Abstract
Ceftolozane-tazobactam is a cephalosporin/β-lactamase inhibitor combination developed for use against some β-lactam- and multidrug-resistant Gram-negative organisms. This study aimed to evaluate the in vitro activity of ceftolozane–tazobactam against clinical bacterial isolates at the University Hospital of Marrakech. This is a descriptive and analytical prospective study. A total of 143 Enterobacterales and 48 Pseudomonas aeruginosa isolates were collected from January 2018 to December 2018 from patients with respiratory, urinary and intra-abdominal infections. The identification was made by Phoenix automated system (BioMérieux). MIC50/90 were tested by broth microdilution for ceftolozane-tazobactam, and other drugs using dried panels. Antimicrobial susceptibility results were interpreted according to CLSI guidelines. Ceftolozane-tazobactam inhibited 98% of Escherichia coli (MIC50/90; 0.25/0.5 μg/mL). The susceptibility rate of Klebsiella pneumoniae to ceftolozane-tazobactam was 68.8% (MIC50/90, 0.5/>32 μg/mL); other Enterobacterales have shown susceptibility rates of 80.4% (MIC50/90; 0.5/8 μg/mL). In carbapenemase-producing K. pneumoniae, the blaOXA-48 mutation was found in two isolates. Susceptibility of P. aeruginosa to ceftolozane-tazobactam was 91.7% (MIC50/90, 0.5/>32 μg/mL). In non-carbapenemase-producing P. aeruginosa, AmpC mutations were found in all isolates. Ceftolozane-tazobactam was satisfactorily active against a wide range of tested isolates and offers clinicians a potential therapeutic option even against resistant strains in patients with intra-abdominal infections, urinary tract infections and nosocomial pneumonia.
Keywords: Antimicrobial susceptibility, ceftolozane-tazobactam, Enterobacterales, minimum inhibitory concentrations, Pseudomonas aeruginosa
Introduction
Enterobacterales are responsible for severe respiratory infection, urinary tract infection and intra-abdominal infection due to antibiotic resistance [1]. They are represented mainly by Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae and Proteus mirabilis [1]. Pseudomonas aeruginosa is a pathogen that has expanded in hospitals, and causes fatal infections [2]. Infectious diseases pose a serious threat to global health [1,2].
Antibiotics have saved millions of lives every year, but today many bacteria are multidrug-resistant. The excessive and irrational use of antibiotics leads to the adaptation of bacteria to develop resistance to antibiotics [3]. The European Center for the Control of Infectious Diseases evaluates 33 000 cases of deaths per year due to bacterial resistance [4]; the problem has become critical in hospitals, because of the therapeutic problems observed mainly in Gram-negative bacteria such as Enterobacterales and P. aeruginosa [3,5].
WHO has issued a global action plan to develop new antibiotics [6], like ceftolozane-tazobactam (Zerbaxa™), which is a combination of ceftolozane, a third-generation cephalosporin, and tazobactam, an inhibitor of several β-lactamases. It is a new antibiotic, with activity against multi-resistant Gram-negative bacteria. Zerbaxa™ was approved by the US Food and Drug Administration and by the European Medicines Agency for complicated intra-abdominal infections, serious kidney infections (acute pyelonephritis), complicated infections of the urinary tract and hospital-acquired pneumonia, including ventilator-associated pneumonia [7,8]. In vitro studies have shown previously that the potential value of ceftolozane-tazobactam lies in its activity against Enterobacterales producing extended-spectrum β-lactamases (ESBL) [9], as part of a carbapenem saving strategy [10], and against P. aeruginosa combining several mechanisms of antibiotic resistance (including efflux pumps and overexpression of AmpC) [11,12].
The aim of this study was to evaluate the in vitro activity of ceftolozane-tazobactam against Enterobacterales and P. aeruginosa collected from different infection sites in the Marrakech University Hospital.
Materials and methods
Type of study method
This is a descriptive and analytical prospective study, extended over 1 year from January 2018 to December 2018, in two university hospital centres in Morocco: Marrakech and Rabat.
