In vitro Activity and Heteroresistance of Omadacycline Against Clinical Staphylococcus aureus Isolates From China Reveal the Impact of Omadacycline Susceptibility by Branched-Chain Amino Acid Transport System II Carrier Protein, Na/Pi Cotransporter Family Protein, and Fibronectin-Binding Protein

Abstract

Omadacycline (Omad), a new tetracycline (Tet)-class broad-spectrum aminomethylcycline, has been reported to exhibit excellent potency against Gram-positive bacteria, including Staphylococcus aureus and Enterococci. The aim of this study was to evaluate the in vitro activity and heteroresistance characteristics of Omad in clinical S. aureus isolates from China and investigate Omad resistance mechanisms. A sample of 263 non-duplicate clinical S. aureus isolates [127 methicillin-resistant (MRSA) and 136 methicillin-sensitive (MSSA)] were collected retrospectively. Our data indicated that Omad exhibited excellent in vitro activity against both MRSA and MSSA. Omad heteroresistance frequencies were 3.17% (4/126) in MRSA and 12.78% (17/133) in MSSA. No mutations in Tet target sites, (five 16SrRNA copies and 30S ribosomal protein S10) were present in heteroresistance-derived clones, whereas Tet target site mutations contribute to induced Omad resistance in S. aureus in vitro. RNA sequencing (RNA-Seq) revealed that overexpression of branched-chain amino acid transport system II carrier protein and Na/Pi cotransporter family protein contributes to Omad heteroresistance emergence. Whole-genome sequencing demonstrated that the genetic mutation of fibronectin-binding protein (FnBP) could increase the Omad MIC. In conclusion, Omad heteroresistance risk should be considered in clinical isolates with MICs ≥ 0.5 mg/L and Omad susceptibility in S. aureus may be affected by efflux pump proteins (i.e., a branched-chain amino acid transport system II carrier protein and an Na/Pi cotransporter family protein), and FnBP.

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

“…The impacts of four candidate genes, including USA300HOU_RS03535, USA300HOU_ RS01625, USA300HOU_RS00550 and tet(K), were further tested by the in vitro overexpression experiments. The overexpression plasmids pRS00550, pRS01625, pRS03535, ptet(K) were successfully constructed and identified as our previous report [6]. Subsequently, the overexpression plasmids pRS00550, pRS01625, pRS03535,ptet(K) were transformed separately into clinical isolates SE4, SE7, SE13, CHS545 and CHS569, which have previously been reported with low expression level of three candidate genes [6].The impact of the overexpression of these four candidate genes on Erava susceptibility was described in Table 2.…”

“…The overexpression plasmids pRS00550, pRS01625, pRS03535, ptet(K) were successfully constructed and identified as our previous report [6]. Subsequently, the overexpression plasmids pRS00550, pRS01625, pRS03535,ptet(K) were transformed separately into clinical isolates SE4, SE7, SE13, CHS545 and CHS569, which have previously been reported with low expression level of three candidate genes [6].The impact of the overexpression of these four candidate genes on Erava susceptibility was described in Table 2. Briefly to say, the protein encoded by these four candidate genes did not result in Erava MICs elevation, however, the transcriptional overexpression of USA300HOU_RS00550 andUSA300HOU_RS01625 participate in the occurrence of Erava heteroresistance.…”

“…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]. All procedures involving human participants were performed in accordance with the ethical standards of Shenzhen University and the 1964…”

“…CHS759, CHS810, CHS820) and two reference strains (MRSA: N315 and MS4), were used to select Erava-resistant isolates in vitro as described previously [6]. Briefly, these isolates were subcultured serially in Mueller-Hinton broth containing gradual increasing Erava concentrations with the initial concentration being MIC followed by successive increases to 2×, 4×, 8×, 16×, 32 × MICs [21] Threshold cycle (Ct) numbers were determined by detection system software and analyzed with the 2 − 44 Ct method.…”

Omadacycline efficacy against Streptococcus agalactiae isolated in China: in vitro activity, resistance analysis, clonality of MIC distribution, and the correlation between resistance and virulence gene and biofilm formation

“…OMC is a new aminomethylcycline antibiotic rst-in-class against Gram-positive and negative aerobic, atypical pathogens and anaerobic [10] . OMC has shown excellent e cacy in the treatment of acute skin, soft tissue infections [11] and community-acquired pneumonia [12] .…”