MICs Of Aztreonam Research Articles

2172. Activity of Cefiderocol and Comparator Agents Against Molecularly Characterized Multidrug-resistant Enterobacterales Clinical Isolates from United States Hospitals (2020–2022)

Abstract Background Cefiderocol (CFDC) is a siderophore cephalosporin that hijacks the iron transport system of Gram-negative bacteria to facilitate cell entry and reach its target. CFDC remains stable to hydrolysis in the presence of serine β-lactamases (ESBLs, KPC, and OXA-type carbapenemases) and metallo-β-lactamases (MBL). CFDC and comparator activities were analyzed against Enterobacterales (ENT), including molecularly characterized isolates, as part of the US SENTRY Antimicrobial Surveillance Program. Methods 11,884 ENT were collected from 33 sites in the USA in 2020–2022. Susceptibility (S) testing was performed by broth microdilution. CFDC testing utilized iron-depleted media. CLSI breakpoints were used. E. coli, K. pneumoniae, and P. mirabilis with ceftriaxone, ceftazidime, or aztreonam MIC ≥ 2 μg/mL plus any ENT displaying an MIC ≥ 2 μg/mL for imipenem (excluding P. mirabilis, P. penneri, and indole-positive Proteeae) or meropenem (MER) were subjected to genome sequencing and screening of β-lactamase genes. Results CFDC (99.8%S), imipenem-relebactam (IMR; 98.0%S), meropenem-vaborbactam (MEV; 100%S), and ceftazidime-avibactam (CZA; 100%S) were active against carbapenem-susceptible ENT that carried ESBL and/or AmpC genes (Table). CFDC (MIC50/90, 0.5/4 μg/mL; 97.6%S) and CZA (MIC50/90, 1/8 μg/mL; 91.5%S) were the most active agents against carbapenem-nonS isolates, whereas IMR (MIC50/90, 0.25/4 μg/mL; 81.2%S) and MEV (MIC50/90, 0.12/8 μg/mL; 87.9%S) had suboptimal activity. CFDC (MIC50/90, 0.5/4 μg/mL), IMR (MIC50/90, 0.12/0.5 μg/mL), MEV (MIC50/90, 0.03/1 μg/mL), and CZA (MIC50/90, 1/2 μg/mL) were active (98.7–100%S) against the KPC subset. CFDC (MIC, 2/4 μg/mL; 90.9%S) was also active against ENT carrying MBL genes, whereas CFDC (MIC, 0.5-2 μg/mL; 100%S) and CZA (0.5-4 μg/mL; 100%S) were active against isolates carrying blaOXA-48–like. Conclusion CFDC activity against ENT was consistent, regardless of isolate phenotypes or genotypes, including against isolates carrying carbapenemase genes other than blaKPC, where approved β-lactam/β-lactamase inhibitor combinations showed limited activity. These data emphasize CFDC as an important option for the treatment of infections caused by ENT and resistant subsets. Disclosures Rodrigo E. Mendes, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|Cipla: Grant/Research Support|Entasis: Grant/Research Support|GSK: Grant/Research Support|Paratek: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support John H. Kimbrough, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support Valerie Kantro, BA, AbbVie: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support Dee Shortridge, PhD, Melinta: Grant/Research Support|Shionogi: Grant/Research Support Helio S. Sader, MD, PhD, FIDSA, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|Cipla: Grant/Research Support|Paratek: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support Mariana Castanheira, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|bioMerieux: Grant/Research Support|Cipla: Grant/Research Support|CorMedix: Grant/Research Support|Entasis: Grant/Research Support|Melinta: Grant/Research Support|Paratek: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support

P14 Surgical source control and colistin therapy for the management of osteomyelitis due to Pseudomonas aeruginosa with difficult-to-treat resistance

Abstract Patient A 45-year-old man from Lagos, Nigeria, now living in the UK, presented to his local hospital with purulent discharge from his knee. During a road traffic accident in 2019, he had sustained open fractures of his femur and tibia. These required surgical fixation and he underwent four surgeries over a 10-month period in Nigeria. He was reportedly on antibiotics throughout this period. In early 2022, he noticed discharge from the knee and was referred to the Bone Infection Unit in Oxford. On examination, left leg shortening and a sinus on the anterior proximal tibia were noted. Knee flexion was reduced to 30 degrees. He was otherwise systemically well. PET-CT revealed two areas of avidity, supporting the clinical diagnosis of fracture-related infection adjacent to a retained tibial plate. Treatment The patient underwent removal of the tibial plate, excision of infected bone, insertion of local antibiotic carrier (Cerament G with vancomycin added) and a medial gastrocnemius flap with split skin grafting. Five out of five intra-operative samples were culture positive for Pseudomonas aeruginosa, with NDM metallo-β-lactamase detected. This was resistant to ceftazidime, meropenem, piperacillin/tazobactam, gentamicin, tobramycin, amikacin, ciprofloxacin, ceftazidime/avibactam, imipenem/cilastatin/relebactam, ceftolozane/tazobactam and cefiderocol. The organism had an aztreonam MIC of 16 mg/mL and a colistin MIC of 2 mg/mL. The patient also had MRSA isolated from all intra-operative samples. Following multidisciplinary team discussion, he was started on aztreonam 2 g QDS and colistin loading with 9 million IU followed by 4.5 million IU BD for the P. aeruginosa and doxycycline 100 mg BD for the MRSA. After 8 days of therapy, he developed a symmetrical body rash, which was felt to be a delayed hypersensitivity reaction to aztreonam and resolved when aztreonam was stopped. He was subsequently treated with colistin monotherapy for 6 weeks via OPAT. Whilst on this treatment, his renal function was monitored regularly with appropriate dose reductions because of renal impairment. Follow-up at 9 months demonstrates good recovery with no pain or symptom recurrence. Conclusions This case illustrates the challenges of managing fracture-related infections with extensively drug-resistant organisms and the importance of multi-disciplinary input. Drug-resistant infections requiring prolonged courses of antibiotics can be successfully managed using an OPAT service. Finally, this case emphasizes the importance of understanding global patterns of antimicrobial resistance and stewardship to identify cases that are at risk of being infected with drug-resistant bacteria especially where there may be long intervals between establishment of the infection and presentation to healthcare services.

