Dissemination of carbapenemase-producing Enterobacteriaceae and associated resistance determinants through global food systems.

Antimicrobial agents are a critical component of modern healthcare systems, fulfilling a core function in patient care and improving individual patient outcomes and consequently overall public health. However, the efficacy of antimicrobial interventions is being consistently eroded by the emergence and dissemination of various antimicrobial resistance (AMR) mechanisms. One highly valued class of antimicrobial compounds is carbapenems, which retain efficacy in treating most multidrug-resistant infections and are considered "last line" agents. Therefore, recent trends in proliferation of carbapenem resistance (CR) via dissemination of carbapenemase-encoding genes among members of the Enterobacteriaceae family pose a significant threat to public health. While much of the focus relating to this has been on nosocomial environments, community-acquired carbapenemase-producing Enterobacteriaceae (CPE) infections and their associated transmission routes are less well studied. Among these community-associated vectors, the role of food chains and contaminated foods is important, since Enterobacteriaceae occupy niches within these settings. This review examines foodborne CPE transmission by exploring how interactions within and between food, the food chain, and agriculture not only promote and disseminate CPE, but also create reservoirs of mobile genetic elements that may lead to further carbapenemase gene proliferation both within and between microbial communities. Additionally, recent developments regarding the global occurrence and molecular epidemiology of CPEs in food chains will be reviewed.

Multiplex loop-mediated isothermal amplification-based lateral flow dipstick for simultaneous detection of 3 food-borne pathogens in powdered infant formula.

In this study, we established a rapid, simple, and sensitive method for visual and point-of-care detection of Salmonella spp., Cronobacter spp., and Staphylococcus aureus in powdered infant formula (PIF) based on multiplex loop-mediated isothermal amplification (mLAMP) combined with lateral flow dipstick (LFD). Three different species-specific target genes, siiA of Salmonella spp., internal transcribed space (ITS) of Cronobacter spp., and nuc of Staph. aureus, were applied in the mLAMP with biotin-, digoxin-, and Texas Red-modified forward inner primers and fluorescein isothiocyanate (FITC)-modified backward inner primers. After mLAMP, a large number of modified amplicons were detected with LFD; one end of the amplicon was conjugated to the anti-FITC antibody on gold nanoparticles and the other end to streptavidin (anti-digoxin or anti-Texas Red antibody) on test lines. Visual inspection of the device relies on the presence of a red band formed by accumulation of sandwich composites. The detection limits of this mLAMP-LFD assay for Salmonella spp., Cronobacter spp., and Staph. aureus in PIF without enrichment were 4.2, 2.6, and 3.4 cfu/g, respectively. The whole method can be completed in less than 1 h. Thus, mLAMP-LFD is a rapid and efficient method for simultaneously detecting Salmonella spp., Cronobacter spp., and Staph. aureus in PIF.

Typing and evaluating heat resistance of Bacillus cereus sensu stricto isolated from the processing environment of powdered infant formula.

Bacillus cereus sensu lato is one of the most harmful bacterial groups affecting the quality and safety of powdered infant formula (PIF). In this study, samples were collected from the raw materials and processing environments of PIF. A total of 84 isolates were identified as Bacillus cereus sensu stricto (B. cereus s. s.) by 16S rRNA analysis, molecular typing technology, and physiological and biochemical tests. The 84 B. cereus s. s. strains were assigned to panC group II, group III, and group IV. Then, the 7 housekeeping genes glpF, gmk, ilvD, pta, pur, pycA, and tpi were selected for multilocus sequence typing. Results showed that the 84 isolates were clustered into 24 sequence types (ST), and 14 novel ST were detected. Among the 24 ST, ST999 (19/84, 22.62%) and ST1343 (13/84, 15.48%) predominated. The correlation between processing areas and ST showed that the processing environments of the production and packing areas were the most susceptible to contamination by B. cereus s. s. Spores of these ST showed different heat resistance phenotypes evaluated by the analysis of DT (time in minutes of spore decimal reduction at each temperature) and Z values (temperature increase required to reduce the DT value to one-tenth of the original). Spores from group III according to panC gene analysis were the most heat resistant. These findings will help us to better understand B. cereus s. s. contamination and control in PIF processing environments.

