Effects of tolC on tolerance to bile salts and biofilm formation in Cronobacter malonaticus

Phenotypic heterogeneity and pathogenicity of Listeria monocytogenes under complex salinities of bile salts and sodium salts stress

Listeria monocytogenes is a foodborne pathogen that is widespread in the environment and food, and can cause zoonotic diseases. Previous studies have explored its growth under various environmental stressors, but little is known about its behavior under the complex effects of bile salts and sodium salts. Therefore, this study aimed to explore the differences of different salinities (Brain Heart Infusion (BHI) and BHI medium with 0.90% NaCl, 0.50% NaCl + 0.04% bile salts, and 0.90% NaCl + 0.04% bile salts) on growth, motility, biofilm formation, and virulence of L. monocytogenes. This study also artificially simulated L. monocytogenes contamination in pork samples. The results showed that the maximum specific growth rate (μmax) of 40 L. monocytogenes isolates was significantly reduced and the lag time (LT) was significantly prolonged under the complex salinity treatment, exhibiting greater growth heterogeneity; serotype 4b isolates exhibited strong resistance under complex salinities. L. monocytogenes biofilm formation was significantly reduced with the increase in complex salinities, motility was inhibited, and pathogenicity was enhanced, especially in serotype 1/2c isolates. Furthermore, the complex salinities also caused damage to the cell membrane of L. monocytogenes. L. monocytogenes grew wildly in pork samples, while its growth was inhibited when bile salts were added to form the complex salinities environment. These results highlight the phenotypic heterogeneity and pathogenicity of L. monocytogenes under complex salinities, offering insights for better risk assessment and pathogen control in food safety.

Bacillus licheniformis B410 Alleviates Inflammation Induced by Lipopolysaccharide and Salmonella by Inhibiting NF-κB and IRF Signaling Pathways in Macrophages

Foodborne bacterial enteritis is a common clinical disease, and its incidence has risen globally. To screen for functional Bacillus strains with anti-inflammatory properties, tolerance to acid and bile salts, and antagonism against Salmonella, 22 strains of Bacillus were employed as candidate strains in this study. An inflammatory cell model was established using J774-Dual NF-κB/IRF reporter macrophages to identify anti-inflammatory Bacillus. The candidate Bacillus strains were assessed through tolerance to acid and bile salts and antibacterial assays, and their inhibitory effects on the inflammatory responses triggered by S. Enteritidis infection were investigated. The findings demonstrated that B. licheniformis B410 was successfully screened, possessing a significant anti-inflammatory effect by suppressing the NF-κB and IRF signaling pathways. B410 exhibited excellent tolerance to acid and bile salts and displayed a favorable antibacterial effect against Salmonella. Co-incubation of B410 with RAW264.7 macrophages did not influence the cell viability. B. licheniformis B410 could significantly inhibit the expression of pro-inflammatory cytokines IL-1β and TNF-α induced by LPS and promote the expression of the anti-inflammatory cytokine IL-10. Additionally, B410 could markedly inhibit the activation of NF-κB and the production of inflammatory cytokines caused by S. Enteritidis infection in macrophages. This study successfully screened a new strain of B. licheniformis B410 that simultaneously had the capabilities of anti-inflammation, acid and bile salt tolerance, and antagonism against Salmonella, providing a new approach for the screening of functional anti-inflammatory probiotics and the development of anti-inflammatory probiotic therapeutic preparations.

Effects of bile acids on the growth, composition and metabolism of gut bacteria

Bile acids (BAs) exert a profound influence on the body's pathophysiology by intricately shaping the composition of gut bacteria. However, the complex interplay between BAs and gut microbiota has impeded a systematic exploration of their impact on intestinal bacteria. Initially, we investigated the effects of 21 BAs on the growth of 65 gut bacterial strains in vitro. Subsequently, we examined the impact of BAs on the overall composition of intestinal bacteria, both in vivo and in vitro. The results unveiled distinct effects of various BAs on different intestinal strains and their diverse impacts on the composition of gut bacteria. Mechanistically, the inhibition of intestinal strains by BAs occurs through the accumulation of these acids within the strains. The intracellular accumulation of deoxycholic acid (DCA) significantly influenced the growth of intestinal bacteria by impacting ribosome transcription and amino-acid metabolism. The metabolomic analysis underscores the pronounced impact of DCA on amino-acid profiles in both in vivo and in vitro settings. This study not only elucidates the effects of BAs on a diverse range of bacterial strains and their role in shaping the gut microbiota but also reveals underlying mechanisms essential for understanding and maintaining a healthy gut microbiota.

Characterization of Cronobacter sakazakii and Cronobacter malonaticus Strains Isolated from Powdered Dairy Products Intended for Consumption by Adults and Older Adults

