ABSTRACT
Eravacycline is a novel, fully synthetic fluorocycline antibiotic developed for the treatment of serious infections, including those caused by multidrug-resistant (MDR) pathogens. Here, we evaluated the in vitro activities of eravacycline and comparator antimicrobial agents against a global collection of frequently encountered clinical isolates of Gram-negative bacilli. The CLSI broth microdilution method was used to determine MIC data for isolates of Enterobacterales (n = 13,983), Acinetobacter baumannii (n = 2,097), Pseudomonas aeruginosa (n = 1,647), and Stenotrophomonas maltophilia (n = 1,210) isolated primarily from respiratory, intra-abdominal, and urinary specimens by clinical laboratories in 36 countries from 2013 to 2017. Susceptibilities were interpreted using both CLSI and EUCAST breakpoints. Multidrug-resistant (MDR) isolates were defined by resistance to agents from ≥3 different antimicrobial classes. The MIC90s ranged from 0.25 to 1 μg/ml for Enterobacteriaceae and were 1 μg/ml for A. baumannii and 2 μg/ml for S. maltophilia, Proteus mirabilis, and Serratia marcescens. Eravacycline’s potency was up to 4-fold greater than that of tigecycline against genera/species of Enterobacterales, A. baumannii, and S. maltophilia. The MIC90s for five of six individual genera/species of Enterobacterales and A. baumannii were within 2-fold of the MIC90s for their respective subsets of MDR isolates, while the MDR subpopulation of Klebsiella spp. demonstrated 4-fold higher MIC90s. Eravacycline demonstrated potent in vitro activity against the majority of clinical isolates of Gram-negative bacilli, including MDR isolates, collected over a 5-year period. This study further underscores the potential benefit of eravacycline in the treatment of infections caused by MDR Gram-negative pathogens.
INTRODUCTION
Gram-negative pathogens causing serious infections are becoming an increasing clinical concern (1–5). Important antimicrobial-resistant Gram-negative pathogens include extended-spectrum-β-lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae; carbapenemase-producing, fluoroquinolone-resistant, and multidrug-resistant (MDR) Enterobacterales; as well as carbapenem-resistant and MDR Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia (1–5). In fact, many of these pathogens have recently been highlighted among Gram-negative MDR pathogens classified as urgent/critical or serious/high public health threats by the Centers for Disease Control and Prevention (CDC) (1) and the World Health Organization (WHO) (6).
Eravacycline is a novel, fully synthetic fluorocycline antibiotic developed for the treatment of serious infections, including those caused by MDR pathogens (5, 7; https://clinicaltrials.gov/ct2/show/NCT01844856). Eravacycline is comprised of a tetracycline core with two novel modifications, a fluorine atom at the C-7 position and a pyrrolidinoacetamido group at the C-9 position, both of which are on the D ring (7, 9). These novel modifications confer enhanced in vitro activity compared to that of other tetracyclines against resistant Gram-negative and Gram-positive bacteria, and the pyrrolidinoacetamido group allows for increased ribosomal binding and steric hindrance to avoid ribosome protection-based tetracycline resistance.
Eravacycline inhibits bacterial protein synthesis (i.e., acyl-tRNA transfer) by binding to the 30S ribosomal subunit (10). Eravacycline demonstrates potent broad-spectrum activity against Gram-negative bacilli (except for P. aeruginosa and Burkholderia spp.) and Gram-positive cocci, including anaerobes, as well as atypical bacterial pathogens and Neisseria gonorrhoeae (5, 11–16), and does not exhibit a loss of antibacterial activity against isolates expressing tetracycline ribosomal protection genes or most tetracycline efflux resistance genes (10, 11, 14).
Eravacycline has successfully completed clinical trials for the treatment of complicated intra-abdominal infection (cIAI) (https://clinicaltrials.gov/ct2/show/NCT01844856) and has been approved for use by both the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA). Additionally, eravacycline has demonstrated in vivo efficacy as a treatment in murine models of systemic, thigh, and lung infection and pyelonephritis.
