ABSTRACT
Ceftolozane/tazobactam, a novel antimicrobial agent with activity against Pseudomonas aeruginosa (including drug-resistant strains) and other common Gram-negative pathogens (including most extended-spectrum-β-lactamase [ESBL]-producing Enterobacteriaceae strains), and comparator agents were susceptibility tested by a reference broth microdilution method against 7,071 Enterobacteriaceae and 1,971 P. aeruginosa isolates. Isolates were collected consecutively from patients in 32 medical centers across the United States during 2011 to 2012. Overall, 15.7% and 8.9% of P. aeruginosa isolates were classified as multidrug resistant (MDR) and extensively drug resistant (XDR), and 8.4% and 1.2% of Enterobacteriaceae were classified as MDR and XDR. No pandrug-resistant (PDR) Enterobacteriaceae isolates and only one PDR P. aeruginosa isolate were detected. Ceftolozane/tazobactam was the most potent (MIC50/90, 0.5/2 μg/ml) agent tested against P. aeruginosa and demonstrated good activity against 310 MDR strains (MIC50/90, 2/8 μg/ml) and 175 XDR strains (MIC50/90, 4/16 μg/ml). Ceftolozane/tazobactam exhibited high overall activity (MIC50/90, 0.25/1 μg/ml) against Enterobacteriaceae and retained activity (MIC50/90, 4/>32 μg/ml) against many 601 MDR strains but not against the 86 XDR strains (MIC50, >32 μg/ml). Ceftolozane/tazobactam was highly potent (MIC50/90, 0.25/0.5 μg/ml) against 2,691 Escherichia coli isolates and retained good activity against most ESBL-phenotype E. coli isolates (MIC50/90, 0.5/4 μg/ml), but activity was low against ESBL-phenotype Klebsiella pneumoniae isolates (MIC50/90, 32/>32 μg/ml), explained by the high rate (39.8%) of meropenem coresistance observed in this species phenotype. In summary, ceftolozane/tazobactam demonstrated high potency and broad-spectrum activity against many contemporary Enterobacteriaceae and P. aeruginosa isolates collected in U.S. medical centers. Importantly, ceftolozane/tazobactam retained potency against many MDR and XDR strains.
INTRODUCTION
Ceftolozane/tazobactam is a novel antibacterial agent with activity against Pseudomonas aeruginosa, including drug-resistant strains, and other common Gram-negative pathogens, including most extended-spectrum-β-lactamase (ESBL)-producing Enterobacteriaceae strains (1). Ceftolozane is a novel antibacterial agent with potent activity (compared with ceftazidime) against P. aeruginosa, including drug-resistant strains, and Enterobacteriaceae (with potency similar to that of other oxyimino-aminothiazolyl cephalosporins) (1–6). However, as with other cephalosporins, ceftolozane's activity is compromised in bacteria producing ESBLs, stably derepressed AmpC β-lactamases, and carbapenemases (1, 7). Tazobactam, a penicillanic acid-sulfone, is a well-established β-lactamase inhibitor that broadens the coverage of β-lactam agents (8). Unlike clavulanate and sulbactam, tazobactam is a moderate inhibitor of inducibly and constitutively expressed AmpC enzymes, although this activity is strain dependent and is less potent against strains with totally derepressed AmpC β-lactamases (9).
During the past decade, nosocomial infections caused by Enterobacteriaceae and P. aeruginosa in intensive care units worldwide have been increasing in prevalence along with increases in antimicrobial resistance and associated increases in morbidity and mortality (10, 11). Empirical and targeted therapies to cover infections with these organisms are increasingly limited. Ceftolozane/tazobactam exploits ceftolozane's potent activity against P. aeruginosa and Enterobacteriaceae and broadens ceftolozane's spectrum of activity against Enterobacteriaceae (1), hence making it an attractive option for clinical development for treatment of some infections caused by multidrug-resistant (MDR) Gram-negative bacteria. Ceftolozane/tazobactam is currently in phase III trials for the treatment of complicated urinary tract infections, complicated intra-abdominal infections, and nosocomial bacterial pneumonia. In the present study, we evaluated the potency of ceftolozane/tazobactam and comparator drugs tested for the first time against a large, contemporary (2011–2012) collection of clinically collected Enterobacteriaceae and P. aeruginosa isolates obtained from patients in U.S. hospitals.
