Rapid and alternative methods for the detection of salmonellas in foods

Methods of Rapid Microbiological Assay and Their Application to Pharmaceutical and Medical Device Fabrication

　There are several rapid microbiological methods becoming available that have useful applications in pharmaceutical and medical devices. They are ATP bioluminescence, fluorescent labeling, electrical resistance, and nucleic acid probes. In choosing to employ rapid methods, the microbiologist should examine their prospective performances against the specific requirements for that sector. Some methods may require expensive equipment and offer full automation, and others represent only a small investment. The regulatory view of these methods is changing and they still officially have not been approved in medical and pharmaceutical area, but it will still be up to the microbiologist to demonstrate that the method chosen is fit for the purpose intended.

Immunochromatographic strip assay for the rapid and sensitive detection ofSalmonellaTyphimurium in artificially contaminated tomato samples

This study was designed to confirm the applicability of a liposome-based immunochromatographic assay for the rapid detection of Salmonella enterica subsp. enterica serovar Typhimurium (Salmonella Typhimurium) in artificially contaminated tomato samples. To determine the detection limit and pre-enrichment incubation time (10, 12, and 18 h pre-enrichment in 1% buffered peptone water), the tests were performed with different cell numbers of Salmonella Typhimurium (3 × 100, 3 × 101, 3 × 102, and 3 × 103CFU·mL−1) inoculated into 25 g of crushed tomato samples. The assay was able to detect as few as 30 Salmonella Typhimurium cells per 25 g of tomato samples (1.2 cells·g−1) after 12 h pre-enrichment incubation. Moreover, when the developed assay was compared with traditional morphological and biochemical culture-based methods as well as colloidal gold nanoparticle-based commercial test strips, the developed assay yielded positive results for the detection of Salmonella Typhimurium within a shorter period time. These findings confirm that the developed assay may have practical application for the sensitive detection of Salmonella Typhimurium in various food samples, including raw vegetables, with a relatively low detection limit and shorter analysis time.

MÉTODOS DIAGNÓSTICOS PARA OS PATÓGENOS ALIMENTARES: CAMPYLOBACTER SP., SALMONELLA SP. E LISTERIA MONOCYTOGENES

RESUMO Os métodos moleculares de detecção rápida e eficaz de lotes de aves infectados por bactérias como Salmonella sp. Campylobacter sp. e Listeria monocytogenes são importantes para reduzir a frequência da transmissão destes patógenos entre os lotes de aves e aos consumidores de produtos de origem animal. Recentemente, as técnicas de biologia molecular, em especial a reação em cadeia polimerase, que permite a amplificação específica de segmentos de DNA, têm possibilitado novos rumos na identificação de bactérias supracitadas, reduzindo o tempo de cultivo e ampliando a confiabilidade das provas diagnósticas. A utilização da biologia molecular por laboratórios de diagnóstico humano e animal, assim como em programas de controle de qualidade de alimentos e produtos de origem animal, já é realidade e tende a se expandir rapidamente. O objetivo deste artigo é fazer uma breve revisão dos testes diagnósticos convencionais e moleculares para identificar Campylobacter sp., Salmonella sp. e Listeria monocytogenes. Concluindo, o diagnóstico molecular é um campo em avanço científico e tecnológico, no qual novas técnicas moleculares estão em desenvolvimento para o diagnóstico de bactérias em alimentos.

Application of an Impedimetric Technique for the Detection of Lytic Infection of Salmonella spp. by Specific Phages

This study was performed to evaluate the adaption of the impedimetric method to detect the lytic infection by Salmonella-specific bacteriophages and to provide a higher selectivity to this rapid method in detecting Salmonella spp. by using specific agents. Three bacteriophages and twelve strains of Salmonella spp. were tested. Each of the twelve strains was used separately to inoculate TSB together with each one of the phages. The inoculum concentration was between 10⁶ and 10⁷ cfu/mL, at a cell: phage ratio of 1 : 100. From the sample analysis, based on conductance (G) measurements (37°C), the infection could be detected, by observation of both detection-time delay and distinct curve trends. The main conclusions were that kinetic detection by impedance microbiology with phage typing constitutes a method of determining whether a test microorganism is sensitive to the bacteriophage and a method to evaluate whether a lytic bacteriophage is present in a sample, by affecting bacterial growth rate/metabolic change.

Detection and Identification of Salmonella Typhimurium in Bovine Diarrhoeic Fecal Samples by Immunomagnetic Separation and Multiplex PCR Assay

