Antisalmonella Activities of Essential Oil of Psidium guajava Leaves: An In vitro and In vivo Study

Background: Life-threatening typhoidal salmonella infection is becoming more difficult to treat due to rising resistance to commonly used antibiotics. This resistance is aided by the biofilm-forming ability of the bacteria. This study investigated the in vitro and in vivo antisalmonella activities of essential oil of Psidium guajava leaves.

Methods: Essential oil was extracted from the leaves of Psidium guajava with solvents. The sensitivity of Salmonella Typhi to the essential oil of Psidium guajava (EOPG) was assessed via the agar well diffusion method. Minimum inhibitory, bactericidal and biofilm-inhibitory concentrations (MIC, MBC and MBIC respectively) were measured using micro-broth dilution and crystal violet assay respectively. The effect of EOPG on the bacterial cell membrane was evaluated by measuring the efflux of potassium ions, inorganic phosphate and pyruvic acid. Bioautography and GC-MS were employed to identify the constituents of the active fraction of the EOPG. Effects of EOPG on the level of bacteremia and bone marrow infection in male Wistar rats were determined by plating caudal blood on salmonella-shigella agar. Selected serum cytokines were measured using ELISA kits. Effect on hepatic DNA was measured by comet assay while histological evaluation of the liver of infected rats was done by Hematoxylin and Eosin staining.

Results: Essential oil of Psidium guajava leaves (EOPG) inhibited the growth of S. Typhi with a zone of inhibition of 13±0.2mm compared to 31±0.3mm recorded by ciprofloxacin. Minimum inhibitory, minimum bactericidal and minimum biofilm inhibitory concentrations were 25, >50 and 12.5 mg/mL respectively. Exposure to EOPG caused efflux of potassium ions, inorganic phosphate and pyruvic acid in S. Typhi. Oral administration of 50 mg/mL of EOPG reduced bacterial load in the blood and bone marrow of S. Typhi-infected rats significantly (P<0.05) when compared to untreated animals. Infection-induced reduction of serum IL-1β and rise in serum IFN-γ were ameliorated considerably in treated animals. The hepatic DNA of infected animals were protected from breakage in the group administered 50 mg/mL/day of EOPG compared with untreated, ciprofloxacin-treated as well as those administered 100 mg/mL/day of EOPG.

Conclusion: EOPG has both in vitro and in vivo anti-salmonella activities, this could be exploited in developing new drug leads for treatment of typhoid fever