Evaluation of the PREVI® Isola automated seeder system compared to reference manual inoculation for antibiotic susceptibility testing by the disk diffusion method

Abstract

The disk diffusion (DD) method remains the most popular manual technique for antibiotic susceptibility testing (AST) in clinical microbiology laboratories. This is because of its simplicity, reproducibility, and limited cost compared to (automated) microdilution systems, which are usually less sensitive at detecting certain important mechanisms of resistance. Here, we evaluate the PREVI® Isola automated seeder system using a new protocol for spreading bacterial suspensions (eight deposits of calibrated inocula of bacteria, followed by two rounds of rotation) in comparison with manual DD reference testing on a large series of clinical and reference strains. The average time required for seeding one agar plate for DD with this new protocol was 51 s per plate, i.e., 70 agar plates/h. Reproducibility and repeatability was assessed on three reference and three randomly chosen clinical strains, as usually requested by the European Committee on Antimicrobial Susceptibility Testing (EUCAST), and was excellent compared to the manual method. The standard deviations of zones of growth inhibition showed no statistical discrimination. The correlation between the two methods, assessed using 294 clinical isolates and a panel of six antibiotics (n = 3,528 zones of growth inhibition measured), was excellent, with a correlation coefficient of 0.977. The new PREVI® Isola protocol adapted for DD had a sensitivity of 99 % and a specificity of 100 % compared to the manual technique for interpreting DD as recommended by the EUCAST.

Noncontiguous finished genome sequence and description of Fusobacterium massiliense sp. nov. isolated from human duodenum

“…Antibiotic susceptibility was tested using a disk diffusion method [22] on Mueller-Hinton E agar (bioMérieux). Seventeen antibiotics were tested (i2a, Montpellier, France): vancomycin 30 μg, colistin 50 μg, gentamycin 15 μg, amoxicillin 25 μg, amoxicillin/clavulanic acid 30 μg, penicillin 10 U, clindamycin 15 μg, metronidazole 4 μg, trimethoprim/sulfamethoxazole 25 μg, oxacillin 5 μg, imipenem 10 μg, tobramycin 10 μg, fosfomycin 50 μg, ceftriaxone 30 μg, rifampicin 30 μg, doxycycline 30 μg and erythromycin 15 μg.…”

Butyricimonas phoceensis sp. nov., a new anaerobic species isolated from the human gut microbiota of a French morbidly obese patient

“…The antibiotic susceptibility of the strain was tested using a disk diffusion method [18] for 21 antibiotics including the following: amoxicillin 25 μg/mL, amoxicillin–clavulanic acid 30 μg/mL, ceftriaxone 30 μg, ciprofloxacin 5 μg, clindamycin (DA15), colistin (CT50), Dalacin 15 μg/mL, doripenem 10 μg/mL, doxycycline 30 IU, erythromycin 15 IU, fosfomycin 10 μg, gentamicin 500 μg, gentamicin 15 μg, imipenem 10 μg/mL, metronidazole 4 μg/mL, oxacillin 5 μg, penicillin G 10 IU, rifampicin 30 μg, sulfamethoxazole 23.75 μg, trimethoprim 1.25 μg, teicoplanin (TEC30) and vancomycin 30 μg (i2a, Montpellier, France). The 1200 scan was used for the interpretation of results (Interscience, Saint-Nom-La-Bretèche, France).…”

Streptococcus xiaochunlingii sp. nov. E24 Isolated From the Oropharynx of Healthy Chinese Children

“…The antibiotic susceptibility of the strain Streptococcus strain E24 was determined using disk diffusion ( Le Page et al, 2015 ) on Mueller-Hinton E agar (bioMérieux, Marcy-l’Étoile, France) consisting of casamino acid 17.5 g/L, beef extract 2.0 g/L, soluble starch 1.5 g/L Agar 17.0 g/L at pH 7.2 ± 0.2 (25°C) (Qingdao Hope Bio-Technology Co., Ltd., Qingdao, China). The antimicrobial agents tested were: vancomycin, ceftriaxone, cefepime, cefotaxime, Rina Thiazole Amine and chloramphenicol (all at 30 μg); ampicillin and penicillin (10 μg); and clindamycin (2 μg).…”