The aim of this study was to use the immunomagnetic separation (IMS) test plus a multiplex polymerase chain reaction (m-PCR) assay to detect Salmonella at genus level and also for the identification of Salmonella enterica serovar Typhimurium in bovine diarrhoeic fecal samples. In all, 400 bovine diarrhoeic fecal specimens were examined by conventional bacterial culture, IMS, and m-PCR. For m-PCR assay, four set primers were selected: 139-141, specific for inv-A gene of Salmonella spp and the RfbJ, FliC and FljB, specific for the rfbJ, FliC and fljB genes of Salmonella Typhimurium or other Salmonella serovars with similar antigenic properties. Thirty-three (8.25%) out of the 400 fecal samples were culture positive for Salmonella serovars. Of these, 66.7% (22 of 33) were Salmonella enterica serovar Typhimurium, and 9.1% (three of 33) were serovar Dublin. In the IMS + m-PCR, four amplified product (663, 526, 284 and 183 bp) were found in all specimens that had serovar Typhimurium (4,5,12:i:1,2), they corresponded, respectively, to the rfbJ, fljB, inv-A and Flic genes of this serovar. In serovar Dublin (1,9,12:g,p:-), Georgia (6,7:b:e,n,z(15)) and, Enteritidis (1,9,12;g,m:-) only one PCR product (284 bp) was amplified from the inv-A gene. In serovars Augustenborg (6,7:i:1,2) and Lindenburg (6,8:i:1,2) three positive bands (526, 284 and 183 bp) were amplified corresponding to the fljB, inv-A and Flic genes, respectively. In serovar Virchow (6,7:r:1,2) two amplified products (284 and 526 bp) from the inv-A and FliC genes were observed. In serovar Gloucster (1,4,12(27):i:1,w) three fragments (183, 284 and 663) from the FliC, inv-A and, rfbJ genes respectively, were observed. In the positive control as expected, four PCR products were amplified corresponding to the FliC, inv-A, fljB and rfbJ genes, respectively. In conclusion, the results of this study showed that detection of Salmonella at genus level with universal ST139-141 primers and identification of Salmonella Typhimurium by using specific primers of O4, H(2):1, 2 and H(1) antigens can potentially permit to more readily evaluate fecal and other types of samples for the presence of these organisms. Compared to bacteriological culture the combination of IMS and m-PCR resulted a faster method for the detection and identification of Salmonella at genus and serovar level by using of universal and specific primers.

A modelling approach to estimate the sensitivity of pooled faecal samples for isolation of Salmonella in pigs

The objective of this study was to develop and parametrize a mathematical model of the sensitivity of pooled sampling of faeces to detect Salmonella infection in pigs. A mathematical model was developed to represent the effect of pooling on the probability of Salmonella isolation. Parameters for the model were estimated using data obtained by collecting 50 faecal samples from each of two pig farms. Each sample was tested for Salmonella at individual sample weights of 0.1, 0.5, 1, 10 and 25 g and pools of 5, 10 and 20 samples were created from the individual samples. The highest test sensitivity for individual samples was found at 10 g (90% sensitivity), with the 25 g test sensitivity equal to 83%. For samples of less than 10 g, sensitivity was found to reduce with sample weight. Incubation for 48 h was found to produce a more sensitive test than incubation for 24 h. Model results found increasing sensitivity with more samples in the pool, with the pools of 5, 10 and 20 being more sensitive than individual sampling, and the pools of 20 being the most sensitive of those considered.

Evaluation of a capillary immunoassay system for detection of Salmonella typhimurium in poultry products

A capillary immunoassay system was constructed and optimized for detection of Salmonella Typhimurium. The system consisted of a capillary bioseparator-bioreactor and a flow-injection electrochemical detector. Three methods were compared for immobilizing antibodies on the inner surface of silica capillary columns; these methods were based on the use of a homobifunctional cross-linker glutaraldehyde, a heterobifunctional cross-linker N-succinimidyl-4-maleimidobutyrate, and biotin-streptavidin chemistry, respectively. The glutaraldehyde method gave the best reproducibility with a relative standard deviation of 1 to 6% for detection of Salmonella Typhimurium. The optimized immunoassay system could detect Salmonella Typhimurium in chicken breast and ground turkey meats with a detection limit of 2.4 x 10(3) and 2.4 x 10(4) CFU/ml, respectively. The total detection time was less than 2.5 h without any preenrichment. When stored at 4 degrees C, the immunocolumns could retain their activities for at least 3 months.

Combination of immunomagnetic separation with real-time PCR for rapid detection of Salmonella in milk, ground beef, and alfalfa sprouts

A rapid, specific, and sensitive method for detecting Salmonella spp. in pasteurized milk, ground beef, and alfalfa sprouts was developed. The method combined immunomagnetic separation with a real-time PCR assay based on the double-stranded DNA binding dye SYBR Green I. The primers used produced a product with a melting temperature of 87+/-0.5 degrees C during the PCR assay by amplifying a 284-bp sequence from the invasive gene (invA) of Salmonella. The method was successful in detecting 20 Salmonella strains, but the expected PCR product was not formed by any of 11 other bacterial strains. To test this combined method for the monitoring of Salmonella, Salmonella enterica serotype Newport was inoculated into 52 samples each of pasteurized milk, ground beef, and alfalfa sprouts. Following a 10-h nonselective enrichment step in buffered peptone water, cells were removed by immunomagnetic separation and DNA extracted using the High Pure PCR template preparation kit. The DNA produced was used as a template in the real-time PCR assay. When spiked pasteurized milk, ground beef, and alfalfa sprout samples were analyzed by this protocol, an initial inoculum of 1 CFU/ml, 25 CFU/25 g, and 1.5 CFU/25 g, respectively, was detectable within 13 h. These results indicate that the combination of immunomagnetic separation and real-time PCR assay was a highly specific and sensitive method for the rapid detection of Salmonella.

