Epidemiologia locale di MRSA, con riferimento alla circolazione di cloni ospedalieri e comunitari e al possibile ruolo della catena alimentare

ABSTRACT Local epidemiology of MRSA,with reference to the circulation of hospital and community strains and the possible role of the food chain Introduction The aim of this PhD project is to evaluate the local epidemiology of MRSA strains and the related risk to the healthcare environment, the community and the food production chain. According to literature, MRSA is a rising problem in different settings and new strains are spreading all over the world. In addition to HA-MRSA, CA-MRSA e LA-MRSA are new important problems to face. In this contest, this study is focused to estimate the frequency of isolation of MRSA in different kind of samples and to analyze the main features of the collected strains. Comparing the isolates each other, it is possible to underline similarities and correlations and finally understand their specify identity. Materials and methods MRSA strains were isolated using Brain Hearth Infusion (BHI) broth and mannitol salt agar plates. After a further incubation at 35°C for 48 h, suspected colonies were confirmed to be S. aureus and tested for resistance in Müller-Hinton agar with oxacillin (6 μg/ml). MRSA strains are analyzed with antibiograms (Kirby-Bauer), E-test and D-test. Molecular typing techniques as MLVA, PCR multiplex for SCCmec determination, MLST, PCR for tst-1were used for the isolated MRSA. A selection of strains is analyzed with microarray, whole genome sequencing and spa typing. Results Between January 2010 and December 2013 samples of different origin were collected and MRSA was detected. In details, we analyzed: 145 food samples, 71 animal samples, 2452 nasal swabs from the children hospitalized in the NICU (Neonatal Intensive Care Unit) in the University Hospital of Palermo and 500 nasal swabs from healthy children up to 3 years old attending public nursery schools in Palermo. From food and animal samples none MRSA was isolated. Within the food samples 12 MSSA strains were collected (8.3%). 7 The study developed in collaboration with the NICU takes is based upon a four-year surveillance program started in June 2009 and now still ongoing. The frequencies of colonization of MRSA fell from 27% in the first year of study 2009/10 to 10% in the fourth years 2012/2013. In contrast, the rate of colonization of MSSA rose from 5% to 16% in the same four-year period. Most of the isolated MRSA do not have important antibiotic resistances and were recognized with a particular MLVA profile. The dominant strain is identified with MLST as ST22 and SSCmec IVa with PCR multiplex for SCCmec determination. This strain was identified with microarray as CC22-MRSA IV tst1+/ UK-EMRSA-15 “Middle Eastern Variant” and confirmed by tst-1 PCR. The whole genome sequencing was used to estimate the presence of about 350-400 SNPs between a selection of strain collected from 2009 to 2013. To have a whole sight of the situation in the NICU it is useful to specify that different MRSA strains were identified during the study and we want to underline especially the spreading of CA-MRSA ST1 for almost five months with 14 cases of colonization. The study in healthy children attending the nursery schools detected 10 MRSA (2%) and 68 MSSA (13.6%). These ten children positive for MRSA were attending nine different day care centers. No association with specific risk factors was found. Eight MRSA isolates were tst1+ as CC22-MRSA IV tst1+/ UK-EMRSA-15 “Middle Eastern Variant” and identified by spa typing as spa t223. The other two isolates were identified ST1-IVa and ST398-V. They tested negative for PVL and tst1 genes and were resistant to clindamycin and erythromycin. ST398-V was also vancomycin resistant with MIC of 3 mg/L. Two isolates, ST22-IVa and ST1-IVa respectively, were recovered from two children attending the same day care center. None of the family members of the child carrying ST398-MRSA-V reported any exposure to livestock. Conclusions The exposure to the hospital environment is the main risk factor for MRSA. The colonization rates are considerably higher in the NICU than in the nursery schools (10% vs 2% in the last year of study). On the other hand, the emergent spreading of MRSA in the community should be monitored locally. In this study it is demonstrated the circulation of the same MRSA strain CC22-MRSA IV tst1+/ UK-EMRSA-15 “Middle Eastern Variant” spa t223 in the NICU and in the nursery schools. A single MRSA strain is able to spread in hospital and community setting as an evidence of the great ability to adaptation. This same strain was before identified in Abu 8 Dhabi and USA from foreign people. In this contest, our evaluation of the local epidemiology of MRSA is very important to understand what is happening globally and what we may expect for the future. In addition, the surveillance program done in the NICU was a very helpful tool to control the circulation of MRSA and reduce the rate of colonization and the study in the nursery schools is important to evaluate the situation in the community.