Cell free preparations of probiotics exerted antibacterial and antibiofilm activities against multidrug resistant E. coli

Abdelhamid, Ahmed G.; Esaam, Aliaa; Hazaa, Mahmoud M.

The bacterial strains used in this study are summarized in Table 1 . Six strains of probiotics belonging to the genera Lactobacillus and Bifidobacterium were grown in Man-Rogosa-Sharpe (MRS, Oxoid, Hampshire, England) agar medium for 24 h at 37°C with 5% CO 2 . A single colony from each strain was transferred into MRS broth under the same incubation conditions for 24 h for the preparation of the cell-free spent medium (CFSM). For pathogenic E. coli isolation and cultivation, clinical specimens from the intensive care unit (ICU) of Benha University Teaching hospital and sewage water samples from Benha city were collected. All samples were collected aseptically and transferred immediately to culture on MacConkey agar and Eosin methylene blue agar (Oxoid) followed by incubation aerobically at 37°C for 24 h. The isolated colonies were further identified using Vitek 2 system (Biomerieux, USA). For the preparation of milk fermented by probiotics, a reconstituted skim milk powder (Nestle, Cairo, Egypt) was heated at 95°C for 30 min and then cooled (4°C) overnight. A 24 h fresh culture of the six probiotic strains was inoculated individually in the milk and then incubated under anaerobic conditions at 37°C for 24 h.