
==== Front
JAC Antimicrob Resist
JAC Antimicrob Resist
jacamr
JAC-Antimicrobial Resistance
2632-1823
Oxford University Press UK

10.1093/jacamr/dlae077
dlae077
Original Article
AcademicSubjects/MED00740
AcademicSubjects/SCI01150
Activity of ceftolozane/tazobactam and imipenem/relebactam against Gram-negative clinical isolates collected in Mexico—SMART 2017–2021
Karlowsky James A IHMA, 2122 Palmer Drive, Schaumburg, IL 60173, USA
Department of Medical Microbiology and Infectious Diseases, Max Rady College of Medicine, Room 543—745 Bannatyne Avenue, University of Manitoba, Winnipeg, MB R3E 0J9, Canada

Lob Sibylle H IHMA, 2122 Palmer Drive, Schaumburg, IL 60173, USA

Siddiqui Fakhar Merck & Co., Inc., 126 East Lincoln Avenue, Rahway, NJ 07065, USA

Polis Thales MSD Brasil, Av. Chucri Zaidan, 296—Vila Cordeiro, São Paulo 04583-110, Brazil

Vallejo Jose L MSD Mexico, Av. San Jerónimo 369, Tizapán San Ángel, Tizapán, Álvaro Obregón, 01090 Mexico City, Mexico

Young Katherine Merck & Co., Inc., 126 East Lincoln Avenue, Rahway, NJ 07065, USA

Motyl Mary R Merck & Co., Inc., 126 East Lincoln Avenue, Rahway, NJ 07065, USA

Sahm Daniel F IHMA, 2122 Palmer Drive, Schaumburg, IL 60173, USA

Corresponding author. E-mail: jkarlowsky@sharedhealthmb.ca
6 2024
24 5 2024
24 5 2024
6 3 dlae07721 2 2024
02 5 2024
© The Author(s) 2024. Published by Oxford University Press on behalf of British Society for Antimicrobial Chemotherapy.
2024
https://creativecommons.org/licenses/by/4.0/ This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Objectives

To investigate the activities of ceftolozane/tazobactam and imipenem/relebactam against Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa isolated from hospitalized patients in Mexico in 2017–2021.

Methods

MICs were determined by CLSI broth microdilution and interpreted using CLSI M100 breakpoints. β-Lactamase genes were identified in ceftolozane/tazobactam-, imipenem/relebactam-, and/or imipenem-non-susceptible isolates.

Results

Ceftolozane/tazobactam and imipenem/relebactam inhibited 89% and 99% of E. coli isolates (n = 2337), and 87% and 94% of K. pneumoniae isolates (n = 1127). Sixty-four percent of E. coli and 47% of K. pneumoniae had an ESBL non-carbapenem-resistant Enterobacterales (ESBL non-CRE) phenotype. Eighty-six percent and 91% of ESBL non-CRE E. coli and K. pneumoniae were ceftolozane/tazobactam susceptible, and 99.9% and 99.8% were imipenem/relebactam susceptible. Ceftolozane/tazobactam was the most active agent studied against P. aeruginosa (n = 1068; 83% susceptible), 9–28 percentage points higher than carbapenems and comparator β-lactams excluding imipenem/relebactam (78% susceptible). Ceftolozane/tazobactam remained active against 35%–58%, and imipenem/relebactam against 32%–42%, of P. aeruginosa in meropenem-, piperacillin/tazobactam-, and cefepime-non-susceptible subsets. The majority of isolates of ceftolozane/tazobactam-non-susceptible E. coli carried an ESBL, whereas among ceftolozane/tazobactam-non-susceptible K. pneumoniae and P. aeruginosa, the majority carried carbapenemases. The most prevalent carbapenemase observed among E. coli (estimated at 0.7% of all isolates), K. pneumoniae (4.8%) and P. aeruginosa (10.0%) was an MBL. Almost all imipenem/relebactam-non-susceptible E. coli and K. pneumoniae carried MBL or OXA-48-like carbapenemases, whereas among imipenem/relebactam-non-susceptible P. aeruginosa, 56% carried MBL or GES carbapenemases.

