The MYSTIC surveillance programme collects data from centres throughout the world that use the antibiotic meropenem, to compare the antibiotic susceptibility of bacterial isolates in specialist and general units year on year.

Meropenem is a carbapenem-class antibiotic that is active against a broad spectrum of bacteria and is used to treat serious infections in hospital where the causative pathogen is unknown.

Resistance to meropenem is assessed by measuring the precise minimum inhibitory concentration (MIC) of the drug necessary to inhibit bacterial growth. Resistance to eight other antibiotics - imipenem, cefotaxime, ceftazidime, cefepime, tazobactum, ciprofloxacin, gentamicin and tobramycin - is also assessed.

Results to date show that meropenem and imipenem, also a carbapenem-class antibiotic, had the lowest MIC values against the strains tested compared to the other antibiotics.

Lead investigator for the MYSTIC programme, Dr Robert Masterton, says: 'Despite the level of usage, these antibiotics have retained their broad-spectrum activity and potency due to their mechanism of resistance, which is less likely to spread or develop compared to the resistance mechanisms of some other classes of antibiotics.'

Indeed the resistance rates of the other antibiotics tested had not changed significantly during the study period, though the resistance of these to bacterial isolates was already much reduced.