Rapid detection of food-borne pathogens by using molecular techniques

Traditional methods of identification of food-borne pathogens, which cause disease in humans, are time-consuming and laborious, so there is a need for the development of innovative methods for the rapid identification of food-borne pathogens. Recent advances in molecular cloning and recombinant DNA techniques have revolutionized the detection of pathogens in foods. In this study the development of a PCR-based technique for the rapid identification of the food-borne pathogens Salmonella and Escherichia coli was undertaken. Suitable primers were designed based on specific gene fimA of Salmonella and gene afa of pathogenic E. coli for amplification. Agarose gel electrophoresis and subsequent staining with ethidium bromide were used for the identification of PCR products. The size of the amplified product was 120 bp as shown by comparison with marker DNA. These studies have established that fimA and afa primers were specific for detecting Salmonella and pathogenic E. coli, respectively, in the environmental samples. Thus a rapid, sensitive and reliable technique for the detection of Salmonella and pathogenic E. coli was developed.

Evaluation of an automated immunomagnetic separation method for the rapid detection of Salmonella species in poultry environmental samples

Automated immunomagnetic separation (AIMS), using Dynabeads anti-Salmonella (Dynal, Oslo), was evaluated for its ability to detect Salmonella spp. in poultry environmental samples in comparison with standard, culture-based method (Health Canada, Health Protection Branch, MFHPB-20). AIMS was found to be more reliable in detecting Salmonella from artificially inoculated enrichment broths at low levels and exhibited a 15.5% higher sensitivity value than the culture method.

Application of an automated immunomagnetic separation-enzyme immunoassay for the detection of Salmonella spp during an outbreak associated with a retail premises

AIMS

The application of an automated immunomagnetic separation-enzyme immunoassay (AIMS-EIA) during the investigation of a suspected outbreak of Salmonella food poisoning at a retail premises.

METHODS AND RESULTS

Six food samples and 24 environmental swabs were taken from the retail premises and six food handlers' submitted faecal samples during the investigation of the outbreak. Isolation and identification of Salmonella from these samples was performed according to established standard operating procedures and by AIMS-EIA. Twelve of the 18 (67%) Salmonella culture positive samples were AIMS-EIA positive on testing pre-enrichment samples after 24 h, whilst 17 (94%) samples were AIMS-EIA positive following selective enrichment for a further 48 h. One food handler was found to be positive for Salmonella by both culture and AIMS-EIA. All Salmonella isolates were confirmed as Salmonella Enteritidis phagetype 21c.

CONCLUSIONS

The AIMS-EIA protocol compliments the conventional culture approach to produce more timely results for the management of the risk to public health without significantly increasing the workload of the laboratory.

SIGNIFICANCE AND IMPACT OF THE STUDY

The food production premise investigated in this study was heavily contaminated with Salmonella Enteritidis. Application of the AIMS-EIA was significant in the effective intervention of control measures for the protection of public health.

Application of a novel immunomagnetic separation-bacteriophage assay for the detection of Salmonella enteritidis and Escherichia coli O157:H7 in food

Salmonella infection is the second most prevalent cause of foodborne illness in most developing countries. Meat, poultry, and dairy products are frequently implicated in outbreaks. The objective of this study was to apply a novel immunomagnetic separation (IMS)-bacteriophage assay to the detection of Salmonella enteritidis in artificially inoculated skimmed milk powder, chicken rinses, and ground beef. In all food types tested, the IMS-bacteriophage assay was able to detect an average of 3 CFU of S. enteritidis in 25 g or ml of food sample. Total assay time including pre-enrichment is about 20 h. The results indicate that the IMS-bacteriophage assay is a rapid and sensitive means of detecting S. enteritidis in these foods. The assay was successfully adapted to the detection of Escherichia coli O157:H7 and was able to detect E. coli in ground beef at the lowest inoculation level tested, 2 CFU/g. The assay was also adapted to the simultaneous detection of S. enteritidis and E. coli. The results indicate that the IMS-bacteriophage assay shows promise for the simultaneous detection of these pathogens, but further development work would be necessary to improve sensitivity and produce reliable results at low inoculation levels.

Detection and identification of salmonellas from poultry-related samples by PCR

A polymerase chain reaction (PCR) assay was developed for the generic detection of Salmonella sp. and the identification of S. Enteritidis (SE), S. Gallinarum (SG), S. Pullorum (SP) and S. Typhimurium (ST) in material collected in the field from poultry. The specificity and sensitivity of the assay combined with Rappaport-Vassiliadis selective enrichment broth (PCR-RV) were determined, and field samples were analyzed to verify the validity of the method application. Specificity of the assay was tested using 29 SE, 11 SG, 10 ST and 10 SP strains, along with 75 strains of 28 other Salmonella serovars and 21 strains of other bacterial genera. The assay was 100% specific for Salmonella detection and ST identification. The primer pair for SE, SG and SP also detected S. Berta. PCR detection limits for Salmonella at the genus level were 2 ST, 8 SE, 1.1x10(3) SG and 1.8x10(5) SP cells. At the serovar level, detection limits were 7 ST, 1.2x10(3) SE, 4.4x10(7) SG and 1.8x10(6) SP cells. At the genus level, PCR-RV detected approximately 128% more positive field samples than the standard microbiological techniques and results were ready in 48h instead of 7 days. PCR-RV method is diagnostic of Salmonella at the genus level and ST at the serovar level, although other tests are needed to identify SE, SG and SP to serovar level.

