Purpose: The purpose of this study was to identify pathogenic bacteria, APCs, coliforms, Escherichia coli, and yeasts/molds on romaine lettuce samples purchased from Houston area grocery stores (low- and high-income neighborhoods).
Methods : Romaine lettuce was purchased from five high-income (HI) and five low-income (LI) grocery stores, based on household median income. Standard methods of detection, as per the Bacteriological Analytical Manual-Food and Drug Administration, were used with some modifications. The lettuce was aseptically weighed and added to a sterile stomacher bag with 45mL peptone buffer, stomached for 120s, serially diluted, and plated on APC and coliform/E.coli petrifilms. Samples were also enriched for selective enumeration using the following media: PALCAM (selective for Listeria spp.), EC Medium with novobiocin (E. coli O157:H7), and Tetrathionate broth (Salmonella spp.).
Results: The APC results demonstrated a statistically significant difference (p<0.05) between lettuce obtained from HI (2.9 Log CFU/g) and from LI (4.7 Log CFU/g) grocery stores, respectively. In addition, the coliform and E. coli results demonstrated a statistically significant difference (p<0.05) between HI (2.9 Log CFU/g) and LI (4.9 Log CFU/g) sampling locations. The PALCAM enriched LI sample exhibited growth. Subsequent plating on Sheep Blood Agar displayed β-hemolysis, suggesting the presence of Listeria monocytogenes.
Significance: The results of this study highlighted the inconsistencies in the handling/holding procedures of Houston grocery stores. There is an increasing need for accessibility of food safety related educational materials for grocery store employees/managers that serve low-income neighborhoods.