E. coli testing
E. coli testing in recreational waters: A novel test method
Urban beach closures due to coliform outbreaks have become disturbing signs of summer, yet water-testing technology has never been fast enough to keep up with changing conditions, nor accessible enough to check all swimming sites. The methods used to detect outbreaks are slow, and tend not to be portable, as they often need a lab-based amplification step prior to testing, causing a time lag between an outbreak and a beach closure.1
A novel and rapid testing method has been developed by a group at McMaster University.2 This test uses a simple paper strip that is based on intracellular enzyme (β-galactosidase (B-GAL) or β-glucuronidase (GUS)) activity and can detect E. coli in recreational water within minutes. The test signal is observed as a change from colorless-to -blue (XG hydrolyzed by GUS, indication of nonpathogenic E. coli) and/or yellow to red-magenta (CPRG hydrolyzed by B-GAL, indication of total coliforms). By using immunomagnetic nanoparticles for selective preconcentration, the limit of detection was ~5 colony-forming units (cfu) per milliliter for E. coli O157:H7 and ~20 cfu/mL for E. coli BL21, within 30 min without cell culturing. Thus, these paper test strips could be suitable for detection of viable total coliforms and pathogens in bathing water samples. Moreover, inclusion of a culturing step allows detection of less than 1 cfu in 100 mL within 8 h, making the paper tests strips relevant for detection of multiple pathogens and total coliform bacteria in beverage and food samples.
E. coli testing for food products: E. coli evade detection by going dormant
Researchers think they now know why a particularly virulent form of E. coli that swept through northern Germany last May was so hard to trace: The germs responsible eluded detection by going into a dormant state. Two new studies show that when stressed, E. coli can turn off most signs of life. That’s a problem for food-safety officials because their germ-screening techniques rely on bacteria reproducing to establish the presence of live organisms. Microbiologists look for life by attempting to culture bacteria in nutrient media, but dormant bacteria don’t reproduce; such bacteria instead become Viable, But Not Culturable (VBNC). Whenever there is a foodborne outbreak and it can’t be traced, it’s likely that the bacteria have become VBNC.
In one new study, microbiologists at the Robert Koch Institute in Germany, tested E. coli O104:H4 isolated from patients who fell ill in this year’s massive food-poisoning outbreak.3 O104:H4 bacteria don’t ordinarily produce deadly toxins or bloody diarrhea. This strain, which probably traveled and spread on tainted sprouts, did both, killing 54 people and sickening more than 3,700 others. In the lab, the scientists stressed the strain by exposing it to copper. Within a few days, many of the bacteria entered the dormant state and remained that way unless the researchers removed copper from the growth medium. Once resuscitated, the bacteria still had all of the features needed to be infective; for example, they had retained the genes to produce their lethal toxin and to make the sticky hairlike features that foster gut attachment.
To simulate what might happen in farm fields, microbiologists at Agriculture and Agri-Food Canada in Summerland, British Columbia, inoculated lettuce with either of two strains of E. coli O157:H7, a strain linked to deaths from eating tainted hamburger, lettuce and other types of produce.4,5 Withholding the nutrients that these bacteria would ordinarily acquire while passing through the gut caused the bacteria to enter hibernation. Within a few days, more than half of the germs were still alive but could not be cultured. They remained active metabolically, but at a very low level. Moreover, even in their dormancy, the cells were a source of toxin. Such data show that VBNC cells may be very important in food safety especially for E. coli types like O157:H7 where very few cells are needed to induce potentially life-threatening disease.
- S. M. Zakir Hossain, Cory Ozimok, Clémence Sicard, Sergio D. Aguirre, M. Monsur Ali, Yingfu Li, John D. Brennan. Multiplexed paper test strip for quantitative bacterial detection. Analytical and Bioanalytical Chemistry, 2012; DOI: 10.1007/s00216-012-5975-x
- Aurass, P. et al., (2011) “EHEC/EAEC O104:H4 strain linked with the 2011 German outbreak of haemolytic uremic syndrome enters into the viable but non-culturable state in response to various stresses and resuscitates upon stress relief”, Environmental Microbiology 13; 3139-3148.
- Dinu, L.-D. and Bach, S. Appl. Environ. Microbiol. (2011) 77; 8295-8302.
- http://www.sciencenews.org/view/generic/id/336725/title/E._coli_evade_detection _by_going _dormant
Selected United States Biological Products
|E3500-03||Escherichia coli, O157, Food, BioAssay™ ELISA Kit|