Rapid acquisition of plant colonization efficiency by Escherichia coli

DUBLAN M DE LOS A; LETT L; CURATTI L

Mar del Plata

Congreso; VIII Congreso de Microbiologia General; 2012

Sociedad Argentina de Microbiologia General

Escherichia coli is a common resident of animal hosts, including humans, mostly as a commensal of the lower intestine of mammals. Due to increasing outbreaks, food contamination with pathogenic E. coli, especially under-cooked meet has become a serious public health concern. In the majority of the cases, the illness resolves in a week; however, in about 5% of the patients, the disease progresses to hemolytic-uremic syndrome, which may result in kidney failure, neurological sequelae, and death.Although the main host reservoir and vector of this kind of food-born disease is cattle, during the last years reports of outbreaks due to contamination of fresh produce with pathogenic E. coli were accumulated progressively.  Generally, it is supposed that although able to vectorize the pathogen, produce might not constitute an alternative host for E. coli, which accesses the non-host by careless agricultural practices or manufacturation by workers. Thus, the life style of E. coli in non-hosts and especially its ability to naturalize to non-host environments are poorly understood.The aim of this study was to characterize some aspects of E. coli colonization of lettuce seedlings. The basic experimental setting consisted in transplanting pre-germinated lettuce seedlings onto agarized medium inoculated with bacteria. After twenty days post-inoculation viable E. coli cells from leafs or roots were determined. The analysis of a large set of data suggested that ?in planta? grown cells, after a cycle of lettuce infection, were more infective than bacterial cells cultivated in LB medium, which mimics the host environment. Reciprocal competitive-index analysis of green- or red-fluorescent protein labeled-cells culture in host (LB) or non-host (lettuce leaves, after infection) confirmed that ?in planta? grown cells were 9-fold more infective after the first cycle of infection and 24-fold after the second one. As expected for a non-rhizospheric bacterium, E. coli became less infected when co-inoculated together with Azospirillum brasilense strain AZ39, however ?in planta? grown E. coli appeared to be less sensitive to interspecific competence. ?In planta? grown cells show considerably higher resistance to oxidative stress (H2O2) in comparison to LB- or M9-cultivated cells.These results show that E. coli has a remarkable ability to naturalize to lettuce and enhanced defense towards oxidative burst by the plant might be in part responsible for its success.