Clonal comparison of Staphylococcus aureus isolates from healthy pig farmers, human controls, and pigs

Abstract

Pig farming is a risk factor for increased nasal Staphylococcus aureus colonization. Using sequence typing and phylogenetic comparisons, we showed that overcolonization of farmers was caused by a few bacterial strains that were not present in nonfarmers but often caused swine infections. This finding suggests a high rate of strain exchange between pigs and farmers.

Figure

Unrooted tree showing the phylogenetic relationships among Staphylococcus aureus isolates from pig farmers (PF), bank or insurance workers (BIW), and swine (S). The tree was obtained by the neighbor-joining method, based on the comparison of partial sequences of 7 housekeeping genes (arcC, aroE, glpF, gmk, pta, tpi, and yqiL). Values (in percentages) above the lines indicate how the tree's branches are supported by the results of bootstrap analysis. Scale bar = accumulated changes per nucleotide. Isolates from PF, BIW, and S are indicated by red, green, and blue triangles, respectively. Letters between square brackets indicate departments where strains were isolated (CA, Côte d'Armor; F, Finistère; IV, Ile et vilaine; M, Morbihan; ML, Maine et Loire;V, Vendée;Y, Yonne). Letters in parenthesis indicate the antimicrobial agents to which strains were resistant (E, erythromycin; G, gentamicin; K, kanamycin; L, lincomycin; M, methicillin; P, penicillin; Pef, pefloxacin; Pri, pristinamycin; and T, tobramycin). ST, sequence type. ST numbers shown on the right of the tree are from the S. aureus multilocus sequence typing database.