Conclusions

Ceftolozane/tazobactam and imipenem/relebactam may provide treatment options for patients infected with β-lactam-non-susceptible Gram-negative bacilli, excluding isolates carrying an MBL- or OXA-48-like carbapenemase.
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pmcIntroduction

ESBL-producing and carbapenem-resistant Enterobacterales (CRE), and carbapenem-resistant Pseudomonas aeruginosa are frequently MDR and leave clinicians with few or no safe and effective treatment choices. Current surveillance data for both newer and established antimicrobial agents across different geographies inform empirical treatment decisions in those locations as well as supporting global resistance monitoring and drug development efforts.1–3

Ceftolozane/tazobactam, an antipseudomonal cephalosporin combined with a longstanding β-lactamase inhibitor, is a newer antimicrobial agent approved in Mexico for the treatment of complicated urinary tract and intra-abdominal infections, and hospital-acquired and ventilator-associated bacterial pneumonia (HAP/VAP).4 Imipenem/relebactam is a combination of imipenem/cilastatin (carbapenem/renal dehydropeptidase inhibitor) with relebactam, a non-β-lactam diazabicyclooctane inhibitor of class A and C β-lactamases,5,6 that is approved by the US FDA for the treatment of complicated urinary tract and intra-abdominal infections, and HAP/VAP,7 and by the EMA for the treatment of infections due to aerobic Gram-negative organisms in adults with limited treatment options; for the treatment of HAP, including VAP, in adults; and for the treatment of bacteraemia that occurs in association with, or is suspected to be associated with, HAP or VAP, in adults.8 Imipenem/relebactam is not approved currently for clinical use in Mexico.

Published surveillance data for ceftolozane/tazobactam and imipenem/relebactam tested against clinical isolates of Enterobacterales and P. aeruginosa from Mexico are very limited.9,10 Therefore, in the current study, we evaluated the activity of ceftolozane/tazobactam, imipenem/relebactam, and nine comparator agents against common Gram-negative pathogens (Escherichia coli, Klebsiella pneumoniae, P. aeruginosa) collected in Mexico by the SMART (Study for Monitoring Antimicrobial Resistance Trends) global surveillance programme and also identified β-lactamase resistance mechanisms in phenotypically resistant isolate subsets.

Materials and methods

Bacterial isolates

From 2017 to 2021, eight clinical laboratory sites in Mexico participated in the SMART global surveillance programme; six of the eight sites participated in all five years, one additional site participated in 2019, and one additional site participated in 2021. Sites were each asked to collect consecutive, clinically significant isolates of aerobic or facultatively anaerobic Gram-negative bacilli from intra-abdominal infection (IAI; 75 isolates in 2017 and 50 isolates/year in 2018–2021), lower respiratory tract infection (LRTI; 100 isolates/year), urinary tract infection (UTI; 75 isolates in 2017 and 50 isolates/year in 2018–2021), and bloodstream infection (BSI; 50 isolates/year in 2018–2021 only) samples. Isolates were restricted to one isolate per patient per Gram-negative species per year. Organism-specific quotas are not used in the collection of isolates by the SMART global surveillance programme. All isolates were shipped to IHMA (Schaumburg, IL, USA) where organism identity was confirmed using MALDI-TOF MS (Bruker Daltonics, Billerica, MA, USA), and antimicrobial susceptibility and molecular testing was performed.

Antimicrobial susceptibility testing

MICs were determined by the CLSI reference broth microdilution method11 on custom-made dehydrated broth microdilution panels manufactured by TREK Diagnostic Systems (Thermo Fisher Scientific, Oakwood Village, OH, USA) in 2017 and frozen broth microdilution panels prepared at IHMA in 2018–2021. MICs were interpreted using 2023 CLSI M100 breakpoints.12 An ESBL non-CRE phenotype was defined for E. coli and K. pneumoniae as an isolate testing as non-susceptible to ceftriaxone (MIC ≥2 mg/L) and susceptible to ertapenem (MIC ≤0.5 mg/L). For E. coli and K. pneumoniae, the EUCAST breakpoint for amikacin13 was used to interpret MIC data for that agent because the concentration range tested did not extend low enough to include the revised 2023 CLSI susceptible breakpoint for that agent.12

Screening for β-lactamase genes

Isolates that were ceftolozane/tazobactam-, imipenem/relebactam-, and/or imipenem-non-susceptible were screened for genes encoding β-lactamase genes by short-read WGS (ResFinder database; only P. aeruginosa isolates collected in 2020 and 2021) or by PCR and Sanger sequencing, as described previously.14–16 All isolates from 2017 to 2019 that met the screening criteria were tested. Isolates characterized in 2020 and 2021 were a random sample of those that met the screening criteria. In total, 274 of 287 (95.5%) Enterobacterales isolates that qualified for molecular characterization in 2020 and 2021 were characterized, as were 185 of 238 (77.7%) qualified P. aeruginosa isolates. The percentage of characterized, qualifying isolates collected in 2020 and 2021 was factored into the estimation of carbapenemase rates.

