Comparative genomic analysis reveals high intra-serovar plasticity within Salmonella Napoli isolated in 2005-2017.

BACKGROUND: Salmonella enterica subsp. enterica serovar Napoli (S. Napoli) is among the top serovars causing human infections in Italy, although it is relatively uncommon in other European countries; it is mainly isolated from humans and the environment, but neither the reservoir nor its route of infection are clearly defined. This serovar is characterized by high genomic diversity, and molecular evidences revealed important similarities with typhoidal serovars. RESULTS: 179 S. Napoli genomes as well as 239 genomes of typhoidal and non-typhoidal serovars were analyzed in a comparative genomic study. Phylogenetic analysis and draft genome characterization in terms of Multi Locus Sequence Typing (MLST), plasmid replicons, Salmonella Pathogenicity Islands (SPIs), antimicrobial resistance genes (ARGs), phages, biocide and metal-tolerance genes confirm the high genetic variability of S. Napoli, also revealing a within-serovar phylogenetic structure more complex than previously known. Our work also confirms genomic similarity of S. Napoli to typhoidal serovars (S. Typhi and S. Paratyphi A), with S. Napoli samples clustering primarily according to ST, each being characterized by specific genomic traits. Moreover, two major subclades of S. Napoli can be clearly identified, with ST-474 being biphyletic. All STs span among isolation sources and years of isolation, highlighting the challenge this serovar poses to define its epidemiology and evolution. Altogether, S. Napoli strains carry less SPIs and less ARGs than other non-typhoidal serovars and seldom acquire plasmids. However, we here report the second case of an extended-spectrum ß-lactamases (ESBLs) producing S. Napoli strain and the first cases of multidrug resistant (MDR) S. Napoli strains, all isolated from humans. CONCLUSIONS: Our results provide evidence of genomic plasticity of S. Napoli, highlighting genomic similarity with typhoidal serovars and genomic features typical of non-typhoidal serovars, supporting the possibility of survival in different niches, both enteric and non-enteric. Presence of horizontally acquired ARGs and MDR profiles rises concerns regarding possible selective pressure exerted by human environment on this pathogen.

Molecular and Epidemiologic Analysis of Reemergent Salmonella enterica Serovar Napoli, Italy, 2011-2015.

Human infections with Salmonella enterica serovar Napoli are uncommon in Europe. However, these infections represented 5.9% of salmonellosis cases in Italy during 2014-2015. The source of infection is unknown. We analyzed surveillance data and compared strain genetic similarities and found that contaminated vegetables and surface water are probable sources of human infection.

Outbreak of unusual Salmonella enterica serovar Typhimurium monophasic variant 1,4 [5],12:i:-, Italy, June 2013 to September 2014.

Monophasic variant of Salmonella enterica subspecies enterica serovar Typhimurium (monophasic S. Typhimurium), with antigenic structure 1,4,[5],12:i:-, appears to be of increasing importance in Europe. In Italy, monophasic S. Typhimurium represented the third most frequent Salmonella serovar isolated from human cases between 2004 and 2008. From June 2013 to October 2014, a total of 206 human cases of salmonellosis were identified in Abruzzo region (Central Italy). Obtained clinical isolates characterised showed S. Typhimurium 1,4,[5],12:i:- with sole resistance to nalidixic acid, which had never been observed in Italy in monophasic S. Typhimurium, neither in humans nor in animals or foods. Epidemiological, microbiological and environmental investigations were conducted to try to identify the outbreak source. Cases were interviewed using a standardised questionnaire and microbiological tests were performed on human as well as environmental samples, including samples from fruit and vegetables, pigs, and surface water. Investigation results did not identify the final vehicle of human infection, although a link between the human cases and the contamination of irrigation water channels was suggested.

Molecular and Epidemiological Analysis of a Campylobacter jejuni Outbreak in Northern Italy in November 2013.

