Adeoti O.M^{1, 2,}, Ogungbola V.D¹, Adeoye K.A^{1, 3}, Olufemi S.O¹, Adesina D.A^{1, 4}

The aim of this study was to investigate the antibacterial activity of Psidium guajava and Azadirachta indica leaf extracts against gram negative bacteria. The extracted plants were rinsed with water to remove dust and air dried at normal room temperature (27°C) for two weeks and the grinded plants extracts preparation was divided into four different concentrations. Bacteria were isolated from the plants rhizosphere and the leaves extracts were diluted serially in different milliliters with discs soaked into the extracts differently and placed on the Mueller Hinton agar by using antibiotic sensitivity according to the Kirby-Bauer technique. The sensitivity of both extracts was initially tested with Escherichia coli and Salmonella spp. Identification of bacterial isolates from the rhizosphere where the two plants grow was subjected to conventional biochemical and molecular sequencing technique. The statistical analysis of the results showed that there was no significant inhibition on the tested organisms at (P>0.05). All bacteria isolates were catalase (+) and oxidase (+). Antibiotic Susceptibility test showed that Pseudomonas aeruginosa and Serratia marcescens were resistant to both plant extracts but yielded remarkable susceptibility to Ofloxacin, gentamycin and Ceftriaxone. Molecular characterization of Pseudomonas aeruginosa strain P1 (KF530797) and Serratia marcescens strain HA 517(KJ535328) indicated the presence of specific amplicons of ampG, ampC, ampD genes and gyrA respectively. Consequently, exchange of resistance genes could have been acquired horizontallybetween both plants and the bacteria population in the rhizosphere.

Serratia marcescens, rhizosphere, Kirby-Bauer, Ceftrizone, amplicons