The Journal of Medical Microbiology, Vol 12, Issue 1 17-28, Copyright © 1979 by Society for General Microbiology
The variable response of bacteria to excess ferric iron in host tissues
A. A. Miles, P. L. Khimji and J. Maskell
The enhancement by exogenous ferric iron, both systemic and local, of the
infectivity of 120 strains of bacteria, representing 17 genera, was
measured in the skin of guinea-pigs. Systemic iron enhanced only 23% of 115
strains, and local iron 49% of 71 strains. Systemic iron, by an apparently
anti-inflammatory action, depressed the size of lesions produced by 27 of
the non-enhanced strains from nine of the genera tested. For most strains,
the degree of enhancement was small, ranging from 2- to 8-fold, and often
evident only with the more effective local iron; among these were some
near-saprophytes like Mycobacterium phlei, M. smegmatis, Bacillus cereus
and Clostridium bifermentans. Substantial enhancement, from 14- to 50-fold,
was observed with the more pathogenic among the strains tested: namely BCG,
Corynebacterium ovis, C. murium, Listeria monocytogenes, Erysipelothrix
rhusiopathiae, Cl. perfringens, Cl. septicum, Cl. oedematiens, and some
strains of Klebsiella spp., Proteus spp. and Aeromonas hydrophila. The
enhancement of BCG by a single dose of iron given locally with the inoculum
was only feebly manifest after 7 days, but substantial after 14--19 days,
indicating the decisive effect of interference with an early humoral
defence on the establishment of chronic infection some time later. Insofar
as guinea-pigs whose antibacterial defences are lowered by substantial
amounts of exogenous iron in the circulation represent human subjects at
risk of infection because of clinical states characterised by excess of
available iron, the results of the survey suggest that only a minority
among the environmental bacteria can take advantage of the decreased
resistance associated with such states; but that this minority is likely to
include the more virulent strains in the environment.
