Abstract Pseudomonas fluorescens is known to have the ability to adhere and produce biofilm. The formation of biofilms is enhanced by cellular motility, particularly when mediated by flagella. Biofilm formed on surfaces such as those used for food production act as points of contamination, releasing pathogenic or deteriorating microorganisms and compromising the quality of products. We assessed two strains of Pseudomonas fluorescens PL5.4 and PL7.1, sampled from raw, chilled, buffalo milk, which was obtained from a dairy farm. Twitching and swarming motility assays were performed, in addition to the biofilm production evaluations at a temperature of 7 °C. Regarding the motility assays, only the PL5.4 strain scored positive for the swarming assay. On microplates, both strains presented themselves as strong biofilm producers at 7 °C. The PL5.4 strain was also able to form biofilm on a stainless steel structure and maintain this structure for up to 72 hours at refrigeration. The Pseudomonas fluorescens PL5.4 isolate was identified on the basis of a 99% sequence identity with Pseudomonas fluorescens A506, a strain used as a biocontrol in agriculture. Biofilm-forming bacteria, when adapted to low temperatures, become a constant source of contamination, damaging the production, quality, safety and shelf-life of products.

Abstract Bacteria of the genus Bacillus sp. present the potential for inhibiting various pathogens, making them a promising starting point in the search for new antimicrobial substances. In this study, bacteria were isolated from sediment samples from humid areas of a Natural Conservation Unit in the state of Rio Grande do Sul, Brazil. The isolate Bacillus sp. sed 1.4 was selected for production of antimicrobial activity, and was characterized by MALDI-TOF and 16S rDNA sequencing. Phylogenetic analysis showed that Bacillus sed 1.4 was closely related to Bacillus altitudinis and Bacillus pumilus. The cell-free supernatant was partially purified using ammonium sulfate precipitation, gel filtration chromatography (Sephadex G-200) and an ultrafiltration membrane. Partial purification resulted in specific activity of 769.23 AU/mg, with a molecular mass of approximately 148 kDa. This antimicrobial substance showed stability at 100°C for 5 min, and was inactivated by proteolytic enzymes. An antimicrobial effect against Listeria species was observed. Considering the importance of the Listeria genus in the area of food safety, this antimicrobial activity should be further explored, specifically in the field of dairy products and with a focus on food biopreservation studies.

Abstract Wetlands are ecosystems rich in biodiversity and their ecological importance is recognized worldwide. Sediment samples were subjected to physical-chemical analysis and organic carbon content varied from 3.0% to 4.8%, the clay between 32 and 40%, silt with 41% and 43%, sand coarse varied between 6 and 11% and fine sand between 7 and 16%. The nitrogen values varied from 0.25% to 0.48%, the pH from 5.4 to 7.5 and the humidity varied from 44 to 56%. The selected isolates were evaluated for enzymatic properties and 64% showed positive results for amylase, 16% for gelatinase, 37% for lipase, 91% for protease and 2.7% for inulinase. Six bacterial isolates were selected for the overlapping assay and Bacillus sp. sed 2.2 showed inhibitory activity against Corynebacterium fimi NCTC 7547, and the antimicrobial substance was partially purified. The characterization of the substance was carried and the substance was stable at 100° C for up to 10 minutes and sensitive to the enzymes papain and trypsin. This substance was active against some species of Listeria, including Listeria monocytogenes ATCC 7644. The microorganims obtained from sediment samples were important sources of bioactive compounds, including enzymes and peptides, being a source of bioactive compounds to be studied.

The antimicrobial activity of the bacteriocin-like substance (BLS) P34 against Listeria monocytogenes was investigated in chicken sausage. The BLS was applied to chicken sausages (256 AU g-1) previously inoculated with a suspension of 10² cfu g-1 of L. monocytogenes. BLS P34 inhibited the indicator microorganism in situ in all incubation times for up to 10 days at 5 °C. The effectiveness of BLS P34 was increased when it was added in combination with nisin. The bacteriocin was also tested in natural eatable natural bovine wrapping (salty semi-dried tripe) against the same indicator microorganism, also showing inhibitory capability in vitro. BLS P34 showed potential to control L. monocytogenes in refrigerated meat products.

The mode of action of cerein 8A, a bacteriocin produced by the soil bacterium Bacillus cereus 8A, was investigated. The effect of cerein 8A was tested against Listeria monocytogenes and a bactericidal effect at 400 arbitrary units (AU)/ml was observed. In addition, cerein 8A was bactericidal against Bacillus cereus at 200 AU/ml, and inhibited the growth of Escherichia coli and Salmonella Enteritidis. Stronger inhibition of these gram-negative bacteria was achieved when the chelating agent EDTA was added together with bacteriocin. The effect of cerein 8A on B. cereus and L. monocytogenes was also investigated by Fourier transform infrared spectroscopy (FTIR). Treated cells had an important frequency increase at 2920 cm-1 and a decrease at 1400 cm-1, corresponding to assignments of fatty acids. Transmission electron microscopy showed damaged cell walls and loss of protoplasmic material. These results suggest that the mode of action of cerein 8A is to interfere with cell membranes and the cell wall.

