The Journal of Medical Microbiology, Vol 35, Issue 1 12-17, Copyright © 1991 by Society for General Microbiology
Pre-opsonisation of Escherichia coli induces resistance to neutrophil killing in serum and urine: relationship to growth phase
R. A. Gargan, W. Brumfitt and J. M. Hamilton-Miller
Department of Medical Microbiology, Royal Free Hospital and School of Medicine, Hampstead, London.
Tests of phagocytosis and killing by polymorphonuclear neutrophil
leucocytes (PMNL) are usually done with pre-opsonised organisms.
Phagocytosis of 11 strains of Escherichia coli, pre-opsonised, and in the
stationary phase, resulted in the killing of only one strain although all
the organisms were phagocytosed. However, when the same strains were added
unopsonised to a PMNL-serum mixture, eight were killed after phagocytosis.
With two of these strains, the amount of killing was inversely proportional
to the time of pre-oposonisation. E. coli incubated for 30 min in dilute
peptone water in Hanks's Balanced Salts Solution before phagocytosis also
became resistant to killing; bacterial division did not occur during this
period. Experiments with bacteria in urine confirmed these findings and
showed that E. coli exposed to serum or urine before phagocytosis became
resistant to killing by PMNL. E. coli rapidly changes its sensitivity to
phagolysosome killing during transition from stationary to lag phase in a
nutrient medium. This resistance is retained through the exponential phase
but is lost during the stationary phase. The killing of Pseudomonas,
Enterobacter, and Acinetobacter by PMNL was unaffected by varying the
method of opsonisation or the phase of growth. If this phenomenon occurs in
vivo it may affect the outcome of infections caused by strains of E. coli
that survive killing by PMNL.
