Listeria Monocytogenes In Samples Research Articles

Ultrasensitive detection of Listeria monocytogenes using solid‐state electrochemiluminescence biosensing based on the quenching effect of ferrocene on ruthenium pyridine

AbstractA solid‐state electrochemiluminescence (ECL) biosensing switch system based on the specific recognition of an aptamer and the destruction of pyridine ruthenium by ferrocene was successfully developed for the detection of Listeria monocytogenes detections. The switching system consisted of two principal parts, the ECL luminescent substrate and the ECL intensity switch. The ECL luminescent substrate was fabricated by attaching an aptamer of Listeria monocytogenes modified with DNA labeled with bipyridine ruthenium complementary to one end of the aptamer, and ferrocene‐labeled DNA complementary to the other end of the aptamer, to an electrode, and so act as an intensity switch. The identification reaction consisted of the specific binding of the aptamer with Listeria monocytogenes causing the labeled ferrocene to be removed from the luminescent substrate, the structural change resulting in a significant increase in the intensity of ECL due to the decreased quenching effect of ferrocene toward the ECL luminescent substrate. Accordingly, the change in ECL intensity indirectly reflected the concentration of Listeria monocytogenes in the sample. The results demonstrated that the system produced a good linear relationship over the concentration range of 1.4 × 101–1.4 × 106 CFU/ml. The present study established that this was a feasible approach for the detection of Listeria monocytogenes in milk and pork samples.

The existence of Listeria monocytogenes in a cattle slaughterhouse and identification of serotypes by mPCR

This study was carried out to investigate the presence of Listeria monocytogenes in samples obtained from a slaughterhouse in Samsun, Turkey. A total of 300 samples (25 samples per month) analyzed by Immunomagnetic Separation (IMS) based on conventional culture method. Then isolates were verified and serotyped by PCR using specific primers. According to the analysis, a total of 18 isolates were identified as L. monocytogenes. Distribution of these isolates were as; 5 isolates (serotype 1/2b or 3b) from 1 cattle carcass, 5 isolates (serotype 1/2b or 3b) from 1 knife, 2 isolates (serotype 4b or 4d, 4e) from 1 knife sharpener, 5 isolates (serotype 1/2a or 3a) from 1 floor sample, 1 isolate (serotype 1/2a or 3a) from 1 cowhide, respectively. As a result, carcasses are considered to pose a hazard to public health due to L. monocytogenes contamination. The development of slaughterhouse conditions and production technology, improving the education level of employees in food safety issues, prevention of contamination of foodborne pathogens to carcasses in slaughterhouses and implementation of effective sanitation methods should be provided

Risk assessment for listeriosis in consumers of Parma and San Daniele hams

Following the detection of Listeria monocytogenes in samples of dry cured ham imported in the USA from Italy, the Italian Ministry of Health planned a risk assessment for listeriosis in ham consumers. The risk assessment was performed according to international guidelines set by FAO and WHO. Expected incidence of illness was 4.7 × 10 −10 cases per serving in the case of normal adult population, 6.1 × 10 −7 in the case of organ transplanted patients, the most susceptible risk sub-population. Due to the low value of water activity even in the deeper parts of the ham, bacterial growth had a very slight effect on the probability of illness.

Listeria spp. in broiler flocks: recovery rates and species distribution investigated by conventional culture and the EiaFoss method

The occurrence of Listeria monocytogenes in samples from broiler houses and cloacal swabs taken at the abattoir was investigated. An automated immunobased method (EiaFoss) was used, and 42 samples were also analysed by conventional culture; both methods were based on a two-step selective enrichment using CHR.4.17; Fraser and Fraser broths. L. monocytogenes was isolated from two of 71 broiler flocks, yielding an estimated flock prevalence of 3%. The flock prevalence of L. inocua was estimated to 13%, and it was speculated that the potential of this apathogenic bacteria to grow faster than L. monocytogenes in enrichment broths may lead to an underestimation of the prevalence of L. monocytogenes. Furthermore, as L. inocua was also detected by the EiaFoss method, a significant amount of bacterial confirmation work had to be done. Of 42 samples analysed by conventional culture, four yielded L. inocua, of which two were not positive by EiaFoss.

Isolation of Listeria species from precooked chilled foods

Cook-chill food prepared commercially was introduced to serve our patients and staff in 1989. The presence of Listeria monocytogenes in samples taken before regeneration was examined over two periods. For period A (April–November 1989), c. 0·2 g of food was examined; 2·7% of 992 meat samples and 0·6% of 1084 samples of other types of food were found to contain the organism. As a result, cold sliced meat was withdrawn from the patients' menu. For period B (February–July 1990), following the introduction of new guidelines, 25 g of food was examined after enrichment. Of the 854 meat samples examined 9% were positive for L. monocytogenes, and of the 1465 samples of other types of food examined 2·29% were positive. The significant increase between the two time periods occurred in the number of samples containing <10 colony forming units (cfu) g −1 of L. monocytogenes. The proportion of positive samples that contained 10–10 3 cfu g −1 remained the same for both periods (0·7%). Isolation of the organism was significantly associated with samples which had total viable counts of >10 4 cfu g −1. There was no specific pattern of distribution of different serotypes in our isolates of L. monocytogenes. In the absence of evidence that small inocula of <10 cfu g −1 in cook-chill food before regeneration could be harmful to patients, we question whether the extra cost involved in following the Department of Health guidelines and examining 25 g of food for the presence of L. monocytogenes is justified.