Abstract
The aim of this study was to characterize multidrug resistant E. faecalis strains from pigs of local origin and to analyse the relationship between resistance and genotypic and proteomic profiles by amplification of DNA fragments surrounding rare restriction sites (ADSRRS-fingerprinting) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI -TOF MS). From the total pool of Enterococcus spp. isolated from 90 pigs, we selected 36 multidrug resistant E. faecalis strains, which represented three different phenotypic resistance profiles. Phenotypic resistance to tetracycline, macrolides, phenicols, and lincomycin and high-level resistance to aminoglycosides were confirmed by the occurrence of at least one corresponding resistance gene in each strain. Based on the analysis of the genotypic and phenotypic resistance of the strains tested, five distinct resistance profiles were generated. As a complement of this analysis, profiles of virulence genes were determined and these profiles corresponded to the phenotypic resistance profiles. The demonstration of resistance to a wide panel of antimicrobials by the strains tested in this study indicates the need of typing to determine the spread of resistance also at the local level. It seems that in the case of E. faecalis, type and scope of resistance strongly determines the genotypic pattern obtained with the ADSRRS-fingerprinting method. The ADSRRS-fingerprinting analysis showed consistency of the genetic profiles with the resistance profiles, while analysis of data with the use of the MALDI- TOF MS method did not demonstrate direct reproduction of the clustering pattern obtained with this method. Our observations were confirmed by statistical analysis (Simpson’s index of diversity, Rand and Wallace coefficients). Even though the MALDI -TOF MS method showed slightly higher discrimination power than ADSRRS-fingerprinting, only the latter method allowed reproduction of the clustering pattern of isolates based on phenotypic resistance and analysis of resistance and virulence genes (Wallace coefficient 1.0). This feature seems to be the most useful for epidemiological purposes and short-term analysis.
Highlights
Bacteria from the genus Enterococcus constitute an important part of the intestinal biota both in humans and in animals
Thirty six resistant strains of E. faecalis belonging to three different phenotypic resistance profiles (A,B and C) met the criteria of multidrug resistance and these strains were selected for further studies (S1 Table)
Phenotypic resistance to tetracycline, macrolides, phenicols, and lincomycin and high-level aminoglycoside resistance to kanamycin, streptomycin, and gentamycin were confirmed by occurrence of at least one corresponding resistance gene in each strain belonging to a particular profile
Summary
Bacteria from the genus Enterococcus constitute an important part of the intestinal biota both in humans and in animals. It has frequently been demonstrated that food animals (including pigs) may constitute a reservoir of resistant bacteria and that the resistance genes may be transferred to the human population [1,2,3]. The phenomenon of spreading the resistance in Enterococcus among humans and animals is mainly due to transfer of conjugative and transferable elements carrying resistance genes during passage of enterococci of animal origin through the intestinal tract. Evidence of human infections caused by animal-origin enterococci has been demonstrated and, such cases are scarce, this path of transmission is possible [4]
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