Blood agar

All specimens were inoculated into nutrient agar, blood agar and MacConkey’s agar media (Oxoid, UK) and incubated aerobically at 37°C for 18-20 h. Identification of bacteria was based on microscopy (gram reaction, shape, arrangement) and colony characteristics (colony morphology, haemolysis on blood agar, changes in the physical appearance of the differential media). Gram-positive isolates were tested for catalase and coagulase while gram-negative isolates were tested for oxidase, citrate utilization, motility indole urease and triple sugar iron tests.12

Biobanked isolates were removed from − 80 °C freezer (Thermo Scientific), thawed and sub-cultured unto three standard growth media: Blood Agar (BA – Columbia agar base supplemented with 5% sheep blood), chocolate agar (CA) and macConkey agar (Mac) (BD, Franklin Lakes, New Jersey, USA) under sterile working condition. All the plates were incubated aerobically overnight at 35 °C–37 °C except for CA plates which was incubated in 5% CO₂ for microaerophilic condition.

In vivo permeability assay was performed to assess barrier function using fluorescein isothiocyanate dextran (FITC-D). For each experiment, mice were divided into 4 groups of 5 mice each. The first group was vehicle-treated control and the second group was given drinking water with DSS only. The third and fourth groups of mice were treated with BS (100 and 200 mg/kg/day) through oral gavage for 3 days, then exposed to 5% DSS in their drinking water for 7 days to induce colitis. Briefly, food and water were withdrawn for 4 h, and mice were inoculated with FITC-D by oral gavage (20 mg/kg). After 4 h, mice serum was collected and fluorescence intensity was measured (excitation, 492 nm; emission, 525 nm). Detection of viable bacteria in mesenteric lymph nodes (MLNs) represented bacterial translocation from the lumen to the MLNs. The MLNs of left colonic regions were removed aseptically and were put into eppendorf tubes with 0.1-mL sterilized PBS and tissues were homogenized by micro grinder (RPI, Mount Prospect, IL, USA). The homogenates were plated on blood agar (Thermo Fisher Scientific, Lenexa, KS, USA) and incubated for 48 h at 37 °C. The number of colonie was counted and the ratio of bacterial translocation was presented for percentages.

To explore the growth of different bacteria in the water traps of sinks over time, environmental samples were collected with ESwabs (Copan Diagnostics Inc., Murrieta, CA, USA) from all 14 patient-associated sinks in the Burn Centre. The sampling took place at 8 a.m. every time, i.e., approximately 4 h after the last disinfection cycle. The swabs were inserted through the strainer and turned around. The collection of samples started directly after the installation of the self-disinfecting sinks in September 2019 and continued on a weekly basis until April 2020, for a total of 35 weeks. Records were kept concerning patient occupancy of each room upon sampling.
The samples were sent to the Department of Clinical Microbiology, Linköping University Hospital, and streaked onto three different types of media using the swabs: blood agar, hematin agar, and chromogenic urinary tract infection (UTI) agar (Thermo Fisher Scientific, Waltham, MA, USA). Discs (Thermo Fisher Scientific, Waltham, MA, USA) with imipenem (10 µg), trimethoprim–sulfamethoxazole (1.25–23.75 µg), and linezolid (10 µg) were placed on the plates, respectively. The plates were incubated at 35 °C for approximately 48 h. Bacteria were identified to the species level with a MALDI Biotyper 3.0 (Bruker Corporation, Karlsruhe, Germany).

Thirteen (0.5 kg) samples of raw milk and traditional fermented milk from indigenous animals procured in Jeddah Province, Saudi Arabia, were used in this study. These samples were collected from the local market and were stored in a fridge until use. MRS agar and MRS broth media (Oxoid^TM, Thermo Fisher Scientific, USA) were used to isolate and support the growth of LAB and to inhibit the growth of unwanted bacteria [35 (link)]. MRS agar and broth were also used to enumerate the LAB. M17 agar and M17 broth (Oxoid, Thermo Fisher Scientific, USA) were used for isolating the streptococci in dairy products [36 (link), 37 ]. Blood agar (Oxoid, Thermo Fisher Scientific, USA) and Muller-Hinton agar media (MHA) (HiMedia, India) were used to evaluate hemolytic activity and antimicrobial activity of the LAB, respectively.