Bacterial isolates
Gram-negative aerobic bacteria, comprising E. coli, Klebsiella spp., Enterobacter spp. and Proteus spp., and Gram-negative anaerobic bacteria, comprising only P. aeruginosa, were isolated from different infection sites including respiratory infections, urinary infections and intra-abdominal infections. They were not collected sequentially (isolated strains were stored at –80°C or −20°C). Bacteria were identified using the Phoenix® automated Microbiology Identification System (Becton Dickinson, Franklin Lakes, NJ, USA).
Antimicrobial susceptibility testing
Antimicrobial susceptibility testing was performed at International Health Management Associates (IHMA) report 2018 following the 2017 Clinical and Laboratory Standards Institute (CLSI) guidelines [13]. Minimum inhibitory concentrations (MIC) were interpreted according to CLSI MIC values for ceftolozane-tazobactam, ceftazidime, meropenem, cefepime, piperacillin-tazobactam, amikacin, ciprofloxacin, ertapenem, imipenem, ceftriaxone, levofloxacin and colistin, and were determined using broth microdilution method panels manufactured by TREK Diagnostic Systems (East Grinstead, UK) according to CLSI guidelines for antimicrobials. A suspension using colonies and normal saline, equivalent to 0.5 McFarland standard concentrations, was incubated at 35°C for 16–20 hours.
For isolates of Enterobacterales, ceftolozane-tazobactam MIC were considered susceptible at ≤2 μg/mL. For isolates of P. aeruginosa, ceftolozane-tazobactam MIC was considered susceptible at ≤4 μg/mL.
Whole-genome sequencing of non-susceptible P. aeruginosa and K. pneumoniae to ceftolozane-tazobactam
Strains with ceftolozane-tazobactam MIC values ≥ 8 μg/mL were examined.
Genomic DNA was extracted using Qiagen DNeasy UltraClean kits (Qiagen, Valencia, CA, USA) and quantified using the Nanodrop™ ND-1000 spectrophotometer (ThermoFisher Scientific, Waltham, MA, USA).
For whole-genome sequencing, DNA sequences were obtained on the Illumina HiSeq sequencing instrument (Illumina, San Diego, CA, USA) with 2 × 150 bp pair-end reads with a target coverage depth of approximately 150×. All analyses were carried out using Qiagen's CLCBio Genomics Workbench version 11.
For β-lactamase resistance, genes were identified by Illumina whole-genome sequencing. β-lactamase gene inclusion was 72% and 80% for minimum nucleotide sequence identity and minimum sequence length, respectively.
For porin gene identification, ompk35 and ompK36 in K. pneumoniae and oprD in P. aeruginosa were searched by TBLASTN; for ftsI (encoding PBP3) gene analysis, searching was on a species-specific basis in de novo assemblies of each genome.
The appropriate multilocus sequence typing scheme and allelic profile of each of the guided assemblies was determined computationally (using the ‘find best match using k-mer spectra’ tool in CLC genomics).
Statistical analysis
Statistical analysis for comparison of susceptibilities of different isolates to ceftolozane-tazobactam was performed using SPSS 18 software (SPSS Inc., Chicago, IL, USA).
Results
The isolates comprised 142 Enterobacterales (49 E. coli, 48 K. pneumoniae, 16 Enterobacter spp. and 16 Proteus spp., 8 Klebsiella oxytoca, 3 Enterobacter aerogenes, 1 Klebsiella variicola and 1 Proteus vulgaris), and 48 P. aeruginosa. The clinical isolates were collected from intensive care units (57.4%, n = 109) and from non-intensive care units (46.6%, n = 81). The 190 Gram-negative isolates included 113 isolates from urinary tract infections, 56 from intra-abdominal infections and 21 from lower respiratory tract infections. Table 1 shows the antibiotics assessed, and the range and MIC values of each drug. Table 2 shows the susceptibility profile of different organisms to several antibiotics and their MIC50/90.
Table 1.