MATERIALS AND METHODS
Sampling sites and organisms.A total of 7,071 Enterobacteriaceae and 1,971 P. aeruginosa isolates were consecutively collected over 2 years (January 2011 to December 2012) from 32 medical centers located across all nine U.S. census regions. All organisms were isolated from documented infections, and only one strain per patient infection episode was included in the surveillance collection. The isolates were derived primarily from bloodstream infections, skin and skin-structure infections (SSSI), and pneumonia in hospitalized patients, urinary tract infections in hospitalized patients, and intra-abdominal infections according to a common surveillance design.
Antimicrobial susceptibility testing.MIC values were determined using the reference Clinical and Laboratory Standards Institute (CLSI) broth microdilution method (M07-A9) (12). Quality control (QC) ranges and interpretive criteria for comparator compounds used the CLSI M100-S23 guidelines (13). The ESBL phenotype was defined as a MIC of ≥2 μg/ml for ceftazidime or ceftriaxone or aztreonam (13). To better evaluate the activities of ceftolozane/tazobactam against β-lactam-resistant Enterobacteriaceae and P. aeruginosa, strains were stratified by patterns of susceptibility to ceftazidime and meropenem. MDR, extensively drug-resistant (XDR), and pandrug-resistant (PDR) bacteria were classified as such per recently recommended guidelines (14) using the following antimicrobial class representative agents and CLSI interpretive criteria (13): for P. aeruginosa, ceftazidime (MIC of ≥16 μg/ml), meropenem (≥4 μg/ml), piperacillin-tazobactam (≥32/4 μg/ml), levofloxacin (≥4 μg/ml), gentamicin (≥8 μg/ml), and colistin (≥4 μg/ml); and for Enterobacteriaceae, ceftriaxone (≥2 μg/ml), meropenem (≥2 μg/ml), piperacillin-tazobactam (≥32/4 μg/ml), levofloxacin (≥4 μg/ml), gentamicin (≥8 μg/ml), tigecycline (≥4 μg/ml), and colistin (≥4 μg/ml). Classifications were based on the following recommended parameters: MDR = nonsusceptible to ≥1 agent in ≥3 antimicrobial classes; XDR = nonsusceptible to ≥1 agent in all but ≤2 antimicrobial classes; PDR = nonsusceptible to all antimicrobial classes (14).
RESULTS
Ceftolozane/tazobactam activity against Enterobacteriaceae.Ceftolozane/tazobactam demonstrated high overall activity (MIC50, 0.25 μg/ml; MIC90, 1 μg/ml) against 7,071 Enterobacteriaceae isolates collected in the United States during 2011 to 2012 (Table 1 and Table 2). Using MIC90 values, ceftolozane/tazobactam showed potency identical to that of cefepime, was 16-fold more active than ceftazidime and piperacillin-tazobactam (MIC90 for both, 16 μg/ml), was at least 16-fold more potent than ceftriaxone (MIC90, >8 μg/ml), and was second in potency against all tested compounds only to meropenem (MIC90, ≤0.06 μg/ml; Table 2). Against 601 (8.5%) MDR isolates, meropenem (MIC50/90, ≤0.06/>8 μg/ml; 77.0% susceptible), ceftolozane/tazobactam (MIC50/90, 4/>32 μg/ml), tigecycline (MIC50/90, 0.5/2 μg/ml; 92.3% susceptible), and colistin (MIC50/90, 0.5/>4 μg/ml) were the only agents tested to retain activity at the MIC50 level (Table 2). Ceftolozane/tazobactam was not active against most XDR strains (n = 86; 1.2%) (MIC50/90, >32/>32 μg/ml), with tigecycline being the most active agent (87.1% susceptible), followed by meropenem and gentamicin, with low susceptibility rates of only 22.1% and 20.9%, respectively (Table 2). No PDR Enterobacteriaceae isolates were collected in this study.
Cumulative MIC distributions of ceftolozane/tazobactam against Enterobacteriaceae by resistance phenotype
Antimicrobial activity of ceftolozane/tazobactam and various comparator agents against Enterobacteriaceae collected in the U.S. during 2011 to 2012
Ceftolozane/tazobactam was highly potent (MIC50/90, 0.25/0.5 μg/ml), inhibiting 99.0% of 2,691 Escherichia coli isolates at a MIC of ≤4 μg/ml and 100.0% of 2,364 non-ESBL-phenotype isolates at a MIC of ≤2 μg/ml (Table 1). Similarly, ceftolozane/tazobactam activity was high against non-ESBL-phenotype Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis (MIC90 for all three, 0.5 μg/ml; Table 1). Although ceftolozane/tazobactam was active against most ESBL-phenotype E. coli isolates (MIC50/90, 0.5/4 μg/ml), its potency was much lower against ESBL-phenotype K. pneumoniae (MIC50/90, 32/>32 μg/ml; Table 1). This observed lower activity for ceftolozane/tazobactam in ESBL-phenotype K. pneumoniae can be explained by the higher rate of meropenem resistance (i.e., carbapenemases) observed in this phenotype (39.8%) compared with ESBL-phenotype E. coli (1.5%; Table 2), supported by the higher activity (MIC90, 1 μg/ml) observed against meropenem-susceptible K. pneumoniae (Table 1).
