Correlation between Broth Microdilution and Disk Diffusion Results when Testing Ceftazidime-Avibactam against a Challenge Collection of Enterobacterales Isolates: Results from a Multilaboratory Study.
ABSTRACT: We assessed the ceftazidime-avibactam disk diffusion breakpoints that provide the lowest discrepancy error rates by testing an Enterobacterales isolate collection with ceftazidime-avibactam MIC values near the breakpoints. Isolates (n?=?112) were susceptibility tested by broth microdilution and disk diffusion methods in 3 laboratories. Current disk diffusion breakpoints (?21/?20?mm for susceptible/resistant) provided the lowest error rates, but confirmatory MIC testing is indicated for isolates with inhibition zones of 20 to 22?mm.
Project description:We evaluated the correlation between MIC and disk diffusion inhibition zones when testing ceftazidime-avibactam, using the 30/20-?g disk and the disk diffusion and MIC breakpoints established by the U.S. FDA and the Clinical and Laboratory Standards Institute (CLSI). Organisms used included 2 groups of Enterobacteriaceae isolates and 2 groups of Pseudomonas aeruginosa isolates; 1 group of each consisted of randomly selected isolates and the second group consisted of a challenge group from thousands of surveillance isolates with an increased proportion of organisms displaying ceftazidime-avibactam MIC values close to the breakpoints. Broth microdilution, disk diffusion tests, and data analysis were performed according to reference standardized methods. Ceftazidime-avibactam breakpoints of ?8/4 (susceptible) and ?16/4 ?g/ml (resistant) for MIC and ?21/?20 mm for disk diffusion, as established by the U.S. FDA and the CLSI, were applied for Enterobacteriaceae and P. aeruginosa Ceftazidime-avibactam MIC and disk zone (30/20-?g disk) correlation were acceptable when testing Enterobacteriaceae (overall, very major [VM] and major [Ma] error rates of 0.4% and 0.0%, respectively) and nearly so when testing P. aeruginosa (2.3% VM and 2.9% Ma errors). In summary, disk diffusion and broth microdilution testing results demonstrated good categorical agreement for ceftazidime-avibactam against Enterobacteriaceae and P. aeruginosa, using 30/20-?g disks.
Project description:<h4>Background</h4>Ceftazidime-avibactam was approved in China in 2019 for treating complicated intra-abdominal infections, hospital-acquired pneumonia, ventilator-associated pneumonia, and infections caused by Enterobacterales and Pseudomonas aeruginosa for which treatment options are limited. However, no currently available commercial systems have been approved for antimicrobial susceptibility testing of ceftazidime-avibactam in China. Here, we evaluated the Etest and disk diffusion method for detecting the activity of ceftazidime-avibactam against Enterobacterales and P. aeruginosa in China.<h4>Results</h4>In total, 194 Enterobacterales and 77 P. aeruginosa isolates, which were divided into a random selection group (140 Enterobacterales and 46 P. aeruginosa isolates) and stock group (54 Enterobacterales and 31 P. aeruginosa isolates), were assessed by the Etest, disk diffusion and broth microdilution methods. Minimum inhibitory concentrations and zone diameters were interpreted according to the CLSI supplement M100 30th edition. For all 271 tested isolates, no very major errors were found by using Etest, whereas the overall major error rate was 2.0% (4/203). The overall categorical agreement rates of Etest for Enterobacterales and P. aeruginosa were 99.5% (193/194) and 96.1% (74/77), respectively, and the essential agreement rates were 95.9% (186/194) and 94.8% (73/77), respectively. The disk diffusion method showed that the very major error and major error rates were 1.5% (3/204) and 2.5% (5/203), respectively. Overall categorical agreement rates values of the disk diffusion method for Enterobacterales and P. aeruginosa were 98.5% (191/194) and 93.5% (72/77) compared with broth microdilution, respectively.<h4>Conclusions</h4>For Enterobacterales and P. aeruginosa, both the Etest and disk diffusion method showed acceptable performance as alternatives to the standard broth microdilution method for clinical treatment interpretation. Application of the disk diffusion method in Enterobacterales was slightly better than that in P. aeruginosa.
