A pig model of acute Staphylococcus aureus induced pyemia

Phages for treatment of Staphylococcus aureus infection

Combating multi-drug resistant bacterial infections should be a universal urgency. The gram- positive Staphylococcus aureus (S. aureus) bacteria are generally harmless; healthy people frequently have them on their skin and nose. These bacteria, for the most part, produce no difficulties or only minor skin diseases. Antibiotics and cleansing of the affected region are usually the treatments of choice. S. aureus can become virulent causing serious infections that may lead to pustules to sepsis or death. Normally, it is thought that antibiotics may solve problems concerning bacterial infection; but unfortunately, Staphylococci have evolved mechanisms to resist drugs. Methicillin-Resistant Staphylococcus aureus (MRSA); both in hospitals and in the community, infections are evolving into dangerous pathogens. Health care practitioners may need to use antibiotics with more adverse effects to treat antibiotic-resistant S. aureus infections. Amid existing efforts to resolve this problem, phage therapy proposes a hopeful alternate to face Staphylococcal infections. When the majority of antibiotics have failed to treat infections caused by multidrug-resistant bacteria, such as methicillin- and vancomycin-resistant S. aureus, phage therapy may be an option. Here, we appraise the potential efficacy, current knowledge on bacteriophages for S. aureus, experimental research and information on their clinical application, and limitations of phage therapy for S. aureus infections.

Vaccination with Detoxified Leukocidin AB Reduces Bacterial Load in a Staphylococcus aureus Minipig Deep Surgical Wound Infection Model

Vaccines against Staphylococcus aureus have eluded researchers for >3 decades while the burden of staphylococcal diseases has increased. Early vaccine attempts mainly used rodents to characterize preclinical efficacy, and all subsequently failed in human clinical efficacy trials. More recently, leukocidin AB (LukAB) has gained interest as a vaccine antigen. We developed a minipig deep surgical wound infection model offering 3 independent efficacy readouts: bacterial load at the superficial and at the deep-seated surgical site, and dissemination of bacteria. Due to similarities with humans, minipigs are an attractive option to study novel vaccine candidates. With this model, we characterized the efficacy of a LukAB toxoid as vaccine candidate. Compared to control animals, a 3-log reduction of bacteria at the deep-seated surgical site was observed in LukAB-treated minipigs and dissemination of bacteria was dramatically reduced. Therefore, LukAB toxoids may be a useful addition to S. aureus vaccines and warrant further study.

Initial Immune Response in Escherichia coli, Staphylococcus aureus, and Candida albicans Bacteremia

Sepsis remains a leading cause of mortality worldwide and is characterized by sustained inflammatory responses, reflected as changes in the expression profile of cytokines with time. The aim of the present study was to investigate the dynamic changes in complete blood count, serum chemistry, procalcitonin (PCT), tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6) in Escherichia coli, Staphylococcus aureus, and Candida albicans bacteremia. Study subjects were 32 healthy male Landrace-Large White pigs, aged 10-15 weeks and of average weight 19 ± 2 kg. Bacteremia was induced by continuous intravenous infusion of microbial suspensions during a period of 8 h. E. coli and S. aureus bacteremia were associated with a significant gradual decrease in white blood cells and platelets, respectively (p = 0.002 and p = 0.004), while candidemia was characterized by a significant gradual decrease in lymphocytes (p = 0.009). Serum PCT levels were either undetectable or very low, with no significant changes with time in all groups. E. coli bacteremia elicited a strong pro-inflammatory response, characterized by a significant increase in TNF-α expression from the onset of bacteremia (p = 0.042). C. albicans exhibited a different profile with an early, moderate increase in TNF-α followed by a subsequent marked increase in IL-6 levels (p = 0.03). The differential regulation of inflammatory and hematological responses depending on the pathogenic agent can reveal differences in the underlying inflammatory mechanisms, which may assist in the ongoing quest for the identification of a panel of circulating biomarkers during bacteremia.