1707. In vitro Activities of Ceftazidime-Avibactam and Comparator Agents against Enterobacterales and Pseudomonas aeruginosa Collected < 48 Hours and ≥48 Hours Post-Admission from Hospitalized Adult Patients, ATLAS Global Surveillance Program 2017-2020

Abstract Background Effective treatments for Gram-negative infections have dwindled with the emergence and dissemination of multi-drug resistant Enterobacterales (Ent) and Pseudomonas aeruginosa (Psa). Fortunately, ceftazidime-avibactam (CAZ-AVI) has activity against Ent and Psa isolates that produce Class A, C and some Class D β-lactamases. This study examined the in vitro activity of CAZ-AVI and comparators against Ent and Psa from presumed community-acquired (CA; cultured < 48 h after hospital admission) and hospital-acquired (HA; cultured ≥48 h post-admission) infections collected from adult patients as part of the ATLAS surveillance program, 2017-2020. Methods 59,904 non-duplicate Ent and 2,504 Psa isolates from adult patients (≥18 y.o.) were collected from 271 sites in 57 countries as part of ATLAS 2017-2020 (excluding North America) for which the length of hospitalization stay was specified. Antimicrobial susceptibility testing was by broth microdilution according to CLSI guidelines and analyzed using CLSI 2022 breakpoints. Ent isolates testing with meropenem MICs >1 µg/mL and Escherichia coli, Klebsiella pneumoniae, K. oxytoca, K. variicola, and Proteus mirabilis testing with ceftazidime and/or aztreonam MICs >1 mg/L were genetically screened for β-lactamases. For Psa, meropenem MIC >2 µg/mL triggered β-lactamase screening. In 2020, approximately 25% of the meropenem non-susceptible isolates were screened. Results For Ent, CAZ-AVI was the most active agent examined against both the CA- and HA-infection population of isolates. The percentage of Ent isolates susceptible to CAZ-AVI was 2.6% and 5.3% higher compared to meropenem for the CA- and HA-infection sets, respectively. Considering both the CA- and HA- infection Psa isolates, CAZ-AVI was also the most active agent among comparators, showing %S rates 12.8% and 19.3% higher than meropenem, respectively. Conclusion Against Ent and Psa from adult patients, CAZ-AVI exhibited excellent in vitro activity regardless of whether the pathogen was isolated < 48 hrs. or ≥48 hrs. post hospital admission. The slightly decreased susceptibility to CAZ-AVI for the HA Psa isolates as compared to the CA isolates, as well as the relatively low %S rates for comparators, reinforces difficult-to-treat nature of nosocomial infections. Disclosures All Authors: No reported disclosures.

1709. In Vitro Activity of Ceftazidime-Avibactam and Comparator Agents Against MDR Enterobacterales and Pseudomonas aeruginosa Collected in Latin America, ATLAS Global Surveillance Program 2018-2020

Abstract Background Multidrug-resistant (MDR) Gram-negative bacteria are an increasing worldwide problem. Ceftazidime-avibactam (CAZ-AVI) is a β-lactam/non-β-lactam β-lactamase inhibitor combination that can inhibit class A, C, and some class D β-lactamases, enzymes that contribute to MDR. This study examined the in vitro activity of CAZ-AVI and comparators against MDR Enterobacterales and Pseudomonas aeruginosa isolates collected from patients in Latin America. Methods 9193 non-duplicate Enterobacterales (Ent) and 3225 P. aeruginosa (Psa) isolates from were collected from 36 sites in 10 Latin American countries as part of ATLAS 2018-2020. Antimicrobial susceptibility testing was by broth microdilution according to CLSI guidelines and analyzed using CLSI 2022 breakpoints. MDR was defined as resistant (R) to ≥3 of 7 sentinel drugs: amikacin (AMK), aztreonam (ATM), cefepime (FEP), colistin (CST), levofloxacin (LVX), meropenem (MEM), and piperacillin-tazobactam (TZP). Ent isolates testing with meropenem MICs >1 µg/mL and Escherichia coli, Klebsiella pneumoniae, K. oxytoca, K. variicola, and Proteus mirabilis testing with ceftazidime and/or aztreonam MICs >1 mg/L were genetically screened for β-lactamases. Psa with meropenem MIC >2 µg/mL were screened in 2018-2019. In 2020, approximately 25% of qualifying Psa were screened. Results The activity of CAZ-AVI and comparators against all isolates and the MDR subsets is shown in the table. CAZ-AVI was active against the full collection of Enterobacterales isolates with 96.7% of the population susceptible and an MIC90 value of 1 µg/mL, and maintained considerable activity against the MDR subset, inhibiting 86.5% of the isolates, a value higher than comparator agents. For the full collection of Psa, 86.6% of the isolates were susceptible to CAZ-AVI, again the highest %S among the comparator drugs. Versus the MDR subset of Psa, CAZ-AVI displayed a 45.8% susceptibility rate, approximately 10% higher than the nearest comparator, amikacin. Conclusion The in vitro data suggest that CAZ-AVI can be an effective therapeutic for infections caused by MDR Enterobacterales in Latin America. MDR among P. aeruginosa remains challenging, although a significant percentage are inhibited by CAZ-AVI. Disclosures All Authors: No reported disclosures.

