[Molecular characterization of Listeria monocytogenes isolates from human and food sources in Argentina, 2018-2023]. / Caracterización molecular de aislamientos de Listeria monocytogenes de origen humano y alimentario en Argentina, 2018-2023.

Human listeriosis is an infectious disease caused by Listeria monocytogenes. The invasive form of this disease leads to a high rate of hospitalizations and fatality. The main mode of transmission is through contaminated ready-to-eat foods such as dairy, vegetables and meat products. The knowledge of the diversity and population dynamics of isolates collected from human and food sources is essential for the detection of clusters and the identification of common sites of infection. The aim of this study was the molecular characterization of L. monocytogenes isolates in Argentina. We sequenced a total of 63 isolates, 35 from human and 28 from food sources, collected between 2018 and 2023. Our genomic study divided the isolates into two lineages, four serogroups, 17 sequence types and 15 clonal complexes (CCs). The hypervirulent clone CC1 (lineage I; serogroup IVb) predominated in human and food samples. The phylogenomic analysis showed a high and possible epidemiological relationship between isolates from human and/or food sources, suggesting the presence of transmission chains in our country. These findings highlight the need to strengthen genomic surveillance of L. monocytogenes in Argentina. The identification of geographic distribution and characteristics of predominant and emerging clones from human and food sources might help to focus action plans and public health policies better directed at the control and prevention of listeriosis.

Strain Differences in Bloodstream and Skin Infection: Methicillin-Resistant Staphylococcus aureus Isolated in 2018-2021 in a Single Health System.

Staphylococcus aureus is a common cause of skin and soft-tissue infections (SSTIs) and has become the most common cause of bloodstream infections (BSIs) in recent years, but whether the strains causing these two clinical syndromes overlap has not been studied adequately. USA300/500 (clonal complex [CC] 8-sequence type [ST] 8) and USA100 (CC5-ST5) have dominated among methicillin-resistant S aureus (MRSA) strains in the United States since the early 2000s. We compared the genomes of unselected MRSA isolates from 131 SSTIs with those from 145 BSIs at a single US center in overlapping periods in 2018-2021. CC8 MRSA was more common among SSTIs, and CC5 was more common among BSIs, consistent with prior literature. Based on clustering genomes with a threshold of 15 single-nucleotide polymorphisms, we identified clusters limited to patients with SSTI and separate clusters exclusively comprising patients with BSIs. However, we also identified eight clusters that included at least one SSTI and one BSI isolate. This suggests that virulent MRSA strains are transmitted from person to person locally in the healthcare setting or the community and that single lineages are often capable of causing both SSTIs and BSIs.

Antimicrobial resistance patterns of Streptococcus uberis isolates from bovine milk in Chiba prefecture, Japan: association between multidrug resistance and clonal complex 996.

Streptococcus uberis is one of major pathogens causing bovine mastitis. However, there is poor information on antimicrobial resistance (AMR) among the Japanese isolates. To provide treatment information for the mastitis caused by S. uberis in Japan, we aimed to clarify AMR patterns of the isolates from bovine milk mainly in Chiba. AMR phenotyping/genotyping [blaZ-erm(A)-erm(B)-mef(A)-linB-lnuD-tet(M)-tet(O)-tet(K)-tet(L)-tet(S)] and multilocus sequence typing were performed to analyze relationships between AMR patterns and clonal complexes (CCs). Resistance to tetracycline-, macrolide-, and lincosamide-classes was mainly associated with possession of tet(O), tet(S), erm(B), linB, and lnuD genes. CC996 was significantly associated with multidrug resistance (P<0.0001). These findings will aid Chiba farm animal clinics in treating bovine mastitis.

Genetic diversity and antimicrobial susceptibility of Streptococcus suis from diseased Swiss pigs collected between 2019 - 2022.

