Microbank system

Microbiological studies were conducted on the reference strain Streptococcus mutans ATCC 25175. The strain was stored in the Microbank system (Biocorp, Warszawa, Poland) in cryopreservation medium in a freezer at −80°C, as described by Lukomska-Szymanska et al. [42 (link)].

The material for the study consisted of field isolates of Campylobacter spp. obtained from the gut (cecum) of 140 broiler chickens directly after slaughter in slaughterhouses in southeastern Poland in September and October. The birds were from different indoor flocks. Presumptive identification of Campylobacter spp. isolates was based on colony morphology, Gram staining, and growth in microaerobic conditions. Initial isolation was carried out in Bolton Broth (Oxoid Ltd., UK). The cultures were incubated at 37°C for 48 hr in microaerophilic conditions (5% O₂, 10% CO₂, 85% N) in the CampyGen system (Oxoid Ltd.). On media that showed growth of gray, flat, and moist bacterial colonies with a tendency to expand, single colonies belonging morphologically to the Campylobacter spp. type were collected, directly transferred to selective mCCDA agar, and incubated at 41.5°C for 48 hr in microaerophilic conditions (Dudzic et al., 2016). The isolates were stored at −80°C in the Microbank system for storage of micro‐organisms (Biocorp, PL).

The isolation and identification of the strains was carried out according to the methodology described previously [2 (link)]. The first step was preliminary propagation of 10 g or 10 mL of the sample in 90 mL of buffered peptone water (Merck, Darmstadt, Germany). After incubation at 37 °C for 24 h the full loop of cultures was inoculated on Slanetz–Bartley agar (Merck, Darmstadt, Germany) and incubated at 37 °C for 48 h. Then, all colonies with enterococcal morphology were subjected to Gram staining and an assay for catalase and oxidase production. Until further analyses were carried out, the strains were stored at −80 °C using the Microbank system (Biocorp., Warszawa, Poland).