Comparative In Vitro Activities of Ceftaroline and Tedizolid against Clinical Strains of Staphylococcus aureus and Enterococcus: Results from the China Antimicrobial Surveillance Network (CHINET) in 2018

The in vitro activities of ceftaroline and tedizolid were compared against Staphylococcus aureus, Enterococcus faecalis, and Enterococcus faecium clinical isolates collected from the China Antimicrobial Surveillance Network. Ceftaroline demonstrated potent activity against S. aureus isolates (MIC50/90, ≤0.25/1 mg/liter). Tedizolid was also highly active against S. aureus (MIC50/90, 0.25/0.5 mg/liter) and Enterococcus (MIC50/90, 0.5/0.5 mg/liter) isolates. Our results support the clinical usefulness of ceftaroline and tedizolid in treating Gram-positive infections.

Impact of Daptomycin Dose Exposure Alone or in Combination with β-Lactams or Rifampin against Vancomycin-Resistant Enterococci in an In Vitro Biofilm Model

Enterococcus faecium strains are commonly resistant to vancomycin and β-lactams. In addition, E. faecium often causes biofilm-associated infections and these infections are difficult to treat. In this context, we investigated the activity of dosing regimens using daptomycin (DAP) (8, 10, 12, and 14 mg/kg of body weight/day) alone and in combination with ceftaroline (CPT), ampicillin (AMP), ertapenem (ERT), and rifampin (RIF) against 2 clinical strains of biofilm-producing vancomycin-resistant Enterococcus faecium (VREfm), namely, strains S447 and HOU503, in an in vitro biofilm model. HOU503 harbors common LiaS and LiaR substitutions, whereas S447 lacks mutations associated with the LiaFSR pathway. MIC results demonstrated that both strains were susceptible to DAP and resistant to CPT, AMP, ERT, and RIF. The 168-h pharmacokinetic/pharmacodynamic (PK/PD) CDC biofilm reactor models (simulating human antibiotic exposures) were used with titanium and polyurethane coupons to evaluate the efficacy of antibiotic combinations. DAP 12 and 14 achieved bactericidal activity against S447 but lacked such effect against HOU503. Addition of ERT and RIF enhanced DAP activity, allowing DAP 8 and 10 plus ERT or RIF to produce bactericidal activity against both strains at 168 h. While DAP 8 and 10 plus CPT improved killing, they did not reach bactericidal reduction against S447. Combination of AMP, CPT, ERT, or RIF resulted in enhanced and bactericidal activity for DAP against HOU503 at 168 h. Our data provide further support for the use of combinations of DAP with AMP, ERT, CPT, and RIF in infections caused by biofilm producing VREfm. Further research involving DAP combinations against biofilm-producing enterococci is warranted.

Chemical Synergy between Ionophore PBT2 and Zinc Reverses Antibiotic Resistance

The World Health Organization reports that antibiotic-resistant pathogens represent an imminent global health disaster for the 21st century. Gram-positive superbugs threaten to breach last-line antibiotic treatment, and the pharmaceutical industry antibiotic development pipeline is waning. Here we report the synergy between ionophore-induced physiological stress in Gram-positive bacteria and antibiotic treatment. PBT2 is a safe-for-human-use zinc ionophore that has progressed to phase 2 clinical trials for Alzheimer's and Huntington's disease treatment. In combination with zinc, PBT2 exhibits antibacterial activity and disrupts cellular homeostasis in erythromycin-resistant group A Streptococcus (GAS), methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococcus (VRE). We were unable to select for mutants resistant to PBT2-zinc treatment. While ineffective alone against resistant bacteria, several clinically relevant antibiotics act synergistically with PBT2-zinc to enhance killing of these Gram-positive pathogens. These data represent a new paradigm whereby disruption of bacterial metal homeostasis reverses antibiotic-resistant phenotypes in a number of priority human bacterial pathogens.IMPORTANCE The rise of bacterial antibiotic resistance coupled with a reduction in new antibiotic development has placed significant burdens on global health care. Resistant bacterial pathogens such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus are leading causes of community- and hospital-acquired infection and present a significant clinical challenge. These pathogens have acquired resistance to broad classes of antimicrobials. Furthermore, Streptococcus pyogenes, a significant disease agent among Indigenous Australians, has now acquired resistance to several antibiotic classes. With a rise in antibiotic resistance and reduction in new antibiotic discovery, it is imperative to investigate alternative therapeutic regimens that complement the use of current antibiotic treatment strategies. As stated by the WHO Director-General, "On current trends, common diseases may become untreatable. Doctors facing patients will have to say, Sorry, there is nothing I can do for you."