Epidemiology of Resistance Determinants Identified in Meropenem-Nonsusceptible Enterobacterales Collected as Part of a Global Surveillance Study, 2018 to 2019

The objective of this study was to describe the frequency of resistance determinants in meropenem-nonsusceptible (MEM-NS) Enterobacterales isolates collected in 2018 and 2019 as a part of the ATLAS global surveillance program. Among a total of 39,368 Enterobacterales isolates collected in 2018 and 2019, 5.7% were MEM-NS (MIC ≥2 μg/mL). Among the different regions, the proportion of MEM-NS isolates ranged from 1.9% (North America) to 8.4% (Asia/Pacific). The majority of MEM-NS isolates collected were of the species Klebsiella pneumoniae (71.5%). Among the MEM-NS Enterobacterales isolates collected, metallo-β-lactamases (MBL) were identified in 36.7%, KPC in 25.5%, and OXA-48-like in 24.1%. The predominance of resistance mechanisms among MEM-NS isolates varied by region: MBLs were dominant in isolates collected in Africa and Middle East (AfME, 49%) and Asia/Pacific (59.4%), OXA-48-like carbapenemases were predominant in Europe (30%), and KPC in Latin America (51.9%) and North America (53.6%). NDM β-lactamases accounted for the majority of MBLs identified (88.4%). Of the 38 carbapenemase variants identified, NDM-1 (68.7%), KPC-2 (54.6%), OXA-48 (54.3%), and VIM-1 (76.1%) were the common variants within their respective families. Among the MEM-NS isolates, 7.9% co-carried two carbapenemases. Notably, the proportion of MEM-NS Enterobacterales increased from 4.9% in 2018 to 6.4% in 2019. The results of this study show a continuation of the trend of increasing carbapenem-resistance within clinical Enterobacterales with mechanisms of resistance varying across different regions. The existential threat to public health posed by the continued spread of nearly untreatable pathogens requires a multifaceted approach to prevent the collapse of modern medicine.

1717. In Vitro Activity of Aztreonam-Avibactam Against Enterobacterales Isolated from Pediatric and Adult Patients Collected During the ATLAS Global Surveillance Program, 2017-2020

Background

The rapid spread of antimicrobial resistance among clinically isolated Enterobacterales (Eba) continues to threaten public health. Aztreonam (ATM) is a monobactam stable to hydrolysis by metallo-β-lactamases (MBLs) and avibactam (AVI) inhibits class A, class C, and some class D serine β-lactamases. ATM-AVI is being developed for use against drug-resistant isolates of Eba, especially those co-producing MBLs and other β-lactamases. This study evaluated the in vitro activity of ATM-AVI and comparators against Eba collected in 2017-2020 from pediatric and adult patients as part of the ATLAS global surveillance program.

Methods

Non-duplicate clinical Eba isolates were collected from 239 sites in 55 countries in Europe, Latin America, Asia/Pacific (excluding mainland China and India), and Middle East/Africa. Susceptibility testing was performed by CLSI broth microdilution and interpreted using CLSI 2022 breakpoints. PCR and sequencing were used to determine the β-lactamase genes present in all isolates with meropenem MIC >1 µg/mL, and Escherichia coli, Klebsiella spp. and Proteus mirabilis with ATM or ceftazidime MIC >1 µg/mL.

Results

MIC₉₀ values for ATM-AVI of 0.12 µg/ml were observed for Eba isolates collected from both pediatric and adult patients. Against all Eba isolates, ≤8 µg/ml of ATM-AVI was sufficient to inhibit 99.97% (pediatric) and 99.95% (adult), whereas ATM alone inhibited only 72.0% and 75.9% of these isolates at ≤8 µg/ml, respectively (table). Among isolates that screened positive for an MBL, MIC₉₀ values were 0.25 µg/ml (pediatric) and 0.5 µg/ml (adult). Among MBL-positive isolates, ATM-AVI inhibited 100% (pediatric) and 99.9% (adult) at concentrations ≤8 µg/ml. In contrast, ATM alone only inhibited 19.0% (pediatric) and 25.3% (adult) of isolates carrying MBLs at ≤8 µg/ml.

