Clinical And Laboratory Standards Institute Criteria Research Articles

1946. In Vitro Activity of Ceftobiprole against Staphylococcus aureus Bacteremia Isolates from the United States (2018–2020)

Abstract Background Ceftobiprole (BPR) is an advanced-generation cephalosporin approved in Europe and many non-European countries for the treatment of community-acquired pneumonia and non–ventilator-associated hospital-acquired pneumonia in adults. A Phase 3 clinical trial (NCT03138733) was recently completed with BPR for the treatment of Staphylococcus aureus (SA) bacteremia, including infective endocarditis. This study evaluated the activity of BPR and comparators against recent SA isolates causing bloodstream infections (BSI) in patients hospitalized at medical centers in the United States (US). Methods A total of 1,946 SA isolates from 32 US medical centers (2018–2020) were collected from patients with BSI. 53 isolates from endocarditis patients were included. Isolates were tested for antimicrobial susceptibility using the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method. MIC interpretations for BPR and comparators utilized European Committee on Antimicrobial Susceptibility Testing (EUCAST) or CLSI criteria, respectively. Multidrug-resistant (MDR) isolates were non-susceptible to ≥ 3 of the following drugs without regard to oxacillin resistance: clindamycin, daptomycin, erthryomycin, gentamicin, levofloxacin, tetracycline, and trimethoprim-sulfamethoxazole. No isolates were resistant to linezolid, tigecycline, or vancomycin. Results BPR inhibited 99.5% of all SA at ≤ 2 mg/L, which is the EUCAST susceptibility breakpoint (MIC50/90, 0.5/2 mg/L). The MIC50/90 values were stable over all 3 surveillance years and identical to previously reported values from analogous isolates collected in 2016–2017. BPR activity was maintained against the methicillin-resistant SA (MRSA) subset (41% of all SA; 98.8% susceptible). All isolates from endocarditis patients were susceptible to BPR. 10 MRSA isolates (0.5%) were resistant to BPR with MIC values of 4 mg/L. Of 288 MDR isolates, 96.9% remained susceptible to BPR, while only 78.8% of the same isolate set was susceptible to ceftaroline. Conclusion These in vitro results extend previous surveillance data that suggest that BPR represents a potential option for treating BSI and endocarditis caused by SA in US hospitals, including MRSA and MDR isolates. Disclosures Leonard R. Duncan, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|CorMedix: Grant/Research Support|Melinta: Grant/Research Support|Pfizer: 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 Jennifer Smart, PhD, Basilea Pharmaceutica International Ltd, Allschwil, Switzerland: Stocks/Bonds Mark E. Jones, PhD, Astellas Pharma Global Development, Inc: Support for the present publication|Basilea Pharmaceutica International Ltd: Employee of Basilea Pharmaceutica International Ltd|Basilea Pharmaceutica International Ltd: Stocks/Bonds 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

2162. In Vitro Antimicrobial Activity of Ceftobiprole against Streptococcus pneumoniae Isolates from the United States (2016–2020)

Abstract Background Ceftobiprole (BPR) is an advanced-generation cephalosporin approved in Europe and many non-European countries for the treatment of community-acquired pneumonia and non–ventilator-associated hospital-acquired pneumonia in adults caused by indicated species, including Streptococcus pneumoniae (SPN). This study evaluated the in vitro antimicrobial activity of BPR and comparator agents against recent SPN isolates causing lower respiratory tract infections in patients at medical centers in the United States (US). Methods A total of 2,793 SPN isolates from 32 US medical centers (2016–2020) were collected from patients with lower respiratory tract infections. Isolates were tested for antimicrobial susceptibility using the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method. MIC interpretations for BPR and comparators utilized European Committee on Antimicrobial Susceptibility Testing (EUCAST) or CLSI criteria, respectively. The EUCAST BPR susceptibility breakpoint for SPN was 0.5 mg/L. Results BPR inhibited 99.5% of all SPN isolates at the EUCAST breakpoint (MIC50/90, 0.015/0.25 mg/L). The MIC50/90 values were stable over all 5 surveillance years. The following comparator agents displayed lower activity against the isolate set: clindamycin (85.5% susceptible [S]), erythromycin (53.2% S), penicillin (63.2% S using oral breakpoints), tetracycline (79.4% S), and trimethoprim-sulfamethoxazole (72.8% S). BPR maintained excellent in vitro activity against each of the isolate subsets resistant to these comparator antimicrobials (95.4–98.8% S to BPR depending on the comparator antimicrobial; 95.4% of the penicillin-resistant isolates were S to BPR). This SPN isolate set was also 99.4% S to levofloxacin, 97.4% S to ceftriaxone (using non-meningitis breakpoints), and 100% S to linezolid and vancomycin. Conclusion BPR exhibited potent in vitro antimicrobial activity against recent SPN clinical isolates collected in US medical centers (2016–2020). These data indicate that BPR merits further investigation as a potential option for the treatment of lower respiratory tract infections caused by SPN in the US. Disclosures Leonard R. Duncan, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|CorMedix: Grant/Research Support|Melinta: Grant/Research Support|Pfizer: 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 Jennifer Smart, PhD, Basilea Pharmaceutica International Ltd, Allschwil, Switzerland: Stocks/Bonds Mark E. Jones, PhD, Astellas Pharma Global Development, Inc: Support for the present publication|Basilea Pharmaceutica International Ltd: Employee of Basilea Pharmaceutica International Ltd|Basilea Pharmaceutica International Ltd: Stocks/Bonds 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

