In vitro Assessment of Selected Antibiotics, Crude Extract of Dalbergia latifolia Leaf and Their Combination on MDR Salmonella enterica Strain

Abstract

Aims: To investigate the susceptibility pattern Salmonella enterica strains to selected antibiotics and extract of Dalbergia latifolia as well as their combinatory effect on (multi-drug resistant) MDR salmonella. Place and Duration of Study: Faculty of Pharmacy, University of Ibadan, Nigeria from October 2012-May 2013. Methodology: In this study, a total of 11 clinical isolates of Salmonella enterica strains were screened in vitro against five antibiotics (ampicillin, amoxycillin, chloramphenicol, cotrimoxazole and ceftriaxone) for their antimicrobial susceptibility patterns, and against methanolic extracts of Dalbergia latifolia leaves. The isolates were also screened in vitro against the combined antibiotics and plant extracts using the agar well diffusion method and their MICs determined. Phytochemical screening was done to determine the secondary metabolites present in the plant extracts. Salmonella enterica serovar Typhimurium ATCC 14028, a type strain, was used as a reference standard in the identification of the isolates. The isolates were collected across hospitals in South West Nigeria. Results: All the isolates were multidrug resistance (with each showing resistance to at least two of the antibiotics), with the exception of one susceptible isolate. All the isolates were resistant to chloramphenicol (100%), while the highest susceptible numbers of isolates were observed against ceftriaxone (27.27%), 18.18% were susceptible to each of ampicillin and amoxycillin, while 9.09% were susceptible to cotrimoxazole. MIC values ranged from of 30 µg/mL to >100 µg/mL. All the isolates were susceptible to the extracts of Dalbergia latifolia leaves with a zone of diameters equating the CSLI recommendation except for two isolates at a concentration of 25 mg/mL showing lesser activities. The MIC values ranged between 3.125 mg/mL to 75 mg/mL. Conclusion: The combined antibiotics and plant extracts showed a potentiative and synergistic effects with Fractional Inhibitory Concentration (FIC) values ranging between 0.45-0.75. Among the 11 isolates, 4 isolates (36.36%) showed an additional effect to the combined activities of the antibiotics and plant extracts with a reduced MIC value. From the in vitro study, the diameter of the zone of inhibition of the combined halved-MICs (MIC*) of both the plant and antibiotics increased significantly than their individual results. The result of this study showed that the extract of Dalbergia latifolia has antimicrobial properties against MDR Salmonella enterica strain.