Development and optimization of a novel immunomagnetic separation- bacteriophage assay for detection of Salmonella enterica serovar enteritidis in broth

Salmonella is the second-leading cause of food-borne illness in most developed countries, causing diarrhea, cramps, vomiting, and often fever. Many rapid methods are available for detection of Salmonella in foods, but these methods are often insensitive or expensive or require a high degree of technical ability to perform. In this paper we describe development and characterization of a novel assay that utilizes the normal infection cycle of bacteriophage SJ2 for detection of Salmonella enterica serovar Enteritidis in broth. The assay consists of four main stages: (i) capture and concentration of target cells by using immunomagnetic separation (IMS); (ii) infection of the target bacterium with phage; (iii) amplification and recovery of progeny phage; and (iv) assay of progeny phage on the basis of their effect on a healthy population of host cells (signal-amplifying cells). The end point of the assay can be determined by using either fluorescence or optical density measurements. The detection limit of the assay in broth is less than 10(4) CFU/ml, and the assay can be performed in 4 to 5 h. The results of this study demonstrate that the IMS-bacteriophage assay is a rapid, simple, and sensitive technique for detection of Salmonella serovar Enteritidis in broth cultures which can be applied to preenriched food samples.

The detection of Salmonella using a combined immunomagnetic separation and ELISA end-detection procedure

The aim of this study was to develop a rapid immunoassay to detect Salmonella bacteria. Skimmed milk powder (SMP) in buffered peptone water was inoculated with six Salmonella strains (Salm. typhimurium, Salm. virchow, Salm. enteritidis, Salm. give, Salm. ealing and Salm. arizonae) at three inoculum levels (about 2-200 cfu 25 g(-1) SMP) and incubated (37 degrees C) overnight. Heat-treated salmonella cells were immobilized on paramagnetic particles and detected within 3 h using the Salmonella genus-specific monoclonal antibody M105 in a microtitre plate based assay. The rapid Salmonella detection method combining immunomagnetic separation and ELISA had a total isolation and detection time of less than 24 h, which is significantly shorter than the conventional techniques requiring 72-96 h. The technique had a sensitivity limit of 10(5)-10(6) cfu ml(-1).

Comparison of two commercial preparations of buffered peptone water for the recovery and growth of Salmonella bacteria from foods

This study compared the performance of two commercial preparations of buffered peptone water. Performance was assessed in terms of ability to resuscitate and recover low numbers of stressed cells, buffering capacity, growth of Salmonella bacteria in pure culture and growth of Salmonella in food pre-enrichments. Although both the preparations of BPW had similar chemical compositions, differences in their recovery performance were found. Brand A recovered significantly higher numbers of heat-injured Salmonella (mean = 0.57 log10 cfu ml(-1) difference) in pure culture compared with brand B when dealing with very low inoculum levels. Although brand B had higher buffering capacity, the pH at the end of the pre-enrichment was found to be similar in both media, even in foods such as milk powder which showed the greatest decline in pH. Both brands were comparable in their ability to grow unstressed Salmonella from different food types. In unstressed cell studies, similar cell numbers were recovered at the end of a 24 h incubation period from both media, although brand B yielded a higher biomass. In the food study with unstressed cells, performance was related more to the food type and the likely association between this and the level and type of competitor organisms present, rather than to the brand of medium used.

Rapid detection of Salmonella typhimurium in chicken carcass wash water using an immunoelectrochemical method

An immunoelectrochemical method coupled with immunomagnetic separation was developed for rapid detection of Salmonella Typhimurium in chicken carcass wash water. Samples of chicken carcass wash water were inoculated with Salmonella Typhimurium at different cell numbers. Possible nonspecified inhibitors in the wash water were minimized by filtration and centrifugation. An approximately 9.4% loss of Salmonella cells was found after filtration (P < 0.01). The samples were mixed with anti-Salmonella-coated magnetic beads (ASCMB) and alkaline phosphatase-labeled anti-Salmonella (APLAS) to form ASCMB-Salmonella-APLAS conjugates. The conjugates were separated from the solution using a magnetic separator and then incubated with phenylphosphate substrate to produce phenol. The number of Salmonella was determined by measuring the phenol concentration using an amperometric tyrosinase carbon paste electrode in a flow injection analysis system. Under optimized parameters (1 mM MgCl2, 0.2 microg/ml APLAS, and 1 mM phenylphosphate in pH 7.0 Tris buffer solution), Salmonella Typhimurium in chicken carcass wash water could be identified and enumerated within 2.5 h with a detection limit of 5 x 10(3) CFU/ml. A linear relationship on a log-log scale was found between Salmonella cell number and the peak current ratio for Salmonella concentrations ranging from 10(3) to 10(7) CFU/ml (R2 = 0.963). The peak currents of multibacteria samples, containing Salmonella Typhimurium, Listeria monocytogenes, and Campylobacter jejuni, were not significantly different from Salmonella-only samples (P > 0.01).

Modifications to methods for the enumeration and detection of injured Escherichia coli O157:H7 in foods

Reliable methods are required for the detection and enumeration of potentially injured E. coli O157 in food in the presence of outnumbering competing bacteria. Selective agents can prevent or inhibit the recovery and subsequent multiplication of injured cells and direct inoculation, either into selective enrichment broths or onto selective agar plates is still used in many methods for E. coli O157 detection and enumeration. When compared with tryptone soya agar (TSA), sorbitol MacConkey agar (SMAC) was shown to underestimate the concentration of viable E. coli O157:H7 subjected to low pH and high NaCl concentration. Using a resuscitation stage on TSA followed by membrane transfer to SMAC improved recovery to levels obtained on TSA. The membrane method was used to monitor the numbers of artificially contaminated E. coli O157:H7 during the fermentation of a meat product and demonstrated better survival when compared to counts on SMAC. Six rapid methods for the detection of E. coli O157 in food (BAX E. coli O157, Reveal 8 E. coli O157-H7 screening test, VIP EHEC, VIDAS E. coli O157 (ECO), EHEC-Tek and Tecra E. coli O157 visual immunoassay), were evaluated using beetburgers, parsley and fermented meat artificially contaminated with injured cells. Methods using direct selective enrichment, with or without an elevated incubation temperature gave false-negative results. The incorporation of a non-selective pre-enrichment medium improved the detection rates of these assays by up to ten fold.

