Abstract
Objective:
To assess in vitro ceftolozane/tazobactam (C/T) and ceftazidime/avibactam (CZA) activity in beta-lactam-resistant Enterobacteriaceae and Pseudomonas aeruginosa clinical isolates from major carbapenem-using Departments at Montpellier University Hospital, France.
Materials and Methods:
We tested third-generation cephalosporin-resistant Enterobacteriaceae (by production of extended spectrum β-lactamase or other mechanisms, mainly AmpC beta-lactamases) and ceftazidime- and/or carbapenem-resistant P. aeruginosa strains isolated from clinical samples of patients hospitalized from January 2017 to May 2017 and August 2016 to July 2017, respectively. We also included all OXA-48 beta-lactamase-producing Enterobacteriaceae strains isolated in the whole hospital from October 2015 to May 2017. We used the 2017 European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines for minimal inhibitory concentration interpretation.
Results:
Among the 62 cephalosporin-resistant Enterobacteriaceae strains, 60 (97%) were susceptible to CZA and 34 (65%) to C/T. The two CZA-resistant Klebsiella pneumoniae isolates produced (i) NDM-carbapenemase and extended-spectrum beta-lactamase (ESBL) and (ii) ESBL CTXM-15 and OXA-1 associated with impermeability. Moreover, 31 of the 42 P. aeruginosa strains (74%) were susceptible to CZA and 37 (88%) to C/T. Finally, 26/27 (96%) of OXA-48 beta-lactamase-producing Enterobacteriaceae were susceptible to CZA and 8/27 (30%) to C/T.
Conclusions:
At our hospital, CZA and C/T offer a carbapenem-sparing alternative for resistant gram-negative pathogens and could be a salvage therapy for carbapenem-resistant pathogens.
Introduction
The ceftolozane/tazobactam (C/T) combination is a novel antibiotic with potent bactericidal activity against multidrug-resistant (MDR) strains of Pseudomonas aeruginosa. 1 A real-life study reported that C/T is an effective option to treat extensively drug-resistant P. aeruginosa, with clinical cure in 10 (67%) of 15 patients. 2 When tested in isolates causing urinary tract and intra-abdominal infections (effective against 93.5% of isolates according to the Clinical and Laboratory Standards Institute breakpoints), C/T was the second most active compound after meropenem (MER) against Enterobacteriaceae and was the most potent of the tested beta-lactam agents against P. aeruginosa (inhibition of 91.7% of isolates at a minimum inhibitory concentration (MIC) of 4 mg/L) 3 .
Avibactam is a potent inhibitor of class A, class C, and some class D enzymes. It restores ceftazidime (CAZ) activity against most CAZ-nonsusceptible Enterobacteriaceae, including extended-spectrum beta-lactamase (ESBL) producers, CTX-M producers, and KPC producers. 4 The ceftazidime/avibactam (CZA) combination shows promising results as salvage therapy for infections caused by carbapenem-resistant organisms. 5
The aim of this study was to examine the activities of C/T and CZA against β-lactam-resistant Enterobacteriaceae and P. aeruginosa clinical isolates from major carbapenem-using departments at Montpellier University Hospital, France, to determine the strategy of their use in our center.
Materials and Methods
Patients and bacterial strains
The study included bacterial strains from relevant clinical samples of patients hospitalized in major carbapenem-using departments (intensive care unit, hematology, gastroenterology, and abdominal surgery) at Montpellier University Hospital. When more than one sample was available for the same patient, the most clinically relevant one (e.g., blood culture and surgical sample) was selected. Strains were isolated from samples of various origins, but mostly urines, intra-abdominal samples, bronchoalveolar specimens, blood, and wounds.
The bacterial strains included in this study were as follows: (i) Enterobacteriaceae resistant to third-generation cephalosporins (ceftriaxone and/or cefotaxime) by producing ESBLs or by other mechanisms (mainly not only by plasmid-mediated AmpC or overproduction of AmpC cephalosporinase but also overexpression of SHV-1, production of oxacillinase, and so on) isolated from January 2017 to May 2017, and (ii) P. aeruginosa resistant to CAZ or carbapenems (intermediate sensitivity or resistant to imipenem or MER) collected from August 2016 to July 2017. Resistance mechanisms were identified phenotypically (to determine the ESBL production) and by multiplex PCR assay and DNA sequencing targeting the most prevalent ESBL- and carbapenemase-encoding genes.6,7
In addition, all OXA-48 beta-lactamase-producing Enterobacteriaceae isolated from October 2015 to May 2017 in the whole hospital (from infections and screening samples) were also analyzed.
In vitro susceptibility test methods
Strains were grown on nonselective agar medium overnight, and then a colony was resuspended in 0.7 mL of sterile 0.9% NaCl. Turbidity was adjusted to 0.5 McFarland with a McFarland densitometer. Mueller–Hinton agar was inoculated and E-test strips were used to determine the MICs for C/T and CZA after an overnight incubation at 35°C in ambient air.
As clinical samples were used, their susceptibility to other antibiotics was routinely determined using disk diffusion antimicrobial tests and, when needed according to the guidelines, using E-test strips for MIC determination. Breakpoints for interpretation of MICs and zone diameters were determined following the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines published in 2017. 8 For Enterobacteriaceae, susceptibility breakpoints were ≤8 mg/L for CZA and ≤1 mg/L for C/T. For P. aeruginosa, they were ≤8 mg/L for CZA and ≤4 mg/L for C/T.