Vibrational spectroscopy combined with transcriptomic analysis for investigation of bacterial responses towards acid stress.

The ability of bacteria to tolerate acid stress plays an important role in their growth and survival. In particular, aciduric bacteria have several survival systems that prevent cell damage from acid stress. In this study, the effect of the bacterial stress induced by pre-adaptation at different pH values on the cellular macromolecules of Lactobacillus plantarum was investigated using Raman spectroscopy and Fourier transform infrared spectroscopy. The expression of key genes was also quantified to provide understanding of the transcriptional response of the cells to lethal acid stress conditions. Principal component analysis of the spectra exhibited marked differences in the spectral regions associated with carbohydrates, lipids, proteins, and nucleic acids for all acid-stressed cells compared to those of untreated control cells. The changes in spectroscopic and transcriptomic profiles that were observed revealed alterations in bacterial cell wall composition after acid treatment. The results suggest the existence of a complex bacterial stress response in which modifications of cellular compounds from pre-adaption at low pH are involved. This study demonstrates the potential application of vibrational spectroscopy techniques to discriminate between intact and injured bacterial cells as well as to study their stress responses after exposure to acid environments during food processing.

Silver nanoparticles: A novel antibacterial agent for control of Cronobacter sakazakii.

Silver nanoparticles (AgNP) have been widely applied because of their broad spectrum of antimicrobial activities against bacteria, fungi, and viruses. However, little research has been done to evaluate their effects on Cronobacter sakazakii, an opportunistic pathogen usually infecting infants and having a high fatality rate. The aims of this work were to investigate the antibacterial property of novel, synthesized, positively charged silver nanoparticles against C. sakazakii and to discuss the potential antibacterial mechanisms involved. In this study, the spherical and face-centered cubic silver nanoparticles had a mean particle size of 31.2 nm and were synthesized by reducing Ag+ using citrate and dispersed by glycerol and polyvinylpyrrolidone (PVP) under alkaline conditions. Minimum inhibitory concentrations (MIC) and inhibition zone tests showed that the AgNP exhibited strong antibacterial activity against 4 tested C. sakazakii strains with mean MIC of 62.5 to 125 mg/L and average inhibition zone diameters of 13.8 to 16.3 mm. Silver nanoparticles caused cell membrane injury accompanied by adsorption of AgNP onto the cell surface, as shown by changes in cell morphology, cell membrane hyperpolarization, and accelerated leakage of intracellular reducing sugars and proteins outward from the cytoplasm. In addition, dysfunction of the respiratory chain was induced after treatment with AgNP, which was supported by a decrease in intracellular ATP and inhibition of related dehydrogenases. This research indicates that AgNP could be a novel and efficient antibacterial agent to control C. sakazakii contamination in environments producing powdered infant formulas from milk.

Characterization of Staphylococcus aureus isolates from raw milk sources in Victoria, Australia.

