Tetracycline-resistant bacteria and ribosomal protection protein genes in soils from selected agricultural fields and livestock farms

Kathyleen Nogrado,Hor-Gil Hur,Ji-Hoon Lee,Tatsuya Unno

doi:10.1186/s13765-021-00613-6

Abstract

Antibiotic resistance in soil environment has eminently been compared and studied between agricultural and pristine soils, and the role of concentrated animal feeding operations has markedly been recognized as one of the major sources of antibiotic resistance. This study described the tetracycline resistance in small-scale farms in pursuit of presenting its possible role and contribution to the persistence of antibiotic resistance in the environment. Results of the study would render additional information on the occurrence of the ribosomal protection protein (RPP) tet genes among the isolated bacteria from the selected agricultural soils. Four tetracycline resistance and RPP genes were determined in two different agricultural soil settings. Both the culture and molecular method were used to determine and measure tetracycline resistance in soils from arable land and animal house. Results revealed a significantly higher number of culturable antibiotic-resistant bacteria in animal houses than arable lands which was suggestive of higher antibiotic resistance in areas where there was direct administration of the antibiotics. However, quantification of the gene copy numbers in the agricultural soils indicated a different result. Higher gene copy number of tetO was determined in one animal house (IAH-3), while the two other tet genes tetQ and tetW were found to be higher in arable lands. Of the total 110 bacterial isolates, tetW gene was frequently detected, while tetO gene was absent in any of the culturable bacterial isolates. Principal component analysis of occurrence and gene copy number of RPP tet genes tetO, tetQ, and tetW also revealed highest abundance of RPP tet genes in the manure and arable soils. Another important highlight of this study was the similarity of the RPP tet genes detected in the isolated bacteria from the agricultural soils to the identified RPP tet genes among pathogenic bacteria. Some of the tetracycline-resistant bacterial isolates were also multidrug resistant as it displayed resistance to tetracycline, erythromycin, and streptomycin using disk diffusion testing.

Highlights

Livestock farming is one of the agricultural sectors identified to have high demand for antibiotics [1]
Ribosomal protection proteins (RPPs), which are second to efflux proteins in terms of the number of tet gene determinants, are tetracycline resistance determinants frequently detected in the environment [10,11,12,13] and have a total of 12 gene determinants [14, 15]
Density of the culturable tetracycline-resistant bacteria was higher in the animal houses (3.13 × 104 ± 5.20 × 103 CFU/g) than in the arable lands (2.89 × 104 ± 5.43 × 103 CFU/g)

Summary

Introduction

Livestock farming is one of the agricultural sectors identified to have high demand for antibiotics [1]. According to Granados-Chinchilla and Rodriguez [2], antibiotics utilized in livestock farming alone amount to approximately two-thirds of the antibiotics produced worldwide. Ribosomal protection proteins (RPPs), which are second to efflux proteins in terms of the number of tet gene determinants, are tetracycline resistance determinants frequently detected in the environment [10,11,12,13] and have a total of 12 gene determinants [14, 15]. RPPs provide bacteria with additional protection from second generation tetracyclines like minocycline and doxycycline [8, 16]

Objectives

Methods

Results