A RAPID IMMUNOFLUORESCENCE TECHNIQUE FOR DETECTING SALMONELLAE IN RAW MEAT

Immunofluorescence technique for the detection of salmonellae in various foods

Salmonella species have been detected in nine food varieties by use of fluorescent antibodies without false-positive or false-negative results. Test antisera were specially prepared, commercially available, conjugated polyvalent O globulin absorbed with cultures of Escherichia coli and Citrobacter freundii, and polyvalent phase II H globulin antibodies. Use of this technique permits a decrease of 24 hr in time normally required for Salmonella detection when compared with cultural Salmonella recovery methods.

Rapid detection of salmonellas in raw meats using a fluorescent antibody-microcolony technique

A fluorescent antibody-microcolony technique was developed for the rapid detection of salmonellas in pure cultures. Examination of microcolonies made the detection of salmonellas by epifluorescence microscopy easier and more reliable than using fluorescent antibody and single cells. After a study of the most effective selective enrichment media for increasing the number of salmonellas, the technique was examined with various samples of raw meats. It was able to detect salmonellas in 24 h and appeared to be as sensitive as conventional cultural techniques. Of the 101 samples studied, complete agreement was obtained with conventional methods for 94 but six apparently false positive results and one false negative result occurred.

Comparative study on Salmonella isolation from sewage-contaminated natural waters

A comparative study of five factors influencing the isolation of salmonellas from sewage-contaminated natural waters was carried out. The effect of pre-enrichment in buffered peptone water was compared with single-step enrichment in NR10 broth incubated at 43 degrees C. A modification of NR10 has been compared with the original composition. Bismuth sulphite agar (BSA), Hektoen enteric agar (HE) and brilliant green agar (BGA) have been used as plating media. Other factors considered have been temperature of the water and sampling site. A total of 759 salmonella strains belonging to 36 different serotypes has been recovered in a two-year study. All five factors considered in the study have shown a significant effect on the recovery of salmonellas. The combination of direct enrichment in NR10, followed by BSA or HE as plating media was most effective for the isolation of Salmonella. The influence of water temperature and characteristics of the sampling sites have also been discussed.

Evaluation of an automated fluorescent antibody procedure for detection of Salmonella in foods and feeds

A prototype automated system using fluorescent antibody (FA) was evaluated for rapid detection of salmonellae in foods. Samples were enriched in selenite cystine and tetrathionate broths. After incubation, both were transferred into fresh selenite cystine for a 4-h "post-enrichment" to dilute possible background fluorescence from product. These cultures were then analyzed automatically, and results were compared with those obtained by the methods of the Association of Official Analytical Chemists (AOAC). Initially, 167 samples of milk powder, dried yeast, and imported frog legs were examined. The AOAC and automated FA methods correlated well with all samples but frog legs. Difficulty with the latter was caused by procedural and mechanical problems coupled with high numbers of competing microorganisms in post-enrichment cultures. Modification of procedure and partial redesign of equipment corrected these difficulties, and excellent correlation was obtained with another 116 frog leg samples. All 89 AOAC-confirmed positives were also detected by the automated FA method, and there were only 4% false FA positives. The system shows potential for screening products for salmonellae; however, all positives should be confirmed by manual biochemical and serological methods.

Evaluation of a fluorescent antibody-enrichment serology combination procedure for the detection of salmonellae in condiments, food products, food by-products, and animal feeds

The reliability of the enrichment serology (ES), fluorescent antibody (FA), and a combination of the FA and ES procedures for the detection of salmonellae were compared to the Salmonella cultural procedure outlined in the U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM). A total of 126 subsamples from 22 different products were analyzed. By utilizing the BAM procedure as the reference standard, a total of 66 samples were positive for salmonellae. Within 44 h approximately 65% of the Salmonella-negative samples could be cleared by the FA test. At the end of 50 h 97% of the Salmonella-negative samples could be cleared by the combination FA-ES test. The FA procedure detected all 66 BAM positives but exhibited a high incidence of presumptive positives which were cultural negatives. The ES procedure detected 64 of the 66 BAM positives but exhibited a low incidence of presumptive positives which were cultural negatives. Incorporating positive FA and positive ES results in a combination FA-ES technique revealed that FA-ES positives were statistically equivalent to BAM positives.