Comparison of methods for the recovery and detection of low levels of injured Salmonella in ice cream and milk powder

This study compared the ability of four rapid methods and a standard cultural method to detect low levels of heat-injured cells of Salmonella typhimurium in ice cream and skimmed milk powder. The detection of Salmonella in samples contaminated with low levels (< 10 cfu 25 g-1) was significantly greater with the novel broth method than with the other methods (P </= 0.01). At contamination levels > 10 cfu 25 g-1, there was no significant difference between the methods except for the novel broth method and a dipstick-based immunoassay (P </= 0.05). The novel broth method, S.P.R.I.N.T. Salmonella, which incorporates a specifically formulated peptone and Oxyrase(R) combination followed by the timed release of selective agents into the recovery medium, was shown to improve the rate of detection of low numbers of injured cells of Salmonella after 24 h enrichment.

Differentiation of Lactobacillus isolates from infant faeces by SDS-PAGE and rRNA-targeted oligonucleotide probes

Isolates of lactobacilli from infant faeces phenotypically characterized as Lactobacillus paracasei subsp. paracasei (six strains), Lact. rhamnosus (six strains), Lact. gasseri (three strains), Lact. acidophilus (one strain) and Lact. fermentum/reuteri (three strains) according to recent classification systems were subjected to SDS-PAGE of whole cell proteins and rRNA-targeted oligonucleotide probe hybridization, in order to confirm the phenotypic characterization and elucidate the exact taxonomic position of the three strains that had properties between fermentum and reuteri. Results suggested a good agreement between the phenotypic characterization, SDS-PAGE and rRNA-targeted oligonucleotide probe hybridization for strains of all species except for the Lact. fermentum/reuteri strains. Results obtained by rRNA probes suggested a possible phylogenetic relatedness of the strains to Lact. reuteri. Isolates from infant faeces with interesting probiotic properties could be used as components of fermented milk products.

Evaluation of two automated enzyme-immunoassays for detection of thermophilic campylobacters in faecal samples from cattle and swine

We evaluated the performance of two enzyme-immunoassays (EIA) for the detection of naturally occurring, thermophilic Campylobacter spp. found in faecal samples from cattle (n = 21 and n = 26) and swine (n = 43) relative to the standard culture method, and also assuming that none of the tests was the definitive standard. The primary isolation both for the culture and the EIA methods was carried out by overnight selective enrichment in Preston broth. The results showed good sensitivities for both EIA methods in cattle (95% and 84%) and swine (88% and 69%) samples. However, when testing cattle samples, EIA-2 method resulted in a rather low specificity (32%). This seemed to be partially due to the isolation of nonthermophilic species. In conclusion, EIA-1 method may provide a simple and fast tool with good accuracy in cattle and swine samples for automated screening of large number of samples.

Comparison of different primers for rapid detection of Salmonella using the polymerase chain reaction

Salmonella is the leading cause of food-borne diarrhoeas in the US. In recent years polymerase chain reaction (PCR) has become the method of choice for rapid and sensitive detection of Salmonellae in contaminated foods. As a result, several different primer sets have been reported for use in PCR-based assay systems. In order to identify an optimal primer set from among the wide range of primers reported in the literature, we synthesized five different pairs and evaluated their relative performance in PCR under uniform assay conditions using a common panel of the target (Salmonella) and non-target (non- Salmonella) bacterial strains. Of the five sets of primers tested, the one designed on the basis of a 199 bp repeat sequence of S. weltevreden[Jitrapakdee et al. (1995) Molecular and Cellular Probes 9, 375-382] gave optimal results with most bacterial strains examined.

Sensitivity, specificity, and predictive values of three Salmonella rapid detection kits using fresh and frozen poultry environmental samples versus those of standard plating

To reduce human exposure to Salmonella spp. in poultry products, broiler chicken flocks have been tested by culture methods. Since the standard techniques may take 3 to 5 days, rapid detection methods have been developed. In this study we tested the performance of three rapid tests originally developed for food samples by using environmental samples obtained from poultry houses. These rapid tests were Reveal, an enzyme-linked immunosorbent assay from Neogen Corp.; BIND, a bacterial ice nucleation detection method from Idetek Corp.; and a filter monitor method from Future Medical Technologies, Inc. For the standard culture, brilliant green with novabiocin and xylose-lysine-tergitol-4 agar were used for presumptive identification, and identities were confirmed by using poly-O antisera. Environmental samples were collected from farms belonging to an integrated poultry company prior to chick placement and 1 week before slaughter. Sensitivities, specificities, and predictive values with 95% confidence intervals were calculated. Statistical differences were determined by using McNemar's chi square test. The sensitivities of the different tests were not stable, varying widely between sample times, and were affected by freezing of the samples. All of the rapid tests had low sensitivities, which led to many false-negative results. All tests were able to detect Salmonella spp. at a concentration of 10 CFU/ml in at least one of four trials. The BIND and Reveal tests were simple to use with multiple samples and reduced laboratory time by up to 1 day. Based on our results, we do not recommend that any of these rapid tests, in their present state of development, be utilized with environmental samples collected with drag swabs.

