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The objective of this research was to assess the microbiological status of leafy greens, sprouts, and melons from U.S. markets. A total of 14,183 samples of leafy greens, 2,652 samples of sprouts, and 3,411 samples of melons were collected throughout the United States from 2009 to 2014. The samples were analyzed for aerobic plate counts, total coliform counts, Escherichia coli counts, and the presence and levels of Salmonella, Shigella, Listeria monocytogenes, and Shiga toxin--producing E. coli (STEC), depending on the year and type of produce. Among the leafy greens, no E. coli O157:H7 or non-O157 STEC were detected from iceberg lettuce samples. The overall prevalences of Salmonella, E. coli O157:H7, non-O157 STEC, and L. monocytogenes in the 14,183 samples of leafy greens were 0.05, 0.01, 0.07, and 0.11%, respectively. Among sprout samples, no Salmonella or E. coli O157:H7 was detected, and the overall prevalences of non-O157 STEC and L. monocytogenes were 0.04 and 0.11%, respectively. Among melon samples, no Salmonella was detected from cucumbers, no L. monocytogenes was detected from cantaloupes, and the overall prevalences of Salmonella and L. monocytogenes were 0.12 and 0.23%, respectively. L. monocytogenes levels were 0.4 to 1,470 most probable number (MPN)/g in leafy greens, 0.36 to 1,100 MPN/g in sprouts, and <0.03 to 150 MPN/g in melons, and most positive samples had low levels of these pathogens. The isolates from these foods were very diverse genetically. Foodborne pathogens, including Salmonella, STEC, and L. monocytogenes, had relatively low prevalences in the produce surveyed. Because these foods are usually consumed raw, measures should be taken to significantly minimize the presence and levels of human pathogens. [ABSTRACT FROM AUTHOR]

Mango has been implicated as food vehicle in several Salmonella-causing foodborne outbreaks. Here, Salmonella enterica subsp. enterica serovarMinnesotawas isolated fromfresh mango fruit imported fromMexico in 2014. The complete genome sequence of S. Minnesota CFSAN017963 was sequenced using single-molecule real-time DNA sequencing. Distinct prophage regions, Salmonella pathogenicity islands, and fimbrial gene clusters were observed in comparative genomic analysis on S. Minnesota CFSAN017963with other phylogenetically closely related Salmonella serovars. Core genomemultilocus sequencing typing analysis of all the S.Minnesota isolates in theGenbank and Enterobase also revealed a high genomic diversity among the genomes analyzed. [ABSTRACT FROM AUTHOR]

Nuts have been identified as a vector for salmonellosis. The objective of this project was to estimate the prevalence and contamination level of Salmonella in raw tree nuts (cashews, pecans, hazelnuts, macadamia nuts, pine nuts, and walnuts) at retail markets in the United States. A total of 3,656 samples of six types of tree nuts were collected from different types of retail stores and markets nationwide between October 2014 and October 2015. These samples were analyzed using a modified version of the Salmonella culture method from the U.S. Food and Drug Administration's Bacteriological Analytical Manual. Of the 3,656 samples collected and tested, 32 were culturally confirmed as containing Salmonella. These isolates represented 25 serotypes. Salmonella was not detected in pecans and in-shell hazelnuts. Salmonella prevalence estimates (and 95% confidence intervals) in cashews, shelled hazelnuts, pine nuts, walnuts, and macadamia nuts were 0.55% [0.15, 1.40], 0.35% [0.04, 1.20], 0.48% [0.10, 1.40], 1.20% [0.53, 2.40], and 4.20% [2.40, 6.90], respectively. The rates of Salmonella isolation from major or big chain supermarkets, small chain supermarkets, discount, variety, or drug stores, and online were 0.64% [0.38, 1.00], 1.60% [0.80, 2.90], 0.00% [0.00, 2.40], and 13.64% [2.90, 35.00], respectively (Cochran-Mantel-Haenszel test: P = 0.02). The rates of Salmonella isolation for conventional and organic nuts were not significantly different. Of the samples containing Salmonella, 60.7% had levels less than 0.003 most probable number (MPN)/g. The highest contamination level observed was 0.092 MPN/g. The prevalence and levels of Salmonella in these tree nut samples were comparable to those previously reported for similar foods. [ABSTRACT FROM AUTHOR]

