Microbiota and metabolic adaptation shape Staphylococcus aureus virulence and antimicrobial resistance during intestinal colonization.

Depletion of microbiota increases susceptibility to gastrointestinal colonization and subsequent infection by opportunistic pathogens such as methicillin-resistant Staphylococcus aureus (MRSA). How the absence of gut microbiota impacts the evolution of MRSA is unknown. The present report used germ-free mice to investigate the evolutionary dynamics of MRSA in the absence of gut microbiota. Through genomic analyses and competition assays, we found that MRSA adapts to the microbiota-free gut through sequential genetic mutations and structural changes that enhance fitness. Initially, these adaptations increase carbohydrate transport; subsequently, evolutionary pathways largely diverge to enhance either arginine metabolism or cell wall biosynthesis. Increased fitness in arginine pathway mutants depended on arginine catabolic genes, especially nos and arcC, which promote microaerobic respiration and ATP generation, respectively. Thus, arginine adaptation likely improves redox balance and energy production in the oxygen-limited gut environment. Findings were supported by human gut metagenomic analyses, which suggest the influence of arginine metabolism on colonization. Surprisingly, these adaptive genetic changes often reduced MRSA's antimicrobial resistance and virulence. Furthermore, resistance mutation, typically associated with decreased virulence, also reduced colonization fitness, indicating evolutionary trade-offs among these traits. The presence of normal microbiota inhibited these adaptations, preserving MRSA's wild-type characteristics that effectively balance virulence, resistance, and colonization fitness. The results highlight the protective role of gut microbiota in preserving a balance of key MRSA traits for long-term ecological success in commensal populations, underscoring the potential consequences on MRSA's survival and fitness during and after host hospitalization and antimicrobial treatment.

Quorum-sensing agr system of Staphylococcus aureus primes gene expression for protection from lethal oxidative stress.

The agr quorum-sensing system links Staphylococcus aureus metabolism to virulence, in part by increasing bacterial survival during exposure to lethal concentrations of H2O2, a crucial host defense against S. aureus. We now report that protection by agr surprisingly extends beyond post-exponential growth to the exit from stationary phase when the agr system is no longer turned on. Thus, agr can be considered a constitutive protective factor. Deletion of agr resulted in decreased ATP levels and growth, despite increased rates of respiration or fermentation at appropriate oxygen tensions, suggesting that Δagr cells undergo a shift towards a hyperactive metabolic state in response to diminished metabolic efficiency. As expected from increased respiratory gene expression, reactive oxygen species (ROS) accumulated more in the agr mutant than in wild-type cells, thereby explaining elevated susceptibility of Δagr strains to lethal H2O2 doses. Increased survival of wild-type agr cells during H2O2 exposure required sodA, which detoxifies superoxide. Additionally, pretreatment of S. aureus with respiration-reducing menadione protected Δagr cells from killing by H2O2. Thus, genetic deletion and pharmacologic experiments indicate that agr helps control endogenous ROS, thereby providing resilience against exogenous ROS. The long-lived 'memory' of agr-mediated protection, which is uncoupled from agr activation kinetics, increased hematogenous dissemination to certain tissues during sepsis in ROS-producing, wild-type mice but not ROS-deficient (Cybb-/-) mice. These results demonstrate the importance of protection that anticipates impending ROS-mediated immune attack. The ubiquity of quorum sensing suggests that it protects many bacterial species from oxidative damage.

Prophage-encoded methyltransferase drives adaptation of community-acquired methicillin-resistant Staphylococcus aureus.

We recently described the evolution of a community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) USA300 variant responsible for an outbreak of skin and soft tissue infections. Acquisition of a mosaic version of the Φ11 prophage (mΦ11) that increases skin abscess size was an early step in CA-MRSA adaptation that primed the successful spread of the clone. The present report shows how prophage mΦ11 exerts its effect on virulence for skin infection without encoding a known toxin or fitness genes. Abscess size and skin inflammation were associated with DNA methylase activity of an mΦ11-encoded adenine methyltransferase (designated pamA). pamA increased expression of fibronectin-binding protein A (fnbA; FnBPA), and inactivation of fnbA eliminated the effect of pamA on abscess virulence without affecting strains lacking pamA. Thus, fnbA is a pamA-specific virulence factor. Mechanistically, pamA was shown to promote biofilm formation in vivo in skin abscesses, a phenotype linked to FnBPA's role in biofilm formation. Collectively, these data reveal a novel mechanism-epigenetic regulation of staphylococcal gene expression-by which phage can regulate virulence to drive adaptive leaps by S. aureus.