Project description:Delafloxacin, a recently approved anionic fluoroquinolone, was tested within an international resistance surveillance program. The in vitro susceptibilities of 7,914 indicated pathogens causing acute bacterial skin and skin structure infections (ABSSSI) were determined using Clinical and Laboratory Standards Institute (CLSI) broth microdilution MIC testing methods. The U.S. Food and Drug Administration (FDA) susceptibility testing breakpoints and quality control ranges for routine broth microdilution and disk diffusion methods were confirmed. The delafloxacin MIC50/90 (% susceptibility) results were as follows: Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), 0.008/0.25 ?g/ml (92.8%); Staphylococcus lugdunensis, 0.016/0.03 ?g/ml (99.3%); Streptococcus pyogenes, 0.016/0.03 ?g/ml (100.0%); Streptococcus anginosus group, 0.008/0.016 ?g/ml (100.0%); Enterococcus faecalis, 0.12/1 ?g/ml (66.2%); and Enterobacteriaceae, 0.12/4 ?g/ml (69.5%). The FDA clinical breakpoints were used to assess intermethod test agreement between delafloxacin MIC and disk diffusion methods for the indicated pathogens. The intermethod susceptibility test categorical agreement for delafloxacin was acceptable, with only 0.4% very major, false-susceptible errors among S. aureus strains. Across all FDA-indicated species, the selected breakpoints produced only 0.0 to 1.7% rates of serious (very major and major errors) intermethod error. Quality control ranges for these standardized delafloxacin susceptibility test methods were calculated from three multilaboratory (12 total sites) studies for six control organisms. In conclusion, the application of FDA MIC breakpoints for delafloxacin against contemporary (2014 to 2016) isolates of ABSSSI pathogens provides additional support for the use of delafloxacin in the treatment of adults with ABSSSI. Delafloxacin MIC and disk diffusion susceptibility testing methods have been standardized for clinical application, achieving high intermethod categorical agreement.
Project description:<b>Objectives:</b> Ceftazidime-avibactam is a novel synthetic beta-lactam + beta-lactamase inhibitor combination. We evaluated the performance of the gradient diffusion strip method and the disk diffusion method for the determination of ceftazidime-avibactam against <i>Enterobacterales</i> and <i>Pseudomonas aeruginosa.</i> <b>Methods:</b> Antimicrobial susceptibility testing of 302 clinical <i>Enterobacterales</i> and <i>Pseudomonas aeruginosa</i> isolates from two centers were conducted by broth microdilution (BMD), gradient diffusion strip method, and disk diffusion method for ceftazidime-avibactam. Using BMD as a gold standard, essential agreement (EA), categorical agreement (CA), major error (ME), and very major error (VME) were determined according to CLSI guidelines. CA and EA rate > 90%, ME rate < 3%, and VME rate < 1.5% were considered as acceptable criteria. Polymerase chain reaction and Sanger sequencing were performed to determine the carbapenem resistance genes of all 302 isolates. <b>Results:</b> A total of 302 strains were enrolled, among which 182 strains were from center 1 and 120 strains were from center 2. A percentage of 18.21% (55/302) of the enrolled isolates were resistant to ceftazidime-avibactam. The CA rates of the gradient diffusion strip method for <i>Enterobacterales</i> and <i>P. aeruginosa</i> were 100% and 98.65% (73/74), respectively, and the EA rates were 97.37% (222/228) and 98.65% (73/74), respectively. The CA rates of the disk diffusion method for <i>Enterobacterales</i> and <i>P. aeruginosa</i> were 100% and 95.95% (71/74), respectively. No VMEs were found by using the gradient diffusion strip method, while the ME rate was 0.40% (1/247). No MEs were found by using the disk diffusion method, but the VME rate was 5.45% (3/55). Therefore, all the parameters of the gradient diffusion strip method were in line with acceptable criteria. For 31 <i>bla</i> <sub><i>KPC</i></sub> , 33 <i>bla</i> <sub><i>NDM</i></sub> , 7 <i>bla</i> <sub><i>IMP</i></sub> , and 2 <i>bla</i> <sub><i>VIM</i></sub> positive isolates, both CA and EA rates were 100%; no MEs or VMEs were detected by either method. For 15 carbapenemase-non-producing resistant isolates, the CA and EA rates of the gradient diffusion strips method were 100%. Whereas the CA rate of the disk diffusion method was 80.00% (12/15), the VME rate was 20.00% (3/15). <b>Conclusion:</b> The gradient diffusion strip method can meet the needs of clinical microbiological laboratories for testing the susceptibility of ceftazidime-avibactam drugs. However, the VME rate > 1.5% (5.45%) by the disk diffusion method. By comparison, the performance of the gradient diffusion strip method was better than that of the disk diffusion method.