Streptococcus suis is an important pathogen causing severe disease in pigs and humans, giving rise to economic losses in the pig production industry. Out of 65 S. suis isolates collected from diseased pigs in Switzerland between 2019 and 2022, 57 isolates were thoroughly examined by phenotypic and whole genome sequence (WGS) based characterization. The isolates' genomes were sequenced allowing for a comprehensive analysis of their distribution in terms of serovar, sequence type (ST), clonal complex (CC), and classical virulence markers. Antimicrobial resistance (AMR) genes were screened, and phenotypic susceptibility to eight classes of antimicrobial agents was examined. Serovar 6, devoid of any resistance genes, was found to be most prevalent, followed by serovars 1, 3, 1/2, and 9. Thirty STs were identified, with ST1104 being the most prevalent. Serovar 2 and serovar 1/2 were associated with CC1, potentially containing the most virulent variants. Based on single nucleotide polymorphism (SNP) analyses, fifteen isolates belonged to one of seven putative transmission clusters each consisting of two or three isolates. High phenotypic AMR rates were detected for tetracyclines (80%) and macrolides (35%) and associated with the resistance genes tet(O) and erm(B), respectively. In contrast, susceptibility to ß-lactam antibiotics and phenicols was high. Determination of phenotypic AMR profiling, including the minimum inhibitory concentrations (MICs) of the tested antimicrobial agents, sets a baseline for future studies. The study provides valuable insights into the genetic diversity and antimicrobial susceptibility of Swiss S. suis isolates, facilitating the identification of emerging clones relevant to public health concerns.

Updated Parameters for Listeria monocytogenes Dose-Response Model Considering Pathogen Virulence and Age and Sex of Consumer.

Better knowledge regarding the Listeria monocytogenes dose-response (DR) model is needed to refine the assessment of the risk of foodborne listeriosis. In 2018, the European Food Safety Agency (EFSA) derived a lognormal Poisson DR model for 14 different age-sex sub-groups, marginally to strain virulence. In the present study, new sets of parameters are developed by integrating the EFSA model for these sub-groups together with three classes of strain virulence characteristics ("less virulent", "virulent", and "more virulent"). Considering classes of virulence leads to estimated relative risks (RRs) of listeriosis following the ingestion of 1000 bacteria of "less virulent" vs. "more virulent" strains ranging from 21.6 to 24.1, depending on the sub-group. These relatively low RRs when compared with RRs linked to comorbidities described in the literature suggest that the influence of comorbidity on the occurrence of invasive listeriosis for a given exposure is much more important than the influence of the virulence of the strains. The updated model parameters allow better prediction of the risk of invasive listeriosis across a population of interest, provided the necessary data on population demographics and the proportional contribution of strain virulence classes in food products of interest are available. An R package is made available to facilitate the use of these dose-response models.

Hypervirulent clonal complex (CC) of Listeria monocytogenes in fresh produce from urban communities.

Introduction: This study aimed to determine the prevalence and virulome of Listeria in fresh produce distributed in urban communities. Methods: A total of 432 fresh produce samples were collected from farmer's markets in Michigan and West Virginia, USA, resulting in 109 pooled samples. Listeria spp. were isolated and L. monocytogenes was subjected to genoserogrouping by PCR and genotyping by pulsed-field gel electrophoresis (PFGE). Multi-locus sequence typing (MLST) and core-genome multi-locus sequence typing (cgMLST) were conducted for clonal identification. Results: Forty-eight of 109 samples (44.0%) were contaminated with Listeria spp. L. monocytogenes serotype 1/2a and 4b were recovered from radishes, potatoes, and romaine lettuce. Four clonal complexes (CC) were identified and included hypervirulent CC1 (ST1) and CC4 (ST219) of lineage I as well as CC7 (ST7) and CC11 (ST451) of lineage II. Clones CC4 and CC7 were present in the same romaine lettuce sample. CC1 carried Listeria pathogenicity island LIPI-1 and LIPI-3 whereas CC4 contained LIPI-1, LIPI-3, and LIPI-4. CC7 and CC11 had LIPI-1 only. Discussion: Due to previous implication in outbreaks, L. monocytogenes hypervirulent clones in fresh produce pose a public health concern in urban communities.

Characterization of pig tonsils as niches for the generation of Streptococcus suis diversity.