MIC values distribution for all antimicrobials tested against Enterobacterales and Pseudomonas aeruginosa isolates
| Organisms | Antimicrobial agent | MICs (μg/mL) |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0.06 | 0.12 | 0.25 | 0.5 | 1 | 2 | 4 | 8 | 16 | 32 | 64 | ||
| Escherichia coli (n = 49) | Ceftolozane-tazobactam | 7 | 26 | 15 | 0 | 0 | 1 | 0 | 0 | 0 | ||
| Piperacillin-tazobactam | 30 | 5 | 6 | 4 | 1 | 3 | ||||||
| Cefoxitin | 4 | 16 | 23 | 6 | ||||||||
| Cefotaxime | 36 | 1 | 0 | 0 | 3 | 9 | ||||||
| Ceftriaxone | 36 | 0 | 0 | 0 | 2 | 11 | ||||||
| Ceftazidime | 38 | 1 | 2 | 2 | 2 | 4 | ||||||
| Cefepime | 37 | 2 | 0 | 4 | 0 | 6 | ||||||
| Meropenem | 49 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | ||||
| Imipenem | 48 | 1 | 0 | 0 | 0 | 0 | 0 | |||||
| Ertapenem | 48 | 0 | 1 | |||||||||
| Aztreonam | 37 | 1 | 2 | 1 | 8 | |||||||
| Amikacin | 32 | 13 | 4 | |||||||||
| Ciprofloxacin | 32 | 2 | 15 | |||||||||
| Levofloxacin | 33 | 0 | 16 | |||||||||
| Colistin | 49 | 0 | 0 | |||||||||
| Klebsiella pneumoniae (n = 48) | Ceftolozane-tazobactam | 1 | 7 | 16 | 6 | 3 | 1 | 7 | 0 | 7 | ||
| Piperacillin-tazobactam | 6 | 8 | 6 | 5 | 9 | 14 | ||||||
| Cefoxitine | 5 | 26 | 8 | 9 | ||||||||
| Cefotaxime | 13 | 2 | 1 | 0 | 0 | 32 | ||||||
| Ceftriaxone | 15 | 0 | 0 | 1 | 0 | 32 | ||||||
| Ceftazidime | 13 | 1 | 1 | 3 | 8 | 22 | ||||||
| Cefepime | 16 | 0 | 0 | 3 | 11 | 18 | ||||||
| Ertapenem | 27 | 3 | 6 | 1 | 1 | 1 | 9 | |||||
| Imipenem | 31 | 7 | 4 | 3 | 1 | 0 | 2 | |||||
| Meropenem | 36 | 1 | 1 | 0 | 3 | 4 | 1 | 2 | ||||
| Aztreonam | 13 | 2 | 1 | 1 | 31 | |||||||
| Amikacin | 45 | 2 | 1 | |||||||||
| Ciprofloxacin | 20 | 3 | 25 | |||||||||
| Levofloxacin | 30 | 2 | 16 | |||||||||
| Colistin | 42 | 0 | 6 | |||||||||
| Enterobacter cloacae (n = 16) | Ceftolozane-tazobactam | 4 | 3 | 0 | 0 | 3 | 3 | 1 | 2 | |||
| Piperacillin-tazobactam | 6 | 1 | 0 | 0 | 1 | 8 | ||||||
| Cefoxitine | 1 | 0 | 15 | |||||||||
| Cefotaxime | 6 | 1 | 0 | 0 | 0 | 9 | ||||||
| Ceftriaxone | 7 | 0 | 0 | 0 | 0 | 9 | ||||||
| Ceftazidime | 7 | 0 | 0 | 0 | 0 | 9 | ||||||
| Cefepime | 8 | 5 | 1 | 0 | 0 | 2 | ||||||
| Ertapenem | 7 | 0 | 0 | 1 | 4 | 2 | 2 | |||||
| Imipenem | 14 | 0 | 0 | 2 | 0 | 0 | 0 | |||||
| Meropenem | 13 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | ||||
| Aztreonam | 7 | 0 | 0 | 0 | 9 | |||||||
| Amikacin | 16 | 0 | 0 | 0 | ||||||||
| Ciprofloxacin | 6 | 0 | 10 | |||||||||
| Levofloxacin | 9 | 1 | 6 | |||||||||
| Colistin | 16 | 0 | 0 | |||||||||
