Phagocytosis and killing of slime-producing Staphylococcus epidermidis bypolymorphonuclear leukocytes. Effects of sparfloxacin

F.J. Morán, C. García, C. Pérez-Giraldo, C. Hurtado, M. T. Blanco and A.C. Gómez-García Department of Microbiology, Faculty of Medicine, University of Extremadura, Badajoz, Spain.

SUMMARY
The interaction of slime-producing Staphylococcus epidermidis (S+ strain) with human polymorphonuclear leukocytes (PMNs) was analyzed. The phagocytosis index (PI) and the killing index (KI) were evaluated, and the effect of subinhibitory concentrations (sub-MICs) of sparfloxacin in this interaction was determined. The study was carried out in parallel with a non-slime-producing strain (S- strain). The MIC values of sparfloxacin against both strains was 0.06 mg/ml. In the S- strain the mean values of PI and KI were 82% and 31%, respectively, whereas in the S+ strain these values diminished to 49% and 8%, respectively (p <0.05) when the inocula were prepared in aerobiosis. In a constant flow atmosphere of 5% CO2, the results were similar to the previous ones in the S- strain (PI = 79% and KI = 27%), whereas in the S+ strain a increase in the PI (59%) and a similar value to the KI (9%) were observed. Significant increases (p <0.05) in the PI were noted when PMNs were preincubated with 1/4 and 1/16 MIC of sparfloxacin, and S. epidermidis S+ grown in aerobiosis were used. In the other assays the variations in PI and KI were not statistically significant (p >0.05). Our results confirm that slime protects against phagocytosis and killing by PMNs, although they also suggest that the S+ strains possess additional properties which make them resistant to the action of the PMNs.
Key words: Slime - Staphylococcus epidermidis- PMNs - Phagocytosis - Killing - Sparfloxacin

Actividad fagocítica y bactericida de los leucocitos polimorfonucleares sobre Staphylococcus epidermidis productor de slime. Efecto de esparfloxacino

RESUMEN
Hemos analizado la interacción de una cepa de Staphylococcus epidermidis productora de slime (cepa S+) con leucocitos polimorfonucleares humanos (PMN). El índice de fagocitosis (PI) y el índice bactericida (KI) se estudiaron utilizando una técnica de ensayo microbiológico. El estudio se ha realizado en paralelo con una cepa de S. epidermidis no productora de slime (cepa S- ). La CMI de esparfloxacino sobre ambas cepas fue 0,06 mg/ml. En la cepa S- los valores medios de PI y KI fueron 82% y 31%, mientras que en la cepa S+ estos valores disminuyeron hasta 49% y 8%, respectivamente, cuando los inóculos se prepararon en aerobiosis. En atmósfera con flujo constante de 5% de CO2 los resultados fueron similares a los anteriores en la cepa S- (PI = 79% y KI = 27%), mientras que en la cepa S+ se observó un incremento del PI (59%) y un valor similar del KI (9%). En presencia de 1/4 CMI y 1/16 CMI de esparfloxacino no se notaron variaciones significativas en el PI ni en el KI. Nuestros resultados confirman que la cepa productora de slime protege frente a la actividad fagocítica y bactericida de los PMN, pero también sugieren que las cepas S+ deben poseer otras propiedades adicionales, aún no determinadas, que las hacen más resistentes a la acción de los PMN.
Palabras clave: Slime - Staphylococcus epidermidis - PMN - Fagocitosis - Efecto bactericida - Esparfloxacino

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