Studies on ampicillin resistance in Achromobacter xylosoxidans. Brief report

Population analyses of susceptibility to ampicillin in ampicillin-susceptible and ampicillin-resistant strains of Achromobacter xylosoxidans revealed the existence of ampicillin-resistant subpopulations in ampicillin-susceptible isolates. Bacteria resistant to a concentration four times the one that inhibited the majority population had a frequency of 10(-3) to 10(-4). Strains isolated from aqueous environments are often found susceptible to ampicillin, while sporadic cases of infections with A. xylosoxidans are often caused by ampicillin-resistant strains. We suggest that the isolation from clinical specimens of ampicillin-susceptible strains, therefore, may be an indication of nosocomial infections due to recently contaminated aqueous solutions or medical equipment.