Results
Among the 1,214 Enterobacteriaceae strains isolated from relevant clinical samples between January and May 2017, 62 strains (5%) were resistant to third-generation cephalosporins (Table 1 summarizes the species and resistance mechanisms of these strains). Among these 62 strains, 60 (97%) were susceptible to CZA and 34 (65%) to C/T (Table 2). The two CZA-resistant strains were identified as Klebsiella pneumoniae. One produced NDM-carbapenemase and ESBL, and the other one produced ESBL CTXM-15 and OXA-1 associated with outer membrane impermeability. Other antibiotic susceptibilities are shown in Table 2.
Description of the Third-Generation Cephalosporin-Resistant Enterobacteriaceae Strains Isolated from Relevant Clinical Samples
ESBL, extended-spectrum beta-lactamase.
In Vitro Activities of Ceftazidime/Avibactam and Ceftolozane/Tazobactam and Susceptibility Profile to Other Antibacterial Agents in the 62 Enterobacteriaceae Isolates Resistant to Third-Generation Cephalosporins
CAZ, ceftazidime; CZA, ceftazidime/avibactam; IMI, imipenem; MIC, minimal inhibitory concentration.
Among the 392 P. aeruginosa strains isolated from relevant clinical samples between August 2016 and July 2017, 42 strains (11%) were resistant to CAZ or carbapenems. Among these 42 strains, 31 (74%) were susceptible to CZA and 37 (88%) to C/T (Table 3). The susceptibility rates to CZA and C/T were 54% (18/28) and 82% (23/28) for the CAZ-resistant strains, 69% (20/29) and 86% (25/29) for the carbapenem-resistant strains, and 47% (7/15) and 73% (11/15) for the CAZ and carbapenem-resistant strains, respectively. Other antibiotic susceptibilities are shown in Table 3.
In Vitro Activities of Ceftazidime/Avibactam and Ceftolozane/Tazobactam and Susceptibility Profile to Other Antibacterial Agents for the 42 Ceftazidime-Resistant and/or Carbapenem-Resistant Pseudomonas aeruginosa Isolates
MER, meropenem; -R, resistant.
Analysis of the 27 OXA-48 beta-lactamase-producing Enterobacteriaceae strains isolated in the whole hospital from October 2015 to May 2017 showed that 26 (96%) were susceptible to CZA and 8 (30%) to C/T. Moreover, 11/27 strains produced ESBL. The only strain resistant to CZA was an ESBL-producing E. coli isolate. Other antibiotic susceptibilities are shown in Table 4.
In Vitro Activities of Ceftazidime/Avibactam and Ceftolozane/Tazobactam and Susceptibility Profile to Other Antibacterial Agents for the 27 OXA-48 Beta-Lactamase-Producing Enterobacteriaceae Isolates
The origin of the resistant clinical samples tested in this study is detailed in Table 5.
Origin of the Third-Generation Cephalosporin-Resistant Enterobacteriaceae and Ceftazidime-Resistant and/or Carbapenem-Resistant Pseudomonas aeruginosa Clinical Isolates
Discussion
This in vitro study was carried out because the recent availability of CZA and C/T at our center required putting in place a strategy for their use that takes into account the local epidemiology. Our results suggest that, in our center, these antibacterial agents should be used for the management of the most difficult-to-treat MDR gram-negative infections.
According to our data, CZA is more effective on ESBL, non-ESBL third-generation cephalosporin-resistant Enterobacteriaceae (mainly AmpC beta-lactamase-producing Enterobacteriaceae) and OXA-48 beta-lactamase-producing Enterobacteriaceae, and could be used empirically when infections by these bacteria are suspected. All Enterobacteriaceae from clinically relevant samples were susceptible to CZA, but for two K. pneumoniae strains. One of these produced NDM-carbapenemase and ESBL, and it is known that CZA is not active on class B metallo-beta-lactamase. 9 Moreover, CZA resistance has emerged during treatment of KPC-producing K. pneumoniae infections 9 ; we did not have any KPC-producing Enterobacteriaceae in our strain collection. CZA is now part of the therapeutic arsenal against MDR P. aeruginosa, 10 but according to our data, susceptibility testing should be done before its prescription for this indication.
C/T showed higher activity on MDR P. aeruginosa, and could be used as empiric therapy when MDR P. aeruginosa infections are suspected. However, data are lacking about its use in critically ill patients. 10 C/T is less effective on MDR Enterobacteriaceae, especially non-ESBL third-generation cephalosporin-resistant Enterobacteriaceae and AmpC beta-lactamase-producing Enterobacteriaceae and should not be used as empiric treatment for this indication.
This study has several limitations: (i) in vitro drug susceptibility testing does not reflect the real activity of these antibiotics at the infection sites (in vivo) and (ii) the low number of tested isolates and the inclusion of a single hospital limit the statistical power of these results that need to be confirmed in a multicenter study. Moreover, this was a pragmatic study and reflected the daily diagnostic practices. Therefore, some susceptibility data and resistance mechanisms were not routinely investigated or were lacking. For instance, no KPC-3-expressing K. pneumoniae isolate was found because this enzyme is very uncommon in France. 11
Conclusion
CZA and C/T offer a carbapenem-sparing alternative for MDR gram-negative pathogens, and could also be used as salvage therapy for most carbapenem-resistant pathogens at Montpellier University Hospital, France.
Footnotes
Acknowledgment
This work was not supported by any external funding agency.
Authors' Contributions
B.V. and S.G. were responsible for the study design; B.V., F.Z.Z., and M.B. were responsible for data collection; B.V., Y.D., H.J.-P., V.L.M., and S.G. were responsible for data analysis and writing the article.
Disclosure Statement
No competing financial interests exist.