Results

A total of 4880 isolates of Enterobacterales and 1068 isolates of P. aeruginosa were collected by the eight laboratories from 2017 to 2021 (Table S1, available as Supplementary data at JAC-AMR Online). E. coli (n = 2337) and K. pneumoniae (n = 1127) were the two most common species of Gram-negative bacilli isolated and accounted for 71% of the 4880 isolates of Enterobacterales. Together, E. coli, K. pneumoniae and P. aeruginosa (the third most frequently isolated species of Gram-negative bacilli) accounted for 67% of all Gram-negative bacilli collected by the SMART global surveillance programme in Mexico from 2017 to 2021. Among E. coli, K. pneumoniae and P. aeruginosa isolates, 13.5%, 37.3% and 51.6%, respectively, were collected from patients with LRTI; 35.5%, 26.0% and 17.7% from patients with UTI; 33.5%, 16.8% and 17.6% from patients with IAI; and 17.5%, 19.9% and 12.7% from patients with BSI (Table S1). An infection source was not identified for 0.1% of E. coli, 0.1% of K. pneumoniae and 0.4% of P. aeruginosa isolates.

Ceftolozane/tazobactam and imipenem/relebactam were active against 89% and 99% of E. coli isolates, respectively, and against 87% and 94% of K. pneumoniae isolates (Table 1). Imipenem, meropenem and ertapenem percent susceptible values ranged from 97% to 99% for E. coli and from 91% to 93% for K. pneumoniae. The addition of relebactam to imipenem had only a minor impact on percent susceptible values for both E. coli (0.5%) and K. pneumoniae (1.4%).

Table 1. Antimicrobial susceptibility of all clinical isolates of E. coli, K. pneumoniae and P. aeruginosa and resistant phenotype subsets collected by the SMART global surveillance programme in Mexico from 2017 to 2021

Species		% Susceptible	
Resistant phenotype	n	C/T	IPM/REL	IMI	MEM	ETP	FEP	CAZ	CRO	TZP	LVXa	AMKb	
E. coli	2337	89.3	99.0	98.5	98.8	97.0	38.4	42.4	33.1	74.1	30.1	90.8	
ESBL non-CREc	1500	86.4	99.9	99.7	100	100	8.3	14.2	0	67.8	13.7	88.3	
K. pneumoniae	1127	87.1	93.6	92.2	92.5	90.6	47.6	48.4	44.3	64.0	55.2	90.4	
ESBL non-CREc	526	91.4	99.8	99.4	99.8	100	7.0	9.5	0	47.5	30.2	89.4	
P. aeruginosa	1068	83.1	77.8	55.1	62.1	NA	73.9	71.9	NA	69.0	65.3	80.1	
MEM-non-susceptible	405	57.5	42.0	2.0	0	NA	43.2	41.7	NA	35.6	31.9	51.4	
TZP-non-susceptible	331	47.4	41.4	19.6	21.1	NA	20.2	16.0	NA	0	26.3	48.3	
FEP-non-susceptible	279	35.1	31.5	16.1	17.6	NA	0	5.7	NA	5.4	19.7	39.1	
AMK, amikacin; CAZ, ceftazidime; CRE, carbapenem-resistant Enterobacterales; CRO, ceftriaxone; C/T, ceftolozane/tazobactam; ETP, ertapenem; FEP, cefepime; IPM, imipenem; IPM/REL, imipenem/relebactam; LVX, levofloxacin; MEM, meropenem; NA, not applicable; TZP, piperacillin/tazobactam.

aLevofloxacin was only tested against Enterobacterales in 2018–2021.

bFor E. coli and K. pneumoniae, the EUCAST breakpoint for amikacin was used because the concentration range tested did not extend low enough to include the revised 2023 CLSI susceptible breakpoint for that agent.

cESBL non-CRE phenotype was defined by an isolate testing non-susceptible to ceftriaxone (MIC ≥2 mg/L) and susceptible to ertapenem (MIC ≤0.5 mg/L).

Among E. coli and K. pneumoniae, 64% and 47% of isolates, respectively, had an ESBL non-CRE phenotype resulting in overall percent susceptible values of <50% for cefepime, ceftazidime and ceftriaxone. Only 61% of all K. pneumoniae isolates, 51% of all E. coli isolates, 34% of ESBL non-CRE K. pneumoniae isolates, and 27% of ESBL non-CRE E. coli isolates had a cefepime-susceptible or cefepime susceptible-dose dependent phenotype. Percent susceptible values for ESBL non-CRE phenotype E. coli and K. pneumoniae were 86% and 91% for ceftolozane/tazobactam and 99.9% and 99.8% for imipenem/relebactam. Only 68% of ESBL non-CRE phenotype E. coli and 48% of ESBL non-CRE phenotype K. pneumoniae were piperacillin/tazobactam-susceptible. Thirty percent or less of ESBL non-CRE phenotype E. coli and K. pneumoniae were levofloxacin-susceptible. As expected, the addition of relebactam to imipenem had only a minor impact on the percent susceptible value (0.4% or less) for ESBL non-CRE phenotype isolates of E. coli and K. pneumoniae as susceptibilities to imipenem alone were ≥99.4%. Percent susceptible values for ceftolozane/tazobactam ranged from 85% (LRTI) to 90% (BSI, IAI and UTI) among E. coli specimen sources and from 83% (BSI) to 91% (IAI) among K. pneumoniae specimen sources (Table S2). Percent susceptible values for imipenem/relebactam had narrower ranges than ceftolozane/tazobactam, from 98% (LRTI) to >99% (IAI and UTI) for E. coli specimen sources, and from 92% (BSI) to 95% (IAI) for K. pneumoniae specimen sources. Amikacin percent susceptible values for ESBL non-CRE phenotype E. coli and K. pneumoniae were ∼10% lower than for imipenem/relebactam, imipenem, meropenem and ertapenem.

