title: Microbial survey of ready-to-eat salad ingredients sold at retail reveals the occurrence and the persistence of Listeria monocytogenes Sequence Types 2 and 87 in pre-packed smoked salmon.
abstract: As the preparation of salads involves extensive handling and the use of uncooked ingredients, they are particularly vulnerable to microbial contamination. This study aimed to determine the microbial safety and quality of pre-packed salads and salad bar ingredients sold in Singapore, so as to identify public health risks that could arise from consuming salads and to determine areas for improvement in the management of food safety.
  
  
  
  The most frequently encountered organism in pre-packed salad samples was B. cereus, particularly in pasta salads (33.3%, 10/30). The most commonly detected organism in salad bar ingredients was L. monocytogenes, in particular seafood ingredients (44.1%, 15/34), largely due to contaminated smoked salmon. Further investigation showed that 21.6% (37/171) of the pre-packed smoked salmon sold in supermarkets contained L. monocytogenes. Significantly higher prevalence of L. monocytogenes and higher Standard Plate Count were detected in smoked salmon at salad bars compared to pre-packed smoked salmon in supermarkets, which suggested multiplication of the organism as the products move down the supply chain. Further molecular analysis revealed that L. monocytogenes Sequence Type (ST) 2 and ST87 were present in a particular brand of pre-packed salmon products over a 4-year period, implying a potential persistent contamination problem at the manufacturing level.
  
  
  
  Our findings highlighted a need to improve manufacturing and retail hygiene processes as well as to educate vulnerable populations to avoid consuming food prone to L. monocytogenes contamination.
authors.affiliation: Environmental Health Institute, National Environment Agency, 11 Biopolis Way, #04-03/04, Helios Block, Singapore, 138667, Singapore.
authors.forename: Man Ling
authors.initials: ML
authors.lastname: Chau
authors.affiliation: Environmental Health Institute, National Environment Agency, 11 Biopolis Way, #04-03/04, Helios Block, Singapore, 138667, Singapore.
authors.forename: Kyaw Thu
authors.initials: KT
authors.lastname: Aung
authors.affiliation: Environmental Health Institute, National Environment Agency, 11 Biopolis Way, #04-03/04, Helios Block, Singapore, 138667, Singapore.
authors.forename: Hapuarachchige Chanditha
authors.initials: HC
authors.lastname: Hapuarachchi
authors.affiliation: Department of Chemistry, Food Science and Technology Programme, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore.
authors.forename: Pei Sze Valarie
authors.initials: PS
authors.lastname: Lee
authors.affiliation: School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore, 637551, Singapore.
authors.forename: Pei Ying
authors.initials: PY
authors.lastname: Lim
authors.affiliation: Environmental Health Institute, National Environment Agency, 11 Biopolis Way, #04-03/04, Helios Block, Singapore, 138667, Singapore.
authors.forename: Joanne Su Lin
authors.initials: JS
authors.lastname: Kang
authors.affiliation: Environmental Health Institute, National Environment Agency, 11 Biopolis Way, #04-03/04, Helios Block, Singapore, 138667, Singapore.
authors.forename: Youming
authors.initials: Y
authors.lastname: Ng
authors.affiliation: Environmental Health Institute, National Environment Agency, 11 Biopolis Way, #04-03/04, Helios Block, Singapore, 138667, Singapore.
authors.forename: Hooi Ming
authors.initials: HM
authors.lastname: Yap
authors.affiliation: Department of Chemistry, Food Science and Technology Programme, National University of Singapore, 3 Science Drive 3, Singapore, 117543, Singapore.
authors.forename: Hyun-Gyun
authors.initials: HG
authors.lastname: Yuk
authors.affiliation: Environmental Health Institute, National Environment Agency, 11 Biopolis Way, #04-03/04, Helios Block, Singapore, 138667, Singapore. Ramona_GUTIERREZ@nea.gov.sg.
authors.forename: Ramona Alikiiteaga
authors.initials: RA
authors.lastname: Gutiérrez
authors.affiliation: Environmental Health Institute, National Environment Agency, 11 Biopolis Way, #04-03/04, Helios Block, Singapore, 138667, Singapore. NG_Lee_Ching@nea.gov.sg.|School of Biological Sciences, Nanyang Technological University, 60 Nanyang Drive, Singapore, 637551, Singapore. NG_Lee_Ching@nea.gov.sg.
authors.forename: Lee Ching
authors.initials: LC
authors.lastname: Ng
mesh_terms: D000818:Animals; D001409:Bacillus cereus / Q000254:growth & development / Q000302:isolation & purification; D015373:Bacterial Typing Techniques; D001483:Base Sequence; D002167:Campylobacter / Q000254:growth & development / Q000302:isolation & purification; D015169:Colony Count, Microbial; D004269:DNA, Bacterial; D004926:Escherichia coli / Q000201:enzymology / Q000254:growth & development / Q000302:isolation & purification; D005506:Food Contamination / Q000032:analysis* / Q000517:prevention & control; D005511:Food Handling / Q000379:methods; D019649:Food Industry / Q000592:standards; D005516:Food Microbiology; D018857:Food Packaging / Q000379:methods / Q000592:standards; D063427:Food Quality; D059022:Food Safety; D006801:Humans; D006920:Hygiene; D008089:Listeria monocytogenes / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*; D008088:Listeriosis / Q000382:microbiology; D010802:Phylogeny; D015995:Prevalence; D011634:Public Health; D012474:Salmon / Q000382:microbiology*; D017747:Seafood / Q000382:microbiology*; D012703:Serotyping / Q000379:methods; D012846:Singapore; D013211:Staphylococcus aureus / Q000302:isolation & purification; D014675:Vegetables / Q000382:microbiology*; D014733:Vibrio / Q000145:classification / Q000302:isolation & purification; D001618:beta-Lactamases / Q000096:biosynthesis
chemical_list: D004269:DNA, Bacterial; D001618:beta-Lactamases
keywords: Food safety; Listeria monocytogenes; Microbial safety and quality; Multi Locus Sequence Typing (MLST); Salads; Smoked salmon