1708. In vitro Activities of Ceftazidime-Avibactam and Comparator Agents against Enterobacterales and Pseudomonas aeruginosa Collected < 48 Hours and ≥48 Hours Post-Admission from Hospitalized Pediatric Patients, ATLAS Global Surveillance Program 2017-2020

Abstract Background Ceftazidime-avibactam (CAZ-AVI) is a β-lactam combined with a diazabicyclooctane-β-lactamase inhibitor for treatment of infections caused by Gram-negative pathogens. Ceftazidime-avibactam is active against Enterobacterales (Ent) and P. aeruginosa (Psa) isolates that produce Class A, C and some Class D β-lactamases. This study examined the in vitro activity of CAZ-AVI and comparators against Ent and Psa from presumed community-acquired (CA; cultured < 48 h after hospital admission) and hospital-acquired (HA; cultured ≥48 h post-admission) infections collected from pediatric patients as part of the ATLAS surveillance program, 2017-2020. Methods 5765 non-duplicate Ent and 1987 Psa isolates from pediatric patients (≤17 y.o.) were collected from 241 sites in 54 countries as part of ATLAS 2017-2020 (excluding North America) for which the length of hospitalization stay was specified. Antimicrobial susceptibility testing was by broth microdilution according to CLSI guidelines and analyzed using CLSI 2022 breakpoints. Ent isolates testing with meropenem MICs >1 µg/mL and Escherichia coli, Klebsiella pneumoniae, K. oxytoca, K. variicola, and Proteus mirabilis testing with ceftazidime and/or aztreonam MICs >1 mg/L were genetically screened for β-lactamases. For Psa, meropenem MIC >2 µg/mL triggered β-lactamase screening. In 2020, approximately 25% of the meropenem non-susceptible isolates were screened. Results Against Ent, the in vitro activity of CAZ-AVI exceeded that of meropenem and other tested agents for both the presumed CA- and HA-infection sets. The addition of AVI to CAZ increased the %S from 76.1% to 97.5% for the CA-infection population, and from 62.2% to 96.1% for the HA-infection population. For Psa There was a larger difference between the %S to CAZ-AVI of the presumed CA set (93.3% S) and the HA set (89.8% S). For both Psa populations, CAZ-AVI was the most active drug among the comparators. Conclusion CAZ-AVI demonstrated potent in vitro activity against Enterobacterales and P. aeruginosa isolates collected globally from pediatric patients in 2017-2020, regardless of whether is infection was community-or hospital-acquired. Disclosures All Authors: No reported disclosures.

642. In Vitro Activity of Cefiderocol and Comparator Agents Against Molecularly Characterized Enterobacterales Clinical Isolates Causing Infection in United States Hospitals (2020-2021)

Abstract Background Cefiderocol (CFDC) is a siderophore cephalosporin that hijacks the Gram-negative bacteria iron transport system to facilitate cell entry and reach its target. CFDC remains stable to hydrolysis in the presence of serine β-lactamases (ESBLs, KPC, and OXA-type carbapenemases) and metallo-β-lactamases (MBL). CFDC and comparator activities were analyzed against Enterobacterales (ENT), including molecularly characterized isolates, as part of the SENTRY Antimicrobial Surveillance Program in the USA. Methods 8,328 ENT were collected from 32 sites in 2020-2021. Susceptibility testing was performed by broth microdilution. CFDC testing used iron-depleted media. CLSI breakpoints were used. E. coli, K. pneumoniae, and P. mirabilis with ceftriaxone, ceftazidime, or aztreonam MIC ≥2 μg/mL, and any ENT displaying MIC ≥2 μg/mL for imipenem (excluded for P. mirabilis, P. penneri, and indole-positive Proteeae) or meropenem (MER), were subjected to genome sequencing and screening of β-lactamase genes. Results In general, CFDC (≥ 99.9% susceptible [S]), imipenem-relebactam (IMR; 99.4-100%S), meropenem-vaborbactam (MEV; 100%S), and ceftazidime-avibactam (CZA; 100%S) were active against carbapenem-susceptible ENT that carried ESBL and/or AmpC genes (Table). CFDC (MIC50/90, 0.5/4 μg/mL; 98.4%S) and CZA (MIC50/90, 1/8 μg/mL; 91.2%S) were the most active agents against carbapenem-nonS isolates, whereas IMR (MIC50/90, 0.25/4 μg/mL; 81.6%S) and MEV (MIC50/90, 0.12/8 μg/mL; 86.4%S) had suboptimal activity. CFDC (MIC50/90, 0.5/2 μg/mL), IMR (MIC50/90, 0.12/0.5 μg/mL), MEV (MIC50/90, 0.03/0.5 μg/mL), and CZA (MIC50/90, 1/2 μg/mL) were active (100%S) against the KPC subset. CFDC (MIC, 0.5-4 μg/mL; 100%S) was also active against ENT carrying MBL genes, whereas CFDC (MIC, 0.5-2 μg/mL; 100%S) and CZA (1-4 μg/mL; 100%S) were active against isolates carrying blaOXA-48-like. Conclusion CFDC activity was consistent, regardless of phenotypes or genotypes, including against isolates carrying carbapenemase genes other than blaKPC, where approved β-lactam/β-lactamase inhibitor combinations showed limited activity. These data reinforce CFDC as an important option for the treatment of infections caused by ENT and resistant subsets. Disclosures Rodrigo E. Mendes, PhD, AbbVie: Grant/Research Support|Cidara: Grant/Research Support|GSK: Grant/Research Support|Melinta: Grant/Research Support|Nabriva Therapeutics: Grant/Research Support|Office for Assistant Secretary of Defense for Health Affairs: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support|Spero Therapeutics: Grant/Research Support John H. Kimbrough, PhD, AbbVie: Grant/Research Support|GSK: Grant/Research Support Valerie Kantro, BA, AbbVie: Grant/Research Support|GSK: Grant/Research Support|Melinta: Grant/Research Support|Shionogi: Grant/Research Support Dee Shortridge, PhD, AbbVie: Grant/Research Support|JMI Laboratory: Employee|Melinta: Grant/Research Support|Menarini: Grant/Research Support|Shionogi: Grant/Research Support Helio S. Sader, MD, PhD, AbbVie: Grant/Research Support|Cidara: Grant/Research Support|Melinta: Grant/Research Support|Nabriva Therapeutics: Grant/Research Support|Pfizer: Grant/Research Support Jennifer M. Streit, BS, MT(ASCP), Cidara: Grant/Research Support|GSK: Grant/Research Support|Melinta: Grant/Research Support|Shionogi: Grant/Research Support Mariana Castanheira, PhD, AbbVie: Grant/Research Support|Cidara: Grant/Research Support|GSK: Grant/Research Support|Melinta: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support.

