Melioidosis is an infectious disease caused by the bacterium, Burkholderia pseudomallei which is found in soil and water. The disease is endemic in parts of south east Asia and northern Australia, and affects other species such as goats, sheep and horses as well as humans. The route of infection is believed to be either through a break in the skin, or through the inhalation of aerosolized B. pseudomallei. The most severe form of the disease is melioidosis septic shock, and mortality remains high despite antibiotic treatment.
A recent report in the journal PLoS elucidates the pathways which confer susceptibility to disease. The research focused on Toll-like receptors (TLRs), which have a central role in the recognition of pathogens and the initiation of the innate immune response. Specifically, the new study looked at the effect of two important adaptor proteins involved in TLR signalling and, using experiments in mice, found that MyD88 but not TRIF is important for host defense against B. pseudomallei.
The authors had previously shown that, although both TLR2 and TLR4 contribute to cellular responsiveness to B. pseudomallei in vitro, only TLR2 knockout mice were protected against B. pseudomallei induced mortality. Together, the data indicate that MyD88 deficiency results in a strongly impaired resistance to melioidosis despite an interruption of harmful TLR2 signalling.
Escherichia coli (E.coli) are bacteria commonly found in the gut of both people and animals. Although many types of E. coli are harmless, infection with Shiga-toxigenic strains of E. coli such as E. coli O111 and E. coli O157 can cause bloody diarrhoea. Infection with Shiga-toxigenic E. Coli can also sometimes lead to haemolytic uraemic syndrome, a condition characterised by kidney failure, bleeding and anaemia which can sometimes be fatal. Infection usually results from consuming contaminated food or water or from contact with infected animals or people.
A letter published online on 29 October in the journal Nature, describes how subtilase cytotoxin, an AB5 type toxin produced by Shiga-toxigenic E. coli, preferentially targets cells expressing glycans terminating in N-glycolylneuraminic acid (Neu5Gc). What is remarkable is that humans are not able to produce Neu5Gc, and so should be resistant to the effects of the toxin. It now seems that red meat and dairy products contain high levels of Neu5Gc which is absorbed into human tissues, including the surface of cells lining the intestines and blood vessels. This means that food contaminated with Shiga-toxigenic E. Coli strains can also provide a ready source of the molecular target for the toxin.
The research emphasizes the need to eat only well cooked meat and pasteurized dairy products, since both processes destroy any contaminating bacteria.