Biodegradation of sulfamethoxazole by a bacterium isolated from the Hurricane overtop sediments

Abstract

Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) are commonly found in Louisiana's waterways, specifically in the waterways of Bayou Lafourche and the Intracoastal Canal. In August of 2021, Hurricane Ida flooded levees in Larose, Louisiana, where the bayou and canal intersect, and deposited sediment contaminated with industrial chemicals, antibiotics, and ARB. Many multidrug resistant bacteria were isolated from the sediments. One of the bacterial isolates, Alcaligenes faecalis, was able to use sulfamethoxazole (SMX) as its sole nitrogen source and was resistant at concentrations of 500 mg/L of SMX. The objective of this study was to find out the ability of this new isolate to degrade SMX. When this bacterium was grown on a basic mineral salt medium with SMX as the sole nitrogen source, 39.81 % SMX was removed in the culture, which was statistically significant compared to other treatment conditions. HPLC analysis showed the production of many metabolites. LC/MS confirmed the identity of two metabolites as 3-amino-5-methylisoxazole (3A-5M) and 3-hydroxy-5-methylisoxazole (3H-5M). A. faecalis hydrolyzed SMX to produce 3A-5M which was oxidatively deaminated further to yield 3H-5M with the release of ammonia. This reaction occurred only when there was no other nitrogen source other than SMX was present in the culture medium, which showed that this unique feature of the bacteria could be used to degrade SMX from the contaminated environment.