ICU stay promotes enrichment and dissemination of multi-resistant coagulase-negative staphylococcal clones

Introduction

Patients in the ICU are prone to be colonized and infected by multi-resistant bacteria [1, 2]. It is previously known that nosocomial infections are often preceded by cross-transmission events [3].

The aim of the present investigation was to study the impact of the patient's length of ICU stay on the resistance patterns, clonal diversity and dissemination of coagulase-negative staphylococci (CoNS) within and between patients.

Methods

Two groups of patients were studied, including 20 consecutive patients sampled within 2 hours from admission (shortstayers, SS), and all patients treated for at least 5 days at the ICU (longstayers, LS), available for sampling every second week (n = 23). Sampling was performed from five sites: oropharynx, nares, neck, axilla and perineum. A total of 868 CoNS isolates deriving from LS patients and 403 isolates from SS patients were analyzed for antimicrobial susceptibility, clonal diversity and dissemination within and between patients. All 1271 CoNS isolates were tested for antimicrobial susceptibility and subtyped to the clonal level according to their phenotype with the PhenePlate™ (PhP) system using PhP-CS plates (PhPlate Microplate Techniques AB, Stockholm, Sweden) designed for typing CoNS. The clonal relationship between CoNS isolates clustered as one phenotype isolated from at least two patients was further confirmed by pulsed-field gel electrophoresis.

Results

The highest resistance rates were seen for oxacillin and ciprofloxacin, being 92% and 83%, respectively. LS were at significantly higher risk of being colonized with CoNS isolates resistant against oxacillin, clindamycin, ciprofloxacin, gentamicin as well as with multi-resistant strains. Genotyping revealed 16 clones that colonized more than one patient. One of the clones was isolated from 10 individuals, including two SS patients, indicating an epidemic strain.

Conclusion

Prolonged ICU stay was significantly correlated to decreased clonal diversity, increased endogenous dissemination of resistant strains and cross-transmission. The results emphasize the importance of barrier treatment and other hygienic measures, especially in this vulnerable group of patients.