The objective of the current study was to determine the in vitro activity of eravacycline relative to that of other antimicrobial agents using a representative global collection of clinical isolates of Gram-negative bacilli.
RESULTS AND DISCUSSION
A total of 17,781 Gram-negative aerobic isolates collected between 2013 and 2017 were included in this study. Enterobacteriaceae accounted for the majority of these isolates (n = 10,531). The MIC distributions for these isolates and the cumulative percentage of isolates inhibited by eravacycline are shown in Table 1. The MIC90 for isolates of A. baumannii was 1 μg/ml, and it was 0.5 μg/ml for the four genera/species of Enterobacteriaceae combined and 2 μg/ml for S. maltophilia. Among the six genera/species of Enterobacterales tested, MIC90 values were as follows: E. coli, 0.25 μg/ml; Klebsiella spp. and Citrobacter spp., 0.5 μg/ml; Enterobacter spp., 1 μg/ml; and Proteus mirabilis and Serratia marcescens, 2 μg/ml. For MDR populations of these organisms, the MIC90 values of eravacycline remained within 2- to 4-fold of the MIC90s indicated above. Given eravacycline’s limited activity against P. aeruginosa (Table 1), concordant with this pathogen’s established intrinsic resistance to tetracyclines, it was excluded from further analyses (17).
Cumulative percentage of all clinical isolates of Enterobacteriaceae, individual genera/species of Enterobacterales, A. baumannii, P. aeruginosa, and S. maltophilia tested from 2013 to 2017 inhibited by eravacycline, by MIC
When isolates were allocated to their respective geographic regions, eravacycline MIC50s and MIC90s were within 1 doubling dilution for all Enterobacteriaceae combined, individual genera/species of Enterobacterales, A. baumannii, and S. maltophilia (see Table S1 in the supplemental material). Similarly, there were no significant differences (a >1-doubling-dilution increase or decrease in the MIC50s or MIC90s) observed in the in vitro activity of eravacycline for any genera/species of Gram-negative bacilli stratified by specimen source (Table S2) or stratified by study period (2013 to 2014, 2015, 2016, 2017) (Table S3). A detailed trend analysis could not be conducted, given that there were changes in participating laboratories and the panel of antimicrobial agents tested over the time period studied (2013 to 2017).
The in vitro activities of eravacycline and comparator agents against Enterobacterales, A. baumannii, and S. maltophilia isolates and their MDR counterparts are shown in Tables 2 and 3, respectively. The rates of susceptibility of Enterobacteriaceae spp. to eravacycline were high, with the susceptibility rates being 98.8% for E. coli, 90.6% for Klebsiella spp., 94.6% for Citrobacter spp., and 89.6% for Enterobacter spp. (Table 2) (18). For MDR organisms, the rates of susceptibility to eravacycline for E. coli remained high (97.5%) and ranged from 77 to 81.9% for the other Enterobacteriaceae (Table 3). Breakpoint interpretations were not available for eravacycline against the other organisms tested.
In vitro activity of eravacycline and comparator agents against Enterobacteriaceae, individual genera/species of Enterobacterales, A. baumannii, and S. maltophilia, cumulative 2013 to 2017 data
In vitro activity of eravacycline and comparator agents against MDR Enterobacteriaceae, individual genera/species of Enterobacterales, and A. baumannii, cumulative 2013 to 2017 data
With regard to the comparator agents tested, the rate of susceptibility among the Enterobacteriaceae by the use of CLSI criteria was the highest for amikacin (99.1%), tigecycline (96.8%), the carbapenems meropenem (97.9%) and ertapenem (94.2%), and gentamicin (91.2%) (Table 2). Similar susceptibility was observed using EUCAST guidelines, with exceptions existing, such as for minocycline and tetracycline, for which no EUCAST breakpoints are given, and for colistin (99.4% susceptible by the use of EUCAST breakpoints), for which CLSI breakpoints are not given. Also, by use of the EUCAST criteria, tigecycline susceptibility was reduced to 70.6%, whereas eravacycline susceptibility remained at 92.6%. Other Enterobacterales, P. mirabilis, and S. marcescens were distinct, with reduced susceptibility to the tetracycline class, especially when susceptibility was evaluated using EUCAST breakpoints (Table 2). Among the Enterobacteriaceae, 19.5% (n = 2,051) were defined as being MDR isolates using CLSI breakpoints and 20.8% (n = 2,186) were defined as being MDR isolates using EUCAST breakpoints. The rates of susceptibility to all other comparators except amikacin, colistin (EUCAST breakpoints only), ertapenem, gentamicin (EUCAST breakpoints only), imipenem, meropenem, and tigecycline (CLSI breakpoints only) were less than 60% for the MDR isolate population. These susceptibilities are similar to those seen in other global surveillance studies (19, 20).
