Shiga-toxin producing Escherichia coli detection in samples from Abruzzo and Molise regions, Italy

Background

Top five serogroups (O157, O111, O26, O103 and O145) of Shiga-toxin producing Escherichia coli (STEC) represent the third most important increasing zoonosis reported in European Union. The ISO methods of analysis, used in foods and environmental samples, quite often does not confirm the molecular detection of STEC genes (stx1 and stx2) in enrichment broth. The aim of this study was to summarize the results of the tests carried out at Istituto Zooprofilattico Sperimentale dell'Abruzzo e del Molise in the last six years (2016-2021), comparing genes detection in enrichment broth and in colonies grown on agar plates.

Methods

Along the 2016-2021, a total of 1716 foods and environmental samples from Abruzzo and Molise regions were tested, according to ISO/TS 13136:2012.

Results

Out of 1716 samples, 16 (0.9%) shown presumptive positive presence of STEC (stx1 and/or stx2) in broth. In spite of that, the presence of STEC (positive colonies for stx1 and/or stx2) was confirmed only in 4 out of 16 samples (one sample of cheese and 3 of minced meat). Then, eae gene was found in 54 samples in broth and only in 3 samples from colonies, during a foodborne outbreak investigation. Serogroup specific targets were detected in 6 broth samples (O26, O145 and O157) and confirmed in colonies only in 2 minced meat samples (O157).

Conclusions

STEC are a heavy hazard for the consumers and the number of cases is slightly increasing since 2015. Our results highlight a low number of presumptive positive samples and even lower number of STEC detection obtained with the ISO classical method. Furthermore, detection of the target genes in broth was rarely confirmed after plating, highlighting a weak point of the analytical method that needs to be investigated. Efforts are necessary to improve the method and the STEC confirmation from colonies. Immunomagnetic beads targeting the top five serogroups and digital PCR could help in increasing the recovery rate of cultivable STEC.

Key messages

The presumptive positive samples for STEC genes in foodstuffs from the Abruzzo and Molise regions are quite rare, even lower is the number of confirmed colonies by agar plate isolation. Specific immunomagnetic beads for the top five STEC serogroups could improve the method and the STEC colonies detection, increasing the recovery rate of cultivable strains.

Genomic persistence of Listeria monocytogenes strains in dairy and meat processing plants in Italy

Background

Persistence of Listeria monocytogenes (Lm) in food processing plants (FPP) is still considered the major source of food contamination during processing. Correlations among different Lm strains and evaluation of the isolates persistence in FPP environments is an essential tool to improve food safety. The aim of this study was to investigate the genomic characteristics of persistent Lm strains (e.g. Metal and Detergent Resistance, SSIs and genomic island).

Methods

Totally 221 strains isolated from 10 FPP in the Abruzzo and Molise regions, Italy, were enrolled (4 of dairy products FPP - DP - and 6 of meat products FPP - MP). Sampling was performed in 6 sessions, from March 2017 to May 2018. Strains were sequenced using Illumina platform. The CCs, cgMLST analysis and Metal and Detergent Resistance, SSIs and genomic island (GI) detection was carried using the Pasteur scheme.

Results

Results returned 13 CCs and 2 singletons. cgMLST clustering showed two persistent clusters DP and 9 clusters in MP. In DP CC3 and CC9 were persistent. While in MP CC5, CC8, CC9, CC37, CC121 and CC155. The presence of SSI-1, was detected in 100% of the persistent strains from DP and 80% from MP, in particular in all strains of CC155, CC5, CC8 and CC9. In CC121 and CC37 it was absent. The presence of loci of Lm GI3, was in 100% of persistent strains of DP and in 52.3% of MP plant, in particular in 100% of CC121, CC8, CC5 and 16.3% of CC9. The 100% of CC121 in DP and MP plant harboured Tn6188 and SSI-2. The inlA PMSC mutations were detected in 100% of CC9 and CC121 strains.

Conclusions

The persistence of strains inside FPP was confirmed using NGS data, most of the strains were characterised by the presence of genes involved in resistance and adaptation. NGS is confirmed to be a powerful tool to study Lm persistence in FPP, looking also at strains' ecology.

Key messages

Most of persistent strains showed genes involved in resistance and adaptation in the food processing environment. NGS could help in facing Lm persistence in food producing plants giving new insights on the genomic characteristics of persistent strains.

Root internalization of Salmonella Typhimurium in basil plants

Background

Foodborne pathogens present in soil or irrigation water have the potential to internalize via root into edible parts of the plants and survive, representing a serious hazard for consumer's health (1). The present work assesses the ability of Salmonella Typhimurium (ST) to enter basil plants (Ocimum basilicum L., cultivar “Napoletano”) from roots. This situation may represent a risk in food safety since that vegetable is largely used raw/undercooked, in the Mediterranean diet.

Methods

Sixteen basil plants were cultivated in hydroponics, from the seeds. Roots from 14 plants at 4 leaves-stage were individually immersed in liquid media contaminated with a suspension of ST isolated from Aterno river in Abruzzo region, Italy (9 log10 cfu/mL final concentration). Two plants were used as negative controls (no ST challenge); surface swabs were taken from leaves and stems to exclude external contaminations. After 24 hours, plants were tested for detection (UNI EN ISO 6579-1:2017) and enumeration (in-house method) of ST in leaves and stems.

