Sessions

One of the greatest global challenges of our time is the widespread emergence and dissemination of antimicrobial resistance (AMR). According to the One Health concept, public health, veterinary medicine, and environmental factors are intricately interconnected, forming a unified system that also plays a critical role in food safety, from farm to fork. In this study, we investigated 93 Escherichia coli isolates obtained from the pressure-relief valve compartments of food transport containers used in institutional catering, in order to assess their potential food safety risks within the food chain.

Phenotypic antimicrobial susceptibility testing was performed according to Clinical and Laboratory Standards Institute (CLSI) guidelines using minimum inhibitory concentration (MIC) determination. Based on the results of extended-spectrum β-lactamase (ESBL) screening, isolates were selected for next-generation sequencing analysis (NGS).

The aim of this investigation was to identify AMR genes that may pose a potential public health threat, along with their possible expression regulatory elements.

Phenotypic screening identified 30 isolates as presumptive ESBL-producers. NGS revealed the chromosomal presence of both ampC and ampH β-lactamase genes in all 30 strains, whereas classical ESBL genes such as CTX-M, SHV, and TEM were not detected.

The positive synergy test results suggesting ESBL production were most likely attributable to ampC overexpression in combination with the activity of multidrug efflux pumps (e.g., acrAB, mdtEF) and their regulatory genes (emrR, baeSR, gadX, CRP).

Additional resistance mechanisms were also identified. While acrD and kdpE genes associated with aminoglycoside resistance were present in all isolates, only three strains exhibited phenotypic resistance to gentamicin. Genes associated with fluoroquinolone, colistin, and tetracycline resistance (e.g., emrAB, eptA, ugd, emrK) were detected in the majority of isolates, although phenotypic resistance was only observed in a minority of cases.

These findings support the notion that the mere presence of resistance genes does not necessarily lead to the expression of phenotypic resistance, which typically requires additional regulatory changes, mutations, or environmental induction.

Our results highlight that E. coli strains potentially capable of developing multidrug resistance can be present on food transport equipment used in mass catering services, even after routine disinfection. This finding carries important public health and food safety implications and underscores the need for environmental AMR surveillance within the One Health framework.