In addition to the Enterobacterales, a large collection of Gram-negative nonfermenters was tested, including A. baumannii (n = 2,097) and S. maltophilia (n = 1,210). For A. baumannii, high rates of resistance to the majority of the comparators were seen, with the levels of susceptibility to colistin (95.1%) and minocycline (67.3%) being the highest. Among the few agents with a breakpoint for S. maltophilia, the rate of susceptibility to minocycline was the highest at 99.0%. Approximately 24% and 15.7% of the isolates were resistant to levofloxacin and trimethoprim-sulfamethoxazole, respectively, similar to the findings of a surveillance study looking at isolates from 1998 to 2008 in Taiwan (21).
In this surveillance study, eravacycline demonstrated improved potency, based on MIC90 values, over tigecycline, showing a 4-fold greater potency than tigecycline against populations of A. baumannii, Klebsiella spp., and P. mirabilis and a 2-fold greater potency against E. coli, Enterobacter spp., Citrobacter spp., and S. maltophilia. Eravacycline and tigecycline showed equivalent potency against S. marcescens. Previous in vitro studies comparing eravacycline and tigecycline have reported similar 2- to 4-fold improvements in the MIC90 values of eravacycline over those of tigecycline (7, 12, 13, 16, 22–26). The tigecycline MIC90s for Enterobacterales spp., A. baumannii, and S. maltophilia determined in this study were equivalent to the MIC90s of tigecycline determined in other global surveillance studies (27, 28).
In addition to greater potency, eravacycline presents additional potential advantages over tigecycline: higher concentrations in serum and tissue (especially in the lung) and improved tolerability (7, 29–31). Previous studies have demonstrated that the in vitro activity of eravacycline is not affected by the presence of many of the resistance mechanisms likely present in the current surveillance population. These include studies which looked at the in vitro activity of eravacycline against ESBL-producing isolates of E. coli and K. pneumoniae; fluoroquinolone-susceptible and fluoroquinolone-resistant isolates of E. coli (including those of the MDR sequence type 131 genotype); polymyxin-resistant (mcr-1-positive) Enterobacteriaceae; carbapenem-resistant Enterobacteriaceae, including KPC-, SME-, VIM-, IMP-, NDM-, and OXA-48-producing isolates; and MDR Enterobacteriaceae and A. baumannii (12, 13, 16, 22–24, 26).
Eravacycline is currently approved for use by both EMA and FDA for the treatment of complicated intra-abdominal infections. As previously described, eravacycline maintains an overall potency advantage over tigecycline across approved organisms. The adoption of restrictive breakpoint criteria for tigecycline and eravacycline in the EUCAST 2019 guidelines, in contrast to the broad, albeit decade-old, tigecycline breakpoints granted by the FDA, makes comparisons of susceptibility between the two agents difficult. While the FDA breakpoints for both agents are granted for Enterobacteriaceae, the clinical efficacy of eravacycline against E. coli, Enterobacter cloacae, Citrobacter freundii, and species of Klebsiella is noted. Current eravacycline breakpoints from EUCAST were published concurrently with a reduction in both the tigecycline breakpoint and the approved organism list. The disconnect between approved interpretative criteria and organism coverage for tigecycline and other agents across these regulatory agencies highlights the need for greater efforts toward the harmonization of breakpoints.