Campylobacter spp. is the most common gastrointestinal pathogen worldwide with a very low reported incidence in Italy. In November of 2013, local and national public health authorities investigated an outbreak caused by Campylobacter jejuni among children in a kindergarten in Northern Italy. A case was defined as a child who had diarrhea with a laboratory-confirmed diagnosis of C. jejuni between 11 and 30 November. Stool samples from the kindergarten kitchen staff and environmental samples from the kitchen were examined for enteric pathogens. As food leftovers were not available, the menu logbook of the refectory was reviewed to identify a possible source of the outbreak. C. jejuni strains were tested for antimicrobial susceptibility and subtyped by pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). We identified 20 cases among 247 schoolchildren (attack rate = 8%), all who reported having lunch in the kindergarten. The stools from the kitchen staff as well as the environmental samples were negative for enteric pathogens. The identified outbreak strains (n = 5) were sensitive to all of the antimicrobials tested; the first four strains showed an identical PFGE profile, whereas the fifth strain showed a PFGE pattern similarity of 89%. Using MLST, all five strains were assigned to a single sequence type (ST), ST451 (clonal complex, CC21); this was the first identification of ST and the third reported outbreak of C. jejuni in Italy. Molecular typing confirmed that most of the cases belonged to a clonal cluster supporting the hypothesis of a common source; however, the source was not identified. Due to a delayed start of the investigation, it was not possible to perform any microbiological evaluation of the food consumed.

Comparison between Salmonella enterica Serotype Enteritidis Genotyping Methods and Phage Type.

A quantitative comparison between discriminatory indexes and concordance among multilocus variable-number tandem-repeat analysis (MLVA), pulsed-field gel electrophoresis (PFGE), automated ribotyping, and phage typing has been performed, testing 238 Salmonella enterica serotype Enteritidis isolates not epidemiologically correlated. The results show that MLVA is the best choice, but each typing method provides a piece of information for establishing clonal relationships between the isolates.

An outbreak of extremely drug-resistant Pseudomonas aeruginosa in a tertiary care pediatric hospital in Italy.

BACKGROUND: Extensively drug-resistant Pseudomonas aeruginosa (XDR-PA) isolates are susceptible to only one or two classes of antibiotics. In 2011-2012, we investigated an outbreak of XDR-PA affecting children with onco-hematological diseases. METHODS: Outbreak investigation included ascertainment of cases, tracing of intestinal carriers and environmental surveillance. Contact precautions were adopted for patients with infection or colonization. Isolates were tested for antimicrobial susceptibility; phenotypic confirmation of carbapenemase production was performed, and carbapenemase genes were tested by multiplex polymerase-chain-reaction (PCR). Genotypes were determined by pulsed-field gel electrophoresis (PFGE). RESULTS: XDR-PA was isolated from 27 patients; 12 had bacteremia, 6 other infections and 9 were colonized. Severe neutropenia was significantly associated with bacteremia. Bloodstream-infection mortality rate was 67%. All isolates were resistant to carbapenems, cephalosporins and penicillins + ß-lactamase inhibitors. Isolates were susceptible only to colistin in 22 patients, to colistin and amikacin in 4, and to ciprofloxacin and colistin in 1. PFGE results identified 6 subtypes of a single genotype, associated with clusters of cases, and 4 sporadic genotypes. Two sporadic isolates were metallo-ß-lactamase producers, negative to PCR. All other isolates were metallo-ß-lactamase producers due to the presence of a VIM carbapenemase. Incidence of XDR-PA infections decreased from 0.72 cases/1,000 inpatient-days in March 2011-March 2012, to 0.34/1,000 in April-December 2012, after implementation of active finding of intestinal carriers on all onco-hematological inpatients. CONCLUSIONS: Control measures targeting intestinal carriers are crucial in limiting in-hospital transmission of XDR-PA polyclonal strains, protecting more vulnerable patients, such as severely neutropenic children, from developing clinical infections.

Escherichia coli of human and avian origin: detection of clonal groups associated with fluoroquinolone and multidrug resistance in Italy.

OBJECTIVES: Poultry have been suggested as a reservoir for fluoroquinolone-resistant extraintestinal pathogenic Escherichia coli (ExPEC). Our aim was to investigate whether genotypes associated with ciprofloxacin and multidrug resistance were shared among human and avian E. coli. METHODS: We compared 277 human ExPEC isolates from urinary tract infection (UTI) and sepsis (142 susceptible and 135 ciprofloxacin resistant) and 101 avian isolates (68 susceptible and 33 ciprofloxacin resistant) by antimicrobial resistance phenotype, phylogenetic group and multilocus sequence type (ST). RESULTS: Most ciprofloxacin-resistant isolates from both human and avian sources were multidrug resistant. Human and avian isolates strongly differed in phylogenetic group assignment (B2 and A predominated among human and avian isolates, respectively), but a shift towards group A associated with ciprofloxacin resistance was observed among human isolates (8/100, 8.0% versus 17/87, 19.5%, P =0.021 for UTI and 5/42, 11.9% versus 15/48, 31.3%, P = 0.028 for sepsis). Heterogeneity of ST clones was observed, with ST131 strongly predominant in human ciprofloxacin-resistant strains (58/135, 43.0%), but not in avian strains. However, two major ST clonal complexes (CCs; CC10 and CC23, both belonging to group A) associated with ciprofloxacin resistance and multiresistance were shared by human and avian isolates. CONCLUSIONS: The major human and avian E. coli ST clones associated with multidrug resistance were identified. A subset of ST clones belonging to CC10 and CC23 poses a potential zoonotic risk.