A US-based national surveillance study for the susceptibility and epidemiology of Clostridioides difficile isolates with special reference to ridinilazole: 2020-2021.

We have previously reported on the susceptibility and epidemiology of Clostridioides difficile isolates from six geographically dispersed medical centers in the United States. This current survey was conducted with isolates collected in 2020-2021 from six geographically dispersed medical centers in the United States, with specific attention to susceptibility to ridinilazole as well as nine comparators. C. difficile isolates or stools from patients with C. difficile antibiotic-associated diarrhea were collected and referred to a central laboratory. After species confirmation of 300 isolates at the central laboratory, antibiotic susceptibilities were determined by the agar dilution method [M11-A9, Clinical and Laboratory Standards Institute (CLSI)] against the 10 agents. Ribotyping was performed by PCR capillary gel electrophoresis on all isolates. Ridinilazole had a minimum inhibitory concentration (MIC) 90 of 0.25 mcg/mL, and no isolate had an MIC greater than 0.5 mcg/mL. In comparison, fidaxomicin had an MIC 90 of 0.5 mcg/mL. The vancomycin MIC 90 was 2 mcg/mL with a 0.7% resistance rate [both CLSI and European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria]. The metronidazole MIC 90 was 1 mcg/mL, with none resistant by CLSI criteria, and a 0.3% resistance rate by EUCAST criteria. Among the 50 different ribotypes isolated in the survey, the most common ribotype was 014-020 (14.0%) followed by 106 (10.3%), 027 (10%), 002 (8%), and 078-126 (4.3%). Ridinilazole maintained activity against all ribotypes and all strains resistant to any other agent tested. Ridinilazole showed excellent in vitro activity against C. difficile isolates collected between 2020 and 2021 in the United States, independent of ribotype.

Evaluation of Variability in Interpretation of Disk Diffusion Testing for Cefiderocol Using Different Brands of Mueller-Hinton Agar.

Cefiderocol is a new antibiotic used to treat infections with antibiotic resistant Gram-negative bacilli. The impact of differences between Mueller-Hinton agar (MHA) brands on susceptibility testing is underexplored. Compounding the implementation of cefiderocol susceptibility testing is a lack of harmonization between different regulatory body breakpoint criteria. We performed Kirby-Bauer disk diffusion using BD, Hardy, and Remel MHA, in addition to broth microdilution for Acinetobacter baumannii (n = 25), Enterobacterales (n = 25), Stenotrophomonas maltophilia (n = 24), and Pseudomonas aeruginosa (n = 23). We analyzed disk diffusion diameters and minimum inhibitory concentrations using interpretive criteria from the Clinical and Laboratory Standards Institute (CLSI), US Food and Drug Administration (FDA), and the European Committee on Antimicrobial Susceptibility Testing (EUCAST). Breakpoint criteria impacted interpretation of susceptibly testing results, for example with the broth microdilution we found 8% (2/25) of A. baumannii isolates change interpretation between CLSI and EUCAST and 32% (8/25) change between CLSI and FDA, 12% (3/25) of Enterobacterales change between CLSI and EUCAST, 13% (3/23) of P. aeruginosa interpretations change between CLSI and FDA, and 4% (1/25) S. maltophilia change between CLSI and FDA. There was a significant difference between the zone disk diffusion diameters for P. aeruginosa and S. maltophilia between Hardy and BD; which changed interpretation (using CLSI criteria) for 8.7% (2/23) for P. aeruginosa but 0% (0/24) for S. maltophilia. Breakpoint criteria impact cefiderocol susceptibility testing interpretation for broth microdilution and disk diffusion. Choice of MHA brand can also affect result interpretation.

Microorganism Distributions and Antimicrobial Susceptibility in Community-Onset Bacteremia: A 6-Year Longitudinal Multicenter Cohort in Southern Taiwan.