Epinecidin-1 Protects against Methicillin Resistant Staphylococcus aureus Infection and Sepsis in Pyemia Pigs

Methicillin resistant Staphylococcus aureus (MRSA) may be found on the skin, nose, and throats of long-term hospitalized patients. While MRSA infections are usually minor, serious infections and death may occur in immunocompromised or diabetic patients, or after exposure of MRSA to blood. This report demonstrates that the antimicrobial peptide (AMP) epinecidin-1 (Epi-1) efficiently protects against MRSA infection in a pyemia pig model. We first found that Epi-1 exhibits bactericidal activity against MRSA. Next, pharmacokinetic analysis revealed that Epi-1 was stable in serum for 4 h after injection, followed by a gradual decrease. This pharmacokinetic profile suggested Epi-1 may bind serum albumin, which was confirmed in vitro. Harmful effects were not observed for doses up to 100 mg/kg body weight in pigs. When Epi-1 was supplied as a curative agent 30 min post-infection, MRSA-induced abnormalities in blood uric acid (UA), blood urea nitrogen (BUN), creatine (CRE), GOT, and GPT levels were restored to normal levels. We further showed that the bactericidal activity of Epi-1 was higher than that of the antibiotic drug vancomycin. Epi-1 significantly decreased MRSA counts in the blood, liver, kidney, heart, and lungs of infected pigs. Elevated levels of serum C reactive protein (CRP), proinflammatory cytokine IL6, IL1β, and TNFα were also attenuated by Epi-1 treatment. Moreover, the MRSA genes, enterotoxin (et)-A, et-B, intrinsic methicillin resistance A (mecA), and methicillin resistance factor A (femA), were significantly reduced or abolished in MRSA-infected pigs after treatment with Epi-1. Hematoxylin and eosin staining of heart, liver, lung, and kidney sections indicated that Epi-1 attenuated MRSA toxicity in infected pigs. A survival study showed that the pyemia pigs infected with MRSA alone died within a week, whereas the pigs post-treated with 2.5 mg/kg Epi-1 were completely protected against death. The present investigation, thus, demonstrates that Epi-1 effectively protects pyemia pigs against pathogenic MRSA without major toxic side effects.

Dietary Bovine Lactoferrin Reduces Staphylococcus aureus in the Tissues and Modulates the Immune Response in Piglets Systemically Infected with S. aureus

BACKGROUND

Bovine lactoferrin (bLf) reduces Staphylococcus aureus infection in premature infants and promotes the growth of Bifidobacterium infantis, a predominant infant gut species. We hypothesized that bLf in combination with B. infantis would reduce the severity of systemic S. aureus infection.

OBJECTIVE

The aim was to determine the effects of oral administration of bLf and B. infantis on the course of systemic S. aureus infection.

METHODS

Colostrum-deprived piglets were fed formulas containing 4 g whey/L (CON group) or bLf (LF group). One-half of the piglets in each group were gavaged with B. infantis (109 colony-forming units/d), resulting in 2 additional groups (BI or COMB, respectively). On day 7, piglets were intravenously injected with S. aureus. Blood samples were collected preinfection and every 12 h postinfection for immune analyses. Tissue samples were collected on day 12 for analysis of bacterial abundance and gene expression.

RESULTS

Preinfection, LF piglets had lower serum interleukin 10 (IL-10), a higher percentage of lymphocytes, and a lower percentage of neutrophils than BI or COMB piglets. After infection, dietary bLf increased piglet weight gain, reduced staphylococcal counts in the kidneys, and tended to lower staphylococcal counts in the lungs and heart. Dietary bLf also decreased kidney IL-10 and increased lung interferon γ (IFN-γ) mRNA. B. infantis increased splenic IFN-γ expression. Renal Toll-like receptor 2 was upregulated in BI piglets but not in COMB piglets. Postinfection, BI piglets had increased serum IL-10 and decreased memory T cell populations. LF and COMB piglets had fewer circulating monocytes and B cells than CON or BI piglets.

CONCLUSIONS

Dietary bLf and B. infantis produced independent and tissue-specific effects. Piglets fed bLf alone or in combination with B. infantis mounted a more effective immune response and exhibited lower bacterial abundance. This study provides biological underpinnings to the clinical benefits of bLf observed in preterm infants but does not support B. infantis administration during S. aureus infection.

