Species identification of 572 clinical isolates of Enterobacteriaceae was determined using an in-house biochemical test panel and API 20E. The overall agreement was 82.7 per cent. When a numerical identification programme for Enterobacteriaceae was used to analyze the results of 440 E.coli isolates, the agreement with API 20E increased from 81.4 to 91.1 per cent. Numerical identification was then employed to evaluate 14 routine biochemical test panels used in 12 Swedish laboratories, and an additional 18 potential new test panel variants. The theoretical identification power of the panels was measured by a scoring system, based on simulated test results for the 14 most common species of Enterobacteriaceae. The results showed wide variations in the performance of different panels, with a number of panels being of insufficient quality. Among the 32 test panels, 6 panels indicated excellent performance. These should be further evaluated for routine laboratory performance. Numerical identification methods constitute powerful tools in the hands of the clinical microbiologist to aid in species identification as well as to analyze the quality of identification charts in use.

The incidence of trimethoprim resistance (MIC greater than 4 micrograms/ml) among urinary pathogens from inpatients was earlier shown to be 1.6-3.6% in Stockholm and 31-49% in Turku in 1977-1978. In strains from this study trimethoprim resistance could be transferred from 13/51 donor strains. Resistance to streptomycin was co-transferred in all matings but 2, and to tetracycline, ampicillin, carbenicillin and chloramphenicol in some cases. Sulphonamide resistance was co-transferred in 2 cases. In all matings but 1 at least 1 plasmid was transferred. A plasmid with similar molecular weight was transferred from 5 Turku and 4 Stockholm donor strains. Restriction enzyme digestion of this plasmid DNA showed many common bands after electrophoresis. In DNA-DNA duplex studies, using 3H-labelled Col E 1::Tn 7 as the probe, the presence of Tn 7 DNA sequences was confirmed in the 5 donor strains from Turku and 1 from Stockholm. Electrophoresis of plasmid DNA with and without digestion with restriction enzymes together with DNA-hybridization were thus useful methods to investigate the presence of genetic determinants for trimethoprim resistance in 2 areas. Other determinants than transposon Tn 7 were also present.

The investigation presents a method of electrophoretic separation of antibacterial drugs which are used in combinations in clinical medicine. Subsequent to electrophoresis in agarose gel, a microbiological assay was performed. This technique permitted the determination of the concentrations of beta-lactam antibiotics, rifampicin, and clindamycin in the presence of aminoglycosides. In therapeutic combinations of fusidic acid and clindamycin, the concentrations of each drug could be determined.

A method for the quantitative determination of plasma concentrations of ampicillin and cloxacillin in mixture is described. The antibiotics were separated by high voltage paper electrophoresis. The high affinity of cloxacillin for albumin seriously interfered with the electrophoretic separation of the antibiotics and the quantitation of cloxacillin. Therefore, prior to electrophoresis, the plasma proteins were digested with trypsin to release cloxacillin. Subsequent to the electrophoretic separation the antibiotics were developed micro‐biologically by agar diffusion using the separated spots on the paper as diffusion centres. The inhibition zones were clearly visible after staining and could be quantitated. The method was evaluated statistically and showed good agreement with the paper disc diffusion method.

Determination of the concentration of each drug in the combination trimethoprim: sulphamethoxazole was performed in patient sera by separation of the drugs by electrophoresis in agarose‐gel followed by microbiological assay. The electrophoretic method was equivalent to the methods used in the routine and showed good reproducibility.