Nucleotide sequence of the chromosomal region conferring multidrug resistance (R-type ASSuT) in Salmonella Typhimurium and monophasic Salmonella Typhimurium strains.

OBJECTIVES: The aim of this study was to sequence the chromosomal region conferring resistance to ampicillin, streptomycin, sulphonamides and tetracycline (R-type ASSuT) in a Salmonella Typhimurium (STM) monophasic strain (4,[5],12:i:-) belonging to the PFGE profile STYMXB.0079. The presence of this resistance region and the analysis of its genetic environment was investigated in a selection of strains. METHODS: A Sau3A1 genomic library was used to determine the nucleotide sequence of the genomic resistance region. PCRs were performed on 10 epidemiologically unrelated Salmonella strains, both STM and monophasic STM, with R-type ASSuT and PFGE profile STYMXB.0079, in order to investigate the presence of the resistance genes, the left and right junctions and the internal regions of the resistance region, as well as the genetic environment. RESULTS: The genomic resistance region consisted of two regions, resistance region 1 (RR1), conferring resistance to ampicillin, streptomycin and sulphonamides, and resistance region 2 (RR2), conferring tetracycline resistance. These resistance regions were both surrounded by IS26 elements and sequence comparative analysis showed 99% sequence identity with a region of plasmid pO111_1 from an Escherichia coli strain. All 10 strains were positive for the four resistance genes, the left and right junctions and the internal regions of RR1 and RR2. Concerning the genetic environment, all the strains lacked the STM1053-1997 and STM2694 genes, while only monophasic STM strains showed deletion of the fljA-fljB operon. CONCLUSIONS: This study describes two resistance regions localized on the bacterial chromosome of a clonal lineage of STM and monophasic STM that are widespread in Italy.

Unusual case of necrotizing fasciitis caused by Vibrio cholerae O137.

We report a case of necrotizing fasciitis caused by Vibrio cholerae O137 in an immunocompromised 49-year-old man. The infection was acquired following a minor traumatic injury and exposure to seawater during the summer of 2009 in Italy. Although highly immunocompromised, the patient survived. The strain was cytotoxic, invasive, and adhesive and contained a fragment of the El Tor-like hemolysin (El Tor hlyA) gene.

Virulotyping of Salmonella enterica serovar Napoli strains isolated in Italy from human and nonhuman sources.

Salmonella enterica serovar Napoli is an emerging serovar in Italy, France, and Switzerland, but little is known about its pathogenicity to humans. A collection of 112 strains of Salmonella Napoli isolated in Italy from human cases, foods of animal origin, and the environment have been characterized by the detection of a set of virulence genes, pulsed-field gel electrophoresis (PFGE), and antibiotic susceptibility. All the strains examined were susceptible to all the antimicrobials tested. The Salmonella pathogenicity islands genes ssaQ, mgtC spi_4D, and sopB were present from 75.0% to 100% of the tested strains. Only one human and four environmental strains showed the avrA gene. The phage-related sopE1 gene was present in 93% of the strains, whereas sodC1 and gipA genes were only in four and two environmental strains, respectively. The bcfC fimbrial gene was present in all the animal/food strains, in the 71.4% of environmental strains, and in 46.8% of the human strains, respectively. Overall, we observed 10 distinct virulence profiles (VP), but VP1-2-3 included 99 out of 112 strains. PFGE showed that 103 out of 111 isolates were grouped in four major clusters and three minor clusters, whereas two strains were totally unrelated. The most represented PFGE clusters mainly correlated with the virulotypes are VP1, VP2, and VP3. Salmonella Napoli shows an array of virulence genes similar to other serovars considered of public health importance and confirming its capability to cause infection in human. Concerning possible source of infection or reservoirs, the results did not point out any, but our hypothesis is that the environment can act as the main reservoir for Salmonella Napoli, and from there it can spill over to animals and humans. Further studies are needed to increase the knowledge on the ecology of Salmonella Napoli serovar and on the main risk factors for human infection.

