A Simplified Method for Testing Bordetella pertussisfor Resistance to Erythromycin and Other Antimicrobial Agents

Present methods of antimicrobial susceptibility testing ofBordetella pertussis are time consuming and require specialized media that are not commercially available. We tested 52 isolates of B. pertussis for resistance to erythromycin, trimethoprim-sulfamethoxazole, chloramphenicol, and rifampin by agar dilution with Bordet-Gengou agar (BGA) containing 20% horse blood (reference method), Etest using BGA and Regan-Lowe agar without cephalexin (RL−C), and disk diffusion using BGA and RL−C. The organisms tested included four erythromycin-resistant isolates ofB. pertussis from a single patient, a second erythromycin-resistant strain of B. pertussis from an unrelated patient in another state, and 47 nasopharyngeal surveillance isolates of B. pertussis from children in the western United States. The results of agar dilution testing using direct inoculation of the organisms suspended in Mueller-Hinton broth were within ±1 dilution of those obtained after overnight passage of the inoculum in Stainer-Scholte medium, which is the traditional method of testing B. pertussis. The Etest method produced MICs similar to those of the agar dilution reference method for three of the four antimicrobial agents tested; the trimethoprim-sulfamethoxazole results were lower with Etest, particularly when the direct suspension method was used. Most of the Etest MICs, except for that of erythromycin, were on scale. Disk diffusion testing using RL−C medium was helpful in identifying the erythromycin-resistant strains, which produced no zone of inhibition around the disk; susceptible isolates produced zones of at least 42 mm. Thus, the antimicrobial susceptibility testing of B. pertussis can be simplified by using the Etest or disk diffusion on RL−C to screen for erythromycin-resistant isolates of B. pertussis.

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Broth Microdilution and Gradient Diffusion Strips vs. Reference Agar Dilution Method: First Evaluation for Clostridiales Species Antimicrobial Susceptibility Testing

Antibiotics ◽

10.3390/antibiotics10080975 ◽

2021 ◽

Vol 10 (8) ◽

pp. 975

Author(s):

Florian Baquer ◽

Asma Ali Sawan ◽

Michel Auzou ◽

Antoine Grillon ◽

Benoît Jaulhac ◽

...

Keyword(s):

Antimicrobial Susceptibility ◽

Susceptibility Testing ◽

Reference Method ◽

Antimicrobial Susceptibility Testing ◽

Dilution Method ◽

Agar Dilution Method ◽

Broth Microdilution ◽

Multicenter Studies ◽

Gradient Diffusion ◽

Agar Dilution

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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Antimicrobial Susceptibility Testing of 59 Strains of Campylobacter fetus subsp. fetus

Antimicrobial Agents and Chemotherapy ◽

10.1128/aac.42.7.1847 ◽

1998 ◽

Vol 42 (7) ◽

pp. 1847-1849 ◽

Cited By ~ 22

Author(s):

Carole Tremblay ◽

Christiane Gaudreau

Keyword(s):

Antimicrobial Susceptibility ◽

Susceptibility Testing ◽

Antimicrobial Susceptibility Testing ◽

Disk Diffusion ◽

Complete Agreement ◽

Campylobacter Fetus ◽

Agar Dilution ◽

Fetus Subsp

The susceptibilities of 59 Campylobacter fetus subsp.fetus isolates to eight antibiotics were studied by the agar dilution, E-test, and disk diffusion methods. None of the isolates were β-lactamase producers. All were susceptible to ampicillin, gentamicin, imipenem, and meropenem as determined by the three methods, with MICs at which 90% of the isolates are inhibited (MIC90s) (determined by agar dilution) of 2, 1, ≤0.06, and 0.12 μg/ml, respectively. Twenty-seven percent of the isolates were resistant to tetracycline, with complete agreement between the agar dilution and disk diffusion results. The MIC90s determined by agar dilution were 2 μg/ml for erythromycin, 1 μg/ml for ciprofloxacin, and 8 μg/ml for cefotaxime.

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Cefiderocol Antimicrobial Susceptibility Testing Considerations: the Achilles' Heel of the Trojan Horse?

Journal of Clinical Microbiology ◽

10.1128/jcm.00951-20 ◽

2020 ◽

Vol 59 (1) ◽

pp. e00951-20 ◽

Cited By ~ 3

Author(s):

Patricia J. Simner ◽

Robin Patel

Keyword(s):

Antimicrobial Susceptibility ◽

Susceptibility Testing ◽

Antimicrobial Susceptibility Testing ◽

Disk Diffusion ◽

Research Use ◽

Gram Negative ◽

Content Type ◽

Mueller Hinton

ABSTRACTCefiderocol (formerly S-649266) is a novel siderophore-conjugated cephalosporin with activity against a broad array of multidrug-resistant (MDR), aerobic Gram-negative bacilli. The siderophore component binds iron and uses active iron transport for drug entry into the bacterial periplasmic space. The cephalosporin moiety is the active antimicrobial component, structurally resembling a hybrid between ceftazidime and cefepime. Like other β-lactam agents, the principal bactericidal activity of cefiderocol occurs via inhibition of bacterial cell wall synthesis by binding of penicillin-binding proteins (PBPs) and inhibiting peptidoglycan synthesis, leading to cell death. Iron concentrations need to be taken into consideration when in vitro antimicrobial susceptibility to cefiderocol is determined. Broth microdilution (BMD) and disk diffusion methods have been developed to determine in vitro activity of cefiderocol. For BMD, cation-adjusted Mueller-Hinton broth (CAMHB) requires iron depletion to provide MICs predictive of in vivo activity. A method to prepare iron-depleted CAMHB (ID-CAMHB) has been described by the Clinical and Laboratory Standards Institute (CLSI). For disk diffusion, standard Mueller-Hinton agar is recommended, presumably because iron is bound in the medium. Currently, clinical FDA and European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints and investigational (research-use-only) CLSI breakpoints exist for interpreting cefiderocol susceptibility results for certain Gram-negative bacilli. Cefiderocol does not have clinically relevant activity against Gram-positive or anaerobic organisms. FDA or EUCAST breakpoints should be applied to interpret results for Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter baumannii complex for patient care until the investigational status has been removed from CLSI breakpoints. Further clinical outcome data are required to assess the effectiveness of cefiderocol for treatment of other Acinetobacter species (non-baumannii complex) and Stenotrophomonas maltophilia at this time, and, as such, antimicrobial susceptibility testing of these organisms should be limited to research use in the scenario of limited treatment options.

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