Penicillin-susceptible Staphylococcus aureus bacteremia: Epidemiological and clinical relevance. Possible therapeutic implications

Abstract

Introduction

The increase in penicillin susceptibility among Staphylococcus aureus (SA-Pen^S) might have therapeutic relevance. We aimed to study the current situation in our environment.

Material and methods

Over a 2.5 years period, all SA isolates from bacteraemia were analysed. For all isolates, antimicrobial susceptibility profile, beta-lactam resistance genes (blaZ, mecA) and Panton-Valentine leucocidine encoding-genes were studied. For SA-Pen^S-blaZ^negative isolates, spa-type, MLST and the presence of other resistance genes were studied.

Results

Among 84 patients with SA bacteraemia (35.7% MRSA and 64.3% MSSA), 77 were analysed; 22.2% of MSSA isolates were Pen^S and blaZ^negative (Pen-MIC ≤0.03 µg/mL) corresponding to 14.3% of the total SA. In MSSA-Pen^S-blaZ^negative isolates, eight spa-types corresponding to seven clonal complexes were detected.

Conclusion

A high prevalence of MRSA/SA and MSSA-Pen^S-blaZ^negative/MSSA was detected in blood cultures. Pen-MIC ≤0,3 µg/mL corresponded to MSSA-Pen^S-blaZ^negative. This situation raises therapeutic options which should be further evaluated in larger studies and clinical trials.

Resumen

Introducción

El aumento de la sensibilidad a penicilina en Staphylococcus aureus (SA-Pen^S) podría tener relevancia terapéutica. Pretendemos conocer esta situación en nuestro medio.

Material y métodos

Se analizaron bacteriemias por SA durante 2,5 años (2015–2017). Estudiamos la sensibilidad a antimicrobianos, genes de resistencia a beta-lactámicos (blaZ, mecA) y presencia de leucocidina de Panton-Valentine. En aislados SA-Pen^S-blaZ^negativo se determinó el tipo de spa, MLST y genes de resistencia a antimicrobianos no-beta-lactámicos.

Resultados

Hubo 84 pacientes con bacteriemia por SA (35,7% SARM y 64,3% SASM), se analizaron 77. El 22% de los SASM estudiados (n = 11) fueron Pen^S- blaZ^negativo (CMI-Pen ≤0,3 µg/mL), correspondiendo a 14,3% del total de SA. En SASM-Pen^S-blaZ^negativo se detectaron ocho tipos de spa asociados a siete complejos clonales.

Conclusión

Detectamos alta prevalencia de SARM/SA y de SASM-Pen^S-blaZ^negativo/SASM en hemocultivos. Una CMI-Pen ≤0,3 µg/mL se correspondió con SASM-Pen^S-blaZ^negativo. Esta situación plantea opciones terapéuticas que deberán reevaluarse con estudios más amplios y ensayos clínicos.