Impact of environmental conditions and gut microbiota on the in vitro germination and growth of Clostridioides difficile

Clostridioides difficile is a spore-forming anaerobic Gram-positive bacterium responsible for a broad spectrum of intestinal symptoms and healthcare-associated diarrhoea. The hypothesis of this work was that different in vitro conditions, notably pH and human faecal microbiota composition, impact the germination and/or the growth of C. difficile. This study aimed to correlate growth kinetics of the bacterium with these two physiochemical parameters by using a static in vitro model. To better understand the initial gut colonisation, several growth curve assays were carried out to monitor the behaviour of the spores and vegetative forms of C. difficile strain 078 under different conditions mimicking the gut environment. When the faeces were added, no spore germination or growth was observed, but C. difficile spores germinated in vitro when the pH was maintained between 6.6 and 6.9 for four different faeces donors. The evolution of microbiota studied by 16S rDNA profiling showed high proportions of Enterobacteriaceae and E. coli/Shigella when C. difficile grew, regardless of the inoculated faeces. This model helped us to understand that the germination and growth of C. difficile are strongly pH dependent, and further research is needed to evaluate the potential impact of the gut microbiota composition on C. difficile.

Effect of five decontamination methods on face masks and filtering facepiece respirators contaminated with Staphylococcus aureus and Pseudomonas aeruginosa

Introduction. In the context of the global pandemic due to SARS-CoV-2, procurement of personal protective equipment during the crisis was problematic. The idea of reusing and decontaminating personal surgical masks in facilities was explored in order to avoid the accumulation of waste and overcome the lack of equipment.

Hypothesis. Our hypothesis is that this work will show the decontamination methods assessed are effective for bacteria, such as Staphylococcus aureus and Pseudomonas aeruginosa .

Aim. We aim to provide information about the effects of five decontamination procedures (UV treatment, dry heat, vaporized H2O2, ethanol treatment and blue methylene treatment) on S. aureus and P. aeruginosa . These bacteria are the main secondary bacterial pathogens responsible for lung infections in the hospital environment.

Methodology. The surgical masks and the filtering facepiece respirators were inoculated with two bacterial strains ( S. aureus ATCC 29213 and P. aeruginosa S0599) and submitted to five decontamination treatments: vaporized H2O2 (VHP), UV irradiation, dry heat treatment, ethanol bath treatment and blue methylene treatment. Direct and indirect microbiology assessments were performed on three positive controls, five treated masks and one negative control.

Results. The five decontaminations showed significant (P<0.05) but different degrees of reductions of S. aureus and P. aeruginosa . VHP, dry heat treatment and ethanol treatment adequately reduced the initial contamination. The 4 min UV treatment allowed only a reduction to five orders of magnitude for face mask respirators. The methylene blue treatment induced a reduction to two orders of magnitude.

Conclusions. The three methods that showed a log10 reduction factor of 6 were the dry heat method, VHP and ethanol bath treatment. These methods are effective and their establishment in the medical field are easy but require economic investment.

Potential resident bacterial microbiota in udder tissues of culled cows sampled in abattoir

While mammary gland tissues (MGTs) are difficult to sample without risks for cow's health or milk production, milk analysis are used in routine to assess dairy cow udder's health. This study aimed to identify, quantify, compare the milk and MGTs microbiota of macroscopically healthy dairy bovine mammary glands (MG) in order to evaluate their degree of similarity. We harvested 13 couples of milk and MGTs samples, originated from the same quarter at culling. 16S rDNA Amplicon Sequencing was performed, showing Corynebacterium as the main bacterial genus in both types of samples but generally found in the milk in higher proportions than in tissues. Species evenness was higher in MGTs while species richness was higher in milk samples. Beta diversity was significantly different between both matrices suggesting the presence of a resident microbiota in MGTs of dairy cows at time of culling partially reflected by the milk microbiota from the same quarter.

Influence of reduced levels or suppression of sodium nitrite on the outgrowth and toxinogenesis of psychrotrophic Clostridium botulinum Group II type B in cooked ham