Streptococcus suis is a gram-positive bacterium that causes meningitis, septicemia, endocarditis, and other disorders in pigs and humans. We obtained 42 and 50 S. suis isolates from lesions of porcine endocarditis and palatine tonsils, respectively, of clinically healthy pigs in Japan; we then determined their sequence types (STs) by multilocus sequence typing (MLST), cps genotypes, serotypes, and presence of classical major virulence-associated marker genes (mrp, epf, and sly). The 42 isolates from endocarditis lesions were assigned to a limited number of STs and clonal complexes (CCs). On the other hand, the 50 isolates from tonsils were diverse in these traits and seemingly in the degree of virulence, suggesting that tonsils can accommodate a variety of S. suis isolates. The goeBURST full algorithm using tonsil isolates obtained in this study and those retrieved from the database showed that major CCs as well as many other clusters were composed of isolates originating from different countries, and some of the STs were very similar to each other despite the difference in country of origin. These findings indicate that S. suis with not only different but also similar mutations in the genome have survived in tonsils independently across different geographical locations. Therefore, unlike the lesions of endocarditis, the tonsils of pigs seemingly accommodate various S. suis lineages. The present study suggests that S. suis acquired its diversity by natural mutations during colonization and persistence in the tonsils of pigs.

Expansion of Neisseria meningitidis Serogroup C Clonal Complex 10217 during Meningitis Outbreak, Burkina Faso, 2019.

During January 28-May 5, 2019, a meningitis outbreak caused by Neisseria meningitidis serogroup C (NmC) occurred in Burkina Faso. Demographic and laboratory data for meningitis cases were collected through national case-based surveillance. Cerebrospinal fluid was collected and tested by culture and real-time PCR. Among 301 suspected cases reported in 6 districts, N. meningitidis was the primary pathogen detected; 103 cases were serogroup C and 13 were serogroup X. Whole-genome sequencing revealed that 18 cerebrospinal fluid specimens tested positive for NmC sequence type (ST) 10217 within clonal complex 10217, an ST responsible for large epidemics in Niger and Nigeria. Expansion of NmC ST10217 into Burkina Faso, continued NmC outbreaks in the meningitis belt of Africa since 2019, and ongoing circulation of N. meningitidis serogroup X in the region underscore the urgent need to use multivalent conjugate vaccines in regional mass vaccination campaigns to reduce further spread of those serogroups.

Obstetric and Neonatal Invasive Meningococcal Disease Caused by Neisseria meningitidis Serogroup W, Western Australia, Australia.

Three mother-baby pairs with invasive meningococcal disease occurred over 7 months in Western Australia, Australia, at a time when serogroup W sequence type 11 clonal complex was the predominant local strain. One mother and 2 neonates died, highlighting the role of this strain as a cause of obstetric and early neonatal death.

Molecular Characterization of Chimeric Staphylococcus aureus Strains from Waterfowl.

Staphylococcus aureus is a versatile pathogen that does not only occur in humans but also in various wild and domestic animals, including several avian species. When characterizing S. aureus isolates from waterfowl, isolates were identified as atypical CC133 by DNA microarray analysis. They differed from previously sequenced CC133 strains in the presence of the collagen adhesin gene cna; some also showed a different capsule type and a deviant spa type. Thus, they were subjected to whole-genome sequencing. This revealed multiple insertions of large regions of DNA from other S. aureus lineages into a CC133-derived backbone genome. Three distinct strains were identified based on the size and extent of these inserts. One strain comprised two small inserts of foreign DNA up- and downstream of oriC; one of about 7000 nt or 0.25% originated from CC692 and the other, at ca. 38,000 nt or 1.3% slightly larger one was of CC522 provenance. The second strain carried a larger CC692 insert (nearly 257,000 nt or 10% of the strain's genome), and its CC522-derived insert was also larger, at about 53,500 nt or 2% of the genome). The third strain carried an identical CC692-derived region (in which the same mutations were observed as in the second strain), but it had a considerably larger CC522-like insertion of about 167,000 nt or 5.9% of the genome. Both isolates of the first, and two out of four isolates of the second strain also harbored a hemolysin-beta-integrating prophage carrying "bird-specific" virulence factors, ornithine cyclodeaminase D0K6J8 and a putative protease D0K6J9. Furthermore, isolates had two different variants of SCC elements that lacked mecA/mecC genes. These findings highlight the role of horizontal gene transfer in the evolution of S. aureus facilitated by SCC elements, by phages, and by a yet undescribed mechanism for large-scale exchange of core genomic DNA.

