Salmonella, Listeria monocytogenes, and Indicator Microorganisms on Hass Avocados Sold at Retail Markets in Guadalajara, Mexico

Abstract

Hass avocados may become contaminated with Salmonella and Listeria monocytogenes at the farm and the packing facility or later during transportation and at retail. In Mexico, avocados are frequently sold in bulk at retail markets, where they are stored at room temperature for several hours or days and exposed to potential sources of microorganisms. These conditions may favor the entry, adhesion, survival, and biofilm formation of Salmonella and L. monocytogenes. The aim of this study was to determine the occurrence of Salmonella, L. monocytogenes, and other Listeria species and the levels of indicator microorganisms on the surface of avocados sold at retail markets. A total of 450 samples (Persea americana var. Hass) were acquired from retail markets located in Guadalajara, Mexico. One group of 225 samples was evaluated for the presence of Salmonella and for enumeration of aerobic plate counts, yeasts and molds, Enterobacteriaceae, coliforms, and Escherichia coli. The other 225 samples were processed for isolation of L. monocytogenes and other Listeria species. Microbial counts (log CFU per avocado) were 4.3 to 9.0 for aerobic plate counts, 3.3 to 7.1 for yeasts and molds, 3.3 to 8.2 for Enterobacteriaceae, 3.3 to 8.4 for coliforms, and 3.3 to 6.2 for E. coli. Eight samples (3.5%) were positive for Salmonella. Listeria spp. and L. monocytogenes were detected in 31 (13.8%) and 18 (8.0%) of 225 samples, respectively. Listeria innocua, Listeria welshimeri, and Listeria grayi were isolated from 7.6, 1.3, and 0.9% of samples. These results indicate that avocados may carry countable levels of microorganisms and could be a vehicle for transmission of Salmonella and L. monocytogenes. HIGHLIGHTS

Antibiotics Resistant Pattern of Bacteria Isolated from Spoiled Avocado Fruit Sold in Sokoto Metropolis

“…The statistical comparisons between the three samples and three locations using one-way ANOVA showed no significant difference (p ≥0.05). The bacterial counts obtained in this research align with the findings of García-Frutos et al 3 , who reported 4.3 to 9.0 CFU/g on Hass avocados sold at retail markets in Guadalajara, Mexico. Similarly, Shiferaw and Kibret 6 reported the mean aerobic mesophilic count of 5.24 log10 CFU/g from avocado peel used to prepare freshly squeezed juices from juice houses of Bahir Dar Town, Northwest Ethiopia.…”

“…However, inoculums were prepared using the whole fruit (i.e., avocado peel, exocarp, and mesocarp). These and other market environmental conditions can lead to higher microbial contaminations in fruit sales in most African retail markets 3 . Other researchers also reported that the variance in microbial loads of fruits might be caused by contamination by microorganisms from the soil, irrigation water, the environment during transit, washing/rinsing water, or process of handling, or it could be part of the fruits' natural flora 3,22-24 .…”

“…In 2019, avocados were recalled in six states of California (Arizona, California, Florida, New Hampshire, North Carolina, and Wisconsin) because of Listeria contamination 5 . García-Frutos et al 3 and Shiferaw and Kibret 6 also reported the presence of E. coli, Salmonella sp., Listeria spp., and L. monocytogenes from avocado samples collected from retail markets located in Guadalajara, Mexico. In African continents, the story is not different; avocado fruits are primarily consumed raw, without further processing.…”

Conditions of In Vitro Biofilm Formation by Serogroups of Listeria monocytogenes Isolated from Hass Avocados Sold at Markets in Mexico

“…In total, 18 L. monocytogenes isolates were evaluated in this study, which were previously obtained from Hass avocados sold at retail markets in Guadalajara, Mexico [12]. Stocks of L. monocytogenes were stored using the protocol described by Avila-Novoa et al [24].…”

“…In addition, the fresh produce supply chain is complex, with increasing potential sources of L. monocytogenes contamination. For example, contamination from irrigation water, fertilization with contaminated manure and contaminated soil (agricultural practices), cross-contamination from surfaces contaminated with pathogens, food spoilage, improper manipulation by food handlers, or processing fresh produce into fresh-cut products increases the risk of bacterial growth by breaking the fruit’s skin and allowing for the spread and potential growth of any pathogens that may be present [ 3 , 8 , 9 , 10 , 11 , 12 ].…”