Effect of pH and Salinity on the Ability of Salmonella Serotypes to Form Biofilm

Abstract

Salmonella is a major cause of food-borne infections in Europe, and the majority of human infections are caused by only a few serotypes, among them are Salmonella enterica subsp. enterica serotype Enteritidis (hereafter Salmonella Enteritidis), Salmonella Typhimurium, and the monophasic variant of S. Typhimurium. The reason for this is not fully understood, but could include virulence factors as well as increased ability to transfer via the external environment. Formation of biofilm is considered an adaptation strategy used by bacteria to overcome environmental stresses. In order to assess the capability of different Salmonella serotypes to produce biofilm and establish whether this is affected by pH and salinity, 88 Salmonella isolates collected from animal, food, and human sources and belonging to 15 serotypes, including those most frequently responsible for human infections, were tested. Strains were grown in tryptic soy broth (TSB), TSB with 4% NaCl pH 4.5, TSB with 10% NaCl pH 4.5, TSB with 4% NaCl pH 7, or TSB with 10% NaCl pH 7, and biofilm production was assessed after 24 h at 37°C using crystal violet staining. A linear mixed effect model was applied to compare results from the different experimental conditions. Among the tested serotypes, S. Dublin showed the greatest ability to form biofilm even at pH 4.5, which inhibited biofilm production in the other tested serotypes. Salmonella Senftenberg and the monophasic variant of S. Typhimurium showed the highest biofilm production in TSB with 10% NaCl pH 7. In general, pH had a high influence on the ability to form biofilm, and most of the tested strains were not able to produce biofilm at pH 4.5. In contrast, salinity only had a limited influence on biofilm production. In general, serotypes causing the highest number of human infections showed a limited ability to produce biofilm in the tested conditions, indicating that biofilm formation is not a crucial factor in the success of these clones.

Host Response of Syrian Hamster to SARS-CoV-2 Infection including Differences with Humans and between Sexes

“…To describe the shedding of viral RNA in males and females and to monitor the hamsters’ weights during infection of males and females versus the corresponding group of mock animals, we performed a descriptive statistical analysis using SAS 9.4 software [ 62 , 63 , 64 ]. We applied a spline mixed model according to sex while taking into account the correlation between different observations of the same hamster over time using a first-order autoregressive (AR(1)) structure for the covariance matrix.…”

Assessing phenotypic virulence of Salmonella enterica across serovars and sources

“…Eighty-seven S. enterica strains, belonging to the selection of isolates already described in Petrin et al (2022) , were included in this study. Briefly, the strains were isolated in Italy between 2009 and 2019 and belonged to the collection of the Italian National Reference Laboratory for Salmonellosis, Istituto Zooprofilattico Sperimentale delle Venezie (IZSVe) and the Istituto Superiore di Sanità (ISS).…”

“…This GLM parameterization was chosen given the positively skewed P(inf) distribution. The same approach was used to test associations between P(inf) and biofilm formation ability under different experimental conditions, as studied by Petrin et al (2022) . Estimates were thus adjusted for differences among serovars and sources of isolations (covariates), and clustering of observation (replicates) at the isolate level using cluster-robust (Sandwich) variance estimators ( Williams, 2000 ).…”

Antimicrobial Activity of Composites-Based on Biopolymers

“…Changing from a planktonic state to a biofilm state confers various advantages to microorganisms, such as antimicrobial resistance, evasion of host immune response, resistance to oxidative stress, and compensation for lack of nutrients [26][27][28][29][30][31]. Several genetic studies have shown that the formation of biofilms depends on factors such as the mobility of microorganisms [31][32][33], the synthesis of exopolysaccharides [33][34][35], environmental conditions: temperature, pH, oxygen availability [36,37], and nutrient availability [38]. Several steps detail the process of biofilm formation.…”