Kofitsyo S. Cudjoe

Immunomagnetic separation of Salmonella from foods and their detection using immunomagnetic particle (IMP)-ELISA

An immunomagnetic particle based ELISA (IMP-ELISA) for the detection of Salmonella from foods has been developed using Dynabeads anti-Salmonella (Dynal, Oslo, Norway). Appropriate sample preparation protocols to allow rapid detection of Salmonella serovariants in processed (powdered egg products) and non-processed (raw chicken) samples have been established. Pre-enriched broths of heat processed samples likely to harbour only low levels of competitive enteric flora, were boiled and used directly for IMP-ELISA. For non-heat processed or raw samples likely to contain higher numbers of such competing organisms, live Salmonella cells were first isolated by immunomagnetic separation (IMS) from standard pre-enrichment broths, and then post-selectively enriched for a short time in M-broth followed by boiling before IMP-ELISA. The total assay time including sample preparation was under 26 h for both types of procedure, with a lower detection limit of 10(5) Salmonella cells/ml of sample. In an evaluation of naturally contaminated poultry samples, all 45 of 48 samples previously shown to contain salmonellae in a comparison of ISO, IMS-Plating, Salmonella-Tek ELISA (Organon Teknika, Inc. Durham, NC) and a modification of the latter based on IMS, were identified as positive. None of the other methods gave positives for all 45.

Outbreak of Yersinia enterocolitica serogroup O:9 infection and processed pork, Norway.

An outbreak involving 11 persons infected with Yersinia enterocolitica O:9 was investigated in Norway in February 2006. A case-control study and microbiologic investigation indicated a ready-to-eat pork product as the probable source. Appropriate control measures are needed to address consumer risk associated with this product.

IMS: a new selective enrichment technique for detection of Salmonella in foods

In a study designed to evaluate the performance of Dynabeads Anti-Salmonella, immunomagnetic separation (IMS) followed by plating (IMS-Plating) proved far superior to the conventional ISO Salmonella methodology and the Modified Semi-solid Rappaport-Vassiliadis (MSRV) method. Salmonella species were isolated and detected from 135 out of the 180 diverse poultry samples by IMS analysis as against 98 by the conventional method and 33 by the MSRV technique. All results were confirmed biochemically and serologically. It appeared from the data generated that some of the salmonellae isolated using IMS were greatly inhibited in Rappaport-Vassiliadis enrichment broth at 42 degrees C and to a lesser extent in selenite cystine broth at 37 degrees C. A moderately selective plating medium like XLD proved to be better in isolating these possible sensitive wild-type strains of salmonellae than the more selective BGA.

Detection of Salmonella from raw food samples using Dynabeads® anti-Salmonella and a conventional reference method

A Dynal core method has been established using Dynabeads anti-Salmonella to detect Salmonella from all categories of food samples. The protocol consists of the standard pre-enrichment of samples in buffered peptone water followed by immunomagnetic separation and subsequent selective enrichment of the bead-bacteria complexes in Rappaport-Vassiliadis Soya Peptone broth before plating onto Salmonella selective media. This modified IMS cultural method is intended to replace or augment traditional cultural methods used for Salmonella detection due to its specificity and increased sensitivity. The optional direct plating of bead-bacteria complexes onto solid media using a swab-streak technique is suitable for processed foods or samples known to have a history of very low resident flora. In an evaluation using 100 naturally contaminated samples, this IMS core method detected 39 of the 44 positive samples detected by all the methods combined, compared to 31 detected by the conventional ISO 6579 reference method. Furthermore, in ten different food matrices inoculated with low levels (1-5 cells/25 g) of twenty Salmonella serovariants, frozen for one month before being examined, the IMS core method, showed a 90% concordance with the ISO method and isolated two more Salmonella positive samples than the conventional ISO method.

Detection of Clostridium perfringens type A enterotoxin in faecal and food samples using immunomagnetic separation (IMS)-ELISA

A simple, rapid and sensitive immunoassay, based on immunomagnetic particles (Dynabeads M-280) was developed for detection and quantitation of Clostridium perfringens type A enterotoxin from faecal and food extracts. The assay had a detection limit of 2.5 ng/ml enterotoxin in homogenates of faeces and inoculated meat extracts. The specificity was confirmed by both crossed immunoelectrophoresis and Western immunoblotting techniques, using a purified enterotoxin as standard.