Association of Polygenic Risk Score and Bacterial Toxins at Screening Colonoscopy with Colorectal Cancer Progression: A Multicenter Case-Control Study.

Colorectal cancer (CRC) is a leading cause of cancer death worldwide, and its incidence is correlated with infections, chronic inflammation, diet, and genetic factors. An emerging aspect is that microbial dysbiosis and chronic infections triggered by certain bacteria can be risk factors for tumor progression. Recent data suggest that certain bacterial toxins implicated in DNA attack or in proliferation, replication, and death can be risk factors for insurgence and progression of CRC. In this study, we recruited more than 300 biopsy specimens from people undergoing colonoscopy, and we analyzed to determine whether a correlation exists between the presence of bacterial genes coding for toxins possibly involved in CRC onset and progression and the different stages of CRC. We also analyzed to determine whether CRC-predisposing genetic factors could contribute to bacterial toxins response. Our results showed that CIF toxin is associated with polyps or adenomas, whereas pks+ seems to be a predisposing factor for CRC. Toxins from Escherichia coli as a whole have a higher incidence rate in adenocarcinoma patients compared to controls, whereas Bacteroides fragilis toxin does not seem to be associated with pre-cancerous nor with cancerous lesions. These results have been obtained irrespectively of the presence of CRC-risk loci.

Evidence for a second genomic island conferring multidrug resistance in a clonal group of strains of Salmonella enterica serovar Typhimurium and its monophasic variant circulating in Italy, Denmark, and the United Kingdom.

During the 2000s, a new clonal group with resistances to ampicillin, streptomycin, sulfonamides, and tetracycline (ASSuT) emerged in Italy among strains of Salmonella enterica serovar Typhimurium and its monophasic variant, Salmonella enterica subspecies enterica serovar 4,[5],12:i:-. The PulseNet Europe database allowed us to identify ASSuT strains of both S. Typhimurium and its monophasic variant, isolated in Denmark and the United Kingdom, with the same or very closely related pulsed-field gel electrophoresis (PFGE) patterns as the Italian strains, suggesting that the ASSuT clonal group is circulating in different European countries. With the aim of analyzing the molecular basis of antibiotic resistance, resistance genes were identified and their localization was investigated in 66 ASSuT strains and, as controls, in 11 strains with different resistance patterns and PFGE profiles, belonging both to S. Typhimurium and to its monophasic variant, isolated from humans in Italy, Denmark, and the United Kingdom. All the ASSuT strains were positive for the following resistance genes: bla(TEM-1), strA-strB, sul2, and tet(B). A localization experiment demonstrated that the ASSuT resistance genes are chromosomally located. This study confirms that a multidrug-resistant clonal group, ASSuT, of S. Typhimurium and its monophasic variant has emerged and is circulating in Italy, Denmark, and the United Kingdom. Moreover, the results of this work demonstrate that the multidrug resistance in this clonal group of Salmonella strains is conferred by a new genomic island.

Polymorphic DNA repair and metabolic genes: a multigenic study on gastric cancer.

Risk factors for gastric cancer (GC) include inter-individual variability in the inflammatory response to Helicobacter pylori infection, in the ability of detoxifying DNA reactive species and repairing DNA damage generated by oxidative stress and dietary carcinogens. To evaluate the association between polymorphic DNA repair genes and GC risk, a case-control study including 314 histologically confirmed GC patients and 548 healthy controls was conducted in a GC high-risk area in Tuscany, Italy. Polymorphic variants of base excision repair (APE1-D148E, XRCC1-R194W, XRCC1-R399Q and OGG1-S326C), nucleotide excision repair (XPC-PAT, XPA-23G>A, ERCC1-19007T>C and XPD-L751Q), recombination (XRCC3-T241M) and alkylation damage reversal (MGMT-L84F) were tested for their potential role in the development of GC by using logistic regression models. The same population was also characterised for GSTT1 and GSTM1 variant alleles to search for possible functional interactions between metabolic and DNA repair genotypes by two-way interactions using multivariate logistic models. No significant association between any single DNA repair genotype and GC risk was detected with a borderline association with the XPC-PAT homozygous genotype [odds ratio (OR) =1.42; 95% confidence interval (CI) 0.94-2.17]. Gene-gene interaction analysis revealed combinations of unfavourable genotypes involving either multiple DNA repair polymorphisms or DNA repair and GST-specific genotypes. The combination of the XPC-PAT and the XPA variant alleles significantly increased GC risk (OR=2.15; 95% CI 1.17-3.93, P=0.0092). A significant interaction was also found between the APE1 wild-type genotype and either the single GSTT1 (OR=4.90; 95% CI 2.38-10.11, P=0.0079) or double GSTM1-GSTT1 null (OR=7.84; 95% CI 3.19-19.22, P=0.0169) genotypes or the XPA-mutant allele (OR=3.56; 95% CI 1.53-8.25, P=0.0012). These findings indicate that a complex interaction between host factors such as oxidative stress, antioxidant capacity and efficiency of multiple DNA repair pathways underlies the inter-individual variability in GC risk.