Transcription-replication interactions reveal bacterial genome regulation.

Organisms determine the transcription rates of thousands of genes through a few modes of regulation that recur across the genome1. In bacteria, the relationship between the regulatory architecture of a gene and its expression is well understood for individual model gene circuits2,3. However, a broader perspective of these dynamics at the genome scale is lacking, in part because bacterial transcriptomics has hitherto captured only a static snapshot of expression averaged across millions of cells4. As a result, the full diversity of gene expression dynamics and their relation to regulatory architecture remains unknown. Here we present a novel genome-wide classification of regulatory modes based on the transcriptional response of each gene to its own replication, which we term the transcription-replication interaction profile (TRIP). Analysing single-bacterium RNA-sequencing data, we found that the response to the universal perturbation of chromosomal replication integrates biological regulatory factors with biophysical molecular events on the chromosome to reveal the local regulatory context of a gene. Whereas the TRIPs of many genes conform to a gene dosage-dependent pattern, others diverge in distinct ways, and this is shaped by factors such as intra-operon position and repression state. By revealing the underlying mechanistic drivers of gene expression heterogeneity, this work provides a quantitative, biophysical framework for modelling replication-dependent expression dynamics.

Staphylococcus aureus senses human neutrophils via PerR to coordinate the expression of the toxin LukAB.

Staphylococcus aureus is a gram-positive pathogen that poses a major health concern, in part due to its large array of virulence factors that allow infection and evasion of the immune system. One of these virulence factors is the bicomponent pore-forming leukocidin LukAB. The regulation of lukAB expression is not completely understood, especially in the presence of immune cells such as human polymorphonuclear neutrophils (hPMNs). Here, we screened for transcriptional regulators of lukAB during the infection of primary hPMNs. We uncovered that PerR, a peroxide sensor, is vital for hPMN-mediated induction of lukAB and that PerR upregulates cytotoxicity during the infection of hPMNs. Exposure of S. aureus to hydrogen peroxide (H2O2) alone also results in increased lukAB promoter activity, a phenotype dependent on PerR. Collectively, our data suggest that S. aureus uses PerR to sense the H2O2 produced by hPMNs to stimulate the expression of lukAB, allowing the bacteria to withstand these critical innate immune cells.IMPORTANCEStaphylococcus aureus utilizes a diverse set of virulence factors, such as leukocidins, to subvert human neutrophils, but how these toxins are regulated is incompletely defined. Here, we identified the peroxide-sensitive repressor, PerR, as a required protein involved in the induction of lukAB in the presence of primary human neutrophils, a phenotype directly linked to the ability of PerR to sense H2O2. Thus, we show that S. aureus coordinates sensing and resistance to oxidative stress with toxin production to promote pathogen survival.

Quorum-sensing agr system of Staphylococcus aureus primes gene expression for protection from lethal oxidative stress.

The agr quorum-sensing system links Staphylococcus aureus metabolism to virulence, in part by increasing bacterial survival during exposure to lethal concentrations of H2O2, a crucial host defense against S. aureus. We now report that protection by agr surprisingly extends beyond post-exponential growth to the exit from stationary phase when the agr system is no longer turned on. Thus, agr can be considered a constitutive protective factor. Deletion of agr increased both respiration and fermentation but decreased ATP levels and growth, suggesting that Δagr cells assume a hyperactive metabolic state in response to reduced metabolic efficiency. As expected from increased respiratory gene expression, reactive oxygen species (ROS) accumulated more in the agr mutant than in wild-type cells, thereby explaining elevated susceptibility of Δagr strains to lethal H2O2 doses. Increased survival of wild-type agr cells during H2O2 exposure required sodA, which detoxifies superoxide. Additionally, pretreatment of S. aureus with respiration-reducing menadione protected Δagr cells from killing by H2O2. Thus, genetic deletion and pharmacologic experiments indicate that agr helps control endogenous ROS, thereby providing resilience against exogenous ROS. The long-lived "memory" of agr-mediated protection, which is uncoupled from agr activation kinetics, increased hematogenous dissemination to certain tissues during sepsis in ROS-producing, wild-type mice but not ROS-deficient (Nox2-/-) mice. These results demonstrate the importance of protection that anticipates impending ROS-mediated immune attack. The ubiquity of quorum sensing suggests that it protects many bacterial species from oxidative damage.

