Standardized broth microdilution antimicrobial susceptibility testing of Francisella tularensis subsp. holarctica strains from Europe and rare Francisella species

Antimicrobial susceptibility testing of anaerobes is challenging. Because MIC determination is recommended by both CLSI and EUCAST, commercial broth microdilution and diffusion strip tests have been developed. The reliability of broth microdilution methods has not been assessed yet using the agar dilution reference method. In this work, we evaluated two broth microdilution kits (MICRONAUT-S Anaerobes® MIC and Sensititre Anaerobe MIC®) and one gradient diffusion strip method (Liofilchem®) for antimicrobial susceptibility testing of 47 Clostridiales isolates (Clostridium, Clostridioides and Hungatella species) using the agar dilution method as a reference. The evaluation focused on comparing six antimicrobial molecules available in both microdilution kits. Analytical performances were evaluated according to the Food and Drug Administration (FDA) recommendations. Essential agreements (EA) and categorical agreements (CA) varied greatly according to the molecule and the evaluated method. Vancomycin had values of essential and categorical agreements above 90% for the three methods. The CA fulfilled the FDA criteria for three major molecules in the treatment of Gram-positive anaerobic infections (metronidazole, piperacillin/tazobactam and vancomycin). The highest rate of error was observed for clindamycin. Multicenter studies are needed to further validate these results.

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Comparative performances of Vitek-2, Disk Diffusion, and Broth Microdilution for antimicrobial susceptibility testing of canine Staphylococcus pseudintermedius

Journal of Clinical Microbiology ◽

10.1128/jcm.00349-21 ◽

2021 ◽

Author(s):

Elisa Rampacci ◽

Michele Trotta ◽

Caterina Fani ◽

Serenella Silvestri ◽

Valentina Stefanetti ◽

...

Keyword(s):

Antimicrobial Susceptibility ◽

Susceptibility Testing ◽

Antimicrobial Susceptibility Testing ◽

Disk Diffusion ◽

Health Concern ◽

Broth Microdilution ◽

Major Error ◽

Staphylococcus Pseudintermedius ◽

Cutaneous Infections ◽

Vitek 2

Staphylococcus pseudintermedius is the primary cause of canine cutaneous infections and sporadically isolated as pathogen from humans. Rapidly emerging antibiotic-resistant strains are creating serious health concern so that accurate and timely antimicrobial susceptibility testing (AST) is crucial for patient care. Here, the performances of AST methods Vitek-2, Disk Diffusion (DD) and Broth Microdilution (BMD) were compared for the determination of susceptibility of 79 S. pseudintermedius isolates from canine cutaneous infections and one from human pyoderma to oxacillin (OXA), amoxicillin/clavulanate (AMC), cephalothin (CEF), gentamicin (GEN), enrofloxacin (ENR), doxycycline (DOX), clindamycin (CLI), inducible clindamycin resistance (ICR), mupirocin (MUP) and trimethoprim-sulfamethoxazole (SXT). Overall, the agreement of DD and Vitek-2 using veterinary AST-GP80 card with reference BMD was ≥ 90%, suggesting reliable AST performances. While DD generated mainly minor errors and one major error for OXA, Vitek-2 produced one very major error for GEN and it failed in identifying one ICR-positive isolate. Moreover, five bacteria were diagnosed as ICR-positive by Vitek-2 but they showed a non-induction resistance phenotype by manual methods. All S. pseudintermedius were interpreted as susceptible or intermediately susceptible to DOX using CLSI breakpoints for human staphylococci that match the DOX concentration range included in AST-GP80. However, this could lead to inappropriate antimicrobial prescription for S. pseudintermedius infections in companion animals. Considering the clinical and epidemiological importance of S. pseudintermedius , we encourage updating action by the system manufacturer to address AST for this bacterium.

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Polymyxin B resistance rates in carbapenem‑resistant Pseudomonas aeruginosa isolates and a comparison between Etest® and broth microdilution methods of antimicrobial susceptibility testing

Experimental and Therapeutic Medicine ◽

10.3892/etm.2020.8777 ◽

2020 ◽

Vol 20 (2) ◽

pp. 762-769

Author(s):

Xu Chen ◽

Jie Xu ◽

Qiongfang Zhu ◽

Yalu Ren ◽

Lina Zhao

Keyword(s):

Pseudomonas Aeruginosa ◽

Antimicrobial Susceptibility ◽

Susceptibility Testing ◽

Polymyxin B ◽

Antimicrobial Susceptibility Testing ◽

Broth Microdilution ◽

Carbapenem Resistant ◽

Resistance Rates

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Multicenter Evaluation of Colistin Broth Disk Elution and Colistin Agar Test: a Report from the Clinical and Laboratory Standards Institute

Journal of Clinical Microbiology ◽

10.1128/jcm.01269-19 ◽

2019 ◽

Vol 57 (11) ◽

Cited By ~ 11

Author(s):

Romney M. Humphries ◽

Daniel A. Green ◽

Audrey N. Schuetz ◽

Yehudit Bergman ◽

Shawna Lewis ◽

...

Keyword(s):

Pseudomonas Aeruginosa ◽

Antimicrobial Susceptibility ◽

Susceptibility Testing ◽

Polymyxin B ◽

Antimicrobial Susceptibility Testing ◽

Broth Microdilution ◽

Content Type ◽

Clinical Laboratories

ABSTRACT Susceptibility testing of the polymyxins (colistin and polymyxin B) is challenging for clinical laboratories. The Clinical and Laboratory Standards Institute (CLSI) Antimicrobial Susceptibility Testing Subcommittee evaluated two methods to enable accurate testing of these agents. These methods were a colistin broth disk elution (CBDE) and a colistin agar test (CAT), the latter of which was evaluated using two inoculum volumes, 1 μl (CAT-1) and 10 μl (CAT-10). The methods were evaluated using a collection of 270 isolates of Enterobacterales, 122 Pseudomonas aeruginosa isolates, and 106 Acinetobacter spp. isolates. Overall, 94.4% of CBDE results were in essential agreement and 97.9% in categorical agreement (CA) with reference broth microdilution MICs. Nine very major errors (VME; 3.2%) and 3 major errors (ME; 0.9%) were observed. With the CBDE, 98.6% CA was observed for Enterobacterales (2.5% VME, 0% ME), 99.3% CA was observed for P. aeruginosa (0% VME, 0.7% ME), and 93.1% CA was observed for Acinetobacter spp. (5.6% VME, 3.3% ME). Overall, CA was 94.9% with 6.8% VME using CAT-1 and improved to 98.3% with 3.9% VME using CAT-10. No ME were observed using either CAT-1 or CAT-10. Using the CAT-1/CAT-10, the CA observed was 99.4%/99.7% for Enterobacterales (1%/0.5% VME), 98.7%/100% for P. aeruginosa (8.3%/0% VME), and 88.5%/92.3% for Acinetobacter spp. (21.4%/14.3% VME). Based on these data, the CLSI antimicrobial susceptibility testing (AST) subcommittee endorsed the CBDE and CAT-10 methods for colistin testing of Enterobacterales and P. aeruginosa.

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