A most-probable-number (MPN) method was used to enumerate Listeria monocytogenes in 2,320 commercial ice cream scoops manufactured on a production line that was implicated in a 2015 listeriosis outbreak in the United States. The analyzed samples were collected from seven lots produced in November 2014, December 2014, January 2015, and March 2015. L. monocytogenes was detected in 99% (2,307 of 2,320) of the tested samples (lower limit of detection, 0.03 MPN/g), 92% of which were contaminated at <20 MPN/g. The levels of L. monocytogenes in these samples had a geometric mean per lot of 0.15 to 7.1 MPN/g. The prevalence and enumeration data from an unprecedented large number of naturally contaminated ice cream products linked to a listeriosis outbreak provided a unique data set for further understanding the risk associated with L. monocytogenes contamination for highly susceptible populations. [ABSTRACT FROM AUTHOR]

The U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM) Chapter 4a describes a Luminex microbead-based suspension array used to screen colonies for 11 clinically relevant Shiga toxin-producing Escherichia coli (STEC) serogroups: 026, 045, 091, 0103, 0104, 0111, 0113, 0121, 0128, 0145, and 0157. We evaluated the usefulness of this method to identify STEC-positive enrichment samples before agar plating. Twelve E. coli strains were added to three types of fresh produce (bagged baby spinach, alfalfa sprouts, and cilantro) at levels near the detection limit of the test. A subset of these strains (six O serogroups) was similarly evaluated in raw milk. For comparison, portions of each of the 168 enrichment cultures were analyzed for serogroup by a real-time PCR assay and a Bio-Plex 200 assay with the bead-based suspensions. No falsepositive results were obtained. Of the 112 samples with a reported cycle threshold (CT) value, 101 undiluted, diluted, or extracted enrichment cultures also produced ratios above 5.0 in the Bio-Plex assay. When PCR CT values approached or were greater than 35, Bio-Plex detection became less reliable. Using undiluted or extracted enrichment cultures resulted in a significantly larger number of positive results. With the same enrichment material prepared for real-time PCR analysis as described in the BAM Chapter 4a, the STEC tnicrobead-based suspension array can accurately screen food enrichment cultures. [ABSTRACT FROM AUTHOR]

The recovery and growth potential of Listeria monocytogenes was evaluated in three flavors of milkshakes (vanilla, strawberry, and chocolate) that were prepared from naturally contaminated ice cream linked to a listeriosis outbreak in the U.S. in 2015, and were subsequently held at room temperature for 14 h. The average lag phase duration of L. monocytogenes was 9.05 h; the average generation time was 1.67 h; and the average population level increase per sample at 14 h was 1.14 log CFU/g. Milkshake flavors did not significantly affect these parameters. The average lag phase duration of L. monocytogenes in milkshakes with initial contamination levels 3 CFU/g (9.50 h) was significantly longer (P < 0.01) than that with initial contamination levels > 3 CFU/g (8.60 h). The results highlight the value of using samples that are contaminated with very low levels of L. monocytogenes for recovery and growth evaluations. The behavior of L. monocytogenes populations in milkshakes prepared from naturally contaminated ice cream linked to the listeriosis outbreak should be taken into account when performing risk based analysis using this outbreak as a case study. [ABSTRACT FROM AUTHOR]