Ceftolozane/tazobactam was the most active of the studied agents against P. aeruginosa, inhibiting 83% of collected isolates, 9–28 percentage points higher than the comparator β-lactams (Table 1). Susceptibility of P. aeruginosa to imipenem/relebactam was 78%, 23 percentage points higher than imipenem alone. Ceftolozane/tazobactam and imipenem/relebactam remained active against 35%–58% and 32%–42% of P. aeruginosa isolates with meropenem-non-susceptible, piperacillin/tazobactam-non-susceptible, and cefepime-non-susceptible phenotypes. Percent susceptible values for ceftolozane/tazobactam ranged from 71% (UTI) to 89% (LRTI) among P. aeruginosa specimen sources compared with a range of percent susceptible values of 66% (UTI) to 82% (LRTI) for imipenem/relebactam (Table S2).

Carbapenemases were relatively rare among clinical isolates of E. coli in Mexico (estimated at 1.3%) but were more common among K. pneumoniae (7.5%) and P. aeruginosa (13.0%) (Table 2). MBL was the most prevalent carbapenemase type, observed among E. coli (0.7% of all isolates), K. pneumoniae (4.8%) and P. aeruginosa (10.0%) isolates. Molecular characterization of ceftolozane/tazobactam-non-susceptible E. coli showed that 96% (234/243) of characterized isolates carried an ESBL, with 77% (187/243) of isolates carrying only an ESBL and no other β-lactamase (Table 3). In comparison, among ceftolozane/tazobactam-non-susceptible K. pneumoniae and P. aeruginosa, the majority of isolates carried carbapenemases, predominantly MBLs, with a smaller number carrying OXA-48-like (K. pneumoniae) or GES (P. aeruginosa) enzymes. Among imipenem/relebactam-non-susceptible E. coli and K. pneumoniae, almost all isolates carried MBL or OXA-48-like carbapenemases, whereas among imipenem/relebactam-non-susceptible P. aeruginosa, 56% (118/212) of characterized isolates carried an MBL or GES carbapenemase. KPC (only identified in isolates of ceftolozane/tazobactam-non-susceptible K. pneumoniae), OXA-48-like (identified in ceftolozane/tazobactam-non-susceptible and imipenem/relebactam-non-susceptible E. coli and K. pneumoniae), and GES (identified in ceftolozane/tazobactam-non-susceptible and imipenem/relebactam-non-susceptible K. pneumoniae and P. aeruginosa) were rarely identified in isolates from Mexico.

Table 2. Estimated carbapenemase rates among E. coli, K. pneumoniae and P. aeruginosa isolates collected by the SMART global surveillance programme in Mexico from 2017 to 2021

	Pathogen (total number of isolates)
Estimated percentage of total number of isolates with carbapenemase	
Carbapenemase	E. coli
(n = 2337)	K. pneumoniae
(n = 1127)	P. aeruginosa
(n = 1068)	
MBL	0.7	4.8	10.0	
KPC	0	0.6	0	
OXA-48-like	0.6	2.0	0	
GES	0	0.1	3.0	
GES, Guiana ESBL; KPC, Klebsiella pneumoniae carbapenemase; OXA, oxacillinase.

Table 3. Acquired β-lactamases detected in ceftolozane/tazobactam-non-susceptible and imipenem/relebactam-non-susceptible E. coli, K. pneumoniae and P. aeruginosaa collected in Mexico by SMART from 2017 to 2021

	Ceftolozane/tazobactam-non-susceptible	Imipenem/relebactam-non-susceptible	
Genotype	E. coli	K. pneumoniae	P. aeruginosa	E. coli	K. pneumoniae	P. aeruginosa	
(n = 251)	(n = 145)	(n = 181)	(n = 23)	(n = 72)	(n = 237)	
MBL ± ESBL ± AmpC	16	53	90	16	52	90	
OXA-48-like ± ESBL ± AmpC	8	21		3	14		
KPC ± ESBL		7					
GES carbapenemase ± ESBL		1	29		1	28	
GES with undefined spectrum			1			1	
AmpC ± ESBL	23						
ESBL only	187	60	22	4	2	22	
None detectedb	9	2	21		3	71	
Not characterized	8	1	18			25	
AmpC, Ambler class C β-lactamase; GES, Guiana ESBL; KPC, Klebsiella pneumoniae carbapenemase; OXA, oxacillinase.

aIntrinsic AmpC found in P. aeruginosa (PDC, Pseudomonas-derived cephalosporinase) is not shown in this analysis.

bNo acquired β-lactamases included in the screening algorithm were detected.

