Enumeration Resuscitation and Infectivity of the Sublethally Injured Erwinia Cells Induced by Mild Acid Treatment

Enumeration, Resuscitation, and Infectivity of the Sublethally Injured Erwinia Cells Induced by Mild Acid Treatment

C.-H. Liao and L. M. Shollenberger. Pages 76-81.Publication no. P-2003-1024-03R.

Submitted to: Phytopathology
Publication Acceptance Date: September 9, 2003
Publication Date: January 1, 2004

Interpretive Summary: Soft-rotting Erwinia are responsible for a very large proportion of postharvest spoilage of fruits and vegetables. Rotted tissue caused by this group of bacteria has been shown to harbor pathogens of public health significance more often than healthy tissue. We investigated the antimicrobial action of acetic acid (AA, an active ingredient of vinegar) on undesirable soft-rotting bacteria associated with fresh produce. It was found that all five Erwinia strains examined were very sensitive to AA treatments. Upon exposure to a low concentration (0.3 percent) of AA, approximately 90 percent of bacteria were killed and over 99.9 percent of surviving bacteria were injured. Injured bacteria were able to repair when incubated on cut surfaces of cucumber fruits or in nutrient broth containing no antimicrobial substances and to resuscitate and cause spoilage of bell pepper fruits. This study demonstrates the potential of AA as a sanitizer for fresh produce and suggests an improved method for detection of potentially injured Erwinia cells in soil, water, or fresh produce samples that have been exposed to various physical or chemical stresses.

Technical Abstract: Studies of injury and repair in phytopathogenic bacteria have not been reported. The objective of this study was to investigate the lethal and sublethal effects of acetic acid (AA) on soft-rot Erwinia and the limitation of using selective media for isolation of injured cells. Following exposure to 0.3 percent AA for 6 min, 90 to 99 percent of E. carotovora subsp. carotovora (Ecc), E. carotovora subsp. atroseptica, and E. chrysanthemi cells were killed. Furthermore, more than 99.9 percent of Erwinia cells that survived acid treatment were able to form colonies on Brain Heart Infusion Agar (BHIA) but not on four selective media including Crystal Violet Pectate (CVP) medium. Lethal and injury effects of AA on Erwinia were influenced by AA concentration and exposure time. Injured Erwinia cells were able to repair when placed in nutrient broth but not in broth containing crystal violet and sodium dodecyl sulfate. Injured cells were also able to resuscitate on cut surfaces of cucumber and to induce soft-rot on green bell pepper fruits. These results suggest that direct use of selective media can limit the detection of injured Erwinia in samples that have exposed to chemical stresses. Further, incubation of the samples in non-selective broth before plating on selective agars improves the detection of injured Erwinia.