Prompt administration of appropriate antimicrobials has been correlated with improved prognoses in patients with bacteremia. Because the Clinical and Laboratory Standards Institute (CLSI) has numerously revised the interpretive criteria of susceptibility to numerous antimicrobials, the updated susceptibility is useful for empirical administration. In the multicenter retrospective cohort study consisting of adults with community-onset bacteremia in the emergency department (ED) during the period between January 2010 and December 2015, causative microorganisms were identified by the Vitek 2 system and prospectively collected. Antimicrobial susceptibility were respectively tested by the disk diffusion method for aerobes and the agar dilution method for anaerobes, in accordance with the contemporary CLSI criteria. Clinical information was retrospectively retrieved by reviewing the medical records. Of the total 3,194 patients and 3,583 causative microorganisms, the leading source of bacteremia was the urinary tract infection (1,034 patients, 32.4%), and Escherichia coli accounted for the majority (1,332 isolates, 37.2%) of the total microorganisms. Overall, the lowest (58.2%) and highest (93.5%) susceptibility to cefazolin and piperacillin/tazobactam were, respectively, observed. In the leading five sources of bacteremia, in terms of the urinary tract infections, pneumonia, intraabdominal infections, skin and soft-tissue infections, and biliary tract infections, cefazolin or cefuroxime was only active against 49.3%-62.3% or 63.2%-74.1% of causative microorganisms, respectively. Notably, E. coli , Klebsiella species, and Proteus mirabilis (EKP) with the production of extended-spectrum beta-lactamases (ESBLs) accounted for 7.4% (142 isolates) of 1,908 EKP and 4.0% of all 3,583 microorganisms; and methicillin-resistant Staphylococcus aureus (MRSA) accounted for 37.7% (158 isolates) of S . aureus and 4.4% of all causative isolates. For adults with community-onset bacteremia, a low incidence (approximate 4%) of ESBL-producing EKP and MRSA among all causative microorganisms, but low susceptibility to cefazolin and cefuroxime were recognized. To achieve favorable prognoses by prompt administration of appropriate antimicrobials in EDs, our findings might offer useful information for the antimicrobial stewardship program.

Investigation of bacterial pollution in Ceyhan River (Turkey) and the resistance levels of gram (+) and gram (-) bacteria to antibiotics

In this study, bacteriological pollution of Ceyhan River flowing into Iskenderun Bay (Northeast Mediterranean) and antibiotic resistance of Gram (+) and Gram (-) bacteria were investigated. Water samples were collected from May 2014 to April 2015 in monthly periods and 222 Gram (-) and 74 Gram (+) bacteria were isolated from collected water samples. The isolates were contained 8 different species (Acinetobacter baumannii, Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, Proteus vulgaris, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis) which have been identified with Vitek II automated culture system. Microorganism susceptibility tests were performed in accordance with CLSI (Clinical and Laboratory Standards Institute, 2015) criteria. Resistance of the isolates to 15 different antibiotics (Amikacin, Meropenem, Levofloxacin, Imipenem, Piperacillin, Gentamycin, Cefepime, Ceftazidime Penicillin, Oxacillin, Clindamycin, Erythromycin, Ciprofloxacin, Vancomycin, Rifampin) was investigated. The highest antibiotic resistance was found in E. faecalis with 37% against Penicillin antibiotics. No resistance to vancomycin antibiotics has been observed. It was concluded that the Ceyhan River was exposed to fecal bacterial contamination, and it was revealed that this situation would adversely affect both the ecosystem and human health. Measures to protect and improve the ecological and microbiological qualities of rivers and lakes are key to preserving the quality and quantity of water resources for the future.

Anti-staphylococcal lysin, LSVT-1701, activity: In vitro susceptibility of Staphylococcus aureus and coagulase-negative staphylococci (CoNS) clinical isolates from around the world collected from 2002 to 2019

LSVT-1701 (previously known as SAL200), is a novel, recombinantly-produced, bacteriophage-encoded lysin that specifically targets staphylococci via cell wall enzymatic hydrolysis. In vitro activities of LSVT-1701 and comparators were tested against 415 Staphylococcus aureus and coagulase-negative staphylococci (CoNS) clinical isolates expressing various resistance phenotypes. The isolates were collected worldwide from 2002 to 2019 and tested for in vitro susceptibility using broth microdilution methodology performed according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Minimum inhibitory concentration (MIC) interpretations were based on CLSI and EUCAST criteria. MIC90 for all S. aureus, methicillin-susceptible S. aureus, methicillin-resistant S. aureus, and CoNS, were 2, 2, 2 and 2 µg/ml, respectively. LSVT-1701’s activity was not adversely affected by resistance to antimicrobial comparators against this worldwide collection of S. aureus and CoNS clinical isolates. The results of this study support further clinical development of LSVT-1701 to treat staphylococcal infections, including those caused by multidrug resistance isolates.

