Methicillin resistant- and Methicillin susceptible Staphylococcus aureus: comparison of genomic similarity of strains isolated from human and veterinary specimens using amplified fragment length polymorphism (AFLP).

In consequence of a previous study on Methicillin-resistant (MRSA) and Methicillin-susceptible (MSSA) Staphylococcus aureus isolated from veterinary samples, a correlated study was carried out to evaluate the genetic relatedness among MRSA and MSSA isolated from human and veterinary specimens using the amplified fragment length polymorphism (AFLP) fingerprinting technique. Twenty-four out of 32 veterinary strains and 21 out of 29 human strains were MRSA. The methicillin resistance was evaluated with E-test and the presence of mec A gene was confirmed with PCR. The results of the genomic analysis revealed that all the isolated strains were distinct. An analysis of molecular variance (AMOVA) was also carried out to verify the distribution of variance a) among and within strains of different origin (human and veterinary) and b) among and within MRSA and MSSA strains. The results showed that in both cases the major component of variance was within strains (76.66 and 92.55%, respectively, for the first and second case). A more accurate molecular technique, like AFLP rather PFGE, and the use of a sophisticate statistical analysis, like AMOVA, are strictly recommended to avoid that different strains are wrongly considered correlated.