Effects of Ultrasound on the growth and cell mass of potential pathogenic microorganisms isolated from the soil environment

Abstract

Although soil microorganisms enhance soil fertility, some pathogenic soil microorganisms can contaminate crops and pose risks to human and animal health. Hence, the aim of this study is to investigate the effects of ultrasound on potential pathogenic and spoilage microorganisms present in the soil environment. Isolation and identification of microorganisms from the soil environment were carried out using standard microbiological techniques. Microbial growth and cell mass was monitored using spectrophotometer at 500 nm. Using a custom-built sono-bioreactor powered by two 27-watt speakers, potential pathogenic microorganisms isolated from soil samples at Crawford University, Nigeria, were exposed to ultrasonic treatments at frequencies of 1 kHz, 4 kHz, and 9 kHz for 24 hours. The organisms isolated were identified as Proteus vulgaris, Bacillus subtilis, Candida albicans and Candida tropicalis. The results demonstrated a statistically significant (p < 0.05), frequency-dependent effect on all test microorganisms. Low-frequency ultrasound at 1 kHz stimulated microbial proliferation, with Bacillus subtilis and Candida tropicalis with the highest growth (1.02x10⁹ and 6.90x10⁷ CFU/mL respectively) and cell mass (1.029 g and 0.690 g respectively) across all isolates. Conversely, increasing the frequency to 4 kHz and 9 kHz progressively suppressed microbial growth and viability. The most pronounced inhibitory effect was produced by treatment at 9 kHz, which reduced the bacterial count of Bacillus subtilis to 2x107 CFU/mL and the cell mass of Candida tropicalis to 0.227 g. The results of this research showed possible application of ultrasound as control measures against pathogenic and food spoilage organisms in medicine and food industries.