A novel metagenomic approach uncovers phage genes as markers for increased disinfectant tolerance in mixed Listeria monocytogenes communities

Listeria monocytogenes is an important human pathogen with a high mortality rate. Consumption of contaminated ready-to-eat food is the main mode of transmission to humans. Disinfectant-tolerant L. monocytogenes have emerged, which are believed to have increased persistence potential. Elucidating the mechanisms of L. monocytogenes disinfectant tolerance has been the focus of previous studies using pure cultures. A limitation of such approach is the difficulty to identify strains with reduced susceptibility due to inter-strain variation and the need to screen large numbers of strains and genes. In this study, we applied a novel metagenomic approach to detect genes associated with disinfectant tolerance in mixed L. monocytogenes planktonic communities. Two communities, consisting of 71 and 80 isolates each, were treated with the food industry disinfectants benzalkonium chloride (BC, 1.75 mg/L) or peracetic acid (PAA, 38 mg/L). The communities were subjected to metagenomic sequencing and differences in individual gene abundances between biocide-free control communities and biocide-treated communities were determined. A significant increase in the abundance of Listeria phage-associated genes was observed in both communities after treatment, suggesting that prophage carriage could lead to an increased disinfectant tolerance in mixed L. monocytogenes planktonic communities. In contrast, a significant decrease in the abundance of a high-copy emrC-harbouring plasmid pLmN12-0935 was observed in both communities after treatment. In PAA-treated community, a putative ABC transporter previously found to be necessary for L. monocytogenes resistance to antimicrobial agents and virulence, was among the genes with the highest weight for differentiating treated from control samples. The undertaken metagenomic approach in this study can be applied to identify genes associated with increased tolerance to other antimicrobials in mixed bacterial communities.

Genomic analysis of Listeria monocytogenes CC7 associated with clinical infections and persistence in the food industry

Listeria monocytogenes clonal complex 7 (CC7), belonging to lineage II, is the most common subtype among clinical listeriosis isolates in Norway, and is also commonly found in Norwegian food industry and outdoor environments. In the present study, the relative prevalence of CCs among clinical isolates of L. monocytogenes in European countries during 2010-2015 was determined. Then, phylogenomic and comparative genomic analyses was performed for 115 Norwegian and 255 international reference genomes from various sources, to examine potential explanations underlying the high prevalence of CC7 among Norwegian listeriosis cases. Selected isolates were also compared using in vitro virulence assays. The results showed a high relative prevalence of CC7 in clinical isolates from Norway and the neighboring Nordic countries Sweden and Finland. In contrast to in most other European countries, lineage II dominated among clinical isolates in these countries. Phylogenetic analysis of the 370 CC7 isolates separated the genomes into four clades, with the majority of Norwegian isolates (69 %) clustered in one of these clades, estimated to have diverged from the other clades around year 1830. The Norwegian isolates within this clade were widely distributed in different habitats; several (poultry) meat processing factories, a salmon processing plant, in nature, farms, and slugs, and among human clinical isolates. In particular, one pervasive CC7 clone was found across three poultry processing plants and one salmon processing plant, and also included three clinical isolates. All analysed CC7 isolates harbored the same set of 72 genes involved in both general and specific stress responses. Divergence was observed for plasmid-encoded genes including genes conferring resistance against arsenic (Tn554-arsCBADR), cadmium (cadA1C1 and cadA2C2), and the biocide benzalkonium chloride (bcrABC). No significant difference in prevalence of these genes was seen between isolates from different habitats or sources. Virulence attributes were highly conserved among the CC7 isolates. In vitro virulence studies of five representative CC7 isolates revealed a virulence potential that, in general, was not significantly lower than that of the control strain EGDe, with isolate-dependent differences that could not be correlated with genetic determinants. The study shows that CC7 is widespread in Norway, and that a pervasive CC7 clone was present in food processing plants. The study highlights the importance of CC7 and lineage II strains in causing listeriosis and shows that more research is needed to understand the reasons behind geographical differences in CC prevalence.

Reduction and Growth Inhibition of Listeria monocytogenes by Use of Anti-Listerial Nisin, P100 Phages and Buffered Dry Vinegar Fermentates in Standard and Sodium-Reduced Cold-Smoked Salmon

Cold-smoked salmon are ready-to-eat products that may support the growth of pathogenic Listeria monocytogenes during their long shelf-life. Consumption of such contaminated products can cause fatal listeriosis infections. Another challenge and potential risk associated with CS salmon is their high levels of sodium salt. Excess dietary intake is associated with serious health complications. In the present study, anti-listerial bacteriocin (nisin), P100 bacteriophages (Phageguard L, PGL) and fermentates (Verdad N6, P-NDV) were evaluated as commercial bio-preservation strategies for increased control of L. monocytogenes in standard (with NaCl) and sodium-reduced (NaCl partially replaced with KCl) CS salmon. Treatments of CS salmon with nisin (1 ppm) and PGL (5 × 107 pfu/cm2) separately yielded significant initial reductions in L. monocytogenes (up to 0.7 log) compared to untreated samples. Enhanced additive reductions were achieved through the combined treatments of nisin and PGL. Fermentates in the CS salmon inhibited the growth of Listeria but did not lead to its eradication. The lowest levels of L. monocytogenes during storage were observed in nisin- and PGL-treated CS salmon containing preservative fermentates and stored at 4 °C, while enhanced growth was observed during storage at an abusive temperature of 8 °C. Evaluation of industry-processed standard and sodium-replaced CS salmon confirmed significant effects with up to 1.7 log reductions in L. monocytogenes levels after 34 days of storage of PGL- and nisin-treated CS salmon-containing fermentates. No differences in total aerobic plate counts were observed between treated (PGL and nisin) or non-treated standard and sodium-reduced CS salmon at the end of storage. The microbiota was dominated by Photobacterium, but with a shift showing dominance of Lactococcus spp. and Vagococcus spp. in fermentate-containing samples. Similar and robust reductions in L. monocytogenes can be achieved in both standard and sodium-replaced CS salmon using the bio-preservation strategies of nisin, PGL and fermentates under various and relevant processing and storage conditions.

Improved microbial and sensory quality of chicken meat by treatment with lactic acid, organic acid salts and modified atmosphere packaging

Microbial contamination and growth play important roles in spoilage and quality loss of raw poultry products. We evaluated the suitability of three commercially available organic acid based antimicrobial compounds, Purac FCC80 (l-lactic acid), Verdad N6 (buffered vinegar fermentate) and Provian K (blend of potassium acetate and diacetate) to prevent growth of the innate microbiota, reduce spoilage and enhance the sensory quality of raw chicken under vacuum, high CO₂ (60/40% CO₂/N₂), and high O₂ (75/25% O₂/CO₂) modified atmosphere (MA) storage conditions. Solutions were applied warm (50 °C) or cold (4 °C) to reflect treatments prior to (Prechill) or after (Postchill) cooling of chicken carcasses, respectively. Single postchill treatments of raw chicken wings with 5% Verdad N6 or Provian K solutions and MA storage enabled complete growth inhibition during the first seven days of storage before growth resumed. Enhanced bacterial control was obtained by combining Prechill lactic acid and Postchill Verdad N6 or Provian K treatments which indicated initial reductions up to 1.1 log and where total bacterial increase after 20 days storage was limited to 1.8-2.1 log. Antibacterial effects were dependent on the concentration of the inhibiting salts used, pH and the storage conditions. Bacterial community analyses showed increased relative levels of Gram-positive bacteria and with reductions of potential spoilage organisms in samples treated with the organic acid salts Verdad N6 and Provian K. Sensory analyses of raw, treated wings showed prominent lower scores in several spoilage associated odour attributes when compared with untreated chicken wings after 13 days storage. For heat-treated chicken, only minor differences for 22 tested attributes were detected between seven antimicrobial treatments and untreated control chicken. Immersion in commercially available organic acid/salt solutions combined with MA storage can reduce bacterial levels, improve microbial and sensory quality, and potentially improve shelf life and reduce food waste of chicken products.

