Occurrence of Coliform and Escherichia coli Contamination and Absence of Escherichia coli O157:H7 on Romaine Lettuce from Retail Stores in the Upper Midwest

A total of 720 whole, romaine lettuce heads were purchased from retail locations in the Upper Midwest and assessed for coliform and Escherichia coli contamination and for the presence of E. coli O157:H7. During a 16-month period (August 2010 through December 2011), coliform and E. coli counts were enumerated on Petrifilm, and the presence of E. coli O157:H7 and the virulence gene eae was evaluated by real-time PCR (qPCR). Over half (400 of 720) of the lettuce samples were processed with an immunomagnetic separation step before the qPCR assay. All retail lettuce samples were negative for E. coli O157:H7 when tested with the R.A.P.I.D. LT qPCR targeting a region of the O-antigen, and only two (0.28%) were positive for the eae gene when tested with LightCycler qPCR. On Petrifilm, coliform counts of most lettuce samples (96.4%) were between <10(1) and 10(3) CFU/g, and E. coli counts for nearly all lettuce samples (98.2%) were <10(1) CFU/g. No seasonal trend in coliform and E. coli counts was observed throughout the examination period nor was a difference in coliform counts observed between packaged and nonpackaged lettuce heads. These results contribute to the limited recorded data and understanding of microbial contamination of whole romaine lettuce heads purchased from retail locations, specifically revealing the absence of E. coli O157:H7 and low levels of contamination with coliforms and other E. coli strains.

Detection of Mycobacterium avium ss. Paratuberculosis in Blau Syndrome Tissues

Background and Aim of the Work. Blau syndrome is an inherited granulomatous inflammatory disorder with clinical findings of uveitis, arthritis, and dermatitis. Although rare, Blau syndrome shares features with the more common diseases sarcoidosis and Crohn's disease. The clinical findings of Blau syndrome are indistinguishable from juvenile sarcoidosis; the mutations of Blau syndrome are on the same gene of chromosome 16 (CARD15) that confers susceptibility to Crohn's disease. The product of this gene is part of the innate immune system. Mycobacterium avium ss. paratuberculosis (MAP) is the putative cause of Crohn's disease and has been implicated as a causative agent of sarcoidosis. Methods. Archival tissues of individuals with Blau syndrome were tested for the presence of MAP. Results. DNA evidence of MAP was detected in all of the tissues. Conclusions. This article finds that MAP is present in Blau syndrome tissue and postulates that it has a causal role. The presence of MAP in Blau syndrome—an autosomal dominant, systemic inflammatory disease—connects genetic and environmental aspects of “autoimmune” disease.

Absence of mycobacterium avium subsp. paratuberculosis in Crohn's patients

BACKGROUND

Mycobacterium avium subspecies paratuberculosis (MAP) has been suspected of involvement in Crohn's disease (CD). We investigated this potential association by testing whole blood from CD patients and healthy controls for the presence of MAP by culture and molecular methods. In addition, each blood sample was analyzed for polymorphisms in the NOD2/CARD15 gene previously associated with CD.

METHODS

Four 4-mL K(2)-EDTA tubes of whole blood were drawn from each subject (n = 260, 130 CD patients and 130 healthy controls). Two tubes of blood were cultured for MAP by the following methods: Mycobacterial Growth Indicator Tube, Herrold's Egg Yolk Agar, BACTEC 460, and Hungate. The remaining 2 tubes of blood were tested for MAP DNA and polymorphisms in the NOD2/CARD15 gene by polymerase chain reaction (PCR).

RESULTS

One healthy control patient was positive for MAP via PCR; however, no viable MAP was cultured from this individual. All blood cultures were negative for MAP. One CD patient's blood was culture-positive for M. tuberculosis complex. CD patients exhibited a higher rate of polymorphism in the NOD2/CARD15 gene than healthy control patients.

CONCLUSIONS

In this study MAP was not recovered from the blood of CD patients or healthy controls. However, CD patients showed higher mutation rates in the NOD2/CARD15 gene, compared with healthy controls, supporting the findings of other investigators. No correlation between these polymorphisms and MAP bacteremia in CD patients could be identified in this study.

