The effects of ethyleneglycoltetra-acetic acid (EGTA) and EGTA+magnesium (MgEGTA) on the viable counts of 10 strains of Escherichia coli O6 have been studied in normal human serum (NHS), heat-inactivated serum (HIS) and in culture media with and without the addition of a β-lactam antibiotic. The addition of EGTA to NHS largely prevented bactericidal activity against serum-sensitive strains while, in contrast, it reduced the growth of a serum-resistant strain. These apparently paradoxical effects are due to the lower growth rate permitted by the reduced amount of available magnesium in the presence of EGTA.
Experiments with equimolar concentrations of EGTA and magnesium indicated that whilst MgEGTA is a reagent allowing alternative complement-pathway activity, such activity must be determined by comparison with results in HIS + MgEGTA rather than in HIS alone, classical-pathway activity being taken as the difference between the results in NHS and in NHS + MgEGTA.
By these criteria, prompt killing by serum was found to occur via the classical pathway while delayed serum bactericidal activity occurred by the alternative pathway in some strains and by the classical pathway in others.
BryanC. S.1974; Sensitization of E. coli to the serum bactericidal system and to lysozyme by ethyleneglycoltetraacetic acid. Proc. Soc. exp. Biol. Med 145:1431
Des PrezR. M.,
BryanC. S.,
HawigerJ.,
ColleyD. G.1975; Function of the classical and alternate pathways of human complement in serum treated with ethylene glycol tetraacetic acid and Mgcl2-ethylene glycol tetraacetic acid. Infect. Immun 11:1235
RobertsA. P.,
LintonJ. D.,
WatermanA. M.,
GowerP. E.,
KoutsaimanisK. G.1975; Urinary and faecal Escherichia coli O-serogroups in symptomatic urinary-tract infection and asymptomatic bacteriuria. J. med. Microbiol 8:311
TaylorP. W.,
RobertsA. P.,
GowerP. E.1972; Evaluation of a technique for the estimation of serum bactericidal activity against gram-negative organisms. Med. lab. Technol 29:272
TraubW. H.,
KleberI.1976; Selective activation of classical and alternative pathways of human complement by “promptly serum-sensitive” and “delayed serum-sensitive” strains of Serratia marcescens. Infect. Immun 13:1343