Antimicrobial Susceptibility of Persister Biofilm Cells of Bacillus cereus and Pseudomonas fluorescens

The present study evaluates the antimicrobial susceptibility of persister cells of Bacillus cereus and Pseudomonas fluorescens after their regrowth in suspension and as biofilms. Two conventional (benzalkonium chloride—BAC and peracetic acid—PAA) and two emerging biocides (glycolic acid—GA and glyoxal—GO) were selected for this study. Persister cells resulted from biofilms subjected to a critical treatment using the selected biocides. All biocide treatments developed B. cereus persister cells, except PAA that effectively reduced the levels of vegetative cells and endospores. P. fluorescens persister cells comprise viable and viable but non-culturable cells. Afterwards, persister cells were regrown in suspension and in biofilms and were subjected to a second biocide treatment. In general, planktonic cultures of regrown persister cells in suspension lost their antimicrobial tolerance, for both bacteria. Regrown biofilms of persister cells had antimicrobial susceptibility close to those regrown biofilms of biocide-untreated cells, except for regrown biofilms of persister P. fluorescens after BAC treatment, which demonstrated increased antimicrobial tolerance. The most active biocide against persister cells was PAA, which did not promote changes in susceptibility after their regrowth. In conclusion, persister cells are ubiquitous within biofilms and survive after critical biocide treatment. The descendant planktonic and biofilms populations showed similar properties as the original ones.

Cymbopogon citratus Essential Oil: Its Application as an Antimicrobial Agent in Food Preservation

Antimicrobial in vitro and in situ efficacies of Cymbopogon citratus essential oil (lemongrass, LGEO) against 17 spoilage microorganisms (bacteria, yeasts and fungi) were evaluated. Additionally, its chemical composition, and antioxidant and antibiofilm activities were investigated. The LGEO exhibited a strong antioxidant activity (84.0 ± 0.1%), and its main constituents were citral (61.5%), geraniol (6.6%) and 1,8-cineole (6.4%). An in vitro antimicrobial evaluation revealed the lowest inhibition zone (1.00 ± 0.00 mm) in Pseudomonas fluorescens, and the highest inhibition zone (18.00 ± 2.46 mm) in Candida krusei. The values for the minimal inhibitory concentration were determined to be the lowest for Salmonella enteritidis and the highest for C. albicans. Furthermore, the concentration of ≥250 µL/L of LGEO suppressed the growth of Penicillium aurantiogriseum, Penicillium expansum, Penicillium chrysogenum and Penicillium italicum. The changes in the molecular structure of the biofilms produced by Pseudomonas fluorescens and Salmonella enteritidis, after their treatment with LGEO, confirmed its action on both biofilm-forming bacteria. Moreover, an in situ antimicrobial activity evaluation displayed the most effective inhibitory effectiveness of LGEO against Micrococcus luteus, Serratia marcescens (250 µL/L) and Penicillium expansum (125, 250 and 500 µL/L) growing on a carrot. Our results suggest that LGEO, as a promising natural antimicrobial agent, can be applied in the innovative packaging of bakery products and different types of vegetables, which combines commonly used packing materials with the addition of LGEO.

Establishment and Evaluation of a Loop-Mediated Isothermal Amplification Assay for Rapid Detection of Pseudomonas fluorescens in Raw Milk

Raw milk is susceptible to microbial contamination during transportation and storage. Pseudomonas fluorescens producing heat-resistant enzymes have become the most common and harmful psychrophilic microorganisms in the cold chain logistics of raw milk. To rapidly detect P. fluorescens in raw milk, the protease gene aprX was selected as a detection target to construct a set of primers with strong specificity, and a loop-mediated isothermal amplification (LAMP) assay was established. The detection thresholds of the LAMP assay for pure cultured P. fluorescens and pasteurized milk were 2.57 × 102 and 3 × 102 CFU/mL, respectively. It had the advantages over conventional method of low detection threshold, strong specificity, rapid detection, and simple operation. This LAMP assay can be used for online monitoring and on-site detection of P. fluorescens in raw milk to guarantee the quality and safety of dairy products.

El papel de los procariotas en la degradación del cianuro

El cianuro es una sustancia tóxica, potencialmente letal, cuya concentración ha incrementado debido a las actividades antropogénicas, lo que genera un impacto negativo en el ecosistema y en la salud de los organismos expuestos. Desde hace un par de décadas se ha utilizado un proceso biotecnológico llamado “biorremediación”, que consiste en aprovechar las capacidades metabólicas de los microorganismos como bacterias y arqueas que degradan o atenúan contaminantes como el cianuro y los compuestos que forma. El presente trabajo tiene como objetivo identificar a las principales especies de bacterias y arqueas con capacidad para degradar el cianuro en sus distintas formas mediante un análisis bibliográfico. Dentro de los microorganismos utilizados para la degradación de cianuro se encuentran Bacillus sp., Escherichia coli, Pseudomonas fluorescens, entre otras especies. Con base en el número de especies descritas y sus eficientes tasas de remoción, se determinó que el proceso de biorremediación del cianuro es una alternativa prometedora, además existe una mayor degradación en el proceso aeróbico comparado con el proceso anaeróbico.

Pengaruh penambahan bio-emulsifier dari Pseudomonas fluorescens pada pakan terhadap performa broiler

Penelitian ini bertujuan untuk mengetahui pengaruh penambahan Bio-emulsifierdari Pseudomonas fluorescenspada pakan terhadap performabroiler dan mengetahui level terbaik penambahan Bio-emulsifierdari Pseudomonas fluorescenspada pakan broiler. Penelitian ini menggunakan Rancangan Acak Lengkap (RAL) dengan 4 perlakuan dan 5 ulangan. Level Bio-emulsifieryang diberikan yaitu P0 = pakan kontrol tanpa Bio-emulsifier, P1 = 0,5 g/kg pakan, P2 = 1 g/kg pakan, P3 = 1,5 g/kg pakan. Parameter penelitian ini yaitu konsumsi pakan (g/ekor), pertambahan bobot badan (g/ekor) dan konversi pakan. Data dianalisis statistik dengan menggunakan uji Annova. Hasil penelitian ini menunjukan perbedaan nyata (P<0,05) terhadap konsumsi pakan broiler. Kesimpulan dari penelitian ini adalah penambahan Bio-emulsifierdari Pseudomonas fluorescenspada pakan berpengaruh terhadap konsumsi pakan, pada level 0,5 g/kg pakan diperoleh konsumsi pakan rendah yaitu 2026,36 g/ekor dengan nilai konversi pakan sebesar 1,75.