Conclusion

Based on MIC₉₀ values, ATM-AVI demonstrated potent in vitro activity against Eba isolated both from pediatric and adult patients. The capability of AVI to potentiate ATM against MBL-positive isolates warrants its continued development.

Disclosures

All Authors: No reported disclosures.

1720. In Vitro Activity of Aztreonam-Avibactam and Comparator Agents Against Enterobacterales from Patients with Urinary Tract Infections Collected During the ATLAS Global Surveillance Program, 2017-2020

Background

β-lactamase-producing Enterobacterales (Eba) frequently carry resistance mechanisms for multiple drug classes, limiting treatment options. Avibactam (AVI) inhibits class A, class C, and some class D serine β-lactamases, while aztreonam (ATM) is refractory to hydrolysis by class B metallo-β-lactamases (MBLs). ATM-AVI is being developed for use against drug-resistant isolates of Eba, especially those co-producing MBLs and serine β-lactamases. This study evaluated the in vitro activity of ATM-AVI and comparators against Eba collected in 2017-2020 from patients with urinary tract infections (UTI) as part of the ATLAS global surveillance program.

Methods

Non-duplicate clinical isolates were collected from 239 sites in 55 countries in Europe, Latin America, Asia/Pacific (excluding mainland China and India), and Middle East/Africa. Susceptibility testing was performed by CLSI broth microdilution and interpreted using CLSI 2022 and FDA (tigecycline) breakpoints. PCR and sequencing were used to determine the β-lactamase genes present in all isolates with meropenem MIC >1 µg/mL, and Escherichia coli, Klebsiella spp. and Proteus mirabilis with ATM or ceftazidime MIC >1 µg/mL.

Results

Based on MIC₉₀ values, ATM-AVI was at least as active as every comparator agent tested against all 15085 Eba isolates collected from UTI (0.12 µg/ml; table), with only five isolates testing with MIC values >8 µg/ml (not shown). Against resistant subsets of isolates, MIC₉₀ values for ATM-AVI were 0.25-0.5 µg/ml, 4- to 8-fold lower than any comparator tested. Against MBL-positive isolates, ATM-AVI MIC values ranged from ≤0.015-2 µg/ml with the exception of one Escherichia coli isolate testing with an MIC value of 16 µg/ml that carried NDM-5, CMY-145, CTX-M-55 and TEM (not shown).

Conclusion

Based on MIC₉₀ values, ATM-AVI was the most potent agent tested against drug-resistant and MBL-positive subsets of Eba collected from UTI. Based on the potent in vitro activity of ATM-AVI, continued development of this combination for treatment of UTI caused by drug-resistant Eba is warranted.

Disclosures

All Authors: No reported disclosures.

1719. In Vitro Activity of Ceftazidime-avibactam and Comparator Agents against Enterobacterales and Pseudomonas aeruginosa Collected from Patients with Bloodstream Infections as Part of the ATLAS Global Surveillance Program, 2017-2020

Background

Avibactam (AVI) is a β-lactamase inhibitor with potent inhibitory activity against Class A, Class C, and some Class D serine β-lactamases. The use of ceftazidime (CAZ) with AVI is approved for several indications. This study evaluated the in vitro activity of CAZ-AVI and comparators against Enterobacterales (Eba) and Pseudomonas aeruginosa (Pae) isolated from the blood of infected patients as part of the ATLAS surveillance program in 2017-2020.

Methods

A total of 67326 Eba and 23051 Pae non-duplicate clinically significant isolates, including 14216 Eba and 3002 Pae isolated from bloodstream infections, were collected in 56 countries in Europe, Latin America, Asia/Pacific (excluding mainland China), and the Middle East/Africa region. Susceptibility testing was performed by CLSI broth microdilution. Meropenem-nonsusceptible (MEM-NS) Eba and Pae isolates were screened for the presence of β-lactamase genes. Only 25% of MEM-NS Pae collected in 2020 were screened.