A Novel Porcine Model of Septic Shock Induced by Acute Respiratory Distress Syndrome due to Methicillin-resistant Staphylococcus aureus

Background:

Sepsis is one of the main causes of mortality in critically ill patients following progression to septic shock. To investigate the pathophysiologic changes of sepsis, we developed a novel porcine model of septic shock induced by acute respiratory distress syndrome (ARDS) due to methicillin-resistant Staphylococcus aureus (MRSA) pneumonia.

Methods:

Twenty-six male Landraces (Lvyuanweiye, Beijing, China) weighing 30 ± 2 kg were divided into four groups: sham group (SH; n = 5); cotton smoke inhalation group (SM; n = 6); MRSA pneumonia group (MR; n = 6); and septic shock group with cotton smoke inhalation + MRSA pneumonia (SS; n = 9). Extensive hemodynamics, oxygen dynamics, and lung function were monitored for 24 h following the injury or until death. Tissues were collected, and histopathology evaluations were carried out.

Results:

Blood cultures from 6 of 9 animals in the SS group were positive for MRSA. Two hours following the injury, decreased mean arterial blood pressure (60–70 mmHg) and cardiac index (<2 L·min⁻¹·m⁻²) were observed in the animals in the SS group, while systemic vascular resistance index was increased. The hemodynamic characteristics of septic shock were only observed in the SS group but not significant in the other groups. The PO₂/FiO₂ in the SM and SS groups decreased to 300 and 100, respectively. In the SS group, extravascular lung water index increased to 20 ml/kg, whereas thoracopulmonary compliance decreased to 10 ml/H₂O after injury. Deterioration of pulmonary function in the SS group was more serious than the SM and MR groups. Severe lung injury in the SS group was confirmed by the histopathology evaluations. The lung injury confirmed by high-resolution thin-section computed tomography and histopathology in the SS group was more serious than those of other groups.

Conclusions:

In the present study, we developed a novel porcine model of septic shock induced by ARDS due to severe MRSA pneumonia with characteristic hyperdynamic and hypodynamic phases in 24 h, which mimicked the hemodynamic changing of septic shock in human.

Port d'Entrée for Respiratory Infections - Does the Influenza A Virus Pave the Way for Bacteria?

Bacterial and viral co-infections of the respiratory tract are life-threatening and present a global burden to the global community. Staphylococcus aureus, Streptococcus pneumoniae, and Streptococcus pyogenes are frequent colonizers of the upper respiratory tract. Imbalances through acquisition of seasonal viruses, e.g., Influenza A virus, can lead to bacterial dissemination to the lower respiratory tract, which in turn can result in severe pneumonia. In this review, we summarize the current knowledge about bacterial and viral co-infections of the respiratory tract and focus on potential experimental models suitable for mimicking this disease. Transmission of IAV and pneumonia is mainly modeled by mouse infection. Few studies utilizing ferrets, rats, guinea pigs, rabbits, and non-human primates are also available. The knowledge gained from these studies led to important discoveries and advances in understanding these infectious diseases. Nevertheless, mouse and other infection models have limitations, especially in translation of the discoveries to humans. Here, we suggest the use of human engineered lung tissue, human ex vivo lung tissue, and porcine models to study respiratory co-infections, which might contribute to a greater translation of the results to humans and improve both, animal and human health.