Outgrowth and toxinogenesis of Clostridium botulinum Group II (non-proteolytic) type B were studied in cooked ham prepared with different NaNO₂ (ranging from 0 to 80 mg/kg) and sodium chloride (NaCl, ranging from 12 to 19 g/kg) incorporation rates. Cured ground pork batters were inoculated with a cocktail of 3 strains of C. botulinum Group II type B at 3.5 log₁₀ CFU/g, portioned and samples of 50 g were vacuum packed then cooked and cooled based on thermal processing employed by the meat processing industry. These cooked ham model samples were stored under reasonably foreseeable conditions of use and storage i.e. for 14 days at 4 °C, followed by a cold chain break for 1 h at 20 °C then up to 33 days at 8 °C. Storage times and temperatures were used to mimic those commonly encountered along the supply chain. Enumeration of C. botulinum and detection of the botulinum neurotoxin type B (BoNT/B) were performed in triplicate at different storage times. Under these experimental conditions, incorporation rates of NaNO₂ ≥ 30 mg/kg prevented the outgrowth and toxinogenesis of C. botulinum Group II type B in the cooked ham model, regardless of the NaCl concentrations tested. In contrast, total removal of nitrite allowed outgrowth and toxin production during storage of the processed meat product. Results showed that the maximum ingoing amount of nitrite (i.e. 150 mg/kg) that may be added according to the EU legislation (Regulation (EC) No 1333/2008) can be reduced in cooked ham while still ensuring control of C. botulinum Group II type B. According to the multiple factors that could affect C. botulinum behavior in processing meat products, outgrowth and toxin production of C. botulinum should be evaluated on a case by case basis, depending on the recipe, manufacturing process, food matrix and storage conditions.

Cell-Free Spent Media Obtained from Bifidobacterium bifidum and Bifidobacterium crudilactis Grown in Media Supplemented with 3'-Sialyllactose Modulate Virulence Gene Expression in Escherichia coli O157:H7 and Salmonella Typhimurium

Complex oligosaccharides from human milk (HMO) possess an antimicrobial activity and can promote the growth of bifidobacteria such as Bifidobacterium bifidum and Bifidobacterium longum subsp. infantis. In addition, fermentation of carbohydrates by bifidobacteria can result in the production of metabolites presenting an antivirulence effect on several pathogenic bacteria. Whey is rich in complex bovine milk oligosaccharides (BMO) structurally similar to HMO and B. crudilactis, a species of bovine origin, is able to metabolize some of those complex carbohydrates. This study focused on the ability of B. bifidum and B. crudilactis to grow in a culture medium supplemented in 3′-sialyllactose (3′SL) as the main source of carbon, a major BMO encountered in cow milk. Next, the effects of cell-free spent media (CFSM) were tested against virulence expression of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium. Both strains were able to grow in presence of 3′SL, but B. crudilactis showed the best growth (7.92 ± 0.3 log cfu/ml) compared to B. bifidum (6.84 ± 0.9 log cfu/ml). Then, CFSM were tested for their effects on virulence gene expression by ler and hilA promoter activity of luminescent mutants of E. coli and S. Typhimurium, respectively, and on wild type strains of E. coli O157:H7 and S. Typhimurium using RT-qPCR. All CFSM resulted in significant under expression of the ler and hilA genes for the luminescent mutants and ler (ratios of −15.4 and −8.1 respectively) and qseA (ratios of −2.1 and −3.1) for the wild type strain of E. coli O157:H7. The 3′SL, a major BMO, combined with some bifidobacteria strains of bovine or human origin could therefore be an interesting synbiotic to maintain or restore the intestinal health of young children. These effects observed in vitro will be further investigated regarding the overall phenotype of pathogenic agents and the exact nature of the active molecules.

Evolutionary relationships between sporadic and epidemic strains of healthcare-associated methicillin-resistant Staphylococcus aureus

National surveillance of healthcare-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) isolates by pulsed-field gel electrophoresis (PFGE) typing allowed identification of rarely occurring 'sporadic' isolates with patterns significantly distinct from those of major epidemic clones of methicillin-resistant S. aureus (MRSA) circulating in Belgian hospitals. The aim of the present study was to compare the genetic background, antibiotic susceptibility profile and in vitro growth rates of 36 MRSA isolates with either 'epidemic' or 'sporadic' PFGE profiles to identify factors that could be involved in the epidemic behaviour of S. aureus. Sequence analysis of seven housekeeping genes (multilocus sequence typing) and seven surface-associated genes, combined with staphylococcal cassette chromosome mec (SCCmec) typing and spa typing results, segregated sporadic isolates into four groups: (1) isolates phylogenetically distant from epidemic HA-MRSA clones that possessed several properties of community-acquired MRSA strains; (2) isolates derived from the same methicillin-susceptible S. aureus ancestor as epidemic isolates but possessing a distinct type of SCCmec; and (3) and (4) isolates that were closely related to epidemic strains, either as recent descendants of these or as intermediate evolutionary steps between epidemic HA-MRSA strains and their putative ancestors. Sporadic isolates did not show slower growth in vitro than epidemic isolates. These findings suggest that the SCCmec type and insertion/deletion of other mobile genetic elements may be involved in modulating the epidemic behaviour of MRSA strains of similar genetic background, independently of fitness cost.