated from Italian sausages.

Enterococci (118) from Italian sausages were tested for the production of antimicrobial substances. Of these, 7.6\% showed antibacterial activity against one or several closely related microorganisms used as indicators. Enterococcus casseliflavus IM 416K1 in particular produced a bacteriocin (Enterocin 416K1) with strong anti-listerial antagonistic activity. The bacteriocin withstood heating at 90 degrees C for 120 min and storage at 4 degrees C for 6 months. The mode of action was identified as bactericidal. The crude activity of Enterocin 416K1 was linked to a molecule with an apparent molecular weight smaller than 5 kDa. Plasmid analysis of E. casseliflavus IM 416K1 revealed the presence of four plasmids with different molecular weights (34, 11, 7 and 3.3 MDa). All the Bac- variants produced by curing experiments showed loss of the single plasmid of 34 MDa. Bacteriocin activity and immunity production may be linked to genes located on that same plasmid

Study of five penicillinase producing Neisseria gonorrhoeae isolated in Italy.

Five penicillinase producing Neisseria gonorrhoeae (PPNG) were isolated from urethral specimens of men admitted to the "Santa Chiara" Hospital (Trento, Italy). All strains proved to be resistant to penicillin and ampicillin, and sensitive to cefuroxime, erythromycin, tetracycline, spectinomycin, nalidixic acid and ciprofloxacin. PPNG plasmid profiles showed that four of the isolates carried the 3.2 MDa "Africa" plasmid and one the 4.5 MDa "Asia" plasmid, the two well-known phenotypes reported in the USA and Europe as well as in Asian and African countries. Membrane matings were performed using N. gonorrhoeae carrying the 24.5 MDa conjugative plasmid as donors and E. coli K12 J 53 as recipient. The transfer of beta-lactamic antibiotic resistance was supported by the presence of 4.5 or 3.2 MDa plasmid bands and by beta-lactamase production in the transconjugants. Restriction analysis of Asian and African plasmids is reported

Essential Oils and Bacteriocin-Based Active Edible Coating: An Innovative, Natural and Sustainable Approach for the Control of Listeria monocytogenes in Seafoods

The anti-Listeria monocytogenes activity of four essential oils (EOs) (Salvia officinalis, Citrus limon, Mentha piperita and Thymus vulgaris) and bacteriocin bacLP17, added alone or in mixture in active edible coatings, was determined in artificially contaminated shrimps. The minimal inhibitory concentration (MIC) values of the EOs were determined against the NCTC 10888 strain of L. monocytogenes by using the broth microdilution method. The checkerboard method was carried out in tryptic soy broth (TSB), using microdilution to obtain the Fractional Inhibitory Concentration Index (FIC-Index) for six associations of EOs, chosen based on the best MIC results. All the EOs confirmed their anti-Listeria activity, both “in vitro” and inside the coatings. The coating matrix was suitable for use in the food field, allowing a gradual release of the EOs in packaged food. When the EOs were used in association (EO/EO) they were demonstrated to act synergistically, leading to a significant reduction in the amount (10–20 times) of EOs needing to be used, and consequently a decrease in the strong smell on the food. This effect was also confirmed when the compounds were incorporated into the coatings. The inclusion of the EOs within the coating not only ensured the anti-Listeria activity by increasing the shelf-life of food products, but also further mitigated the strong smell of the EOs, improving the organoleptic impact on the food and its sensory properties. Keywords: Listeria monocytogenes; shrimp; essential oils; bacteriocin; edible coating

Antilisterial Activity of Bacteriocins Produced by Lactic Bacteria Isolated from Dairy Products

Sixty-nine Lactic Acid Bacteria (LAB) and bifidobacteria were isolated and identified from Italian dairy products (raw milk, cream, butter, soft cheese and yoghurt) to find new antimicrobial compounds to use as food bio-preservatives. All the isolates were preliminarily screened by the deferred antagonism method for bacteriocin production. Afterwards, to evaluate the release of bacteriocin in liquid medium, the Cell-Free Supernatant Fluid (CFSF) of the best producers was tested by agar well diusion assay. The study allowed the selection of three bacteriocin producing strains (Enterococcus faecium E23, Bifidobacterium thermophilum B23 and Lactobacillus bulgaricus L21), endowed with the strongest and broadest inhibitory capability against the pathogen Listeria monocytogenes. The molecular characteristics and the chemical–physical properties of both producers and the respective bacteriocins were studied and compared. The results showed that E. faecium E23 was the best producer strain and its class IIa bacteriocins, called enterocin E23, exhibited a good spectrum of activity towards L. monocytogenes. Enterocin E23 was stable over a wide range of pH and at low temperatures for at least four months and, for this reason, it can be employed in refrigerated foods for the control of L. monocytogenes, the major concern in dairy products

Eco-Friendly Edible Packaging Systems Based on Live-Lactobacillus kefiri MM5 for the Control of Listeria monocytogenes in Fresh Vegetables

To meet consumer requirements for high quality food free of chemical additives, according to the principles of sustainability and respect for the environment, new “green” packaging solutions have been explored. The antibacterial activity of edible bioactive films and coatings, based on biomolecules from processing by-products and biomasses, added with the bacteriocin producer Lactobacillus kefiri MM5, has been determined in vegetables against L. monocytogenes NCTC 10888 (i) “in vitro” by a modified agar diffusion assay and (ii) “on food” during storage of artificially contaminated raw vegetable samples, after application of active films and coatings. Both polysaccharides-based and proteins-based films and coatings showed excellent antilisterial activity, especially at 10 and 20 days. Protein-based films displayed a strong activity against L. monocytogenes in carrots and zucchini samples (p < 0.0001). After 10 days, both polysaccharide-based and protein-based films demonstrated more enhanced activity than coatings towards the pathogen. These edible active packagings containing live probiotics can be used both to preserve the safety of fresh vegetables and to deliver a beneficial probiotic bacterial strain. The edible ingredients used for the formulation of both films and coatings are easily available, at low cost and environmental impact

Antimicrobial activity of silver doped fabrics for the production of hospital uniforms

Among several alternatives to control hospital-acquired infections (HAIs), a strategy could be the use of hospital uniforms imbued with antimicrobial substances. For this purpose we evaluated the antibacterial activity of two different silver doped fabrics employed for the production of hospital uniforms. The study was conducted in two-step. In the first the antimicrobial activity was evaluated in vitro against Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 6538, Enterococcus faecalis ATCC 29212. In the second, we tested the total viable counts detected from beginning to end of the work shift on experimental silver doped uniforms worn by doctors, nurses, allied health assistants in different hospital wards. The in vitro tests showed a remarkable antibacterial activity of both silver doped samples (>99.9% reduction within 4h of exposure for Gram-positive and within 24 h for Gram-negative bacteria). The experimental uniforms provided results only slightly in agreement with in vitro data. Even if the increase of total viable counts was somewhat lower for experimental uniforms than traditional ones, significant differences were not observed. Despite the results on the uniforms worn, the addition of silver in fabrics to make medical equipment (supplies) remains an interesting option for HAI control