Improved control of Listeria monocytogenes during storage of raw salmon by treatment with the fermentate Verdad N6 and nisin

Fresh Atlantic salmon (Salmo salar) represents a healthy, nutritious food with global distribution and increasing consumption and economic value. Contaminating Listeria monocytogenes in fresh salmon represents a health hazard to consumers, is linked to extensive product recalls and is a major challenge for salmon processors. Verdad N6, a commercially available buffered vinegar, was evaluated as a treatment for raw salmon fillets either alone or in combination with the antimicrobial peptide nisin, with regard to anti-listerial effects under processing and storage, and influence on sensory quality and background microbiota. Salmon fillets were surface contaminated with L. monocytogenes and immersed in solutions of Verdad N6 or treated with nisin or a combination of these two treatments. Levels of L. monocytogenes were determined during vacuum-pack refrigerated storage. The use of Verdad N6 resulted in increased lag times and substantially reduced growth of L. monocytogenes. The inhibitory effects were dependent on Verdad N6 levels, immersion time, and storage time and temperature. A 5 s immersion in 10% Verdad N6 solution at 4 °C reduced growth of L. monocytogenes from log 2.8 to log 1 after 12 days of storage. Nisin (0.2-1 ppm) had listericidal effects up to 1 log but did not inhibit regrowth when used alone. Appropriate combinations of Verdad N6 and nisin led to L. monocytogenes levels no higher after 12 days of storage than the initial levels. The inhibitory effects were markedly lower at 7 °C than at 4 °C. Salmon with Verdad N6 showed reduced levels of total counts during storage indicating a longer shelf-life, and a shift in the dominating bacteria with reduced and increased relative levels of Enterobacteriaceae and lactic acid bacteria, respectively. Sensory analyses of raw and cooked Verdad N6 treated a non-treated salmon resulted in small differences. In summary, Verdad N6 is an option for production of high-quality raw salmon with increased shelf-life and enhanced food safety through its Listeria inhibiting effects. The application of Verdad N6 in combination with nisin treatment can further reduce the listeria-risks of these products.

Listeria Monocytogenes Biofilm Removal Using Different Commercial Cleaning Agents

Effective cleaning and disinfection (C&D) is pivotal for the control of Listeria monocytogenes in food processing environments. Bacteria in biofilms are protected from biocidal action, and effective strategies for the prevention and removal of biofilms are needed. In this study, different C&D biofilm control strategies on pre-formed L. monocytogenes biofilms on a conveyor belt material were evaluated and compared to the effect of a conventional chlorinated, alkaline cleaner (agent A). Bacterial reductions up to 1.8 log were obtained in biofilms exposed to daily C&D cycles with normal user concentrations of alkaline, acidic, or enzymatic cleaning agents, followed by disinfection using peracetic acid. No significant differences in bactericidal effects between the treatments were observed. Seven-day-old biofilms were more tolerant to C&D than four-day-old biofilms. Attempts to optimize biofilm eradication protocols for four alkaline, two acidic, and one enzymatic cleaning agent, in accordance with the manufacturers' recommendations, were evaluated. Increased concentrations, the number of subsequent treatments, the exposure times, and the temperatures of the C&D agents provided between 4.0 and >5.5 log reductions in colony forming units (CFU) for seven-day-old L. monocytogenes biofilms. Enhanced protocols of conventional and enzymatic C&D protocols have the potential for improved biofilm control, although further optimizations and evaluations are needed.

Discriminatory Power, Typability, and Accuracy of Single Nucleotide Extension Microarrays

Despite great conceptual promise, the use of microarrays in typing approaches has not yet gained wide acceptance. The establishment of proper criteria for determining discriminatory power as well as typability and the accuracy of microarray data remains to be solved. Purely experimental estimations of these parameters would far exceed what is experimentally practical. We therefore used simulations in combination with experimental results in parameter estimations. Our assay was based on 26 single nucleotide polymorphisms (SNPs) identified in the Campylobacter jejuni Multi Locus Sequence Typing (MLST) database (<ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://pubmlst.org/campylobacter/">http://pubmlst.org/campylobacter/</ext-link>). The SNPs were detected using a single nucleotide extension (SNE) typing microarray. Unknown isolates were assigned to the known sequence type(s) by calculating weighted sum of matches minus a weighted sum of mismatches between predicted and candidate genotype. The weights were set according to the Bayesian posterior probability of the SNP classification. These studies showed that any typing or profiling method based on binary data requires an accuracy of <23% error for each datapoint (in our case SNPs) to classify the isolates to the correct allelic profile in 90% of the cases. The classification error for our experimental data was 3.2% (after removing 5 high error SNPs). We therefore conclude that SNE microarrays are promising for future high-throughput typing of bacteria.

Reduction and inhibition of Listeria monocytogenes in cold-smoked salmon by Verdad N6, a buffered vinegar fermentate, and UV-C treatments

Contamination, survival and growth of Listeria monocytogenes in cold-smoked salmon represent serious health hazards to consumers and major challenges for salmon processors. Verdad N6, a commercially available buffered vinegar, was evaluated as an ingredient in cold-smoked salmon with regard to anti-listerial effects under processing and storage, sensory quality and consumer preference, effects on background microbiota and yield during production. Cold-smoked salmon with Verdad N6 added in the dry-salting process was produced. Salmon fillets were surface contaminated with a mix of L. monocytogenes. Levels of L. monocytogenes were determined during vacuum pack refrigerated storage for 29 days. The use of Verdad N6 resulted in increased lag times and reduced growth rates of L. monocytogenes. The inhibitory effects were dependent on Verdad N6 levels (0-2%), storage time and temperature (4 or 8 °C), type of contamination (between slices or on non-sliced salmon) and degree of smoking. The presence of dextrose (1%) in the recipe had no significant effects on L. monocytogenes levels after storage. On sliced salmon, complete growth inhibition at 4 °C storage could be obtained using 1% Verdad N6 compared to a 3 log increase in L. monocytogenes counts in control salmon. At abuse temperatures (8 °C), corresponding L. monocytogenes levels increased <2 log and 5-6 log during 29 days storage. On non-sliced salmon, 1% Verdad N6 provided complete growth reductions at 4 and 8 °C storage while L. monocytogenes in control salmon increased 2.3 and 4.6 log, respectively, in the same period. The use of Verdad N6 in combination with bactericidal UV-C treatments (fluence 50 mJ/cm²) provided an initial 0.8 log reduction and complete L. monocytogenes growth inhibition on subsequent storage at 4 and 8 °C. Salmon with Verdad N6 showed reduced levels of total counts during storage and a shift in the dominating bacteria with reduced and increased relative levels of Photobacterium and lactic acid bacteria, respectively. A consumer test showed no consistent differences in liking of salmon with and without Verdad N6. In summary, Verdad N6 is an option for the production of high quality cold-smoked salmon with enhanced food safety through its robust listeriostatic effects. The application of Verdad N6 in combination with listericidal UV-C light treatment can further reduce the listeria-risks of this ready-to-eat food product category.