Results

Of all isolates collected, 97.3% Eba and 90.4% Pae were susceptible to CAZ-AVI (MIC₉₀ values of 0.5 and 8 µg/ml, respectively), more than any comparator tested (table). This was true of blood isolates as well, with 96.9% (Eba) and 90.4% (Pae) isolates susceptible to CAZ-AVI. CAZ-AVI was active against 89.9% of Eba collected from blood that were CAZ-nonsusceptible (NS), more than the comparators tested. While this was not true of CAZ-NS Pae blood isolates (52.9% susceptible to CAZ-AVI), the next most active comparator, amikacin, was active against only 3.9 percentage points more isolates. More MEM-NS isolates that screened negative for MBLs were susceptible to CAZ-AVI than any comparator tested (97.8% of Eba and 80.1% of Pae).

Conclusion

CAZ-AVI provides a valuable therapeutic option for treating bloodstream infections caused by Eba and Pae, except those carrying MBLs.

Disclosures

All Authors: No reported disclosures.

1718. In Vitro Activity of Imipenem/Relebactam against Class C β-lactamase-Positive Enterobacterales in the Asia/Pacific Region: SMART 2018-2020

Background

Imipenem/relebactam (IMR) is a combination of imipenem/cilastatin with the β-lactamase inhibitor relebactam, an inhibitor of class A and C β-lactamases. We evaluated the activity of IMR and comparators against AmpC- and extended-spectrum β-lactamase (ESBL)-producing E. coli and K. pneumoniae as well as against isolates of intrinsic AmpC-producing Enterobacterales species that were collected in 9 countries in Asia/Pacific as part of the global SMART surveillance program.

Methods

In 2018-2020, 48 clinical laboratories in Australia, Hong Kong, Malaysia, New Zealand, Philippines, South Korea, Taiwan, Thailand, and Vietnam each collected up to 250 consecutive, aerobic or facultative, gram-negative pathogens per year from patients with bloodstream, intraabdominal, lower respiratory tract, and urinary tract infections. MICs were determined using CLSI broth microdilution and interpreted with 2022 CLSI breakpoints. Isolates that were ertapenem- (2018 only), imipenem-, IMR-, or ceftolozane/tazobactam-nonsusceptible were screened by PCR and Sanger sequencing for β-lactamases.

Results

As shown in the table, IMR maintained activity against ≥96% K. pneumoniae and E. coli that carried ampC with or without ESBL as well as against those intrinsic ampC carriers (except S. marcescens, 92.7%) among which no additional β-lactamases other than ESBLs were identified. The addition of relebactam increased the susceptibility to imipenem alone by 8-55 percentage points for K. pneumoniae and E. coli carrying AmpC with or without ESBL. Among intrinsic ampC carriers, the largest increase was seen among K. aerogenes (28 percentage points). Relebactam restored susceptibility to 97.3% of imipenem-nonsusceptible (NS) ampC-positive K. pneumoniae (n=73) and to 95.7%, 98.6%, and 37.7% of imipenem-NS isolates of E. cloacae complex (n=92), K. aerogenes (n=147), and S. marcescens (n=61) that carried no acquired β-lactamases. Among the imipenem-NS S. marcescens isolates, 50.8% tested with an IMR MIC of 2 µg/mL, which would be susceptible according to EUCAST guidelines.

Conclusion

IMR showed strong activity against clinical Enterobacterales isolates that carried either acquired or intrinsic ampC with or without ESBL collected in Asia/Pacific.

Disclosures

Fakhar Siddiqui, MD, MBA, Merck & Co., Inc.: employee|Merck & Co., Inc.: Stocks/Bonds Katherine Young, M.S., Merck & Co., Inc.: Stocks/Bonds.