In vitro activity of iclaprim and comparator agents against Listeria monocytogenes clinical isolates from 2012 to 2018

ObjectivesThis study examined the in vitro activity of iclaprim and comparators against 40 Listeria monocytogenes clinical isolates mostly (95%) from patients with bloodstream infection (BSI) from the USA, Australia/New Zealand, Latin America and Europe collected between 2012–2018. MethodsAntimicrobial susceptibility testing was performed according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Minimum inhibitory concentration (MIC) interpretations were based on CLSI criteria. ResultsThe iclaprim MIC90 value for all L. monocytogenes was 0.015 μg/mL. The MIC50/90 values for iclaprim were 4-fold lower than trimethoprim, the only FDA-approved dihydrofolate reductase inhibitor, against all L. monocytogenes. ConclusionIclaprim demonstrated lower MIC values than trimethoprim against a collection (2012–2018) of L. monocytogenes clinical isolates mostly from patients with BSI from the USA, Australia/New Zealand, Latin America and Europe.

Evaluation of a Phenotypic Algorithm to Direct Carbapenemase Testing in Pseudomonas aeruginosa: Validation in a Multicenter German Cohort.

Pseudomonas aeruginosa remains a prominent nosocomial pathogen. Detection of carbapenemase-producing P. aeruginosa is vital to dictate antimicrobial therapy and infection control measures. A pragmatic, minimum inhibitory concentration-based algorithm using imipenem AND meropenem-resistant plus ceftazidime-, cefepime-, and piperacillin/tazobactam-nonsusceptible criterion was derived to guide carbapenemase testing in P. aeruginosa. This study was an assessment of the algorithm's test performance in a cohort of 985 nonduplicate P. aeruginosa isolates collected from 20 German medical laboratories. Susceptibility data were assessed in the algorithm using both Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) interpretations. Sensitivity and specificity were calculated to evaluate algorithm test performance. The original algorithm criteria resulted in high specificity (95-97%) using both CLSI and EUCAST criteria; however, it failed to capture five carbapenemase-harboring isolates testing piperacillin/tazobactam susceptibility (CLSI/EUCAST). Two carbapenemase-producing isolates were also meropenem susceptible per EUCAST. A modified algorithm utilizing imipenem OR meropenem-resistant plus ceftazidime and cefepime nonsusceptible, improved the sensitivity of the criteria without significantly compromising specificity (CLSI sensitivity/specificity: 96%/94% and EUCAST sensitivity/specificity: 96%/95%). Application of the modified algorithm criteria resulted in high sensitivity and specificity using both CLSI and EUCAST interpretations in a large cohort of clinical P. aeruginosa. Utilization of this algorithm can improve the efficiency of carbapenemase testing in the clinical laboratory.

192. A Hematology/Oncology Unit-Specific Antibiogram Emphasizes the Need for Intensified Local Stewardship

BackgroundAntibiograms are important stewardship tools for empiric antibiotic prescribing. Appropriate therapy is particularly important in patients with hematologic malignancies and bone marrow transplants being treated for febrile neutropenia. These patients are at high risk for multi-drug resistance based on extensive prior antibiotic and hospital exposures, and therefore, hospital-wide antibiograms may not reliably reflect resistance patterns for this population. We created a unit-specific antibiogram for a closed hematology/oncology unit and hypothesized there would be decreased antibiotic susceptibilities compared to the hospital-wide antibiogram.MethodsAll positive cultures with antimicrobial susceptibilities on a closed 32-bed hematology-oncology unit from 7/2016-6/2019 were obtained from the microbiology laboratory. Based on recommendations by the Clinical and Laboratory Standards Institute (CLSI), only organisms with > 30 isolates were included in antibiogram analysis. Susceptibilities were compared to those reported in our hospital-wide antibiograms from the same time period using Fisher’s exact test.ResultsTwo organisms met CLSI criteria: Escherichia coli (n=83) and Klebsiella pneumoniae (n=31). Unit Escherichia coli isolates were significantly more resistant to almost all commonly tested antibiotics (Table 1). Klebsiella pneumoniae unit susceptibilities were significantly lower for many antibiotics, including aztreonam, ceftriaxone, cefepime, levofloxacin, piperacillin-tazobactam and tobramycin (Table 1).Table 1: Percentage of Escherichia coli and Klebsiella pneumoniae isolates susceptible to reported antibiotic agents ConclusionOur hematology-oncology antibiogram showed significantly lower antibiotic susceptibilities in Escherichia Coli and Klebsiella pneumoniae compared with the hospital-wide antibiogram. These findings can help guide prescribers toward appropriate broad-spectrum empiric therapy. Additionally, results suggest a need for intensified stewardship measures to prevent multi-drug resistance in this population.Disclosures All Authors: No reported disclosures

In vitro activity of ceftaroline against bacterial pathogens isolated from patients with skin and soft tissue and respiratory tract infections in the Middle East and Africa: AWARE global surveillance programme 2015–2018

