Localization of viable bacteria and bacterial antigens in arthritic joints of Erysipelothrix rhusiopathiae-infected pigs

Chondrocyte Invasion May Be a Mechanism for Persistent Staphylococcus Aureus Infection In Vitro

BACKGROUND

Recurrent bone and joint infection with Staphylococcus aureus is common. S. aureus can invade and persist in osteoblasts and fibroblasts, but little is known about this mechanism in chondrocytes. If S. aureus were able to invade and persist within chondrocytes, this could be a difficult compartment to treat.

QUESTION/PURPOSE

Can S. aureus infiltrate and persist intracellularly within chondrocytes in vitro?

METHODS

Cell lines were cultured in vitro and infected with S. aureus. Human chondrocytes (C20A4) were compared with positive controls of human osteoblasts (MG63) and mouse fibroblasts (NIH3T3), which have previously demonstrated S. aureus invasion and persistence (human fibroblasts were not available to us). Six replicates per cell type were followed for 6 days after infection. Cells were treated daily with antibiotic media for extracellular killing. To determine whether S. aureus can infiltrate chondrocytes, fluorescence microscopy was performed to qualitatively assess the presence of intracellular bacteria, and intracellular colony-forming units (CFU) were enumerated 2 hours after infection. To determine whether S. aureus can persist within chondrocytes, intracellular CFUs were enumerated from infected host cells each day postinfection.

RESULTS

S. aureus invaded human chondrocytes (C20A4) at a level (2.8 x 105 ± 5.5 x 104 CFUs/mL) greater than positive controls of human osteoblasts (MG63) (9.5 x 102 ± 2.5 x 102 CFUs/mL; p = 0.01) and mouse fibroblasts (NIH3T3) (9.1 x 104 ± 2.5 x 104 CFUs/mL; p = 0.02). S. aureus also persisted within human chondrocytes (C20A4) for 6 days at a level (1.4 x 103 ± 5.3 x 102 CFUs/mL) greater than that of human osteoblasts (MG63) (4.3 x 102 ± 3.5 x 101 CFUs/mL; p = 0.02) and mouse fibroblasts (NIH3T3) (0 CFUs/mL; p < 0.01). S. aureus was undetectable within mouse fibroblasts (NIH3T3) after 4 days. There were 0 CFUs yielded from cell media, confirming extracellular antibiotic treatment was effective.

CONCLUSION

S. aureus readily invaded human chondrocytes (C20A4) in vitro and persisted viably for 6 days after infection, evading extracellular antibiotics. Chondrocytes demonstrated a greater level of intracellular invasion and persistence by S. aureus than positive control human osteoblast (MG63) and mouse fibroblast (NIH3T3) cell lines.

CLINICAL RELEVANCE

Chondrocyte invasion and persistence may contribute to recurrent bone and joint infections. Additional research should assess longer periods of persistence and whether this mechanism is present in vivo.

Erysipelothrix rhusiopathiae-specific T-cell responses after experimental infection of chickens selectively bred for high and low serum levels of mannose-binding lectin

Erysipelas, caused by infection with Erysipelothrix rhusiopathiae (ER) is an important emerging disease in laying hens. We have earlier observed prominent mannose-binding lectin (MBL) acute phase responses in experimentally ER infected chickens. The present study aimed to further examine immune responses to ER by using chickens selectively bred for high (L10H) and low (L10L) serum MBL levels. Chickens were infected with ER at 3 weeks of age and immune parameters and bacterial load were monitored in blood until day 18 after infection. Blood and spleen leukocytes collected on day 18 were stimulated in vitro with ER antigens and blast transformation of different T-cell populations was assessed. The ER infection gave a very varied outcome and no clear differences were observed between L10H and L10L chickens with respect to leukocyte counts, bacterial load or clinical outcome. Nonetheless, rapid innate responses, e.g., heterophilia and increased serum MBL levels were noted in bacteraemic chickens. All ER infected chickens also showed transient increased expression of mannose receptor MRC1L-B and decreased expression of major histocompatibility complex II on monocytes day 1 after infection indicating monocyte activation or relocation. In vitro ER stimulation showed antigen specific blast transformation of CD4+, TCRγ/δ-CD8αβ+ and TCRγ/δ+CD8αβ+ spleen cells from all infected chickens. For CD4+ and TCRγ/δ-CD8αβ+ cells the proportions of blast transformed cells were significantly higher for samples from L10L chickens than those for samples from L10H chickens. This is the first observation of ER-specific T-cells in chickens and interestingly a Th1-type response comprising cytotoxic T-cells was indicated.

Intracellular Staphylococcus aureus in bone and joint infections: A mechanism of disease recurrence, inflammation, and bone and cartilage destruction

Bone and joint infections are devastating afflictions. Although medical interventions and advents have improved their care, bone and joint infections still portend dismal outcomes. Indeed, bone and joint infections are associated with extremely high mortality and morbidity rates and, generally, occur secondary to the aggressive pathogen Staphylococcus aureus. The consequences of bone and joint infections are further compounded by the fact that although they are aggressively treated, they frequently recur and result in massive bone and articular cartilage loss. Here, we review the literature and chronicle the fact that the fundamental cellular components of the musculoskeletal system can be internally infected with Staphylococcus aureus, which explains the ready recurrence of bone and joint infections even after extensive administration of antibiotic therapy and debridement and offer potential treatment solutions for further study. Moreover, we review the ramifications of intracellular infection and expound that the massive bone and articular cartilage loss is caused by the sustained proinflammatory state induced by infection and offer potential combination therapies for further study to protect bone and cartilage.