Antimicrobial overproduction sustains intestinal inflammation by inhibiting Enterococcus colonization.

Loss of antimicrobial proteins such as REG3 family members compromises the integrity of the intestinal barrier. Here, we demonstrate that overproduction of REG3 proteins can also be detrimental by reducing a protective species in the microbiota. Patients with inflammatory bowel disease (IBD) experiencing flares displayed heightened levels of secreted REG3 proteins that mediated depletion of Enterococcus faecium (Efm) from the gut microbiota. Efm inoculation of mice ameliorated intestinal inflammation through activation of the innate immune receptor NOD2, which was associated with the bacterial DL-endopeptidase SagA that generates NOD2-stimulating muropeptides. NOD2 activation in myeloid cells induced interleukin-1ß (IL-1ß) secretion to increase the proportion of IL-22-producing CD4+ T helper cells and innate lymphoid cells that promote tissue repair. Finally, Efm was unable to protect mice carrying a NOD2 gene variant commonly found in IBD patients. Our findings demonstrate that inflammation self-perpetuates by causing aberrant antimicrobial activity that disrupts symbiotic relationships with gut microbes.

Transcription-replication interactions reveal principles of bacterial genome regulation.

Organisms determine the transcription rates of thousands of genes through a few modes of regulation that recur across the genome1. These modes interact with a changing cellular environment to yield highly dynamic expression patterns2. In bacteria, the relationship between a gene's regulatory architecture and its expression is well understood for individual model gene circuits3,4. However, a broader perspective of these dynamics at the genome-scale is lacking, in part because bacterial transcriptomics have hitherto captured only a static snapshot of expression averaged across millions of cells5. As a result, the full diversity of gene expression dynamics and their relation to regulatory architecture remains unknown. Here we present a novel genome-wide classification of regulatory modes based on each gene's transcriptional response to its own replication, which we term the Transcription-Replication Interaction Profile (TRIP). We found that the response to the universal perturbation of chromosomal replication integrates biological regulatory factors with biophysical molecular events on the chromosome to reveal a gene's local regulatory context. While the TRIPs of many genes conform to a gene dosage-dependent pattern, others diverge in distinct ways, including altered timing or amplitude of expression, and this is shaped by factors such as intra-operon position, repression state, or presence on mobile genetic elements. Our transcriptome analysis also simultaneously captures global properties, such as the rates of replication and transcription, as well as the nestedness of replication patterns. This work challenges previous notions of the drivers of expression heterogeneity within a population of cells, and unearths a previously unseen world of gene transcription dynamics.

MRSA lineage USA300 isolated from bloodstream infections exhibit altered virulence regulation.

The epidemic community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) USA300 lineage has recently become a leading cause of hospital-associated bloodstream infections (BSIs). Here, we leveraged this recent introduction into hospitals and the limited genetic variation across USA300 isolates to identify mutations that contribute to its success in a new environment. We found that USA300 BSI isolates exhibit altered virulence regulation. Using comparative genomics to delineate the genes involved in this phenotype, we discovered repeated and independent mutations in the transcriptional regulator sarZ. Mutations in sarZ resulted in increased virulence of USA300 BSI isolates in a murine model of BSI. The sarZ mutations derepressed the expression and production of the surface protein ClfB, which was critical for the pathogenesis of USA300 BSI isolates. Altogether, these findings highlight ongoing evolution of a major MRSA lineage and suggest USA300 strains can optimize their fitness through altered regulation of virulence.

The tempo and mode of gene regulatory programs during bacterial infection.

Innate immune recognition of bacterial pathogens is a key determinant of the ensuing systemic response, and host or pathogen heterogeneity in this early interaction can impact the course of infection. To gain insight into host response heterogeneity, we investigate macrophage inflammatory dynamics using primary human macrophages infected with Group B Streptococcus. Transcriptomic analysis reveals discrete cellular states within responding macrophages, one of which consists of four sub-states, reflecting inflammatory activation. Infection with six additional bacterial species-Staphylococcus aureus, Listeria monocytogenes, Enterococcus faecalis, Yersinia pseudotuberculosis, Shigella flexneri, and Salmonella enterica-recapitulates these states, though at different frequencies. We show that modulating the duration of infection and the presence of a toxin impacts inflammatory trajectory dynamics. We provide evidence for this trajectory in infected macrophages in an in vivo model of Staphylococcus aureus infection. Our cell-state analysis defines a framework for understanding inflammatory activation dynamics in response to bacterial infection.