An ANI gap within bacterial species that advances the definitions of intra-species units.

IMPORTANCE: Bacterial strains and clonal complexes are two cornerstone concepts for microbiology that remain loosely defined, which confuses communication and research. Here we identify a natural gap in genome sequence comparisons among isolate genomes of all well-sequenced species that has gone unnoticed so far and could be used to more accurately and precisely define these and related concepts compared to current methods. These findings advance the molecular toolbox for accurately delineating and following the important units of diversity within prokaryotic species and thus should greatly facilitate future epidemiological and micro-diversity studies across clinical and environmental settings.

Distribution of Extended-Spectrum-ß-Lactamase-Producing Diarrheagenic Escherichia coli Clonal Complex 10 Isolates from Patients with Diarrhea in the Republic of Korea.

ESBL-producing E. coli is a public health concern in healthcare settings and the community. Between 2009 and 2018, a total of 187 ESBL-producing pathogenic E. coli isolates were identified, and clonal complex (CC) 10 was the predominant clone (n = 57). This study aimed to characterize the ESBL-producing pathogenic E. coli CC10 strains obtained from patients with diarrhea to improve our understanding of CC10 distribution in the Republic of Korea. A total of 57 CC10 strains were selected for comprehensive molecular characterization, including serotype identification, the analysis of antibiotic resistance genes, the investigation of genetic environments, the determination of plasmid profiles, and the assessment of genetic correlations among CC10 strains. Among the CC10 isolates, the most prevalent serotype was O25:H16 (n = 21, 38.9%), followed by O6:H16 (10, 19.6%). The most dominant ESBL genes were blaCTX-M-15 (n = 31, 55%) and blaCTX-M-14 (n = 15, 27%). Most blaCTXM genes (n = 45, 82.5%) were located on plasmids, and these incompatibility groups were confirmed as IncB/O/K/Z, IncF, IncI1, and IncX1. The mobile elements located upstream and downstream mainly included ISEcp1 (complete or incomplete) and IS903 or orf477. Phylogenetic analysis showed that the CC10 strains were genetically diverse and spread among several distinct lineages. The results of this study show that ESBL-producing pathogenic E. coli CC10 has been consistently isolated, with CTX-M-15-producing E. coli O25:H16 isolates being the major type associated with the distribution of CC10 clones over the past decade. The identification of ESBL-producing pathogenic E. coli CC10 isolates underscores the possible emergence of resistant isolates with epidemic potential within this CC. As a result, continuous monitoring is essential to prevent the further dissemination of resistant ESBL-producing E. coli CC10 strains.

Aerotolerance and Multi-Locus Sequence Typing of Campylobacter jejuni Isolated from Commercial Broiler Processing Plants.

Campylobacter jejuni is one of the leading causes of acute diarrhea in the United States. Despite being a microaerophilic pathogen, C. jejuni continues to endure within the domain of food production, especially in poultry processing. Recent research on aerotolerance indicates that close monitoring of this pathogen is necessary. A total of 40 C. jejuni isolates previously obtained from commercial broiler processing plants were analyzed for aerotolerance and genetic diversity. In addition, the effect of aerotolerance and storage time (days) on the survival of C. jejuni on broiler drumsticks at refrigeration (4 °C) and freezing conditions (-20 °C) was also evaluated. Out of 40 isolates, 25 (62.5%) were aero-sensitive (AS), 10 (25%) were intermediately aerotolerant (IAT), and 5 (12.5%) were hyper aerotolerant (HAT). The isolates belonged to four clonal complexes (CCs) and six sequence types, with the majority of isolates assigned to the CC-353 clonal complex. C. jejuni counts were reduced by 0.40 log CFU/g after 7 days at 4 °C and by 1.50 log CFU/g after 14 days at -20 °C, respectively, irrespective of aerotolerance (p < 0.001). At both refrigeration (p < 0.013) and freezing (p < 0.001), HAT showed greater reductions as compared to AS and IAT. These findings suggest that both refrigeration and freezing reduce C. jejuni counts.