Absence of mycobacterium avium subsp. paratuberculosis in Crohn's patients

BACKGROUND

Mycobacterium avium subspecies paratuberculosis (MAP) has been suspected of involvement in Crohn's disease (CD). We investigated this potential association by testing whole blood from CD patients and healthy controls for the presence of MAP by culture and molecular methods. In addition, each blood sample was analyzed for polymorphisms in the NOD2/CARD15 gene previously associated with CD.

METHODS

Four 4-mL K(2)-EDTA tubes of whole blood were drawn from each subject (n = 260, 130 CD patients and 130 healthy controls). Two tubes of blood were cultured for MAP by the following methods: Mycobacterial Growth Indicator Tube, Herrold's Egg Yolk Agar, BACTEC 460, and Hungate. The remaining 2 tubes of blood were tested for MAP DNA and polymorphisms in the NOD2/CARD15 gene by polymerase chain reaction (PCR).

RESULTS

One healthy control patient was positive for MAP via PCR; however, no viable MAP was cultured from this individual. All blood cultures were negative for MAP. One CD patient's blood was culture-positive for M. tuberculosis complex. CD patients exhibited a higher rate of polymorphism in the NOD2/CARD15 gene than healthy control patients.

CONCLUSIONS

In this study MAP was not recovered from the blood of CD patients or healthy controls. However, CD patients showed higher mutation rates in the NOD2/CARD15 gene, compared with healthy controls, supporting the findings of other investigators. No correlation between these polymorphisms and MAP bacteremia in CD patients could be identified in this study.

Detection of Mycobacterium avium subspecies paratuberculosis: comparing fecal culture versus serum enzyme-linked immunosorbent assay and direct fecal polymerase chain reaction

Mycobacterium avium ssp. paratuberculosis (MAP) is the etiologic agent of Johne's disease in cattle. The disease causes diarrhea, reduced milk production, poor reproductivity, emaciation, and eventually death. Culture on Herrold's egg yolk agar is considered to be the definitive test for diagnosis of Johne's in cattle. This method has moderate sensitivity (30 to 50%) and is 100% specific; however, it can take up to 16 wk due to the slow growth of MAP. Currently, serum ELISA is used to screen herds for Johne's disease, but positive tests must be confirmed culturally or by PCR. The current research sought to evaluate an in-house direct fecal PCR procedure and directly compare it to ELISA using culture as the gold standard. Serum and fecal samples were collected from cows (n = 250) with unknown Johne's status. Fecal samples were processed for culture on Herrold's egg yolk agar and direct PCR. Serum samples were tested using the Parachek serum ELISA. Overall, 67/250 [26.8%, 95% confidence interval (CI) 21.4 to 32.8] animals were culturally confirmed to be shedding MAP. The PCR and ELISA detected 74/250 (29.6%, 95% CI 24 to 35.7) and 25/250 (10%, 95% CI 6.6 to 14.4), respectively. Culture and PCR were able to detect more positive animals than ELISA. Overall, direct fecal PCR was 70.2% sensitive and 85.3% specific when using culture as the gold standard. The ELISA method was 31.3% sensitive and 97.8% specific. When culture reported <10 cfu, the sensitivity and specificity of PCR and ELISA were 57.1 and 85.3%, and 4.8 and 97.8%, respectively. When culture reported 10 to <40 cfu, the sensitivity of PCR and ELISA were 75 and 50%, respectively. When culture reported > or =40 cfu, the sensitivity of PCR and ELISA were 100 and 88.2%, respectively. Specificity could not be calculated at these levels because there were no negative samples. The direct PCR outperformed the ELISA in detecting animals potentially infected with MAP and was not significantly different when compared with culture. The direct fecal PCR method described here provides faster results than traditional culture and is more sensitive than ELISA at detecting animals suspected of Johne's disease. These data support the use of PCR as an alternative method for screening herds for prevalence and diagnosis of Johne's disease.

