Biomedical subjects
Publications and source records attributed to B Olsson-Liljequist.
The usefulness of the E-Test, a method for determining minimum inhibitory concentrations of antibiotics against bacteria, in the reference work of susceptibility testing is described. Examples are given on the establishment of reference collections of bacterial strains and on quality control, areas that should also be valid for routine clinical bacteriology laboratories.
The antibiotic susceptibility of Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pyogenes and Streptococcus pneumoniae was investigated in five different geographical areas of Sweden in 1990 and compared with results from similar investigations performed in 1983 and 1986. Tests on 100 isolates per species and laboratory were performed by the disk diffusion method, and 10% of the strains plus all resistant ones were sent to the central laboratory for determination of MICs of ampicillin, phenoxymethylpenicillin, cefaclor, loracarbef, erythromycin, tetracycline and trimethoprim/sulfamethoxazole. Beta-lactamase production was found in 7% of H. influenzae and 71% of M. catarrhalis, and reduced susceptibility to penicillin in 3% of S. pneumoniae. Low frequencies (1-3%) of tetracycline resistance were found in H. influenzae and in the 2 streptococcal species, in which also less than 1% of the strains were resistant to erythromycin. Resistance to trimethoprim/sulfamethoxazole occurred in 7% (range 3-14%) of H. influenzae and in 3% of S. pneumoniae. Cefaclor was active against all streptococci except against S. pneumoniae with reduced susceptibility to penicillin. It was active against beta-lactamase negative strains of M. catarrhalis but had, according to the SIR-system, intermediate activity against H. influenzae. Loracarbef was twice as active as cefaclor against H. influenzae but equally active against the 3 other species tested.
Clarithromycin and its 14-hydroxy metabolite (A-62671), were tested against 20 strains of Haemophilus influenzae. Minimum inhibitory and bactericidal concentrations of the two compounds alone and in combination were determined in a microbroth system which allowed continuous turbidimetric measurement for the construction of growth curves. MICs of clarithromycin were 2-8 and 1-4 mg/l for A-62671 for the majority of strains. MBCs were identical to or one dilution higher than the respective MICs. Combinations of the two compounds were inhibitory or bactericidal at concentrations that were lower than the MICs or MBCs. On the basis of fractional inhibitory (FIC) or fractional bactericidal (FBC) concentration indices, the interactions between clarithromycin and its metabolite were defined as additive.
Blood and CSF isolates (n = 629) from Swedish infants up to one year of age were tested in vitro against 13 antimicrobial agents in order to update the guidelines for empiric therapy of septicaemia and meningitis. Ampicillin plus gentamicin provided inadequate empiric therapy for meningitis, due to the poor CSF penetration of the aminoglycoside and the frequent occurrence of bacterial resistance to ampicillin. Ceftazidime and cefuroxime were moderately active, particularly against isolates from small infants. Cefotaxime today seemed to provide the best empiric therapy of septicaemia and meningitis in infants. Because of the occurrence of Listeria and enterococcal infections, ampicillin should initially be added and other combinations are also advisable for the occasional cases of Enterobacter, Citrobacter, Serratia, and Pseudomonas infections. For coagulase-negative staphylococci only vancomycin offered a broad activity (100% at achievable serum levels).
Fusidic acid was shown to be effective in vitro against 30 clinical isolates of Mycobacterium tuberculosis at concentrations of 32-64 mg/l, concentrations which are readily achieved in serum. All but one of 17 Mycobacterium avium complex strains were resistant to fusidic acid at concentrations up to 64 mg/l. However, synergistic effects were shown for 11 of the 17 strains when fusidic acid was combined with ethambutol. Five of the strains were fully susceptible to the combination of fusidic acid (64 mg/l) and ethambutol (4 mg/l). It is suggested that fusidic acid should be evaluated clinically as a potential supplementary drug for treatment of mycobacterial infections.
A national quality control study was performed in 1986 to investigate the standard of performance of the disc diffusion antimicrobial susceptibility testing of Haemophilus influenzae in Sweden. The accuracy of susceptibility interpretations was unacceptably low. A new standardized method for susceptibility testing of H. influenzae was then worked out, and a new method of setting interpretive zone breakpoints was introduced. The susceptibility category of the main population of clinical isolates was determined according to the MIC50 of the strains. The zone histograms of clinical isolates from five reference laboratories were used for the calculation of interpretive breakpoints. For instance, for susceptible strains the mean of the combined zone values from these laboratories +/- 2 S.D. covered the zone range of the susceptible group, and one more S.D. below covered the intermediate/indeterminate group. The new zone breakpoints would place the main population of clinical isolates in the correct susceptibility group, and even make it possible to detect strains with different degrees of reduced susceptibility in the routine test. In a follow-up quality control study in 1988 the interpretive errors for clinical isolates were eliminated for all antibiotics except doxycycline in some laboratories. Laboratory-related zone breakpoints for doxycycline calculated by the single strain regression analysis method led to correct susceptibility interpretations also in these cases.
The in vitro activity of norfloxacin was compared to that of ampicillin, doxycycline, chloramphenicol, trimethoprim in combination with sulfamethoxazole (1/20), and erythromycin, against 272 clinical isolates of gastro-intestinal pathogens. Norfloxacin was the most active compound of those tested with MICs in the range 0.004-2 mg/l. Concentrations inhibiting 90% of the strains (MIC 90) were 0.008 mg/l for Vibrio cholerae, 0.016 mg/l for Aeromonas hydrophila, 0.032 mg/l for Vibrio cholerae non 01, 0.064 mg/l for Vibrio parahaemolyticus, Yersinia enterocolitica 03, enterotoxigenic (ETEC) and enteropathogenic (EPEC) Escherichia coli and Shigella species, 0.125 mg/l for Salmonella species, and 0.5 mg/l for Campylobacter species. Resistance to one or several of the other drugs was seen with higher or lower frequency in all the bacterial species tested. No cross-resistance between any of the other agents and norfloxacin was recorded.
Ciprofloxacin, ofloxacin and norfloxacin were ineffective at clinically relevant concentrations against the Mycobacterium avium complex (MAC) in vitro as measured by radiometric respirometry. Only two of 30 clinical isolates of MAC were susceptible to any of the tested quinolones. By contrast good antibacterial activity was obtained when any of the quinolones was combined with ethambutol. The synergistic effect was most pronounced for the combination of ethambutol and ciprofloxacin, to which 76 of 100 strains were susceptible. It is suggested that the synergism is based on an enhanced penetration of the quinolones by ethambutol.
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The activity of Sch 34343 was determined against 575 strains of anaerobic bacteria by an agar-dilution method. Its activity was compared with that of benzylpenicillin, piperacillin, cefoxitin, imipenem, clindamycin, metronidazole, chloramphenicol, vancomycin, fusidic acid and bacitracin. Sch 34343 and imipenem were the most active agents tested. Based on these results, Sch 34343 appears to be a promising antimicrobial agent for anaerobic infections and warrants further clinical investigations.