Direct fluorescent-antibody technique for the microbiological examination of food and environmental swab samples for salmonellae

Comparative studies of a modified fluorescent-antibody procedure and the 5 to 7 day method used by the Association of Official Analytical Chemists for the detection of Salmonella were made on 151 samples of wheat products and 183 swab samples. The agreement between the two methods for the 334 samples tested was 92.5%. Food samples yielded 94.7% agreement, whereas the swab samples yielded 90.7% agreement. There were 7.5% false positives for the total number of samples tested. No false negatives were obtained by using the fluorescent-antibody method.

Evaluation of the salmonellae fluoro-kit for fluorescent-antibody staining

An evaluation of the newly developed Clinical Sciences, Inc. Salmonellae Fluoro-Kit, which attempts to standardize the various aspects of the fluorescent-antibody (FA) procedure, was performed with 120 naturally contaminated human food, animal feed, and raw material samples. The Association of Official Analytical Chemists (AOAC) method for the detection of salmonellae was used as the control method. The Fluoro-Kit was found to be simple and conveniento to use. The results of this preliminary study show an industrially acceptable rate of recovery of salmonellae by using the Fluoro-Kit in comparison with the A.O.A.C. method. The Fluoro-Kit shows promise as a rapid, salmonellae FA screening method. Problems originally encountered in the application of the Fluoro-Kit are discussed. According to the manufacturer, strict adherence to the now revised procedures included in the Fluoro-Kit will control these problems.

Microfermentation series for identification of single colonies of Enterobacteriaceae

Microfermentation tests for members of the family Enterobacteriaceae were devised by using agar solutions in disposable, multi-welled, plastic trays. The tests could be made directly from isolated colonies picked from agar plates and represented a considerable saving in time, labor, and materials over the conventional methods. Tests were formulated for determining carbohydrate fermentations, citrate utilization, motility, amino acid decarboxylation, and production of H(2)S, indole, urease, and acetyl-methyl-carbinol.

Twenty-four-hour immunofluorescence technique for the detection of salmonellae in nonfat dry milk

A detection procedure was developed in which a newly devised lysine-iron medium was used as a one-step selective and enrichment medium for detection of salmonellae by the fluorescent-antibody technique. Incubation was conducted in two steps: initially at 30 C for 5 hr to resuscitate sublethally stressed cells, followed by incubation at 39 C for 17 hr. Twenty-seven strains of salmonellae from groups A-I were utilized in the development of this procedure which was sensitive enough to detect one Salmonella bacterium in 100 g of nonfat dry milk.

Rapid detection of Salmonella microcolonies by fluorescent antibody

A microcolony fluorescent-antibody (FA) procedure for detecting salmonellae was compared to the usual direct FA procedure on 304 environmental, food, and feed samples. The microcolony FA test detected all of the specimens found positive by culture, whereas the direct FA missed 3.1% of them. Both FA tests revealed stained organisms in some of the culturally negative specimens. The microcolony FA test has several advantages over the direct FA test: ease of examining the smears, elimination of the fluorescent background material, and increased sensitivity.

Salmonella isolations in abattoirs in Greece

The prevalence of salmonellas in drain swabs from three abattoirs of Athens was studied with the use of conventional methods of Salmonella isolation as well as with a new procedure which involves secondary enrichment from the usual selenite broth or Muller-Kauffmann's tetrathionate broth in Rappaport's medium slightly modified.In all groups studied the secondary enrichment in Rappaport's medium led to an increase in the number of positive swabs, in the number of Salmonella serotypes, and in the total number of strains isolated.The frequency of Salmonella isolations was higher in samples from abattoirs killing only pigs and lower in samples from abattoirs killing only cattle or only sheep.The predominant serotype in abattoirs dealing with cattle was Salmonella tennessee, and S. typhimurium in abattoirs dealing with sheep. No predominant serotype was found in samples from abattoirs dealing mostly with pigs.S. abony, S. drypool, S. emek, S. indiana, S. muenchen and S. tennessee were isolated for the first time in Greece.