The FDA Bacteriological Analytical Manual (BAM) Chapter 4a recommends several agars for isolating non-O157 Shiga toxin-producing Escherichia coli (STEC); not all have been thoroughly tested for recovering STECs from food. Using E. coli strains representing ten clinically relevant O serogroups (O26, O45, O91, O103, O104, O111, O113, O121, O128, O145) in artificially-contaminated fresh produce – bagged baby spinach, alfalfa sprouts, cilantro, and raw milk – we evaluated the performance of 8 different agars. Performance was highly dependent upon strain used and the presence of inhibitors, but not necessarily dependent on food matrix. Tellurite resistant-negative strains, O91:–, O103:H6, O104:H21, O113:H21, and O128, grew poorly on CHROMagar STEC, Rainbow agar O157, and a modified Rainbow O157 (mRB) agar. Although adding washed sheep's blood to CHROMagar STEC and mRB agars improved overall performance; however, this also reversed the inhibition of non-target bacteria provided by original formulations. Variable colony coloration made selecting colonies from Rainbow agar O157 and mRB agars difficult. Study results support a strategy using inclusive agars (e.g. L-EMB, SHIBAM) in combination with selective agars (R & F E. coli O157:H7, CHROMagar STEC) to allow for recovery of the most STECs while increasing the probability of recovering STEC in high bacterial count matrices. [ABSTRACT FROM AUTHOR]

Abstract: The FDA Bacteriological Analytical Manual (BAM) method for the detection/isolation of Shiga toxin-producing Escherichia coli (STEC) involves enrichment of produce rinses, blended homogenates or stomached homogenates. However, the effectiveness of rinsing produce to remove attached bacteria is largely unknown. Moreover, PCR inhibitors can be released under physical treatment. The study objective was to determine the relative effectiveness of recovery methods for STEC contaminated produce. Spinach, lettuce, and cilantro were contaminated with E. coli O157:H7 or a non-O157 STEC, subjected to both the BAM method and a soak method, and tested by real-time PCR and cultural methods. For O157:H7 and non-O157:H7 STECs, the soak method was significantly more productive than leafy green rinses. Of 320 test portions, PCR of recovered colonies confirmed 148 were positive by rinsing and 271 were positive by soaking (an 83% increase in sensitivity). For recovery of O157:H7 from cilantro, of 60 test portions, positives were 38 by soaking, 41 by stomaching, and 28 by blending. Soaking and stomaching were significantly more productive than blending, although soaking was only arithmetically superior to stomaching. Based upon these results, it is recommended that a soak method replace the current BAM procedures. [Copyright &y& Elsevier]

Abstract: Escherichia coli serogroup O157 is the pathogen most commonly associated with foodborne disease outbreaks, but epidemiological studies suggest that non-O157 Shiga toxin-producing E. coli (STEC) is a major player as well. The ten most clinically relevant STECs belong to serogroups O26, O103, O111, O145, O157, O91, O113, O128, O45, and O121; but emerging strains, such as O104:H4 that was identified with the 2011 German outbreak, could become more prevalent in the future. A 75-min conventional multiplex PCR assay, IS-5P, targeting the four virulence factors stx1, stx2, eae, and ehxA plus the O157:H7-specific +93 uidA single nucleotide polymorphism was developed to better assess the potential pathogenicity of STEC isolates. All 212 STEC DNAs showed one to five amplification products, while the non-E. coli DNA did not react to this multiplex PCR assay. Enrichment broths obtained from baby spinach, alfalfa sprouts, and cilantro artificially inoculated with O26, O103, and O121 STECs reacted positively to the multiplex assay. Unlike the current FDA BAM 5P PCR, designed for the specific detection of O157:H7, IS-5P will identify potentially harmful O157:H7 and non-O157 STECs so they can be removed from the nation's food supply. [Copyright &y& Elsevier]