BACKGROUND: Highly pathogenic strains of Staphylococcus aureus can cause disease in both humans and animals. In animal species, including ruminants, S. aureus may cause severe or sub-clinical mastitis. Dairy animals with mastitis frequently shed S. aureus into the milk supply which can lead to food poisoning in humans. The aim of this study was to use genotypic and immunological methods to characterize S. aureus isolates from milk-related samples collected from 7 dairy farms across Victoria. RESULTS: A total of 30 S. aureus isolates were collected from milk and milk filter samples from 3 bovine, 3 caprine and 1 ovine dairy farms across Victoria, Australia. Pulsed Field Gel Electrophoresis (PFGE) identified 11 distinct pulsotypes among isolates; all caprine and ovine isolates shared greater than 80 % similarity regardless of source. Conversely, bovine isolates showed higher diversity. Multi-Locus Sequence Typing (MLST) identified 5 different sequence types (STs) among bovine isolates, associated with human or ruminant lineages. All caprine and ovine isolates were ST133, or a single allele variant of ST133. Two new novel STs were identified among isolates in this study (ST3183 and ST3184). With the exception of these 2 new STs, eBURST analysis predicted all other STs to be founding members of their associated clonal complexes (CCs). Analysis of genetic markers revealed a diverse range of classical staphylococcal enterotoxins (SE) among isolates, with 11 different SEs identified among bovine isolates, compared with just 2 among caprine and ovine isolates. None of the isolates contained mecA, or were resistant to oxacillin. The only antibiotic resistance identified was that of a single isolate resistant to penicillin; this isolate also contained the penicillin resistance gene blaZ. Production of SE was observed at 16 °C and/or 37 °C in milk, however no SE production was detected at 12 °C. CONCLUSION: Although this study characterized a limited number of isolates, bovine-associated isolates showed higher genetic diversity than their caprine or ovine counterparts. This was also reflected in a more diverse SE repertoire among bovine isolates. Very little antibiotic resistance was identified among isolates in this study. These results suggest maintaining the milk cold chain will minimise any risk from SE production and highlights the need to prevent temperature abuse.

Seasonal occurrence and molecular diversity of clostridia species spores along cheesemaking streams of 5 commercial dairy plants.

Five commercial dairy plants were monitored over a 17-mo period to determine the seasonal occurrence of Clostridium spores in streams from the cheesemaking process. Every 2 mo, samples of raw milk (RM), separated cream (SC), pasteurized and standardized vat milk (PSVM), PSVM + lysozyme (PSVM+L), and manufactured cheese aged for 60 to 90 d were processed for analysis. Molecular diversity of the main species identified was determined using repetitive element palindromic PCR. The mean anaerobic spore counts (µ ± SE) were 3.16±0.054, 3.00±0.054, 2.89±0.059, and 2.03±0.054 log10 most probable number/L for RM, PSVM, PSVM+L, and SC, respectively. Although spore counts did not differ between dairy plants, seasonal variation was observed; spore counts of RM, PSVM, and PSVM+L were higher during winter (June to August) and summer (December to February) months, but no seasonal variation was seen in SC counts. The most frequently isolated species was Clostridium tyrobutyricum, ranging from 50 to 58.3% of isolates from milk and cream samples. Clostridium sporogenes was the second most common species identified (16.7-21.1%); Clostridium beijerinckii and Clostridium butyricum were also found, although at lower prevalence (7.9-13.2%). Analysis of the C. tyrobutyricum and C. sporogenes population structure through repetitive element palindromic PCR indicated a high diversity, with unique isolates found in each positive sample. The occurrence of Clostridia spores in incoming streams to cheesemaking was most prominent in the winter and summer seasons, with higher prevalence of C. tyrobutyricum in the months of June and August.

Characterization of the spore-forming Bacillus cereus sensu lato group and Clostridium perfringens bacteria isolated from the Australian dairy farm environment.

BACKGROUND: The Bacillus cereus sensu lato group and Clostridium perfringens are spore-forming bacteria often associated with food spoilage and which can cause emetic and diarrheal syndromes in humans and ruminants. This study characterised the phenotypes and genotypes of 50 Bacillus cereus s. l. isolates and 26 Clostridium perfringens isolates from dairy farms environments in Victoria, Australia. RESULTS: Five of the seven B. cereus s. l. species were isolated, and analysis of the population diversity using Pulsed-Field Gel Electrophoresis (PFGE) suggested that the populations are largely distinct to each farm. Enterotoxin production by representative isolates of each B. cereus s. l. species identified was typically found to be reduced in milk, compared with broth. Among the C. perfringens isolates, only two different toxin types were identified, type A and D. Bovine and ovine farms harbored only type A whereas both type A and D were found on two of the three caprine farms. CONCLUSIONS: This study showed that the B. cereus s. l. populations on the sampled farms exhibit a broad diversity in both species and genotypes. The risk of toxin-induced diarrheal illness through consumption of contaminated milk may be limited, in comparison with other food matrices. Type A strains of C. perfringens were the most abundant on dairy farms in Victoria, however type D may be of concern on caprine farms as it can cause enterotoxemia in goats.