Resistance to aztreonam-avibactam due to CTX-M-15 in the presence of penicillin-binding protein 3 with extra amino acids in Escherichia coli.

Aztreonam-avibactam is a promising combination to treat carbapenem-resistant Enterobacterales including coverage for metallo-β-lactamases. Escherichia coli strains resistant to aztreonam-avibactam have emerged but resistance mechanisms remain to be elucidated. We performed a study to investigate the mechanism for aztreonam-avibactam in a carbapenem-resistant Escherichia coli clinical strain. This strain was resistant to aztreonam-avibactam (aztreonam MIC, 16 mg/L in the presence of 4 mg/L avibactam). Whole genome sequencing revealed that the strain carried metallo-β-lactamase gene bla NDM-4 and the extended-spectrum β-lactamase (ESBL) gene bla CTX-M-15 and had a YRIK four amino acid insertion in penicillin-binding protein 3 (PBP3). bla CTX-M-15 was cloned into pET-28a(+), followed by the transformation, with the gene, of E. coli strain 035125∆pCMY42 possessing the YRIK insertion in PBP3 and strain BL21 with the wildtype PBP3. bla CTX-M-14, another common ESBL gene, and bla CTX-M-199, a hybrid of bla CTX-M-14 and bla CTX-M-15 were also individually cloned into both E. coli strains for comparison. Aztreonam-avibactam resistance was only observed in the E. coli strains with the YRIK insertion in PBP3 that produced CTX-M-15 or its hybrid enzyme CTX-M-199. Checkerboard titration assays were performed to determine the synergistic effects between aztreonam-avibactam and ceftazidime or meropenem. Doubling avibactam concentration in vitro reversed aztreonam-avibactam resistance, while the combination of aztreonam-avibactam and ceftazidime or meropenem did not. In conclusion, CTX-M enzymes with activity against aztreonam, (e.g., CTX-M-15 and CTX-M-199), can confer resistance in the combination of PBP3 with YRIK insertions in metallo-β-lactamase-producing carbapenem-resistant E. coli. Doubling the concentration of avibactam may overcome such resistance.

Efficient Suppression of Natural Plasmid-Borne Gene Expression in Carbapenem-Resistant Klebsiella pneumoniae Using a Compact CRISPR Interference System.

There is an urgent need for efficient tools for genetic manipulation to assess plasmid function in clinical drug-resistant bacterial strains. To address this need, we developed an all-in-one CRISPR interference (CRISPRi) system that easily inhibited the gene expression of a natural multidrug-resistant plasmid in an sequence type 23 (ST23) Klebsiella pneumoniae isolate. We established an integrative CRISPRi system plasmid, pdCas9gRNA, harboring a dcas9 gene and a single guide RNA (sgRNA) unit under the control of anhydrotetracycline-induced and J23119 promoters, respectively, using a one-step cloning method. This system can repress the single resistance gene blaNDM-1, with a >1,000-fold reduction in the meropenem MIC, or simultaneously silence the resistance genes blaNDM-1 and blaSHV-12, with a 16-fold and 8-fold respective reduction in the meropenem and aztreonam MIC on a large natural multidrug-resistant pNK01067-NDM-1 plasmid in an ST23 K. pneumoniae isolate. Furthermore, an sgRNA targeting the blaNDM-1 promoter region can silence the entire blaNDM-1-bleMBL-trpF operon, confirming the existence of the operon. We also used this tool to knock down the multicopy resistance gene blaKPC-2 in pathogenic Escherichia coli, increasing the susceptibility to meropenem. In a word, the all-in-one CRISPRi system can be used for efficient interrogation of indigenous plasmid-borne gene functions, providing a rapid, easy genetic manipulation tool for clinical K. pneumoniae isolates.

