Growth and Virulence Properties of Biofilm-FormingSalmonellaentericaSerovar Typhimurium under Different Acidic Conditions

Abstract

This study was designed to characterize the viability and potential virulence of bofilm-forming Salmonella enterica serovar Typhimurium under different pH levels, ranging from 5 to 7. The plate count method and real-time reverse transcription-PCR (RT-PCR) were used to evaluate the survival of S. Typhimurium grown in Trypticase soy broth (TSB) adjusted to pH 5, 6, and 7 (TSB-5, TSB-6, and TSB-7, respectively) at 37°C for 10 days. In TSB-5 and TSB-6, the numbers of viable cells estimated by using the real-time RT-PCR were greater than the culturable counts enumerated by the plate count method. Reflectance micro-Fourier transform infrared (micro-FTIR) spectroscopy was used to evaluate the biochemical changes in biofilm cells. Considerable changes in chemical components were observed in the biofilm cells grown in TSB-5 and TSB-6 when compared to the cells grown in TSB-7. The enterotoxin production and invasive ability of planktonic and biofilm S. Typhimurium cells were inferred by the relative levels of expression of stn and invA. The levels of expression of stn and invA were significantly increased in biofilm S. Typhimurium cells grown in TSB-5 (1.9-fold and 3.2-fold) and TSB-6 (2.1-fold and 22.3-fold) after 10 days of incubation. These results suggest that the biofilm-forming S. Typhimurium under different pH levels might change the virulence production and stress response mechanisms.

Antimicrobial Susceptibility and Biofilm Production by Salmonella sp. Strains Isolated from Frozen Poultry Carcasses

“…Biofilms on equipment and tools used in food processing are reservoirs of pathogenic and spoilage microorganisms, increasing the risk of microbial contamination in food processing plants (Shi & Zhu, 2009;Xu et al, 2010;Hasegawa et al, 2011;Wang et al, 2013). Bacteria in biofilms are protected from damaging environmental agents, such as disinfectants.…”

Invasion and Survival of Salmonella in the Environment: The Role of Biofilms

“…Legendre et al (2011) showed that adhered S. enterica serovar Enteritidis bacteria were more resistant to antibacterial agents than their planktonic counterparts. Xu et al (2010) found that the enterotoxin production and invasion ability of biofilm S. enterica serovar Typhimurium cells is enhanced under acidic stress conditions. Further, cells of S. enterica serovar Typhimurium, collected from a biofilm, showed increased adhesive ability within the spleens of mice.…”

“…The survival of Salmonella on equipment and instruments in the food industry might be one of the most important contributing factors to food contamination and the subsequent foodborne infection. Further, the biofilm formation ability of foodborne pathogens has attracted much attention in the medical field and food industry due to its potential risks, including transfer of antimicrobial resistance and virulence factors (Xu et al, 2010). Hasegawa et al (2011) found that the ability of Salmonella strains to survive in the presence of acetic acid and rice vinegar paralleled their ability to form biofilms.…”

Criteria for Selection of Surrogates Used To Study the Fate and Control of Pathogens in the Environment

“…One important consideration is that some pathogens, such as the Salmonella genus, can have stress response mechanisms when exposed to lethal acidic conditions. This is known as the cross-protection phenomenon, in which these acid-adapted cells become tolerant to multiple "heat, cold, osmotic and oxidative stresses" (84). Although there may be other pathogens and potential microbial surrogates that can exhibit this response, the consideration is not relevant to experimental contexts involving transport or removal.…”