Antibacterial effects of <i>Annona muricata</i> bark and seeds extracts on coagulase-negative <i>Staphylococcus</i> isolates from wounds of patients attending a tertiary healthcare facility in Calabar, Nigeria

Annona (A.) muricata bark and seeds extracts were evaluated for antibacterial effects on coagulase-negative Staphylococcus (CoNS) isolates from wounds of patients attending University of Calabar Teaching Hospital, Calabar, Nigeria. Ethanolic and aqueous extracts of A. muricata bark and seeds were prepared by Soxhlet method and tested for antibacterial activity against 20 isolates of CoNS using agar-well diffusion assay. Minimum Inhibitory Concentration (MIC) of the extracts was determined using broth dilution method. Antibiotic susceptibility of the isolates was determined using Kirby-Bauer disc diffusion method. A. muricata bark extracts produced a concentration-dependent antibacterial activity against the CoNS isolates with MIC of 50mg/ml, while the seed extracts showed no antibacterial effect. The ethanolic bark-extract showed a higher efficacy and inhibited more isolates [11(55%)] than the aqueous extract [10(50%)], with a mean inhibition-zone diameter of 17.2 ± 2.2 mm and 14.0 ± 1.8 mm, respectively. The size of the inhibition-zones correlated significantly, in direct proportion, with concentrations of the extracts (p= 0.00012). Although the antibacterial activity of the bark extracts was lower than that of Ciprofloxacin (90%), Cefuroxime (80%), Meropenem (70%), and Ceftriaxone (60%), the ethanolic extract produced an activity equal to that of Gentamicin (55%). Unlike the seed extract, A. muricata bark extracts exhibited promising antibacterial potential that could be optimized, with improvement of the extraction process to include identification and isolation of the specific antimicrobial substances present in the crude extracts, for maximal activity against multidrug resistant pathogens.