Mycobacterium avium subsp. paratuberculosis in scavenging mammals in Wisconsin

The presence of Mycobacterium avium subsp. paratuberculosis (MAP) in non-ruminant wildlife has raised questions regarding the role of these species in Johne's disease transmission. In this study we tested 472 tissues from 212 animals of six different species of scavenging mammals. All animals were taken from within a 210-square-mile area in Dane and Iowa counties of south central Wisconsin from September to May in 2003-04 and tested for the presence of MAP. We detected MAP-specific DNA in 81 of 212 (38%) scavenging mammals, in 98 of the 472 (21%) tissues; viable MAP was cultured from one coyote's ileum and lymph node tissue. Despite the low numbers of viable MAP isolated in this study, our data adds to the increasing evidence demonstrating the potential for transmission and infection of MAP in nonruminant species and provides possible evidence of interspecies transmission. The apparently high exposure of nonruminant wildlife provides potential evidence of a spill-over of MAP to wildlife species and raises the question of spillback to domestic and wild ruminants. These results demonstrate the importance of understanding the role of wildlife species in developing management strategies for Johne's disease in domestic livestock.

Detection of Mycobacterium avium subspecies paratuberculosis genetic components in retail cheese curds purchased in Wisconsin and Minnesota by PCR

Research has been focused on the detection of Mycobacterium avium subspecies paratuberculosis (MAP) in pasteurized milk; however, pasteurized milk is a key ingredient in a variety of food products. Therefore, MAP contamination in milk-derived products must be investigated. We undertook a six-month study to investigate the presence of viable MAP and MAP genetic components in cheese curds purchased from retail outlets in the northern and southern regions of Wisconsin and Minnesota. A total of 98 retail cheese curd samples were tested for MAP by PCR prescreen, culture on Herrold's egg yolk agar slants with mycobactin J and amphoteracin B, naladixic acid, and vancomycin, and slant rinse PCR using IS900 and hspX primer sets. Although no viable MAP were able to be cultured, 5% of the samples were PCR positive with both the IS900 and hspX primer sets (MAP-specific DNA) when prescreened and 1% of the samples were PCR positive with both the IS900 and hspX primer sets when culture slants were rinsed and tested.

Design and development of an internal control plasmid for the detection of Mycobacterium avium subsp. paratuberculosis using real-time PCR

Mycobacterium avium subspecies paratuberculosis (MAP) is the etiological agent of Johne's disease in ruminants. The hspX gene and insertion sequence IS900 can be used to diagnose Johne's with PCR. Generally, a single PCR tube containing the DNA sequence of interest is run as a positive control with each set of reactions. Single reactions within a PCR run can fail while the positive control does not. Thus, a single positive control tube does not determine if all PCR reactions worked properly. Our objective was to construct a plasmid to use as an internal control in each reaction. A plasmid containing an insert of M. bovis-hspX-M. bovis DNA was modified to remove a portion of the hspX insert used by the reverse hspX primer. The remaining insert was ligated back together and transformed into competent cells. Sequencing confirmed removal of 71 bp. PCR reactions using three primers (TB/M. bovis reverse, hspX forward and reverse) for hspX gene detection and four primers (IS900 forward and reverse, hspX forward, and TB/M. bovis reverse) for IS900 detection were optimized by titrating various amounts of plasmid against varied amounts of MAP genomic DNA. Plasmid insert amplification confirms a successful PCR reaction and identifies true positives and negatives within each individual reaction. The optimal plasmid amounts are 10 fg/reaction (hspX detection) and 1 fg/reaction (IS900 detection).

Survival of Listeria monocytogenes and Escherichia coli O157:H7 during sauerkraut fermentation

Sauerkraut was produced from shredded cabbage, as is typical in the United States, and from whole head cabbages, which is a traditional process in parts of Eastern Europe. The sauerkraut was inoculated with five strain mixtures of Escherichia coli O157:H7 and Listeria monocytogenes, and the populations of these bacteria, as well as lactic acid bacteria, pH, and titratable acidity, were monitored over the course of fermentation. Fermentation variables were temperature (18 and 22 degrees C) and salt concentration (1.8, 2.25, and 3%). For most of the analyses, the type of cabbage processing was a significant factor, although within cabbage type, neither salt nor fermentation temperature had significant effects. The final pH of the whole-head sauerkraut was lower than the shredded sauerkraut, but the titratable acidity was significantly higher in the shredded sauerkraut. E. coli O157:H7 and L. monocytogenes persisted in the brines for most of the fermentation, although at the end of the fermentations (15 days for shredded, 28 days for whole head), neither pathogen had detectable populations. E. coli populations decreased more rapidly in the shredded sauerkraut even though the pH was higher because of the higher total acidity in the shredded sauerkraut. Acid-tolerant strains of E. coli and L. monocytogenes were isolated from both shredded and whole-head sauerkraut at different salt concentrations and temperatures after 15 days of fermentation and could be detected at 35 days in the wholehead sauerkraut.

