Evaluation of antimicrobial susceptibility testing of Nocardia spp. isolates by broth microdilution with resazurin and spectrophotometry

Abstract

Background Nocardia species are ubiquitous in natural environments and can cause nocardiosis. In the present study, the use of Resazurin salt and Spectrophotometry were proposed as alternative methods to reduce subjectivity in the interpretation of susceptibility results to antimicrobials by the broth microdilution method for Nocardia spp. Results The susceptibility of Nocardia spp. isolates to Amikacin, Ciprofloxacin, Minocycline and Trimethoprim-Sulfamethoxazole was evaluated by Minimum Inhibitory Concentration (MIC) determinations by the broth microdilution method. To verify cellular growth, the colour-changing dye Resazurin was applied, the Optical Densities were measured on a spectrophotometer, and both were compared to Clinical and Laboratory Standards Institute (CLSI) Gold Standard method (visual MIC determination). Percentages of essential and categorical agreements and interpretative categorical errors were calculated within each method (intra-reading) and between them (inter-reading). The Gold Standard visual reading demonstrated 100% of essential and categorical intra-reading agreements for Amikacin, and there was no error when compared with the alternative methods. For Ciprofloxacin, the comparison between the Gold Standard and the Spectrophotometric reading showed 91.5% of essential agreement. In the categorical intra-reading analysis for Minocycline, there were 88.1 and 91.7% in the Gold Standard and in the Spectrophotometric readings, respectively, and 86.4% of concordance between them. High rates of categorical agreement were also observed on the Trimethoprim-Sulfamethoxazole analyses, with 93.7% for the Gold Standard, 84.9% for the Resazurin readings, and 80.5% between them. Conclusions The alternative methods with Resazurin and Spectrophotometric readings showed high agreement rates with the Gold Standard.

Potential Antimicrobial and Antibiofilm Properties of Copper Oxide Nanoparticles: Time-Kill Kinetic Essay and Ultrastructure of Pathogenic Bacterial Cells

“…The lowest concentration of CuONPs in which the change in dye’s color occurred was taken as the MIC value. The MBC value was determined when no colony growth was observed after plating directly the contents of wells with concentrations higher than the MIC value [ 40 ]. MIC index (MBC/MIC) was used to describe antibacterial activity.…”

Ephedra alte extracts' GC-MS profiles and antimicrobial activity against multidrug-resistant pathogens (MRSA)

“…Specific structural features, such as functional groups, aromatic systems, stereochemistry, and size/shape, influence the compound's ability to interact with microbial targets and inhibit microbial growth. Understanding this relationship is crucial for identifying key structural determinants and designing effective antimicrobial agents [ [16] , [17] , [18] , [19] ].…”

“…The biological activity of the extracts was evaluated as antimicrobial agents against Salmonella typhimurium (S. typhimurium) ATCC 14028 (Gram-negative bacterium), MRSA, ATCC 43300 (Gram-positive bacterium resistant to antibiotics) and Candida albicans (C. albicans) ATCC 60193 (pathogenic yeast) using disk diffusion and two-fold broth microdilution assays according to Bavelaar et al (2021) [ 16 ], Caso Coelho et al (2021) [ 17 ] and Yücesoy et al (2001) [ 18 ]. Briefly, for the disk diffusion method, sterile disks (6 mm) were loaded with 10 mg of the extract and the disk gently was placed on the surface of Mueller–Hinton agar (Scharlab, S.L., Spain) inculcated by tested microorganisms.…”

Six-Year Prescription Pattern of Antimicrobial Use in Cats at the Veterinary Teaching Hospital of the University of Pisa

“…Antimicrobial susceptibility tests (ASTs): The susceptibility of bacterial isolates was evaluated by broth microdilution tests, allowing for the determination of the minimum inhibitory concentration (MIC) [27].…”