Methicillin resistance and vancomycin heteroresistance in Staphylococcus aureus in cystic fibrosis patients

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) infections are increasingly being reported among cystic fibrosis (CF) populations worldwide. In this paper, we sought to examine at the epidemiology, the molecular characterisation and the antibiotic resistance of MRSA isolates in our cohort of CF patients. All MRSA strains were collected prospectively at the University Hospital of Catania, Italy, during a two-year study between mid 2005 to mid 2007 and underwent molecular, pathotype and susceptibility characterisations. Our study demonstrates persisting infections with both hospital-associated (HA-) and community-associated (CA-)MRSA, including Panton-Valentine leukocidin (PVL)-positive strains, in our CF population with an overall prevalence of 7.8%. We demonstrated that, in these patients, persistence was sustained by either identical clones that underwent subtle changes in their toxin content or by different clones over time. The isolation of MRSA in our CF population aged 7-24 years was associated with an increased severity of the disease even if, due to the small sample of patients included and the paucity of data on the clinical outcome, these results cannot be conclusive. Furthermore, three strains were heteroresistant vancomycin-intermediate S. aureus (hVISA), questioning the use of glycopeptides in the treatment of MRSA infections in these patients.

Panton-Valentine leukocidin and biofilm production of Staphylococcus aureus isolated from respiratory tract

“…We detected a higher and stronger biofilm production in CF patients than in non-CF patients. Cafiso et al [12] also stated that all strains isolated from CF patients were medium or strong biofilm producers and this result seemed to be consistent with the ability of these microorganisms to adhere and persist in the lungs of these patients.…”

“…This result is similar with findings of Molina et al [11] who detected PVL gene in any of the 98 MRSA-CF isolates but described a multiresistant biofilm forming clone in most of the patients. In a period between 2005 and 2007, 64 CF patients in Italy were screened and PVL was detected in only 2 isolates [12]. Elizur et al [6] described the emergence of PVL + MRSA infection in 15% of CF patients and demonstrated that the patients who acquired a PVL + organism were more likely to have a focal pulmonary infiltrate on chest radiograph, a markedly greater decline in FEV 1 suggesting that early identification and treatment of CF patients with newly acquired PVL + MRSA may be crucial.…”

Pharmacokinetics and Pharmacodynamics of Aerosolized Antibacterial Agents in Chronically Infected Cystic Fibrosis Patients

“…The first glycopeptide-intermediate S. aureus strain with a vancomycin MIC of 4 to 8 mg/liter was isolated from a CF patient in 1999. Since then, several additional cases in CF patients were reported; vancomycin heteroresistance has been observed in approximately 3% to 5% of CF patients harboring S. aureus (112)(113)(114)(115)(116)(117).…”

Exposure of Staphylococcus aureus to Subinhibitory Concentrations of β-Lactam Antibiotics Induces Heterogeneous Vancomycin-Intermediate Staphylococcus aureus

“…In clinical situations, certain patient populations, such as cystic fibrosis patients, are more chronically exposed to beta-lactam antibiotics than others. In this context, h-VISA strains have been isolated from patients who were not previously exposed to glycopeptides (12,13). A retrospective study of cystic fibrosis patients' clinical characteristics that was conducted at our hospital suggested that ceftazidime (CAZ), a beta-lactam largely used to treat Pseudomonas aeruginosa infections in such patients, may be a risk factor for the development of h-VISA (14).…”