| Proteus mirabilis (n = 16) | Ceftolozane-tazobactam | 6 | 9 | 1 | 0 | 0 | 0 | 0 | 0 | |||
| Piperacillin-tazobactam | 16 | 0 | 0 | 0 | 0 | 0 | ||||||
| Cefoxitine | 9 | 6 | 0 | 1 | ||||||||
| Cefotaxime | 16 | 0 | 0 | 0 | 0 | 0 | ||||||
| Ceftriaxone | 16 | 0 | 0 | 0 | 0 | 0 | ||||||
| Ceftazidime | 16 | 0 | 0 | 0 | 0 | 0 | ||||||
| Cefepime | 16 | 0 | 0 | 0 | 0 | 0 | ||||||
| Ertapenem | 16 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | ||||
| Imipenem | 3 | 10 | 3 | 0 | 0 | 0 | 0 | |||||
| Meropenem | 16 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | ||||
| Aztreonam | 16 | 0 | 0 | 0 | 0 | 0 | ||||||
| Amikacin | 14 | 2 | 0 | 0 | ||||||||
| Ciprofloxacin | 1 | 0 | 0 | |||||||||
| Levofloxacin | 1 | 0 | 0 | |||||||||
| Pseudomonas aeruginosa (n = 48) | Ceftolozane-tazobactam | 24 | 11 | 1 | 6 | 0 | 0 | 6 | ||||
| Piperacillin-tazobactam | 12 | 19 | 4 | 1 | 12 | |||||||
| Cefepime | 3 | 19 | 8 | 4 | 4 | 10 | ||||||
| Ceftazidime | 0 | 18 | 15 | 2 | 5 | 8 | ||||||
| Meropenem | 10 | 10 | 0 | 7 | 1 | 2 | 5 | 3 | ||||
| Imipenem | 1 | 4 | 26 | 7 | 1 | 1 | 4 | 5 | ||||
| Aztreonam | 1 | 26 | 8 | 13 | ||||||||
| Amikacin | 39 | 4 | 1 | 4 | ||||||||
| Ciprofloxacin | 35 | 4 | 0 | 9 | ||||||||
| Levofloxacin | 35 | 5 | 8 | |||||||||
| Colistin | 47 | 1 | 0 | |||||||||
| Other Enterobacterales (n = 14) | Ceftolozane-tazobactam | 11 | 3 | |||||||||
| Piperacillin-tazobactam | 9 | 5 | ||||||||||
| Cefoxitin | 3 | 7 | 1 | 3 | ||||||||
| Cefotaxime | 14 | |||||||||||
| Ceftazidime | 14 | |||||||||||
| Ceftriaxone | 14 | |||||||||||
| Cefepime | 14 | |||||||||||
| Ertapenem | 14 | |||||||||||
| Imipenem | 11 | 3 | ||||||||||
| Meropenem | 14 | |||||||||||
| Aztreonam | 14 | |||||||||||
| Amikacin | 14 | |||||||||||
| Ciprofloxacin | 14 | |||||||||||
| Levofloxacin | 14 | |||||||||||
| Colistin | 13 | 1 | ||||||||||
Table 2.
MIC50/90 and percentage susceptible of antimicrobials tested against 190 isolates
| Organism | Antimicrobial agent | %S CLSIa | MIC50b | MIC90b) | Range |
|---|---|---|---|---|---|
| Pseudomonas aeruginosa (n = 48) | Ceftolozane-tazobactam | 87.5 | 0.5 | >32 | 0.5 to >32 |
| Amikacin | 91.7 | ≤4 | 16 | ≤4 to >32 | |
| Aztreonam | 72.9 | 4 | >16 | 2 to >16 | |
| Cefepime | 70.8 | 4 | 32 | ≤1 to >32 | |
| Ceftazidime | 72.9 | 4 | >32 | 2 to >32 | |
| Ciprofloxacin | 81.3 | ≤0.25 | >2 | ≤0.25 to >2 | |
| Colistin | 100 | ≤1 | ≤1 | ≤1 to 2 | |
| Imipenem | 77.1 | 1 | 32 | ≤0.5 to >32 | |
| Levofloxacin | 83.3 | ≤1 | >4 | ≤1 to >4 | |
| Meropenem | 79.2 | 0.5 | 8 | ≤0.12 to >16 | |
