Interacting networks of resistance, virulence and core machinery genes identified by genome-wide epistasis analysis by Skwark, M, Croucher, N, Puranen, S, Chewapreecha, C, Pesonen, M, Xu, Y, Turner, P, Harris, S, Beres, S, Musser, J, Parkhill, J, Bentley, S, Aurell, E, Corander, J