Escherichia coli and Proteus mirabilis are important urinary tract pathogens. The constant increase in the antibiotic resistance of clinical bacterial strains has become an important clinical problem. The aim of this study was to compare the antibiotic resistance of 141 clinical (Sweden and Poland) and 42 laboratory (Czech Republic) P.mirabilis strains and 129 clinical (Poland) uropathogenic E. coli strains. The proportion of unique versus diverse patterns in Swedish clinical and laboratory P. mirabilis strain collections was comparable. Notably, a similar proportion of unique versus diverse patterns was observed in Polish clinical P. mirabilis and E. coli strain collections. Mathematical models of the antibiotic resistance of E. coli and P. mirabilis strains based on Kohonen networks and association analysis are presented. In contrast to the three clinical strain collections, which revealed complex associations with the antibiotics tested, laboratory P. mirabilis strains provided simple antibiotic association diagrams. The monitoring of antibiotic resistance patterns of clinical E. coli and P. mirabilis strains plays an important role in the treatment procedures for urinary tract infections and is important in the context of the spreading drug resistance in uropathogenic strain populations. The adaptability and flexibility of the genomes of E. coli and P.mirabilis strains are discussed.

INTRODUCTIONThere are only a few papers concerning the sites of phage adsorption in Rhizobium. Barnet & Vincent (1970) suggested that the receptor site for phages 7,7cr, and 8 was associated with the somatic antigen of Rhizobium. Atkins & Hayes (1972) found alterations in lipopolysaccharide (LPS) and lipoprotein (LP) of Rhizobium trifolii mutants that adsorbed phage poorly.To elucidate the attachment site of phage IP to Rhizobium, we studied cell walls and their LPS preparations as phage receptors. METHODSBacterial andphage strains. Rhizobium trifolii strains 24SM, HR, 1 5 2 4~~ and XSM were used in these experiments. Mutants HR and 15, resistant to phage IP, were derived from 2 4~~. The former was obtained by U.V. treatment, whereas the latter was a spontaneous mutant isolated by selection with phage IP. Phage IP propagated on R. trijiolii 2 4 s~ was employed in assays of receptor activity of cell walls and LPS. It does not require divalent ions for its attachment to bacteria (Staniewski, 1968).Media. Bacteria were grown in medium 4, containing (g/l glass-distilled water) : K2HP0,, 3-6; MgS04.7Hz0, 0.5; NaCl, 0.5; ferric ammonium citrate, 0.05; Casamino acids, 3.0; glucose, 10.0; pH 7-6. Bacetylation of cell walls and LPS by NaOH and NH40H. Cell walls and LPS (5 mg/ml) Preparation of cell walls, LPS and polysaccharides (PS).were treated with 0.1 M-NaOH or 2.5 M-NH,OH at 37 "C for I h. The mixture was chilled, neutralized with 0.1 M-HCl and centrifuged. The pellet was washed three times and ly ophilized. LPS oxidation with NaI04. LPS was oxidized according to a modification of the procedure of Foster, Davies & Crumpton (1958). One ml of LPS (10 mg/ml) was mixed with 0.5 ml of 2 % (w/v) NaIO, and incubated at 20 "C for 12 min. Excess NaIO, was decomposed by ethylene glycol. After 20 min, 0.5 ml of I % (w/v) NaBH, was added. Excess NaBH, was then decomposed by acetic acid (0.2 ml) and dialysed owmight against distilled water.Inactivation of phage IP. Cell walls of LPS, at a concentration of I to 50 ,ug/ml in tris-HC1 buffer pH 7.4, were mixed with an equal volume of phage IP containing 6 x IO* plaque forming units (p.f.u.). The mixture was incubated at 37 "C without shaking. At intervals, samples were removed and tested for phage survival using R. trifolii 24SM as the indicator culture. 24Y I C 90Downloaded from www.microbiologyresearch.org by

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