[Detection of Salmonella Choleraesuis var. Kunzendorf in a fattening pig with septicaemic salmonellosis. A case report]

The present case reports the detection of Salmonella (S.) Choleraesuis var. Kunzendorf and porcine circovirus type 2 in an organic fattening pig suffering from septicaemic salmonellosis and porcine dermatitis and nephropathy syndrome. Six weeks after pigs had been housed in an organic fattening farm, an increase in mortality, diarrhea and coughing was observed. In recent years, S. choleraesuis var. Kunzendorf has been frequently detected in wild boars in Germany, whereas the same serovar did not play an important role in the Western European domestic pig population. A direct transmission of this serovar from wild boars to domestic pigs in this case could not be proven. However, because wild boars are important reservoirs for the spread of epizootic diseases to the domestic pig population, this case emphasises the importance of taking epidemiological relationships under consideration and to comply with biosecurity measures according to German law (Schweinehaltungshygieneverordnung).

Acute and Chronic Erysipelothrix rhusiopathiae Infection in Lambs

Polyarthritis caused by Erysipelothrix rhusiopathiae is a relatively common infection in lambs characterized by low mortality and high morbidity. E. rhusiopathiae is a ubiquitous Gram-positive bacterium that is both a commensal and a pathogen of vertebrates. The disease was studied during an outbreak in a Norwegian Spæl sheep flock. In the acute phase, 48 of 230 (20%) lambs developed clinical signs and 4 died (1.7%). One acute case was necropsied and E. rhusiopathiae was cultured from all major organs investigated and from joints. There was a fibrinous polyarthritis, increased presence of monocytes in vessels, and necrosis of Purkinje cells. Sixteen of the diseased animals (33%) developed a chronic polyarthritis. Eight of these lambs were necropsied; all had lesions in major limb joints, and 3 of 8 also had lesions in the atlanto-occipital joint. At this stage, E. rhusiopathiae was cultured only from the joints in 7 of 8 (87.5%) lambs, but by real-time polymerase chain reaction, we showed persistence of the bacterium in several organs. Pulsed-field gel electrophoresis typing of the bacterial isolates indicated that the same strain caused the acute and chronic disease. Five of 6 (83%) chronically affected animals had amyloidosis of the spleen, and 6 of 8 (75%) had amyloidosis of the liver. All chronically affected animals had a glomerulonephritis, and 6 of 8 (75%) had sparse degeneration in the brain. Ceruloplasmin and haptoglobin were significantly increased in the chronically diseased lambs. These results show that chronic ovine erysipelas is not restricted to joints but is a multisystemic disease.

Development and Validation of an Immunohistochemical Method for Rapid Diagnosis of Swine Erysipelas in Formalin-Fixed, Paraffin-Embedded Tissue Samples

The objective of the study was to develop an immunohistochemical (IHC) assay for rapid detection of Erysipelothrix rhusiopathiae. Serotypes 1a, 1b, and 2 are most frequently associated with clinical disease in pigs. Antiserum against serotypes 1a, 1b, and 2 was produced in rabbits, pooled, and applied to formalin-fixed, paraffin-embedded tissue sections of pigs (lungs, heart, spleen, and skin). The results obtained with the IHC assay were compared with direct culture on tissue samples from experimentally inoculated pigs either treated ( n = 6) with antibiotics or untreated ( n = 8) as well as on samples from field cases ( n = 170) submitted to the Veterinary Diagnostic Laboratory at Iowa State University. The agreement between direct culture and IHC staining was found to be substantial. The results of the present study indicate that the IHC assay is highly sensitive and specific in detecting E. rhusiopathiae antigen in formalin-fixed, paraffin-embedded tissues. Results indicated that the IHC is particularly useful in cases in which pigs had been treated with antibiotics prior to submission and in which direct cultures of organs were negative. In addition, the IHC was found to be useful for detection of E. rhusiopathiae antigen in skin lesions, which are often culture negative.

Bacteria associated with immunoregulatory cells in mice

This study examined bacteria-immune interactions in a mouse model possessing microbiota-dependent immune regulatory features similar to those occurring in human atopy, colitis, and immune regulation. Associations between the abundance of several bacterial phylotypes and immunoregulatory target cell types were identified, suggesting that they may play a role in these phenotypes.

Evaluation of Erysipelothrix rhusiopathiae vaccines in pigs by intradermal challenge and immune responses

In a vaccine trial, pigs were challenged intradermally with eight E. rhusiopathiae strains of serovars 1a, 1b or 2 given concurrently. The strains were derived from six herds affected with vaccine breakdowns in 1997-1999, one herd without vaccine breakdown and a serovar 2 reference strain. Responses to two commercial bacterins (one implicated in the vaccine breakdowns), and two experimental bacterins (based on field isolates from affected herds) showed distinct differences in protection, particularly in clinical responses measured at 72 h. Less protection was afforded against serovar 1 challenge by the vaccine implicated in the vaccine breakdowns. Antibody and cell-mediated immune (CMI) responses were significantly different between treatments, and highlighted a similar post-vaccinal antibody response was produced against serovar 2 lysate by all vaccines, but only those providing significant protection against serovar 1 [corrected] produced significantly elevated antiserovar I lysate [corrected] antibodies. Vaccination in general significantly reduced CMI responses to the mitogens concanavalin A and phytohaemagglutinin. This experimental pig challenge system was readily able to confirm suboptimal performance of a commercial bacterin that had passed potency tests in mice but was associated with vaccine failure in commercial herds. This vaccine was also the most immunosuppressive to CMI responses associated with E. rhusiopathiae-specific and non-specific stimulation. The best vaccine response was associated with the highest mean serovar 1 antibody response and the highest CMI response (by lymphoproliferation assay) to serovar 2.