Rapid detection of the foodborne pathogen Escherichia coli O157:H7 is of vital importance for public health worldwide. Among detection methods, reporter phages represent unique and sensitive tools for the detection of E. coli O157:H7 from food as they are host-specific and able to differentiate live cells from dead ones. Upon infection, target bacteria become identifiable since reporter genes are expressed from the engineered phage genome. The E. coli O157:H7 bacteriophage ΦV10 was modified to express NanoLuc luciferase (Nluc) derived from the deep-sea shrimp Oplophorus gracilirostris. Once infected by the ΦV10 reporter phage, E. coli O157:H7 produces a strong bioluminescent signal upon addition of commercial luciferin (Nano-Glo®). Enrichment assays using E. coli O157:H7 grown in LB broth with a reporter phage concentration of 1.76 × 102 pfu ml−1 are capable of detecting approximately 5 CFU in 7 hours. Comparable detection was achieved within 9 hours using 9.23 × 103 pfu ml−1 of phage in selective culture enrichments of ground beef as a representative food matrix. Therefore we conclude that this NanoLuc reporter phage assay shows promise for detection of E. coli O157:H7 from food in a simple, fast and sensitive manner.

Bacteriophage PhiV10 is a temperate phage, which specifically infects Escherichia coli O157:H7. The nucleotide sequence of the PhiV10 genome is 39 104 bp long and contains 55 predicted genes. PhiV10 is closely related to two previously sequenced phages, the Salmonella enterica serovar Anatum (Group E1) phage epsilon15 and a prophage from E. coli APEC O1. The attachment site of PhiV10, like those of its two closest relatives, overlaps the 3' end of guaA in the host chromosome. PhiV10 encodes an O-acetyltransferase, which modifies the O157 antigen. This modification is sufficient to block PhiV10 superinfection, indicating that the O157 antigen is most likely the PhiV10 receptor.

No abstract

Ready-to-eat (RTE) meat and poultry product samples collected between 2005 and 2017 from RTE producing establishments for the Food Safety and Inspection Service’s (FSIS’s) ALLRTE/RTEPROD_RAND (random) and RTE001/RTEPROD_RISK (risk-based) sampling projects were tested for Listeria monocytogenes ( Lm ). Data for 45,897 ALLRTE/RTEPROD_RAND samples collected from 3607 unique establishments and 112,347 RTE001/RTEPROD_RISK samples collected from 3283 unique establishments were analyzed for the presence of Lm . These data were also analyzed based upon the percentages of establishments with positive samples, as well as annual production volume, sanitation control alternative, geographic location and season/month of sample collection.  Results showed low occurrences of Lm -positive samples from the random and risk-based sampling projects, with 152 positive samples (0.33%) for ALLRTE/RTEPROD_RAND and 403 positive samples (0.36%) for RTE001/RTEPROD_RISK, respectively. The percentages of positive samples significantly decreased over time, from about 0.7% in 2005-2006 to about 0.2% in 2017 (P<0.05). During the 2005-2017 time period, 3.9% of establishments sampled under the ALLRTE/RTEPROD_RAND sampling project had at least one Lm -positive sample.  Similarly, 10.0% of establishments sampled under the RTE001/RTEPROD_RISK sampling project had at least one positive sample. Positive Lm samples were found in all geographic regions in all months.  Thus, in 13 years of RTE product sampling in FSIS-regulated establishments (2005-2017), less than 0.4% of samples were positive for Lm in both risk-based and random sampling projects. The low percentage of Lm in these products suggests that the combination of FSIS policies and industry practices may be effective in controlling Lm contamination. Information obtained from these sampling projects is relevant to the ongoing prevention of foodborne Lm illnesses from RTE meat and poultry products.