Tested against Enterobacter spp., Citrobacter spp., and Serratia spp., ceftolozane/tazobactam exhibited 8-fold-greater activity (MIC50, 0.25 to 0.5 μg/ml) than piperacillin-tazobactam (MIC50, 2 to 4 μg/ml), activity similar to that of ceftriaxone (MIC50, 0.12 to 0.25 μg/ml) and ceftazidime (MIC50, 0.25 μg/ml for all three genera), and activity similar to or lower than that of cefepime (MIC50, ≤0.5 μg/ml; Table 2). Ceftolozane/tazobactam was also very active (MIC50/90, 0.25/1 μg/ml) against 368 indole-positive Proteus spp. (Table 1).
Ceftolozane/tazobactam activity against P. aeruginosa.Ceftolozane/tazobactam was the most potent (MIC50/90, 0.5/2 μg/ml) agent tested against 1,971 P. aeruginosa isolates, inhibiting 96.1% at a MIC of ≤4 μg/ml (Tables 3 and 4). Ceftolozane/tazobactam was at least 4-fold more active than ceftazidime (MIC50/90, 2/32 μg/ml), at least 8-fold more active than cefepime (MIC50/90, 4/16 μg/ml), at least 16-fold more active than piperacillin-tazobactam (MIC50/90, 8/>64 μg/ml), and slightly more potent than meropenem (MIC50/90, 0.5/8 μg/ml) when tested against the entire collection of P. aeruginosa isolates (Table 4). After colistin (MIC50/90, 1/2 μg/ml; 98.4% susceptible), ceftolozane/tazobactam was the most active (MIC50/90, 2/8 μg/ml) agent tested against 310 MDR P. aeruginosa isolates, with resistance for all other agents ranging from 36.5% for gentamicin to 70.6% for levofloxacin (Table 4). Similarly, against 175 XDR strains, ceftolozane/tazobactam retained activity (MIC50/90, 4/16 μg/ml), whereas resistance to other agents was high—ranging from 49.7% for gentamicin to 88.0% for levofloxacin (Table 4). Most XDR strains remained susceptible to colistin (97.7% susceptible), while in contrast, high levels of resistance to ceftazidime (73.7% resistant) and meropenem (76.0% resistant) were observed (Table 4). Only one PDR P. aeruginosa strain was detected, and ceftolozane/tazobactam demonstrated no observable activity (MIC, >32 μg/ml; Table 3) against this strain. Ceftolozane/tazobactam also had good activity against many ceftazidime-nonsusceptible (MIC50/90, 4/8 μg/ml), meropenem-nonsusceptible (MIC50/90, 1/8 μg/ml), piperacillin-tazobactam-nonsusceptible (MIC50/90, 2/8 μg/ml), cefepime-nonsusceptible (MIC50/90, 4/8 μg/ml), levofloxacin-nonsusceptible (MIC50/90, 1/8 μg/ml), and gentamicin-nonsusceptible (MIC50/90, 1/8 μg/ml) isolates (Table 3). Ceftolozane/tazobactam also had moderate activity against many isolates with combined ceftazidime and meropenem nonsusceptibility (MIC50/90, 4/32 μg/ml) and combined ceftazidime and meropenem and piperacillin-tazobactam nonsusceptibility (MIC50/90, 4/32 μg/ml; Table 3).
Cumulative MIC distributions of ceftolozane/tazobactam against P. aeruginosa by resistance phenotype
Antimicrobial activity of ceftolozane/tazobactam and various comparator agents against P. aeruginosa isolates collected in the United States during 2011 to 2012
DISCUSSION
Resistance mechanisms in Enterobacteriaceae and P. aeruginosa are extremely diverse, and there is currently no antimicrobial agent or combination that allows complete coverage of these important pathogens in the hospital setting. In in vitro studies to date, ceftolozane/tazobactam has demonstrated the greatest overall in vitro activity, compared with other agents tested, against this combined group of Gram-negative pathogens (1, 7, 15). The data from this large multicenter U.S. surveillance study confirm the data presented in earlier studies and demonstrate that ceftolozane/tazobactam had high in vitro potency and a broad spectrum of activity against many nosocomial isolates of Enterobacteriaceae and P. aeruginosa circulating in the United States during 2011 and 2012. In addition, this larger set of contemporary data supports the previously reported activity against a collection of ceftazidime- and/or carbapenem-resistant Enterobacteriaceae and P. aeruginosa isolates (1).