1265. In Vitro Activity of Aztreonam-Avibactam against Klebsiella pneumoniae Isolates Analyzed by Epidemic Lineage and Hypervirulence Factors Collected in China as Part of the ATLAS Global Surveillance Study in 2019

Background

Hypervirulent Klebsiella pneumoniae (hvKp), unlike classical K. pneumoniae (cKp), are often responsible for community-acquired infections in otherwise healthy individuals. The acquisition of hypervirulence genes by sequence type 11 (ST11) carbapenem-resistant (CR) Kp endemic in Asia is a grave threat. Aztreonam-avibactam (ATM-AVI) is a monobactam combined with a β-lactamase inhibitor for the treatment of infections caused by Enterobacterales isolates that carry Class A, B, C and some Class D β-lactamases.

Methods

487 K. pneumoniae isolates were collected from 17 sites in China in 2019 as a part of the ATLAS global surveillance study. 220 isolates with MICs >1 µg/ml to meropenem (MEM), ceftazidime or ATM were selected for whole genome sequencing (Illumina Hiseq 2x150 bp reads). Analyses were carried out using the CLC Genomics Workbench (Qiagen). Presence of the aerobactin synthesis locus differentiated hvKp and cKp. Antimicrobial susceptibility was determined by CLSI broth microdilution.

Results

Of the 487 isolates, MIC₉₀ values for ATM-AVI (0.5 µg/ml; Table) were lower than those for any comparator tested, with only two isolates testing with MIC >4 µg/ml. Of the isolates sequenced, 82/220 (37.3%) were ST11. 53/82 (64.6%) of these ST11 isolates were hvKp (ATM-AVI, MIC₉₀ 1 µg/ml; range, 0.25-4 µg/ml) and showed percentages of susceptibility < 90% to three last-line agents (0% MEM-susceptible (S); 18.9% amikacin (AMK)-S; 88.7% tigecycline (TGC)-S). Isolates of other STs (Non-ST11) were less frequently identified as hvKp (24/138, 17.4%) and more Non-ST-11 hvKp and cKp alike were S to MEM and AMK relative to isolates of ST11 (75.0-86.8% MEM-S; 83.3-96.5% AMK-S). Likewise, the ATM-AVI MIC₉₀ value (0.25 µg/ml) was 4-fold lower for Non-ST11 isolates.

Results Table

Conclusion

CR ST11 hvKp represented at least 10.9% of the collected Kp isolates. ATM-AVI retained potent in vitro activity against these isolates which displayed resistance to a range of last-line agents. CST and TGC also displayed some activity but are limited in utility due to nephrotoxicity and poor accumulation in blood, respectively. The spread of virulence factors leading to the complicated clinical presentation of hvKp infection into multidrug-resistant lineages warrants continued surveillance.

Disclosures

Mark Estabrook, PhD, IHMA (Employee)Pfizer, Inc. (Independent Contractor) Krystyna Kazmierczak, PhD, IHMA (Employee)Pfizer, Inc. (Independent Contractor) Francis Arhin, PhD, Pfizer, Inc. (Employee) Daniel F. Sahm, PhD, IHMA (Employee)Pfizer, Inc. (Independent Contractor)

Molecular characterization of clinical isolates of Enterobacterales with elevated MIC values for aztreonam-avibactam from the INFORM global surveillance study, 2012-2017

OBJECTIVES

While aztreonam-avibactam is a potent β-lactam-β-lactamase-inhibitor combination, reduced in vitro activity against some Enterobacterales isolates has been reported. In this study, globally collected clinical isolates of Enterobacterales with elevated minimum inhibitory concentrations (MICs) for aztreonam-avibactam were examined for potential resistance mechanisms.

METHODS

Isolates with aztreonam-avibactam MICs ≥8 μg/mL (n = 55: Escherichia coli, n = 38; Enterobacter cloacae, n = 10; Klebsiella pneumoniae, n = 3; others, n = 4) and <8 μg/mL (n = 18) collected for the INFORM global surveillance programme were characterized by short read whole-genome sequencing. Sequences were inspected for the presence of β-lactamase genes, penicillin-binding protein (PBP) mutations, and disruptions in the coding sequences of porin genes.