Microbiome-Independent Effects of Antibiotics in a Murine Model of Nosocomial Infections.

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most common causes of hospital-acquired pneumonia. To better manage patients with MRSA pneumonia, we require a greater understanding of the host-pathogen interactions during infection. MRSA research focuses on highly virulent and cytotoxic strains, which demonstrate robust phenotypes in animal models of infection. However, nosocomial infections are often caused by hospital-acquired MRSA (HA-MRSA) isolates that exhibit low cytotoxicity and few or no phenotypes in mice, thereby confounding mechanistic studies of pathogenesis. Consequently, virulence pathways utilized by HA-MRSA in nosocomial pneumonia are largely unknown. Here, we report that conditioning mice with broad-spectrum antibiotics lowers the barrier to pneumonia, thereby transforming otherwise avirulent HA-MRSA isolates into lethal pathogens. HA-MRSA isolates are avirulent in gnotobiotic mice, mimicking results in conventional animals. Thus, the observed enhanced susceptibility to infection in antibiotic-treated mice is not due to depletion of the microbiota. More generally, we found that antibiotic conditioning leads to increased susceptibility to infection by diverse antimicrobial-resistant (AMR) pathogens of low virulence. Treatment with antibiotics leads to dehydration and malnutrition, suggesting a potential role for these clinically relevant and reducible hospital complications in susceptibility to pathogens. In sum, the model described here mitigates the impact of low virulence in immunocompetent mice, providing a convenient model to gain fundamental insight into the pathogenesis of nosocomial pathogens. IMPORTANCE Antimicrobial-resistant (AMR) pathogens are responsible for over 2.8 million infections and over 35,000 deaths per year in the United States. To study these microbes, animal models that are susceptible to these pathogens are required. However, many of these pathogens exhibit low virulence in conventional mice, which has negatively impacted mechanistic studies. Here, we show that mice treated with antibiotics in their drinking water become exquisitely susceptible to low-virulence AMR pathogens. Surprisingly, the increased susceptibility was independent of the impact of antibiotics on the microbiome and seems to be due to an unintended consequence of antibiotic treatment: weight loss due to dehydration and caloric restriction. Unlike other models used to sensitize mice to low-virulence pathogens, our model does not reduce phagocyte numbers. Thus, here, we describe an immunocompetent mouse model to facilitate the identification of novel targets and accelerate the development of preventives and therapeutics to combat infections by AMR pathogens.

A regulatory cascade controls Staphylococcus aureus pathogenicity island activation.

Staphylococcal pathogenicity islands (SaPIs) are a family of closely related mobile chromosomal islands that encode and disseminate the superantigen toxins, toxic shock syndrome toxin 1 and superantigen enterotoxin B (SEB). They are regulated by master repressors, which are counteracted by helper phage-encoded proteins, thereby inducing their excision, replication, packaging and intercell transfer. SaPIs are major components of the staphylococcal mobilome, occupying five chromosomal att sites, with many strains harbouring two or more. As regulatory interactions between co-resident SaPIs could have profound effects on the spread of superantigen pathobiology, we initiated the current study to search for such interactions. Using classical genetics, we found that, with one exception, their regulatory systems do not cross-react. The exception was SaPI3, which was originally considered defective because it could not be mobilized by any known helper phage. We show here that SaPI3 has an atypical regulatory module and is induced not by a phage but by many other SaPIs, including SaPI2, SaPIbov1 and SaPIn1, each encoding a conserved protein, Sis, which counteracts the SaPI3 repressor, generating an intracellular regulatory cascade: the co-resident SaPI, when conventionally induced by a helper phage, expresses its sis gene which, in turn, induces SaPI3, enabling it to spread. Using bioinformatics analysis, we have identified more than 30 closely related coancestral SEB-encoding SaPI3 relatives occupying the same att site and controlled by a conserved regulatory module, immA-immR-str'. This module is functionally analogous but unrelated to the typical SaPI regulatory module, stl-str. As SaPIs are phage satellites, SaPI3 and its relatives are SaPI satellites.