Results

ST detection gave positive results in 14/14 plants; in particular, ST was present in 14/14 plants in the leaves and for 9/14 plants also in the stems. The internalized ST strains were also enumerated in 10/14 plants. In particular, 3/14 plants gave positive results both in the leaves and stems, 2/14 only in the stems and other 5/14 only in the leaves. The average ST counts were of 4 log10 cfu/g in leaves and stems. All negative ctr/surface swabs were negative to ST.

Conclusions

Even though antimicrobial properties of basil plants have been described (2), this study demonstrated the potential of ST to internalize, survive and spread to edible parts. The findings highlight the risk of human infections by ST in plant following root uptake, suggesting the importance of applying appropriate preventive pre-harvest strategies.

Biblio

EFSA. E. Jour. (2014);12(3):3600 Tenore et al. (2017). Natural product research, 31(17), 2067-2071

Key messages

The ability of Salmonella Typhimurium to internalize, survive and spread to edible parts of basil plants. Pathogenic bacteria root uptake represents a potential risk for human health.

Multidrug-resistant Klebsiella pneumoniae: risks to food safety and public health

Background

Klebsiella pneumoniae (Kp) is a Gram-negative hospital-acquired pathogen. Kp also poses a potential food safety hazard, since a significant increase of multidrug-resistant (MDR) Kp was observed in foods. The purpose of this study was to characterize MDR Kp strains in order to evaluate the presence of beta-lactams, quinolones and aminoglycosides resistance genes.

Methods

A total of 13 Kp strains, isolated from chicken (n.8), raw milk (n.2), waste water (n.2), human faeces (n.1), and identified as MDR by microdilution test, were selected to evaluate antimicrobial resistance profiles, focusing on beta-lactams, quinolones and aminoglycosides. Next Generation Sequencing (NGS), with NextSeq 500 Illumina platform, was performed to acquire genome sequences. The antimicrobial resistance profiles were obtained using ResFinder (https://cge.cbs.dtu.dk/services/ResFinder/).

Results

From the 13 Kp considered, 6 strains (46.2 %) showed the presence of several beta-lactam genes. The blaSHV gene was carried by 12 Kp (92.3%); of these strains, 5 also carried blaTEM (41.7%) and 3 also blaCTX-M (25.0%) genes. Only 1 Kp strain showed the presence of blaOKP-A gene. All the 13 Kp carried the oqxA and oqxB genes. Of these strains, 4 also highlighted the presence of qnrB or qnrS plasmid-mediated gene for quinolone resistance. Regarding aminoglycoside resistance, 6 Kp strains (46.2%) carried aph, aadA and aaC genes, linked to gentamicin and streptomycin resistance protein.

Conclusions

These preliminary results emphasize the need of further studies on more several samples, to better understand the antimicrobial resistance of Kp strains, the hypothetical transmission of MDR Kp from foods to consumers and the potential risk posed to food safety, environmental and public health.

Key messages

The increasing prevalence of multidrug-resistant Klebsiella pneumoniae requires the need to investigate more foods and environmental samples to ensure consumer safety and public health. Public health safety requires a major knowledge of the hypothetical mechanisms and routes of transmission of multidrug-resistant Klebsiella pneumoniae.

Detection of Klebsiella pneumoniae complex in carrots

Background

Klebsiella pneumoniae (Kp) is an opportunistic pathogen now acknowledged as an urgent threat to human health because it is multi-drug resistant bacteria. The role of food as reservoir or carrier of Kp is under investigation, at the same time the optimization of the method to detect Kp in food is ongoing. The study was aimed to detect Kp in carrots using conventional method and to screen Real-time PCR performances, targeting intergenic sequence between zur and khe, based on INRA and Pasteur Institute method

Methods

A total of 60 samples of carrots were tested. The samples (25 g) were added to 225 ml of Buffered peptone water and incubated at 37 °C and at 44 °C for 24h. After incubation broths were subjected to Real-Time PCR, and one loop streaked on SCAI + inositol agar. Plates were then incubated at 37 °C and at 44 °C for 48 h. After incubation a maximum of 5 typical colonies were selected, subcultered on Nutritive agar and identified by MALDI-TOF MS.

Results

The RT PCR gave 29 positive samples, according to the presence of Kp detected at least in one of the two temperature conditions of broths incubation and 31 negative samples. Conventional culture gave, instead, 13 positive and 47 negative samples. Discordance was highlighted in 16 samples, all positives in RT-PCR and negatives with culture method.

Conclusions

Real-Time PCR gave not false negative results, then PCR decrease the time needed to perform the detection in negative samples. The discordance of results could be linked to lack of selectivity of the SCAI agar + inositol, not able to distinguish colonies of Klebsiella spp. Vs similar colonies not Klebsiella spp., the presence of DNA and not viable cells. The process of validation of the detection method is still ongoing, trying to improve selectivity using two selective media for plating. It's necessary to do new trials and to select more typical colonies to increase the probability to detect Kp colonies.

Key messages

Real-Time PCR is able to detect all positive samples, and to shorten the length of the analytical method. To improve sensibility of the analytical method more selective media need to be used.