Microbiological Survey of Locally Grown Lettuce Sold at Farmers' Markets in Vancouver, British Columbia

Abstract

Increased consumer demand for fresh leafy produce has been paralleled by an increase in outbreaks and illness associated with these foods. Presently, data on the microbiological quality and safety of produce harvested in the Lower Mainland of British Columbia is lacking. Therefore, fresh green, red, and romaine lettuce samples (n = 68) were obtained from five regional farmers' markets in late summer of 2012 and subsequently analyzed to determine total numbers of aerobic bacteria, coliforms, and Escherichia coli. Additionally, enrichment procedures were used to detect low concentrations of E. coli. Obtained E. coli isolates were subjected to multiplex PCRs to determine phylogenetic groupings and the presence of virulence genes (eaeA, hlyA, stx1, and stx2). All E. coli were tested for resistance to 15 antibiotics using a disk diffusion assay. Lettuce samples yielded mean aerobic colony counts of 6.3 log CFU/g. Coliforms were detected in 72% of samples, with a median concentration of 1.9 log CFU/g. Of samples, 13% were found to harbor E. coli, with a median level of 0.7 log CFU/g. Antibiogram typing of all E. coli (n = 33) revealed that 97% possessed resistance to one or more antimicrobials, with resistance to amikacin (58%), trimethoprim (48%), and trimethoprim-sulfamethoxazole (45%) being the most common. Phylogroup typing showed that 79% of these isolates belonged to group B1, with the remaining assigned to groups A (9%) or D (12%); no virulence genes were detected. Considering that phylogroup indicators suggestive of fecal contamination (groups A and D E. coli) were recovered in lettuce samples presented at retail, further work is required to explore at what point along the food chain contamination occurs. Also, this study shows the presence of multidrug-resistant E. coli in fresh vegetables. Summed, these data provide important information on the microbiological quality of leafy vegetables grown in British Columbia through the detection and characterization of frequently used indicator organisms.

Microbiological characterization of vegetables and their rhizosphere soil in Eastern Poland

“…The AMB levels in 5 kinds of fresh vegetables (FV) taken immediately from soil were within the range of 3.54-6.32 log 10 CFU g -1 , for isolates recovered at 30 o C. The AMB levels in the same kinds of vegetables sold at retail in the markets (VR), described often in the literature as unprocessed vegetables (UV) [4], were significantly lower, ranging from 0.00-5.55 log 10 CFU g -1 . The levels of AMB noted in the presented study for FV and VR were similar to those reported by Nguz et al [6] (Zambia), Aycicek et al [1] (Turkey), Oliveira et al [7] and Soriano et al [25] (Spain), Seow et al [8] (Singapore), Cardamone et al [4] (Italy), Johnston et al [26,27] (USA), Ryu et al [3] (Korea), and by Wood et al [28] (Canada), but lower compared to data reported by Abadias et al [2] and Ercolani [29] (Spain), De Giusti et al [11] (Italy), Viswanathan and Kaur [5] (India), and by Hagenmaier and Baker [30], Valentin-Ban et al [31] and Korir et al [32] (USA).…”

Prevalence of antimicrobial-resistant Escherichia coli from raw vegetables in Lebanon

“…Overall, a lower resistance was recorded to gentamicin (22%), which is in line with various studies [10,39], highlighting the promising treatment of E. coli by gentamicin as demonstrated by Fadlallah et al [40].…”

Microbiological and Nutritional Analysis of Lettuce Crops Grown on the International Space Station

“…The four samples of mizuna, the only leafy green tested, were grown in different Lada root modules at different times and counts ranged from 3.1 × 10 3 -8.7 × 10 5 . When compared to field grown or market produce of similar types these numbers are well within the expected range of microbial densities or even lower (Holvoet et al, 2015;Wood et al, 2015;Fröhling et al, 2018;Hummerick et al, unpublished data).…”

“…Bacterial and fungal counts on fresh plant material are not necessarily an indication of the food quality and microbiological safety of the item and vary depending on the type of plant (Leff and Fierer, 2013;Qadri et al, 2015). Studies show that leafy greens grown in the field or greenhouse have a range of approximately 4-8 log 10 CFU bacterial counts per gram of sample while yeast and mold counts on lettuce are reported in the range of 2-5 log 10 (Valentin-Bon and Jacobson, 2008;Rastogi et al, 2012;Jackson et al, 2013;Holvoet et al, 2015;Wood et al, 2015;Hagenmair and Baker, 2016;Oyinlola et al, 2017;Fröhling et al, 2018;Zhang et al, 2018). The microbial counts on lettuce leaves grown on ISS in VEG-01A, B and both harvests from VEG-03A were relatively low on average when compared to farm or market produce counts of similar type.…”

“…The bacterial counts on lettuce leaves grown on ISS in VEG-01A, B and both harvests from VEG-03A were relatively low on average, 3.53, 4.86, 2.89, and 2.14 log 10 CFU/g respectively (Figure 2), when compared to farm or market produce counts of similar type (Valentin-Bon and Jacobson, 2008;Rastogi et al, 2012;Jackson et al, 2013;Holvoet et al, 2015;Wood et al, 2015;Hagenmair and Baker, 2016;Oyinlola et al, 2017;Fröhling et al, 2018;Zhang et al, 2018). Fungal counts on Veggie grown lettuce ranging from 2.3 to 4.3 log 10 CFU/g were within the range of yeast and mold counts on lettuce reported in the literature (Figure 3) (Oliveira et al, 2010).…”