Control of Listeria species food safety at a poultry food production facility.

Surveillance and control of food-borne human pathogens, such as Listeria monocytogenes, is a critical aspect of modern food safety programs at food production facilities. This study evaluated contamination patterns of Listeria species at a poultry food production facility, and evaluated the efficacy of procedures to control the contamination and transfer of the bacteria throughout the plant. The presence of Listeria species was studied along the production chain, including raw ingredients, food-contact, non-food-contact surfaces, and finished product. All isolates were sub-typed by pulsed-field gel electrophoresis (PFGE) to identify possible entry points for Listeria species into the production chain, as well as identifying possible transfer routes through the facility. The efficacy of selected in-house sanitizers against a sub-set of the isolates was evaluated. Of the 77 different PFGE-types identified, 10 were found among two or more of the five categories/areas (ingredients, food preparation, cooking and packing, bulk packing, and product), indicating potential transfer routes at the facility. One of the six sanitizers used was identified as unsuitable for control of Listeria species. Combining PFGE data, together with information on isolate location and timeframe, facilitated identification of a persistent Listeria species contamination that had colonized the facility, along with others that were transient.

Phylogenetic profiles of in-house microflora in drains at a food production facility: comparison and biocontrol implications of Listeria-positive and -negative bacterial populations.

Listeria species experience complex interactions with other microorganisms, which may promote growth and colonization of the organism in local environments or negatively affect them. This study investigated the microbial community at a food production facility, examining interactions between Listeria and the associated microbiome. Listeria species can be transferred between zones in the production environment by individuals or equipment, and drains may act as a reservoir for the organism, reflecting the microbial flora potentially in the production environment. Drains that were colonized by Listeria species and those determined to be free of Listeria were examined. In each case, 16S rRNA gene analysis was performed using the PhyloChip platform. Some general similarities in bacterial population structure were observed when Listeria-negative and -positive drain communities were compared, with some distinct differences also noted. These included increased populations of the genera Prevotella and Janthinobacterium associated with the absence of Listeria species, whereas Enterococcus and Rhodococcus were in higher abundance in drains colonized by Listeria species. Based on these results, a selection of bacterial species were grown in coculture biofilm with a Listeria monocytogenes strain identified as having colonized a drain at the facility. Mixed-species biofilm experiments showed that Janthinobacterium inhibited attachment and subsequent biofilm formation of L. monocytogenes; however, Enterococcus gallinarum significantly increased it. The results of this study suggest the microbial community in food processing facilities can impact the colonization of Listeria species and that influencing the microbiome in favor of antilisterial species may reduce the colonization of Listeria species and limit the likelihood of product/process contamination.

Prevalence and characterization of foodborne pathogens from Australian dairy farm environments.