Listeria monocytogenes strains show large variations in competitive growth in mixed culture biofilms and suspensions with bacteria from food processing environments

Interactions and competition between resident bacteria in food processing environments could affect their ability to survive, grow and persist in microhabitats and niches in the food industry. In this study, the competitive ability of L. monocytogenes strains grown together in separate culture mixes with other L. monocytogenes (L. mono mix), L. innocua (Listeria mix), Gram-negative bacteria (Gram- mix) and with a multigenera mix (Listeria + Gram- mix) was investigated in biofilms on stainless steel and in suspensions at 12 °C. The mixed cultures included resident bacteria from processing surfaces in meat and salmon industry represented by L. monocytogenes (n = 6), L. innocua (n = 5) and Gram-negative bacteria (n = 6; Acinetobacter sp., Pseudomonas fragi, Pseudomonas fluorescens, Serratia liquefaciens, Stenotrophomonas maltophilia). Despite hampered in growth in mixed cultures, L. monocytogenes established in biofilms with counts at day nine between 7.3 and 9.0 log per coupon with the lowest counts in the Listeria + G- mix that was dominated by Pseudomonas. Specific L. innocua inhibited growth of L. monocytogenes strains differently; inhibition that was further enhanced by the background Gram-negative microbiota. In these multispecies and multibacteria cultures, the growth competitive effects lead to the dominance of a strong competitor L. monocytogenes strain that was only slightly inhibited by L. innocua and showed strong competitive abilities in mixed cultures with resident Gram-negative bacteria. The results indicates complex patterns of bacterial interactions and L. monocytogenes inhibition in the multibacteria cultures that only partially depend on cell contact and likely involve various antagonistic and bacterial tolerance mechanisms. The study indicates large variations among L. monocytogenes in their competitiveness under multibacterial culture conditions that should be considered in further studies towards understanding of L. monocytogenes persistence in food processing facilities.

Survival of Five Strains of Shiga Toxigenic Escherichia coli in a Sausage Fermentation Model and Subsequent Sensitivity to Stress from Gastric Acid and Intestinal Fluid

The ability of foodborne pathogens to exhibit adaptive responses to stressful conditions in foods may enhance their survival when passing through the gastrointestinal system. We aimed to determine whether Escherichia coli surviving stresses encountered during a model dry-fermented sausage (DFS) production process exhibit enhanced tolerance and survival in an in vitro gastrointestinal model. Salami sausage batters spiked with five E. coli isolates, including enterohaemorrhagic E. coli strains isolated from different DFS outbreaks, were fermented in a model DFS process (20°C, 21 days). Control batters spiked with the same strains were stored at 4°C for the same period. Samples from matured model sausages and controls were thereafter exposed to an in vitro digestion challenge. Gastric exposure (pH 3) resulted in considerably reduced survival of the E. coli strains that had undergone the model DFS process. This reduction continued after entering intestinal challenge (pH 8), but growth resumed after 120 min. When subjected to gastric challenge for 120 min, E. coli that had undergone the DFS process showed about 2.3 log10⁡ lower survival compared with those kept in sausage batter at 4°C. Our results indicated that E. coli strains surviving a model DFS process exhibited reduced tolerance to subsequent gastric challenge at low pH.

Cleaning and Disinfection of Biofilms Composed of Listeria monocytogenes and Background Microbiota from Meat Processing Surfaces

Surfaces of food processing premises are exposed to regular cleaning and disinfection (C&D) regimes, using biocides that are highly effective against bacteria growing as planktonic cells. However, bacteria growing in surface-associated communities (biofilms) are typically more tolerant toward C&D than their individual free-cell counterparts, and survival of pathogens such as Listeria monocytogenes may be affected by interspecies interactions within biofilms. In this study, Pseudomonas and Acinetobacter were the most frequently isolated genera surviving on conveyor belts subjected to C&D in meat processing plants. In the laboratory, Pseudomonas, Acinetobacter, and L. monocytogenes dominated the community, both in suspensions and in biofilms formed on conveyor belts, when cultures were inoculated with eleven-genus cocktails of representative bacterial strains from the identified background flora. When biofilms were exposed to daily C&D cycles mimicking treatments used in food industry, the levels of Acinetobacter and Pseudomonas mandelii diminished, and biofilms were instead dominated by Pseudomonas putida (65 to 76%), Pseudomonas fluorescens (11 to 15%) and L. monocytogenes (3 to 11%). The dominance of certain species after daily C&D correlated with high planktonic growth rates at 12°C and tolerance to C&D. In single-species biofilms, L. monocytogenes developed higher tolerance to C&D over time, for both the peracetic acid and quaternary ammonium disinfectants, indicating that a broad-spectrum mechanism was involved. Survival after C&D appeared to be a common property of L. monocytogenes strains, as persistent and sporadic subtypes showed equal survival rates in complex biofilms. Biofilms established preferentially in surface irregularities of conveyor belts, potentially constituting harborage sites for persistent contamination.IMPORTANCE In the food industry, efficient production hygiene is a key measure to avoid the accumulation of spoilage bacteria and eliminate pathogens. However, the persistence of bacteria is an enduring problem in food processing environments. This study demonstrated that environmental bacteria can survive foam cleaning and disinfection (C&D) at concentrations used in the industrial environment. The phenomenon was replicated in laboratory experiments. Important characteristics of persisting bacteria were a high growth rate at low temperature, a tolerance to the cleaning agent, and the ability to form biofilms. This study also supports other recent research suggesting that strain-to-strain variation cannot explain why certain subtypes of Listeria monocytogenes persist in food processing environments while others are found only sporadically. The present investigation highlights the failure of regular C&D and a need for research on improved agents that efficiently detach the biofilm matrix.

Microbial dynamics in mixed culture biofilms of bacteria surviving sanitation of conveyor belts in salmon-processing plants

AIMS

The microbiota surviving sanitation of salmon-processing conveyor belts was identified and its growth dynamics further investigated in a model mimicking processing surfaces in such plants.