Characterization of the plasmid-borne quinolone resistance gene qnrB19 in Salmonella enterica serovar Typhimurium.

A qnrB19 gene variant, carried by an IncL/M-like plasmid, was detected in a multidrug Salmonella enterica serovar Typhimurium human strain with reduced susceptibility to ciprofloxacin. The genetic environment around the gene was fully sequenced (20 kb). A large gene cluster, containing the aph, qnrB19, and blaSHV-12-like resistance genes, is inserted inside a Tn3 transposon.

First report of plasmid-mediated quinolone resistance determinant qnrS1 in an Escherichia coli strain of animal origin in Italy.

A qnrS1-positive strain of Escherichia coli was detected among 73 poultry isolates showing ciprofloxacin MICs of > or =0.125 microg/ml. The qnrS1 gene was associated with a Tn3-like transposon, as previously described to occur in a Salmonella enterica serovar Infantis strain of animal origin, but the plasmid scaffold carrying this element resembled that of a plasmid previously identified in Salmonella enterica serovar Dublin. These elements suggest genetic exchanges among Salmonella and E. coli and a potential animal reservoir for the qnr genes.

Molecular characterization of multidrug-resistant strains of Salmonella enterica serotype Typhimurium and Monophasic variant (S. 4,[5],12:i:-) isolated from human infections in Italy.

Salmonella enterica serovar Typhimurium (STM) represents the prevalent cause of foodborne gastroenteritis in Italy with the majority of isolates exhibiting multidrug resistance. A resistant pattern that includes ampicillin (A), streptomycin (S), sulfonamide (Su), and tetracycline (T) (ASSuT) but lacks resistance to chloramphenicol (C) has recently emerged in Italy among strains of STM and of its monophasic variant, S. enterica subspecies enterica serovar S. 4,[5],12:i:-. With the aim to evaluate their clonal relationships, 553 strains of STM and S. 4,[5],12:i:- with the ASSuT and ACSSuT resistance patterns isolated in Italy from human infections between 2003 and 2006 were characterized by pulsed-field gel electrophoresis (PFGE) according to the PulseNet-Europe protocol and nomenclature. Among both the STM and S. 4,[5],12:i:- ASSuT strains, the predominant PFGE profile was STYMXB.0079 (53.2-73.0% of strains, respectively), while the STM ACSSuT strains belonged to the STYMXB.0061 (37.2% of strains) and STYMXB.0067 (29.9% of strains). Bionumerics cluster analysis of the nonunique PFGE profiles showed that more than 90% of ASSuT and ACSSuT-resistant strains were included in two distinct clusters with a genetic homology of 73% each other, suggesting that the ASSuT-resistant strains belong to a same clonal lineage different from that of the ACSSuT strains. Phage typing showed that 23% of the ASSuT STM strains were not typeable and 22.3% were U302. The same phage types were observed among the ASSuT strains of S. 4,[5],12:i:-. A different figure was observed for the ACSSuT strains: the STM isolates mostly belonged to DT104 (70.2%), while none of the S. 4,[5],12:i:- strains belonged to this phage type. This study indicates that the tetra-resistant ASSuT strains of STM and S. 4,[5],12:i:-, increasingly isolated in Italy, belong to a same clonal lineage and that the S. 4,[5],12:i:- strains circulating in our country mainly derive from this STM clonal lineage.

Human infections due to Salmonella Napoli: a multicountry, emerging enigma recognized by the Enter-net international surveillance network.

Human infections caused by Salmonella enterica serovar Napoli are relatively uncommon in Europe. Napoli was ranked 22nd in the Enter-net Salmonella database for 2006 with 295 cases (0.28%) of the 105,635 from 29 European countries. For the 18 countries that provided data for all the years 2000-2006, the number of cases rose from 122 out of 116,915 (0.10%) in 2000 to 293 out of 80,318 (0.36%) in 2006-an increase of 140.2%. Over 87% of cases came from three countries, France, Italy, and Switzerland. The epidemiology of the human cases showed an increased frequency in those aged under 5 or over 64, and both sexes were equally represented. Napoli isolates were also reported from nonhuman sources, mainly environmental samples and poultry. Strains compared by pulsed-field gel electrophoresis exhibited high levels of diversity between human, animal, and environmental sources. No single factor has been recognized as causing this rise, hence no public health interventions can be made or advice given to ensure that it does not persist. A 140% rise in 7 years indicates that the public health problem will continue, and further multidisciplinary investigations are needed to solve this enigma.

