Changing Italian nosocomialcommunity trends and h

Authors: F Campanile D Bongiorno M Falcone F Vailati M B Pasticci M Perez A Raglio F Rumpianesi C Scuderi F Suter M Venditti C Venturelli V Ravasio M Codeluppi S Stefani

Publish Date: 2011/08/07

Volume: 31, Issue: 5, Pages: 739-745

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Abstract

Bloodstream infections due to Staphylococcus aureus BSI are serious infections both in hospitals and in the community possibly leading to infective endocarditis IE The use of glycopeptides has been recently challenged by various forms of lowlevel resistance This study evaluated the distribution of MSSA and MRSA isolates from BSI and IE in 4 Italian hospitals their antibiotic susceptibility—focusing on the emergence of hVISA—and genotypic relationships Our results demonstrate that the epidemiology of MRSA is changing versus different STs possessing features between communityacquired CA and hospitalacquired HAMRSA groups furthermore different MSSA isolated from BSI and IE were found with the same backgrounds of the Italian CAMRSA The hVISA phenotype was very frequent 195 and occurred more frequently in isolates from IE and in both the MSSA and MRSA strains As expected hVISA were detected in MRSA with vancomycin minimum inhibitory concentrations MICs of 1–2 mg/l frequently associated with the major SCCmec I and II nosocomial clones this phenotype was also detected in some MSSA strains The few cases of MRhVISA infections evaluated in our study demonstrated that 5 out of 9 patients 55 receiving a glycopeptide died Future studies are required to validate these findings in terms of clinical impactStaphylococcus aureus has become an increasing cause of nosocomial and community acquired bloodstream infections BSI possibly leading to infective endocarditis IE with a high risk of mortality despite aggressive therapy 1 2 Since 1990 the incidence of Saureus bacteremia has increased because of the extensive use of indwelling intravenous catheters Predisposing factors for S aureus infections include severe underlying conditions prolonged hospital stay previous antibiotic treatment and nasal carriage In this context the emergence of methicillinresistant Saureus MRSA is a major clinical challenge particularly for the poor outcome related to such serious infections and for the increasing therapeutic failures In fact the use of glycopeptides has been recently challenged by various forms of reducedsusceptibility VISA and hVISA phenotypes with consequential effects on vancomycin efficacy in MRSA bacteremia and endocarditis 3 4 5Until now only a few studies have compared the clinical and molecular features of MSSA versus MRSA in patients with infective endocarditis or bacteremia 6 7 8 9 10 11 12 Additional knowledge could be useful to understand and correlate the impact of specific genotypic markers with clinical outcomesThis study was undertaken to evaluate MSSA and MRSA distribution in strains from BSI and IE isolated in four Italian hospitals in order to evaluate their genotypic relationship pvl gene distribution antibiotic susceptibility patterns and presence of hVISA strainsThe microbial population consisted of 128 S aureus clinical isolates belonging to 76 patients with definite S aureus IE according to the modified Duke criteria 13 and 52 patients with definite BSI Patients were admitted to four Italian hospitals Modena Bergamo Perugia and Rome between 2007 and 2009 The S aureus isolates randomly selected multiple isolates from the same patient and from other patients at the same time in the same ward were excluded among all S aureus isolates were sent to our laboratory for further characterizations Infection classification was performed as follows nosocomial infection was defined as an IE developing in a patient hospitalized for 48 h before the onset of signs and symptoms consistent with IE and nonnosocomial healthcareassociated infection was defined as an IE diagnosed within 48 h of admission in an outpatient with extended healthcare contact Persistent bacteremia was defined as 3 days of bacteremia despite receipt of an antibiotic to which the isolate was susceptible in vitro 14Both groups of strains BSI and IE were all isolated from blood cultures All staphylococci were reidentified at the species level by the catalase test the S aureus agglutination test Staphylase Test Oxoid Basingstoke Hampshire UK and biochemical tests APIStaph system bioMérieux Bagno a Ripoli FI Italy Methicillin resistance was evaluated by the cefoxitin disk diffusion method and correlated with the presence of the mecA gene 15 16 17Antimicrobial susceptibility was determined by the disk diffusion method according to CLSI guidelines 15 All isolates were tested against a panel of nine antimicrobial agents as follows ampicillin—1 μg ciprofloxacin—5 μg chloramphenicol—30 μg gentamicin—10 μg erythromycin—15 μg clindamycin—2 μg trimethoprimsulfamethoxazole—25 μg rifampin—5 μg and tetracycline—30 μg Oxoid Milan ItalyIn vitro susceptibility testing for vancomycin Sigma Chemical St Louis MO USA teicoplanin quinupristin/dalfopristin Aventis West Malling UK linezolid Pfizer Groton CT USA tigecycline Wyeth Pharmaceuticals Collegeville PA UK and daptomycin Novartis Basel Switzerland was further performed by the broth microdilution method to determine the minimum inhibitory concentrations MICs following the CLSI guidelines The EUCAST guidelines were also used for comparison 15 16 Heteroresistance to glycopeptides was screened using the macro Etest bioMérieux and confirmed by the reference PAP/AUC method S aureus Mu3 hVISA Mu50 VISA and ATCC 29213 were used as control strains as previously described 18

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