ObjectivesTo report antimicrobial susceptibility testing surveillance data for ceftaroline and comparative agents from the AWARE global surveillance programme for bacterial pathogens causing skin and soft tissue infections (SSTIs) and lower respiratory infections (RTIs) in Middle East and African countries from 2015 to 2018. MethodsPathogens were identified by MALDI-TOF/MS. Antimicrobial susceptibility testing was performed using the Clinical and Laboratory Standards Institute (CLSI) broth microdilution method. MICs were interpreted by both CLSI (M100, 2020) and European Committee on Antimicrobial Susceptibility Testing (EUCAST) (v 10.0, 2020) breakpoints. ResultsAll MSSA (n = 1125) and 93.9% of MRSA (n = 1235) were susceptible to ceftaroline (MIC ≤ 1 μg/mL, CLSI and EUCAST). The maximum ceftaroline MIC observed for MRSA was 2 μg/mL; no ceftaroline-resistant MRSA were identified among SSTI (CLSI and EUCAST) and RTI (CLSI) isolates. All isolates of β-haemolytic Streptococcus (n = 324), and penicillin-susceptible (PSSP) and -intermediate Streptococcus pneumoniae (PISP; n = 369) were susceptible to ceftaroline. Rates of susceptibility to ceftaroline for penicillin-resistant S. pneumoniae (penicillin MIC ≥ 2 μg/mL; n = 175), and β-lactamase-negative (BLNHI; n = 224) and β-lactamase-positive Haemophilus influenzae (n = 49) were 99.4%, 98.7%, and 98.0% (CLSI) and 92.6%, 98.2%, and 83.7% (EUCAST), respectively. Rates of susceptibility to ceftaroline for ESBL-negative Escherichia coli (n = 442), Klebsiella pneumoniae (n = 381), and Klebsiella oxytoca (n = 103) were 92.1%, 93.2%, and 96.1%, respectively. ConclusionCeftaroline-resistant isolates of MRSA causing SSTIs were not identified in Middle East and African countries in 2015–2018 using recently revised CLSI (in 2019) or EUCAST (in 2018) breakpoint criteria. Common bacterial pathogens causing SSTIs (Staphylococcus aureus, β-haemolytic Streptococcus) and lower RTIs (PSSP, PISP, BLNHI) demonstrated no resistance or low levels of resistance (0–1.8%) to ceftaroline.

Low but Increasing Prevalence of Reduced Beta-lactam Susceptibility Among Invasive Group B Streptococcal Isolates, US Population-Based Surveillance, 1998-2018.

Invasive group B Streptococcus (iGBS) isolates with mutations in the pbp2x gene that encodes penicillin binding protein 2x can have reduced beta-lactam susceptibility (RBLS) when susceptible by Clinical and Laboratory Standards Institute (CLSI) criteria. We assessed the emergence and characteristics of RBLS strains in US iGBS isolates. We analyzed iGBS isolates from 8 multistate population-based surveillance sites from 1998 to 2018. During 1998-2014, phenotypic antimicrobial susceptibility was determined by broth microdilution; criteria for 6 antibiotics were used to identify RBLS, followed by whole-genome sequencing (WGS). WGS for all isolates was added in 2015; we used phenotypic and genotypic results of >2000 isolates to validate phenotypic RBLS criteria and genotypic predictions. Since 2016, WGS has been used to screen for RBLS with broth microdilution confirmation of predicted RBLS isolates. Of 28 269 iGBS isolates, 28 (0.1%) were nonsusceptible by CLSI criteria; 137 (0.5%) met RBLS criteria. RBLS isolates were detected in all Active Bacterial Core surveillance sites. The RBLS proportion increased, especially since 2013 (odds ratio, 1.17; 95% CI, 1.03-1.32); the proportion that were nonsusceptible remained stable. The RBSL proportion was low but increasing among US iGBS isolates. Ongoing monitoring is needed to detect emerging threats to prevention and treatment of GBS infections.

Trends in antimicrobial resistance in Neisseria gonorrhoeae in Hanoi, Vietnam, 2017\u20132019

