Antibiotic Resistance in Phosphate Solubilizing Burkholderia cepacia: Eco-Safety Implications for Application of Microbial Inoculants in Sustainable Agriculture

Abstract

The challenges of food insecurity and soil degradation posed by the use of agro-chemicals have led to the search for green strategies (microbial inoculants) to ensure sustainable agriculture. However, it has been reported that certain microorganisms with the potential for use as microbial inoculants express antibiotic resistance which presents safety implications for environmental and public health if these microorganisms are employed as inoculants. This study evaluated the antibiotic resistance profile of a phosphate-solubilizing bacterium recovered from a farm soil. Composite soil samples were collected from farmland at Onuebum Community, Bayelsa State. The samples were analysed for pesticide residues and physico-chemical properties using standard methods. Isolation and screening of bacterial isolates for phosphate solubilization potential were performed following standard microbiological techniques. Out of six (6) isolates recovered, only one bacterium was positive for phosphate solubilization. The bacterium was evaluated for antibiotic resistance using Kirby Bauer disc diffusion method, and was further identified via 16S rRNA sequencing. Detection of antibiotic resistance genes was performed via polymerase chain reaction (PCR). Results revealed that the soil had an organochlorine pesticide residue [Heptachlor epoxide (4.08 µg/kg)] above the maximum residue limit (0.6 µg/kg). Soil pH, nitrate, and phosphate were 4.10, 1.46 mg/kg and 0.82 mg/kg, respectively. The bacterium was identified as Burkholderia cepacia. B. cepacia expressed multi-antibiotic resistance (MAR) to cephalosporins, macrolides, aminoglycosides, and a β-lactam combination agent, with a MAR index of 0.6. PCR confirmed the presence of erm and blaTEM genes in Burkholderia cepacia, providing genetic evidence for its resistance to macrolides and cephalosporins. These findings suggest that while Burkholderia cepacia has potential as a biofertilizer due to its phosphate-solubilizing ability, its MAR raises ecological safety concerns regarding its use as an inoculant. Therefore, further research involving the exploration of plant growth-promoting traits in soil microorganisms and eco-safety assessments is recommended to determine their suitability for application as inoculants in agriculture.