METHODS AND RESULTS

A diverse microbiota dominated by Gram-negative bacteria was isolated after regular sanitation in three salmon processing plants. A cocktail of 14 bacterial isolates representing all genera isolated from conveyor belts (Listeria, Pseudomonas, Stenotrophomonas, Brochothrix, Serratia, Acinetobacter, Rhodococcus and Chryseobacterium) formed stable biofilms on steel coupons (12°C, salmon broth) of about 10(9) CFU cm(-2) after 2 days. High-throughput sequencing showed that Listeria monocytogenes represented 0·1-0·01% of the biofilm population and that Pseudomonas spp dominated. Interestingly, both Brochothrix sp. and a Pseudomonas sp. dominated in the surrounding suspension.

CONCLUSIONS

The microbiota surviving sanitation is dominated by Pseudomonas spp. The background microbiota in biofilms inhibit, but do not eliminate L. monocytogenes.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results highlights that sanitation procedures have to been improved in the salmon-processing industry, as high numbers of a diverse microbiota survived practical sanitation. High-throughput sequencing enables strain level studies of population dynamics in biofilm.

Biofilm Matrix Composition Affects the Susceptibility of Food Associated Staphylococci to Cleaning and Disinfection Agents

Staphylococci are frequently isolated from food processing environments, and it has been speculated whether survival after cleaning and disinfection with benzalkonium chloride (BC)-containing disinfectants is due to biofilm formation, matrix composition, or BC efflux mechanisms. Out of 35 food associated staphylococci, eight produced biofilm in a microtiter plate assay and were identified as Staphylococcus capitis (2), S. cohnii, S. epidermidis, S. lentus (2), and S. saprophyticus (2). The eight biofilm producing strains were characterized using whole genome sequencing. Three of these strains contained the ica operon responsible for production of a polysaccharide matrix, and formed a biofilm which was detached upon exposure to the polysaccharide degrading enzyme Dispersin B, but not Proteinase K or trypsin. These strains were more tolerant to the lethal effect of BC both in suspension and biofilm than the remaining five biofilm producing strains. The five BC susceptible strains were characterized by lack of the ica operon, and their biofilms were detached by Proteinase K or trypsin, but not Dispersin B, indicating that proteins were major structural components of their biofilm matrix. Several novel cell wall anchored repeat domain proteins with domain structures similar to that of MSCRAMM adhesins were identified in the genomes of these strains, potentially representing novel mechanisms of ica-independent biofilm accumulation. Biofilms from all strains showed similar levels of detachment after exposure to alkaline chlorine, which is used for cleaning in the food industry. Strains with qac genes encoding BC efflux pumps could grow at higher concentrations of BC than strains without these genes, but no differences were observed at biocidal concentrations. In conclusion, the biofilm matrix of food associated staphylococci varies with respect to protein or polysaccharide nature, and this may affect the sensitivity toward a commonly used disinfectant.

Effect of relevant environmental stresses on survival of enterohemorrhagic Escherichia coli in dry-fermented sausage

Dry-fermented sausages (DFSs) have been linked to several serious foodborne outbreaks of enterohemorrhagic Escherichia coli (EHEC). The ability of pathogens to utilize adaptive responses to different stressful conditions intended to control their growth in foods, food preparation and production processes may enhance their survival. In certain cases, induced tolerance to one type of stress may lead to enhanced resistance to the applied stress as well as to other stresses. We exposed two EHEC strains, MF3582 of serotype O157:H- and MF5554 of serogroup O145, to different stresses commonly encountered during a production process. The two EHEC strains, previously shown to have different abilities to survive DFS production process conditions, were subjected to low temperatures (4°C and 12°C), 5% NaCl or 1% lactic acid for 6days prior to being added to sausage batters. Survival of EHEC was recorded in salami of two recipes, fermented at two temperatures (20°C and 30°C). The results showed that recipe type had the largest impact on EHEC reductions where Moderate recipe (MR) salami batters containing increased levels of NaCl, glucose and NaNO2 provided enhanced EHEC reductions in salami (2.6 log10) compared to Standard recipe (SR) salami (1.7 log10). Effects of pre-exposure stresses were dependent both on strain and recipe. While acid adaptation of MF5554 provided enhanced log10 reductions from 2.0 to 3.0 in MR sausages, adaptation to a combination of acid and salt stress showed the opposite effect in SR sausages with reductions of only 1.1 log10 as compared to the average of 1.8 log10 for the other SR sausages. Otherwise, the salt and acid adaptation single stresses had relatively small effects on EHEC survival through the DFS production process and subsequent storage and freeze/thaw treatments. Growing cells and cells frozen in batter survived poorly in MR sausages with an average reduction of 3.4 and 3.2 log10, respectively. The reductions of EHEC after storage of DFS increased with higher temperature and storage time. Up to 3.7 log10 additional reduction was obtained when MF3582 was stored for 2months at 20°C. In conclusion, adaptation of EHEC to acid, salt and low temperatures prior to being introduced in a DFS production process has limited, but strain dependent effects on EHEC reductions. Producers should avoid conditions leading to acid and salt adapted cells that can contaminate the sausage batter. Recipe parameters had the largest impact on EHEC reductions while storage at 20°C is effective for enhanced reductions in finished products.

Genome Analysis of Listeria monocytogenes Sequence Type 8 Strains Persisting in Salmon and Poultry Processing Environments and Comparison with Related Strains

Listeria monocytogenes is an important foodborne pathogen responsible for the disease listeriosis, and can be found throughout the environment, in many foods and in food processing facilities. The main cause of listeriosis is consumption of food contaminated from sources in food processing environments. Persistence in food processing facilities has previously been shown for the L. monocytogenes sequence type (ST) 8 subtype. In the current study, five ST8 strains were subjected to whole-genome sequencing and compared with five additionally available ST8 genomes, allowing comparison of strains from salmon, poultry and cheese industry, in addition to a human clinical isolate. Genome-wide analysis of single-nucleotide polymorphisms (SNPs) confirmed that almost identical strains were detected in a Danish salmon processing plant in 1996 and in a Norwegian salmon processing plant in 2001 and 2011. Furthermore, we show that L. monocytogenes ST8 was likely to have been transferred between two poultry processing plants as a result of relocation of processing equipment. The SNP data were used to infer the phylogeny of the ST8 strains, separating them into two main genetic groups. Within each group, the plasmid and prophage content was almost entirely conserved, but between groups, these sequences showed strong divergence. The accessory genome of the ST8 strains harbored genetic elements which could be involved in rendering the ST8 strains resilient to incoming mobile genetic elements. These included two restriction-modification loci, one of which was predicted to show phase variable recognition sequence specificity through site-specific domain shuffling. Analysis indicated that the ST8 strains harbor all important known L. monocytogenes virulence factors, and ST8 strains are commonly identified as the causative agents of invasive listeriosis. Therefore, the persistence of this L. monocytogenes subtype in food processing facilities poses a significant concern for food safety.