BackgroundAntimicrobial resistance (AMR) in Neisseria gonorrhoeae is an emerging global health threat. Surveillance of AMR in N. gonorrhoeae in the Western Pacific Region is important, as resistant strains have typically emerged from this region. There are sparse data regarding antibiotic susceptibility of N. gonorrhoeae from Vietnam. This study aimed to provide updated data on antibiotic susceptibilities in N. gonorrhoeae isolates from Hanoi, Vietnam.MethodsFrom 2017 to 2019, 409 N. gonorrhoeae clinical isolates were collected at the National Hospital for Venereology and Dermatology in Hanoi, Vietnam. Antibiotic susceptibility testing was performed by disk diffusion method according to the Clinical and Laboratory Standards Institute (CLSI) protocol. The zone diameters of inhibition were recorded and interpreted according to standard CLSI criteria, except for azithromycin, due to the absence of CLSI interpretation. Categorical variables were analyzed by Chi-square and Fisher’s exact tests. Linear regression was used to evaluate zones of inhibition by year.ResultsAmong the 409 isolates, no isolates were susceptible to penicillin, 98.3% were resistant to ciprofloxacin, and all isolates were susceptible to spectinomycin. There were 122/407 (30.0%) isolates resistant to azithromycin and there was an association between resistance and year (p < 0.01), ranging from 15.3% of isolates in 2017 to 46.7% of the isolates in 2018. Resistance to cefixime was found in 13/406 (3.2%) of isolates and there was no association by year (p = 0.30). Resistance to ceftriaxone occurred in 3/408 (0.7%) of isolates. Linear regression indicated the zone of inhibition diameters decreased by 0.83 mm each year for ceftriaxone (95% CI: − 1.3, − 0.4; p < 0.01) and decreased by 0.83 mm each year (95% CI: − 1.33, − 0.33; p < 0.01) for azithromycin; the association was not significant for cefixime (p = 0.07).ConclusionsWe found decreasing susceptibility of N. gonorrhoeae to ceftriaxone and azithromycin, as well as a high prevalence of resistance to azithromycin, among isolates in Hanoi, Vietnam from 2017 to 2019. The trends of decreasing susceptibility to first-line treatments are concerning and highlight the urgency of addressing antimicrobial resistance in N. gonorrhoeae. Expanded surveillance efforts within the Western Pacific Region are critical to monitoring trends and informing treatment guidelines.

Worldwide surveillance of Iclaprim activity: In Vitro susceptibility of gram-positive pathogens collected from patients with skin and skin structure infections from 2013 to 2017

Iclaprim is a novel diaminopyrimidine, which inhibits bacterial dihydrofolate reductase, and it is active against Gram-positive pathogens including emerging drug-resistant pathogens. In vitro activity of iclaprim and comparators against 1365 Gram-positive clinical isolates from patients with skin and skin structure infections (SSSI) from the United States, Asia Pacific, Latin America, Europe, Africa or Middle East collected between 2013 and 2017 were tested. Susceptibility testing was performed according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Minimum inhibitory concentration (MIC) interpretations were based on CLSI criteria. MIC90 for all S.aureus, methicillin-susceptible S. aureus, methicillin-resistant S. aureus, Streptococcus pyogenes, S. agalactiae, S. anginosus, S. constellatus, S. dysgalactiae and S. intermedius were 0.12, 0.12, 0.5, 0.03, 0.5, ≤0.004, ≤0.004, 0.12, and 0.008 μg/ml, respectively. The MIC for iclaprim was 8 to 32-fold lower than trimethoprim, the only FDA approved dihydrofolate reductase inhibitor, against all Gram-positive isolates including resistant phenotypes. Iclaprim demonstrated lower MICs than trimethoprim against a collection (2013–2017) of Gram-positive clinical isolates from patients with SSSI from the United States, Asia Pacific, Latin America, and Europe.

Identification of Fosfomycin Heteroresistance Among Multidrug-Resistant Enterobacteriaceae Urinary Isolates

Fosfomycin is an orally bioavailable bactericidal agent which concentrates significantly in urine and is being increasingly prescribed for patients with Multidrug Resistant Enterobacteriaceae (MDRE) urinary isolates. According to the Clinical and Laboratory Standards Institute (CLSI), disc diffusion (DD) and agar dilution (AD) are the standards for fosfomycin susceptibility testing for urinary Escherichia coli and Enterococcus faecalis isolates, whereas the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines suggest both AD and broth microdilution (BD), but not DD. A prospective study was done in the Department of Microbiology in a tertiary care teaching hospital in Kolkata. MDRE urinary isolates that were resistant to oral and third-generation cephalosporins, either ciprofloxacin or levofloxacin and either of cotrimoxazole or nitrofurantoin were included in the study and tested further for fosfomycin. DD was carried out on Mueller-Hinton agar (MHA) supplemented with 25 μ/ml G6P with 50 and 200 μg discs. E-test was carried out on the same medium with drug concentrations ranging from 0.064 to 1024 μ/ml. Broth dilution was carried out on G6P supplemented Mueller Hinton broth with drug concentrations ranging from 0.25 to 1024 μ/ml. A total of 723 urine samples were obtained in a 2-month period, which yielded 79 Enterobacteriaceae, out of which 30 were MDRE. About 26 (86.67%) of these isolates were susceptible to fosfomycin by CLSI criteria and 25 (83.33%) by EUCAST criteria for minimum inhibitory concentration (MIC) by E-test and broth dilution. Only 4 (13.33%) were resistant to fosfomycin by DD. However, heteroresistant colonies were found among 21 (70%) isolates by E-test. None of these were picked up by DD or BD. The MIC of fosfomycin was between 0.25 and 512 μ/ml. These heteroresistant colonies when further subjected to E-test and BD showed resistance with MIC ≥512 μg/ml, depicting prevalence of heteroresistance. E-test can be used as a simple and effective screening method for identifying the fosfomycin heteroresistance and in turn changing the myth of the so high susceptibility rates among MDRE.

