Staphylococci with markers of antibiotic resistance collected from blood cultures

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Vittorio Focarelli *
Vincenzo Rondinelli
Stefania Giglio
Raffaele Saraceno
Pasquale Minchella
Maria Gabriella Lepore
Nicola Iiritano
Paolo Opipari
Sandra Castagna
Teresa Alcaro
Rosanna Masciari
(*) Corresponding Author:
Vittorio Focarelli | r.masciari@teletu.it

Abstract

Introduction: Blood culture is still the gold standard for the detection of the causative agent of sepsis. Especially in intensive care patients and those with vascular catheters, the most common organisms isolated are coagulase-negative staphylococci (CoNS) and Staphylococcus aureus, both characterized by multidrug resistance. Purposes of our work are the study of the incidence of markers of resistance in staphylococci and evaluation of potential changes over the years. Materials and methods: In the period January 2008-June 2011 5239 blood cultures were analyzed.They were mainly obtained from the departments of Intensive Care, Cardiology, Hematology, General Medicine, Emergency Medicine, Infectious Diseases, Oncology, Pulmonology and Pediatric Hematoncology. The vials containing the blood were incubated in the BACTEC 9120 automated tool of Becton Dickinson and susceptibility testing performed with the Phoenix instrument of the same company. Results:Within a total of 5239 blood cultures, 3967 (75.7%) were negative and 1272 (24.3%) positive. Fungi were isolated in 6.2% (79) of the positive ones, Gram-negative bacteria in 24.6% (313) and Gram-positive bacteria in 69.2% (880). Within the latter, 187 (21.2%) were not staphylococcal isolates, 693 (78.8%) were stafiloccocci mainly represented by S. epidermidis, S. aureus, S. hominis, S. haemolyticus and S. saprophyticus. Of the 693 staphylococcal isolates, 436 (62.9%) were b lactamase producers, and between them 336 (77.1%) were methicillin resistant, while only 3 of 436 (0.69%) were S. aureus resistant to vancomycin as well.The incidence of markers of resistance was very high, especially in patients in intensive care and cardiac surgery, who are usually subjected to combined antibiotic therapy. In the three years studied there were no statistically significant differences in the resistance of staphylococci. Conclusions: The data show an alarming high number of multi-resistant staphylococci, which is often a real therapeutic challenge for the clinician. The interpretation of the meaning of the isolation of CoNS entails a thorough evaluation because they are commonly isolated from contaminated blood cultures.

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