Pathogens Found on Brazilian Citrus Fruit Present Emerging Food Safety Concerns
During the screening of lactic acid bacteria on Rangpur limes (a hybrid citrus rather than a true lime), scientists in Brazil discovered the presence of two emerging pathogens with traits that raise concerns for food safety and One Health.
The pathogens were identified in the initial phase of a research project focused on analyzing beneficial microbes on various tropical fruits, conducted by researchers from the University of São Paulo and the Polytechnic University of Viana do Castelo. While the researchers were evaluating the growth of bacterial isolates, the researchers recorded that some of the isolates were negative (no growth) in modified culture media where glucose was replaced with lactose, sucrose, or rhamnose; however, other initial isolates showed reasonable bacterial growth in the same modified media. The bacteria were further identified as Escherichia albertii and Kosakonia cowaniii. Driven by scientific curiosity, these bacteria were further investigated.
The three studied strains, chosen for their high frequency in microbial isolates obtained from fruit samples, were found to be hemolytic, resistant to ampicillin with intermediate susceptibility to nalidixic acid, and carrying certain virulence genes including fim and hly. They were also positive for β-galactosidase, an enzyme that helps opportunistic pathogens survive, colonize, and persist outside their primary host environments; and showed presumptive amino acid decarboxylase activity (indicating potential for production of biogenic amines), an important parameter in food safety, as the accumulation of biogenic amines can result in serious toxicological effects for consumers.
Limes Grown in Proximity to Poultry Farms
The Rangpur limes tested in the study were cultivated in a rural area outside of São Paulo, Brazil, where fruit trees were grown and poultry were raised in proximity. According to the researchers, their findings not only support the view that fresh fruits grown at animal–crop interfaces can possibly serve as reservoirs of opportunistic and emerging bacteria, but also suggest that fruit grown in the region of the studied limes may harbor pathogens of relevance to food safety and One Health surveillance.
Findings Suggest Food Safety, Public Health Risks
Moreover, the identification of E. albertii and K. cowanii on citrus fruit presents a “serious food safety challenge,” said the researchers, because it indicates microbial resilience to the naturally acidic environment of the fruit. They cited emerging evidence that enteric and phytopathogenic bacteria can deploy stress-response mechanisms, including amino acid decarboxylase systems and biofilm formation, to withstand acidity.
From an epidemiologic perspective, the presence of these species on fruit intended for consumption without a final kill-step presents risks to the consumer. E. albertii represents a high-priority, emerging human pathogen equipped with pathogenicity islands seen in the genomes of pathogenic bacteria like enteropathogenic and enterohemorrhagic E. coli (EPEC and EHEC), as well as Shiga toxin-encoding sequences capable of causing severe gastrointestinal disease and complications. Although predominantly characterized as a tissue-necrotizing plant pathogen, K. cowanii displayed opportunistic traits capable of causing infections in immunocompromised host populations.
Calls for Further Analysis, Heightened Surveillance, Preharvest Prevention
“Ultimately, the isolation of these organisms points to potential agricultural contamination, likely via irrigation water or soil amendments, and underscores the necessity for heightened post-harvest surveillance,” the researchers concluded. “A pathogen that is considered strictly associated with the animal gut but can be recorded on fruits and vegetables needs to be evaluated with more attention related to potential food safety.”
Further identification, such as with whole genome sequencing (WGS), and bioinformatic analyses are necessary next steps in exploring the pathogenicity of the selected strains of E. albertii and K. cowanii. Rather than indicating an immediate public health threat, the researchers stressed that their findings should be interpreted within the context of an exploratory study based on a limited number of isolates that require additional study, underlining the importance of microbiological surveillance, accurate identification of atypical isolates, and preventive practices in primary production systems.
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