Eravacycline activity against clinical S. aureus isolates from China: in vitro activity, MLST profiles and heteroresistance

Abstract

BackgroundMortality rates for patients with Staphylococcus aureus (S. aureus) infections have improved only modestly in recent decades and S. aureus infections remain a major clinical challenge This study investigated the in vitro antimicrobial activity of erevacycline (erava) against clinical S. aureus isolates from China, as well as the heteroresistance frequency of erava and sequence types (STs) represented in the sample.ResultsA sample of 328 non-duplicate clinical S. aureus isolates, including 138 methecillin-resistant (MRSA) and 190 methecillin-sensitive (MSSA) isolates, were collected retrospectively in China. Erava exhibited excellent in vitro activity (MIC50 ≤ 0.25 mg/L) against MRSA and MSSA, including isolates harboring Tet specific resistance genes. The frequency of erava heteroresistance in MSSA with erava MICs = 0.5 mg/L was 13.79% (4/29); no MRSA with erava MICs ≤0.5 mg/L exhibited heteroresistance. Heteroresistance- derived clones had no 30S ribosome subunit mutations, but their erava MICs (range, 1–4 mg/L) were suppressed dramatically in the presence of efflux protein inhibitors.ConclusionsConclusively, erava exhibited excellent in vitro activity against S. aureus, however hints of erava heteroresistance risk and MIC creep were detected, particularly among MSSA with MICs of 0.5 mg/L.Electronic supplementary materialThe online version of this article (10.1186/s12866-018-1349-7) contains supplementary material, which is available to authorized users.

Eravacycline susceptibility was impacted by genetic mutation of 30S ribosome subunits, and branched-chain amino acid transport system II carrier protein, Na/Pi cotransporter family protein in Staphylococcus aureus

“…Our previous report indicated the occurrence of Erava heteroresistance in S. aureus and this phenomenon would enhance the difficulty for the treatment of S. aureus infection with Erava. Our previous Although the high detection frequency of tetK and tetL in S. aureus was reported in our previous study[7], it remained unknown that whether the overexpression of tetK and tetL would impact the Erava susceptibility. Our data indicated that the overexpression of USA300HOU_RS00550 and USA300HOU_RS01625 would enhance the occurrence of Erava heteroresistance but have no direct impact on Erava MIC creep, demonstrating their overexpression can result in Erava MIC elevation under Erava pressure in vitro.…”

“…N315 and MS4 are two standard S. aureus isolates reserved in our lab. The parental MSSA isolates CHS237, CHS632, CHS62, CHS239 and their heteroresistant derived clones CHS237-E1, CHS6 32-E1, CHS62-E1, CHS239-E1, included in this study, have been described in our previous research for the investigation of Erava heteroresistance [7]. The S. aureus isolates, including SE4, SE7, SE13, CHS545 and CHS569, were used as reference isolates for the overexpression experiments as described previously [6].…”

“…Omada, Tige and Erava were purchased from the Medicines Company (Med Chem Express, Monmouth Junction, NJ) and their MICs were determined by the agar dilution method according to CLSI guidelines [19]. Because the CLSI guidelines provide no recommendation for the Erava MIC susceptibility breakpoints against S. aureus, we adopted an MIC susceptibility breakpoint of 0.5 mg/L, the value recommended for tigecycline nonsusceptibility in Gram-positive bacteria and defined heteroresistance as growth in 0.5 mg/L Erava [7,20]. Erava heteroresistance was defined as the observation of subpopulations isolated from the erava-containing plates able to grow in the presence of 0.5 mg/L erava (detection limit, ≥ 5 colony forming units/plate).…”

“…Genomic DNA of all clinical isolates was extracted and used as templates for PCR amplification in lysis buffer for microorganisms to direct PCR (Takara Bio Inc., Japan). The presence of 30S ribosomal subunit mutations, including five separate copies of the 16S rRNA gene, the genes encoding the 30S ribosomal proteins S3 and S10, were analyzed by PCR and sequence alignment as described previously [7].…”

“…High level of transcriptional expression of tetracycline specific resistance factors, such as tet(M) and tet(K), have been found to mediate the Tige MIC creep in E. faecium isolates [8,9]. Our previous data indicated that tet(K) was frequently detected in MSSA with Erava MIC ≥ 0.5 mg/L and it's still unknown whether tet(K) participated in the Erava heteroresistance or resistance [7]. The reduced susceptibility to Tige have been widely explained by the emergent mutations in genes encoding several 30S ribosome subunits, including 16S rRNA and 30S ribosome protein S10 [8][9][10][11][12][13][14][15][16][17].…”