Molecular epidemiology and virulence of Escherichia coli O16:H5-ST131: comparison with H30 and H30-Rx subclones of O25b:H4-ST131.

The present study was carried out to evaluate the prevalence of the clonal subgroup O16:H5-ST131 and the H30 and H30-Rx subclones among E. coli isolates causing extraintestinal infections and to know their virulence potential. The ST131 clonal group accounted for 490 (16%) of the 2995 isolates obtained from clinical samples in five Spanish hospitals during the study period (2005-2012). Among those 490 ST131 isolates, 456 belonged to serotype O25b:H4, 27 to O16:H5 and seven were O-non-typeable:H4 (ONT:H4). All 27 O16:H5 isolates showed fimH41, whereas fimH30 and fimH22 alleles were the most frequently detected among O25b:H4 isolates. The majority (381/490; 78%) of ST131 isolates belonged to H30 subclone, and 302 of 381 (79%) H30 isolates belonged to the H30-Rx subclone. Of the 27 O16:H5 isolates, 48% produced CTX-M-14; however, none produced CTX-M-15. In contrast, 46% of O25b:H4 isolates produced CTX-M-15 while only 2% produced CTX-M-14. More than a half of the O16:H5 isolates (56%) showed the ExPEC status which was significantly more prevalent within O25b:H4 isolates (81%) (P<0.01), especially among H30-Rx (97%) isolates. In the present study, a modified virotype scheme was applied within which approximately half (52%) of the O16:H5 isolates showed the C1 specific virotype. Despite their low virulence-gene score (mean of virulence genes 6.4 versus 8.5 in O25b:H4 isolates), six out of the 10 O16:H5 isolates assayed showed high virulence in the mouse model of sepsis (killed 90-100% of mice challenged). Furthermore, four O16:H5 isolates of virotypes A and C1, carrying K2 variant of group II capsule, showed lethality at 24h. Thus, certain O16:H5 fimH41 isolates show a similar in vivo virulence to that reported with the highly virulent O25b:H4 H30-Rx isolates (Mora et al., PLOS ONE 2014, e87025), supporting their potential virulence for humans.

[Recommendations for selecting antimicrobial agents for in vitro susceptibility studies using automatic and semiautomatic systems]. / Recomendaciones para la selección de antimicrobianos en el estudio de la sensibilidad in vitro con sistemas automáticos y semiautomáticos.

The number of clinical microbiology laboratories that have incorporated automatic susceptibility testing devices has increased in recent years. The majority of these systems determine MIC values using microdilution panels or specific cards, with grouping into clinical categories (susceptible, intermediate or resistant) and incorporate expert systems to infer resistance mechanisms. This document presents the recommendations of a group of experts designated by Grupo de Estudio de los Mecanismos de Acción y Resistencia a los Antimicrobianos (GEMARA, Study group on mechanisms of action and resistance to antimicrobial agents) and Mesa Española de Normalización de la Sensibilidad y Resistencia a los Antimicrobianos (MENSURA, Spanish Group for Normalizing Antimicrobial Susceptibility and Antimicrobial Resistance), with the aim of including antimicrobial agents and selecting concentrations for the susceptibility testing panels of automatic systems. The following have been defined: various antimicrobial categories (A: must be included in the study panel; B: inclusion is recommended; and C: inclusion is secondary, but may facilitate interpretative reading of the antibiogram) and groups (0: not used in therapeutics but may facilitate the detection of resistance mechanisms; 1: must be studied and always reported; 2: must be studied and selectively reported; 3: must be studied and reported at a second level; and 4: should be studied in urinary tract pathogens isolated in urine and other specimens). Recommended antimicrobial concentrations are adapted from the breakpoints established by EUCAST, CLSI and MENSURA. This approach will lead to more accurate susceptibility testing results with better detection of resistance mechanisms, and allowing to reach the clinical goal of the antibiogram.

Recomendaciones para la selección de antimicrobianos en el estudio de la sensibilidad in vitro con sistemas automáticos y semiautomáticos / Recommendations for selecting antimicrobial agents for in vitro susceptibility studies using automatic and semiautomatic systems

En los últimos años han aumentado los laboratorios de microbiología clínica que han incorporado sistemas automáticos para la determinación de la sensibilidad de los microorganismos a los antimicrobianos. La mayoría, mediante paneles o tarjetas de microdilución, obtienen valores de concentración inhibitoria mínima (CIM) que traducen en categorías clínicas (sensible, intermedio o resistente) e incorporan sistemas expertos para inferir mecanismos de resistencia. Este documento recoge las recomendaciones de un grupo de expertos, designados por GEMARA (Grupo de Estudio de los Mecanismos de Acción y Resistencia a los Antimicrobianos) y MENSURA (Mesa Española de Normalización de la Sensibilidad y Resistencia a los Antimicrobianos), para la inclusión de antimicrobianos y selección de concentraciones en los paneles de sensibilidad de los sistemas automáticos. Se definen diferentes categorías de antimicrobianos (A: deben incluirse en el panel de estudio; B: es recomendable su inclusión, y C: su inclusión es secundaria pero facilita la lectura interpretada) y grupos de antimicrobianos (0: no utilizados en clínica pero útiles para la detección de mecanismos de resistencia; 1: deben estudiarse e informarse como norma; 2: deben estudiarse de manera habitual e informarse selectivamente; 3: deben estudiarse en un segundo nivel e informarse selectivamente, y 4: deben estudiarse en patógenos urinarios aislados en orina y muestras relacionadas). Las concentraciones recomendadas cubren las concentraciones críticas o puntos de corte establecidos por EUCAST (European Committee on Antimicrobial Susceptibility Testing), CLSI (Clinical and Laboratory Standards Institute) y MENSURA. Estos criterios redundarán en una mejor calidad de los resultados, una mejor detección de los mecanismos de resistencia y un cumplimiento del objetivo clínico del antibiograma (AU)

The number of clinical microbiology laboratories that have incorporated automatic susceptibility testing devices has increased in recent years. The majority of these systems determine MIC values using microdilution panels or specific cards, with grouping into clinical categories (susceptible, intermediate or resistant) and incorporate expert systems to infer resistance mechanisms. This document presents the recommendations of a group of experts designated by Grupo de Estudio de los Mecanismos de Acción y Resistencia a los Antimicrobianos (GEMARA, Study group on mechanisms of action and resistance to antimicrobial agents) and Mesa Española de Normalización de la Sensibilidad y Resistencia a los Antimicrobianos (MENSURA, Spanish Group for Normalizing Antimicrobial Susceptibility and Antimicrobial Resistance), with the aim of including antimicrobial agents and selecting concentrations for the susceptibility testing panels of automatic systems. The following have been defined: various antimicrobial categories (A: must be included in the study panel; B: inclusion is recommended; and C: inclusion is secondary, but may facilitate interpretative reading of the antibiogram) and groups (0: not used in therapeutics but may facilitate the detection of resistance mechanisms; 1: must be studied and always reported; 2: must be studied and selectively reported; 3: must be studied and reported at a second level; and 4: should be studied in urinary tract pathogens isolated in urine and other specimens). Recommended antimicrobial concentrations are adapted from the breakpoints established by EUCAST, CLSI and MENSURA. This approach will lead to more accurate susceptibility testing results with better detection of resistance mechanisms, and allowing to reach the clinical goal of the antibiogram (AU)