Aislamiento de Candida dubliniensis en distintos materiales clínicos: Análisis de métodos fenotípicos de diferenciación con Candida albicans / Isolation of Candida dubliniensis in different clinical samples: Analysis of phenotypical methods to differenciate from Candida albicans

Con el objeto de estimar la frecuencia de aislamientos de Candida dubliniensis en materiales clínicos en el Hospital de Infecciosas F. J. Muñiz, se identificaron 388 levaduras entre setiembre de 2005 y agosto de 2007. Doscientos doce aislamientos presentaban color verde en CHROMagar® y producían tubos germinativos y clamidoconidias en agarleche. Para diferenciar cuales de ellos correspondían a Candida albicans o a C. dubliniensis, se utilizaron distintos métodos fenotípicos y se evaluó la utilidad de cada técnica a fin de proponer un algoritmo de identificación simple, económico y confiable. Se estudió el color en 2 medios con sustratos cromogénicos, la producción de clamidoconidias en medios de Staib, agar tomate-zanahoria y agar-tabaco; en este último medio también se evaluaron las características macromorfológicas de las colonias; se evaluó la presencia de actividad lipolítica (medio-opacidad), capacidad de desarrollo a 45 °C y asimilación de D-xilosa. El 6,1% (13/212 aislamientos) correspondió a C. dubliniensis (3,3% del total de levaduras). No se pudo diferenciar entre ambas especies por el color en los medios cromogénicos usados. Las pruebas que resultaron más sensibles y específicas fueron crecimiento a 45 °C, asimilación de D-xilosa, color y desarrollo en agar-tabaco. C. albicans produjo clamidoconidias en los 3 medios diferenciales, entre 11,6% y 15,1% de los casos. La presencia de lipasas se evidenció en el 95,6% de C. albicans pero 2 de las 13 cepas de C. dubliniensis también presentaron halo de opacidad. Consideramos que se deben usar, al menos, 3 métodos diferentes para discriminar entre estas levaduras ya que ninguna prueba es absolutamente sensible o específica.

In order to estimate the frequence of Candida dubliniensis in clinical samples in F. J. Muñiz Infectious Diseases Hospital, a total of 388 yeasts from September 2005 to August 2007. There were 212 isolates which presented a green color on CHROMagar® Candida medium and produced germ tubes and chlamidoconidiae in milk-agar; so as to distinguish whether they corresponded to Candida albicans or C. dubliniensis, different phenotypical methods were utilized. It was also evaluated the usefulness of each one in order to suggest a simple, economic and reliable identification algorithm. Each isolate was subcultured in two chromogenic media and then, the following determinations were done: chlamidospores production in Staib-agar, tomato-carrot-agar and tobacco-agar, colonies macromorphology was also studied in the last medium; opacity-test in Tween 80-CaCl2 agar (lipase activity), growing capacity at 45 °C, and D-xylose assimilation. Thirteen strains (6.1%) corresponded to C. dubliniensis. The difference in color between both species on chromogenic media was not so stressed as it is pointed out in some works. The more specific and sensitive tests were the ability to grow at 45 °C, D-xylose assimilation, color and macroscopic appearance in tobacco-agar. Between 11.6% and 15.1% of C. albicans strains produced chlamidoconidiae in the 3 differential media tested. The opacity halo (lipase) was evident in 95.6% of C. albicans isolates but 2 out of 13 C. dubliniensis also presented precipitation halo. We consider that at least 3 different phenotypical methods should be used to distinguish properly these two species since none of the tests is absolutely sensitive or specific.

[Isolation of Candida dubliniensis in different clinical samples. Analysis of phenotypical methods to differentiate it from Candida albicans]. / Aislamiento de Candida dubliniensis en distintos materiales clínicos. Análisis de métodos fenotípicos de diferenciación con Candida albicans.

In order to estimate the frequence of Candida dubliniensis in clinical samples in F. J. Muñiz Infectious Diseases Hospital, a total of 388 yeasts from September 2005 to August 2007. There were 212 isolates which presented a green color on CHROMagar Candida medium and produced germ tubes and chlamidoconidiae in milk-agar; so as to distinguish whether they corresponded to Candida albicans or C. dubliniensis, different phenotypical methods were utilized. It was also evaluated the usefulness of each one in order to suggest a simple, economic and reliable identification algorithm. Each isolate was subcultured in two chromogenic media and then, the following determinations were done: chlamidospores production in Staib-agar, tomato-carrot-agar and tobacco-agar, colonies macromorphology was also studied in the last medium; opacity-test in Tween 80-CaCl2 agar (lipase activity), growing capacity at 45 degrees C, and D-xylose assimilation. Thirteen strains (6.1%) corresponded to C. dubliniensis. The difference in color between both species on chromogenic media was not so stressed as it is pointed out in some works. The more specific and sensitive tests were the ability to grow at 45 degrees C, D-xylose assimilation, color and macroscopic appearance in tobacco-agar. Between 11.6% and 15.1% of C. albicans strains produced chlamidoconidiae in the 3 differential media tested. The opacity halo (lipase) was evident in 95.6% of C. albicans isolates but 2 out of 13 C. dubliniensis also presented precipitation halo. We consider that at least 3 different phenotypical methods should be used to distinguish properly these two species since none of the tests is absolutely sensitive or specific.