| Piperacillin-tazobactam | 72.9 | 8 | >64 | 4 to >64 | |
| Escherichia coli (n = 49) | Ceftolozane-tazobactam | 98.0 | 0.25 | 0.5 | 0.12–4 |
| Amikacin | 100 | ≤4 | 8 | ≤4 to 16 | |
| Aztreonam | 81.6 | ≤1 | >16 | ≤1 to >16 | |
| Cefepime | 79.6 | ≤1 | >32 | ≤1 to >32 | |
| Cefotaxime | 73.5 | ≤1 | >32 | ≤1 to >32 | |
| Cefoxitin | 87.8 | 8 | 16 | ≤2 to >16 | |
| Ceftazidime | 83.7 | ≤1 | 16 | ≤1 to >32 | |
| Ceftriaxone | 73.5 | ≤1 | >32 | ≤1 to >32 | |
| Ciprofloxacin | 67.4 | ≤0.25 | >2 | ≤0.25 to >2 | |
| Colistin | 100 | ≤1 | ≤1 | ≤1 to ≤1 | |
| Ertapenem | 100 | ≤0.06 | ≤0.06 | ≤0.06 to 0.25 | |
| Imipenem | 100 | ≤0.5 | ≤0.5 | ≤0.5 to 1 | |
| Levofloxacin | 67.4 | ≤1 | >4 | ≤1 to >4 | |
| Meropenem | 100 | ≤0.12 | ≤0.12 | ≤0.12 to ≤0.12 | |
| Piperacillin-tazobactam | 91.8 | ≤2 | 16 | ≤2 to 64 | |
| Klebsiella pneumoniae (n = 48) | Ceftolozane-tazobactam | 68.8 | 0.5 | >32 | 0.12 to >32 |
| Amikacin | 100 | ≤4 | ≤4 | ≤4 to 16 | |
| Aztreonam | 33.3 | >16 | >16 | ≤1 to >16 | |
| Cefepime | 33.3 | 16 | >32 | ≤1 to >32 | |
| Cefotaxime | 27.1 | >32 | >32 | ≤1 to >32 | |
| Cefoxitin | 81.3 | 4 | >16 | ≤2 to >16 | |
| Ceftazidime | 31.3 | 16 | >32 | ≤1 to >32 | |
| Ceftriaxone | 31.3 | >32 | >32 | ≤1 to >32 | |
| Ciprofloxacin | 47.9 | 2 | >2 | ≤0.25 to >2 | |
| Colistin | 87.5 | ≤1 | >4 | ≤1 to >4 | |
| Ertapenem | 77.1 | ≤0.06 | >4 | ≤0.06 to >4 | |
| Imipenem | 79.2 | ≤0.5 | 4 | ≤0.5 to >32 | |
| Levofloxacin | 66.7 | ≤1 | >4 | ≤1 to >4 | |
| Meropenem | 79.2 | ≤0.12 | 4 | ≤0.12 to >16 | |
| Piperacillin Tazobactam | 52.1 | 16 | >64 | ≤2 to >64 | |
| Other 22Enterobacterales (n = 46) | Ceftolozane-tazobactam | 80.4 | 0.5 | 8 | 0.25 to >32 |
| Amikacin | 100 | ≤4 | ≤4 | ≤4 to 8 | |
| Aztreonam | 80.4 | ≤1 | >16 | ≤1 to >16 | |
| Cefepime | 93.5 | ≤1 | 2 | ≤1 to 32 | |
| Cefotaxime | 76.1 | ≤1 | >32 | ≤1 to >32 | |
| Cefoxitin | 58.7 | 4 | >16 | ≤2 to >16 | |
| Ceftazidime | 80.4 | ≤1 | >32 | ≤1 to >32 | |
| Ceftriaxone | 78.3 | ≤1 | >32 | ≤1 to >32 | |
| Ciprofloxacin | 71.7 | ≤0.25 | >2 | ≤0.25 to >2 | |
| Colistin | 63.0 | ≤1 | >4 | ≤1 to >4 | |
| Ertapenem | 82.6 | ≤0.06 | 1 | ≤0.06 to >4 | |
| Imipenem | 89.1 | ≤0.5 | 2 | ≤0.5 to 4 | |
| Levofloxacin | 80.4 | ≤1 | 4 | ≤1 to >4 | |
| Meropenem | 95.7 | ≤0.12 | ≤0.12 | ≤0.12 to 8 | |
| Piperacillin Tazobactam | 80.4 | ≤2 | 64 | ≤2 to >64 |
%S, represents the percent susceptible by CLSI 2017 guidelines (EUCAST guidelines for colistin were applied for Enterobacterales).
MIC50, MIC90, and range in μg/mL; no intermediate breakpoint.