The ability of foodborne pathogens to gain entry into food supply systems remains an ongoing concern. In dairy products, raw milk acts as a major vehicle for this transfer; however, the sources of pathogenic bacteria that contaminate raw milk are often not clear, and environmental sources of contamination or the animals themselves may contribute to the transfer. This survey examined the occurrence of 9 foodborne pathogens in raw milk and environments of 7 dairy farms (3 bovine, 3 caprine, and 1 ovine farm) in summer and autumn, in Victoria, Australia. A total of 120 samples were taken from sampling points common to dairy farms, including pasture, soil, feed, water sources, animal feces, raw milk, and milk filters. The prevalence of the Bacillus cereus group, Campylobacter, Clostridium perfringens, Cronobacter, Shiga-toxigenic Escherichia coli, Listeria, Salmonella, coagulase-positive staphylococci (CPS), and Yersinia enterocolitica across the farms was investigated. The 2 most prevalent bacteria, which were detected on all farms, were the B. cereus group, isolated from 41% of samples, followed by Cl. perfringens, which was isolated from 38% of samples. The highest occurrence of any pathogen was the B. cereus group in soil, present in 93% of samples tested. Fecal samples showed the highest diversity of pathogens, containing 7 of the 9 pathogens tested. Salmonella was isolated from 1 bovine farm, although it was found in multiple samples on both visits. Out of the 14 occurrences where any pathogen was detected in milk filters, only 5 (36%) of the corresponding raw milk samples collected at the same time were positive for the same pathogen. All of the CPS were Staphylococcus aureus, and were found in raw milk or milk filter samples from 6 of the 7 farms, but not in other sample types. Pathogenic Listeria species were detected on 3 of the 7 farms, and included 4 L. ivanovii-positive samples, and 1 L. monocytogenes-positive water sample. Shiga-toxigenic Escherichia coli were identified in fecal samples from 3 of the 7 farms and in a single raw milk sample. Cronobacter species were identified on 4 of the 7 farms, predominantly in feed samples. No Y. enterocolitica was detected. Results of this study demonstrate high standards of pathogen safety across the 7 farms, with a low incidence of pathogens detected in raw milk samples. Monitoring feed contamination levels may help control the spread of bacterial species such as Cl. perfringens and B. cereus through the farm environment, which is a natural reservoir for these organisms.

Draft genome sequence of Streptomyces poriferorum RTGN2, a bacterial endophyte isolated from Alnus glutinosa root nodules.

Herein is reported the draft genome sequence of Streptomyces poriferum RTGN2, a bacterial isolate of Alnus glutinosa root nodules, collected from Saltwell Park, Gateshead, United Kingdom. The assembly is 9.5 Mbp in size, composed of 187 contigs, with a N50 of 189,630 bp, presenting a GC content of 71.2%.

Draft genome sequences of five Mycobacterium strains, isolated from Alnus glutinosa root nodules.

Mycobacterium is a clinically relevant genus of bacteria, with this paper reporting draft genomes of five Mycobacterium strains derived from Alnus glutinosa root nodules. The genome sizes of the isolates ranged from 6.1 to 6.9 Mbp, composed of 22-59 contigs. The N50 values ranged from 303,875 to 865,751 bp, presenting a GC% of 66.07%-66.96%.

Draft genome sequence of Amycolatopsis camponoti RTGN1, a bacterial endophyte isolated from Alnus glutinosa root nodules.

Here, we report the draft genome sequence of Amycolatopsis camponoti RTGN1, a bacterial endophyte of Alnus glutinosa root nodules, collected from Saltwell Park, United Kingdom. The genome is 11.9 Mbp in size, composed of 147 contigs, with an N50 of 179,211 bp and presenting a GC content of 70.9%.

Draft genome sequences of two Micromonospora strains isolated from the root nodules of Alnus glutinosa.

In this paper, the draft genomes of Micromonospora RTGN7 and RTP1Z1, derived from Alnus glutinosa root nodules, are reported. The assembly of RTGN7 is 6.6 Mbp, composed of 59 contigs, with an N50 of 321,872. RTP1Z1's assembly is 6.3 Mbp, composed of 151 contigs, with an N50 of 76,442 bp.

Profiling the Enterobacterales community isolated from retail foods in England.