Antimicrobial peptide Epinecidin-1 promotes complete skin regeneration of methicillin-resistant Staphylococcus aureus-infected burn wounds in a swine model

This report shows that the antimicrobial peptide (AMP) Epinecidin-1 (Epi-1) efficiently heals MRSA-infected heat burn injuries and provides protection from infection in a pig model. The presence of an optimal level of Epi-1 induces cell proliferation by promoting cell cycle progression through an increase in S-phase cells. Epi-1 also induces proliferation to cover the wounded region in an in vitro cell proliferation assay using immortalized human epithelial HaCaT cells. Next, the in vivo wound healing efficiency of Epi-1 was tested in heat-burned pig skin infected with MRSA under in vivo conditions. Treatment of the injury with Epi-1 for 1 h at six hours post-infection completely healed the wound within 25 days. Conversely, the injury in the untreated control was not healed 25 days post-infection. Histological staining of wound sections with H&E showed that Epi-1 enhanced vascularization and increased epithelial activities in the wound region. Neutrophil recruitment to the wounded region in the Epi-1-treated sections was visualized by Giemsa staining. Additionally, Masson's trichrome staining of wound sections confirmed that Epi-1 enhanced extracellular collagen compound formation. The induction of sepsis-associated blood C-reactive protein (CRP) and the pro-inflammatory cytokine IL-6 in response to MRSA infection was also suppressed in pigs that received Epi-1. Taken together, the results demonstrate that the biomaterial Epi-1 heals wounds through increasing epithelial cell proliferation, vascularization, and the formation of collagen and controls MRSA infection-mediated sepsis in pigs.

Utility of 11C-methionine and 11C-donepezil for imaging of Staphylococcus aureus induced osteomyelitis in a juvenile porcine model: comparison to autologous 111In-labelled leukocytes, 99m Tc-DPD, and 18F-FDG

The aim of this study was to compare ¹¹C-methionine and ¹¹C-donepezil positron emission tomography (PET) with ¹¹¹In-labeled leukocyte and ^99m Tc-DPD (Tc-99m 3,3-diphosphono-1,2-propanedicarboxylic acid) single-photon emission computed tomography (SPECT), and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET to improve detection of osteomyelitis. The tracers' diagnostic utility where tested in a juvenile porcine hematogenously induced osteomyelitis model comparable to osteomyelitis in children. Five 8-9 weeks old female domestic pigs were scanned seven days after intra-arterial inoculation in the right femoral artery with a porcine strain of Staphylococcus aureus. The sequential scan protocol included Computed Tomography, ¹¹C-methionine and ¹¹C-donepezil PET, ^99m Tc-DPD and ¹¹¹In-labelled leukocytes scintigraphy, and ¹⁸F-FDG PET. This was followed by necropsy of the pigs and gross pathology, histopathology, and microbial examination. The pigs developed a total of 24 osteomyelitic lesions, 4 lesions characterized as contiguous abscesses and pulmonary abscesses (in two pigs). By comparing the 24 osteomyelitic lesions, ¹⁸F-FDG accumulated in 100%, ¹¹¹In-leukocytes in 79%, ¹¹C-methionine in 79%, ¹¹C-donepezil in 58%, and ^99m Tc-DPD in none. Overall, ¹⁸F-FDG PET was superior to ¹¹¹In-leukocyte SPECT and ¹¹C-methionine in marking infectious lesions.

Human microbiota-associated swine: current progress and future opportunities

Gnotobiotic (GN) rodent models have provided insight into the contributions of the gut microbiota to host health and preventing disease. However, rodent models are limited by several important physiological and metabolic differences from humans, and many rodent models do not dependably replicate the clinical manifestations of human diseases. Due to the high degree of similarity in anatomy, physiology, immunology and brain growth, the domestic pig (Sus scrofa) is considered a clinically relevant model to study factors influencing human gastrointestinal, immune, and brain development. Gnotobiotic piglet models have been developed and shown to recapitulate key aspects of GN rodent models. Human microbiota-associated (HMA) piglets have been established using inocula from infants, children, and adults. The gut microbiota of recipient HMA piglets was more similar to that of the human donor than that of conventionally reared piglets harboring a pig microbiota. Moreover, Bifidobacterium and Bacteroides, two predominant bacterial groups of infant gut, were successfully established in the HMA piglets. Thus, the HMA pig model has the potential to be a valuable model for investigating how the gut microbiota composition changes in response to environmental factors, such as age, diet, vaccination, antibiotic use and infection. The HMA also represents a robust model for screening the efficacy of pre- and probiotic interventions. Lastly, HMA piglets can be an ideal model with which to elucidate microbe-host interactions in human health and disease due to the similarities to humans in anatomy, physiology, developmental maturity at birth, and the pathophysiology of many human diseases.