Ceftolozane-tazobactam activity against Enterobacterales
The activity of ceftolozane-tazobactam against E. coli was high (MIC50/90; 0.25/0.5 μg/mL). Ceftolozane-tazobactam susceptibility rate against E. coli was 98%. Susceptibility rates to other antibiotics were 100% to carbapenem; 100% to amikacin and 100% to colistin (Table 3).
Table 3.
Whole-genome sequencing data for Klebsiella pneumoniae examined
| MIC C/T (μg/mL) | OmpK 35 | OmpK 36 | PBP3-ftsIa | β-lactamase summary (72% ident, 80% coverage)b | MLST |
|---|---|---|---|---|---|
| 8 | No lesion | Lesion | WT | CTX-M-15; OXA-1; SHV-1; TEM-1B | 628 |
| >32 | No lesion | No lesion | WT | CTX-M-15; OXA-48; SHV-1-like | Novel-2 |
| >32 | Lesion | No lesion | WT | CTX-M-15; OXA-1; OXA-48; SHV-11 | 37 |
| 8 | No lesion | Lesion | WT | CTX-M-15; OXA-1; SHV-11-like; TEM-1B-like | 392 |
Abbreviations: MLST, multilocus sequence typing; WT, wild-type.
PBP3-ftsl: Peniclin Binding Porin 3- FtsI gene.
Threshold for β-lactamase gene inclusion was 72% and 80% for minimum nucleotide sequence identity and minimum sequence length, respectively.
Susceptibility rate of K. pneumoniae to ceftolozane-tazobactam was 68.8%, with medium activity (MIC50/90, 0.5/>32 μg/mL), with higher susceptibility to amikacin (100%), colistin (87.5%), imipenem (79.2%), meropenem (79.2%) and ertapenem (77.1%) (Table 2).
Ceftolozane-tazobactam showed 80.4% inhibition (MIC50/90; 0.5/8 μg/mL) against Enterobacterales (Enterobacter cloacae, Proteus mirabilis, K. oxytoca, K. variicola, Enterobacter aerogenes, Proteus vulgaris) compared with susceptibilities to colistin of 63%, to meropenem of 89.1% and to amikacin of 100%.
From 15 ceftolozane-tazobactam non-susceptible K. pneumoniae isolates, molecular analysis of the resistance support was detected in 4/15 (27%). The carbapenemase gene blaOXA-48 was found in two isolates. ESBL production was confirmed in all isolates—blaCTX-M-15 (four of four), blaSHV-1 (two of four), blaOXA-1 (two of four) and blaTEM-1B (two of four). Mutations of ompK35 and ompK36 were detected in three of the isolates tested (Table 3).
Ceftolozane-tazobactam activity against P. aeruginosa
The susceptibility rate to ceftolozane-tazobactam against P. aeruginosa was 91.7%, with (MIC50/90 values of 0.5/>32 μg/mL) (Table 3). Colistin was the most active drug with 100% of isolates susceptible (MIC50/90, ≤1/≤1 μg/mL); susceptibility to amikacin-cefepime was 91.7%.
All six ceftolozane-tazobactam-resistant P. aeruginosa isolates produced PDC (Ampc mutation) and blaOXA-50; four had the β-lactamases genes blaPER-1 and blaVIM-2, and two had blaOXA-4. Mutation of oprD was detected in three isolates; all isolates were wild-type for ftsI (Table 4).
Table 4.
Whole-genome sequencing data for Pseudomonas aeruginosa isolates examined
| C/T MIC (μg/mL) | oprD | PBP3(ftsI) | WGS β-lactamase summarya | Class C (intrinsic) | MLSTb |
|---|---|---|---|---|---|
| >32 | Lesion | WT | PDC-252-like; OXA-50-like; PER-1; VIM-2; OXA-4 | PDC-252-like | 233 |
| >32 | No lesion | WT | PDC-40-like; VIM-2; OXA-50-like | PDC-40-like | 270 |
| >32 | No lesion | WT | PDC-72-like; OXA-50-like; PER-1 | PDC-72-like | 277 |
| >32 | Lesion | WT | PDC-119-like; VIM-2; PER-1; OXA-4; OXA-50-like | PDC-119-like | 233 |
| >32 | No lesion | WT | PDC-183-like; OXA-50-like; VIM-2 | PDC-183-like | 769 |
| >32 | Lesion | WT | PDC-252-like; OXA-50-like; PER-1 | PDC-252-like | 233 |
Abbreviations: MLSTb, multilocus sequence typing; WGSa, whole-genome sequencing; WT, wild-type.