Enterobacterales include foodborne pathogens of importance to public health, and are often targeted in food surveillance programmes as both safety and hygiene indicators. Furthermore, Enterobacterales are important in the context of antimicrobial resistance dissemination, also impacting infection treatment efficacy. In this study, the prevalence and characteristics of Enterobacterales in UK retail foods were examined. From 110 retail food samples, 253 Enterobacterales were recovered, with 16S rRNA sequencing revealing a diverse species community, including enteropathogens; the most common were Proteus mirabilis and Escherichia coli (18% each). Antimicrobial resistance was common, with 160/253 (63%) isolates were resistant to at least 1 antimicrobial. Resistance to all tested antimicrobials was observed. Thirteen percent of isolates were multidrug resistant, including 2 isolates each resistant to 8 or 9 of 9 antimicrobials tested. Klebsiella isolates possessed relatively higher levels of antimicrobial resistance to other species. Hafnia, Kluyvera, and Proteus isolates produced significantly higher biofilm biomass than Klebsiella (p=0.038, 0.028, and 0.042, respectively) or Escherichia (p=0.001, 0.008, and 0.001, respectively). Simultaneous curli fimbriae and cellulose production was noted in 7% of isolates at 37°C, but not at 15°C. This research demonstrates a high diversity of Enterobacterales within UK retail foods, alongside notable antimicrobial resistance phenotypes in enteropathogenic species, highlighting the need for effective surveillance and interventions.

Synergistic nanocoating with layer-by-layer functionalized PCL membranes enhanced by manuka honey and essential oils for advanced wound healing.

Chronic wounds represent a significant global health concern, statistically impacting 1-2% of the population in developed countries throughout their lifetimes. These wounds cause considerable discomfort for patients and necessitate substantial expenditures of time and resources for treatment. Among the emerging therapeutic approaches, medicated dressings incorporating bioactive molecules, including natural compounds, are particularly promising. Hence, the objective of this study was to develop novel antimicrobial dressings for wound treatment. Specifically, polycaprolactone membranes were manufactured using the electrospinning technique and subsequently coated with natural polyelectrolytes (chitosan as a polycation and a mixture of manuka honey with essential oils nanoemulsions as a polyanion) employing the Layer-by-Layer assembly technique. Physico-chemical and morphological characterization was conducted through QCM-D, FTIR-ATR, XPS, and SEM analyses. The results from SEM and QCM-D demonstrated successful layer deposition and coating formation. Furthermore, FTIR-ATR and XPS analyses distinguished among different coating compositions. The coated membranes were tested in the presence of fibroblast cells, demonstrating biocompatibility and expression of genes coding for VEGF, COL1, and TGF-ß1, which are associated with the healing process (assessed through RT-qPCR analysis). Finally, the membranes exhibited excellent antibacterial activity against both Staphylococcus aureus and Pseudomonas aeruginosa, with higher bacterial strain inhibition observed when cinnamon essential oil nanoemulsion was incorporated. Taken together, these results demonstrate the potential application of nanocoated membranes for biomedical applications, such as wound healing.

Genome characteristics of the optrA-positive Clostridium perfringens strain QHY-2 carrying a novel plasmid type.

Clostridium perfringens is a bacterial species of importance to both public and animal health. The gene optrA is the first gene that confers resistance to the tedizolid, a last-resort antimicrobial agent in human medicine. Herein, we whole-genome sequenced and analyzed one optrA-positive C. perfringens strain QHY-2 from Tibetan sheep in Qinghai province and identified one optrA plasmid pQHY-2. The plasmid shared similar structure with the optrA-positive plasmids p2C45 and p21-D-5b previously identified in C. perfringens, demonstrating the potential horizontal transmission of the optrA plasmids among C. perfringens strains. Annotation of the optrA-positive plasmids showed optrA and erm(A) located on a segment flanked by IS element IS1216E, and fexA, optrA, and erm(A) located on a segment flanked by IS element ISVlu1, which revealed the possible dissemination mechanism. Additionally, a Tn6218-like transposon carrying aac(6')-aph(2″) and erm(B) was also detected on pQHY-2, demonstrating the transposition of Tn6218 and spread of antibiotic resistance among Clostridium bacteria. Molecular analysis indicated the optrA-positive plasmids belonged to a plasmid type distinct from the pCW3-like plasmids, pCP13-like plasmids, or pIP404-like plasmids. Further structure analysis showed they might be formed by inserting segments into plasmid pCPCPI53k-r1_1, which coexist with two pCW3-like plasmids and one pCP13-like plasmid in C. perfringens strain CPI 53k-r1 isolated from a healthy human in Finland. IMPORTANCE Antimicrobial resistance is now a global concern posing threats to food safety and public health. The pCW3-like plasmids can encode several main toxin genes and three antibiotic resistance genes (ARGs), including tetA(P), tetB(P), and erm(B), which used to be considered as the main carrier of ARGs in Clostridium perfringens. In this study, we found the optrA plasmids, which belonged to a novel plasmid type, could also harbor many other ARGs, indicating this type of plasmid might be the potential repository of ARGs in C. perfringens. Additionally, this type of plasmid could coexist with the pCW3-like plasmids and pCP13-like plasmids that encoded toxin genes associated with gastrointestinal diseases, which showed the potential threat to public health.

