Aims: To determine survival and colonization of Escherichia coli O157:H7 on spinach leaves as affected by inoculum level and carrier, temperature and relative humidity (r.h.). Methods and Results: Spinach leaves were inoculated with suspensions of E. coli O157:H7 in distilled water (DW) and 0·1% peptone water (PW) and incubated at 4, 12 and 25°C and 43, 85 and 100% r.h. The number of E. coli O157:H7 on leaves (5·6 or 1·9log CFU per leaf) inoculated using DW as a carrier medium increased significantly at 25°C and 100% r.h. within 120h but remained constant or decreased significantly under other test conditions. E. coli O157:H7 on leaves (5·4log CFU per leaf) inoculated using PW as a carrier increased significantly within 72 and 24h, respectively, at 12 or 25°C and 100% r.h.; counts using a low inoculum (2·2log CFU per leaf) increased significantly within 24h at 25°C. Conclusions: Escherichia coli O157:H7 can colonize on spinach leaves at 12 or 25°C in a 100% r.h. environment. Organic matter in the inoculum carrier may provide protection and nutrients which enhance survival and colonization. Significance and Impact of the Study: Colonization of E. coli O157:H7 on spinach leaves as affected by organic matter in the inoculum, temperature and r.h. was determined. These observations will be useful when developing strategies to prevent growth of E. coli O157:H7 on pre- and postharvest spinach.
- Escherichia coli O157:H7
- Mesophilic aerobic bacteria
- Moulds and yeasts
ASJC Scopus subject areas
- Applied Microbiology and Biotechnology