For this investigation, as described in Materials and Methods, we classified MDR, XDR, and PDR for both Enterobacteriaceae and P. aeruginosa according to guidelines recently published by an international expert panel (14). To achieve this, we tested representative antimicrobials from different classes in our laboratory to determine nonsusceptibility within each class. In addition, we used current (2013) CLSI MIC interpretive criteria to determine nonsusceptibility (13). It should be noted that current (2013) European Committee on Antimicrobial Susceptibility Testing (EUCAST) interpretive criteria (16) differ from the CLSI interpretive criteria for many of the organism/antimicrobial combinations (for example, for Enterobacteriaceae, nonsusceptibility to meropenem is ≥2 μg/ml by CLSI and ≥4 μg/ml by EUCAST). With these caveats, these data show that, although the level was reduced, ceftolozane/tazobactam retained good activity against MDR and XDR strains of P. aeruginosa and MDR strains of Enterobacteriaceae—but low activity against most strains of XDR Enterobacteriaceae due to the high prevalence of carbapenemase-producing K. pneumoniae in the XDR population (Table 2). This is in contrast to other agents (except colistin) that demonstrated reduced susceptibility (MDR/XDR)—22.6/9.1% ceftazidime-susceptible and 19.4/7.4% meropenem-susceptible P. aeruginosa (Table 3) isolates and 22.0/2.3% ceftazidime-susceptible and 77.0/22.1% meropenem-susceptible Enterobacteriaceae isolates (Table 1). Overall, in this U.S. surveillance study performed from 2011 through 2012, 15.7% of P. aeruginosa isolates were classified as MDR and 8.9% were classified as XDR (Table 3), and 8.4% of Enterobacteriaceae isolates were classified as MDR and only 1.2% as XDR (Table 1). Only one strain was classified as PDR. In this study, ceftolozane/tazobactam activity was most compromised against the XDR Enterobacteriaceae (only 1.2% of Enterobacteriaceae isolates).
In summary, these data for ceftolozane/tazobactam that have been collected over 2 years from 32 medical centers located across all nine U.S. census regions demonstrate high potency and broad-spectrum activity of this antibacterial agent tested against contemporary Enterobacteriaceae and P. aeruginosa strains. Importantly, ceftolozane/tazobactam retained clear activity against many MDR and XDR strains. The in vitro surveillance data presented here, coupled with favorable results published from pharmacokinetic, safety, animal infection, and in vitro studies (15, 17–20), suggest the potential usefulness of ceftolozane/tazobactam for the treatment of some infections caused by MDR Gram-negative organisms and warrant further clinical development.
ACKNOWLEDGMENTS
We express our appreciation to S. Benning, M. Stilwell, and M. Janecheck in the preparation of the manuscript and to the JMI staff members for scientific assistance in performing this study.
This study was funded by research grants from Cubist Pharmaceuticals (Lexington, MA). Cubist Pharmaceuticals was involved in the study design and decision to present these results. Cubist Pharmaceuticals had no involvement in the collection, analysis, or interpretation of data. JMI Laboratories, Inc., has received research and educational grants in 2009 to 2011 from Achaogen, Aires, American Proficiency Institute (API), Anacor, Astellas, AstraZeneca, Bayer, bioMérieux, Cempra, Cerexa, Contrafect, Cubist Pharmaceuticals, Daiichi, Dipexium, Enanta, Furiex, GlaxoSmithKline, Johnson & Johnson, LegoChem Biosciences Inc., Meiji Seika Kaisha, Merck, Nabriva, Novartis, Paratek, Pfizer, PPD Therapeutics, Premier Research Group, Rempex, Rib-X Pharmaceuticals, Seachaid, Shionogi, The Medicines Co., Theravance, ThermoFisher, TREK Diagnostics, and some other corporations. Some JMI employees are advisors/consultants for Astellas, Cubist, Pfizer, Cempra, Cerexa-Forest, J&J, and Theravance. In regard to speaker bureaus and stock options, we declare that we have no conflicts of interest.
FOOTNOTES
- Received 20 August 2013.
- Returned for modification 22 September 2013.
- Accepted 1 October 2013.
- Accepted manuscript posted online 7 October 2013.
- Copyright © 2013, American Society for Microbiology. All Rights Reserved.