Shiga toxin-producing Escherichia coli (STEC) belonging to certain serogroups (e.g., O157 and O26) can cause serious conditions like hemolytic-uremic syndrome (HUS), but other strains might be equally pathogenic. While virulence factors, like stx and eae, have been well studied, little is known about the prevalence of the E. coli hemolysin genes (hlyA, ehxA, e-hlyA, and sheA) in association with these factors. Hemolysins are potential virulence factors, and ehxA and hlyA have been associated with human illness, but the significance of sheA is unknown. Hence, 435 E. coli strains belonging to 62 different O serogroups were characterized to investigate gene presence and phenotypic expression of hemolysis. We further investigated ehxA subtype patterns in E. coli isolates from clinical, animal, and food sources. While sheA and ehxA were widely distributed, e-hlyA and hlyA were rarely found. Most strains (86.7%) were hemolytic, and significantly more hemolytic (95%) than nonhemolytic strains (49%) carried stx and/or eae (P<0.0001). ehxA subtyping, as performed by using PCR in combination with restriction fragment length polymorphism analysis, resulted in six closely related subtypes (>94.2%), with subtypes A/D being eae-negative STECs and subtypes B, C, E, and F eae positive. Unexpectedly, ehxA subtype patterns differed significantly between isolates collected from different sources (P<0.0001), suggesting that simple linear models of exposure and transmission need modification; animal isolates carried mostly subtypes A/C (39.3%/42.9%), food isolates carried mainly subtype A (81.9%), and clinical isolates carried mainly subtype C (66.4%). Certain O serogroups correlated with particular ehxA subtypes: subtype A with O104, O113, and O8; B exclusively with O157; C with O26, O111, and O121. [ABSTRACT FROM AUTHOR]

The FDA Bacteriological Analytical Manual (BAM) Salmonella culture method takes at least 3 days for a presumptive positive result. The FDA developed a quantitative PCR (qPCR) method to detect Salmonella from 24-h preenriched cultures, using ABI 7500 PCR system. The qPCR method has been evaluated as a rapid screening method for a broad range of foods by single laboratory validation (SLV) studies. The present multi-laboratory validation (MLV) study was aimed to measure the reproducibility of this qPCR method and compare its performance with the culture method. Sixteen laboratories participated in two rounds of MLV study to analyze twenty-four blind-coded baby spinach test portions each. The first round yielded ∼84% and ∼82% positive rates across laboratories for the qPCR and culture methods, respectively, which were both outside the fractional range (25%–75%) required for fractionally inoculated test portions by the FDA's Microbiological Method Validation Guidelines. The second round yielded ∼68% and ∼67% positive rates. The relative level of detection (RLOD) for the second-round study was 0.969, suggesting that qPCR and culture methods had similar sensitivity (p > 0.05). The study demonstrated that the qPCR yields reproducible results and is sufficiently sensitive and specific for the detection of Salmonella in food. • FDA qPCR method of Salmonella detection was evaluated in a Multi-Laboratory Validation study. • FDA qPCR method has high reproducibility, specificity, and sensitivity. • FDA qPCR method can be used as a reliable screening tool for Salmonella in leafy greens. • Laboratory cross-contamination during a MLV study could happen. [ABSTRACT FROM AUTHOR]

Three commonly used enrichment schemes were evaluated for the detection of Listeria spp. from environmental surfaces: one-step 48 h enrichment in buffered Listeria enrichment broth (BLEB); 26 h primary enrichment in University of Vermont modified (UVM) broth, followed by a transfer of 100 μl primary enrichment culture to Fraser broth (FB) for 24–48 h secondary enrichment; and 26 h primary enrichment in half-Fraser broth (HF), followed by a transfer of 100 μl primary enrichment culture to FB for 24–48 h secondary enrichment. Low levels (20–300 CFU/sample) of Listeria were artificially inoculated onto eight types of surfaces, desiccation stressed, and then collected by swab/sponge samplers for subsequent analysis. Results showed that low levels of desiccation-stressed Listeria recovered and grew rather slowly: 26 h primary enrichment in UVM and HF could not consistently yield 1 cell in 100 μl of enrichment culture, as demonstrated by enumeration of 100 μl primary enrichment culture and transfer of 100 μl enrichment culture to secondary enrichment. We further discovered that, using 20 samples per scheme and for certain Listeria strains on certain surfaces, one-step 48 h enrichment in BLEB generated significantly higher numbers of positive results than the two-step enrichment schemes when there were no competing background microflora. Higher numbers of positive results from two-step schemes were achieved by increasing the duration of primary enrichment for an additional 22 h. Therefore, to improve the detection of desiccation-stressed Listeria in the environment, we must allow sufficient time for primary enrichment and/or transfer a sufficient amount of primary enrichment culture to the secondary enrichment. The study also highlights the importance of using low levels of inoculum and physiologically injured cells for method comparison and evaluation. [ABSTRACT FROM AUTHOR]