Emerging Resistance among Uropathogens: Is Fosfomycin Revival the Best Hope?

Introduction: Increasing bacterial resistance and the non-availability of newer antimicrobial agents have necessitated the re-evaluation of old antimicrobial agents. Although an old antibiotic, Fosfomycin gives a ray of hope as it has a unique property of not sharing structural similarity with other antibiotics and with no cross-resistance. Aim: To retrospectively evaluate the invitro activity of Fosfomycin against Extended-Spectrum Beta-Lactamase (ESBL) producing and Carbapenem Resistant Enterobacteriaceae (CRE). Materials and Methods: The study period was from December 2018 to November 2019. Antibiotic sensitivity was carried out according to the Clinical and Laboratory Standards Institute (CLSI) guidelines using the automated Vitek-2 Compact (Bio-Merieux, France). Fosfomycin susceptibility was determined by E-test (Biomereiux, India). The interpretive criteria according to CLSI for Fosfomycin is given only for E.coli and not for other Enterobacteriaceae, hence the results were interpreted as per CLSI criteria given for E. coli (i.e., susceptibility at a Minimum Inhibitory Concentration (MIC) of ≤64 μg). Results: Overall, 91.07% (102/112) isolates were susceptible to Fosfomycin with 91.67% (88/96) susceptibility for ESBL producing Enterobacteriaceae and 87.5% (14/16) for CRE. Fosfomycin has shown good invitro activity against ESBL producers as well as CRE. Conclusion: Fosfomycin showed promising results as a re-emerging antibiotic for the treatment of Urinary Tract Infection (UTI) because of its unique mechanism of action, low incidence of resistance, oral availability with single-dose administration and little tendency to display cross-resistance to other antibiotics.

Phenotypic and Genotypic Correlates of Penicillin Susceptibility in Nontoxigenic Corynebacterium diphtheriae, British Columbia, Canada, 2015-2018.

In 2015, the Clinical and Laboratory Standards Institute (CLSI) updated its breakpoints for penicillin susceptibility in Corynebacterium species from <1 mg/L to <0.12 mg/L. We assessed the effect of this change on C. diphtheriae susceptibility reported at an inner city, tertiary care center in Vancouver, British Columbia, Canada, during 2015–2018 and performed whole-genome sequencing to investigate phenotypic and genotypic resistance to penicillin. We identified 44/45 isolates that were intermediately susceptible to penicillin by the 2015 breakpoint, despite meeting previous CLSI criteria for susceptibility. Sequencing did not reveal β-lactam resistance genes. Multilocus sequence typing revealed a notable predominance of sequence type 76. Overall, we saw no evidence of penicillin nonsusceptibility at the phenotypic or genotypic level in C. diphtheriae isolates from our institution. The 2015 CLSI breakpoint change could cause misclassification of penicillin susceptibility in C. diphtheriae isolates, potentially leading to suboptimal antimicrobial treatment selection.

Definitive Cefazolin Treatment for Community-Onset Enterobacteriaceae Bacteremia Based on the Contemporary CLSI Breakpoint: Clinical Experience of a Medical Center in Southern Taiwan.

Cefazolin is traditionally active against Escherichia coli, Klebsiella species, and Proteus mirabilis (EKP) isolates. The Clinical and Laboratory Standards Institute (CLSI) has twice updated cefazolin susceptibility breakpoints for EKP since 2010, but its role in the definitive treatment of cefazolin-susceptible EKP bacteremia remains debated. To assess its efficacy as a definitive agent, the 8-year cohort study consisted of 941 adults with monomicrobial cefazolin-susceptible EKP bacteremia, based on the CLSI criteria issued in 2019, was retrospectively established in a medical center. Based on the definitive antimicrobial prescription, eligible patients were categorized into the cefazolin (399 patients, 42.4%) and broader-spectrum antibiotic (BSA) (542, 57.6%) groups. Initially, fewer proportions of patients with fatal comorbidities (the McCabe classification) and the critical illness (a Pitt bacteremia score ≥4) at the onset and day 3 of the bacteremia episode were found in the cefazolin group, compared to the BSA group. After propensity-score matching, no significant difference of patient proportions between the cefazolin (345 patients) and BSA (345) groups was observed, in terms of the elderly, types and severity of comorbidities, bacteremia severity at the onset and day 3, major bacteremia sources, and the 15-day and 30-day crude mortality. In early outcomes, lengths of time to defervescence, intravenous (IV) antimicrobial administration, and hospitalization were similar in the two matched groups; lower costs of IV antimicrobial administration were observed in the cefazolin group. Notably, for late outcomes, lower proportions of post-treatment infections caused by antimicrobial-resistant pathogens (ARPs) and post-treatment mortality rates were evidenced in the cefazolin group. Conclusively, cefazolin is definitively efficacious and cost-effective for adults with community-onset cefazolin-susceptible EKP bacteremia in this one-center study, compared to BSAs. However, a prospective multicenter study should be conducted for external validation with other communities.