Use of ferrous sulphate and immunomagnetic separation to recover Salmonella enteritidis from raw eggs

Contaminated eggs or foods containing eggs have been a source of food borne salmonellosis, with a significant proportion of these outbreaks being attributed to Salmonella enteritidis. Since the level of contamination in individual eggs or a pool of such eggs may be low, enrichment to increase cell numbers can take several days. Pre-enrichment of raw blended eggs which have been supplemented with ferrous sulphate at a concentration of 35 mg/l, for 6 h at 37 degrees C, significantly enhanced the growth of Salmonella. Using Dynabeads Anti-Salmonella (Dynal, Oslo), a new commercial product for selective enrichment of Salmonella from food samples, we have defined a protocol based on immunomagnetic separation, specially for raw eggs. The application of this protocol enables definitive detection of Salmonella enteritidis from eggs within 30 h.

Yersinia enterocolitica Outbreak Associated with Ready-to-Eat Salad Mix, Norway, 2011

In 2011, an outbreak of illness caused by Yersinia enterocolitica O:9 in Norway was linked to ready-to-eat salad mix, an unusual vehicle for this pathogen. The outbreak illustrates the need to characterize isolates of this organism, and reinforces the need for international traceback mechanisms for fresh produce.

The effect of lactic acid sprays on the keeping qualities of meat during storage.

Spraying the meat surface of skinned cow heads with 1% v/v lactic acid resulted in significant reduction in total viable counts of bacteria at storage temperatures of 4, 15 and 20 degrees C. The number of coliform bacteria was also reduced at all three temperatures but the reductions were not statistically significant on most occasions. However, after five and two days at 15 degrees C and 20 degrees C, respectively, when the initial effect of acid appeared to be lost, the number of coliforms on sprayed heads exceeded those on unsprayed heads. The shelf lives of all sprayed heads were observed to have been extended for about three days at 4 degrees C and one day for both 15 degrees C and 20 degrees C.

Identification of thermotolerant Campylobacter species from poultry using an enzyme-labelled oligonucleotide DNA probe

A commercially available enzyme-labelled DNA probe for human Campylobacter strains has been tested and also found to hybridize with DNA from C. jejuni and C. coli isolates from poultry. DNA from 11 enteric, non-campylobacter organisms, included in the test as negative controls, failed to hybridize with the probe indicating that the probe might be used for identification of campylobacter from poultry too.

A Shigella sonnei outbreak traced to imported basil - The importance of good typing tools and produce traceability systems, Norway, 2011

On 9 October 2011, the University Hospital of North Norway alerted the Norwegian Institute of Public Health (NIPH) about an increase in Shigella sonnei infections in Tromsø. The isolates had an identical ‘multilocus variable-number tandem repeat analysis’ (MLVA) profile. Most cases had consumed food provided by delicatessen X. On 14 October, new S. sonnei cases with the same MLVA-profile were reported from Sarpsborg, south-eastern Norway. An outbreak investigation was started to identify the source and prevent further cases. All laboratory-confirmed cases from both clusters were attempted to be interviewed. In addition, a cohort study was performed among the attendees of a banquet in Tromsø where food from delicatessen X had been served and where some people had reported being ill. A trace-back investigation was initiated. In total, 46 cases were confirmed (Tromsø= 42; Sarpsborg= 4). Having eaten basil pesto sauce or fish soup at the banquet in Tromsø were independent risk factors for disease. Basil pesto was the only common food item that had been consumed by confirmed cases occurring in Tromsø and Sarpsborg. The basil had been imported and delivered to both municipalities by the same supplier. No basil from the specific batch was left on the Norwegian market when it was identified as the likely source. As a result of the multidisciplinary investigation, which helped to identify the source, the Norwegian Food Safety Authority, together with NIPH, planned to develop recommendations for food providers on how to handle fresh plant produce prior to consumption.