Biofilm-forming Gram-positive Bacteria Isolation

Two Gram-positive bacteria frequently found in the food industry, especially in the milk or meat industry were selected because of their strong biofilm forming ability [25 (link)]. Microbacterium lacticum (M. lacticum) D84 (EF 204392) was isolated from extended shelf-life (ESL) milk, and Staphylococcus capitis subsp. capitis (S. capitis) was isolated from an air decontamination step prior to packaging at a meat production facility. Bacterial stock and working cultures were maintained and prepared according to Zand et al. [25 (link)]. The isolates were preserved in a 50% (v/v) glycerol stock at −80 °C. To obtain a stock culture, bacteria were sub-cultured overnight in tryptic soy broth (TSB; Carl Roth, Karlsruhe, Germany) at 37 °C and in 0.8% (v/v) skimmed milk broth (MB; Carl Roth) at 30 °C, for S. capitis and M. lacticum, respectively. Subsequently, stock cultures were then streaked onto either tryptic soy agar (TSA) or milk agar (MA) (Carl Roth) and incubated at 37 °C or 30 °C overnight and stored at 4 °C. Before each experiment, one colony was inoculated in 10 mL fresh TSB or MB, and the optical density₆₀₀ (OD) was standardized to 0.1 to obtain a working culture.