Project description:<h4>Objectives</h4>To assess the <i>in vitro</i> activity of ceftazidime/avibactam against a recent, 2015-18, collection of clinical isolates of Gram-negative bacilli from Middle Eastern and African countries with a focus on isolates from ICUs and with MDR and difficult-to-treat resistance (DTR) phenotypes.<h4>Methods</h4>Antimicrobial susceptibility testing of 4608 isolates of Enterobacterales (997 isolates from ICU patients) and 1358 isolates of <i>Pseudomonas aeruginosa</i> (374 isolates from ICU patients) was performed by CLSI broth microdilution methodology in a central laboratory. MICs were interpreted using both CLSI (2020) and EUCAST (2020) MIC breakpoints.<h4>Results</h4>Most isolates of Enterobacterales (Middle East: ICU, 99.1% susceptible, non-ICU, 99.1%; Africa: ICU, 96.9% susceptible, non-ICU, 98.3%) and <i>P. aeruginosa</i> (Middle East: ICU, 93.4%, non-ICU, 92.1%; Africa: ICU, 89.8%; non-ICU, 94.1%) were susceptible to ceftazidime/avibactam. Applying CLSI and EUCAST breakpoints, MDR rates were similar for Enterobacterales (27.8%-36.0% of isolates) and <i>P. aeruginosa</i> (25.0%-36.4%) while DTR rates were lower for Enterobacterales (1.6%-1.8%) than for <i>P. aeruginosa</i> (5.2%-7.4%). Percentage susceptible rates for ceftazidime/avibactam for MDR Enterobacterales were 96.8%-97.5% (Middle East) and 92.5%-94.3% (Africa) while rates for <i>P. aeruginosa</i> were 70.1%-80.0% (Middle East) and 69.5%-78.2% (Africa). 60.5%-65.8% (Middle East) and 38.9%-52.2% (Africa) of isolates of Enterobacterales with DTR phenotypes were ceftazidime/avibactam susceptible as were 29.2%-31.1% (Middle East) and 28.2%-35.8% (Africa) of DTR <i>P. aeruginosa</i>.<h4>Conclusions</h4>Overall, the isolates of Enterobacterales and <i>P. aeruginosa</i> tested from Middle Eastern and African countries were highly susceptible to ceftazidime/avibactam. Most MDR and many DTR isolates of Enterobacterales and <i>P. aeruginosa</i> were susceptible to ceftazidime/avibactam.
