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Issue Date: 2-Mar-2012
Authors: Spina, Daniela
Title: Pathogenicity of human and animal Staphylococcus aureus isolates
Abstract: Staphylococcus aureus is a commensal and pathogenic organism, adapted to survive in many niches and causing, by the production of a large array of virulence factors, a wide variety of human and animal infections such as Atopic Dermatitis (AD), Cystic Fibrosis (CF), and Bovine Mastitis (BM). The aim of our study was to analyze the biofilm-formation capacity and the virulence-gene content of three different S.aureus groups, collected from sputum of Cystic Fibrosis patients (CF clinical group), lesions or skin of patients affected by Atopic Dermatitis (AD clinical group) and from mammary-gland epithelium of cows affected by Bovine Mastitis (BM animal group) to determine their similarities/differences in terms of antimicrobial-resistance profiles, biofilm production ability, virulence determinant distribution and combinations, and to evaluate if the genetic background of the microrganisms could to be linked to a specific type of infection. Our results show that all samples from the three groups studied were mainly constituted by Methicillin-Susceptible S.aureus (MSSA) strains, whereas Methicillin-Resistant S.aureus isolates (MRSA), were found only in the CF clinical group and the BM animal group, in percentages of 7.8% and 7.14%, respectively. In the CF clinical group, agr-I and II were equally distributed (29 and 30%, respectively) whereas, a prevalence of microrganisms belonging to agr-I genotype, in the AD clinical group strains (42%) and in the BM animal group (89%) was evident. Biofilm production assays showed a higher number of biofilm producer strains, belonging mainly to agr-I, in the AD (88%) and CF (80.73%) clinical groups compared to the BM animal one (64.28%). A different distribution of cap5/8 was found among the same agr-genotypes, only in both AD and CF clinical groups. All S.aureus strains possessed a chromosomal ¿core¿ of virulence genes (icaA, atl, sdrC, clfA/B, and spa adhesion genes, and ¿-toxin, ¿-toxin, and ¿-toxin genes) and an ¿accessory¿ virulence group, present in variable quantity (sdrE, cna, and fnbA adhesion genes, and sea, sec, sed, seq, sek, sej, eta, tst, and lukS/F toxins genes), prevalent in a different manner within all three groups. Studies of gene associations evidenced a specific distribution of accessory virulence determinants both among the four different agr-genotypes, and two capsular antigen types in the AD and CF clinical groups. Moreover, the analysis of the associations among accessory virulence genes showed a prevalence of adhesin genes, strongly associated among themselves, and with one or more accessory toxin genes i.e. sea and tst in the CF clinical group; sea, sec, sej, sek, seq, and tst in the AD clinical group. In conclusion, our data support the hypothesis that specific virulence backgrounds are strongly related to the capacity of S.aureus to colonize specific host districts, such as CF patient lung, AD patient skin and bovine mammary gland, defining ¿infection-specific¿ strains, able to induce diverse diseases.
Appears in Collections:Area 06 - Scienze mediche

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