Listeriosis is an invasive illness typically caused by the ingestion of foods contaminated with Listeria monocytogenes. In 2015, an outbreak of listeriosis was linked to ice cream products produced on a specific production line at Facility X. The United States Food and Drug Administration (FDA) obtained samples representing several lots of three products manufactured on that line from May 2014 through January 2015. Two of these products, A and B, while not linked to any reported illnesses, were analyzed to determine the frequency of contamination and the contamination level for risk assessment and dose-response analyses. These enumerations were performed utilizing a Most Probable Number (MPN) method, with a lower detection limit of 0.03 MPN/g, on 344 samples of Product A and 95 samples of Product B. Ten lots of Product A were analyzed and 77% of the samples tested were found to be positive for L. monocytogenes . Five lots of Product B were analyzed and 46% of the tested samples were found to be positive. Additionally, the level of contamination of positive Product B samples was always less than 1 MPN/g. The contamination levels of both products, overall, were low with median values of 0.1 MPN/g and 0.02 MPN/g for Products A and B, respectively. A majority of Product A samples (52%) were contaminated at levels of less than 1 MPN/g and only one sample was above 100 MPN/g. Whole genome sequencing (WGS) of L. monocytogenes isolated from ice cream samples produced in the line suggested minor strain differences related to product type, possibly due to differences in the food matrices and/or differences in the manufacturing equipment. Overall, the data showed a consistent low level of contamination in products produced from a single production line over a nine month period. [ABSTRACT FROM AUTHOR]

A precise and accurate method for enumeration of low level of Listeria monocytogenes in foods is critical to a variety of studies. In this study, paired comparison of most probable number (MPN) and direct plating enumeration of L. monocytogenes was conducted on a total of 1730 outbreak-associated ice cream samples that were naturally contaminated with low level of L. monocytogenes . MPN was performed on all 1730 samples. Direct plating was performed on all samples using the RAPID' L.mono (RLM) agar (1600 samples) and agar Listeria Ottaviani and Agosti (ALOA; 130 samples). Probabilistic analysis with Bayesian inference model was used to compare paired direct plating and MPN estimates of L. monocytogenes in ice cream samples because assumptions implicit in ordinary least squares (OLS) linear regression analyses were not met for such a comparison. The probabilistic analysis revealed good agreement between the MPN and direct plating estimates, and this agreement showed that the MPN schemes and direct plating schemes using ALOA or RLM evaluated in the present study were suitable for enumerating low levels of L. monocytogenes in these ice cream samples. The statistical analysis further revealed that OLS linear regression analyses of direct plating and MPN data did introduce bias that incorrectly characterized systematic differences between estimates from the two methods. [ABSTRACT FROM AUTHOR]