2396. Fosfomycin Resistance Among Carbapenem-Resistant Enterobacteriaceae Clinical Isolates in Connecticut, 2017

BackgroundFosfomycin is among the limited treatment options for carbapenem-resistant Enterobacteriaceae (CRE) infections. Despite its use, prevalence of fosfomycin resistance among CRE in the United States is largely unknown. In 2017, submission of Enterobacteriaceae isolates resistant to ≥1 carbapenem became mandated in Connecticut (CT), allowing further characterization at the state public health laboratory (SPHL). We analyzed fosfomycin resistance among CRE isolates in CT during 2017, and explored demographic and molecular factors potentially associated with resistance.MethodsAfter confirming carbapenem resistance, SPHL tests fosfomycin susceptibility using disk diffusion. For each CRE patient, the isolate most resistant to fosfomycin was included in this analysis. We used the Clinical and Laboratory Standards Institute (CLSI) fosfomycin breakpoint for Escherichia coli (nonsusceptible <16 mm) to evaluate associations among fosfomycin resistance and demographic factors, carbapenemase activity (modified carbapenem inactivation method, mCIM) and carbapenemase genes tested at SPHL. We report fosfomycin resistance rate by European Committee on Antimicrobial Susceptibility Testing (EUCAST, resistance <24 mm for E. coli) criteria for comparison.ResultsAmong 138 CRE isolates, 39 (28.3%) were fosfomycin nonsusceptible by CLSI criteria. Most nonsusceptible isolates were Enterobacter cloacae (18; 46.2%) or Klebsiella pneumoniae (17; 43.6%). Isolates from patients aged ≥65 years were more likely to be fosfomycin nonsusceptible than isolates from patients aged <65 years (χ2 = 3.8; P = 0.050). No other demographic characteristics were statistically significant. Of fosfomycin nonsusceptible isolates, 12 (30.8%) produced a carbapenemase (mCIM-positive), and 9 (23.1%) had the blaKPC gene. By EUCAST criteria, 96 (69.6%) CRE isolates were fosfomycin resistant.ConclusionA substantial proportion of CRE in CT during 2017 were fosfomycin nonsusceptible, and nonsusceptibility was associated with older patient age. Fosfomycin resistance risk factors and molecular mechanisms need further exploration. The substantial proportion of isolates with results falling between CLSI and EUCAST breakpoints warrants evaluation.Disclosures All authors: No reported disclosures.

In Vitro Susceptibilities of Non-albicans Candida Species to Echinocandins, Azoles, and Amphotericin B in Tokat, Turkey

Background: Prophylactic and therapeutic uses of antifungal agents have given rise to a significant shift to more resistant non-albicans Candida species associated with fungal infections. Objectives: This study aimed at identifying the distribution and antifungal susceptibility patterns of non-albicans Candida spp. isolated from clinical specimens in Tokat, Turkey. Methods: The authors determined the susceptibility of 103 non-albicans Candida isolates to the following antifungal agents: amphotericin B, anidulafungin, caspofungin, fluconazole, ketoconazole, itraconazole, voriconazole, and posaconazole, using the Etest method. Interpretation of susceptibility was carried out using species specific breakpoints suggested by the Clinical and Laboratory Standards Institute (CLSI) M27-S4 document. Results: The most frequently isolated non-albicans Candida species were Candida kefyr (44 isolates, 42.8%) followed by C. tropicalis (36 isolates, 35%), C. parapsilosis (17 isolates, 16.5%), C. glabrata (four isolates, 3.8%) and C. famata (two isolates, 1.9%). None of the strains had MIC values of > 2 µg/mL for amphotericin B except three of the 44 C. kefyr isolates. Resistance to caspofungin and anidulafungin were not detected in C. tropicalis, C. parapsilosis, and C. glabrata isolates. Only two of the 36 C. tropicalis isolates were categorized as intermediate resistant to anidulafungin, according to the new CLSI criteria. None of the C. parapsilosis isolates were found to be resistant to azole drugs. Conclusions: Most of the non-albicans Candida species were found to be susceptible to tested antifungal drugs. Therefore, use of routine antifungal agents like amphotericin B and fluconazole, which are available in this region, are suggested.