1264. In Vitro Activity of Ceftazidime-Avibactam and Comparator Agents Against Enterobacterales and Pseudomonas aeruginosa Collected < 48 Hours and ≥48 Hours Post-Admission from Pediatric Patients, ATLAS Surveillance Program 2016-2019

BackgroundCeftazidime-avibactam (CAZ-AVI) is a β-lactam/non-β-lactam β-lactamase inhibitor combination with in vitro activity against Enterobacterales (Ent) and Pseudomonas aeruginosa (Psa) carrying Class A, C and some Class D β-lactamases. We examined the in vitro activity of CAZ-AVI and comparators against presumed community-acquired (CA; cultured < 48 h after hospital admission) and hospital-acquired (HA; cultured ≥48 h post-admission) isolates collected from pediatric patients as part of the ATLAS surveillance program.Methods6654 non-duplicate isolates were collected in 52 countries in Europe (n=3423), Latin America (n=1323), Middle East/Africa (n=1177), and Asia/Pacific (excluding China; n=731) from patients (newborn to 17 y) with lower respiratory tract (LRTI; n=1687), urinary tract (UTI; n=1631), bloodstream (BSI; n=1149), skin and soft tissue (SSTI; n=1122), and intra-abdominal (IAI; n=981) infections. Susceptibility testing was performed by CLSI broth microdilution and values were interpreted using CLSI 2021 breakpoints. CAZ-AVI was tested at a fixed concentration of 4 µg/mL AVI. Isolates with CAZ or aztreonam MICs ≥2 µg/mL (Escherichia coli, Klebsiella spp., Proteus mirabilis) or meropenem MICs ≥2 µg/mL (all Ent species) or ≥4 µg/mL (Psa) were screened for β-lactamase genes.ResultsThe in vitro activity of CAZ-AVI exceeded that of meropenem and other tested β-lactams against Ent (97.8% susceptible (S)) and Psa (92.1% S) collected globally from pediatric patients (Table). Percentages of susceptibility to CAZ-AVI ranged from 95.4-99.2% among CA Ent from different infection types and were reduced 0.6-1.3% among HA isolates from LRTI, UTI, SSTI, and IAI. Susceptibility to CAZ-AVI was also similar (92.6-95.8% S) among CA Psa from different infection types and was reduced 1.2-7.0% among HA isolates. Larger differences in susceptibility were typically seen for the tested comparator β-lactams. For Ent, the lowest percentages of susceptibility to the tested β-lactams were observed among isolates from BSI, while the pattern was less clear for Psa.Results Table ConclusionCAZ-AVI could provide a valuable therapeutic option for treatment of CA and HA infections caused by Ent and Psa in pediatric patients.Disclosures Krystyna Kazmierczak, PhD, IHMA (Employee)Pfizer, Inc. (Independent Contractor) Sibylle Lob, PhD, IHMA (Employee)Pfizer, Inc. (Independent Contractor) Gregory Stone, PhD, AztraZeneca (Shareholder, Former Employee)Pfizer, Inc. (Employee) Daniel F. Sahm, PhD, IHMA (Employee)Pfizer, Inc. (Independent Contractor)

Pseudomonas aeruginosa Susceptibility Patterns and Associated Clinical Outcomes in People with Cystic Fibrosis following Approval of Aztreonam Lysine for Inhalation.

The approval of aztreonam lysine for inhalation solution (AZLI) raised concerns that additional antibiotic exposure would potentially affect the susceptibility profiles of Pseudomonas aeruginosa isolates from cystic fibrosis (CF) patients. This 5-year, prospective, observational study tracked susceptibility changes and clinical outcomes in CF patients in the United States with chronic P. aeruginosa infection. Sputum cultures were collected annually (2011 to 2016). The primary study endpoint was the proportion of subjects whose least susceptible P. aeruginosa isolate had an aztreonam MIC that was >8 μg/ml (parenteral breakpoint) and increased ≥4-fold compared with the least susceptible isolate from the previous year. Annualized data for pulmonary exacerbations, hospitalizations, and percent of predicted forced expiratory volume in 1 s (FEV1% predicted) were obtained from the CF Foundation Patient Registry and compared between subjects meeting and those not meeting the primary endpoint. A total of 510 subjects were enrolled; 334 (65%) completed the study. A consistent proportion of evaluable subjects (13 to 22%) met the primary endpoint each year, and AZLI use during the previous 12 months was not associated with meeting the primary endpoint. While the annual declines in lung function were comparable for subjects meeting and those not meeting the primary endpoint, more pulmonary exacerbations and hospitalizations were experienced by those who met it. The aztreonam susceptibility of P. aeruginosa remained consistent during the 5-year study. The relationship between P. aeruginosa isolate susceptibilities and clinical outcomes is complex; reduced susceptibility was not associated with an accelerated decline in lung function but was associated with more exacerbations and hospitalizations, likely reflecting increased overall antibiotic exposure. (This study has been registered at ClinicalTrials.gov under identifier NCT01375036.).

What's left in the cupboard? Older antimicrobials for treating gonorrhoea.

Neisseria gonorrhoeae has developed resistance to all antimicrobials used to treat gonorrhoea, with even ceftriaxone being undermined. It is therefore important to examine any potential to redeploy older antimicrobials routinely used for other infections to treat ceftriaxone-resistant gonococcal infections. We examined the susceptibility of N. gonorrhoeae to aztreonam, chloramphenicol, co-trimoxazole, fosfomycin, piperacillin/tazobactam and rifampicin. N. gonorrhoeae isolates (n = 94) were selected to include a range of antimicrobial susceptibilities: 58 were collected in the Gonococcal Resistance to Antimicrobials Surveillance Programme; 17 were clinical isolates referred to the PHE reference laboratory; and 19 were control strains. MICs were determined by agar dilution for the six study antimicrobials and for ceftriaxone and azithromycin as comparators. There was correlation between piperacillin/tazobactam and ceftriaxone MICs, but all five isolates with high ceftriaxone MICs (>0.5 mg/L) were inhibited by piperacillin/tazobactam at 0.06-0.5 mg/L. Aztreonam MICs for ceftriaxone-resistant isolates exceeded those of ceftriaxone. Among non-β-lactams, fosfomycin and co-trimoxazole had low, tightly clustered MICs, suggesting widespread susceptibility, rifampicin split the collection into highly susceptible and highly resistant groups and chloramphenicol had a wide MIC distribution. Although unsuitable for empirical use, piperacillin/tazobactam, fosfomycin, co-trimoxazole, rifampicin and, possibly, chloramphenicol could be considered for individual patients with ceftriaxone-resistant gonococcal infection once MICs are known. Wider surveillance of the susceptibility of N. gonorrhoeae to these agents is needed, along with clinical trials and the establishment of clinical breakpoints for N gonorrhoeae.

