Characterising the inhibition profile of an antimicrobial produced by Enterococcus

Antibiotic resistance is one of the greatest problems facing the 21st century with few new classes of antibiotics being discovered. The forefront of antibiotic discovery has been the soil microbiome and it is still a valuable resource for identifying microbes with possible antibiotic producing capabilities leading to novel classes of antibiotics. This justifies continuing investigation into the soil microbiome for antibiotic producing bacteria, to help tackle the growing trend in antibiotic resistance. A bacterial soil isolate was found to inhibit Enterococcus faecalis ATCC 29212 and the aim of this work was to further characterise the inhibition profile of the antibacterial.

Bacterial plug and supernatant assays were used to access the inhibition ability of a soil bacterial isolate against the WHO ‘priority pathogens’. Identification of the bacteria was carried out using 16S rRNA and whole genome sequencing. Synergy tests were carried out using broth dilution assays.

The soil isolate (N5) was identified as Enterococcus and showed antibacterial activity against Staphylococcus aureus MRSA and E. faecalis VanA. This antibacterial is secreted into the supernatant which still showed inhibitory activity against MRSA and VRE. Synergy with N5 and ciprofloxacin (0.2  µg ml−1) against E. faecalis ATCC 29212 was also observed.

Both VRE and MRSA are important players in nosocomial infections and are displaying high levels of resistance. Further study of this antibacterial could lead to the development of a new compound to help overcome resistance mechanisms or a novel antimicrobial.