The Clinical and Laboratory Standards Institute (CLSI) Subcommittee on Antimicrobial Susceptibility Testing (AST) develops and publishes standards and guidelines for AST methods and results ...interpretation in an annual update to the
(M100). This minireview will discuss changes to M100 for the 31st edition, including new and revised breakpoints and testing recommendations. New MIC and disk diffusion breakpoints are described for azithromycin (
spp.), imipenem-relebactam (
, Pseudomonas aeruginosa, and anaerobes), and lefamulin (Staphylococcus aureus, Haemophilus influenzae, and Streptococcus pneumoniae), and disk breakpoints are described for azithromycin and Neisseria gonorrhoeae. The rationale behind revised oxacillin MIC breakpoints for select staphylococci is discussed. Updates to test methods include a method for disk diffusion using positive blood culture broth and use of linezolid to predict tedizolid susceptibility. There is clarification on which drugs to suppress on bacteria isolated from the cerebrospinal fluid and clarification on the use of a caret symbol attached to the intermediate category ("I^") to indicate those antimicrobials that concentrate in the urine.
The Clinical and Laboratory Standards Institute (CLSI) has revised several breakpoints since 2010 for bacteria that grow aerobically. In 2019, these revisions include changes to the ciprofloxacin and ...levofloxacin breakpoints for the
and
, daptomycin breakpoints for
spp., and ceftaroline breakpoints for
Implementation of the revisions is a challenge for all laboratories, as not all systems have FDA clearance for the revised (current) breakpoints, compounded by the need for laboratories to perform validation studies and to make updates to laboratory information system/electronic medical record builds in the setting of limited information technology infrastructure. This minireview describes the breakpoint revisions in the M100 supplement since 2010 and strategies for the laboratory on how to best adopt these in clinical testing.
Nutritionally variant streptococci (NVS) are fastidious Gram-positive cocci comprised of the species Abiotrophia defectiva, Granulicatella adiacens, and Granulicatella elegans. NVS are an important ...cause of bacteremia and infective endocarditis (IE) associated with significant morbidity and mortality. Antimicrobial susceptibility testing (AST) was performed for 14 antimicrobials using the broth microdilution MIC method described in the Clinical and Laboratory Standards Institute (CLSI) M45 guideline. A total of 132 clinical NVS blood isolates collected from 2008 to 2014 were tested. Species level identification of NVS isolates was achieved by 16S rRNA gene sequencing and/or matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). Ninety isolates were identified as G. adiacens, 37 as A. defectiva, and 5 as G. elegans. All isolates were susceptible to vancomycin (MIC90 = 1 μg/ml), and none displayed high-level resistance to aminoglycosides. G. adiacens was considerably more susceptible to penicillin than A. defectiva (38.9% versus 10.8% of isolates susceptible) but was less susceptible to cephalosporins than was A. defectiva (43.3% versus 100% of isolates susceptible to ceftriaxone). Several isolates were resistant to levofloxacin (6%), erythromycin (51%), and clindamycin (10%). The MIC90 for daptomycin was ≥ 4 μg/ml for G. adiacens and A. defectiva. G. elegans isolates were 100% susceptible to all antimicrobials tested, with the exception of erythromycin, to which only 20% were susceptible. This study provides antimicrobial susceptibility data for a recent collection of NVS and demonstrates important NVS species-related differences with respect to susceptibility to penicillin, cephalosporins, carbapenems, and daptomycin. Species-level identification of NVS organisms when susceptibility testing is not readily available may aid in treatment decisions.
Effective evaluations of antimicrobial susceptibility tests (ASTs) require robust study design. The Clinical and Laboratory Standards Institute (CLSI) Subcommittee on Antimicrobial Susceptibility ...Testing has recognized that many published studies reporting the performance of commercial ASTs (cASTs) suffer from major design and/or analysis flaws, rendering the results difficult or impossible to interpret. This minireview outlines the current consensus of the Methods Development and Standardization Working Group of the CLSI Subcommittee on Antimicrobial Susceptibility Testing regarding best practices for systematic evaluation of the performance of an AST, including the analysis and presentation of essential data intended for publication.