RESULTS

All isolates of E. coli testing with aztreonam-avibactam MIC values ≥8 μg/mL carried a previously documented four-amino-acid insertion in PBP3 at position 333 of YRI(K/N/P). Such mutations were absent in isolates with MICs <2 μg/mL (n = 6). Among other species, carriage of PER- or VEB-type β-lactamases was identified in 10/17 (58.8%) of isolates testing with aztreonam-avibactam MICs ≥8 μg/mL, but no isolates with lower MIC values (n = 11).

CONCLUSIONS

PBP3 mutations are known to confer resistance to aztreonam in E. coli, providing a rationale for the elevated MIC values for aztreonam-avibactam in these isolates. Elevated MICs in other isolates were associated with the carriage of PER-type β-lactamases, which have been previously shown to be inhibited less effectively by avibactam than other Class A β-lactamases and may contribute to this phenotype. Other resistance mechanisms contributing to poor in vitro activity for aztreonam-avibactam in some of these isolates are not yet elucidated.

2448. In vitro Activity of Ceftazidime–Avibactam Against Enterobacteriaceae Causing Intra-abdominal, Urinary Tract and Lower Respiratory Tract Infections Collected in Latin America as Part of the INFORM Global Surveillance Program, 2012–2016

Background

The dissemination of multi-drug-resistant Enterobacteriaceae (MDR Eba) threatens the treatment of Gram-negative infections. Ceftazidime–avibactam (CAZ-AVI) is a novel antimicrobial with activity against Eba producing Class A, C and some Class D β-lactamases. This study evaluates the in vitro activity of CAZ-AVI against Eba isolates from urinary tract infections (UTI), intra-abdominal infections (IAI) and lower respiratory tract infections (LRTI) gathered in Latin America (LA) from 2012 to 2016.

Methods

A total of 7,037 non-duplicate Eba were collected from UTI, IAI, or LRTI in 26 sites in 6 countries in LA, as a part of the INFORM surveillance study from 2012 to 2016. Susceptibility testing was by broth microdilution using CLSI 2018 breakpoints. CAZ-AVI was tested with a fixed concentration of 4 µg/mL avibactam. Meropenem nonsusceptibility prompted β-lactamase screening by PCR and sequencing.

Results

CAZ-AVI demonstrated potent in vitro activity against Eba from UTIs, IAIs and LRTIs (99.6%, 99.8%, and 99.5% susceptible, respectively). CAZ-AVI was active against colistin-resistant and MDR Eba as well as meropenem-non-susceptible Eba not encoding metallo-β-lactamases (96.5%, 98.4% and 99.4% susceptible, respectively) (table).

Conclusion

CAZ-AVI exhibited potent in vitro activity against Eba from UTIs, IAIs and LRTIs isolated in Latin America from 2012 to 2016 and provides a vital alternative to colistin and meropenem when MBLs are not present.

Disclosures

M. Estabrook, Pfizer, Inc.: Consultant, Consulting fee. IHMA, Inc.: Employee, Salary. K. Kazmierczak, Pfizer Inc.: Consultant, Consulting fee. IHMA, Inc.: Employee, Salary. G. G. Stone, Pfizer Inc.: Employee, Salary. AstraZeneca: Former Employee and Shareholder, Salary. D. Sahm, Pfizer Inc.: Consultant, Consulting fee. IHMA, Inc.: Employee, Salary.

Activity of Ceftazidime–Avibactam Against Respiratory Isolates of Enterobacteriaceae and Pseudomonas aeruginosa Collected in Latin America as Part of the INFORM Global Surveillance Program, 2014–2016

Background

The β-lactam/non-β-lactam β-lactamase inhibitor combination ceftazidime-avibactam (CAZ-AVI) is active in vitro against isolates producing class A, C, and some class D β-lactamases, including extended-spectrum β-lactamases, stably derepressed AmpC, and serine carbapenemases. This study evaluated the in vitro activity of CAZ-AVI and comparators against respiratory isolates of Enterobacteriaceae (Eba) and Pseudomonas aeruginosa (Pae) collected in Latin America from 2014–2016 as part of the INFORM surveillance program.