Rapid PCR detection of enterohemorrhagic Escherichia coli (EHEC) in bovine food products and feces

Although Escherichia coli (E. coli) O157:H7 is a major cause of foodborne illness, other types of E. coli can also cause illness. E. coli that possess the eae gene for attachment and effacing have the potential to cause disease. Many real-time, molecular-based assays have been developed to detect Enterohemorrhagic E. coli (EHEC) including E. coli O157:H7. However, no assay currently exists to detect the eae gene present in E. coli O157:H7 and other EHEC strains with a confirmed positive or negative result in less than 12 h. Raw beef food products (raw ground beef and raw boneless beef) at 25 and 375 g samples and bovine fecal samples at 2 g were inoculated with 10(1), 10(3), 10(4), and 10(5) organisms of E. coli O157:H7 to test the sensitivity of this assay. Fourteen different foodborne bacteria (including E. coli O157:H7) and 19 various E. coli strains, obtained from the United States Department of Agriculture-Agricultural Research Service (USDA-ARS) were tested for specificity. E. coli O157:H7 was detected at the level of 10(1) organisms in both 25 and 375 g samples of raw ground and raw boneless beef products as well as 2 g samples of bovine feces after pre-enrichment and concentration. None of the 14 foodborne bacteria screened for cross-reactivity was detected. All USDA E. coli strains confirmed to contain the eae gene were detected.

Detection of Mycobacterium avium subspecies paratuberculosis in free-ranging bison (Bison bison) by PCR

Bacterial culture is the 'gold standard' for detecting Mycobacterium avium subspecies paratuberculosis (MAP) infection, but is time consuming, laborious, and recovery of organism varies with species of animal tested. PCR has been used for detection of MAP DNA in feces and tissues. We used PCR to detect MAP DNA isolated from tissues from 25 free-ranging North American bison (Bison bison), each with clinical signs compatible with Johne's disease. We report the performance of PCR to detect MAP DNA in both frozen and paraffin-embedded ileum, jejunum, and ileocecal lymph node samples collected at the time of slaughter. Specific oligonucleotide primers for PCR amplification were derived from 16S rRNA sequence M. avium subspecies (MAs) and insertion elements IS1245 (MAs avium), IS901 (MAs avium), IS900 (MAP), and hspX (MAP). Genomic DNA samples were prepared three different ways; crude DNA from frozen tissues, crude DNA from paraffin-embedded tissues, and purified DNA from paraffin-embedded tissues. An animal was considered infected if MAP DNA was detected in at least two separate tissues using the IS900 primer set. Using these criteria, 25 of 25 bison tested were positive for MAP. The data indicate that these free-ranging bison have been infected by MAP.

Detection of viable Mycobacterium avium subsp. paratuberculosis in retail pasteurized whole milk by two culture methods and PCR