Emergence and spread of worldwide Staphylococcus aureus clones among cystic fibrosis patients.

BACKGROUND: The aim of this study was to assess the relatedness of molecular types of Staphylococcus aureus isolates colonizing cystic fibrosis (CF) patients with their antimicrobial resistance and prevalence of toxin genes. METHODS: A total of 215 isolates from the airways of 107 patients with CF were tested for spa and SCCmec type, antimicrobial resistance and carriage of toxin genes. RESULTS: t015, t084, t091, t700 and t002 were the largest group (approximately 25%) among all 69 identified spa types. Five new spa types, t14286, t14287, t14288, t14289 and t14290, were identified and registered. Isolates from CF patients were clustered into 11 multi-locus sequence typing clonal complexes, with CC30, CC22, CC97, CC45, CC15 and CC5 being the most frequent ones. Twelve (5.6%) methicillin-resistant S. aureus (MRSA) isolates and 102 (47.7%) multidrug-resistant isolates were identified, along with three SCCmec types (I, III and V). All isolates (both MRSA and methicillin-sensitive S. aureus) were Panton-Valentine leucocidin-negative, and 56.7% harbored egc genes. This was the first study documenting the presence of ST398-V-t571 livestock-associated MRSA in a European patient with CF. CONCLUSION: These findings imply that individuals with CF can also be colonized with animal-related ST398 MRSA, and justify constant monitoring of staphylococcal colonization and identification of epidemic S. aureus clones in this group.

Production of Staphylococcal Enterotoxins D and R in Milk and Meat Juice by Staphylococcus aureus Strains.

Seventeen Staphylococcus aureus strains were tested for production of staphylococcal enterotoxin D (SED) and staphylococcal enterotoxin R (SER) in milk and meat juice. SED was secreted in milk by 12 S. aureus strains at 6-54 ng/mL at 24 h and 9-98 ng/mL at 48 h. Another five strains secreted SED at 0.9-1.9 µg/mL at 24 h and at 1.2-2.4 µg/mL at 48 h. Strains producing high levels of SED in milk secreted 77-666 µg/mL of SED in meat juice at 24 h and 132-1225 µg/mL at 48 h. Strains producing lower amounts of SED in milk secreted 228-1109 ng/mL of SED at 24 h and 377-1782 ng/mL at 48 h in meat juice. Tested S. aureus strains produced SER in milk at 33-183 ng/mL at 24 h and 41-832 ng/mL at 48 h. Fourteen strains produced more SER in meat juice than in milk (17- to 232-fold and 15- to 269-fold more at 24 and 48 h, respectively). Three S. aureus strains secreted less than 74 ng/mL of SER in meat juice. Expression pattern of known enterotoxin regulators, that is, agrA, sarA, hld, rot, and sigB, was similar in selected strong and weak SED producers grown in both food matrices and could not explain differences in enterotoxin protein level. This suggests that enterotoxin regulation is more complex than previously thought. We demonstrated that in a number of tested S. aureus strains, production of SED and SER was significantly decreased in milk when compared with meat juice, supporting previous reports. However, certain strains secreted high amounts of SED and SER, irrespective of environment, likely contributing to higher food safety risk.

Midkine is up-regulated in both cancerous and inflamed bowel, reflecting lymph node metastasis in colorectal cancer and clinical activity of ulcerative colitis.

Midkine is a multifunctional cytokine and growth factor displaying proinflammatory and pro-tumorigenic activity. Its association with bowel diseases has not been fully elucidated. Our purpose was to delineate midkine expression pattern by RT-qPCR in inflamed/cancerous bowel (n=208) and whole blood (n=150) in colorectal cancer (CRC), Crohn's disease (CD), and ulcerative colitis (UC) and to evaluate midkine dynamics in early postoperative period following colorectal surgery. The expression of midkine was significantly up-regulated in stage III CRC and independently associated with lymph node metastasis. The expression of midkine in whole blood was up-regulated solely in N1 CRC. Midkine expression in cancer-free tissue (CRC) was also elevated and dependent on CRC advancement. In IBD, inflammation increased the bowel expression of midkine solely in UC, in a manner proportional to the disease clinical activity. Large and small bowel differed with respect to the expression of midkine in quiescent tissue (higher in small bowel) and to its correlation pattern with chemokines (in a large bowel) and angiogenic factors and cell cycle regulators (in a small bowel). Circulating midkine and its expression in whole blood dropped directly following colorectal surgery; however, the concentration of midkine in serum was restored on postoperative day three. Midkine is involved in bowel inflammation in UC and lymph node metastasis in CRC, rendering midkine an attractive target for their treatment. Owing to midkine elevation in early postoperative period and its overexpression in tumor-adjacent tissue, targeting midkine might be considered also as a prevention of CRC recurrence following curative tumor resection.