Project description:Nosocomial pneumonia (NP), including ventilator-associated pneumonia (VAP), is increasingly associated with multidrug-resistant Gram-negative pathogens. This study describes the in vitro activity of ceftazidime-avibactam, ceftazidime, and relevant comparator agents against bacterial pathogens isolated from patients with NP, including VAP, enrolled in a ceftazidime-avibactam phase 3 trial. Gram-positive pathogens were included if coisolated with a Gram-negative pathogen. In vitro susceptibility was determined at a central laboratory using Clinical and Laboratory Standards Institute broth microdilution methods. Of 817 randomized patients, 457 (55.9%) had ?1 Gram-negative bacterial pathogen(s) isolated at baseline, and 149 (18.2%) had ?1 Gram-positive pathogen(s) coisolated. The most common isolated pathogens were Klebsiella pneumoniae (18.8%), Pseudomonas aeruginosa (15.8%), and Staphylococcus aureus (11.5%). Ceftazidime-avibactam was highly active in vitro against 370 isolates of Enterobacteriaceae, with 98.6% susceptible (MIC90, 0.5??g/ml) compared with 73.2% susceptible for ceftazidime (MIC90, >64??g/ml). The percent susceptibility values for ceftazidime-avibactam and ceftazidime against 129 P. aeruginosa isolates were 88.4% and 72.9% (MIC90 values of 16??g/ml and 64??g/ml), respectively. Among ceftazidime-nonsusceptible Gram-negative isolates, ceftazidime-avibactam percent susceptibility values were 94.9% for 99 Enterobacteriaceae and 60.0% for 35 P. aeruginosa MIC90 values for linezolid and vancomycin (permitted per protocol for Gram-positive coverage) were within their respective MIC susceptibility breakpoints against the Gram-positive pathogens isolated. This analysis demonstrates that ceftazidime-avibactam was active in vitro against the majority of Enterobacteriaceae and P. aeruginosa isolates from patients with NP, including VAP, in a phase 3 trial. (This study has been registered at ClinicalTrials.gov under identifier NCT01808092.).
Project description:The in vitro activities of ceftazidime-avibactam and comparators against 9,149 isolates of Enterobacteriaceae and 2,038 isolates of Pseudomonas aeruginosa collected by 42 medical centers in nine countries in the Asia-Pacific region from 2012 to 2015 were determined as part of the International Network for Optimal Resistance Monitoring (INFORM) global surveillance program. Antimicrobial susceptibility testing was conducted by Clinical and Laboratory Standards Institute (CLSI) broth microdilution, and isolate subset analysis was performed on the basis of the resistant phenotypes and ?-lactamase content. Ceftazidime-avibactam demonstrated potent in vitro activity (MIC, ?8 ?g/ml) against all Enterobacteriaceae tested (99.0% susceptible) and was the most active against isolates that were metallo-?-lactamase (MBL) negative (99.8% susceptible). Against P. aeruginosa, 92.6% of all isolates and 96.1% of MBL-negative isolates were susceptible to ceftazidime-avibactam (MIC, ?8 ?g/ml). The rates of susceptibility to ceftazidime-avibactam ranged from 97.0% (Philippines) to 100% (Hong Kong, South Korea) for Enterobacteriaceae and from 83.1% (Thailand) to 100% (Hong Kong) among P. aeruginosa isolates, with lower susceptibilities being observed in countries where MBLs were more frequently encountered (Philippines, Thailand). Ceftazidime-avibactam inhibited 97.2 to 100% of Enterobacteriaceae isolates, per country, that carried serine ?-lactamases, including extended-spectrum ?-lactamases, AmpC cephalosporinases, and carbapenemases (KPC, GES, OXA-48-like). It also inhibited 91.3% of P. aeruginosa isolates that were carbapenem nonsusceptible in which no acquired ?-lactamase was detected. Among MBL-negative Enterobacteriaceae isolates that were ceftazidime nonsusceptible, meropenem nonsusceptible, colistin resistant, and multidrug resistant, ceftazidime-avibactam inhibited 96.1, 87.7, 100, and 98.8% of isolates, respectively, and among MBL-negative P. aeruginosa isolates that were ceftazidime nonsusceptible, meropenem nonsusceptible, colistin resistant, and multidrug resistant, ceftazidime-avibactam inhibited 79.6, 83.6, 83.3, and 68.2% of isolates, respectively. Overall, clinical isolates of Enterobacteriaceae and P. aeruginosa collected in nine Asia-Pacific countries from 2012 to 2015 were highly susceptible to ceftazidime-avibactam.