One-day fluorescent-antibody procedure for detecting salmonellae in frozen and dried foods

The indirect fluorescent-antibody technique was used to examine 422 food samples for the presence of salmonellae. A cultural phase involving a 16-hr preenrichment in buffered nutrient broth-milk medium followed by a 4- to 5-hr subculture into fresh medium of the same composition was evaluated. This procedure yielded a sufficient population of salmonellae so that no false-negative results were obtained. Of the 31 false-positives obtained, 12 samples yielded positive cultural results upon extensive subculture of the original enrichment broths. Yeast cells and both vegetative and spore forms of bacilli were observed to fluoresce when stained with anti-Salmonella serum. Efforts to ascertain the cause of these cross-reactions and several alternate explanations are discussed.

Accelerated immunofluorescence procedure for the detection of Salmonella in foods and animal by-products

An accelerated, direct immunofluorescent-antibody procedure was developed for the detection of Salmonella in food products. This method includes pre-enrichment and selective enrichment but eliminates many of the washing and smear treatments present in existing methods. Commercially available fluorescein-conjugated somatic antiserum was used in comparing this method with conventional culture, biochemical, and serological procedures. The 894 samples tested represented 39 different products. The fluorescent-antibody procedure detected Salmonella in 216 test samples as compared to 205 positives recovered by using the standard culture procedures. In no instance did the fluorescent-antibody procedure fail to detect a Salmonella positive which had been detected by the standard procedure. With a three-tube, most-probable-number procedure, the fluorescent-antibody method was able to detect Salmonella at a level of 0.036 organism per g. In addition to being a more rapid method for the detection of Salmonella, it has proven to be comparable to conventional culture procedures.

Immunofluorescent staining of Salmonella species with flagellar sera

Salmonellae stained with flagellar sera by either the direct or indirect fluorescent-antibody technique fluoresced at the cell surface. Investigations showed that fimbriae, flagellar material, and capsule antigens were not the participating antigens in this reaction. Cell surface staining was inhibited by mannose but was unaffected by glucose, galactose, lactose, maltose, and sucrose. Specific absorption of the flagellar sera by intact cells and purified somatic antigen showed that O antigens were the site of the surface staining. The advantages of using flagellar sera in fluorescent-antibody screening of materials for the presence of salmonellae are discussed.

Increased sensitivity of immunofluorescent assay for Salmonella in nonfat dry milk

The necessity of developing a quick, sensitive, and reliable test for Salmonella in nonfat dry milk (NDM) is evident from the recent tracing of Salmonella outbreaks to this product. Normally, coagulation of casein occurs when assaying NDM under regular cultural conditions, raising the possibility of trapped bacteria. After 20 hr of incubation of NDM in preenrichment lactose broth, enrichment was achieved by using Selenite-Cystine Broth. Smears from the enrichment broth were examined by the fluorescent-antibody technique (FAT) with a commercially available polyvalent O globulin conjugated with fluorescein. Standard cultural methods (SCM) were performed for comparison with FAT. Sensitivity of FAT was definitely improved by the use of trypsin. Casein coagulation of NDM can be avoided by addition of trypsin to samples during initial preenrichment in lactose broth. Samples containing approximately one Salmonella per 10 g were easily detected by FAT with the use of trypsin-treated samples. The method required only 42 hr to complete. Additionally, the use of trypsin enhanced recovery of Salmonella by use of SCM, as evidenced by alteration in the observed coliform to Salmonella ratios.

