Imipenem resistance in aerobic Gram-negative bacteria

A prospective study was undertaken to observe the emergence of resistance to imipenem, if any, among aerobic Gram-negative bacteria. A total of 736 isolates were tested during 1994-95 and less than 1% of them were resistant to imipenem, whereas the next year ('95-'96) the rate increased to 11 of the 903 isolates tested. The resistant isolates during '94-'95 were all Stenotrophomonas maltophilia whereas the spectrum of resistant bacterial species increased in '95-'96 to include Pseudomonas aeruginosa, Burkholderia cepacia, Acinetobacter calcoaceticus, Enterobacter cloacae, Proteus mirabilis and Morganella morganii with a tendency to an increase in the minimum inhibitory concentration (MIC) in the later part of the year. A majority (72%) of the resistant isolates were from patients with burns, and burn wounds were most frequently infected with such organisms. These data suggest that over a period of time aerobic Gram-negative bacteria may develop resistance to imipenem and the pool of such bacteria increases with extensive use of the drug. Non-fermentative aerobic bacteria tend to develop resistance faster with widespread dissemination than Enterobacteriaceae. Hospital Burn Units are a potential source of development of such resistance.