Phosphorylation residue T175 in RsbR protein is required for efficient induction of sigma B factor and survival of Listeria monocytogenes under acidic stress / 浙江大学学报（英文版）（B辑：生物医学和生物技术）

Listeria monocytogenes is an important zoonotic foodborne pathogen that can tolerate a number of environmental stresses. RsbR, an upstream regulator of the sigma B (SigB) factor, is thought to sense environmental challenges and trigger the SigB pathway. In Bacillus subtilis, two phosphorylation sites in RsbR are involved in activating the SigB pathway and a feedback mechanism, respectively. In this study, the role of RsbR in L. monocytogenes under mild and severe stresses was investigated. Strains with genetic deletion (ΔrsbR), complementation (C-ΔrsbR), and phosphorylation site mutations in the rsbR (RsbR-T175A, RsbR-T209A, and RsbR-T175A-T209A) were constructed to evaluate the roles of these RsbR sequences in listerial growth and survival. SigB was examined at the transcriptional and translational levels. Deletion of rsbR reduced listerial growxth and survival in response to acidic stress. Substitution of the phosphorylation residue RsbR-T175A disabled RsbR complementation, while RsbR-T209A significantly upregulated SigB expression and listerial survival. Our results provide clear evidence that two phosphorylation sites of RsbR are functional in L. monocytogenes under acidic conditions, similar to the situation in B. subtilis.

Evaluación de la actividad de cultivos probióticos sobre Listeria monocytogenes durante la producción y almacenamiento de yogur / Evaluation of the activity of probiotic cultures over Listeria monocytogenes during the production and storage of yogurt

The effect of probiotic cultures over Listeria monocytogenes during the production and storage of yogurt was evaluated. A yogurt mixture (10.6 per cent non-fat solid liquids, 3 per cent fat and 0.3 per cent gelatin) was prepared, homogenized and pasteurized. Yogurt was inoculated with 0, 10(2), 10(4) and 10(6) CFU/mL of L. monocytogenes and 0.02 per cent of traditional lactic culture YC 180 (Streptococcus thermophilus and Lactobacillus bulgaricus) and probiotic culture ABY-1 (Bifidobacterium longum, B. bifidum, B, infantis, Lactobacillus acidophilus, Streptococcus thermophilus y Lactobacillus delbrueckii subsp. bulgaricus). It was incubated for 3 h at 43 degrees C until pH reached an approximate value of 4.8, followed by refrigeration at 5 degrees C for 21 days. During fermentation, samples were taken every hour, and during storage every 3 days, analyzing pH and lactic, bifidobacteria and pathogen count for each time. It was demonstrated that there was no significant simple effect for the type of culture used (ABY-1 and YC 180) (p = 0.684) over the amount of L. monocytogenes present in yogurt during the fermentation and storage periods. The presence of bifidobacteria in the ABY-1 culture did not present a significant effect over L. monocytogenes. Neither the effect of time presented a significant effect over L. monocytogenes (p = 0.448). In this case, the ABY-1 and YC 180 cultures present a bacteriostatic effect over the pathogen. The probiotic cultures had a bacteriostatic but not bactericidal effect over L. monocytogenes. This is not related to the protective effect of these cultures in bowel, since in-vivo conditions favor the production of antimicrobial substances, such as bacteriocins that act over pathogens.

Efecto de agregado de ácidos y temperatura sobre el desarrollo de listeria monocytogenes / Acids aggregated effect and temperature over listeria monocytogenes development

Listeria monocytogenes es un microorganismos patógeno asociado a enfermedades de origen alimentario que puede crecer y sobrevivir a temperaturas de refrigeración y a pH bajos. Se analiza el efecto de pH 3.0-6.5 dado por diferentes concentraciones de acidulantes (ac. cítrico, ac. láctico, y ac ascórbico) y de la temperatura de refrigeración (4 y 10ºC sobre el desarrollo y supervivencia de listeria monocytogenes en caldo de cultivo triptona soya y extracto de levadura. Se observó disminución de velocidad de desarrollo de l. monocytogenes al disminución la temperatura. El ácido cítrico resultó tener acción antimicrobiana más efectiva manteniendo los recuentos en fase de latencia a baja concentración. El ácido ascórbico fue el menos efectivo ya que la acción bactericida. Se observó a concentraciones muy altas, este junto con el ac. láctico presentaron un efecto inicial en el recuento de microorganismos. La información obtenida fue sintetizada mediante el índice de inhibición (II) y el efecto inhibitiorio (EI).

Obtención de mutantes dicloxacilina resistentes en Listeria monocytogenes / Isolation of dicloxacillin resistant mutants from Listeria monocytogenes

A partir de la cepa sensible de Listeria monocytogenes ATCC: 15313 se obtuvieron 10 mutantes espontáneas Dicloxacilina resistentes, indiferenciables de la cepa parenteral mediante pruebas bioquímicas convencionales y análisis electroforético de sus perfiles proteicos en presencia de detergentes. La disminución en la susceptibilidad frente a Dicloxacilina no fue en todas las cepas acompañada por una disminución paralela en la susceptibilidad frente a Penicilina G. Estudios morfológicos demostraron que algunas de las mutantes, creciendo a dosis subinhibitorias de Dicloxacilina, presentan profundas alteraciones en su morfología, entre la que se cuenta la formación de estructuras helicoidales