First Report of Campylobacter jejuni Strains Belonging to ST-21 Clonal Complex Isolated from Human, Poultry and Wild Birds in Croatia: Antimicrobial Resistance and Genetic Distance.

In the era of growing antimicrobial resistance, a threat affecting humans, endangering animals, as well as livelihoods and food security worldwide, we wanted to find possible explanations for its continuous spread from a new perspective. The ubiquity of resistance genes requires a One Health approach to finding the explanations for continuous AMR spread. The natural transformability of Campylobacter jejuni, its high incidence of infections, and emerging resistance worldwide inspired us to choose C. jejuni ST-21CC to be our pathogen for analyzing its contribution and connection to the cycle of AMR dissemination. ST-21CC is known as a generalist among humans and broilers, the most prevalent lineage worldwide, but it is rarely found in wild birds. Emerging in wild birds, genetic relatedness and similar resistance profiles were expected. We analyzed 23 Croatian C. jejuni strains belonging specifically to ST-21CC from humans, broilers, and wild birds. The genomic data obtained through whole genome sequencing and phenotypic susceptibility data of strains were compared. Our findings suggest high fluoroquinolone resistance in ST-21CC strains, with more diverse genetic backgrounds in wild birds. Intriguing were three isolates of ST-822 (from human and storks), sharing a similar genetic fingerprint.

Genomic changes underpinning the emergence of a successful Mycobacterium tuberculosis Latin American and Mediterranean clonal complex.

Introduction: The Latin American and Mediterranean sublineage (L4.3/LAM) is the most common generalist sublineage of Mycobacterium tuberculosis lineage 4 (L4), yet certain L4.3/LAM genotypes appear to be confined to particular geographic regions. This is typically the case of a L4.3/LAM clonal complex (CC), TUN4.3_CC1, which is the most preponderant in Tunisia (61.5% of L4.3/LAM). Methods: Here, we used whole-genome sequencing data of 346 globally distributed L4 clinical strains, including 278 L4.3/LAM isolates, to reconstruct the evolutionary history of TUN4.3_CC1 and delineate critical genomic changes underpinning its success. Results and Discussion: Phylogenomic coupled to phylogeographic analyses indicated that TUN4.3_CC1 has evolved locally, being confined mainly to North Africa. Maximum likelihood analyses using the site and branch-site models of the PAML package disclosed strong evidence of positive selection in the gene category "cell wall and cell processes" of TUN4.3_CC1. Collectively, the data indicate that TUN4.3_CC1 has inherited several mutations, which could have potentially contributed to its evolutionary success. Of particular interest are amino acid replacements at the esxK and eccC2 genes of the ESX/Type VII secretion system, which were found to be specific to TUN4.3_CC1, being common to almost all isolates. Because of its homoplastic nature, the esxK mutation could potentially have endowed TUN4.3_CC1 with a selective advantage. Moreover, we noticed the occurrence of additional, previously described homoplasic nonsense mutations in ponA1 and Rv0197. The mutation in the latter gene, a putative oxido-reductase, has previously been shown to be correlated with enhanced transmissibility in vivo. In sum, our findings unveiled several features underpinning the success of a locally evolved L4.3/LAM clonal complex, lending further support to the critical role of genes encoded by the ESX/type VII secretion system.

Temporal dynamics of genetically heterogeneous extended-spectrum cephalosporin-resistant Escherichia coli bloodstream infections.

