LENTICULE discs provide a homogenous format for external quality assessment samples: a comparison with freeze-dried samples for shellfish microbiology

Abstract

Aims:The aim was to compare the variability in Escherichia coli enumeration data and detection of Salmonella spp. between four samples of LENTICULE discs and freeze-dried samples for the Health Protection Agency's External Quality Assessment (EQA) scheme for shellfish microbiology. Methods and Results: Four samples of known but undisclosed microbiological content were dispatched in both freeze-dried and LENTICULE disc formats to 57 participating laboratories in 20 countries. Participants examined samples using their routine methods for the most probable number (MPN) of E. coli per 100 g and the presence/ absence of Salmonella spp. There was no significant difference between the Food and Environmental Proficiency Testing Unit and participating laboratories for E. coli and Salmonella spp. results. There were significantly less outlying results using the LENTICULE discs than freeze-dried sample format and equivalent or less variance for the former for E. coli MPN. There was no significant difference between LENTICULE discs and freeze-dried samples for the presence/absence of Salmonella spp. Conclusions: Overall the results indicated that there was equivalent or less variance in results for the LENTICULE discs than for freeze-dried samples, therefore LENTICULE discs are a homogenous and stable matrix for EQA samples. Significance and Impact of the Study: This study provides validation data for the replacement of freeze-dried samples by LENTICULE discs for the Health Protection Agency Shellfish EQA Scheme.

Genetic stability of strains preserved on LENTICULE discs and by freeze-drying: a comparison using fluorescent amplified fragment length polymorphism analysis

“…The discs can be prepared to contain a wide range of bacteria at levels ranging from 10 to 10 8 colony‐forming units per disc. These have been shown to provide suitable control material for internal and external quality assessment in food and environmental microbiology laboratories (Lightfoot et al , 2001; Prior et al , 2005). The preparation of LENTICULE discs does not require expensive specialized equipment; they are provided in a ready‐to‐use format eliminating the risks associated with opening glass ampoules.…”

Assessment of the stability of cell-surface components of microorganisms by MALDI-TOF-MS following preservation on lenticule discs

“…The stability and activity of the viable microorganisms can be preserved over long periods of time in this format. The mechanism for the procedure relies on the preservative properties of trehalose on membranes, proteins and biomolecules (Prior et al , 2005).…”

“…Microbial cell preservation on lenticule discs has been proposed as an alternative to freeze-drying as a mechanism for culture transfer among laboratories and to provide suitable control material for internal and external quality assessment in food and environmental microbiology laboratories (Lightfoot et al, 2001;Prior et al, 2005) including those laboratories using molecular procedures (Murphy et al, 2007). Lenticule discs provide a matrix for preserving microorganisms and consist of control-dried discs In all cases the closest match was between the corresponding lenticule disc and freeze-dried strains.…”

“…The stability and activity of the viable microorganisms can be preserved over long periods of time in this format. The mechanism for the procedure relies on the preservative properties of trehalose on membranes, proteins and biomolecules (Prior et al, 2005). The lenticule disc process has the advantage of providing accurate homogeneous quantitative cultures (Codd et al, 1998); freeze-drying is more commonly used for qualitative controls.…”

The development of LENTICULES™ as reference materials for noroviruses

“…LENTICULES™ containing bacterial determinands are now well established and widely employed by the HPA’s Food and Environmental Proficiency Testing Unit (FEPTU) as both RMs and in a range of commercial food and water external quality assurance schemes (Lightfoot et al. 2001; Prior et al. 2005).…”