Fluorescent-antibody technique in detection of salmonellae in animal feed and feed ingredients

Comparative studies of fluorescent antibody procedure and a cultural method for the detection of Salmonella were made on 1,013 feed and feed-ingredient samples. The agreement between the two methods was 92.1%. There were more false positives (5.7%) than false negatives (2.2%). Of the 22 false negatives, 15 (68%) were obtained on meat meal. Of the total number of samples, 37% were meat meal. An additional study of 73 samples of meat meal indicated that correlation between methods was better than correlation between samples.

Detection of Salmonella by a single-culture technique

Dulcitol-selenite enrichment medium in a motility flask was used for the detection of Salmonella in food. A drop in pH of the dulcitol-selenite enrichment motility broth indicated the presence of Salmonella; this phenomenon was confirmed by fluorescent-antibody staining. A complete correlation was found between fluorescent-antibody staining and recovery on Brilliant Green agar. Testing of 332 samples of 8 different kinds of foods and feeds indicated no significant difference in sensitivity between the new technique and a conventional Salmonella detection technique. The new technique permitted detection of even small numbers of Salmonella in 1 to 2 days.

Elevated temperature incubation of enrichment media for the isolation of salmonellas from heavily contaminated materials

In three separate series, samples were examined for salmonellas by culture in selenite F broths incubated at 37 and 43° C. The samples used were:

(1) Gauze swabs placed in sewage.

(2) Gauze swabs placed in drains in abattoirs.

(3) Sewage-polluted river water.

In each series the higher temperature gave better results.

The modification of tetrathionate broth for incubation at 43° C. and the adjustment of the incubation temperature to suit more inhibitory enrichment broths is discussed. The medium of Rappaport, Konforti & Navon (1956) is not suited to incubation at 43° C.

We should like to acknowledge the help of Prof. Scott Thomson in the preparation of this paper, and the capable technical assistance of Mr T. R. Liddington and Mr John Morgan. We are also indebted to Dr H. Campbell, Senior Lecturer in Medical Statistics in the Welsh National School of Medicine, for his advice and to Mr M. C. Finniear, Deputy Public Analyst of the Glamorgan County Public Health Laboratory, for the calculation of molar tetrathionate in Rolfe's tetrathionate broth.

Somatic and flagellar immunofluorescence of Salmonella

Caldwell, W. J. (The Child Research Center of Michigan, Detroit, Mich.), C. S. Stulberg, and W. D. Peterson, Jr. Somatic and flagellar immunofluorescence of Salmonella. J. Bacteriol. 92:1177-1187. 1966.-Labeled globulin fractions of flagellar (H) antisera, prepared against 20 frequently occurring Salmonella serotypes belonging to five major somatic (O) groups, were characterized for O and H immunofluorescence and for O and H agglutinin titers against 32 serotypes. The feasibility of immunofluorescent identification of both somatic and flagellar antigens was enhanced by staining formaldehyde-treated organisms in suspension. Relationships between homologous, partial, and unrelated antigen-antibody systems were then analyzed, and a high degree of correlation was shown between the results obtained by the two serological procedures. Flagellar staining was highly specific, and was bright, faint, or inapparent, depending on the relationship between the antigen-antibody systems involved. Somatic staining was also specific, but somewhat more difficult to interpret, because cells in the same preparation might exhibit a mixture of bright, faint, or no fluorescent intensities. Correlation was shown between the percentage of brightly staining cells found in these preparations and the agglutination titers of the comparable antigen-antibody systems. The phenomenon of a "percentage" reaction was unexplained. Absorption studies further confirmed the specificity of reactions. The techniques developed were applied to surveillance of several mouse colonies for the presence of Salmonella. Broth cultures of fecal specimens were treated with formaldehyde and stained in suspension with "polyvalent" labeled antibody reagents. Agreement was found in 97.6% of the instances between results obtained by immunofluorescence and cultural methods. In addition, preliminary evidence indicated the feasibility of presumptive serotyping of Salmonella isolates by immunofluorescence.