Phytochemical Screening and Antimicrobial Activity of Methanol Extracts of Usteria guineensis and Sphaerocoryne gracilipes on Pathogens and ESBL-Producing Escherichia coli

Antibiotic resistance of microbial pathogens has become a threat to public health, with observed increase in outbreak of infections, therapeutic failure, morbidity and mortality. Pathogenic Escherichia coli and other extended spectrum beta lactamase (ESBL) producing bacteria causes serious health challenges due to antimicrobial resistance. This has caused an increasing research on medicinal plants as a source of alternative potential therapeutic agents. In this study, antimicrobial activity of Usteria guineensis (UG) and Sphaerocoryne gracilipes (SG) was investigated on standard organisms and clinical isolates of ESBL-producing E. coli.

The leaves of Usteria guineensis and Sphaerocoryne gracilipes were extracted using methanol. Phytochemical analysis was carried out on the medicinal plants according to standard procedure. The clinical isolates of E. coli were screened for the production of ESBL using double disc synergy test, with E. coli ATCC 25922 as standard. Agar well diffusion method was used to determine antibacterial activity of the extracts at 100 and 25 mg/mL while Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were assessed using broth micro-dilution method. Statistical analysis was done using ANNOVA.

The two plants contain cardiac glycoside, alkaloids and saponin and 11/15 (80%) of the E. coli isolates show the production of the ESBL. The extracts of the two plants showed antibacterial activity against ESBL E. coli with zone of inhibition ranging between 11 to 18 mm for Usteria guineensis and 12 to 15 mm for Sphaerocoryne gracilipes. The MIC of the extracts ranged between 0.78 to 50 mg/mL and MBC from 12.5 to >50 mg/mL for the ESBL producers and the standard strains.

Therefore, the two plants, especially Usteria guineensis have potentials to be developed as alternative therapeutic agents for the treatment of infections caused by ESBL-producing pathogens like Escherichia coli.