1568. In Vitro Activity of Ceftazidime-Avibactam and Comparator Agents Against Enterobacterales and Pseudomonas aeruginosa Collected &amp;lt; 48 Hours and ≥48 Hours Post-Admission from Pediatric Patients, ATLAS Surveillance Program 2015-2018

BackgroundCeftazidime-avibactam (CAZ-AVI) is a β-lactam/non-β-lactam β-lactamase inhibitor combination with in vitro activity against Enterobacterales (Ent) and Pseudomonas aeruginosa (Psa) carrying Class A, C and some Class D β-lactamases. We examined the in vitro activity of CAZ-AVI and comparators against presumed community-acquired (CA; cultured < 48 h after hospital admission) and hospital-acquired (HA; cultured ≥48 h post-admission) isolates collected from pediatric patients as part of the ATLAS surveillance program.Methods6023 non-duplicate isolates were collected in 50 countries in Europe (n=3122), Latin America (n=1220), Middle East/Africa (n=1007), and Asia/Pacific (excluding China; n=674) from patients (newborn to 17 y) with lower respiratory tract (LRTI; n=1641), urinary tract (UTI; n=1595), skin and soft tissue (SSTI; n=1027), intra-abdominal (IAI; n=949), and bloodstream (BSI; n=811) infections. Susceptibility testing was performed by CLSI broth microdilution and values were interpreted using CLSI 2020 breakpoints. CAZ-AVI was tested at a fixed concentration of 4 µg/mL AVI. Isolates with CAZ or aztreonam MICs ≥2 µg/mL (Escherichia coli, Klebsiella spp., Proteus mirabilis) or meropenem MICs ≥2 µg/mL (all Ent species) or ≥4 µg/mL (Psa) were screened for β-lactamase genes.ResultsThe in vitro activity of CAZ-AVI exceeded that of meropenem and other tested β-lactams against Ent (98.5% susceptible (S)) and Psa (93.1% S) collected globally from pediatric patients (Table). Percentages of susceptibility to CAZ-AVI ranged from 96.8-99.3% among CA Ent from different infection types and were reduced 0.4-1.0% among HA isolates from SSTI, IAI and BSI. Susceptibility to CAZ-AVI was also similar (92.7-95.4% S) among CA Psa from different infection types and was reduced 0.1-4.4% among HA isolates. For both Ent and Psa, the lowest percentages of susceptibility to the tested β-lactams were observed among isolates from BSI, which included a higher proportion of isolates carrying extended-spectrum β-lactamases and/or carbapenemases than isolates from other infection types.Table ConclusionCAZ-AVI could provide a valuable therapeutic option for treatment of CA and HA infections caused by Ent and Psa in pediatric patients.DisclosuresKrystyna Kazmierczak, PhD, IHMA (Employee)Pfizer, Inc. (Consultant) Greg Stone, PhD, AztraZeneca (Shareholder, Former Employee)Pfizer, Inc. (Employee) Daniel F. Sahm, PhD, IHMA (Employee)Pfizer, Inc. (Consultant)Shionogi & Co., Ltd. (Independent Contractor)

1607. Dual Therapy with Aztreonam &amp; Ceftazidime/Avibactam Against Multi-Drug Resistant Stenotrophomonas maltophilia on Tricuspid Valve Endocarditis

BackgroundAntimicrobial resistance in Stenotrophomonas maltophilia is one of the most complex among Gram-negatives. Presence of regulating non-specific antimicrobial class efflux pumps and chromosomal encoded L1 metallo-betalactamase (Ambler Class B) and L2 betalactamase (Ambler Class A) are responsible for few clinically active antimicrobials and pan-drug resistant strains.MethodsA 38 year old male with a history of IV drug use, chronic hepatitis C, and recent MSSA endocarditis was admitted with sepsis. Workup revealed tricuspid valve endocarditis with pulmonary septic emboli due to S. maltophilia. Initial antibiotics were levofloxacin (LVX), metronidazole, and piperacillin-tazobactam (TZP) followed by LVX and minocycline (MIN). He had valve replacement on day 6. Repeat blood cultures and valve tissue culture revealed pan-resistant S. maltophilia (resistant: ceftazidime (CAZ), LVX, MIN, TMP/SMX, chloramphenicol; intermediate: MIN; eravacycline MIC 8 μg/mL; tigecycline MIC 16 μg/mL). Microbiology Department was consulted for additional antimicrobial options. In vitro testing for aztreonam (ATM) with ceftazidime/avibactam (CZA) was recommended.ResultsSynergy testing between ATM and CZA was performed by positioning ATM strip over the area where CZA had been previously been placed and removed after 10 minutes of incubation. The interception of the growth with the ATM strip was read. In presence of avibactam, ATM MIC was 4 μg/mL, 6 two-fold dilutions lower than ATM without CZA. MIC for ATM (256 μg/mL), CAZ (256 μg/mL) and CZA (32 μg/mL) were tested individually. ATM with CZA was recommended as a salvage treatment based on in vitro result. Patient completed 6 weeks of ATM with CZA along with MIN. He achieved microbiologic clearance and clinical recovery from infection. At the end of treatment, he experienced episodes of refractory ascites. With complex comorbidities, patient was not a transplant candidate and transitioned to hospice two weeks later.ConclusionAlthough the surgical excision was key, treatment with ATM and CZA provided effective antimicrobial treatment in the setting of persistent positive blood culture. ATM with CZA should be considered for cases of pan-drug resistant S. maltophilia with limited treatment options.Disclosures All Authors: No reported disclosures