Biodistribution of the radionuclides (18)F-FDG, (11)C-methionine, (11)C-PK11195, and (68)Ga-citrate in domestic juvenile female pigs and morphological and molecular imaging of the tracers in hematogenously disseminated Staphylococcus aureus lesions

Approximately 5-7% of acute-care patients suffer from bacteremia. Bacteremia may give rise to bacterial spread to different tissues. Conventional imaging procedures as X-ray, Computed Tomography (CT), Magnetic Resonance Imaging (MRI), and ultrasound are often first-line imaging methods for identification and localization of infection. These methods are, however, not always successful. Early identification and localization of infection is critical for the appropriate and timely selection of therapy. The aim of this study was thus; a head to head comparison of (18)F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET) to PET with tracers that potentially could improve uncovering of infectious lesions in soft tissues. We chose (11)C-methionine, (11)C-PK11195, and (68)Ga-citrate as tracers and besides presenting their bio-distribution we validated their diagnostic utility in pigs with experimental bacterial infection. Four juvenile 14-15 weeks old female domestic pigs were scanned seven days after intra-arterial inoculation in the right femoral artery with a porcine strain of S. aureus using a sequential scanning protocol with (18)F-FDG, (11)C-methionine, (11)C-PK11195 and (68)Ga-citrate. This was followed by necropsy of the pigs consisting of gross pathology, histopathology and microbial examination. The pigs primarily developed lesions in lungs and neck muscles. (18)F-FDG had higher infection to background ratios and accumulated in most infectious foci caused by S. aureus, while (11)C-methionine and particularly (11)C-PK11195 and (68)Ga-citrate accumulated to a lesser extent in infectious foci. (18)F-FDG-uptake was seen in the areas of inflammatory cells and to a much lesser extent in reparative infiltration surrounding necrotic regions.

Whole-Genome Sequence of Staphylococcus aureus S54F9 Isolated from a Chronic Disseminated Porcine Lung Abscess and Used in Human Infection Models

We obtained a draft genome sequence of Staphylococcus aureus strain S54F9, which was isolated from a chronic disseminated porcine lung abscess and used in porcine infection models. Genes coding for a number of toxins, including enterotoxins and superantigen, were demonstrated in this strain.

Comparison of autologous (111)In-leukocytes, (18)F-FDG, (11)C-methionine, (11)C-PK11195 and (68)Ga-citrate for diagnostic nuclear imaging in a juvenile porcine haematogenous staphylococcus aureus osteomyelitis model

The aim of this study was to compare (111)In-labeled leukocyte single-photon emission computed tomography (SPECT) and (18)F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET) to PET with tracers that potentially could improve detection of osteomyelitis. We chose (11)C-methionine, (11)C-PK11195 and (68)Ga-citrate and validated their diagnostic utility in a porcine haematogenous osteomyelitis model. Four juvenile 14-15 weeks old female pigs were scanned seven days after intra-arterial inoculation in the right femoral artery with a porcine strain of Staphylococcus aureus using a sequential scan protocol with (18)F-FDG, (68)Ga-citrate, (11)C-methionine, (11)C-PK11195, (99m)Tc-Nanocoll and (111)In-labelled autologous leukocytes. This was followed by necropsy of the pigs and gross pathology, histopathology and microbial examination. The pigs developed a total of five osteomyelitis lesions, five lesions characterized as abscesses/cellulitis, arthritis in three joints and five enlarged lymph nodes. None of the tracers accumulated in joints with arthritis. By comparing the 10 infectious lesions, (18)F-FDG accumulated in nine, (111)In-leukocytes in eight, (11)C-methionine in six, (68)Ga-citrate in four and (11)C-PK11195 accumulated in only one lesion. Overall, (18)F-FDG PET was superior to (111)In-leukocyte SPECT in marking infectious and proliferative, i.e. hyperplastic, lesions. However, leukocyte SPECT was performed as early scans, approximately 6 h after injection of the leukocytes, to match the requirements of the 18 h long scan protocol. (11)C-methionine and possibly (68)Ga-citrate may be useful for diagnosis of soft issue lesions.

