Preliminary Investigation on Metal Tolerance and Antibiotic Resistance Profiles of Indigenous Bacteria Isolated from Blast-Impacted Soil in Lokoja, Nigeria

Abstract

Soil contamination with heavy metal causes serious environmental threats, particularly in mining areas affected by blasting. The bacterial diversity, heavy-metal tolerance, and bacteria antibiotic susceptibility were investigated from a previously active blast-site soil in Lokoja, Nigeria. Soil physicochemical analysis revealed a slightly alkaline pH (8.6) and appreciable organic matter content (8.87%). Six bacterial isolates were isolated from previously active blast site in Crusher, Lokoja and identified as Bacillus cereus, Bacillus subtilis, Pseudomonas luteola, Escherichia coli, and two species of Staphylococcus. Metal resistance screening showed that most isolates were highly tolerant to lead and arsenic, while cadmium exerted stronger inhibitory effects. Cadmium gradient and Minimum Inhibitory Concentration (MIC) analyses confirmed a response that was dose-dependent, with cadmium showing the lowest tolerance thresholds. Bacillus spp. and Pseudomonas luteola exhibited the highest overall metal tolerance with B. subtilis having the highest MIC values for cadmium and lead (50mg/mL, 500mg/mL), B. cereus for lead (500mg/mL) and P. luteola for cadmium (50mg/mL). All isolate showed growth at the highest tested arsenic concentration (700mg/mL) except for the second Staphylococcus species - Staphylococcus2 (300mg/mL). Antibiotic susceptibility testing indicated that the isolates were highly sensitive, with a single resistance recorded by Staphylococcus1 to the antibiotic Co-Trimoxazole. This study revealed that blast impacted soils host indigenous bacteria tolerant to heavy metals which have strong bioremediation potentials.