Intra- and inter-species interactions within biofilms of important foodborne bacterial pathogens

A community-based sessile life style is the normal mode of growth and survival for many bacterial species. Under such conditions, cell-to-cell interactions are inevitable and ultimately lead to the establishment of dense, complex and highly structured biofilm populations encapsulated in a self-produced extracellular matrix and capable of coordinated and collective behavior. Remarkably, in food processing environments, a variety of different bacteria may attach to surfaces, survive, grow, and form biofilms. Salmonella enterica, Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus are important bacterial pathogens commonly implicated in outbreaks of foodborne diseases, while all are known to be able to create biofilms on both abiotic and biotic surfaces. Particularly challenging is the attempt to understand the complexity of inter-bacterial interactions that can be encountered in such unwanted consortia, such as competitive and cooperative ones, together with their impact on the final outcome of these communities (e.g., maturation, physiology, antimicrobial resistance, virulence, dispersal). In this review, up-to-date data on both the intra- and inter-species interactions encountered in biofilms of these pathogens are presented. A better understanding of these interactions, both at molecular and biophysical levels, could lead to novel intervention strategies for controlling pathogenic biofilm formation in food processing environments and thus improve food safety.

Coaggregation between Rhodococcus and Acinetobacter strains isolated from the food industry

In this study, coaggregation interactions between Rhodococcus and Acinetobacter strains isolated from food-processing surfaces were characterized. Rhodococcus sp. strain MF3727 formed intrageneric coaggregates with Rhodococcus sp. strain MF3803 and intergeneric coaggregates with 2 strains of Acinetobacter calcoaceticus (MF3293, MF3627). Stronger coaggregation between A. calcoaceticus MF3727 and Rhodococcus sp. MF3293 was observed after growth in batch culture at 30 °C than at 20 °C, after growth in tryptic soy broth than in liquid R2A medium, and between cells in exponential and early stationary phases than cells in late stationary phase. The coaggregation ability of Rhodococcus sp. MF3727 was maintained even after heat and Proteinase K treatment, suggesting its ability to coaggregate was protein independent whereas the coaggregation determinants of the other strains involved proteinaceous cell-surface-associated polymers. Coaggregation was stable at pH 5–9. The mechanisms of coaggregation among Acinetobacter and Rhodococcus strains bare similarity to those displayed by coaggregating bacteria of oral and freshwater origin, with respect to binding between proteinaceous and nonproteinaceous determinants and the effect of environmental factors on coaggregation. Coaggregation may contribute to biofilm formation on industrial food surfaces, protecting bacteria against cleaning and disinfection.

Survival of Shiga toxin-producing Escherichia coli and Stx bacteriophages in moisture enhanced beef

Moisture enhancement of meat through injection is a technology to improve the sensory properties and the weight of meat. However, the technology may increase the risk of food borne infections. Shiga toxin-producing Escherichia coli (STEC) or bacteriophages carrying cytotoxin genes (Shiga toxin genes, stx), which is normally only present on the surface of intact beef, may be transferred to the inner parts of the muscle during the injection process. Pathogens and bacteriophages surviving the storage period may not be eliminated in the cooking process since many consumers prefer undercooked beef. Measures to increase the microbial food safety of moisture enhanced beef may include sterilization or washing of the outer surface of the meat before injection, avoiding recycling of marinade and addition of antimicrobial agents to the marinade. This paper reviews the literature regarding microbial safety of moisture enhanced beef with special emphasis on STEC and Stx bacteriophages. Also, results from a European Union research project, ProSafeBeef (Food-CT-16 2006-36241) are presented.

Microbial background flora in small-scale cheese production facilities does not inhibit growth and surface attachment of Listeria monocytogenes

The background microbiota of 5 Norwegian small-scale cheese production sites was examined and the effect of the isolated strains on the growth and survival of Listeria monocytogenes was investigated. Samples were taken from the air, food contact surfaces (storage surfaces, cheese molds, and brine) and noncontact surfaces (floor, drains, and doors) and all isolates were identified by sequencing and morphology (mold). A total of 1,314 isolates were identified and found to belong to 55 bacterial genera, 1 species of yeast, and 6 species of mold. Lactococcus spp. (all of which were Lactococcus lactis), Staphylococcus spp., Microbacterium spp., and Psychrobacter sp. were isolated from all 5 sites and Rhodococcus spp. and Chryseobacterium spp. from 4 sites. Thirty-two genera were only found in 1 out of 5 facilities each. Great variations were observed in the microbial background flora both between the 5 producers, and also within the various production sites. The greatest diversity of bacteria was found in drains and on rubber seals of doors. The flora on cheese storage shelves and in salt brines was less varied. A total of 62 bacterial isolates and 1 yeast isolate were tested for antilisterial activity in an overlay assay and a spot-on-lawn assay, but none showed significant inhibitory effects. Listeria monocytogenes was also co-cultured on ceramic tiles with bacteria dominating in the cheese production plants: Lactococcus lactis, Pseudomonas putida, Staphylococcus equorum, Rhodococcus spp., or Psychrobacter spp. None of the tested isolates altered the survival of L. monocytogenes on ceramic tiles. The conclusion of the study was that no common background flora exists in cheese production environments. None of the tested isolates inhibited the growth of L. monocytogenes. Hence, this study does not support the hypothesis that the natural background flora in cheese production environments inhibits the growth or survival of L. monocytogenes.

Attachment and biofilm formation by foodborne bacteria in meat processing environments: causes, implications, role of bacterial interactions and control by alternative novel methods

Attachment of potential spoilage and pathogenic bacteria to food contact surfaces and the subsequent biofilm formation represent serious challenges to the meat industry, since these may lead to cross-contamination of the products, resulting in lowered-shelf life and transmission of diseases. In meat processing environments, microorganisms are sometimes associated to surfaces in complex multispecies communities, while bacterial interactions have been shown to play a key role in cell attachment and detachment from biofilms, as well as in the resistance of biofilm community members against antimicrobial treatments. Disinfection of food contact surfaces in such environments is a challenging task, aggravated by the great antimicrobial resistance of biofilm associated bacteria. In recent years, several alternative novel methods, such as essential oils and bacteriophages, have been successfully tested as an alternative means for the disinfection of microbial-contaminated food contact surfaces. In this review, all these aspects of biofilm formation in meat processing environments are discussed from a microbial meat-quality and safety perspective.

Effects of post-processing treatments on sensory quality and Shiga toxigenic Escherichia coli reductions in dry-fermented sausages

The effects of post-processing treatments on sensory quality and reduction of Shiga toxigenic Escherichia coli (STEC) in three formulations of two types of dry-fermented sausage (DFS; salami and morr) were evaluated. Tested interventions provided only marginal changes in sensory preference and characteristics. Total STEC reductions in heat treated DFS (32°C, 6days or 43°C, 24h) were from 3.5 to >5.5 log from production start. Storing of sausages (20°C, 1month) gave >1 log additional STEC reduction. Freezing and thawing of sausages in combination with storage (4°C, 1month) gave an additional 0.7 to 3.0 log reduction in STEC. Overall >5.5 log STEC reductions were obtained after storage and freezing/thawing of DFS with increased levels of glucose and salt. This study suggests that combined formulation optimisation and post-process strategies should be applicable for implementation in DFS production to obtain DFS with enhanced microbial safety and high sensory acceptance and quality.