Methods

Non-duplicate isolates from hospitalized patients with lower respiratory tract infections were collected from 24 medical centers in Argentina, Brazil, Chile, Colombia, Mexico, and Venezuela. Susceptibility (S) testing was performed by broth microdilution and interpreted using CLSI breakpoints except for CAZ-AVI (U.S. FDA) and colistin (EUCAST; Ebaonly). AVI was tested at a fixed concentration of 4 µg/mL with doubling dilutions of CAZ. Multidrug resistance (MDR) phenotype was defined as resistant by CLSI breakpoints to sentinel agents from ≥3 drug classes. Isolates were screened for β-lactamase genes by PCR and sequencing.

Results

CAZ-AVI showed potent in vitro activity against Eba isolates (MIC90, 0.5 µg/mL; 99.3% S) and against CAZ-non-susceptible (CAZ-NS), colistin-resistant (CST-R) and MDR subsets (&gt;93% S). CAZ-AVI activity against meropenem-non-susceptible (MEM-NS) Eba (89.7% S) was reduced due to production of metallo-β-lactamases (MBL); MEM-NS MBL-negative isolates were 100% S. CAZ-AVI showed greater in vitro activity against Pae isolates (MIC90, 32 µg/mL; 85.4% S) than CAZ (69.2% S) or MEM (59.9% S). CAZ-AVI activity against CAZ-NS, CST-R, MEM-NS, MEM-NS MBL-negative, and MDR Paeisolates (50.4–92.6% S) also exceeded that of CAZ and MEM against these resistant subsets.

Conclusion

CAZ-AVI is a potential treatment option for respiratory infections in Latin America that are caused by Eba and Pae resistant to commonly used and last-in-line agents.

Funding: This study was sponsored by AstraZeneca. The AstraZeneca product ceftazidime-avibactam was acquired by Pfizer in December 2016.

Disclosures

G. G. Stone, Pfizer: Employee, Salary AstraZeneca: Shareholder, Capital Gains

Variation in phenotypic expression of the Opa outer membrane protein and lipooligosaccharide of Neisseria meningitidis serogroup C causing periorbital cellulitis and bacteremia

Expression of the Opa outer membrane protein varies widely among isolates of Neisseria meningitidis; the clinical significance of this variation is unclear. A sialic-acid acceptor is present in the lipooligosaccharide of some strains of Neisseria and has been shown to render Neisseria gonorrhoeae serum-resistant. We report the case of a patient who had an unusual clinical manifestation of infection due to N. meningitidis serogroup C, periorbital cellulitis with concomitant bacteremia. Clinical isolates from the blood and aspirate of the periorbital cellulitis were identical except for the phenotypic expression of the Opa outer membrane protein in the isolate from the periorbital cellulitis and in the lipooligosaccharide phenotype of the sialic-acid acceptor as defined by monoclonal antibodies. We discuss the laboratory and clinical implications of these findings.

Meningococcal molecular mimicry and the search for an ideal vaccine

The carbohydrates expressed on the surface of meningococcal strains of groups B and C mimic those commonly found on human cells and thus are not functionally antigenic in infancy. In order to develop an effective vaccine, it will be necessary to find ways of circumventing this molecular mimicry. Three possible ways of achieving this are discussed. (i) The surface polysaccharides can theoretically present conformationally different epitopes, some of which might be recognized as antigenic by the host. Experimental evidence is presented that such differences do indeed exist; what is needed is to determine which of these conformations are unique to the organism and hence potentially antigenic. (ii) Precursors of the surface lipooligosaccharides may be unable to mimic human antigens, and so may be potential candidates for vaccine development. (iii) Natural immunity to some strains of meningococci develops in young children who are colonized with strains of Neisseria lactamica, and it is possible that its development could be enhanced by widespread intentional colonization by N. lactamica strains that are particularly efficient inducers of broad immunity.