Serotype 012 Pseudomonas aeruginosa resistant to
gentamicin (MIC greater than 4 mg/l) and
carbenicillin (MIC greater than 128 mg/l) occur widely in Europe and are homogeneous in their phenotypic and genetic properties. It has been suggested that a single multiresistant strain of this serotype has become widespread. This study examined the resistance mechanisms present in multiresistant serotype 012 P. aeruginosa isolates from Austria, Belgium, France, Greece, Italy, Holland, West Germany and the UK. Disseminated isolates produced a PSE-1 type
beta-lactamase, correlating with their resistance to the known substrates of this
enzyme (
carbenicillin,
azlocillin and
cefsulodin). These isolates also reacted with gene probes for the
aminoglycoside modifying
enzymes AAC(6')I and ANT(3'). The probe for AAC(6')I is known to cross-react with the gene for AAC(6')II. The fact that the organisms were resistant to
netilmicin,
gentamicin,
sisomicin and
tobramycin, but less so to
amikacin, suggested that the latter
enzyme was produced rather than AAC(6')I.
PSE-1 beta-lactamase and the gene for AAC(6')I/AAC(6')II were absent from the International Antigenic Typing Scheme 012 reference strain, which was sensitive to
beta-lactams and
aminoglycosides, and also from a multiresistant serotype 012 strain isolated at a London
burns unit in 1987. These organisms have been shown previously to be distinct from the disseminated multiresistant strain in their phenotypic properties. Two 012 isolates appeared to have additional resistance determinants to
amikacin and
isepamicin.