In 2014, the identification of stone fruits contaminated with Listeria monocytogenes led to the subsequent identification of a multistate outbreak. Simultaneous detection and enumeration of L. monocytogenes were performed on 105 fruits, each weighing 127 to 145 g, collected from 7 contaminated lots. The results showed that 53.3% of the fruits yielded L. monocytogenes (lower limit of detection, 5 CFU/fruit), and the levels ranged from 5 to 2,850 CFU/fruit, with a geometric mean of 11.3 CFU/fruit (0.1 CFU/g of fruit). Two serotypes, IVb-v1 and 1/2b, were identified by a combination of PCR- and antiserum-based serotyping among isolates from fruits and their packing environment; certain fruits contained a mixture of both serotypes. Single nucleotide polymorphism (SNP)-based whole-genome sequencing (WGS) analysis clustered isolates from two case-patients with the serotype IVb-v1 isolates and distinguished outbreak-associated isolates from pulsed-field gel electrophoresis (PFGE)-matched, but epidemiologically unrelated, clinical isolates. The outbreak-associated isolates differed by up to 42 SNPs. All but one serotype 1/2b isolate formed another WGS cluster and differed by up to 17 SNPs. Fully closed genomes of isolates from the stone fruits were used as references to maximize the resolution and to increase our confidence in prophage analysis. Putative prophages were conserved among isolates of each WGS cluster. All serotype IVb-v1 isolates belonged to singleton sequence type 382 (ST382); all but one serotype 1/2b isolate belonged to clonal complex 5. [ABSTRACT FROM AUTHOR]

The objective of this research was to assess the microbiological status of leafy greens, sprouts, and melons from U.S. markets. A total of 14,183 samples of leafy greens, 2,652 samples of sprouts, and 3,411 samples of melons were collected throughout the United States from 2009 to 2014. The samples were analyzed for aerobic plate counts, total coliform counts, Escherichia coli counts, and the presence and levels of Salmonella, Shigella, Listeria monocytogenes, and Shiga toxin-producing E. coli (STEC), depending on the year and type of produce. Among the leafy greens, no E. coli O157:H7 or non-O157 STEC were detected from iceberg lettuce samples. The overall prevalences of Salmonella, E. coli O157:H7, non-O157 STEC, and L. monocytogenes in the 14,183 samples of leafy greens were 0.05, 0.01, 0.07, and 0.11%, respectively. Among sprout samples, no Salmonella or E. coli O157:H7 was detected, and the overall prevalences of non-O157 STEC and L. monocytogenes were 0.04 and 0.11%, respectively. Among melon samples, no Salmonella was detected from cucumbers, no L. monocytogenes was detected from cantaloupes, and the overall prevalences of Salmonella and L. monocytogenes were 0.12 and 0.23%, respectively. L. monocytogenes levels were 0.4 to 1,470 most probable number (MPN)/g in leafy greens, 0.36 to 1,100 MPN/g in sprouts, and <0.03 to 150 MPN/g in melons, and most positive samples had low levels of these pathogens. The isolates from these foods were very diverse genetically. Foodborne pathogens, including Salmonella, STEC, and L. monocytogenes, had relatively low prevalences in the produce surveyed. Because these foods are usually consumed raw, measures should be taken to significantly minimize the presence and levels of human pathogens.

