The Journal of Medical Microbiology, Vol 18, Issue 3 377-384, Copyright © 1984 by Society for General Microbiology
The variable response of bacteria to free haemoglobin in the tissues
J. P. Maskell and A. A. Miles
The local enhancement of infection by exogenous ferric iron, as ferric
ammonium citrate, and by ferrous iron as guinea-pig haemoglobin, was
assessed in studies with 55 strains of bacteria injected into the skin of
guinea-pigs. The test organisms included Staphylococcus aureus,
Streptococcus spp., Klebsiella spp., Escherichia coli and Pseudomonas
aeruginosa. Four strains of Bacteroides spp. were tested with haemoglobin
only. As previously reported with other strains, enhancement of infection
by members of a given species by ferric iron was variable; in this study
infection with only 11 of 59 strains was enhanced. Haemoglobin either of
equal or lesser iron content was a more potent enhancer, affecting 27 of
the 59 strains. The enhancement ranged from two-fold to 80-fold, the higher
figures on the whole being characteristic of haemoglobin enhancement. Some
few instances of depression by both haemoglobin and ferric ammonium citrate
were noted. A few tests were made with systemic haemoglobin but the
concentrations attainable were largely ineffective. Enhancement of
infection did not appear to be related to the capacity of a strain to lyse
or digest host red blood cells. In so far as guinea-pigs, whose
antibacterial defences are lowered by ferric or ferrous iron, represent
human subjects at risk of infection because of clinical circumstances
characterised by excess of available iron--either exogenous or as a result
of haemolysis--our results with organisms of a kind commonly associated
with infection in hospitals suggest that only a small proportion of
environmental bacteria can take advantage of any decreased resistance
associated with iron excess.