Project description:Clinical susceptibility breakpoints against Enterobacteriaceae and Pseudomonas aeruginosa for the ceftazidime-avibactam dosage regimen of 2,000/500 mg every 8 h (q8h) by 2-h intravenous infusion (adjusted for renal function) have been established by the FDA, CLSI, and EUCAST as susceptible (MIC, ?8 mg/liter) and resistant (MIC, >8 mg/liter). The key supportive data from pharmacokinetic/pharmacodynamic analyses, in vitro surveillance, including molecular understanding of relevant resistance mechanisms, and efficacy in regulatory clinical trials are collated and analyzed here.
Project description:Ceftazidime/avibactam (CZA) and ceftolozane/tazobactam (C/T) are novel antibiotics with activity against multidrug-resistant Gram-negative pathogens. Nevertheless, resistance to both agents has been reported emphasizing the need for accurate and widely accessible susceptibility testing. In the present study, Vitek 2 and Etest CAZ and C/T MIC results for 100 non-repetitive clinical isolates (83 <i>Enterobacterales</i> and 17 <i>P. aeruginosa</i>, whereof 69 challenge isolates) were compared to the standard broth microdilution (BMD) method. EUCAST breakpoints were used for assessing the categorical (CA) and essential (EA) agreement between the methods along with the corresponding error rates. The Vitek 2 performance was comparable to that of BMD for testing both antimicrobial agents exceeding the ISO requirements (CA 98-99%, EA 96-100%, major errors (MEs) 0-1%, very major error (VMEs) 1%). Likewise, the Etest provided accurate results for CZA and C/T testing against <i>Enterobacterales</i> and <i>P. aeruginosa</i>, respectively (CA 100%, EA 97-100%, MEs 0%, VMEs 0%). On the contrary, EA of 85% and 6% VME rate were found for CZA Etest and <i>P. aeruginosa</i>. Overall, Vitek 2 measurements of CZA and C/T susceptibility correlated closely with the reference BMD, indicating that it can represent a suitable alternative to BMD for susceptibility testing of <i>Enterobacterales</i> and <i>P. aeruginosa</i>. The Etest did not fulfill the ISO performance criteria of EA and VME for CZA and <i>P. aeruginosa</i>. Further studies are needed to assess whether the Etest allows a reliable assessment of CZA and C/T EUCAST MICs.
Project description:β-lactam-avibactam combinations have been proposed as carbapenem-sparing therapies, but little data exist on their in vitro activities in infections with high bacterial inocula. We investigated the in vitro efficacies and the inoculum effects of ceftazidime-avibactam and aztreonam-avibactam against extended-spectrum β-lactam-resistant Enterobacterales blood isolates. A total of 228 non-repetitive extended-spectrum β-lactam-resistant <i>Escherichia coli</i> and <i>Klebsiella pneumoniae</i> blood isolates were prospectively collected in a tertiary center. In vitro susceptibilities to ceftazidime, aztreonam, meropenem, ceftazidime-avibactam, and aztreonam-avibactam were evaluated by broth microdilution method using standard and high inocula. An inoculum effect was defined as an eightfold or greater increase in MIC when tested with the high inoculum. Of the 228 isolates, 99% were susceptible to ceftazidime-avibactam and 99% had low aztreonam-avibactam MICs (≤8 mg/L). Ceftazidime-avibactam and aztreonam-avibactam exhibited good in vitro activities; MIC<sub>50</sub>/MIC<sub>90</sub> values were 0.5/2 mg/L, 0.125/0.5 mg/L, and ≤0.03/0.25 mg/L, respectively, and aztreonam-avibactam was more active than ceftazidime-avibactam. The frequencies of the inoculum effect with ceftazidime-avibactam and aztreonam-avibactam were lower than with meropenem (14% vs. 38%, <i>p</i> < 0.001 and 30% vs. 38%, <i>p</i> = 0.03, respectively). The β-lactam-avibactam combinations could be useful as carbapenem-sparing strategies, and aztreonam-avibactam has the better in vitro activity but is more subject to the inoculum effect than ceftazidime-avibactam.