Genetics of lactobacilli in food fermentations

Lactobacilli play a substantial role in food biotechnology and influence our quality of life by their fermentative and probiotic properties. Despite their obvious importance in fermentation ecology and biotechnology only recent years have brought some insight into the genetics of lactobacilli. These genetic investigations allow the elucidation of traits determinative for competitiveness and ecology and thus product safety and quality. They have concentrated only on a small selection of lactobacilli whereas others are hardly touched or remained recalcitrant to genetic analysis and manipulation. The knowledge gained on the biochemistry, physiology, ecology and especially genetics is a prerequisite for the deliberate application and improved handling of lactobacilli in traditional and novel applications. In this review, the achievements in the genetics of lactobacilli are described including detection systems, genetic elements, host vector systems, gene cloning and expression and risk assessment of genetically engineered lactobacilli.

Direct detection of viable bacteria, molds, and yeasts by reverse transcriptase PCR in contaminated milk samples after heat treatment

A fast, sensitive, and target contaminant-modulable method was developed to detect viable bacteria, molds, and yeasts after heat treatment. By reverse transcriptase PCR with elongation factor gene (EF-Tu or EF-1 alpha)-specific primers, the detection level was 10 cells ml of milk-1. The simplicity and rapidity (4 h) of the procedure suggests that this method may be easily transposable to other foods and other contaminants.

Comparison of conventional culture methods and two commercial enzyme immunoassays for detection of Salmonella in porcine fecal samples and cecal contents

Two commercial enzyme immunoassays, designated EIA-1 and EIA-2, for the detection of salmonella in feces and cecal contents were compared to conventional culture methods. Out of 362 cecal content samples, 35 were positive by EIA-1 and 30 were positive by EIA-2 and conventional methods. Out of 189 fecal samples, 41 were positive by EIA-1, 30 were positive by EIA-2, and 24 were positive by conventional culture methods. The EIA-1 assay method detected more positive samples overall, although only comparison of the fecal samples was statistically significant. The results indicate that the EIA-1 method is rapid, requiring only 24 hours, and may be more sensitive than the EIA-2 assay and conventional culture techniques. Enzyme immunoassays for the detection of salmonella in fecal samples or cecal contents provide a reasonable alternative to conventional culture techniques.

Multiplex polymerase chain reaction for simultaneous detection of Lawsonia intracellularis, Serpulina hyodysenteriae, and salmonellae in porcine intestinal specimens

Proliferative enteritis, swine dysentery, and porcine salmonellosis are the most common enteric bacterial diseases affecting pigs in the growing and finishing stages of production. Currently, diagnoses of these diseases by standard cultural techniques of intestinal specimens can be laborious, time consuming, and expensive (swine dysentery, porcine salmonellosis) or impossible (proliferative enteritis). Amplification by polymerase chain reaction (PCR) of DNA sequences specific for each bacterial agent is a highly sensitive and specific method that overcomes the limitations associated with standard detection methods. A multiplex PCR (M-PCR) assay was developed for simultaneous detection and identification of the etiologic agents associated with proliferative enteritis, swine dysentery, and porcine salmonellosis in a single reaction using total DNA obtained directly from intestinal specimens. Purified DNA obtained from pure cultures of each bacterial agent alone or mixed in different combinations and concentrations and total DNA from intestinal specimens were amplified using the Lawsonia intracellularis-, Serpulina hyodysenteriae-, and salmonellae-specific M-PCR assay. Intestinal specimens consisted of feces and mucosal scrapings obtained from field cases of each disease alone or in combinations and feces obtained from pigs challenged with S. hyodysenteriae. The banding pattern of the amplified PCR products, after agarose gel electrophoresis and staining, indicated the presence of individual or combinations of etiologic agents in each specimen. Results from this study indicated that simultaneous amplification of L. intracellularis-, S. hyodysenteriae-, and salmonellae-specific DNA sequences by M-PCR can be used for specific detection and identification of three major enteric bacterial pathogens associated with proliferative enteritis, swine dysentery, and porcine salmonellosis occurring alone or in combinations. Also, the M-PCR assay can be done using DNA obtained directly from intestinal specimens submitted for diagnostic investigation.

Rapid detection of Salmonella enterica with primers specific for iroB

The iroB gene of Salmonella enterica is absent from the chromosome of the related organism Escherichia coli. We determined the distribution of this gene among 150 bacterial isolates, representing 51 serotypes of different Salmonella species and subspecies and 8 other bacterial species which are frequent contaminants during routine enrichment procedures by Southern hybridization. An iroB-specific DNA probe detected homologous sequences in all strains of S. enterica, including serotypes of S. enterica subsp. enterica (I), salamae (II), diarizonae (IIIb), and houtenae (IV). No hybridization signal was obtained with strains of Salmonella bongori or other bacterial species. In contrast, hybridization with a DNA probe specific for purD, a purine biosynthesis gene, detected homologs in all bacterial species tested. Primers specific for iroB were used to amplify this gene from 197 bacterial isolates by PCR. The iroB gene could be PCR amplified from S. enterica subsp. enterica (I), salamae (II), diarizonae (IIIb), houtenae (IV), arizonae (IIIa), and indica (VI), but not from S. bongori or other bacterial species. Thus, PCR amplification of iroB can be used to distinguish between S. enterica and other bacterial species, including S. bongori. A combination of preenrichment in buffered peptone water supplemented with ferrioxamine E and amplification of iroB by magnetic immuno-PCR allowed detection of S. enterica in albumen within 24 h. In conclusion, PCR amplification of iroB is a new sensitive and selective method which has the potential to rapidly detect S. enterica serotypes.