A rabbit model of non-typhoidal Salmonella bacteremia

Bacteremia is an important cause of morbidity and mortality in humans. In this study, we focused on the development of an animal model of bacteremia induced by non-typhoidal Salmonella. New Zealand White rabbits were inoculated with a human isolate of non-typhoidal Salmonella strain CVD J73 via the intra-peritoneal route. Blood samples were collected at specific time points and at euthanasia from infected rabbits. Additionally, tissue samples from the heart, lungs, spleen, gastrointestinal tract, liver and kidneys were obtained at euthanasia. All experimentally infected rabbits displayed clinical signs of disease (fever, dehydration, weight loss and lethargy). Tissues collected at necropsy from the animals exhibited histopathological changes indicative of bacteremia. Non-typhoidal Salmonella bacteria were detected in the blood and tissue samples of infected rabbits by microbiological culture and real-time PCR assays. The development of this animal model of bacteremia could prove to be a useful tool for studying how non-typhoidal Salmonella infections disseminate and spread in humans.

Brain microabscesses in a porcine model of Staphylococcus aureus sepsis

BACKGROUND

Sepsis caused by Staphylococcus aureus often leads to brain microabscesses in humans. Animal models of haematogenous brain abscesses would be useful to study this condition in detail. Recently, we developed a model of S. aureus sepsis in pigs and here we report that brain microabscesses develop in pigs with such induced S. aureus sepsis.Twelve pigs were divided into three groups. Nine pigs received an intravenous inoculation of S. aureus once at time 0 h (group 1) or twice at time 0 h and 12 h (groups 2 and 3). In each group the fourth pig served as control. The pigs were euthanized at time 12 h (Group 1), 24 h (Group 2) and 48 h (Group 3) after the first inoculation. The brains were collected and examined histopathologically.

RESULTS

All inoculated pigs developed sepsis and seven out of nine pigs developed brain microabscesses. The microabscesses contained S. aureus and were located in the prosencephalon and mesencephalon. Chorioditis and meningitis occurred from 12 h after inoculation.

CONCLUSIONS

Pigs with experimental S. aureus sepsis often develop brain microabscesses. The porcine brain pathology mirrors the findings in human sepsis patients. We therefore suggest the pig as a useful animal model of the development of brain microabscesses caused by S. aureus sepsis.

Disseminated intravascular coagulation in a novel porcine model of severe Staphylococcus aureus sepsis fulfills human clinical criteria

Sepsis is a common and often fatal complication in human patients in intensive care units. Relevant and well characterized animal models of sepsis may provide valuable information on pathophysiological mechanisms and be a mean of testing new therapeutic strategies. Large animal models of Staphylococcus aureus sepsis are rare, even though S. aureus increasingly affects human patients. Sepsis changes the haemostatic balance and leads to endothelial cell (EC) activation, coagulopathy and, in severe cases, disseminated intravascular coagulation (DIC). The aim of this study was to characterize the haemostatic and vascular alterations in a novel porcine model of severe S. aureus sepsis, investigating whether the changes fulfill the human clinical criteria for DIC. Five pigs were inoculated intravenously with S. aureus and two control animals were sham-inoculated. Blood samples were collected for thromboelastography (TEG) and assessment of plasma-based haemostatic parameters. Tissue was collected for histopathology and reverse transcriptase quantitative real-time polymerase chain reaction for measurement of mRNA encoding EC markers. All infected animals developed DIC; including procoagulant activation represented by hypercoagulable TEG profiles and prolonged clotting time. Histologically, numerous pulmonary thrombi were present in one pig. Inhibitor consumption was represented by decreasing antithrombin levels in infected pigs. Hyaline globules were found in three infected pigs, confirming fibrinolytic activation. EC activation was identified by expression of von Willebrand factor in small vessels together with elevated mRNA encoding activated EC markers. Severe haemostatic and vascular changes fulfilling the human criteria for DIC were therefore seen in all infected pigs. A tendency towards uncompensated DIC was seen in two animals.

