Evaluation of Staphylococcus aureus nasal carriage rate among patients on haemodialysis - isolation of community-acquired methicillin-resistant Staphylococcus aureus

Abstract number: 1134_02_185

Szczepanik A., Koziol-Montewka M., Baranowicz I., Jozwiak L., Ksiazek A., Kaczor D., Al-Doori Z., Morrison D.

Nasal carriage of Staphylococcus aureus (SA) appears to play a key role in the pathogenesis of infection, particularly in patients on haemodialysis. Compounding the problem is dissemination of methicillin-resistant Staphylococcus aureus (MRSA) and changing epidemiology of this microorganism. MRSA, besides having established itself as a major nosocomial pathogen, has also begun to appear outside hospital settings as community-acquired MRSA (CA-MRSA).

The aim of the study was evaluation of SA nasal carriage rate in haemodialysed patients and molecular analysis of cultured isolates.

Methods:

Nasal swabs were collected from 43 haemodialysed patients. SA isolates were identified using conventional diagnostic methods. Antibiotic susceptibility was determined using the Vitek automated system and the disc diffusion method according to recommendations given by the National Reference Centre for Antimicrobial Susceptibility Testing in Poland. SA isolates were analysed by Pulsed Field Gel Electrophoresis (PFGE) and PCR assays for staphylococcal cassette chromosome mec (SCCmec) typing and detection of the nuc and pvl genes.

Results:

12 (27.9%) patients were SA nasal carriers, but only 1 MRSA isolate was identified. The carrier of MRSA was a 56–year-old male suffering from chronic renal failure and malignancy (true polycythaemia). The patient had a history of previous hospitalization. The MRSA strain was resistant only to B-lactams and tetracycline. The remaining SA isolates were methicillin-susceptible (MSSA) and demonstrated high rates of resistance to penicillin (81.8%) and tetracycline (63.6%). Molecular analysis revealed that the MRSA strain had genetic markers of CA-MRSA: SCCmec type IV, a PFGE pattern corresponding to the common European CA-MRSA (MLST Type ST80) and the pvl locus encoding for Panton-Valentine leukocidin toxin. Among MSSA isolates, several genotypes were identified by PFGE, with the lack of one specific colonizing strain.

Conclusions:

To our knowledge, this is the first report of CA-MRSA in Poland. The results of the study indicate that colonization and the increased risk of subsequent invasive infection associated with significant pathogenic potential of CA-MRSA can occur among persons with predisposing risk factors such as patients on haemodialysis. Although the rate of MRSA colonization was low among examined patients, the risk of endogenous infections associated with MSSA carriage must also be considered.