Impact of Bat Guano Fertilizer on Soil Bacteria Community Structure and Antibiogram of Associated Bacteria: An Alert to Food Insecurity

Aim: To evaluate the impact of Bat guano fertilization on soil microbial community structure and antibiotic resistance pattern of recovered isolates.

Study Design: Soil experiment with various Bat guano fertilized farmland soils.

Place and Duration of Study: Department of Microbiology, Renaissance University, Enugu State, Nigeria, between May, 2021 and July, 2021.

Methodology: Physicochemical and microbiological analyses of test soil samples were done following standard methods. Bacterial isolates were identified via an analytical profile index (API 20E) test kit, antibiotic resistance pattern of the bacterial species was ascertained using the Kirby Bauer disc diffusion method.

Results: The highest total culturable heterotrophic bacteria count recorded was from bat guano-fertilized soil (8.0 × 105 CFU/g) relative to control (1.09 × 105 CFU/g). Cultured isolates from bat guano-fertilized soils belonged to the genera Escherichia, Klebsiella, Enterobacter, Hafnia, Staphylococcus, Salmonella, Pleisiomonas, Pseudomonas and Aeromonas, relative to the control which had Aeromonas and Staphylococcus. Enterobacter spp. and Staphylococcus spp. had the highest frequency of occurrence (18.4%) across the bat guano-fertilized soils. Bat guano also impacted the microbial structure of the soil, introducing potential enteric pathogens, pathogenic bacteria implicated in human and animal diseases and multi-drug resistant bacterial pathogens. Antibiotic susceptibility test revealed that four of the bacterial isolates (Hafnia alvei, Salmonella typhimurium, Pleisomonas sp., and Klebsiella spp.) expressed multi-antibiotic resistance to Gentamycin, Cefuroxime, Chloramphenicol, Augmentin, Streptomycin, Septrin, Ofloxacin, Amoxicillin and Ampiclox. Multi-antibiotic resistance indexes of these bacteria were greater than the 0.2 threshold, suggesting the species originated from a potentially dangerous source (i.e. bat guano) and were likely introduced into the soils via faecal contamination (i.e. guano fertilization of soils).

Conclusion: The use of bat guano as organic fertilizer in agricultural lands pose health risks to farmers and consumers of foods (especially those eaten raw or slightly cooked) cultivated with them.This thus, alerts scientific community on the insecurity of food and human health posed by the use of bat guano fertilizer.