Extended-spectrum cephalosporin-resistant Escherichia coli (ESC-R-Ec) is an urgent public health threat with sequence type clonal complex 131 (STc131), phylogroup B2 strains being particularly concerning as the dominant cause of ESC-R-Ec infections. To address the paucity of recent ESC-R-Ec molecular epidemiology data in the United States, we used whole-genome sequencing (WGS) to fully characterize a large cohort of invasive ESC-R-Ec at a tertiary care cancer center in Houston, Texas, collected from 2016 to 2020. During the study time frame, there were 1,154 index E. coli bloodstream infections (BSIs) of which 389 (33.7%) were ESC-R-Ec. Using time series analyses, we identified a temporal dynamic of ESC-R-Ec distinct from ESC-susceptible E. coli (ESC-S-Ec), with cases peaking in the last 6 months of the calendar year. WGS of 297 ESC-R-Ec strains revealed that while STc131 strains accounted for ~45% of total BSIs, the proportion of STc131 strains remained stable across the study time frame with infection peaks driven by genetically heterogeneous ESC-R-Ec clonal complexes. bla CTX-M variants accounted for most ß-lactamases conferring the ESC-R phenotype (89%; 220/248 index ESC-R-Ec), and amplification of bla CTX-M genes was widely detected in ESC-R-Ec strains, particularly in carbapenem non-susceptible, recurrent BSI strains. Bla CTX-M-55 was significantly enriched within phylogroup A strains, and we identified bla CTX-M-55 plasmid-to-chromosome transmission occurring across non-B2 strains. Our data provide important information regarding the current molecular epidemiology of invasive ESC-R-Ec infections at a large tertiary care cancer center and provide novel insights into the genetic basis of observed temporal variability for these clinically important pathogens. IMPORTANCE Given that E. coli is the leading cause of worldwide ESC-R Enterobacterales infections, we sought to assess the current molecular epidemiology of ESC-R-Ec using a WGS analysis of many BSIs over a 5-year period. We identified fluctuating temporal dynamics of ESC-R-Ec infections, which have also recently been identified in other geographical regions such as Israel. Our WGS data allowed us to visualize the stable nature of STc131 over the study period and demonstrate a limited but genetically diverse group of ESC-R-Ec clonal complexes are detected during infection peaks. Additionally, we provide a widespread assessment of ß-lactamase gene copy number in ESC-R-Ec infections and delineate mechanisms by which such amplifications are achieved in a diverse array of ESC-R-Ec strains. These data suggest that serious ESC-R-Ec infections are driven by a diverse array of strains in our cohort and impacted by environmental factors suggesting that community-based monitoring could inform novel preventative measures.

Genetic population structure of Listeria monocytogenes strains isolated from salmon and trout sectors in France.

Smoked salmon and smoked trout are ready-to-eat and potentially contaminated with the pathogenic bacterium Listeria monocytogenes making them high risk for the consumer. This raises questions about the presence of hypervirulent or persistent strains in the salmon and trout industries. Knowledge of the genetic diversity of circulating strains in these sectors is essential to evaluate the risk associated with this pathogen and improve food safety. We analyzed the genetic structure of 698 strains of L. monocytogenes isolated from 2006 to 2017 in France, based on their serogroup, lineage and clonal complexes (CCs) determined by Multilocus sequence typing (MLST). Most of the CCs were identified by mapping the strains PFGE profiles and a novel high-throughput real-time PCR method for CC identification. We identified thirteen CCs and one sequence type (ST) with variable distribution in salmon and trout samples (food, environment). The three most prevalent CCs were CC121, CC26 and CC204. Strains from ST191 and CC54 were detected for the first time in these sectors, while less than 0.6% of the isolates belonged to the hyper-virulent CC1, CC6 and CC20. No CC was exclusively associated with the salmon sector. This project allowed us to assess the population diversity of CCs of L. monocytogenes in the salmon and trout industries.

New Multilocus Sequence Typing Scheme for Enterococcus faecium Based on Whole Genome Sequencing Data.

