Multiresistant plasmids from Pseudomonas aeruginosa highly resistant to either or both gentamicin and carbenicillin

The patterns and transmissibility of antibiotic resistance among clinical strains of Pseudomonas aeruginosa

Four hundred and ninety-eight predominantly pyocin-type 10 clinical strains of Pseudomonas aeruginosa were analyzed for resistance to carbenicillin, cefoperazone, cefotaxime, ceftazidime, gentamicin, amikacin and netilmicin. Based on NCCLS-recommended MIC breakpoints, 245 strains were found to be resistant, of which 41.6% were resistant to carbenicillin, 38% to gentamicin, 37.8% to netilmicin, 26.3% to cefoperazone, 17.9% to cefotaxime, 0.6% to amikacin and none to ceftazidime. Quadruple resistance to carbenicillin, cefoperazone, gentamicin and netilmicin was the most frequent pattern observed. Resistance to older antibiotics (kanamycin, streptomycin and tetracycline) and to mercuric chloride were also common. Conjugation experiments suggested that self-transmissible and non-transmissible plasmids occurred in at least 66 strains.

Characteristics of gentamicin resistance in nosocomial infections

Characteristics of gentamicin resistance were studied in gram-negative bacilli from 50 consecutive patients with nosocomial infection, during a time when gentamicin resistance had recently become prevalent at Medical University Hospital. Burns, decubitus ulcers, and cystic fibrosis were common precipitating factors for acquisition of gentamicin-resistant organisms. Pseudomonas aeruginosa accounted for 76% and Enterobacteriaceae for 24% of isolates. There was high prevalence of cross-resistance to amikacin (61%) and tobramycin (58%). Of the P aeruginosa strains 36% possessed plasmids which were rapidly detected by agarose gel electrophoresis. None of the isolates transferred gentamicin resistance. Representative isolates failed to elaborate aminoglycoside-modifying enzymes or to take up labelled amikacin. Multiple immunotypes of P aeruginosa were identified. These data suggest that a nonplasmid mediated resistance mechanism such as impermeability was responsible for the emergence of gentamicin resistance.

Antibacterial activity of apalcillin (PC-904) against gram-negative bacilli, especially ampicillin-, carbenicillin-, and gentamicin-resistant clinical isolates

Apalcillin (PC-904) is active against carbenicillin- and ampicillin-resistant strains of gram-negative bacilli. Among Pseudomonas aeruginosa strains highly resistant to carbenicillin (>/=3,200 mug/ml), half of them were susceptible to PC-904 at a concentration of 50 to 1,600 mug/ml. The minimal inhibitory concentration of PC-904 against P. aeruginosa strains resistant to carbenicillin (400 to 1,600 mug/ml) ranged from 3.1 to 25 mug/ml. Ampicillin- and carbenicillin-resistant Enterobacteriaceae strains were similarly susceptible to PC-904. However, drug resistance to PC-904 was already apparent among some strains of P. aeruginosa, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, P. vulgaris, and P. morganii, recently isolated in Japan; i.e., 4, 35, 32, 4, 6, and 14% of strains isolated were resistant. PC-904 was more active, on the other hand, than ampicillin and carbenicillin against antibiotic-susceptible Enterobacteriaceae and also showed high activity against most species of Pseudomonadaceae, especially P. cepacia and P. aeruginosa. The minimum inhibitory concentrations of PC-904 were greatly affected by inoculum size when the organisms tested were strains producing large amounts of beta-lactamase.

Cross infection in a surgical ward caused by Pseudomonas aeruginosa with transferable resistance to gentamicin and tobramycin

An outbreak of gentamicin- and tobramycin-resistant Pseudomonas aeruginosa infection occurred in a surgical ward over a three-month period. Resistant Ps. aeruginosa strains with the same serological, phage, and pyocin type were cultured from the urine of six patients. Identical organisms were found on urine bottles, bedpans, and the hands of attendant staff. Inadequate disinfection played a major role in cross-infection. Isolates of the epidemic strain from each of the patients and of an unrelated but similarly resistant Ps. aeruginosa from one of them could transfer resistance to a recipient strain of Ps. aeruginosa. Resistance to gentamicin, kanamycin, tobramycin, sulphonamides, and mercuric chloride was determined by R factors belonging to Pseudomonas incompatibility group P-3. Aminoglycoside resistance was due to acetylation.