IN VITRO CYTOTOXIC EFFECT OF α‐HEMOLYTIC AND NONHEMOLYTIC ESCHERICHIA COLI ON HUMAN BLOOD GRANULOCYTES AND MONOCYTES

Abstract

The in vitro cytotoxic effect of Escherichia coli on human phagocytic blood cells in the presence of fresh autologous plasma was assessed using (i) a technique by which cell damage was quantified by measuring the release of chromium 51 from labelled granulocytes and (ii) a technique based on the degree of morphological cell damage induced in monocytes. All of 109 α‐hemolytic strains were cytotoxic, the cytotoxic effect ranging from very weak to strong. Log‐phase cultures had the strongest cytotoxic effect, the individual microorganisms being most cytotoxic in the early log‐phase. Plateau‐phase cultures progressively lost their cytotoxic ability and 24 h old cultures were almost noncytotoxic. Strongly cytotoxic strains induced high degrees of cell injury, caused an abrupt damage during the first 20 min of incubation and were able to induce injury with few bacteria present. Weakly cytotoxic strains induced only low degrees of cell injury, caused a more gradually developing damage, and were able to induce injury with only high numbers of bacteria present. All of 75 nonhemolytic and 3 β‐hemolytic strains were noncytotoxic.

RTX proteins: a highly diverse family secreted by a common mechanism

“…The so-called RTX ‘hemolysins’ were initially found to exhibit a limited target cell and species specificity, while the activity of leukotoxins was considered to be species and cell-type specific (Welch, 1991; Coote, 1992;). For example, E. coli α-hemolysin (HlyA) appears to be rather promiscuous, exhibiting a well-detectable cytotoxic activity on a wide spectrum of cells from various species, including erythrocytes, granulocytes, monocytes, endothelial cells or renal epithelial cells from mice, ruminants and primates (Gadeberg & Orskov, 1984; Keane et al , 1987; Bhakdi et al , 1989, 1990; Mobley et al , 1990; Suttorp et al , 1990; Crosby & Kachlany, 2007). In turn, the leukotoxins of A. actinomycetemcomitans (LtxA) and M. haemolytica (LktA) appear to be quite selective and cytotoxic only to a restricted group of cell types in a species-specific manner (Shewen & Wilkie, 1982; Taichman et al , 1984, 1987; Strathdee & Lo, 1989).…”

The RTX Pore-Forming Toxin α-Hemolysin of Uropathogenic Escherichia Coli : Progress and Perspectives

“…However, it has long been appreciated that HlyA can also effectively lyse other host cell types, including epithelial cells and leukocytes from a variety of human and animal hosts [6,35,51–53]. Interestingly, this lytic promiscuity is not a conserved characteristic of all RTX toxins.…”

Different Types of Cell Death Induced by Enterotoxins

“…HlyA possess cytotoxicity in different cells such as erythrocytes [86], granulocytes [87,88,89,90], monocytes [91], endothelial cells [92], renal tubular epithelial cells [93], and T cells [94]. The toxic effect of HlyA is due to the generation of the transmembrane pore after its insertion into the plasma membrane [86].…”