In 2014, the identification of stone fruits contaminated with Listeria monocytogenes led to the subsequent identification of a multistate outbreak. Simultaneous detection and enumeration of L. monocytogenes were performed on 105 fruits, each weighing 127 to 145 g, collected from 7 contaminated lots. The results showed that 53.3% of the fruits yielded L. monocytogenes (lower limit of detection, 5 CFU/fruit), and the levels ranged from 5 to 2,850 CFU/fruit, with a geometric mean of 11.3 CFU/fruit (0.1 CFU/g of fruit). Two serotypes, IVb-v1 and 1/2b, were identified by a combination of PCR- and antiserum-based serotyping among isolates from fruits and their packing environment; certain fruits contained a mixture of both serotypes. Single nucleotide polymorphism (SNP)-based whole-genome sequencing (WGS) analysis clustered isolates from two case-patients with the serotype IVb-v1 isolates and distinguished outbreak-associated isolates from pulsed-field gel electrophoresis (PFGE)-matched, but epidemiologically unrelated, clinical isolates. The outbreak-associated isolates differed by up to 42 SNPs. All but one serotype 1/2b isolate formed another WGS cluster and differed by up to 17 SNPs. Fully closed genomes of isolates from the stone fruits were used as references to maximize the resolution and to increase our confidence in prophage analysis. Putative prophages were conserved among isolates of each WGS cluster. All serotype IVb-v1 isolates belonged to singleton sequence type 382 (ST382); all but one serotype 1/2b isolate belonged to clonal complex 5., Importance: WGS proved to be an excellent tool to assist in the epidemiologic investigation of listeriosis outbreaks. The comparison at the genome level contributed to our understanding of the genetic diversity and variations among isolates involved in an outbreak or isolates associated with food and environmental samples from one facility. Fully closed genomes increased our confidence in the identification and comparison of accessory genomes. The diversity among the outbreak-associated isolates and the inclusion of PFGE-matched, but epidemiologically unrelated, isolates demonstrate the high resolution of WGS. The prevalence and enumeration data could contribute to our further understanding of the risk associated with Listeria monocytogenes contamination, especially among high-risk populations., (Copyright © 2016 Chen et al.)

A most-probable-number (MPN) method was used to enumerate Listeria monocytogenes in 2,320 commercial ice cream scoops manufactured on a production line that was implicated in a 2015 listeriosis outbreak in the United States. The analyzed samples were collected from seven lots produced in November 2014, December 2014, January 2015, and March 2015. L. monocytogenes was detected in 99% (2,307 of 2,320) of the tested samples (lower limit of detection, 0.03 MPN/g), 92% of which were contaminated at <20 MPN/g. The levels of L. monocytogenes in these samples had a geometric mean per lot of 0.15 to 7.1 MPN/g. The prevalence and enumeration data from an unprecedented large number of naturally contaminated ice cream products linked to a listeriosis outbreak provided a unique data set for further understanding the risk associated with L. monocytogenes contamination for highly susceptible populations.

A quantitative real-time PCR (qPCR) designed to detect Salmonella enterica subsp. enterica serovar Enteritidis, targeting the sdf gene, generated positive results for S. enterica subsp. enterica serovar Typhimurium (CFSAN033950) and S. enterica subsp. enterica serovar Nottingham (CFSAN006803) isolated from food samples. Both strains show pulsed-field gel electrophoresis (PFGE) patterns distinct from those of S Enteritidis. Here, we report the genome sequences of these two strains., (Copyright © 2016 Wang et al.)

The recovery and growth potential of Listeria monocytogenes was evaluated in three flavors of milkshakes (vanilla, strawberry, and chocolate) that were prepared from naturally contaminated ice cream linked to a listeriosis outbreak in the U.S. in 2015, and were subsequently held at room temperature for 14 h. The average lag phase duration of L. monocytogenes was 9.05 h; the average generation time was 1.67 h; and the average population level increase per sample at 14 h was 1.14 log CFU/g. Milkshake flavors did not significantly affect these parameters. The average lag phase duration of L. monocytogenes in milkshakes with initial contamination levels ≤ 3 CFU/g (9.50 h) was significantly longer (P < 0.01) than that with initial contamination levels > 3 CFU/g (8.60 h). The results highlight the value of using samples that are contaminated with very low levels of L. monocytogenes for recovery and growth evaluations. The behavior of L. monocytogenes populations in milkshakes prepared from naturally contaminated ice cream linked to the listeriosis outbreak should be taken into account when performing risk based analysis using this outbreak as a case study.

We report the genome sequence of Salmonella enterica subsp. enterica serovar Give (CFSAN012622), isolated from imported chili powder in 2014. This genome contains genes previously reported to be specific only to S. enterica serovar Enteritidis. This strain shows a unique pulsed-field gel electrophoresis (PFGE) pattern clustering with serovar Enteritidis (JEG X01.0005)., (Copyright © 2015 Wang et al.)