Discussion

Published studies describing in vitro surveillance data for ceftolozane/tazobactam tested against clinical isolates of Enterobacterales or P. aeruginosa from Mexico or countries in Latin America are very limited.10 The current study expands upon our previous publication describing the in vitro data for imipenem/relebactam tested against clinical isolates of Enterobacterales and P. aeruginosa from Latin American countries, including Mexico. The current study tests and describes a more current (2017–2021), larger isolate dataset from hospitalized patients in Mexico, includes testing of ceftolozane/tazobactam, and offers more in-depth analyses than our earlier publication.

We observed that ceftolozane/tazobactam inhibited 89% of E. coli and 87% of K. pneumoniae isolates (Table 1). An ESBL phenotype was frequently seen among both E. coli (64%) and K. pneumoniae (47%) in Mexico resulting in overall percent susceptible values of <50% for cefepime, ceftazidime and ceftriaxone. Previous studies of clinical isolates have also reported similar or even higher percentages of ESBL-positive E. coli and K. pneumoniae in Mexico.17–19 Ceftolozane/tazobactam was considerably more active than piperacillin/tazobactam (by 15 to 23 percentage points) against both E. coli (74% piperacillin/tazobactam-susceptible) and K. pneumoniae (64%) (Table 1). Ceftolozane/tazobactam percent susceptible values were also >18% higher for ESBL non-CRE phenotype E. coli (86% susceptible versus 68%) and K. pneumoniae (91% versus 48%) than values for piperacillin/tazobactam. A smaller study of 69 E. coli and 15 K. pneumoniae isolates collected in Mexico in 2016–2017 and tested against ceftolozane/tazobactam reported similar results to ours for all isolates tested and for isolates with an ESBL non-CRE phenotype.10 Cumulatively, these data argue strongly against the empirical use of piperacillin/tazobactam, cefepime, ceftazidime and ceftriaxone to treat a serious infection known or suspected to be caused by E. coli, K. pneumoniae or other less common Enterobacterales pathogens in Mexico without review of an isolate-specific antibiogram.

Seventy-seven percent (187/243) of ceftolozane/tazobactam-non-susceptible E. coli were shown to carry an ESBL as their only β-lactamase, 10% (24/243) carried an MBL or an OXA-48-like carbapenemase, 9% (23/243) carried AmpC (22 were CMY-type and one was MIR-type) with or without an ESBL, and 4% (9/243) of isolates did not have an acquired β-lactamase gene identified (Table 3). In contrast, the majority of ceftolozane/tazobactam-non-susceptible K. pneumoniae isolates (57%, 82/144) carried a carbapenemase gene (mostly an MBL or OXA-48-like carbapenemase). The 5%–6% difference observed between E. coli and K. pneumoniae in the percentages of isolates susceptible to imipenem/relebactam and the carbapenems (Table 1) is explained by a similar difference in the percentage of E. coli and K. pneumoniae isolates that carried an MBL or OXA-48-like carbapenemase gene (Table 2). Relebactam is inactive against Ambler class B (MBLs) and class D carbapenemases (e.g. OXA-48-like) and would not be expected to augment the activity of imipenem against isolates carrying these carbapenemases.6

Ceftolozane/tazobactam was the most active agent studied against P. aeruginosa, inhibiting 83% of isolates (Table 1). An earlier, smaller study of 127 P. aeruginosa isolates collected in Mexico in 2016–2017 reported a 19% lower percent susceptible value (64%) than our study; however, the isolates in the former study were also 17% to 22% less susceptible to meropenem (45%), piperacillin/tazobactam (50%) and ceftazidime (50%) than the isolates we tested and details of isolate collection and inclusion were not provided.10 In the current study, imipenem/relebactam (78% susceptible) was 5% less active than ceftolozane/tazobactam. However, a previous study reported that imipenem/relebactam remained active against a subset of ceftolozane/tazobactam-non-susceptible isolates, depending upon the β-lactamases and other resistance mechanisms present in the isolates, suggesting that both agents should be tested against clinical isolates, if possible.20 Specifically, the earlier study observed that in isolates of P. aeruginosa without a detected non-intrinsic β-lactamase gene, the presence of both a PDC (Pseudomonas-derived cephalosporinase) mutation and an indicator of PDC up-regulation frequently resulted in an imipenem/relebactam-susceptible/ceftolozane/tazobactam-non-susceptible phenotype.20 A second study confirmed the finding that ceftolozane/tazobactam-non-susceptible P. aeruginosa isolates without detected non-intrinsic β-lactamase genes were associated with mutations in PDC in combination with PDC up-regulation.21 Percent susceptible values for carbapenems, third- and fourth-generation cephems, piperacillin/tazobactam, and levofloxacin against P. aeruginosa were all compromised in the current study, ranging from 55% to 74% susceptible. Seventy-four percent (120/163) of characterized ceftolozane/tazobactam-non-susceptible P. aeruginosa isolates carried a carbapenemase gene and 13% carried only an ESBL; acquired β-lactamase genes were not detected in 13% of ceftolozane/tazobactam-non-susceptible P. aeruginosa isolates (Table 3).

