First Description in Greece of mphC-Positive Staphylococci Causing Subclinical Mastitis in Ewes

The aim of the present study was to describe the first mphC-positive staphylococci, including two Staphylococcus lentus (Sle-087lar and Sle-091lar) and one Staphylococcus xylosus (Sxy-228lar), isolated from samples of animal origin, in Greece. Isolates Sle-087lar and Sxy-228lar were resistant to erythromycin, whereas Sle-091lar was resistant to erythromycin and lincomycin. All three isolates were susceptible to the remaining antibiotics. PCR screening showed that isolate Sle-091lar carried also ermB. For Sxy-228lar, whole-genome sequencing (WGS) and de novo assembly obtained an mphC-positive contig of 57.3-kb exhibiting high similarity with the genome of mphC-negative S. xylosus S170. However, mphC of Sxy-228lar was 91% similar to that found in plasmid pJW2311 from S. xylosus JW2311. Additionally, WGS data showed that Sle-087lar and Sle-091lar harbored mphC-carrying sequences being highly similar to the recently announced genome of the mphC-carrying S. lentus isolate 050AP from Tanzania. However, differences were observed in the mphC environment, suggesting the independent acquisition of the gene by each isolate. Sle-091lar also harbored transposon Tn917, which carries ermB resistance gene, integrated into S. lentus chromosome. These findings indicated that acquisition of resistance genes can lead to the emergence of multiresistant staphylococci, causing animal infections with economic burden.

Creation of Staphylococcal Mutant Libraries Using Transposon Tn917

Non-directed mutagenesis of the staphylococcal genome is a global approach that can be used to identify the genetic basis for phenotypes of interest as well as for identifying regulators of gene expression. One such approach that has been widely used in the study of S. aureus and S. epidermidis is transposon Tn917 mutagenesis to generate random libraries of mutants. This chapter describes the use of plasmid pLTV1 (containing Tn917-lac) to generate Tn917 transposon mutants. Through the use of temperature manipulation and antibiotic selection, staphylococcal strains harboring this plasmid can be effectively mutagenized to create random libraries amenable to subsequent phenotypic screening and identification of transposon insertion sites.