Effect of copper hydroxide sprays for citrus canker control on wild-type Escherichia coli.

AIMS: To show that application of copper hydroxide citrus sprays mixed with field source water (possibly contaminated) will not support Escherichia coli on plant surfaces. Environmental stresses of transient phyllosphere bacteria and presence of copper will eradicate these bacteria before harvest. METHODS AND RESULTS: Studies were performed in vitro with bacteria grown in broth and then subjected to field spray copper hydroxide concentrations in the broth and on citrus leaves. Escherichia coli exposed to copper hydroxide in vitro were eradicated from the broth within 6-8 h depending on the broth pH. Even with near neutral pH (7·2), cells began to die immediately after exposure to copper. No E. coli survived on leaf surfaces sprayed with copper. CONCLUSIONS: Copper field sprays mixed with water that may contain E. coli can help eliminate E. coli from plant surfaces. SIGNIFICANCE AND IMPACT OF THE STUDY: HACCP mandates are becoming more restrictive because of the increased illness resulting from food pathogens on fresh produce. Use of potable water in fields, a proposed mandate, is not feasible for large grove owners. These data show that copper sprays aimed at reducing citrus canker also affect E. coli and may help to ease water quality mandates.

A simple method for screening antimicrobial compounds with application to plant disease and fruit quality.

AIMS: It is often difficult to extrapolate information from a Petri dish and apply it to commercial applications as with antimicrobial assays. Often large volumes of commodities are used for a virtually untested protocol and result in an unnecessary expenditure of time and materials. An intermediate method, where experimental compounds could be tested directly on a specific commodity without expending large quantities of either sample or compound, would be practical and economical. METHODS AND RESULTS: A method was developed that employs the use of a small experimental chamber in which pieces of natural materials (e.g. fruit) can be tested with antimicrobial compounds. This method uses a type of autoclavable incubation chamber with a filter paper base, hydrating sponge pieces and a sterile glass sample platform. The chamber offers a sterile, controlled environment and can be manipulated to serve a number of studies. CONCLUSION: The chamber results are more analogous to what happens on whole fruit than the Petri dish. SIGNIFICANCE AND IMPACT OF THE STUDY: This method is presently used to screen for antimicrobial compounds and treatments needed to control serious economic pests compromising Florida's agriculture.