Cattle with Johne's disease can shed live Mycobacterium avium subsp. paratuberculosis (MAP) in their milk, and MAP can survive under simulated commercial pasteurization conditions. In several studies conducted in the United Kingdom and Canada, MAP DNA has been detected in retail pasteurized milk samples; however, in one study in the United Kingdom viable MAP was identified in commercially pasteurized milk. A double-blind study involving two laboratories was undertaken to evaluate retail pasteurized whole milk in the United States. Marshfield Clinic Laboratories used solid culture medium (Herrold's egg yolk agar slants with mycobactin J and amphotericin B, nalidixic acid, and vancomycin), and TREK Diagnostic Systems, Research and Development used liquid culture medium (ESP culture system). Cultures at both laboratories were confirmed by PCR. A total of 702 pints of retail whole milk were purchased in three of the top five milk-producing states (233 from California, 234 from Minnesota, and 235 from Wisconsin) over a 12-month period and were tested for the presence of viable MAP. The criteria used for identifying samples as positive for viable MAP were similar to those followed by most laboratories (positive culture with PCR confirmation). The combined data from the two laboratories revealed the presence of viable MAP in 2.8% of the retail whole milk pints tested. Although the number of samples containing viable MAP was similar among states (P > 0.05), there was a seasonal effect on the presence of viable MAP in retail milk (P = 0.05). More MAP-positive samples were identified during the third quarter of the year (July through September). Of the 22 brands of retail milk tested, 12 (55%) yielded at least one sample positive for viable MAP.

Twelve hour real-time PCR technique for the sensitive and specific detection of Salmonella in raw and ready-to-eat meat products

Rapid pathogen testing is vital to the food industry. Enzyme immunoassays (EIA) provide reliable negative results in 48 h, but a presumptive positive (suspect) EIA result must be confirmed by traditional culture methods, requiring an additional 72 h. Polymerase chain reaction (PCR) testing technology is accepted as an accurate diagnostic tool. However, traditional PCR techniques can require several days. We sought to develop a rapid, real-time quantitative PCR technique for detecting Salmonella spp. in food products. Salmonella spp. was inoculated into raw and ready-to-eat beef products. Total DNA was extracted and used as template for PCR amplification in the LightCycler (Roche Diagnostics Corp., Idaho Technology Inc., Idaho Falls, ID) PCR instrument. Salmonella-specific PCR primers were designed to amplify a 251 base pair product from the junction of SipB and SipC. Fluorescently-labeled hybridization probes were designed to anneal to SipB and SipC. Salmonella was detected down to 1 colony forming unit/ml in food products. The results of real-time PCR correlated 100% to those of visual immunoprecipitate and culture. PCR methods using the LightCycler can detect and confirm the presence or absence of Salmonella spp. in raw and ready-to-eat beef products within 12 h with increased sensitivity compared to traditional culture and EIA methods.

Comparison of PCR prescreening to two cultivation procedures with PCR confirmation for detection of Mycobacterium avium subsp. paratuberculosis in U.S. Department of Agriculture fecal check test samples

Mycobacterium avium subsp. paratuberculosis (MAP) is the etiologic agent in Johne's disease in cattle and causes diarrhea, decreased milk production, emaciation, and frequently death. The ability to detect MAP rapidly and accurately is an integral part of herd management. However, detection of this bacterium is complicated due to its slow division time and its ability to enter dormancy. Culture methods are considered the "gold standard," but they have their limitations. Many enzyme-linked immunosorbent assay methods and conventional PCR methods have been used as diagnostic tools. The present study compares the results of a PCR prescreen to two culture methods of detection paired with confirmatory PCR to determine the most accurate, rapid, and sensitive method using U.S. Department of Agriculture (USDA) fecal check samples. This study involving two laboratories (Marshfield Clinic Laboratories, using solid culture medium [Herrold's egg yolk agar], and TREK Diagnostic Systems Research and Development, using liquid culture medium [ESP Culture System II]) showed that the PCR prescreening method used in this study lacked specificity and sensitivity as a stand-alone test in fecal samples. However, the combination of liquid enrichment culture using the ESP II system, and PCR confirmation with the hspX primer set, was not only 100% sensitive and specific but also correlated with viable MAP and USDA culture results.

Growth, Congo Red agar colony morphotypes and antibiotic susceptibility testing of Mycobacterium avium subspecies paratuberculosis

OBJECTIVE

Mycobacterium avium subspecies (subsp.) paratuberculosis (MAP) is the causative agent of Johne's disease in ruminants and has been associated with Crohn's disease in humans. We sought to test growth rates and susceptibilities of various strains of MAP in two available growth media.

DESIGN

Paired comparison design.

METHODS

Using the BACTEC macrobroth radiometric growth system and Congo Red-staining agar media, we determined inherent differences in growth characteristics of three bovine and two human strains of MAP and compared susceptibility results obtained in each growth system.

