Ana Carolina Ritter

Toxigenic potential of Aspergillus flavus tested in different culture conditions

O objetivo do presente trabalho foi avaliar a capacidade produtora de aflatoxina de tres isolados de Aspergillus flavus sob diferentes condicoes de crescimento. O experimento foi baseado num delineamento experimental 23, tendo como variaveis independentes a temperatura (20-40 °C), tempo de incubacao (7-21 dias) e pH (2,0 e 6,0) em dois meios de cultura diferentes. As melhores condicoes encontradas foram empregadas com isolados nao toxigenicos testados previamente em Agar Coco. A aflatoxina B1 foi extraida com cloroformio, diretamente dos meios sinteticos. A identificacao e a quantificacao do composto foram efetuadas por Cromatografia em Camada Delgada e Fotometria Fotografica. Como resultados preliminares, o meio de cultura YES se mostrou como uma alternativa para detectar o potencial toxigenico de Aspergillus flavus, nas seguintes condicoes: pH 5,2, temperatura de 25 °C e tempo de incubacao de 11 dias, com uma producao de 206,05 ng.UFC-1 de aflatoxina B1. Dos 30 isolados nao toxigenicos, 12 apresentaram resultado positivo nas condicoes e meios de cultura testados.

Expression of essential genes for biosynthesis of antimicrobial peptides of Bacillus is modulated by inactivated cells of target microorganisms

Certain Bacillus strains are important producers of antimicrobial peptides with great potential for biological control. Antimicrobial peptide production by Bacillus amyloliquefaciens P11 was investigated in the presence of heat-inactivated cells of bacteria and fungi. B. amyloliquefaciens P11 exhibited higher antimicrobial activity in the presence of inactivated cells of Staphylococcus aureus and Aspergillus parasiticus compared to other conditions tested. Expression of essential genes related to biosynthesis of the antimicrobial peptides surfactin (sfp), iturin A (lpa-14 and ituD), subtilosin A (sboA) and fengycin (fenA) was investigated by quantitative real-time PCR (qRT-PCR). The genes lpa-14 and ituD were highly expressed in the presence of S. aureus (inactivated cells), indicating induction of iturin A production by B. amyloliquefaciens P11. The other inducing condition (inactivated cells of A. parasiticus) suppressed expression of lpa-14, but increased expression of ituD. A twofold increase in fenA expression was observed for both conditions, while strong suppression of sboA expression was observed in the presence of inactivated cells of S. aureus. An increase in antimicrobial activity was observed, indicating that synthesis of antimicrobial peptides may be induced by target microorganisms.

Investigation of rpoS and dps genes in sodium hypochlorite resistance of Salmonella Enteritidis SE86 isolated from foodborne illness outbreaks in southern Brazil.

In Rio Grande do Sul, southern Brazil, Salmonella Enteritidis is one of the principal microorganisms responsible for foodborne disease. The present study was conducted to compare the sodium hypochlorite resistance of Salmonella Enteritidis SE86 with that of other strains of Salmonella Enteritidis isolated from different regions of the world and to investigate the involvement of the rpoS and dps genes in resistance to this disinfectant. We tested five Salmonella Enteritidis wild-type (WT) strains isolated from different countries, two mutant strains of Salmonella Enteritidis SE86, and two tagged (3XFLAG) strains of Salmonella Enteritidis SE86 for their resistance to sodium hypochlorite (200 ppm). The survival of the WT and attenuated strains was determined based on bacterial counts, and tagged proteins (Dps and RpoS) were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting with anti-FLAG antibodies. None of the WT strains of Salmonella Enteritidis were totally inactivated after 20 min. The SE86 strain lacking dps was more sensitive to sodium hypochlorite than was the WT SE86 strain, with a 2-log reduction in counts after 1 min. The RpoS and Dps proteins were actively expressed under the conditions tested, indicating that in Salmonella Enteritidis SE86 these genes, which are expressed when in contact with sodium hypochlorite, are related to oxidative stress.

Diferentes pré-inóculos, temperaturas e tempos de incubação na produção aflatoxina B1 em arroz

The production of aflatoxin in rice by three isolates of Aspergillus flavus was investigated for different culture conditions (temperature and incubation time) and previous inoculum (YES- Yeast Extrat Sucrose and CYA- Czapeck Yeast Extrat). All strains withdrawn from the previous inoculum medium YES and inoculated in the rice in temperature of 25°C/18 days and 20°C/14 days, produced aflatoxin B1. The medium CYA had lower performance since the three strains tested did not produce aflatoxin B1 in the combination 20°C/14 days. At 25°C/11 days of incubation time aflatoxin was not detectable.

Comparative proteomic analysis of foodborne Salmonella Enteritidis SE86 subjected to cold plasma treatment

The increasing demand for high quality and safe food led to important technological innovations in food processing. Cold plasma appears as an emerging technology that has demonstrated efficiency in the removal of microbial contamination from fresh and minimally processed food. In this study, the proteomic profile of Salmonella Enteritidis SE86 subjected to cold plasma treatment was investigated. The number of viable S. Enteritidis SE86 cells was analyzed at different time intervals upon exposure to cold plasma and approximately 100 μg of S. Enteritidis SE86 protein extracts were analyzed by Multidimensional Protein Identification Technology (MudPIT). The results demonstrated that no significant changes in cell counts were detected for up to 20 min exposure to cold plasma, and 2 log reduction was achieved after 60 min. Overall, 1096 proteins were identified, with 249 detected only in plasma-treated samples, and 9 exclusive in non-treated control samples. The proteins uniquely detected in cold plasma-treated cells that showed higher abundance were glyoxalase I, ABC transporter substrate-binding protein and transcriptional activator OsmE, followed by some oxidoreductases. Proteins related with carbohydrate and nucleotide metabolism were mostly overexpressed in cold plasma treated cells, suggesting energy metabolism was increased.

Antimicrobial Activities of Metal Nanoparticles

Metals have been used since ancient times to combat infectious diseases. With the introduction of nanotechnology, metal nanoparticles have gaining increased attention as antimicrobial agents due to their broad inhibitory spectrum against bacteria, fungi, and viruses. Although silver nanoparticles have been mostly investigated due to their recognized antimicrobial properties, while other metal nanoparticles have received increasing interest as antimicrobials. These include gold, zinc oxide, titanium oxide, copper oxide, and magnesium oxide nanoparticles, since their antibacterial effects have been described. Metal nanoparticles can exert their effect on microbial cells by generating membrane damage, oxidative stress, and injury to proteins and DNA. In addition, metal nanoparticles can be associated with other nanostructures and used as carriers to antimicrobial drugs, improving the array of potential applications.