Heterogeneity in resistance to food-related stresses and biofilm formation ability among verocytotoxigenic Escherichia coli strains

This study assessed the resistance of ten verocytotoxigenic Escherichia coli (VTEC) isolates of commonly encountered serogroups/-types and two non-pathogenic E. coli strains to various food-related stresses (acid, alkaline, heat and high hydrostatic pressure treatments) and their biofilm formation ability. In addition, the global changes in the cellular composition in response to the exposure to these adverse environments were monitored by Fourier Transform Infrared (FT-IR) spectroscopy for two of the strains. Large inter-strain variations in stress resistance were observed. The most tolerant strains belonged to serogroup O157 which included both the O157:H7 type strain EDL933 and a representative isolate of the sorbitol fermenting O157:H- VTEC clone (strain MF3582). Strain C-600, a non-pathogenic laboratory strain, was sensitive to multiple stresses. Although wide variation in biofilm-forming ability was observed among VTEC isolates, no consistent relationships between biofilm-forming ability and capacity to withstand stress exposures were found. Analysis of the allelic status of the rpoS gene, involved in the general stress response of stationary-phase cells, allowed detection of loss-of-function mutations for two strains, E218/02 and MF2411, both of them showing as common features a high sensitivity to alkaline and heat treatments and a poor ability to form mature biofilms. Evidences found in this study confirm rpoS as a highly mutable gene in nature, and suggest its relevance not only for the mount of an active stress response but also for the establishment of mature biofilm communities. Our findings contribute to increase the knowledge on the resistance of VTEC to environmental stresses commonly encountered in the food chain, which can lead to improved strategies for preventing VTEC infections.

Microarray-based transcriptome ofListeria monocytogenesadapted to sublethal concentrations of acetic acid, lactic acid, and hydrochloric acid

Listeria monocytogenes , an important foodborne pathogen, commonly encounters organic acids in food-related environments. The transcriptome of L. monocytogenes L502 was analyzed after adaptation to pH 5 in the presence of acetic acid, lactic acid, or hydrochloric acid (HCl) at 25 °C, representing a condition encountered in mildly acidic ready-to-eat food kept at room temperature. The acid-treated cells were compared with a reference culture with a pH of 6.7 at the time of RNA harvesting. The number of genes and magnitude of transcriptional responses were higher for the organic acids than for HCl. Protein coding genes described for low pH stress, energy transport and metabolism, virulence determinates, and acid tolerance response were commonly regulated in the 3 acid-stressed cultures. Interestingly, the transcriptional levels of histidine and cell wall biosynthetic operons were upregulated, indicating possible universal response against low pH stress in L. monocytogenes. The opuCABCD operon, coding proteins for compatible solutes transport, and the transcriptional regulator sigL were significantly induced in the organic acids, strongly suggesting key roles during organic acid stress. The present study revealed the complex transcriptional responses of L. monocytogenes towards food-related acidulants and opens the roadmap for more specific and in-depth future studies.

Micro ecosystems from feed industry surfaces: a survival and biofilm study of Salmonella versus host resident flora strains

BACKGROUND

The presence of Salmonella enterica serovars in feed ingredients, products and processing facilities is a well recognized problem worldwide. In Norwegian feed factories, strict control measures are implemented to avoid establishment and spreading of Salmonella throughout the processing chain. There is limited knowledge on the presence and survival of the resident microflora in feed production plants. Information on interactions between Salmonella and other bacteria in feed production plants and how they affect survival and biofilm formation of Salmonella is also limited. The aim of this study was to identify resident microbiota found in feed production environments, and to compare the survival of resident flora strains and Salmonella to stress factors typically found in feed processing environments. Moreover, the role of dominant resident flora strains in the biofilm development of Salmonella was determined.

RESULTS

Surface microflora characterization from two feed productions plants, by means of 16 S rDNA sequencing, revealed a wide diversity of bacteria. Survival, disinfection and biofilm formation experiments were conducted on selected dominant resident flora strains and Salmonella. Results showed higher survival properties by resident flora isolates for desiccation, and disinfection compared to Salmonella isolates. Dual-species biofilms favored Salmonella growth compared to Salmonella in mono-species biofilms, with biovolume increases of 2.8-fold and 3.2-fold in the presence of Staphylococcus and Pseudomonas, respectively.

CONCLUSIONS

These results offer an overview of the microflora composition found in feed industry processing environments, their survival under relevant stresses and their potential effect on biofilm formation in the presence of Salmonella. Eliminating the establishment of resident flora isolates in feed industry surfaces is therefore of interest for impeding conditions for Salmonella colonization and growth on feed industry surfaces. In-depth investigations are still needed to determine whether resident flora has a definite role in the persistence of Salmonella in feed processing environments.

Reduction of verotoxigenic Escherichia coli by process and recipe optimisation in dry-fermented sausages

Outbreaks of verotoxigenic Escherichia coli (VTEC) linked to dry-fermented sausages (DFSs) have emphasized the need for DFS manufacturers to introduce measures to obtain enhanced safety and still maintain the sensory qualities of their products. To our knowledge no data have yet been reported on non-O157:H7 VTEC survival in DFS. Here, the importance of recipe and process variables on VTEC (O157:H7 and O103:H25) reductions in two types of DFS, morr and salami, was determined through three statistically designed experiments. Linear regression and ANOVA analyses showed that no single variable had a dominant effect on VTEC reductions. High levels of NaCl, NaNO(2), glucose (low pH) and fermentation temperature gave enhanced VTEC reduction, while high fat and large casing diameter (a(w)) gave the opposite effect. Interaction effects were small. The process and recipe variables showed similar effects in morr and salami. In general, recipes combining high batter levels of salt (NaCl and NaNO(2)) and glucose along with high fermentation temperature that gave DFS with low final pH and a(w), provided approximately 3 log(10) reductions compared to approximately 1.5 log(10) reductions obtained for standard recipe DFS. Storage at 4 degrees C for 2 months provided log(10) 0.33-0.95 additional VTEC reductions and were only marginally affected by recipe type. Sensory tests revealed only small differences between the various recipes of morr and salami. By optimisation of recipe and process parameters, it is possible to obtain increased microbial safety of DFS while maintaining the sensory qualities of the sausages.

Reduction of verotoxigenic Escherichia coli by process and recipe optimisation in dry-fermented sausages

Outbreaks of verotoxigenic Escherichia coli (VTEC) linked to dry-fermented sausages (DFSs) have emphasized the need for DFS manufacturers to introduce measures to obtain enhanced safety and still maintain the sensory qualities of their products. To our knowledge no data have yet been reported on non-O157:H7 VTEC survival in DFS. Here, the importance of recipe and process variables on VTEC (O157:H7 and O103:H25) reductions in two types of DFS, morr and salami, was determined through three statistically designed experiments. Linear regression and ANOVA analyses showed that no single variable had a dominant effect on VTEC reductions. High levels of NaCl, NaNO(2), glucose (low pH) and fermentation temperature gave enhanced VTEC reduction, while high fat and large casing diameter (a(w)) gave the opposite effect. Interaction effects were small. The process and recipe variables showed similar effects in morr and salami. In general, recipes combining high batter levels of salt (NaCl and NaNO(2)) and glucose along with high fermentation temperature that gave DFS with low final pH and a(w), provided approximately 3 log(10) reductions compared to approximately 1.5 log(10) reductions obtained for standard recipe DFS. Storage at 4°C for 2months provided log(10) 0.33-0.95 additional VTEC reductions and were only marginally affected by recipe type. Sensory tests revealed only small differences between the various recipes of morr and salami. By optimisation of recipe and process parameters, it is possible to obtain increased microbial safety of DFS while maintaining the sensory qualities of the sausages.

