Summary, One hundred and sixty-eight strains of Escherichia coli were isolated from cases of pyelonephritis (24) and lower urinary tract infections (UTI) (144) from hospitalised and outpatient children up to 2 years old. These strains were investigated for the expression of P fimbriae (PF), mannose-resistant and mannose-sensitive haemagglutination, cell-surface hydrophobicity, serum resistance and the production of a-haemolysin (AH), colicins and aerobactin. PF, AH, aerobactin production and serum resistance were significantly more frequent amongst strains expressing mannose-resistant haemagglutination. PF and AH production was significantly more frequent in pyelonephritogenic strains than in lower UTI strains. Serotypes 0 6 and 0 1 12 were isolated most frequently and plasmids were found in the majority of strains tested.
Summary. The role of a-haemolysin (AH) in the resistance of Escherichia coli strains, isolated from patients with extra-intestinal diseases or diarrhoea, to the bactericidal activity of human serum and intracellular killing in polymorphonuclear leucocytes (PMNL) was investigated in uitro. Sets of a-haemolytic and non-haemolytic E. coli strains and sets of isogenic E. coli strains, which included wild-type a-haemolytic strains and derived strains with a reduced production of AH, were used. Compared with non-haemolytic strains, a-haemolytic strains were significantly more resistant to the bactericidal activity of 10 YO and 100 YO human serum and to intracellular killing in PMNL. Higher resistance to serum killing and to intracellular killing in PMNL was also found in wild-type a-haemolytic E. coli than in isogenic bacteria with reduced production of AH. These results provide evidence that production of AH in E. coli strains counteracts both the bactericidal activity of serum and intracellular killing in PMNL.
Thirty-three uropathogenic strains of Pseudomonas aeruginosa were investigated for hemolytic activity in both bacterial broth culture filtrates and isolate lyzates, resistance to bactericidal activity of fresh human serum, resistance to six antibiotics and plasmid DNA profile. Twenty-four of the 33 (73%) bacterial filtrates showed lysis of rabbit erythrocytes, as did the three after guinea-pig erythrocyte treatment. Twelve of 33 isolate lysates showed in parallel lysis of both types of erythrocytes used. Serum resistance was found in 17 (52%) isolates, intermediate resistance in 15 (45 %) isolates and only one isolate showed serum sensitivity. Resistance to antibiotics was detected as follows (in %): tetracycline 94, kanamycin 79, chloramphenicol 76, septrin 73, ampicillin 64, streptomycin 45, gentamicin 18. None of the isolates investigated showed resistance to colistine. With the exception of one isolate, plasmid DNA was detected in all P. aeruginosa strains.
A total of 80 Escherichia coli strains were examined for expression of P‐fimbriae, mannose‐sensitive haemagglutination (MSHA) and mannose‐resistant haemagglutination (MRHA) of human group A erythrocytes and guinea pig erthrocytes, cell surface hydrophobicity and resistance to serum bactericidal activity. Isolates were obtained from urine of children and adults, either with acute pyelonephritis (n = 15 and n = 12) or lower urinary tract infection (UTI) (n = 30 and n = 23, respectively). Results obtained showed that, in E. coli strains isolated both from children and adults with lower UTI, significant differences were not found concerning the incidence of P‐fimbriae, cell surface hydrophobicity and serum resistance. In pyelonephritogenic E. coli isolated from children and adults, the incidence of P‐fimbriae and cell surface hydrophobicity was associated more frequently with the former (87% vs. 42% and 100% vs. 67%, P < 0.05), while serum resistance was associated with the latter (47% vs. 67%, P < 0.05).
The present paper describes isolation and purification of alpha-hemolysin of Escherichia coli. The optimum production medium was found to be the Todd-Hewitt broth. Out of thirteen fractions obtained after separation on Sephadex G-200, two fractions possessed the highest relative specific activity.
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