Screening of Salmonella in naturally contaminated feeds with rapid methods

Five commercially available screening methods, the Oxoid MSRV, Merck SALMOSYST-RAMBACH AGAR combination, Organon Teknika SALMONELLA-TEKTM, Dynal DYNABEADS ANTI-SALMONELLA and Foss Electric EIAFOSS, were compared to the conventional culture procedure for the detection of Salmonella in naturally contaminated feed samples. A total of 217 feed samples from animal as well as from vegetable origin were examined. Twenty one samples were found to be positive for Salmonella by all methods combined. The conventional culture method detected 17 (81,0%), MSRV 19 (90,5%), SALMOSYST-RAMBACH 8 (38,1%), SALMONELLA-TEK 19 (90,5%), DYNABEADS ANTI-SALMONELLA 7 (33,3%) and EIAFOSS 21 (100%) of the 21 total Salmonella contaminated samples.

Detection and serogroup differentiation of Salmonella spp. in food within 30 hours by enrichment-immunoassay with a T6 monoclonal antibody capture enzyme-linked immunosorbent assay

We previously described an antigen capture enzyme-linked immunosorbent assay which makes use of monoclonal antibody T6, which recognizes an epitope on the outer core polysaccharide of Salmonella lipopolysaccharide molecules that is common to almost all Salmonella serovars. In this paper, we show that this assay can detect between 10(5) and 10(7) Salmonella cells per ml even in the presence of excess Escherichia coli. A total of 153 of 154 (99%) serogroup A to E strains and 51 of 78 (71%) serogroup F to 67 strains were reactive as determined by this assay. This corresponds to a detection rate of approximately 98% of all salmonellae known to affect humans. None of the 65 strains of non-Salmonella bacteria tested positive. Taking advantage of the O-factor polysaccharides also present on the antigen captured by the immobilized T6 antibody, we showed that 136 of 154 Salmonella serogroup A to E strains (88%) were correctly differentiated according to their serogroups by use of enzyme conjugates of a panel of O-factor-specific monoclonal antibodies. We evaluated this assay for the detection and serogroup differentiation of salmonellae directly from enrichment cultures of simulated food, eggs, pork, and infant formula milk. All 26 samples which had been contaminated with Salmonella spp. were detected by T6 (100% sensitivity), with only one false-positive result from 101 samples not contaminated by Salmonella spp. (99% specificity). The detection time was substantially reduced to between 17 and 29 h, depending on the enrichment methods used. Since there were no false-negative results, we concluded that this enrichment-immunoassay method can afford rapid screening for Salmonella spp. in food samples.

Monoclonal antibodies directed against unique and common determinants on the lipopolysaccharide molecule of Salmonella serogroups A, B, and D

A panel of monoclonal antibodies (MAbs) directed against lipopolysaccharide (LPS) of Salmonella serogroups A, B, and D was generated. Nine most productive hybrid clones were selected from several fusions of mouse myeloma cells with splenocytes from BALB/c mice, immunized with the corresponding heat-killed bacteria. The MAbs were characterized by enzyme immunoassay, Western blot analysis, and dot-immunoblotting with LPS and whole bacteria of Salmonella serogroups A-E and some other representatives of the Enterobacteriaceae family. Seven MAbs were reactive with the sole Salmonella strain used as an immunogen; one MAb, SD:10D9H, reacted with the five major serogroups of Salmonella species (A, B, D, E1, and E2); and one MAb, SA:5D12A, reacted with Salmonella serogroups A-E and a rough strain of S. cholerae-suis. None of the MAbs reacted with LPS of E. coli 055:B5 or whole bacteria of E. coli K12, Klebsiella pneumoniae, or Proteus vulgaris. The typical ladder-like patterns of bands were observed after immunoblotting of MAbs against electrophoretically resolved LPS from Salmonella serogroups A-E, which thus confirmed their LPS-directed specificity. MAbs affinity constants were determined by noncompetitive enzyme immunoassay using serial dilutions of both LPS as antigen (coating the plate) and antibodies. On the base of the results obtained, the presumed epitopes for each of the MAbs were discussed. The usefulness of MAbs generated for diagnostic and protective purposes was declared.

Combined PCR-oligonucleotide ligation assay for rapid detection of Salmonella serovars

We have developed a rapid and sensitive assay for the detection of Salmonella serovars in veterinary clinical specimens. This method utilizes a short cultivation period followed by PCR. For detection of the amplified product, an enzyme-linked immunosorbent assay (ELISA)-based oligonucleotide ligation assay (OLA) was used. In this study, the PCR-OLA technique was compared with conventional culture and membrane hybridization for the detection of Salmonella bacteria. In evaluating the PCR-OLA with Salmonella serovars and non-Salmonella strains of bacteria, A490 readings for 51 Salmonella strains, representing 28 serovars, were significantly higher (P < 0.05) than those for 25 non-Salmonella bacteria. With serial 10-fold dilutions of Salmonella CFU or with known concentrations of purified chromosomal DNA from Salmonella typhimurium ATCC 29946, the PCR-OLA was able to detect > or = 20 CFU per assay or > or = 80 fg of chromosomal DNA (corresponding to 160 molecules of DNA). Of 102 suspect clinical specimens screened, 15 were positive for Salmonella bacteria by both culture and the PCR-OLA procedure (100% sensitivity), and 3 samples were positive only by PCR-OLA (96.6% specificity), indicating a positive predictive value of 83.3% and a negative predictive value of 100%. In all experiments, the PCR-OLA was as sensitive as membrane hybridization. These results indicate that a limited enrichment cultivation and PCR-OLA could be used as a presumptive screening test for the detection of Salmonella serovars from any sample that currently requires extensive cultivation and that this assay would be adaptable to automation.

