GC-MS analysis and in silico assessment of constituents of Psidium guajava leaf extract against DNA gyrase of Salmonella enterica serovar Typhi

Background: Typhoid fever is caused by the ingestion of food/water contaminated with Salmonella enterica serovar Typhi (S. Typhi). Treatment of typhoid fever has been by use of antibiotics but it appears the bacterium has mastered the act of resistance against each and every drug targeted at it. Drug discovery in the traditional wet laboratory procedures are cumbersome, costly and slow compared to the rate of emergence and distribution of multidrug resistant strain of S. Typhi. In silico investigations offer quick interventions in screening of small drug-like molecules against target protein(s) in order to hasten up the process of drug discovery. Psidium guajava is native to the tropics and has a high fidelity level among plants used traditionally for the treatment of typhoid fever in Nigeria. In vitro and in vivo antisalmonella activities have also been documented. Screening of phytochemicals of plants like P. guajava with documented evidence of anti-salmonella activities will increases the chances that a ‘drugable’ molecule will be found. Methods: P, guajava leaves were air-dried, powdered and extracted by maceration in methanol. The suspension was filtered and filtrate was concentrated in vacuo. Phyto-constituents were identified by Gas Chromatography-Mass spectrometry. DNA gyrase Subunit A-inhibiting properties of identified compounds were studied in silico by molecular docking while the physico-chemical and ADMET profile were retrieved from online webservers. Results: GC-MS revealed a total of 74 compounds in methanol extract of P. guajava leaves. All 74 compounds were drug-like according to Lipinski's “Rule of 5”. Ten compounds (6, 28, 29, 30, 31, 32, 33, 44, 45 and 56) has no interaction with the target protein while 4 compounds (3, 27, 57 and 61) have better binding affinities (between −6.6 and −7.4 kcal/mol) relative to ciprofloxacin (−6.4 kcal/mol). ADMET profiling of the successful ligands revealed that compound 57 is predicted to be less toxic compared to other compounds and ciprofloxacin. Conclusion: Compounds 3, 27, 57 and 61 (4-[5-(4-pyridinyl)-1,2,4-oxadiazol-3-yl]-1,2,5-Oxadiazol-3-amine; Cholesta-3,5-diene; 2-hydroxy-Cyclopentadecanone; Oxane-2,4-dione, 6-(4-methoxypheny l)-3,3,5,5-tetramethyl-) might have contributed to anti salmonella activities reported for P. guajava however only compound 57 is proposed for optimization owing to a better ADMET profile and could be considered further as potential lead molecule for optimization