In vitro efficacy of ceftazidime-avibactam, aztreonam-avibactam and other rescue antibiotics against carbapenem-resistant Enterobacterales from the Arabian Peninsula

ObjectivesOur aim was to assess the susceptibility of carbapenem-resistant Enterobacterales (CRE) from the Arabian Peninsula to a broad spectrum of antibiotics, including fosfomycin, ceftazidime-avibactam, and aztreonam-avibactam. Methods1192 non-repeat CRE isolated in 2009–2017 from 33 hospitals in five countries of the Arabian Peninsula were tested. The minimum inhibitory concentration of 14 antibiotics was determined. Carbapenemase and 16S methylase genes were detected by PCR. Clonality was assessed by PFGE. ResultsThe highest rate of susceptibility was detected to aztreonam-avibactam (95.5%) followed by colistin (79.8%), fosfomycin (71.8%) and tigecycline (59.9%). Isolates co-producing two carbapenemases (12.4%) were the least susceptible. Aminoglycoside susceptibility was affected by the frequent production of a 16S methylase. Susceptibility to ceftazidime-avibactam was impacted by the high rate of metallo-beta-lactamase producers (46.3%), while aztreonam-avibactam resistance occurred mostly in clonally unrelated, carbapenemase non-producing Escherichia coli. ConclusionOf the currently available drugs: colistin, tigecycline, and ceftazidime-avibactam co-administered with aztreonam appear to be the most effective to treat CRE infections. However, the presence of non-clonal CRE isolates, in which avibactam does not lower the aztreonam MIC below the clinical breakpoint, is of notable concern. Based on the relatively high rate of fosfomycin susceptibility, it would be desirable to license parenteral fosfomycin in the region.

In vitro selection of aztreonam/avibactam resistance in dual-carbapenemase-producing Klebsiella pneumoniae.

To examine the in vitro selection of aztreonam/avibactam resistance among MBL-producing Klebsiella pneumoniae and to understand the mechanism of increased resistance. The MICs of aztreonam were determined with and without avibactam (4 mg/L) using a broth microdilution method. Single-step and multi-step mutant selection was conducted on five MBL-producing K. pneumoniae strains, including two dual carbapenemase producers. Genomic sequencing and gene cloning were performed to investigate the mechanism of increased resistance. We examined the MICs for 68 MBL-producing K. pneumoniae isolates, including 13 dual carbapenemase producers. Compared with aztreonam alone, the addition of avibactam (4 mg/L) reduced the MICs for all isolates by >128-fold, with MIC50 and MIC90 values of 0.25 and 1 mg/L, respectively. One NDM-1-, OXA-48-, CTX-M-15- and CMY-16-positive ST101 K. pneumoniae strain was selected to be resistant to aztreonam/avibactam, with a >16-fold increase in MIC (>128 mg/L). WGS revealed that the resistant mutants lost the blaNDM-1 gene, but acquired amino acid substitutions in CMY-16 (Tyr150Ser and Asn346His). Construction of blaCMY-16 mutants confirmed that the substitutions (Tyr150Ser and Asn346His) were primarily responsible for the decreased susceptibility to aztreonam/avibactam. In addition, transfer of blaCMY-16 mutant (Tyr150Ser and Asn346His) plasmid constructs into certain clinical carbapenemase-producing isolates demonstrated >64-fold increased MICs of aztreonam/avibactam and aztreonam/avibactam/ceftazidime. Aztreonam in combination with avibactam showed potent in vitro activity against MBL-producing K. pneumoniae. However, our study suggested the likelihood of aztreonam/avibactam resistance among MBL- and AmpC-co-producing strains and clinical practice should beware of the possibility of the emerging resistance.

Synergistic in vitro activity between aztreonam and amoxicillin-clavulanate against Enterobacteriaceae-producing class B and/or class D carbapenemases with or without extended-spectrum β-lactamases.

Introduction. Carbapenemase-producing Enterobacteriaceae have become a major public health concern over the last decade and treatment options are limited.Aims. We evaluated the synergistic activity of the combination of aztreonam (ATM) and clavulanate for 41 β-lactam-resistant clinical isolates harbouring class B or/and class D carbapenemases combined or not with extended-spectrum β-lactamases (ESBLs).Methodology. The MICs of ATM, with and without amoxicillin-clavulanate (AMC), were determined. Time-kill assays were performed for three representative strains.Results. The ATM-AMC combination had a synergistic effect on 34/41 (83 %) isolates. The MIC of ATM, in the presence of clavulanate, was ≤1 mg l-1 for 15/41 (37 %) isolates and ≤4 mg l-1 for 29/41 (71 %) isolates. Synergistic activity was observed for 34/37 (92 %) isolates producing ESBLs and carbapenemases, compared to 0/4 (0 %) for ESBL-negative strains. Complete or partial bactericidal activity was obtained when the MIC of the combination was 0.5 mg l-1 and 1.5 mg l-1 or 8 mg l-1, respectively.Conclusion. The combination of ATM and AMC could be an attractive unconventional treatment for infections due to carbapenemase- and ESBL-producing Enterobacteriaceae.