O modo de ação da cereina 8A, uma bacteriocina produzida pela bactéria do solo Bacillus cereus 8A, foi investigado. O efeito da cereina 8A foi testado contra Listeria monocytogenes, resultando em um efeito bactericida com uma concentração de 400 unidades arbitrárias (UA)/ml. A cereina 8A também foi bactericida contra Bacillus cereus à 200 UA/ml. A bacteriocina inibiu o crescimento de Escherichia coli e Salmonella Enteritidis. Uma maior inibição contra estas bactérias gram-negativas foi alcançada quando o agente quelante EDTA foi adicionado junto com a bacteriocina. O efeito da cereina 8A sobre B. cereus e L. monocytogenes também foi investigado por espectroscopia de infravermelho com transformada de Fourier (FTIR). As células tratadas mostraram um importante aumento de frequência em 2920 cm-1 e uma diminuição na banda de 1400 cm-1, correspondendo a designações de ácidos graxos. A microscopia eletrônica de transmissão mostrou que as células apresentaram danos na parede celular com perda de protoplasma. Estes resultados sugerem que o modo de ação da cereina 8A é interferindo nas membranas celulares e parede celular.

Se investigó el modo de acción de la cereína 8A, una bacteriocina producida por la bacteria del suelo Bacillus cereus 8A. El efecto de la cereína 8A fue probado contra Listeria monocytogenes, obteniendo un efecto bactericida a concentraciones de 400 unidades arbitrarias (AU)/ml. La cereína 8A también tuvo un efecto bactericida contra Bacillus cereus a una concentración de 200 AU/ml. La bacteriocina inhibió el crecimiento de Escherichia coli y Salmonella Enteritidis. Mayor inhibición contra estas bacterias gram-negativas se consiguió cuando a la bacteriocina se le añadió el agente quelante EDTA. El efecto de la cereína 8A sobre B. cereus y L. monocytogenes también fue investigado por espectroscopía de infrarrojos de transformación de Fourier (FTIR). Las células tratadas mostraron un importante crecimiento en frecuencia de 2920 cm-1 y un decrecimiento de 1400 cm-1 de banda, correspondiéndose con la asignación de los ácidos grasos. La microscopía electrónica de transmisión mostró que las células habían padecido daños en la pared celular, con pérdida de material protoplásmico. Los resultados sugieren que el modo de acción de la cereína 8A se produce mediante su intervención en las membranas celulares y en la pared celular.

Bactérias produtoras de atividade antimicrobiana foram identificadas entre 86 isolados de ambientes aquáticos da Bacia Amazônica. Destes, 59 isolados (68.6%) apresentaram atividade antimicrobiana contra pelo menos uma bactéria indicadora. A atividade inibitória foi principalmente observada contra bactérias Gram-positivas, como Listeria monocytogenes e Bacillus cereus. As substâncias antimicrobianas produzidas por 19 linhagens que demonstraram maior atividade inibitória foram parcialmente caracterizadas, apresentando resistência térmica até 100°C e resistência parcial ao tratamento proteolítico. Algumas substâncias foram parcialmente inativadas somente quando tratadas com ácido tricloroacético ou com pronase E na concentração de 2 mg ml-1. A detecção da atividade antimicrobiana em géis de poliacrilamida mostrou que os compostos apresentaram peso molecular inferior à 14 kDa. Várias linhagens apresentaram atividade antibacteriana, que em alguns casos estaria relacionada com peptídios antimicrobianos. O potencial destes microrganismos para produzir substâncias antimicrobianas é grande e merece ser mais explorado.

Bacteria producing antimicrobial activity were identified among 86 isolates from aquatic environments of Brazilian Amazon Basin. Antimicrobial activity against at least one indicator strain was detected for 59 isolates (68.6%). Inhibitory activity was mostly against Gram-positive bacteria, such as Listeria monocytogenes and Bacillus cereus. The antimicrobial substances produced by 19 strains that showed higher inhibitory activity were partially characterized. These antimicrobial substances showed thermal resistance for up to 100°C and partial resistance to proteolytic treatment. Some antimicrobials were partially resistant to pronase E at 2 mg ml-1 or to treatment with trichloroacetic acid. Detection of antimicrobial activity on polyacrylamide gels revealed that the molecular weight of the compounds was lower than 14 kDa. Several strains showed antibacterial activity, which in some cases appear to be related to antimicrobial peptides. The potential of these microorganisms to produce useful antimicrobial compounds is great and must be better explored.