A comparison of immunomagnetic separation plus enrichment with conventional Salmonella culture in the examination of raw sausages

Immunomagnetic separation with additional enrichment was used in conjunction with improved selective media to improve the isolation of salmonellae from raw sausages. The isolation rate achieved was almost double that of conventional culture with no increase in processing time. The selective media gave an overall specificity of approximately 74%; all false-positive pickoffs being identified as Citrobacter freundii. It is believed that this method represents a significant advance in the isolation of salmonellae from foods, although the ideal media both for enrichment and selection have yet to be found.

An evaluation of immunomagnetic separation for the detection of salmonellas in raw chicken carcasses

Immunomagnetic separation techniques were used in the isolation of salmonella from raw chicken carcasses. Improved isolation rates were achieved with increased specificity and decreased processing time, although several technical difficulties remain to be addressed. Immunomagnetic separation offers significant potential for improvement on existing microbiological systems for the isolation of salmonella.

Detection of Salmonella enteritidis in eggs and chicken with enzyme-linked immunosorbent assay

An ELISA previously developed for the rapid detection of Salmonella enteritidis (SE) in environmental samples was modified and applied to food samples. A sandwich ELISA was designed that employs affinity-purified rabbit polyclonal antibodies for the capture stage and highly specific monoclonal antibodies for the detection stage. Thirty-nine species of bacteria other than SE, including 32 Salmonella species, were included in cross-reactivity testing with ELISA. Results showed no reactivity with any species tested besides SE. Salmonella enteritidis was added to homogenized food samples (chicken skin, meat, and eggs) to test ELISA sensitivity. The lower limit for ELISA detection of SE was 10(4) cells/mL for pure cultures and in 10% meat (wt/vol), 10(5) cells/mL in 10% skin (wt/vol), and 10(7) cells/mL in 10% eggs (wt/vol). Salmonella enteritidis detection with ELISA was confirmed with the Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM) method. Results were obtained within 24 h for ELISA method compared to 96 h for the BAM procedure. Results show that sensitivity of ELISA can vary with the type of food tested for detection of SE.

The detection of Salmonella in skimmed milk powder enrichments using conventional methods and immunomagnetic separation

Skimmed milk powders were spiked with one of three Salmonella serovars and incubated in buffered peptone water for 24 h. No false-negative results were obtained by immunomagnetic separation (IMS), compared to seven for selenite cysteine, one for Müller-Kauffmann tetrathionate and two for Rappaport-Vassiliadis enrichment broths. Salmonella virchow was detected and enumerated during the pre-enrichment incubation by IMS and indirect conductance techniques. The Salm. virchow cell number did not increase after 12 h incubation and remained at 3 x 10(6) cfu ml-1. IMS was able to capture Salm. virchow cells at cell numbers ca 50 ml-1 in the presence of a 1000 greater number of non-salmonella cells.

Activity of p-aminobenzoic acid compared with other organic acids against selected bacteria

The antibacterial activity of p-aminobenzoic acid against Listeria monocytogenes, Salmonella enteritidis and Escherichia coli was compared with the activity of commonly used acidulants: formic, propionic, acetic, lactic and citric acids. Viable count evaluations and MIC determinations indicated that p-aminobenzoic acid caused greater inhibitory effects than the other organic acids. The activity of p-aminobenzoic acid on the growth of the test organisms at selected pH values indicated that p-aminobenzoic acid was more active at low pH than at high pH. Uptake studies showed that the uptake of p-aminobenzoic acid by E. coli was markedly decreased as the pH values increased. Electron micrographs of E. coli cells grown in the presence of p-aminobenzoic acid indicate that p-aminobenzoic acid caused marked damage to the cell envelope. It is suggested that p-aminobenzoic acid has at least two mechanisms of action: one mechanism in common with other organic acids and the other mechanism by interfering with the synthesis of the peptidoglycan layer by an action on the dihydrofolate reductase enzyme.

Immunochemical detection methods for Salmonella spp., Escherichia coli O157:H7, and Listeria monocytogenes in foods

Immunochemical assays should prove to be a significant improvement over standard culture methods for the detection of foodborne pathogens. These techniques take advantage of the specificity and sensitivity of the antibody/antigen reaction for analyte detection. ELISA is the most useful form of immunochemical method for the detection of foodborne pathogens in the food-processing setting, based on their simplicity and ability to analyze large numbers of samples at a time. Concerns with immunochemical techniques include problems with cross-reactivity and difficulties obtaining species specific assays. Also, most immunochemical methods continue to require an enrichment technique; however, subsequent identification is quite rapid when compared with standard culture methods, therefore allowing for the quicker release of negative products.