Antimicrobial drug resistance in human nontyphoidal Salmonella isolates in Europe 2000-2004: a report from the Enter-net International Surveillance Network.

A 5-year survey, from 2000 to 2004, of results of antimicrobial susceptibility testing for 11 antimicrobials for 134,310 isolates of nontyphoidal salmonellas from cases of human infection in 10 European countries has demonstrated an overall increase in the occurrence of resistance, from 57% to 66% over the period of study. In contrast, multiple resistance (to four or more antimicrobial drugs) has declined from 18% to 15%. The most significant increase in resistance has been to nalidixic acid (14% to 20%), particularly in Salmonella enterica serovar Enteritidis (10% to 26%), the most common serovar. For England and Wales this increase has for the most part been attributed to infections linked to contaminated eggs originating outside the United Kingdom. For Salmonella Typhimurium, the second most prevalent serovar, there has been an overall decline in the occurrence of resistance to ampicillin, chloramphenicol, and tetracyclines, attributed to a decline in the occurrence of multiresistant Salmonella Typhimurium DT 104. For Salmonella Virchow, a serotype with a predilection for invasive disease, there has been a substantive increase in resistance to most antimicrobials, attributed to the spread of drug-resistant strains associated with poultry. Because of the widespread importation of foods, it is important that controls to reduce the emergence and spread of drug-resistant strains of Salmonella are internationally implemented.

Outbreak of Salmonella Thompson infections linked to imported rucola lettuce.

On November 15, 2004, a cluster of three cases of Salmonella Thompson infection was registered by the Norwegian reference laboratory. In the following days further cases occurred, prompting a case-control study among the first 13 cases and 26 matched controls. By December 31, 21 cases had been reported, with the first onset on October 24. Consumption of rucola lettuce (Eruca sativa, also known as rocket salad or arugula) (OR 8,8 [1,2-infinity]) and mixed salad (OR 5,0 [1,0-infinity]) was associated with illness. On November 26, Swedish authorities notified the finding of Salmonella Thompson in rucola lettuce through the EU Rapid Alert System for Food and Feed. Later, several countries reported finding this and other Salmonella serovars and Campylobacter in rucola produced in Italy. In response to our alert through the international Enter-net surveillance network, Sweden and England also reported an increase of cases. Salmonella Thompson isolates from products and patients from several countries showed high similarity by pulsed-field gel electrophoresis, but some isolates showed significant differences. We think that the outbreak in Norway reflected a larger international outbreak caused by rucola imported from one Italian producer. Findings of other pathogens indicate a massive contamination, possibly caused by irrigation with nonpotable water. Rapid international information exchange is invaluable when investigating outbreaks caused by internationally marketed products.

Fresh produce and microbial contamination: persistence during the shelf life and efficacy of domestic washing methods.

The transmission of enteric pathogens by fresh produce depends on the survival of the bacteria organisms during the product shelf-life. The removal of any potentially hazardous microorganism from the vegetables is therefore dependent on the washing and sanitizing techniques employed by individual households. For this purpose, in this work we investigated the persistence of enteric bacteria, using as model Salmonella enterica serovar Napoli (S. Napoli) and Yersinia enterocolitica, in vegetables stored at refrigeration temperature (4 °C). The efficiency of tap water and different chlorine solutions for cleaning vegetables experimentally contaminated with Y. enterocolitica were tested. The results showed that in lettuce spiked with different concentrations of S. Napoli and Y. enterocolitica, both microorganisms were still detected after seven days of storage at 4 °C. Lettuce contaminated with low concentrations of Y. enterocolitica was not decontaminated by washing with tap water or with water added with 60 ppm of chlorine. The presence of Y. enterocolitica in lettuce was reduced of about 1-2 logs after washing with water added with 220 ppm of chlorine. The addition of low concentration of chlorine in post harvest washing processes represents a useful tool to reduce the contamination of the vegetables, with consequent reduction of the risks. However, since complete decontamination was not achieved, foodborne infections linked to fresh produce can still be possible, although contamination is avoided during primary production.