Human Oral Lower Palate Isolates and their Antagonistic Effect on Phytopathogenic Fungi Pathogens

Abstract

Production of certain substances that inhibit other microorganisms in the microbial environment of the oral cavity could serve as aggressive by product that may eliminate competitors and pathogens. Hence, this study was carried out to isolate and identify microorganisms from the oral cavity (lower palate of the mouth) and challenge these organisms with some selected strains of pathogenic fungi. The samples were aseptically collected using sterile swab sticks and transported to the Microbiology laboratory, for morphological, biochemical, and antagonistic tests in vitro. Nutrient Agar (NA) and MacConkey Agar (MCA) were used for the isolation of bacteria, Potato Dextrose Agar (PDA) for fungi and Malt Extract Agar (MEA) for antagonistic test. The isolated oral bacteria were Bacillus sp., Lactobacillus sp., Staphylococcus aureus and Streptococcus salivarius. Antagonistic effect was measured by zone of inhibition between the fungal plug and bacterial streak. The inhibition varied with different fungi. Results revealed that there were considerable variations in inhibitory activity. The zone of inhibition was more apparent in Bacillus sp. against Fusarium oxysporum (57.2±0.1:     P = .05). There was no inhibition/antagonistic activity with S. aureus and S. salivarius against all the selected fungi (0.0 - 0.1±0.1: P = .05). Antibiotics susceptibility test was carried out on the isolated oral microorganisms. The highest zone of inhibition was found in cotrimoxazole against Lactobacillus (23 mm), while the lowest zone of inhibition was found in ciprofloxacin against Lactobacillus sp. S. salivarius exhibited resistance to all antibiotics (0-12 mm). Bacillus sp., Lactobacillus sp. and S. aureus showed susceptibility to gentamycin. None of the bacterial isolates showed susceptibility to perfloxacin and streptomycin. Hence, gentamycin could be used to treat oral/dental infections caused by these bacterial isolates. Result from preliminary antagonistic studies showed that Bacillus sp. and Lactobacillus sp. could prove to be potent against all selected pathogenic fungi. Therefore, the metabolites produced by these isolates could be further studied for use as biocontrol agents of diseases caused by these fungi.