In the current study, imipenem, meropenem and ertapenem percent susceptible values ranged from 97% to 99% for E. coli (>99% for ESBL non-CRE isolates) and from 91% to 93% for K. pneumoniae (>99% for ESBL non-CRE isolates) (Table 1). Earlier data for Enterobacterales isolates collected in Mexico from 2005 to 2015 showed comparable meropenem and imipenem percent susceptible values for E. coli (95% to >99%) but higher percent susceptible values for K. pneumoniae (95%–99%).19,22,23 In one report, 33% of Enterobacterales isolates from Mexico in 2012–2015 (n = 1862) were ESBL-positive and only 0.8% of isolates carried a carbapenemase.22 We estimated that 1.3% of E. coli, 7.5% of K. pneumoniae and 13.0% of P. aeruginosa isolates infecting hospitalized patients in Mexico in 2017–2021 carried a carbapenemase (Table 2), suggesting an increase in carbapenemase carriage among Enterobacterales over time. MBLs were the most prevalent carbapenemase type observed among E. coli (0.7% of all E. coli isolates), K. pneumoniae (4.8%) and P. aeruginosa (10.0%). In P. aeruginosa, the rate in the current study (10.0%) is double that reported in an earlier study from 2015 to 2017 (4.8% MBL among 524 isolates) from Mexico.24 Imipenem/relebactam percent susceptible values for E. coli and K. pneumoniae correlated closely with the presence of MBLs and OXA-48-like carbapenemases in the current study.

Seventy-eight percent of P. aeruginosa isolates in the current study were imipenem/relebactam-susceptible compared with percent susceptible values of 55% for imipenem and 62% for meropenem (Table 1). A previous report of 1794 P. aeruginosa isolates collected in hospitals in Mexico in 2012–2015 similarly reported that 65% of isolates were meropenem-susceptible.22 Fifty-six percent of characterized imipenem/relebactam-non-susceptible P. aeruginosa in the current study carried an MBL or GES carbapenemase; ESBLs were only identified in 10% of isolates and no acquired β-lactamase was detected in 33% of isolates (Table 3). In the isolates with ESBLs only or where no acquired β-lactamase gene was detected, OprD loss/mutation in combination with PDC derepression likely contributed to the imipenem/relebactam-non-susceptible phenotypes.25 Imipenem is known to be a strong inducer of PDC, and PDC expression levels have been correlated to imipenem MICs in P. aeruginosa with defects in OprD.26 Imipenem/relebactam activity against P. aeruginosa is unaffected by efflux-based resistance and is less affected by OprD loss than imipenem alone.6 Imipenem/relebactam also retains in vitro activity against isolates with KPC or PDC mutations that result in resistance to ceftazidime/avibactam or ceftolozane/tazobactam.27

Amikacin inhibited 91% of E. coli, 90% of K. pneumoniae, and 80% of P. aeruginosa using EUCAST breakpoints (Table 1). Even though it appears highly active in vitro, use of amikacin and other aminoglycosides is widely discouraged in clinical guidelines and by CLSI and EUCAST laboratory in vitro testing standards as all are associated with major toxicity and therapeutic limitations.12,13,28

The strengths of the current study are that it collected isolates from the same six sites in Mexico according to a consistent protocol for 5 years and used reference broth microdilution antimicrobial susceptibility testing and molecular testing performed in a central laboratory. Study limitations include that the number of medical centres participating was limited; sample quotas were used to collect isolates from different infection types that may affect the overall estimates of resistance and β-lactamase prevalence; isolates susceptible to ceftolozane/tazobactam and imipenem/relebactam were not molecularly characterized; and an ESBL non-CRE phenotype was defined as an isolate of E. coli and K. pneumoniae testing as non-susceptible to ceftriaxone (MIC ≥2 mg/L) and susceptible to ertapenem (MIC ≤0.5 mg/L) and did not include clavulanic acid-based phenotypic confirmatory testing.12

Based on our in vitro data, we conclude that ceftolozane/tazobactam and imipenem/relebactam may provide important treatment options for many patients infected with β-lactam-non-susceptible Gram-negative bacilli, including ESBL non-CRE E. coli and K. pneumoniae and β-lactam-non-susceptible P. aeruginosa. Increases in the prevalence of MBL-positive isolates of Gram-negative bacilli have been documented in Mexico and in Latin America and will erode the activities of all newer β-lactam/β-lactamase inhibitor combinations, including ceftolozane/tazobactam and imipenem/relebactam. Ongoing surveillance of the in vitro activities of established and newer antimicrobial agents against Gram-negative pathogens and monitoring for the spread of β-lactamase genes, particularly for MBLs, is critical.