RESULTS

Significant differences were observed in growth rate as well as mycobactin J dependence between strains and between a laboratory-adapted isolate of the same strain in the macrobroth system. Similarly, colonial morphology and Congo Red staining on agar media were observed. Two strains, one human and one bovine, demonstrated a 100% rough transparent colony with white coloration on Congo Red agar, while one bovine isolate exclusively grew as a smooth opaque colony with red coloration on Congo Red agar. The remaining strains exhibited mixtures of these two colonial morphotypes on agar media. Comparative susceptibility results between the BACTEC radiometric macrobroth method and the agar proportionality method showed good correlation for most antibiotics/inhibitors tested. However, erratic or poor growth in the macrobroth system prevented minimal inhibitory concentration determinations for two bovine strains by this method.

CONCLUSION

This study demonstrates the variability in the colonial morphology of MAP on Congo Red agar as well as the correlation of antibiotic susceptibility results between the BACTEC macro broth method and the agar proportionality method. This study also emphasizes the need for the development of improved, standardized culture and susceptibility test methods for MAP.

Absence of Mycobacterium avium subspecies paratuberculosis components from Crohn's disease intestinal biopsy tissues

BACKGROUND

Crohn's disease is a chronic human intestinal inflammatory disorder for which an etiologic agent has not been identified. Johne's disease is a similar chronic enteric granulomatous disease of ruminant species and has been used as a model of Crohn's disease. Johne's disease has been proven to be caused by Mycobacterium avium subspecies paratuberculosis (M. avium ss paratuberculosis). It has been proposed that M. avium ss paratuberculosis may also cause Crohn's disease. This is of particular concern because the organism may be spread to humans through inadequately pasteurized dairy products.

OBJECTIVE

We sought to determine whether M. avium ss paratuberculosis could be detected using identical techniques in paraffin-embedded tissue samples of bovine Johne's disease and human Crohn's, ulcerative colitis and diverticular diseases. Samples were obtained for analysis from national tissue banks.

DESIGN

Cross-species and cross-disease sample comparisons by multiple detection techniques.

METHODS

Histology, immunocytochemistry and polymerase chain reaction (PCR) were utilized to test and compare the presence of M. avium ss paratuberculosis components. Insertion sequence IS900, present in multiple copies and found only in M. avium ss paratuberculosis, was utilized in both PCR and immunocytochemical analyses.

RESULTS

The IS900 sequence was demonstrable in all samples of confirmed positive Johne's disease tissue. The sequence was not identified in the 35 Crohn's, 36 ulcerative colitis, and 21 diverticular disease samples.

CONCLUSION

M. avium ss paratuberculosis was not associated with the lesions in these Crohn's disease samples, using these methods.

Transmission of Salmonella enterica serotype typhimurium DT104 to infants through mother's breast milk

This study documents the first reported transmission of Salmonella enterica serotype Typhimurium definitive type 104 (DT104) to premature fraternal twins via their mother's breast milk. When premature twin neonates developed severe enteritis in the neonatal intensive care unit (NICU), stool samples and the mother's breast milk were cultured for the presence of Salmonella. Antibacterial susceptibility patterns were determined. Semiquantitative organism abundance data were retrospectively gathered on 54 stored breast milk samples collected on 34 different days using a rapid, real-time polymerase chain reaction (PCR) methodology (LightCycler PCR). Fecal samples from other infants in the NICU at that time were also tested. Pulsed-field gel electrophoresis (PFGE) was used to assess the genetic composition of the isolated organisms. The twins' neonatal stools and mother's breast milk cultures revealed a resistance pattern (R-type) to ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline. LightCycler PCR analysis of sequential breast milk samples confirmed this to be the likely source of transmission. In the subsequent outbreak investigation, none of the NICU surveillance fecal samples proved positive for this organism. The genetic composition of organisms isolated from the maternal breast milk was indistinguishable from those isolated from neonatal specimens as determined by PFGE. Antibiotic susceptibility tests coupled with PFGE patterns suggested that these Salmonella isolates were DT104. Because the prevalence of DT104 infections is rising in the United States, neonatologists should be aware of breast milk as a potential mode of transmission.