Molecular identification of Giardia duodenalis isolates from domestic dogs and cats in Wroclaw, Poland.

INTRODUCTION: Giardia duodenalis (G. intestinalis) is a common protozoan causing gastrointestinal disorders in many species of mammals. The genus of Giardia has high molecular diversity. Dogs and cats, in addition to their typical infection with assemblages C, D and F, may be a reservoir of zoonotic assemblages (A and B). OBJECTIVE: The aim of this study was a genetic characteristic of Giardia isolates of dogs and cats from the area of Wroclaw (Poland). MATERIALS AND METHOD: A total of 128 and 33 faecal samples from dogs and cats, respectively, were analyzed by routine coprological methods. The animals were diagnosed on the presence of G. duodenalis antigens in faeces soluble with the use of SNAP Giardia (IDEXX Laboratories) immunosorbent assay. 27 DNA isolates of Giardia were subjected to molecular identification (PCR-RFLP). RESULTS AND CONCLUSIONS: The prevalence of G. duodenalis was 21.1% (27/128) in dogs and 15.1% (5/33) in cats. In dogs, C assemblage was present in 18 (81%) positive stool samples, D assemblage in 2 (9%) samples, B assemblage present in one (4.5%), and mixed assemblages (C and D) occurred in one (4.5%) sample. F assemblage was found in 4 (80%) cats' positive stool samples and A assemblage occurred in one case (20%). Confirmation of the presence of A and B zoonotic assemblages suggests that infected pets can be a threat to human health. This study describes for the first time the presence of mixed infections within host-specific C and D assemblages in dogs in Poland.

Production of staphylococcal enterotoxins in microbial broth and milk by Staphylococcus aureus strains harboring seh gene.

Twenty Staphylococcus aureus strains harboring seh gene, including one carrying also sec gene and 11 sea gene, were grown in BHI+YE broth and milk and were tested for SEA, SEC and SEH production. All strains decreased pH of BHI+YE broth at 24h and increased them at 48h. Seventeen S. aureus strains grown in milk changed pH for no >0.3 unit until 48h. Three other S. aureus strains significantly decreased pH during growth in milk. All S. aureus produced SEH in BHI+YE broth in amounts ranging from 95 to 1292ng/ml, and from 170 to 4158ng/ml at 24 and 48h, respectively. SEH production in milk by 17 strains did not exceed 23ng/ml at 24h and 36ng/ml at 48h. Three S. aureus strains able to decrease milk pH produced 107-3029ng/ml and 320-4246ng/ml of SEH in milk at 24 and 48h, respectively. These strains were grown in milk and BHI+YE broth with pH stabilized at values near neutral leading to a significant decrease of SEH production. Representative weak SEH producers were grown in milk at reduced pH resulting in moderate increase in SEH production. SEA was produced in milk by 10S. aureus strains at 24-151ng/ml at 24h, and 31-303ng/ml at 48h. SEA production in milk was higher or comparable as in BHI+YE broth in 3 strains and lower for remaining strains. Production of SEC by sec-positive S. aureus strains was lower in milk than in BHI+YE broth, ranging from 131 to 2319ng/ml at 24 and 48h in milk and 296-30,087ng/ml in BHI+YE at 24 and 48h. Both lacE and lacG transcripts involved in lactose metabolism were significantly up-regulated in milk in strong SEH producers. In these strains hld, rot and sarA transcripts were up-regulated in milk as compared to weak SEH producers. Stabilization of milk pH at a value of raw milk significantly down-regulated hld, rot and sarA RNA in strong SEH producers. Milk was generally found unfavorable for enterotoxin production. However, certain S. aureus strains were not restricted in SEH and SEA expression in milk, unlike SEC which remained down-regulated in this environment. Therefore, low safety risk related to S. aureus producing SEC in milk, as suggested previously, may not pertain to certain SEA and SEH-producing strains.

Serum availability affects expression of common house-keeping genes in colon adenocarcinoma cell lines: implications for quantitative real-time PCR studies.

