N VITRO TIGECYCLINE RESISTANT Staphylococcus aureus MUTANTS CROSS-SELECTED WITH MINOCYCLINE PRESENT MUTATIONS IN rpsJ AND mepA

HAIM MS; DI GREGORIO S; VIELMA VALLENILLA J; RAGO L; DI CONZA J; MOLLERACH M

Buenos Aires

Congreso; V International Congress on Translational Medicine; 2022

Universidad de Buenos Aires

Background and aims: Tigecycline (TGC) is a broad-spectrum antibiotic derived from minocycline (MIN) used for the treatment of complicated infections caused by multidrug-resistant organisms. We have previously reported the first TGC-non-susceptible Staphylococcus aureus clinical isolates in Argentina associated with rpsJ and mepA mutations, recovered from a cystic fibrosis (CF) patient treated with multiple antibiotics, including MIN. The aim of this study was to explore the capacity of MIN to select TGC-resistant mutants and to study the molecular bases associated with this phenotype. Methods: Two parental TGC-susceptible strains recovered from one patient with CF (CF38) and one with skin infection (S63) were subjected to serial passages in BHI broth with increasing concentrations of MIN, starting with a concentration of 1/2MIC. The MICs for TGC and other antibiotics were evaluated by Etest and agar dilution, respectively. The clonal relationship between the parental and mutants strains was studied by PFGE and they were characterized by SCCmec and agr typing. Genes associated with increases in TGC MIC (rpsJ, mepA, mepR) were amplified and sequenced. Results: 4 mutants were characterized (ST5-IV-agrII), all undistinguishable by PFGE to their parental strains: CF38A8, CF38B8 and S63A8 (selected with 8 µg/ml of MIN) and S63B4 (4 µg/ml). The MIC for TGC increased from 0.5 µg/ml in CF38 to 1 and 1.5 µg/ml for CF38A8 and CF38B8, respectively, both resistant to TGC. Although the S63-derived mutants were susceptible to TGC, MICs increased 3-6 times for S63A8 and S63B4, respectively. The increase in MIC to TGC was associated with changes in the MIC to other antibiotics. Analysis of rpsJ revealed the occurrence of K57M in S63B4 and S63A8 and additionally Y58F in the latter. No changes in rpsJ were observed between parental CF38 and its mutants, but additional mutations in mepA were observed in CF388A. Conclusions: To our knowledge, no cases of cross-selection have been reported in TGC-resistant S. aureus mutants. Therefore, it is essential to highlight the potential capacity of MIN to select resistance to TGC- an antibiotic of a broader spectrum-, detected in this study, when it is used for the treatment of infections caused by S. aureus