Lincomycin resistance gene lnu(D) in Streptococcus uberis

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Streptococcus uberis is a significant cause of bovine mastitis.
• Antibiotic resistance in mastitis-causing pathogens poses a threat to animal health and food safety.
• Understanding the genetic basis of antibiotic resistance is essential for developing effective treatment strategies.

Purpose of the Study:

• To identify and characterize the genetic determinant responsible for lincomycin and clindamycin resistance in Streptococcus uberis UCN 42.
• To elucidate the mechanism of action of the identified resistance gene.
• To explore the evolutionary relationship of the identified gene with other known resistance genes.

Main Methods:

• Cloning of a DNA fragment from S. uberis UCN 42 into Escherichia coli.
• Gene sequencing and analysis.
• Biochemical assays to determine enzyme activity (inactivation of antibiotics).
• Mass spectrometry to identify the enzymatic reaction products.

Main Results:

• A novel gene, designated lnu(D), was identified and cloned, conferring intermediate resistance to lincomycin and susceptibility to clindamycin in S. uberis.
• The lnu(D) gene encodes a 164-amino-acid protein homologous to known lincosamide nucleotidyltransferases.
• The Lnu(D) enzyme was shown to inactivate lincomycin and clindamycin via adenylylation in the presence of ATP and MgCl2.
• A conserved domain was identified in Lnu(D) and other related nucleotidyltransferases.

Conclusions:

• The lnu(D) gene is responsible for lincomycin and clindamycin resistance in the studied S. uberis strain.
• The Lnu(D) enzyme confers resistance through antibiotic adenylylation, a mechanism previously observed for other lincosamide resistance genes.
• This discovery contributes to the understanding of antibiotic resistance mechanisms in Gram-positive bacteria and has implications for veterinary antibiotic use.