The MLST scheme currently used for Enterococcus faecium typing was designed in 2002 and is based on putative gene functions and Enterococcus faecalis gene sequences available at that time. As a result, the original MLST scheme does not correspond to the real genetic relatedness of E. faecium strains and often clusters genetically distant strains to the same sequence types (ST). Nevertheless, typing has a significant impact on the subsequent epidemiological conclusions and introduction of appropriate epidemiological measures, thus it is crucial to use a more accurate MLST scheme. Based on the genome analysis of 1,843 E. faecium isolates, a new scheme, consisting of 8 highly discriminative loci, was created in this study. These strains were divided into 421 STs using the new MLST scheme, as opposed to 223 STs assigned by the original MLST scheme. The proposed MLST has a discriminatory power of D = 0.983 (CI95% 0.981 to 0.984), compared to the original scheme's D = 0.919 (CI95% 0.911 to 0.927). Moreover, we identified new clonal complexes with our newly designed MLST scheme. The scheme proposed here is available within the PubMLST database. Although whole genome sequencing availability has increased rapidly, MLST remains an integral part of clinical epidemiology, mainly due to its high standardization and excellent robustness. In this study, we proposed and validated a new MLST scheme for E. faecium, which is based on genome-wide data and thus reflects the tested isolates' more accurate genetic similarity. IMPORTANCE Enterococcus faecium is one of the most important pathogens causing health care associated infections. One of the main reasons for its clinical importance is a rapidly spreading resistance to vancomycin and linezolid, which significantly complicates antibiotic treatment of infections caused by such resistant strains. Monitoring the spread and relationships between resistant strains causing severe conditions represents an important tool for implementing appropriate preventive measures. Therefore, there is an urgent need to establish a robust method enabling strain monitoring and comparison at the local, national, and global level. Unfortunately, the current, extensively used MLST scheme does not reflect the real genetic relatedness between individual strains and thus does not provide sufficient discriminatory power. This can lead directly to incorrect epidemiological measures due to insufficient accuracy and biased results.

Assessment of the relationship between the MLST genetic diversity of Listeria monocytogenes and growth under selective and non-selective conditions.

Listeria monocytogenes can grow under stressful conditions and contaminate various food categories. Progresss in DNA sequencing-based identification methods, such as multi-locus sequence typing (MLST) now allow for more accurate characterization of pathogens. L. monocytogenes MLST genetic diversity is reflected by the different prevalence of the "clonal complexes" (CCs) in foods or infections. Better understanding of the growth potentials of L. monocytogenes is essential for quantitative risk assessment and efficient detection across CCs genetic diversity. Using optical density measurements taken with an automated spectrophotometer, we compared the maximal growth rate and lag phase of 39 strains from 13 different CCs and various food origins, in 3 broths mimicking stresful food conditions (8 °C, aw 0.95 and pH5) and in ISO Standard enrichment broths (Half Fraser and Fraser). This is important as growth could influence risk through pathogen multiplication in food. Besides, enrichment problems could lead to a lack of detection of some CCs. Despite small differences highlighting natural intraspecific variability, our results show that growth performances of L. monocytogenes strains under the conditions tested in selective and non-selective broth do not appear to be strongly correlated to CCs and cannot explain higher CC "virulence" or prevalence.

Staphylococcus aureus from Atopic Dermatitis Patients: Its Genetic Structure and Susceptibility to Phototreatment.

We characterized the population of Staphylococcus aureus from patients with atopic dermatitis (AD) in terms of (i) genetic diversity, (ii) presence and functionality of genes encoding important virulence factors: staphylococcal enterotoxins (sea, seb, sec, sed), toxic shock syndrome 1 toxin (tsst-1), and Panton-Valentine leukocidin (lukS/lukF-PV) by spa typing, PCR, drug resistance profile determination, and Western blot. We then subjected the studied population of S. aureus to photoinactivation based on a light-activated compound called rose bengal (RB) to verify photoinactivation as an approach to effectively kill toxin-producing S. aureus. We have obtained 43 different spa types that can be grouped into 12 clusters, indicating for the first-time clonal complex (CC) 7 as the most widespread. A total of 65% of the tested isolates had at least one gene encoding the tested virulence factor, but their distribution differed between the group of children and adults, and between patients with AD and the control group without atopy. We detected a 3.5% frequency of methicillin-resistant strains (MRSA) and no other multidrug resistance. Despite genetic diversity and production of various toxins, all isolates tested were effectively photoinactivated (bacterial cell viability reduction ≥ 3 log10 units) under safe conditions for the human keratinocyte cell line, which indicates that photoinactivation can be a good option in skin decolonization. IMPORTANCE Staphylococcus aureus massively colonizes the skin of patients with atopic dermatitis (AD). It is worth noting that the frequency of detection of multidrug-resistant S. aureus (MRSA) in AD patients is higher than the healthy population, which makes treatment much more difficult. Information about the specific genetic background of S. aureus accompanying and/or causing exacerbations of AD is of great importance from the point of view of epidemiological investigations and the development of possible treatment options.