Treatment of complicated intra-abdominal infection (cIAI) involves a combination of surgery and empirical antimicrobial therapy. Antimicrobial therapy must be sufficient to encompass a wide range of pathogens, including Gram-positive and Gram-negative aerobic and anaerobic bacteria (32–34). In cIAI patients, the most commonly encountered Gram-negative pathogens include E. coli, Klebsiella spp., and Enterobacter spp. (35). A. baumannii is less common in cIAI infections but has been noted to be an increasing cause of postoperative infections in hospital settings (36–38).
Eravacycline demonstrated potent in vitro activity against the clinically important Gram-negative organisms associated with cIAIs in humans. For all organisms, including A. baumannii and S. maltophilia, the MIC90s of eravacycline were 2- to 4-fold lower than those of tigecycline. This global surveillance investigation highlights the broad-spectrum potency of eravacycline against Gram-negative bacteria, including MDR strains, and further underscores its potential benefit for the treatment of cIAIs and other polymicrobial infections caused by resistant pathogens.
MATERIALS AND METHODS
Bacterial isolates.From 2013 through 2017, clinical isolates of Enterobacterales (n = 13,983), A. baumannii (n = 2,097), P. aeruginosa (n = 1,647), and S. maltophilia (n = 1,210) were collected by laboratories in 36 countries (in the Asia-Pacific region, Australia, Hong Kong, Japan, South Korea, Malaysia, New Zealand, Philippines, Singapore, Taiwan, Thailand, and Vietnam; in Europe, Austria, Belgium, Croatia, Czech Republic, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Netherlands, Poland, Portugal, Romania, Russia, Serbia, Spain, Sweden, Switzerland, Turkey, and the United Kingdom; and in North America [the United States]). In the Asia-Pacific region, isolates were collected only in 2015 through 2017, and some other countries also did not participate in all years.
Table S1 in the supplemental material summarizes the numbers of isolates of Enterobacteriaceae, A. baumannii, and S. maltophilia collected by geographic region. For the Enterobacteriaceae and A. baumannii, approximately 40 to 45% of the isolates came from North America and Europe and 15% came from the Asia-Pacific region. For S. maltophilia, approximately 50% of the isolates came from Europe, 30% came from North America, and 20% came from the Asia-Pacific region. In total, there were 6,559, 5,667, 5,305, and 1,406 isolates, respectively, from respiratory, intra-abdominal, urinary, and other specimen sources.
The identity of each isolate was confirmed using matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry (Bruker Biotyper; Bruker Daltonics, Bremen, Germany). Isolates were limited to one per patient, determined by the participating laboratory algorithms to be clinically significant, and collected irrespective of their antimicrobial susceptibility profile and independently of patient gender or age. The study was not designed to directly compare the prevalence of antimicrobial-resistant pathogens across specific geographic locations but, rather, was designed to evaluate the in vitro activities of eravacycline and comparator antimicrobial agents against a global collection of frequently encountered clinical isolates of Gram-negative bacilli collected from 2013 to 2017.
Antimicrobial susceptibility testing.The in vitro susceptibilities of isolates were determined using the CLSI-defined broth microdilution method in 96-well broth microdilution panels (17, 39). The antimicrobial agents used in panel production were acquired as laboratory-grade powders from their respective manufacturers or from a commercial source. The list of antimicrobial agents tested in each of the four study periods varied slightly, in that some agents, in addition to those tested in the 2013 to 2014 period, were included in the 2015 to 2017 testing periods. Ten antimicrobial agents (aztreonam, cefepime, ceftazidime, ceftriaxone, eravacycline, gentamicin, levofloxacin, piperacillin-tazobactam, tetracycline, and tigecycline) were tested against all isolates in each study period from 2013 to 2017. Of note, imipenem was tested in 2013 and 2014, while ertapenem and meropenem were tested in 2015 to 2017; colistin was tested against Enterobacteriaceae only in 2013 and 2014; amoxicillin-clavulanate was tested only in 2015; ampicillin-sulbactam was tested only in 2015 and 2016; and cefotaxime, minocycline, and trimethoprim-sulfamethoxazole were tested only in 2015 to 2017. The eravacycline MICs for Gram-negative bacilli were read following the current CLSI standard for dilution method testing; MIC endpoints were read following panel incubation at 35°C in ambient air for 16 to 20 h (Enterobacteriaceae, P. aeruginosa) or 20 to 24 h (A. baumannii, S. maltophilia) (17). Quality control testing for eravacycline and other antimicrobial agents was performed on each day of testing as specified by the CLSI (39) using the CLSI-defined control strains E. coli ATCC 25922 and P. aeruginosa ATCC 27853.