Biofilm forming abilities of Salmonella are correlated with persistence in fish meal- and feed factories

BACKGROUND

Feed contaminated with Salmonella spp. constitutes a risk of Salmonella infections in animals, and subsequently in the consumers of animal products. Salmonella are occasionally isolated from the feed factory environment and some clones of Salmonella persist in the factory environment for several years. One hypothesis is that biofilm formation facilitates persistence by protecting bacteria against environmental stress, e.g. disinfection. The aim of this study was to investigate the biofilm forming potential of Salmonella strains from feed- and fishmeal factories. The study included 111 Salmonella strains isolated from Norwegian feed and fish meal factories in the period 1991-2006 of serovar Agona, serovar Montevideo, serovar Senftenberg and serovar Typhimurium.

RESULTS

Significant differences were found between serovars regarding the abilities to form biofilm on polystyrene (microtiter plate assay) and in the air-liquid interface of nutrient broth (pellicle assay). Strains of serovar Agona and serovar Montevideo were good biofilm producers. In Norwegian factories, clones of these serovars have been observed to persist for several years. Most serovar Senftenberg clones appear to persist for a shorter period, and strains of this serovar were medium biofilm producers in our test systems. Strains of the serovar Typhimurium were relatively poor biofilm producers. Salmonella ser. Typhimurium clones have not been observed to persist even though this serovar is resident in Norwegian wild life. When classifying strains according to persistence or presumed non-persistence, persistent strains produced more biofilm than presumed non-persisting strains.

CONCLUSION

The results indicate a correlation between persistence and biofilm formation which suggests that biofilm forming ability may be an important factor for persistence of Salmonella in the factory environment.

Discriminatory power, typability, and accuracy of single nucleotide extension microarrays

Despite great conceptual promise, the use of microarrays in typing approaches has not yet gained wide acceptance. The establishment of proper criteria for determining discriminatory power as well as typability and the accuracy of microarray data remains to be solved. Purely experimental estimations of these parameters would far exceed what is experimentally practical. We therefore used simulations in combination with experimental results in parameter estimations. Our assay was based on 26 single nucleotide polymorphisms (SNPs) identified in the Campylobacterjejuni Multi Locus Sequence Typing (MLST) database (http:///pubmist.org/campylobacter/). The SNPs were detected using a single nucleotide extension (SNE) typing microarray. Unknown isolates were assigned to the known sequence type(s) by calculating weighted sum of matches minus a weighted sum of mismatches between predicted and candidate genotype. The weights were set according to the Bayesian posterior probability of the SNP classification. These studies showed that any typing or profiling method based on binary data requires an accuracy of <2-3% error for each datapoint (in our case SNPs) to classify the isolates to the correct allelic profile in 90% of the cases. The classification error for our experimental data was 3.2% (after removing 5 high error SNPs). We therefore conclude that SNE microarrays are promising for future high-throughput typing of bacteria.

Triclosan and Antimicrobial Resistance in Bacteria: An Overview

Triclosan is a widely used biocide that is considered as an effective antimicrobial agent against different microorganisms. It is included in many contemporary consumer and personal health-care products, like oral and dermal products, but also in household items, including plastics and textiles. At bactericidal concentrations, triclosan appears to act upon multiple nonspecific targets, causing disruption of bacterial cell wall functions, while at sublethal concentrations, triclosan affects specific targets. During the 1990s, bacterial isolates with reduced susceptibility to triclosan were produced in laboratory experiments by repeated exposure to sublethal concentrations of the agent. Since 2000, a number of studies have verified the occurrence of triclosan resistance amongst dermal, intestinal, and environmental microorganisms, including some of clinical relevance. Of major concern is the possibility that triclosan resistance may contribute to reduced susceptibility to clinically important antimicrobials, due to either cross-resistance or co-resistance mechanisms. Although the number of studies elucidating the association between triclosan resistance and resistance to other antimicrobials in clinical isolates has been limited, recent laboratory studies have confirmed the potential for such a link in Escherichia coli and Salmonella enterica. Thus, widespread use of triclosan may represent a potential public health risk in regard to development of concomitant resistance to clinically important antimicrobials.

Deletion of pT181-like sequence in an smr-encoding mosaic plasmid harboured by a persistent bovine Staphylococcus warneri strain

OBJECTIVES

The aim was to study the persistence and characteristics of Staphylococcus warneri strains resistant to quaternary ammonium compounds (QACs), including sequencing and analysis of two plasmids proved to carry the smr gene.

METHODS

During a 3.5 year period quarter milk samples were collected on three occasions from all lactating cows in a dairy herd. The samples were screened with regard to QAC-resistant bacteria using a selective medium. Thirty randomly selected QAC-resistant S. warneri were typed by PFGE and subjected to plasmid isolation and analysis followed by gene detection using PCR. Two smr-containing plasmids in S. warneri isolates were sequenced.

RESULTS

All isolates from the initial collection of quarter milk contained smr residing on a 5.8 kb plasmid (pSW174), which contained regions with high similarities to various plasmids, including pT181, pSK108 and pPI-2. The pT181-like sequence was flanked by 148 bp direct repeats, denoted ISLE49, with high similarity to previously reported sequences of approximately 148 bp, including ISLE39 flanking the insertion sequence IS257 in methicillin-resistant Staphylococcus aureus. All isolates from subsequent collections of quarter milk harboured a smaller smr-containing plasmid (pSW49). Sequence analyses revealed pSW49 (3552 bp) to be an in-part deleted version of pSW174 (5767 bp).

CONCLUSIONS

The IS-associated elements found in this study may have a wider role in the integration and excision of DNA sequences in staphylococci than previously reported. The mosaic plasmid structure based on genetic elements of various origins contributes to further knowledge on the flexibility of smr-encoding plasmids.

Widespread distribution of disinfectant resistance genes among staphylococci of bovine and caprine origin in Norway

We demonstrate here a widespread distribution of genes mediating efflux-based resistance to quaternary ammonium compounds (QACs) in staphylococci from unpasteurized milk from 127 dairy cattle herds and 70 dairy goat herds. QAC resistance genes were identified in 21% of the cattle herds (qacA/B, smr, qacG, and qacJ) and in 10% of the goat herds (qacA/B and smr). Further examination of 42 QAC-resistant bovine and caprine isolates revealed the following genes: qacA/B (12 isolates) was present in four different species of coagulase-negative staphylococci (CoNS), smr (27 isolates) was detected in eight different CoNS species and in Staphylococcus aureus on a previously reported plasmid (pNVH99), qacG (two isolates) was detected on two plasmids (pST94-like) in Staphylococcus cohnii and Staphylococcus warneri, and qacJ (two isolates) was found in Staphylococcus hominis and Staphylococcus delphini on a plasmid (pNVH01) previously found in equine staphylococci. Isolation of indistinguishable pulsed-field gel electrophoresis (PFGE) CoNS types from tank milk and mammary quarter milk samples in a dairy cattle herd suggested that these QAC-resistant staphylococci were of intramammary origin. Indistinguishable or closely related PFGE types of bovine QAC-resistant CoNS were observed in different herds. One particular bovine S. warneri PFGE type was isolated repeatedly from samples collected during a 30-month period in a herd, showing long-term persistence. In conclusion, it seems that the widespread distribution of staphylococci carrying QAC resistance genes in Norwegian dairy cattle and goat herds is the result of both the intra- and interspecies spread of QAC resistance plasmids and the clonal spread of QAC-resistant strains.

