Evaluation of Early Reading of Broth Microdilution Technique for Polymyxin B.

Delay in the results of standard phenotypic susceptibility tests is the main obstacle to adequate antibiotic treatment. For this reason, the European Committee for Antimicrobial Susceptibility Testing has proposed the Rapid Antimicrobial Susceptibility Testing for the disk diffusion method directly from blood culture. However, to date, there are no studies evaluating early readings of polymyxin B broth microdilution (BMD), the only standardized methodology for assessing susceptibility to polymyxins. This study aimed to evaluate modifications in the BMD technique for polymyxin B using fewer antibiotic dilutions and reading after an incubation time of 8-9 hr (early reading) in comparison to 16-20 hr of incubation (standard reading) for isolates of Enterobacterales, Acinetobacter baumannii complex, and Pseudomonas aeruginosa. A total of 192 isolates of gram-negative bacteria were evaluated and the minimum inhibitory concentrations were read after early and standard incubations. The early reading presented 93.2% of essential agreement and 97.9% of categorical agreement with the standard reading of BMD. Only three isolates (2.2%) presented major errors and only one (1.7%) presented a very major error. These results indicate a high agreement between the early and the standard reading times of BMD of polymyxin B.

Clonal diversity of Acinetobacter clinical isolates producing NDM-type carbapenemase in Cuba, 2013-19.

Objectives: Our study aimed to elucidate the clonal diversity of carbapenem-resistant Acinetobacter clinical isolates producing NDM-type carbapenemase collected through national surveillance in Cuba during a 7-year period (2013-19). Methods: A total of 199 isolates of Acinetobacter spp. from 37 hospitals in 12 provinces were genetically analyzed for their species, carbapenemase genes and genotypes. Sequence type (ST) and OXA-51-like gene type were determined for bla NDM-positive isolates. Results: Most isolates (95%) were identified as species of Acinetobacter calcoaceticus-baumannii complex, with A. baumannii being the majority. Acquired carbapenemase genes were assigned to bla OXA or bla NDM type; the most commonly detected gene was bla OXA-23-like (49%), followed by bla OXA-24-like (20%) and bla NDM (15%). Twenty-nine bla NDM-positive isolates (22 A. baumannii, 2 A. pittii, 2 A. johnsonii, 3 other species) were differentiated into 19 STs, including the most common, ST23. Though NDM genes were mostly typed as bla NDM-1, a novel bla NDM-42 was identified in an ST79 A. baumannii isolate. bla OXA-51-like genes of NDM-positive A. baumannii were discriminated into 10 OXA types, including 2 novel ones. Conclusions: Our study indicated the spread of bla NDM to various clones of A. baumannii and other Acinetobacter spp. in Cuba.

Sensibilidad in vitro de cepas chilenas de Cryptococcus neoformans de origen clínico / In vitro susceptibility of Chilean Cryptococcus neoformans strains of clinical source

Resumen Introducción: Las infecciones por levaduras del género Cryptococcus afectan principalmente a pacientes con déficit de la inmunidad mediada por células. Han sido escasos los estudios de sensibilidad realizados para este género en Chile. Objetivos: Determinar la sensibilidad in vitro de Cryptococcus sp a antifúngicos de uso habitual y evaluar la concordancia esencial entre sensibilidad determinada por microdilución en caldo y por difusión en agar con tiras comerciales. Materiales y Método: Estudio descriptivo de 21 cepas aisladas desde liquido céfalo-raquídeo y sangre. Las CIM50 y CIM90 para fluconazol, voriconazol y anfotericina B se determinaron por microdilución en caldo (Sensititre Yeast One®) y por difusión en agar con tiras comerciales (MIC Test Strips). Resultados: Todas las cepas correspondieron a C. neoformans. Los rangos de CIM50 y CIM90 para cada antifúngico estudiado fueron amplios por ambos métodos. La concordancia esencial entre microdilución y difusión en agar con tiras comerciales fue de 24, 62 y 29% para fluconazol, voriconazol y anfotericina B, respectivamente. Conclusiones: La prueba de Sensititre Yeast One® y la de difusión en agar con tiras comerciales, MIC Test Strips, tienen una pobre concordancia esencial para fluconazol y anfotericina B.

Abstract Background: Cryptococcus yeast infections primarily affect immunocompromised patients. There have been few susceptibility studies conducted for this genus in Chile. Aims: To determine the in vitro susceptibility to commonly used antifungals and evaluate the concordance between susceptibility determined by microdilution in broth and commercially available strips. Methods: Descriptive study of 21 Cryptococcus strains, isolated from cerebrospinal fluid and blood. The MIC50 and MIC90 for fluconazole, voriconazole and amphotericin B was determined by broth microdilution (Sensititre Yeast One®) and by commercial drug sensitivity strips (MIC Test Strips). Results: All strains corresponded to C. neoformans. The ranges of MIC50 and MIC90 for each antifungal studied were wide by both methods. The essential agreement between Sensititre Yeast One test and strips was 24, 62 and 29% for fluconazole, voriconazole and amphotericin B, respectively. Conclusions: The Sensititre Yeast One test and MIC Test Strips exhibited poor essential concordance, especially for fluconazole and amphotericin B.