Discussion
Ceftolozane-tazobactam could be an important treatment option, including against multidrug-resistant strains. This type of study is interesting to evaluate the activity of ceftolozane-tazobactam against a selection of P. aeruginosa and Enterobacterales isolates. Our study is the first in Morocco.
In the current study, ceftolozane-tazobactam was active against 82.4% of Enterobacterales: 98% of E. coli, 68.8% of K. pneumonia and 80.4% of other Enterobacterales, which is similar to other studies assessing the activity of ceftolozane-tazobactam against Gram-negative isolates. Karlowsky et al. [14] reported a susceptibility of 89.7% of Enterobacterales, Kuo et al. [15] found 81.9% of K. pneumoniae and 91.9% of E. coli, Sader et al. [16] reported 98.5% of E. coli and 89.6% of K. pneumoniae, and Shortridge et al. [17] reported 95.5% of Enterobacterales. The variation in susceptibility profiles to ceftolozane-tazobactam can be explained by intrinsic and extrinsic mechanisms.
In our study, the susceptibility of K. pneumoniae to ceftolozane-tazobactam was the weakest. This was due to the incidence of carbapenemase and ESBL in this microorganism, most of them having a high rate of ceftolozane hydrolysis, such as blaOXA-48, blaCTX-M15, SHV and TEM. This is in accord with the results of Tuon et al. [18]. Carbapenem use results in heightened rates of carbapenem-resistant infections, limiting treatment options and growing mortality. Carbapenem resistance and ESBL detected in Enterobacterales, usually due to plasmid β-lactamases enzymes, have also become important issues [19].
In this study, the susceptibility of ceftolozane-tazobactam was 87.5% against P. aeruginosa, similar to reported susceptibility rates above 80% [[15], [16], [17],20,21]. Ceftolozane-tazobactam was the third most active of the β-lactam agents tested against P. aeruginosa after colistin and amikacin-meropenem. The same result was reported by Garcia-Fernandez et al. [22], who found a susceptibility rate of 91.3%, which was the third most active, after colistin (95.0%) and amikacin (93.8%). The activity of ceftolozane-tazobactam is specifically more important in the context of intensive care units, where this microorganism is an extreme worry in the management of nosocomial infections because of its resistance to different antibiotics.
Our results show the presence of intrinsic mechanisms in ceftolozane-tazobactam-resistant P. aeruginosa isolates by producing AmpC overexpression by single point mutations in the blaPDC gene (AmpC gene), and of extrinsic mechanisms by the presence of metallo-β-lactamase (VIM), associated with mutation of porin (OprD). This result is consistent with four studies demonstrating the presence of a carbapenemase in ceftolozane-tazobactam-resistant P. aeruginosa [[23], [24], [25], [26]]. Ceftolozane-tazobactam has a better safety profile compared with colistin, which has high frequencies of nephrotoxicity, neurotoxicity, and allergic and topical reactions, as do aminoglycosides [27].
The main strength of this study was the genome sequencing of ceftolozane-tazobactam-resistant P. aeruginosa and K. pneumonie and the isolates collected were tested using a broth microdilution MIC method semi-quantitatively, which remains the reference method. It is also highly accurate in particular for these antimicrobials: colistin, cefepime and more recently, ceftolozane-tazobactam [[28], [29], [30], [31], [32], [33]].
2A study limitation was the low number of Enterobacterales that were ceftolozane-tazobactam-resistant with genome sequencing. Although the study provided new information about the activity of ceftolozane-tazobactam against Enterobacterales and P. aeruginosa isolates. The study does not provide data about the incidence of infections in a given region.
Conclusions
Ceftolozane-tazobactam demonstrated relevant activity against most of the Enterobacterales and P. aeruginosa isolates. Ceftolozane-tazobactam could be considered a therapeutic alternative for the treatment of complicated urinary infections, complicated intra-abdominal infections and nosocomial pneumonia.
Funding
This study was part of EM200 surveillance programme funded by Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc., Kenilworth, NJ, USA, which included funding for services related to preparing this manuscript.
Conflicts of interest
The authors have stated that there are no conflicts of interest.
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