Molecular epidemiology of Salmonella spp. isolates from gulls, fish-meal factories, feed factories, animals and humans in Norway based on pulsed-field gel electrophoresis

The molecular epidemiology of 98 isolates of Salmonella serovar Agona (n = 27), S. Montevideo (n = 42) and S. Senftenberg (n = 29) from wild-living gulls, fish-meal factories, feed factories, humans and domestic animals was investigated using pulsed-field gel electrophoresis (PFGE) and computerized numerical analysis. Two of the S. Agona profiles were identified both in gulls and in two of the factories. In addition, one of these profiles was detected in two infected poultry farms. Two of the S. Montevideo profiles were also identified both in gulls and in two of the factories, and one of these profiles was observed in a human isolate. Four factories shared an identical S. Senftenberg profile. The S. Senftenberg profile found in gulls was not identified in any other source investigated. The presence of isolates with identical PFGE profiles indicates potential epidemiological links between different factories, as well as between gulls and factories.

Molecular epidemiology and disinfectant susceptibility of Listeria monocytogenes from meat processing plants and human infections

We have investigated the molecular epidemiology of Listeria monocytogenes from the meat processing industry producing cold cuts and from cases of human listeriosis by discriminative pulsed-field gel electrophoresis (PFGE). A subset of the isolates was also investigated for susceptibility to a disinfectant based on quaternary ammonium compounds (QAC) frequently used in the meat processing industry. The purpose of this investigation was to obtain knowledge of sources, routes of contamination and genetic types of L. monocytogenes present along the production line in the meat processing industry, and to compare meat industry isolates and human isolates. Of the 222 isolates from four meat-processing plants, 200 were from two plants responsible for nearly 50% of the production of cold cuts in the Norwegian market. The strain collection included historical routinely sampled isolates (1989-2002) and isolates systematically sampled through a one year period (November 2001 to November 2002) from fresh meat and production environments in three plants. No isolates were obtained in samples from employees (throat, faeces). Human strains included all available reported isolates from Norwegian patients in selected time periods. The L. monocytogenes PFGE data showed a large genetic heterogeneity, with isolates separated into two genetic lineages and further subdivided into 56 different PFGE profiles. Certain profiles were observed on both sides of production (before and after heat treatment) indicating contamination of end products by fresh meat or fresh meat environments. While fresh meat isolates almost exclusively grouped within lineage I, isolates from end products showed a more balanced distribution between lineages I and II. Ten profiles were common among isolates from human and meat industry. Typing of human isolates identified a previously unrecognised outbreak. Generally, a higher QAC resistance incidence was observed among isolates from the meat processing industry than among human isolates although large plant to plant differences were indicated. No correlation between resistance and PFGE profile or resistance and persistence was observed.

Outbreak of Salmonella Livingstone infection in Norway and Sweden due to contaminated processed fish products

In Europe, the number of reported sporadic human cases of Salmonella Livingstone infection is low, and outbreaks are rare. We report the largest S. Livingstone outbreak described in the literature having an identified source of infection. In February 2001, an increased incidence of infection caused by S. Livingstone was observed in Norway and Sweden. By July 2001, 44 cases were notified in Norway and 16 in Sweden. The median age was 63 years, and 40 were women. There were three deaths, and 22 patients were hospitalized. Based on standardized questionnaires and retrospective studies of S. Livingstone strains in Norway and Sweden, food items with egg powder were suspected, and S. Livingstone was subsequently recovered from a processed fish product at the retail level. Analysis by pulsed-field gel electrophoresis documented that isolates from the fish product belonged to the same clone as the outbreak strain.

Prevalence and characterization of integrons in blood culture Enterobacteriaceae and gastrointestinal Escherichia coli in Norway and reporting of a novel class 1 integron-located lincosamide resistance gene

Background

Class 1 integrons contain genetic elements for site-specific recombination, capture and mobilization of resistance genes. Studies investigating the prevalence, distribution and types of integron located resistance genes are important for surveillance of antimicrobial resistance and to understand resistance development at the molecular level.

Methods

We determined the prevalence and genetic content of class 1 integrons in Enterobacteriaceae (strain collection 1, n = 192) and E. coli (strain collection 2, n = 53) from bloodstream infections in patients from six Norwegian hospitals by molecular techniques. Class 1 integrons were also characterized in 54 randomly selected multiresistant E. coli isolates from gastrointestinal human infections (strain collection 3).

Results

Class 1 integrons were present in 10.9% of the Enterobacteriaceae blood culture isolates of collection 1, all but one (S. Typhi) being E. coli. Data indicated variations in class 1 integron prevalence between hospitals. Class 1 integrons were present in 37% and 34% of the resistant blood culture isolates (collection 1 and 2, respectively) and in 42% of the resistant gastrointestinal E. coli. We detected a total of 10 distinct integron cassette PCR amplicons that varied in size between 0.15 kb and 2.2 kb and contained between zero and three resistance genes. Cassettes encoding resistance to trimethoprim and aminoglycosides were most common. We identified and characterized a novel plasmid-located integron with a cassette-bound novel gene (linF) located downstream of an aadA2 gene cassette. The linF gene encoded a putative 273 aa lincosamide nucleotidyltransferase resistance protein and conferred resistance to lincomycin and clindamycin. The deduced LinF amino acid sequence displayed approximately 35% identity to the Enterococcus faecium and Enterococcus faecalis nucleotidyl transferases encoded by linB and linB'

Conclusions

The present study demonstrated an overall low and stable prevalence of class 1 integron gene cassettes in clinical Enterobacteriaceae and E. coli isolates in Norway. Characterization of the novel lincosamide resistance gene extends the growing list of class 1 integron gene cassettes that confer resistance to an increasing number of antibiotics.

Molecular epidemiology and population genetics of Salmonella subspecies diarizonae in sheep in Norway and Sweden

Fifty-four isolates of Salmonella enterica subsp. diarizonae (IIIb) in Norway, Sweden, England, the United States, France and Australia were characterized by pulsed-field gel electrophoresis (PFGE). This study focuses on serovar 61:k:1,5,(7) [S. IIIb 61:k:1,5,(7)] isolated from sheep. Digestion of the bacterial DNA with restriction enzyme XhaI yielded 15 distinct PFGE profiles comprising 12-16 fragments in the range 48.5-630.5 kbp. Four different profiles were identified in Norwegian sheep isolates and a single profile in Swedish isolates. The spatial and temporal distribution of profiles is discussed.