ICU Stay Promotes Enrichment and Dissemination of Multiresistant Coagulase-negative Staphylococcal Strains

Patients in the intensive care unit (ICU) are prone to be colonized and infected by multi-resistant bacteria. It is previously known that nosocomial infections are often preceded by cross-transmission events. The aim of the present investigation was to study the impact of the patient's length of ICU stay on the resistance patterns, diversity and dissemination of coagulase-negative staphylococci (CoNS) within and between patients. Two groups of patients were studied, including 20 consecutive patients sampled within 2 h from admission (short-stayers, SS), and all patients treated for at least 5 d in the ICU (long-stayers, LS), available for sampling every second week (n = 15). Sampling was performed from 5 sites: oropharynx, nares, neck, axilla and perineum. A total of 868 CoNS isolates deriving from LS patients and 403 isolates from SS patients were analysed for antimicrobial susceptibility, clonal diversity and dissemination within and between patients. The highest resistance rates were seen for oxacillin and ciprofloxacin, being 92% and 83%, respectively. Long-stayers were at significantly higher risk of being colonized with CoNS isolates resistant against oxacillin, clindamycin, ciprofloxacin, gentamicin as well as with multiresistant strains. By genotyping 22 phenotypes that were shared among at least 2 patients, 32 PFGE types of which 16 colonized more than 1 individual were identified. One of the clones was isolated from 10 individuals, including 2 SS patients, indicating an epidemic strain. 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 good infection control practice, especially in this vulnerable group of patients.