The zeitgeist of resistance.

The accumulation of bacterial antibiotic resistance is a dramatic demonstration of Darwin's dictum of the survival of the fittest, with serious practical consequences for the treatment of infection. Patterns and mechanisms of resistance undergo continuous evolution and, while the prevalence of methicillin-resistant Staphylococcus aureus has stabilized in the UK, other resistances are proliferating rapidly, notably those to cephalosporins and quinolones among Gram-negative bacteria; carbapenem resistance is growing too, notably in Acinetobacter spp. In contrast, several much-feared resistances, for example to vancomycin in staphylococci, have failed to accumulate significantly, despite repeated emergence. For a resistance to 'succeed', it needs to have a mechanism that imposes little fitness burden, along with a biologically 'fit' host strain or strains. Once this combination arises, control is extremely difficult.