Conditions Necessary for the Transfer of Antimicrobial Resistance in Poultry Litter

• Main Authors: Aaron Oxendine (Author), Allison A. Walsh (Author), Tamesha Young (Author), Brandan Dixon (Author), Alexa Hoke (Author), Eda Erdogan Rogers (Author), Margie D. Lee (Author), John J. Maurer (Author)
• Format: Book
• Published: MDPI AG, 2023-06-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.

Summary

Animal manures contain a large and diverse reservoir of antimicrobial resistance (AMR) genes that could potentially spillover into the general population through transfer of AMR to antibiotic-susceptible pathogens. The ability of poultry litter microbiota to transmit AMR was examined in this study. Abundance of phenotypic AMR was assessed for litter microbiota to the antibiotics: ampicillin (Ap; 25 μg/mL), chloramphenicol (Cm; 25 μg/mL), streptomycin (Sm; 100 μg/mL), and tetracycline (Tc; 25 μg/mL). qPCR was used to estimate gene load of streptomycin-resistance and sulfonamide-resistance genes <i>aadA1</i> and <i>sul1</i>, respectively, in the poultry litter community. AMR gene load was determined relative to total bacterial abundance using 16S rRNA qPCR. Poultry litter contained 10⁸ CFU/g, with Gram-negative enterics representing a minor population (<10⁴ CFU/g). There was high abundance of resistance to Sm (10⁶ to 10⁷ CFU/g) and Tc (10⁶ to 10⁷ CFU/g) and a sizeable antimicrobial-resistance gene load in regards to gene copies per bacterial genome (<i>aadA1</i>: 0.0001-0.0060 and <i>sul1</i>: 0.0355-0.2455). While plasmid transfer was observed from <i>Escherichia coli</i> R100, as an F-plasmid donor control, to the <i>Salmonella</i> recipient in vitro, no AMR <i>Salmonella</i> were detected in a poultry litter microcosm with the inclusion of <i>E. coli</i> R100. Confirmatory experiments showed that isolated poultry litter bacteria were not interfering with plasmid transfer in filter matings. As no R100 transfer was observed at 25 °C, conjugative plasmid pRSA was chosen for its high plasmid transfer frequency (10⁻⁴ to 10⁻⁵) at 25 °C. While <i>E. coli</i> strain background influenced the persistence of pRSA in poultry litter, no plasmid transfer to <i>Salmonella</i> was ever observed. Although poultry litter microbiota contains a significant AMR gene load, potential to transmit resistance is low under conditions commonly used to assess plasmid conjugation.

Item Description

10.3390/antibiotics12061006
2079-6382