Surface Survival and Internalization of Salmonella through Natural Cracks on Developing Cantaloupe Fruits, Alone or in the Presence of the Melon Wilt Pathogen Erwinia tracheiphila

Abstract

Outbreaks of foodborne illness attributed to the consumption of Salmonella-tainted cantaloupe have occurred repeatedly, but understanding of the ecology of Salmonella on cantaloupe fruit surfaces is limited. We investigated the interactions between Salmonella enterica Poona, the plant pathogenic bacterium Erwinia tracheiphila, and cantaloupe fruit. Fruit surfaces were inoculated at the natural cracking stage by spreading S. enterica and E. tracheiphila, 20 µl at 107 cfu/ml, independently or together, over a 2×2 cm rind area containing a crack. Microbial and microscopic analyses were performed at 0, 9 and 24 days post inoculation (DPI). Even at 24 DPI (fruit maturity) S. enterica was detected on 14% and 40% of the fruit inoculated with S. enterica alone and the two-pathogen mixture, respectively. However, the population of S. enterica declined gradually after initial inoculation. E. tracheiphila, inoculated alone or together with Salmonella, caused watersoaked lesions on cantaloupe fruit; but we could not conclude in this study that S. enterica survival on the fruit surface was enhanced by the presence of those lesions. Of fruit inoculated with E. tracheiphila alone and sampled at 24 DPI, 61% had watersoaked lesions on the surface. In nearly half of those symptomatic fruits the watersoaking extended into the sub-rind mesocarp, and E. tracheiphila was recovered from that tissue in 50% of the symptomatic fruit. In this work, E. tracheiphila internalized through natural cracks on developing fruits. S. enterica was never detected in the fruit interior (ca. 2–3 mm below rind surface) under the limited conditions of our experiments, but the possibility that it, or other human pathogens that contaminate fresh produce, might also do so should be investigated under a wider range of conditions and produce types.

Attachment of Salmonella enterica on Mangoes and Survival Under Conditions Simulating Commercial Mango Packing House and Importer Facility

“…Similarly, 6 log CFU of S. typhimurium was recovered from mango skin sections following an inoculum contact time of 24 h ( Fernandes et al, 2014 ). Beyond attachment, using SEM, Gautam et al (2014) demonstrated the presence and survival of Salmonella Poona on cantaloupe rinds until 24 days post-inoculation. Survival of pathogens on fresh produce, particularly in the post-harvest environment is primarily influenced by ambient fruit handling/storage conditions (temperature and relative humidity) and packing house practices such as waxing ( Guo et al, 2002 ; Kenney and Beuchat, 2002 ; Shi et al, 2007 ; Collignon and Korsten, 2010 ; Huff et al, 2012 ; Tian et al, 2013 ; Zhou et al, 2014 ).…”

“…In this regard, mangoes can get contaminated within the pre and post-harvest environments ( Fatica and Schneider, 2011 ; Penteado, 2017 ). In the orchards, mango trees are cultivated and fruit are harvested in their natural environment where they are exposed to a variety of contamination sources including soil, irrigation water, manure, and animals in or near the field ( Fatica and Schneider, 2011 ; Huff et al, 2012 ; Gautam et al, 2014 ). This of particular significance with pathogens such as Salmonella since they normally reside in the intestinal tract of animals and can therefore gain entry into the pre-harvest environment through contaminated animal feces ( Fatica and Schneider, 2011 ; Tomas-Callejas et al, 2011 ).…”

Effectiveness of Aqueous Chlorine Dioxide in Minimizing Food Safety Risk Associated with Salmonella, E. coli O157:H7, and Listeria monocytogenes on Sweet Potatoes

“…Aqueous ClO 2 (3 ppm) reduced the L. monocytogenes population by 3.7 log CFU when bell pepper surfaces were not injured and by 0.44 when injured [38]. Reduced efficacy of the treatments in our study may be due to a higher level of bruises and attached soiled particles which may have allowed bacterial cells to hide better in the surfaces limiting the access to the sanitizer solutions [43,44]. However, a further rigorous study is needed to better understand the influence of individual factors on the efficacy of the sanitizer.…”

Attachment strength and on-farm die-off rate of Escherichia coli on watermelon surfaces

“…Bacterial cells embedded within the crevices and fissures of the watermelon rind may be another factor. Cracks and fissures on melon rind surfaces may allow bacterial cells to enter interior tissues [64]; this phenomenon may limit the access of bacterial cells to the applied sanitizer solutions. E .…”