Ceftazidime-avibactam is the first antimicrobial approved by the U.S. FDA for the treatment of carbapenem-resistant Enterobacteriaceae. Avibactam, a non-β-lactam β-lactamase inhibitor, inactivates ...class A serine carbapenemases, including Klebsiella pneumoniae carbapenemase (KPC). We report a KPC-producing K. pneumoniae isolate resistant to ceftazidime-avibactam (MIC, 32/4 μg/ml) from a patient with no prior treatment with ceftazidime-avibactam.
Ceftolozane-tazobactam (C/T) and ceftazidime-avibactam (CZA) MICs were evaluated for a collection of 309 beta-lactam-resistant isolates of
recovered from three institutions in the area of Los ...Angeles, CA. Overall, 12.0% of isolates were susceptible to imipenem, 15.9% were susceptible to meropenem, 20.7% were susceptible to piperacillin-tazobactam, 24.6% were susceptible to ceftazidime, 25.9% were susceptible to cefepime, 72.5% were susceptible to C/T, and 61.8% were susceptible to CZA. Among C/T-resistant isolates, 9.1% were CZA susceptible, whereas 36.4% of CZA-resistant isolates were susceptible to C/T.
Antimicrobial resistance is the most pressing medical challenge of the past decade. At the front line are clinical laboratories, which are responsible for accurately reporting antimicrobial ...susceptibility test (AST) results to clinicians and public health authorities. The ability of the laboratory to detect resistance has been hampered by several factors. In 2016, the 21st Century Cures Act was signed into law, marking an important step toward resolving many regulatory dilemmas that hampered development and updates to commercial AST systems (cASTs). We describe the pathway and history of U.S. regulation of cASTs and outline both the rewards and unmet needs possible from the 21st Century Cures Act.
Antibacterial susceptibility testing (AST) is performed to guide therapy, perform resistance surveillance studies, and support development of new antibacterial agents. For 5 decades, broth ...microdilution (BMD) has served as the reference method to assess
activity of antibacterial agents against which both novel agents and diagnostic tests have been measured. BMD relies on in vitro inhibition or killing of bacteria. It is associated with several limitations: it is a poor mimic of the
milieu of bacterial infections, requires multiple days to perform, and is associated with subtle, difficult to control variability. In addition, new reference methods will soon be needed for novel agents whose activity cannot be evaluated by BMD (e.g., those that target virulence). Any new reference methods must be standardized, correlated with clinical efficacy and be recognized internationally by researchers, industry, and regulators. Herein, we describe current reference methods for in vitro assessment of antibacterial activity and highlight key considerations for the generation of novel reference methods.
Limited methods for colistin MIC determination are available to clinical microbiology laboratories. The purpose of this study was to evaluate the accuracy of the colistin broth disk elution (CBDE) ...test compared to that of broth microdilution (BMD) for identifying colistin MICs. CBDE was compared to colistin BMD using a collection of Gram-negative bacilli tested at two U.S. microbiology laboratories. The isolates tested included 121 retrospective clinical isolates, 45 prospective clinical isolates, and 6
-positive
isolates. CBDE was performed with four 10-ml cation-adjusted Mueller-Hinton broth tubes per isolate, to which 0, 1, 2, and 4 colistin 10-µg disks were added, generating final concentrations in the tubes of 0 (growth control), 1, 2, and 4 µg/ml, respectively. MICs were evaluated visually and interpreted using Clinical and Laboratory Standards Institute breakpoints. Site 2 also compared CBDE to the reference broth macrodilution (BMAD) method (
= 110 isolates). Overall, CBDE yielded a categorical agreement (CA) and essential agreement (EA) of 98% and 99%, respectively, compared to the results of colistin BMD. Very major errors occurred for
-producing strains, with MICs fluctuating from 2 to 4 µg/ml on repeat testing. The results for all other isolates were in CA with those of BMD. CBDE versus BMAD had an EA of 100% and a CA of 100%. Compared to currently used techniques, CBDE is an easy and practical method to perform colistin MIC testing. Some
-producing isolates yielded MICs of 2 µg/ml by CBDE and 4 µg/ml by BMD. As such, the results for isolates with colistin MICs of 2 µg/ml by CBDE should be confirmed by the reference BMD method, and isolates with MICs of ≥2 µg/ml should be evaluated for the presence of
genes.
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