Careful selection of housekeeping genes (HKG) is prerequisite to yield sound qPCR results. HKG expression varies in response to hypoxia but the effect of manipulations of serum availability, a common experimental procedure, remains unknown. Also, no data on HKG expression stability across colon adenocarcinoma lines that would aid selection of normalizers suitable for studies involving several lines are available. Thus, we evaluated the effect of serum availability on the expression of commonly used HKG (ACTB, B2M, GAPDH, GUSB, HPRT1, IPO8, MRPL19, PGK1, PPIA, RPLP0, RPS23, SDHA, TBP, UBC, and YWHAZ) in seven colon adenocarcinoma cell lines (Caco-2, DLD-1, HCT116, HT29, Lovo, SW480, and SW620). Sets of stably expressed line-specific and pan-line HKG were validated against absolutely quantified CDKN1A, TP53, and MDK transcripts. Both serum availability and line type affected HKG expression. UBC was fourfold down-regulated and HPRT1 1.75-fold up-regulated in re-fed HT29 cultures. Line-to-line variability in HKG expression was more pronounced than that caused by altering serum availability and could be found even between isogenic cell lines. PPIA, RPLP0, YWHAZ, and IPO8 were repeatedly highly ranked while ACTB, B2M, UBC, and PGK1 were ranked poorly. Normalization against PPIA/RPLP0/SDHA was found optimal for studies involving various colon adenocarcinoma cell lines subjected to manipulations of serum availability. We found HKG expression to vary, more pronouncedly by line type than growth conditions with significant differences also between isogenic cell lines. Although using line-specific normalizers remains optimal, a set of pan-line HKG that yields good estimation of relative expression of target genes was proposed.

Genotype and enterotoxigenicity of Staphylococcus epidermidis isolate from ready to eat meat products.

We have previously shown that potentially pathogenic isolates of Staphylococcus epidermidis occur at high incidence in ready-to-eat food. Now, within 164 samples of ready-to-eat meat products we identified 32 S. epidermidis isolates. In 8 isolates we detected the genes encoding for staphylococcal enterotoxins, but in 7 S. epidermidis isolates these genes were not stable over passages. One isolate designated 4S was shown to stably harbour sec and sel genes. In the genome sequence of S. epidermidis 4S we identified 21,426-bp region flanked by direct-repeats, encompassing sec and sel genes, corresponding to the previously described composite staphylococcal pathogenicity island (SePI) in S. epidermidis FRI909. Alignment of S. epidermidis 4S and S. epidermidis FRI909 SePIs revealed 6 nucleotide mismatches located in 5 of the total of 29 ORFs. Genomic location of S. epidermidis 4S SePI was the same as in FRI909. S. epidermidis 4S is a single locus variant of ST561, being genetically different from FRI909. SECepi was secreted by S. epidermidis 4S to BHI broth ranging from 14 to almost 36µg/mL, to milk ranging from 6 to 9ng/mL, to beef meat juice from 2 to 3µg/mL and to pork meat juice from 1 to 2µg/mL after 24 and 48h of cultivation, respectively. We provide the first evidence that S. epidermidis occurring in food bears an element encoding an orthologue to Staphylococcus aureus SEC, and that SECepi can be produced in microbial broth, milk and meat juices. Regarding that only enterotoxins produced by S. aureus are officially tracked in food in EU, the ability to produce enterotoxin by S. epidermidis pose real risk for food safety.

Isolation of Staphylococcus microti from milk of dairy cows with mastitis.

The present paper is a case-report of multiple udder infections in a dairy herd caused by Staphylococcus microti. Over a 22-month period, eleven S. microti isolates from milk samples from 9 cows were collected. The animals experienced subclinical (with one exception) intramammary infections with a high self-cure rate. The identification of the microorganism was carried out by means of two independent approaches: nucleotide sequence analysis of the 16S rRNA gene, as well as some housekeeping genes (sodA, rpoB, dnaJ), and matrix-assisted laser desorption ionization-time of flight mass spectrometry. All S. microti isolates belonged to an apparently single clone (as detected by the RAPD analysis), indicating that the microorganism could adapt, to some degree, to the bovine mammary gland or even spread from cow to cow in a contagious manner. This report is, to our knowledge, the first ever case of bovine mastitis caused by S. microti and the first instance of isolation of this microorganism from domesticated animals.