Supplementary Material

dlae077_Supplementary_Data

Acknowledgements

We thank all laboratory participants for their contributions to the SMART global surveillance programme.

Funding

Funding for this research, which included compensation for services related to preparing this manuscript, was provided by Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA.

Transparency declarations

S.H.L. and D.F.S. work for IHMA, which receives funding from Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA for the SMART global surveillance programme. J.A.K. is a consultant to IHMA. F.S., T.P., J.L.V., K.Y. and M.R.M. are employees of Merck Sharp & Dohme LLC, and own stock in Merck & Co. The IHMA authors and J.A.K. have no personal financial interests in the sponsor of this article (Merck Sharp & Dohme LLC).

Supplementary data

Tables S1 and S2 are available as Supplementary data at JAC-AMR Online.
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References

1 Kazmierczak  KM, de Jonge  BLM, Stone  GG  et al  Longitudinal analysis of ESBL and carbapenemase carriage among Enterobacterales and Pseudomonas aeruginosa isolates collected in Europe as part of the international network for optimal resistance monitoring (INFORM) global surveillance programme, 2013–2017. J Antimicrob Chemother  2020; 75 : 1165–73. 10.1093/jac/dkz571 32040168
2 Kiratisin  P, Kazmierczak  KM, Stone  GG. In vitro activity of ceftazidime/avibactam and comparators against carbapenemase-producing Enterobacterales and Pseudomonas aeruginosa isolates collected globally between 2016 and 2018. J Glob Antimicrob Resist  2021; 27 : 132–41. 10.1016/j.jgar.2021.08.010 34478880
3 Bush  K, Bradford  PA. Epidemiology of β-lactamase-producing pathogens. Clin Microbiol Rev  2020; 33 : e00047-19. 10.1128/CMR.00047-19 32102899
4 Merck Sharp & Dohme LLC. ZERBAXA® (ceftolozane and tazobactam) for injection, for intravenous use, prescribing information. 2022. https://www.merck.com/product/usa/pi_circulars/z/zerbaxa/zerbaxa_pi.pdf
5 Livermore  DM, Warner  M, Mushtaq  S. Activity of MK-7655 combined with imipenem against Enterobacteriaceae and Pseudomonas aeruginosa. J Antimicrob Chemother  2013; 68 : 2286–90. 10.1093/jac/dkt178 23696619
6 Young  K, Painter  RE, Raghoobar  SL  et al  In vitro studies evaluating the activity of imipenem in combination with relebactam against Pseudomonas aeruginosa. BMC Microbiol  2019; 19 : 150. 10.1186/s12866-019-1522-7 31272373
7 Merck Sharp & Dohme LLC. RECARBRIO™ (imipenem, cilastatin, and relebactam) for injection, for intravenous use, package insert. 2021. https://www.merck.com/product/usa/pi_circulars/r/recarbrio/recarbrio_pi.pdf
8 European Medicines Agency . Recarbrio (imipenem/cilastatin/relebactam), for intravenous use, product information. 2020. https://www.ema.europa.eu/en/medicines/human/EPAR/recarbrio
9 Karlowsky  JA, Lob  SH, Siddiqui  F  et al  In vitro activity of imipenem/relebactam against non-Morganellaceae Enterobacterales and Pseudomonas aeruginosa in Latin America: SMART 2018–2020. Braz J Infect Dis  2023; 27 : 102775. 10.1016/j.bjid.2023.102775 37169345
10 Garcia-Betancur  JC, De La Cadena  E, Mojica  MF  et al  Comparative in vitro activity of ceftolozane/tazobactam against clinical isolates of Pseudomonas aeruginosa and Enterobacterales from five Latin American countries. Antibiotics  2022; 11 : 1101. 10.3390/antibiotics11081101 36009970
11 CLSI . Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically: M07. 2018.
12 CLSI . Performance Standards for Antimicrobial Susceptibility Testing—Thirty-Third Edition: M100. 2023.
13 EUCAST. Breakpoint tables for interpretation of MICs and zone diameters. Version 13.0, 2023. http://www.eucast.org/clinical_breakpoints/
