89 Molecular characterization of strains of methicillin-resistant Staphylococcus aureus (MRSA) in patients with cystic fibrosis (CF)

Objectives To evaluate the molecular profile of MRSA strains isolated from the low respiratory tract of CF patients chronically colonized, in order to investigate its origin (HA-MRSA or CA-MRSA) and to examine, in a subgroup of patients, the acquisition of strains with a different molecular profile in the course of time. Methods Forty-four patients (9%) out of the 793 followed at the CF Centre of Milan suffer from MRSA chronic infection. Seventy-eight MRSA strains isolated from these patients have been characterized by: Multiplex PCR ( mec A gene and the SCC mec -type), spa -typing and a specific PCR for Panton Valentine (PVL) gene. Thirty-four out of 44 patients have been monitored over time (T1 = 2012; T2=2014) in order to investigate the molecular profile of MRSA strains isolated after the first infection. Results All 78 MRSA strains have the mecA gene; 76% present SCC mec type IV (CA-MRSA), 21% belong to spa-type t032 (UK-EMRSA-15) and 20% to spa-type t008. Among 4 strains with spa-type t008 and SCC mec type IVa (USA-300), only two show the PVL gene. The remaining 24% present SCC mec type I (HA-MRSA). The molecolar profile of the strains isolated in T2 was the same of the one isolated at T1 in 29/34 patient while 5/34 had different profile. Conclusion The molecular characterization of MRSA strains isolated at Milan CF Centre has shown a high prevalence of CA-MRSA (SCC mec type IV). The distribution of spa-type shows to be similar to that described in other European countries. The different MRSA molecular profiles suggest to carry out genotyping analyses as well, in order to highlight the presence of clones in our CF population.