The diabetic ocular environment facilitates the development of endogenous bacterial endophthalmitis

PURPOSE

We tested the hypothesis that changes in the diabetic ocular environment facilitate the development of endogenous bacterial endophthalmitis (EBE).

METHODS

C57BL/6J mice were rendered diabetic with streptozotocin (STZ) for 1, 3, or 5 months' duration. Diabetic and age-matched nondiabetic mice were tail vein-injected with 10(8) CFU of Klebsiella pneumoniae, a common cause of EBE in diabetics. After either 2 or 4 days postinfection, the EBE incidence was assessed by electroretinography, histology, bacterial counts, and myeloperoxidase ELISAs. Blood-retinal barrier (BRB) permeability in uninfected diabetic mice also was determined.

RESULTS

No cases of EBE were observed among the 1-month diabetic group. Extending the time from diabetes induction to 3 months resulted in a 23.8% EBE incidence after 2 days, and a 22% incidence after 4 days. The incidence of EBE increased to 27% in the 5-month diabetic group. Infected eyes had an average 8.01 × 10(2) and 6.19 × 10(4) CFU/eye for the 3- and 5-month diabetic groups, respectively. There was no significant difference in BRB permeability between control and 1-month uninfected diabetic mice. However, 3- and 5-month diabetic mice had significantly greater BRB permeability than control mice. These results suggested that increasing the time from STZ diabetes induction to 3 and 5 months resulted in an ocular environment more conducive to the development of EBE.

CONCLUSIONS

These results demonstrated a correlation between an increase in BRB permeability and an increase in EBE incidence, supporting the hypothesis that diabetic ocular changes contribute to the development of EBE.

The use of sequential organ failure assessment parameters in an awake porcine model of severe Staphylococcus aureus sepsis

The human sequential organ failure assessment (SOFA) scoring system is used worldwide in intensive care units for assessing the extent of organ dysfunction/failure in patients with severe sepsis. An increasing number of septic cases are caused by Gram-positive bacteria as Staphylococcus aureus. The aim of the current study was to apply the human SOFA parameters in an awake, porcine model of severe S. aureus sepsis. Five pigs were inoculated intravenously with S. aureus and two control animals were sham-inoculated. Extensive clinical monitoring and sequential blood sampling was obtained and analysed for SOFA parameters. Dysfunction/failure was observed in the respiratory, haemostatic and hepatic system of all infected animals, together with initial cardiovascular dysfunction. The pulmonary system was the first to fail clinically, which corresponds with similar human findings, whereas the liver was affected earlier in pigs compared to humans. The use of human SOFA parameters was valuable in identifying dysfunctional/failing organs and showed consistency between this porcine model and human severe sepsis. Applying SOFA parameters in this model increased the relevance for comparison to clinical methods of evaluating human severe sepsis. Changes in SOFA parameters may in future porcine studies serve as a target for monitoring the effect of therapeutic intervention.

The pig: a model for human infectious diseases

An animal model to study human infectious diseases should accurately reproduce the various aspects of disease. Domestic pigs (Sus scrofa domesticus) are closely related to humans in terms of anatomy, genetics and physiology, and represent an excellent animal model to study various microbial infectious diseases. Indeed, experiments in pigs are much more likely to be predictive of therapeutic treatments in humans than experiments in rodents. In this review, we highlight the numerous advantages of the pig model for infectious disease research and vaccine development and document a few examples of human microbial infectious diseases for which the use of pigs as animal models has contributed to the acquisition of new knowledge to improve both animal and human health.

