Pesticide-treated Versus Untreated Agro-soils: Phenotypic and Genetic Signatures of Antibiotics Resistance in Recovered Bacteria

Abstract

This study evaluated and compared the antibiotic resistance profile and antibiotic resistance genes in multi-antibiotic-resistant bacterial species isolated/recovered from pesticide-treated and untreated agro-soils. The soil samples were obtained from a pesticide-treated and untreated farmland. The samples were analyzed for pesticide residues using gas chromatography–mass spectrometry. Isolation and enumeration of bacteria were performed, after which the isolates were evaluated for their antibiotic resistance using the Kirby-Bauer disc diffusion method. The multi-antibiotic-resistant isolates were further characterized for the presence of antibiotic resistance genes (blaTEM, blaCTX-M, ermC, AAC) using the polymerase chain reaction (PCR). The multi-antibiotic-resistant bacteria were identified using 16S rRNA gene sequencing. Results revealed that the pesticide-treated agro-soil had 5 organochlorine pesticide residues [Alpha-BHC (11.55 µg/kg), Aldrin (12.93 µg/kg), Heptachlor Epoxide (1.05 µg/kg), Gamma chlordane (16.39 µg/kg) and Endosulfan II (10.83 µg/kg) above maximum residue limits (MRL) (7.4, 5, 0.6, 4, and 4 µg/kg) respectively. In contrast, the untreated agro-soil had only Heptachlor epoxide (4.08 µg/kg) above the MRL (0.6 µg/kg). However, organophosphate residues in both soils were all below MRLs. A total of 9 isolates were recovered from the pesticide-treated agro-soil, of which 3 exhibited multi-antibiotic resistance to β-lactam combination agents, cephalosporins, fluoroquinolones. In contrast, 1 bacterium out of 6 isolates recovered from the untreated agro-soil was multi-antibiotic-resistant. PCR revealed the presence of blaCTX-M and ermC genes in the multi-antibiotic-resistant species from the pesticide-treated agro-soil, confirming the genetic blueprint for resistance to β-lactams and macrolides. In contrast, blaTEM and ermC genes were present in the multi-antibiotic-resistant bacterium from the untreated agro-soil. Some of the multi-antibiotic-resistant species from the pesticide-treated agro-soil were identified as Lysinibacillus sphaericus, Chryseobacterium gleum, Klebsiella quasipneumoniae. The multi-antibiotic-resistant bacterium from the untreated agro-soil was identified as Serratia sp. and Burkholderia cepacia. The percentage of antibiotic-resistant bacterial species from the untreated agro-soil was 60%, while that from pesticide-treated agro-soil was 100%. This study suggests that the pesticide-treated agro-soil is a reservoir of multi-antibiotic-resistant bacteria and genes compared to the untreated agro-soil. This may pose a significant risk to environmental and public health through transmission to food crops. These findings thus emphasize the emerging threat arising from pesticide use in agro-systems and the need to sensitize farmers on the importance of seeking eco-friendly alternatives to pesticide use.