Pharmacodynamic modelling of β-lactam/β-lactamase inhibitor checkerboard data: illustration with aztreonam–avibactam

ObjectivesCheckerboard experiments followed by fractional inhibitory concentration (FIC) index determinations are commonly used to assess in vitro pharmacodynamic interactions between combined antibiotics, but FIC index cannot be determined in case of antibiotic/non-active compound combinations. The aim of this study was to use a simple modelling approach to quantify the in vitro activity of aztreonam-avibactam, a new β-lactam–β-lactamase inhibitor combination. MethodsMIC checkerboard experiments were performed with 12 Enterobacteriaceae with diverse β-lactamases profiles. Aztreonam MICs in the absence and presence of avibactam at different concentrations (ranging from 0.0625 to 4 mg/L) were determined. Aztreonam MIC versus avibactam concentrations were fitted by an inhibitory Emax model with a baseline effect parameter. ResultsA concentration-dependent relationship was observed with a steep initial reduction of aztreonam MIC at low avibactam concentrations and reaching a maximum at higher avibactam concentrations that was adequately fitted by the model. Maximum avibactam effect was characterized by the ratio of aztreonam MICs in the absence of avibactam (MIC0) and when avibactam concentration tends toward infinity (MIC∞), and this ratio ranged between 90 and 10 068 depending on the strain. Avibactam potency was characterized by avibactam concentrations corresponding to 50% of the maximum effect (IC50 values between 0.00022 and 0.053 mg/L). ConclusionsAn inhibitory Emax model with a baseline effect could quantify maximum avibactam effect and potency among various strains. This simple modelling approach can be used to compare the activity of other combinations of antibiotics with non-antibiotic drugs when FIC index is inappropriate.

Mutations in NalC induce MexAB-OprM overexpression resulting in high level of aztreonam resistance in environmental isolates of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunistic pathogen with high resistance to a wide variety of antimicrobials. The multidrug resistance pump MexAB-OprM promotes the efflux of various antibiotics, mostly when mutations accumulate in the transcriptional regulators MexR, NalC and NalD, thereby causing MexAB-OprM overexpression. In this work, a characterization of 50 P. aeruginosa isolates obtained from Brazilian agricultural soils to determine the reasons of their resistance to aztreonam was done. The majority of the isolates showed higher aztreonam resistance than wild-type strain by MIC method. DNA sequence analysis of mexR, nalC and nalD genes from 13 of these isolates showed the amino acid substitution in NalC for all tested isolates, just one mutation was detected in MexR and none in NalD. Furthermore, an increase in the level of mexA expression by real-time RT-PCR analysis in eight isolates harboring mutations in NalC was found. Although there was not a relationship between MIC of aztreonam and the level of mexA expression, on the other hand, the results presented here suggest that novel mutations in NalC, including Arg97-Gly and Ala186-Thr, are related to MexAB-OprM overexpression causing aztreonam resistance in P. aeruginosa environmental isolates.

In vitro pharmacokinetics/pharmacodynamics of the combination of avibactam and aztreonam against MDR organisms.

The combination of aztreonam and avibactam has been proposed for the treatment of infections caused by metallo-β-lactamase-producing Gram-negative organisms, given the stability of aztreonam against metallo-β-lactamases plus the broad coverage of avibactam against AmpC β-lactamases and ESBLs. This study aimed to evaluate the efficacy of the combination against four clinical isolates with defined but diverse β-lactamase profiles. The MICs of aztreonam were determined without and with avibactam (1, 2, 4, 8 and 16 mg/L). Using the MIC values, the static time-kill kinetic studies were designed to encompass aztreonam concentrations of 0.25, 0.5, 1, 2 and 4 times the MIC at the respective avibactam concentrations from 0 to 8 mg/L. Aztreonam and avibactam concentrations were determined by LC-MS/MS during the course of the time-kill kinetic studies to evaluate whether avibactam protects aztreonam from degradation. Three of the four isolates had aztreonam MICs ≥128 mg/L in monotherapy. Dramatically increasing susceptibility associated with a decrease in aztreonam MIC was observed with increasing avibactam concentration. Against all isolates, the combinations resulted in greater killing with a much lower dose requirement for aztreonam. The resulting changes in base-10 logarithm of cfu/mL at both the 10 h and 24 h references (versus 0 h) were synergistic. In contrast, a significantly higher concentration of aztreonam in the monotherapy was required to produce the same kill as that in the combination therapy, due to rapid aztreonam degradation in two isolates. The aztreonam/avibactam combination protects aztreonam from hydrolysis and provides synergy in antimicrobial activity against multiple β-lactamase-expressing strains with a wide MIC range.

Activities of ceftazidime, ceftaroline, and aztreonam alone and combined with avibactam against isogenic Escherichia coli strains expressing selected single β-lactamases

Avibactam is a novel β-lactamase inhibitor that restores the activity of otherwise hydrolyzed β-lactams against Gram-negative bacteria expressing different classes of serine β-lactamases. In the last decade, β-lactam–avibactam combinations were tested against a variety of clinical isolates expressing multiple commonly encountered β-lactamases. Here, we analyzed isogenic Escherichia coli strains expressing selected single β-lactamase genes that were not previously tested or were not characterized in an isogenic background. The activities of ceftazidime, ceftaroline, and aztreonam alone and in combination with 4mg/L of avibactam, as well as comparator agents, were assessed against a unique collection of isogenic strains of E. coli carrying selected extended-spectrum, inhibitor-resistant, and/or carbapenem-hydrolyzing bla genes. When combined with avibactam, ceftazidime, ceftaroline, or aztreonam MICs were reduced for 91.4%, 80.0%, and 80.0% of isolates, respectively. The data presented add to our understanding of the microbiologic spectrum of these β-lactams with avibactam and serve as a reference for further studies.