Colonization kinetics of different methicillin-resistant Staphylococcus aureus sequence types in pigs and host susceptibilities

In this study we investigated the kinetics of colonization, the host susceptibility and transmissibility of methicillin-resistant Staphylococcus aureus (MRSA) after nasal treatment of pigs with three different MRSA strains of distinctive clonal lineages (sequence type 398 [ST398], ST8, and ST9), and origin in weaning piglets. The colonization dose of 5.0 × 10(8) CFU/animal was determined in preliminary animal studies. A total of 57 piglets were randomly divided into four test groups and one control group. Each of three test groups was inoculated intranasally with either MRSA ST8, MRSA ST9, or MRSA ST398. The fourth group was a mixture of animals inoculated with MRSA ST398 and noninoculated "sentinel" animals. Clinical signs, the nasal, conjunctival, and skin colonization of MRSA, fecal excretion, and organ distribution of MRSA, as well as different environmental samples were examined. After nasal inoculation with MRSA piglets of all four test groups showed no clinical signs of an MRSA infection. MRSA was present on the nasal mucosa, skin, and conjunctiva in all four test groups, including sentinel animals. Likewise, fecal excretion and internal colonization of MRSA ST8, ST9, and ST398 could be shown in each group. However, fecal excretion and the colonization rate of the nasal mucosa with MRSA ST9 were significantly lower in the first days after infection than in test groups infected with ST8 and ST398. The results of this study suggest differences in colonization potential of the different MRSA types in pigs. Furthermore, colonization of lymph nodes (e.g., the ileocecal lymph node) with MRSA of the clonal lineage ST398 was demonstrated.

A porcine model of acute, haematogenous, localized osteomyelitis due to Staphylococcus aureus: a pathomorphological study

A porcine model of acute, haematogenous, localized osteomyelitis was established. Serial dilutions of Staphylococcus aureus [5-50-500-5000-50 000 CFU/kg body weight (BW) suspended in saline or saline alone] were inoculated into the right brachial artery of pigs (BW 15 kg) separated into six groups of two animals. During the infection, blood was collected for cultivation, and after the animals were killed from day 5 to 15, they were necropsied and tissues were sampled for histopathology. Animals receiving ≤500 CFU/kg BW were free of lesions. Pigs inoculated with 5000 and 50 000 CFU/kg BW only developed microabscesses in bones of the infected legs. In the centre of microabscesses, S. aureus was regularly demonstrated together with necrotic neutrophils. Often, bone lesions resulted in trabecular osteonecrosis. The present localized model of acute haematogenous osteomyelitis revealed a pattern of development and presence of lesions similar to the situation in children. Therefore, this model should be reliably applied in studies of this disease with respect to e.g. pathophysiology and pathomorphology. Moreover, because of the regional containment of the infection to a defined number of bones, the model should be applicable also for screening of new therapy strategies.

Intravenous inoculation of Staphylococcus aureus in pigs induces severe sepsis as indicated by increased hypercoagulability and hepatic dysfunction

Nine pigs were inoculated intravenously once or twice with 10(8) Staphylococcus aureus per kilogram body weight and sacrificed 12, 24 and 48 h after inoculation. Three sham-infected pigs served as controls. Blood samples were taken for bacteriology, haematology and clinical chemistry. A necropsy was carried out and tissue samples were collected for bacteriology and histology. The onset of clinical disease was seen at 7-8 h after inoculation. The blood bacterial counts remained low throughout the study. All infected pigs developed sepsis characterized by fever, neutrophilia, increased levels of C-reactive protein (CRP) and IL-6, and decreased levels of serum iron. The CRP and IL-6 levels peaked at 36 h, whereas IL-1beta and tumour necrosis factor-alpha showed no obvious changes. Thromboelastography showed increasing hypercoagulability from 12 h and onwards, whereas the platelet numbers declined slightly throughout the experiment. The levels of serum aspartate aminotransferase and bilirubin were elevated at 24 and 36 h. In conclusion, sepsis and severe sepsis were induced as evidenced by dysfunction of the blood clotting system and the liver.

Animal models of sepsis

In this review, we start with a general discussion of relevant factors that can determine the validity of a sepsis animal model. We briefly review some of the currently used animal models of sepsis (small animal models and large animal models). We discuss the clinical relevance of animal models in sepsis research today and address potential reasons for the apparent underperformance of animal models in predicting therapeutic success of novel drugs in clinical trials.