14 Lob  SH, Biedenbach  DJ, Badal  RE  et al  Antimicrobial resistance and resistance mechanisms of Enterobacteriaceae in ICU and non-ICU wards in Europe and North America: SMART 2011–2013. J Glob Antimicrob Resist  2015; 3 : 190–7. 10.1016/j.jgar.2015.05.005 27873708
15 Estabrook  M, Kazmierczak  KM, Wise  M  et al  Molecular characterization of clinical isolates of Enterobacterales with elevated MIC values for aztreonam-avibactam from the INFORM global surveillance study, 2012–2017. J Glob Antimicrob Resist  2021; 24 : 316–20. 10.1016/j.jgar.2021.01.010 33524556
16 Bortolaia  V, Kaas  RS, Ruppe  E  et al  ResFinder 4.0 for predictions of phenotypes from genotypes. J Antimicrob Chemother  2020; 75 : 3491–500. 10.1093/jac/dkaa345 32780112
17 Jones  RN, Guzman-Blanco  M, Gales  AC  et al  Susceptibility rates in Latin American nations: report from a regional resistance surveillance program (2011). Braz J Infect Dis  2013; 17 : 672–81. 10.1016/j.bjid.2013.07.002 24120834
18 Sader  HS, Castanheira  M, Farrell  DJ  et al  Tigecycline antimicrobial activity tested against clinical bacteria from Latin American medical centres: results from SENTRY antimicrobial surveillance program (2011–2014). Int J Antimicrob Agents  2016; 48 : 144–50. 10.1016/j.ijantimicag.2016.04.021 27291285
19 Ponce-de-Leon  A, Rodriguez-Noriega  E, Morfin-Otero  R  et al  Antimicrobial susceptibility of gram-negative bacilli isolated from intra-abdominal and urinary-tract infections in Mexico from 2009 to 2015: results from the study for monitoring antimicrobial resistance trends (SMART). PLoS One  2018; 13 : e0198621. 10.1371/journal.pone.0198621 29927958
20 Karlowsky  JA, Lob  SH, Estabrook  MA  et al  Susceptibility profile and β-lactamase content of global Pseudomonas aeruginosa isolates resistant to ceftolozane/tazobactam and/or imipenem/relebactam—SMART 2016–21. JAC Antimicrob Resist  2023; 5 : dlad080. 10.1093/jacamr/dlad080 37388237
21 Mojica  MF, De La Cadena  E, Rios  R  et al  Molecular mechanisms leading to ceftolozane/tazobactam resistance in clinical isolates of Pseudomonas aeruginosa from five Latin American countries. Front Microbiol  2022; 13 : 1035609. 10.3389/fmicb.2022.1035609 36353456
22 Karlowsky  JA, Kazmierczak  KM, Bouchillon  SK  et al  In vitro activity of ceftazidime-avibactam against clinical isolates of Enterobacteriaceae and Pseudomonas aeruginosa collected in Latin American countries: results from the INFORM global surveillance program, 2012 to 2015. Antimicrob Agents Chemother  2019; 63 : e01814-18. 10.1128/AAC.01814-18 30670424
23 Morfin-Otero  R, Rodriguez-Noriega  E, Dowzicky  MJ. Antimicrobial susceptibility trends among gram-positive and -negative clinical isolates collected between 2005 and 2012 in Mexico: results from the tigecycline evaluation and surveillance trial. Ann Clin Microbiol Antimicrob  2015; 14 : 53. 10.1186/s12941-015-0116-y 26667651
24 Stone  GG, Ponce-de-Leon  A. In vitro activity of ceftazidime-avibactam and comparators against gram-negative bacterial isolates collected from Latin American centres between 2015 and 2017. J Antimicrob Chemother  2020; 75 : 1859–73. 10.1093/jac/dkaa089 32277820
25 Nichols  WW, de Jonge  BLM, Kazmierczak  KM  et al  In vitro susceptibility of global surveillance isolates of Pseudomonas aeruginosa to ceftazidime-avibactam (INFORM 2012 to 2014). Antimicrob Agents Chemother  2016; 60 : 4743–9. 10.1128/AAC.00220-16 27216074
26 Huber  JL, Young  K, Painter  RE  et al  Inhibition of IMP-1 metallo-β-lactamase in clinical isolates by two succinic acid derivatives. Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), September 17–20, 2000, Toronto, Canada. Abstract 1226.
27 O’Donnell  JN, Lodise  TP. New perspectives on antimicrobial agents: imipenem-relebactam. Antimicrob Agents Chemother  2022; 66 : e00256-22. 10.1128/aac.00256-22 35727059
28 EUCAST. Breakpoints in brackets in EUCAST tables. 2021. http://www.eucast.org/clinical_breakpoints_and_dosing/breakpoints_in_brackets
