Scientists from a university in Singapore have found strains of foodborne E. coli have different tolerances towards acidic conditions.

E. coli O157:H7 is widely recognized due to the severity of illnesses it causes. There are another six serogroups identified by the United States Food and Drug Administration as emerging pathogens commonly found in foodborne disease outbreaks. E. coli O26, O45, O103, O111, O121, and O145 are known as the “big six.”

A research team led by Professor Hongshun Yang from the Department of Food Science and Technology at the National University of Singapore (NUS) used metabolomics technologies to study the adaptive response of pathogens under different inactivation stresses such as electrolyzed water, ultrasound and a natural antibacterial agent.

They investigated the metabolic profiles of eight serotypes including E. coli O157:H7, O26:H11, O45:H2, O103:H11, O111, O121:H19, O145 and non-pathogenic E. coli ATCC 25922 using nuclear magnetic resonance (NMR).

Scientists said it was important to be able to characterize these pathogens and understand their behavior so more effective control measures can be developed.

Results, published in the journal Food Microbiology, showed metabolic diversity existed among the eight and different strains exhibited different tolerance towards acidic conditions.

Large differences between non-pathogenic and pathogenic strains were recorded and the most varied pair being ATCC 25922 and O26:H11 were further analyzed.

Understanding acid tolerance
Researchers found the pathogenic serotypes require higher energy production to fuel their physiological activities when compared to the non-pathogenic strain. Metabolic differences under acid stress indicate that energy and amino acid metabolisms contributed to the different acidic adaptive capacities of the E. coli serotypes.

Findings suggest the control of related metabolic pathways during sanitizing treatments could potentially improve bacteria inactivation.

Thirty-eight metabolites were identified in the eight E. coli strains. Metabolites including lysine, arginine, alpha-ketoglutaric acid, adenosine, and fumaric acid were responsible for the separation of E. coli ATCC 25922.

Pathogenic O26:H11 had higher acid tolerance than the non-pathogenic surrogate. Glutamic acid dependent system was the major acid resistance mechanism of this strain.

Traditional bacteria characterizations involve using cultured bacteria on different media. These tests are time consuming, complex, and labor-intensive. NMR provides a non-destructive and mostly automated method of obtaining a metabolic profile of the microorganisms.

Lin Chen, a student working on the project, said: “By monitoring the changes of microbial metabolomics, a precise snapshot of cells with different physicochemical states can be obtained. The research outcomes from the metabolomics analysis of the big six pathogens provided a better understanding of food safety related bacterial properties.”

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