Structural investigation of a polysaccharide from the mycelium of Enterobacter cloacae and its antibacterial activity against extensively drug-resistant E. cloacae producing SHV-12 extended-spectrum β-lactamase.

In this study, a polysaccharide (ECP) was isolated from the mycelium of Enterobacter cloacae and was found to exhibit strong antibacterial activities against E. cloacae producing SHV-12 ESBL with the increase of the inhibition zone diameter. Its minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were 12.5 mg/L and 25 mg/L, respectively. ECP at these concentrations immediately inhibited planktonic growth of the bacteria especially at the time from 2 to 10 h. Flow cytometry analysis further revealed that almost all the bacterial cells were damaged following ECP treatment. The permeability of the cytoplasmic membrane of E. cloacae was increased when ECP concentrations increasing, as evidenced by an influx of Na and an efflux of K, P or S, the leakage of intracellular ATP and the UV-absorbing substances, as well as the depolarization of the cytoplasmic membrane, indicating that bactericidal activity of ECP was achieved by inducing cell membrane damage.