Clostridium perfringens associated with dairy farm systems show diverse genotypes.

Clostridium perfringens is a bacterial species of importance to both public and animal health. Frequently found in food system environments, it presents a risk to food animal health such as dairy herds, and may cross contaminate associated ingredients or food products, with potential to cause sporadic and outbreaks of disease in human populations, including gastroenteric illness. In this study, we characterized C. perfringens isolated from bovine, caprine, and ovine dairy farm systems (n = 8, 11 and 4, respectively). Isolates were phenotypically screened for antimicrobial sensitivity profiling, and subjected to whole genome sequencing to elucidate related genetic markers, as well as examine virulence gene markers, mobile genetic elements, and other features. Both toxin type A and type D isolates were identified (78 % and 22 % of isolates, respectively), including 20 novel sequence types. Resistance to clindamycin was most prevalent among antibiotics screened (30 %), followed by erythromycin (13 %), then penicillin and tetracycline (4 %), although an additional 3 isolates were non-susceptible to tetracycline. Most isolates harboured plasmids, which mobilised virulence markers such as etx, cpb2, and resistance markers tetA(P), tetB(P), and erm(Q), on conjugative plasmids. The presence of type D isolates on caprine farms emphasizes the need for control efforts to prevent infection and potential enterotoxemia. Clostridium perfringens enterotoxin (cpe) was not identified, suggesting lower risk of gastrointestinal illness from contaminated foods, the presence of other virulence and antimicrobial resistance markers suggests farm hygiene remains an important consideration to help ensure food safety of associated dairy foods produced.

Physiological and transcriptional characterization of persistent and nonpersistent Listeria monocytogenes isolates.

This study aimed to characterize physiological differences between persistent and presumed nonpersistent Listeria monocytogenes strains isolated at processing facilities and to investigate the molecular basis for this by transcriptomic sequencing. Full metabolic profiles of two strains, one persistent and one nonpersistent, were initially screened using Biolog's Phenotype MicroArray (PM) technology. Based on these results, in which major differences from selected antimicrobial agents were detected, another persistent strain and two nonpersistent strains were characterized using two antimicrobial PMs. Resistance to quaternary ammonium compounds (QACs) was shown to be higher among persistent strains. Growth of persistent and nonpersistent strains in various concentrations of the QACs benzethonium chloride (BZT) and cetylpyridinium chloride (CPC) was determined. Transcriptomic sequencing of a persistent and a presumed nonpersistent strain was performed to compare gene expression among these strains in the presence and absence of BZT. Two strains, designated "frequent persisters" because they were the most frequently isolated at the processing facility, showed overall higher resistance to QACs. Transcriptome analysis showed that BZT induced a complex peptidoglycan (PG) biosynthesis response, which may play a key role in BZT resistance. Comparison of persistent and nonpersistent strains indicated that transcription of many genes was upregulated among persistent strains. This included three gene operons: pdu, cob-cbi, and eut. These genes may play a role in the persistence of L. monocytogenes outside the human host.