MICs were interpreted using 2019 CLSI MIC breakpoints (17) and 2019 EUCAST MIC breakpoints (18), with the following exceptions: FDA MIC interpretative breakpoints for eravacycline and tigecycline (29) were used in place of CLSI MIC breakpoints, which are not currently published for these agents. Additionally, tigecycline breakpoints were lowered with the 2019 EUCAST MIC guidelines, while simultaneously, the label was restricted to E. coli and Citrobacter koseri from the Enterobacteriaceae; in order to perform a more accurate and complete comparison between eravacycline and tigecycline susceptibilities, the current breakpoints for both eravacycline and tigecycline were applied to susceptibility percentages for all Enterobacteriaceae species.
An MDR phenotype was defined as resistance to one or more agents from three or more antimicrobial agent classes recommended for testing for a specific pathogen or pathogen family (Enterobacteriaceae) and possessing MIC interpretative breakpoints published by CLSI (17) or EUCAST (18). Eravacycline and tigecycline were excluded from the list of agents used for the MDR determination. Because the list of antimicrobial agents tested in each study year varied slightly, the identified MDR populations also varied slightly in each study year. Identification of MDR isolates of S. maltophilia was excluded from the analysis because of the very limited number of antimicrobial agents with either CLSI (17) or EUCAST (18) MIC breakpoints for that species. Resistance to levofloxacin and trimethoprim-sulfamethoxazole was captured for this organism, as these represent the current treatment of choice and a proposed alternative, respectively (40).
ACKNOWLEDGMENTS
We thank all laboratories participating in this eravacycline global surveillance study for their contributions, as well as Sophie Magnet for her coordination of the laboratory work.
Funding for this research was provided by Tetraphase Pharmaceuticals, Inc., Watertown, MA, USA, which also included compensation fees for services in relation to preparing the manuscript.
C.F. and M.O. are employees of Tetraphase Pharmaceuticals. I.M. and S.H. and are employees of IHMA Europe Sàrl. S.H.L. works for IHMA, Inc. Both IHMA laboratories have received research funding from Tetraphase Pharmaceuticals, Inc. J.A.K. is a consultant to IHMA, Inc. The authors employed by IHMA and J.A.K. do not have personal financial interests in the sponsor of this paper (Tetraphase Pharmaceuticals, Inc.). M.B. has participated in advisory boards and/or received speaker honoraria from Achaogen, Angelini, Astellas, AstraZeneca, Bayer, Basilea, Cidara, Gilead, Menarini, MSD, Nabriva, Paratek, Pfizer, The Medicines Company, Tetraphase, and Vifor. G.R.C. has received consulting fees from Cempra Pharmaceuticals, PRA International, Furiex Pharmaceuticals, Inimex Pharmaceuticals, Dr. Reddy’s Laboratories, Cerexa/Forest Laboratories, AstraZeneca, GlaxoSmithKline, Merck, ContraFect, Theravance, and Astellas; has received research grants from Theravance, Innocoll, and The Medicines Company; and has served on the advisory boards of Pfizer, Polymedix, Tetraphase Pharmaceuticals, Seachaid Pharmaceuticals, BioCryst Pharmaceuticals, Durata, Achaogen, ContraFect, and Nabriva.
FOOTNOTES
- Received 22 August 2019.
- Returned for modification 8 October 2019.
- Accepted 9 December 2019.
- Accepted manuscript posted online 16 December 2019.
Supplemental material is available online only.
- Copyright © 2020 Morrissey et al.
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.