The objective of this study was to characterize Cronobacter spp. and related organisms isolated from powder dairy products intended for consumption by adults and older adults using whole-genome sequencing (WGS), and to identify genes and traits that encode antibiotic resistance and virulence. Virulence (VGs) and antibiotic resistance genes (ARGs) were detected with the Comprehensive Antibiotic Resistance Database (CARD) platform, ResFinder, and MOB-suite tools. Susceptibility testing was performed using disk diffusion. Five presumptive strains of Cronobacter spp. were identified by MALDI-TOF MS and ribosomal MLST. Three C. sakazakii strains were of the clinical pathovar ST1, one was ST31, and the remaining isolate was C. malonaticus ST60. In addition, Franconibacter helveticus ST345 was identified. The C. sakazakii ST1 strains were further distinguished using core genome MLST based on 2831 loci. Moreover, 100% of the strains were resistant to cefalotin, 75% to ampicillin, and 50% to amikacin. The C. sakazakii ST1 strains were multiresistant (MDR) to four antibiotics. Additionally, all the strains adhered to the N1E-115 cell line, and two invaded it. Eighteen ARGs mainly involved in antibiotic target alteration and antibiotic efflux were detected. Thirty VGs were detected and clustered as flagellar proteins, outer membrane proteins, chemotaxis, hemolysins, and genes involved in metabolism and stress. The pESA3, pSP291-1, and pCMA1 plasmids were detected, and the prevalent mobile genetic elements (MGEs) were ISEsa1, ISEc52, and IS26. The isolates of C. sakazakii and C. malonaticus exhibited multiresistance to antibiotics, harbored genes encoding various antibiotic resistance proteins, and various virulence factors. Consequently, these contaminated powdered dairy products pose a risk to the health of hypersensitive adults.

VP3 Phage Combined with High Salt Promotes the Lysis of Biofilm-Associated Vibrio cholerae

Cholera, caused by pathogenic Vibrio cholerae, poses a significant public health risk through water and food transmission. Biofilm-associated V. cholerae plays a crucial role in seasonal cholera outbreaks as both a reservoir in aquatic environments and a direct source of human infection. Although VP3, a lytic phage, shows promise in eliminating planktonic V. cholerae from the aquatic environment, its effectiveness against biofilm-associated V. cholerae is limited. To address this limitation, our proposed approach aims to enhance the efficacy of VP3 in eliminating biofilm-associated V. cholerae by augmenting the availability of phage receptors on the surface of Vibrio cholerae. TolC is a receptor of VP3 and a salt efflux pump present in many bacteria. In this study, we employed NaCl as an enhancer to stimulate TolC expression and observed a significant enhancement of TolC expression in both planktonic and biofilm cells of V. cholerae. This enhancement led to improved adsorption of VP3. Importantly, our findings provide strong evidence that high salt concentrations combined with VP3 significantly improve the elimination of biofilm-associated V. cholerae. This approach offers a potential strategy to eliminate biofilm-formation bacteria by enhancing phage-host interaction.

Genomic Characterization of Cronobacter spp. and Salmonella spp. Strains Isolated From Powdered Infant Formula in Chile

This study characterized five Cronobacter spp. and six Salmonella spp. strains that had been isolated from 155 samples of powdered infant formula (PIF) sold in Chile and manufactured in Chile and Mexico in 2018–2020. Two strains of Cronobacter sakazakii sequence type (ST) ST1 and ST31 (serotypes O:1 and O:2) and one strain of Cronobacter malonaticus ST60 (O:1) were identified. All Salmonella strains were identified as Salmonella Typhimurium ST19 (serotype O:4) by average nucleotide identity, ribosomal multilocus sequence typing (rMLST), and core genome MLST (cgMLST). The C. sakazakii and C. malonaticus isolates were resistant to cephalothin, whereas the Salmonella isolates were resistant to oxacillin and ampicillin. Nineteen antibiotic resistance genes were detected in the C. sakazakii and C. malonaticus isolates; the most prevalent were mcr-9.1, bla_CSA, and bla_CMA. In Salmonella, 30 genes encoding for aminoglycoside and cephalosporin resistance were identified, including aac(6′)-Iaa, β-lactamases ampH, ampC1, and marA. In the Cronobacter isolates, 32 virulence-associated genes were detected by WGS and clustered as flagellar proteins, outer membrane proteins, chemotaxis, hemolysins, invasion, plasminogen activator, colonization, transcriptional regulator, survival in macrophages, use of sialic acid, and toxin-antitoxin genes. In the Salmonella strains, 120 virulence associated genes were detected, adherence, magnesium uptake, resistance to antimicrobial peptides, secretion system, stress protein, toxin, resistance to complement killing, and eight pathogenicity islands. The C. sakazakii and C. malonaticus strains harbored I-E and I-F CRISPR-Cas systems and carried Col(pHHAD28) and IncFIB(pCTU1) plasmids, respectively. The Salmonella strains harbored type I-E CRISPR-Cas systems and carried IncFII(S) plasmids. The presence of C. sakazakii and Salmonella in PIF is a health risk for infants aged less than 6 months. For this reason, sanitary practices should be reinforced for its production and retail surveillance.

Wolf in Sheep's Clothing: Clostridioides difficile Biofilm as a Reservoir for Recurrent Infections

The microbiota inhabiting the intestinal tract provide several critical functions to its host. Microorganisms found at the mucosal layer form organized three-dimensional structures which are considered to be biofilms. Their development and functions are influenced by host factors, host-microbe interactions, and microbe-microbe interactions. These structures can dictate the health of their host by strengthening the natural defenses of the gut epithelium or cause disease by exacerbating underlying conditions. Biofilm communities can also block the establishment of pathogens and prevent infectious diseases. Although these biofilms are important for colonization resistance, new data provide evidence that gut biofilms can act as a reservoir for pathogens such as Clostridioides difficile. In this review, we will look at the biofilms of the intestinal tract, their contribution to health and disease, and the factors influencing their formation. We will then focus on the factors contributing to biofilm formation in C. difficile, how these biofilms are formed, and their properties. In the last section, we will look at how the gut microbiota and the gut biofilm influence C. difficile biofilm formation, persistence, and transmission.