RESUMO
Methicillin-resistant Staphylococcus aureus (MRSA) was found in a dog for the first time in Sweden in 2006. Between October 2006 and May 2007, MRSA was diagnosed in 7 more dogs that had been treated in 3 different small animal hospitals, located 150-200 km apart, in different counties of Sweden. Screening of the animal hospital staff and environment in these small animal hospitals showed 20 of 152 staff to be positive for MRSA, with rates between 2% and 18% in the different hospitals, while all 128 environmental samples were negative. All MRSA isolates from dogs and staff belonged to spa type t032, were Panton-Valentine leukocidin (PVL)-negative, and had indistinguishable pulsed-field gel electrophoresis patterns, except for 2 isolates with closely related patterns. To our knowledge, this is the first report of multiple outbreaks of MRSA in dogs caused by the same strain within a short time frame, and appearing in a country with low prevalence of MRSA in both humans and dogs. This highlights the importance of infection control programs in animal hospitals and in animal health care. Awareness of MRSA as an occupational risk for veterinary personnel is essential.
Assuntos
Infecção Hospitalar/epidemiologia , Infecção Hospitalar/veterinária , Surtos de Doenças/veterinária , Doenças do Cão/epidemiologia , Staphylococcus aureus Resistente à Meticilina/isolamento & purificação , Infecções Estafilocócicas/epidemiologia , Infecções Estafilocócicas/veterinária , Técnicos em Manejo de Animais , Animais , Infecção Hospitalar/microbiologia , Surtos de Doenças/estatística & dados numéricos , Doenças do Cão/microbiologia , Cães , Hospitais Veterinários , Humanos , Infecções Estafilocócicas/microbiologia , Suécia/epidemiologia , Zoonoses/epidemiologia , Zoonoses/microbiologiaRESUMO
Epithelial cells are vital to sense the presence of bacteria, thereby initiating a proper innate immune response. This occurs via different mechanisms, e.g. recognition by pattern recognition receptors (TLR), or alteration of the cellular Ca2+ homeostasis. The Escherichia coli toxin cytolysin A (ClyA) is naturally delivered to target cells as active pore assemblies within outer membrane vesicles (OMVs), and we here investigate a possible role of ClyA-containing OMVs (ClyA+ (OMV)) for induction of proinflammatory responses via the above-mentioned mechanisms. We report that low, sublytic concentrations of ClyA+ (OMV) affect the Ca2+ homeostasis in epithelial cells by induction of slow, intracellular Ca2+ oscillations, while increased concentrations act cytolytically. Thus, ClyA belongs to the novel group of pore-forming toxins shown to elicit such biphasic responses. Ca2+ waves in the minute range have been shown to regulate gene transcription of, e.g. interleukin (IL)-6 and -8. While the periodicity of ClyA+ (OMV)-induced Ca2+ waves (22.9 +/- 0.9 min) fail to induce an IL-8 response, our data fit to the general concept of frequency-specific gene expression. Molecular investigations of the signal transduction pathway reveals that ClyA+ (OMV) utilize a different one as compared with those previously reported for other toxins causing Ca2+ waves. The ClyA protein per se and ClyA pore assemblies are non-immunogenic, while lipopolysaccharide present on the OMVs induces a TLR4-dependent proinflammatory response as expected. Additional membrane components of the OMV, e.g. OmpW, was also found to elicit proinflammatory responses that was independent of TLR4 and Ca2+ signalling.
Assuntos
Sinalização do Cálcio , Células Epiteliais/imunologia , Proteínas de Escherichia coli/metabolismo , Proteínas Hemolisinas/metabolismo , Glicoproteínas de Membrana/fisiologia , Receptores de Superfície Celular/fisiologia , Animais , Proteínas da Membrana Bacteriana Externa/imunologia , Cálcio/metabolismo , Células Cultivadas , Células Epiteliais/microbiologia , Escherichia coli/imunologia , Proteínas de Escherichia coli/imunologia , Feminino , Humanos , Imunidade Inata , Imunidade nas Mucosas , Interleucina-6/metabolismo , Interleucina-8/metabolismo , Lipopolissacarídeos/toxicidade , Ratos , Ratos Sprague-Dawley , Sistemas do Segundo Mensageiro , Transdução de Sinais , Receptor 4 Toll-Like , Receptores Toll-LikeRESUMO
Although human mucosal linings are continuously exposed to microbes, the microbes rarely induce disease. This is because mucosal surfaces are protected by a first line of defence termed the innate immunity system. Inflammatory processes are activated as a consequence of a complex interplay between microbes and host target cells. Although inflammation is essential for clearing out infectious agents, it can also be harmful to the host and is therefore subjected to tight control at multiple levels. It was recently discovered that the bacterial protein toxin alpha-haemolysin (HlyA), secreted by uropathogenic Escherichia coli, induces constant, low-frequency Ca2+ oscillations in renal epithelial cells. Ca2+ oscillation occurs at a characteristic periodicity of 12 min, and affects gene expression in target epithelial cells. Specifically, the proinflammatory cytokine interleukin-6 (IL-6) and chemokine IL-8 were induced by HlyA-induced Ca2+ oscillations. A few additional bacterial protein toxins have been reported to induce Ca2+ oscillations in target epithelial cells, although their effects are poorly understood. However, the pioneering work on HlyA demonstrates a novel feature of bacterial protein toxins on host target cells: as inducers of second messenger responses which fine-tune gene expression in target epithelial cells.
Assuntos
Toxinas Bacterianas/metabolismo , Cálcio/metabolismo , Escherichia coli/patogenicidade , Inflamação/microbiologia , Homeostase , Humanos , Mucosa Nasal/microbiologia , Mucosa Nasal/fisiologia , Transdução de SinaisRESUMO
Renal scarring after pyelonephritis is common in infancy. In this experimental study performed on tissue from 10-d-old infant and 40-d-old pubertal rats, several aspects of the renal innate immune response to a pyelonephritogenic strain of alpha-hemolysin-expressing Escherichia coli were compared. The kidney typically responds to urinary tract infection with release of proinflammatory cytokines, e.g. IL-6. Basal production of IL-6 from 10-d-old renal cortical tissue was approximately 20% of that from 40-d-old tissue. Six-hour incubation in the presence of supernatant from the E. coli culture caused an approximately 15-fold increase of IL-6 release in 10-d-old tissue and a 5-fold increase in 40-d-old tissue. The absolute level of IL-6 release in stimulated tissue was, however, significantly lower at 10 d than at 40 d. Lipopolysaccharide, the most immunogenic component of E. coli, signals via Toll-like receptor 4. Reverse transcriptase PCR performed on outer renal cortex indicated that expression of Toll-like receptor 4 mRNA was similar in both ages. Microdissection studies revealed that Toll-like receptor 4 mRNA was expressed in proximal tubules but not in glomeruli. The exotoxin alpha-hemolysin, expressed by a majority of uropathogenic E. coli isolates, stimulates IL-6 release via an alternative pathway that signals via intracellular calcium oscillations. We conclude that the higher susceptibility to pyelonephritic scarring is unlikely related to immaturity of innate immune system, as measured by cellular release of IL-6. Instead, the underlying mechanisms for pyelonephritic scarring are most likely multifactorial and may be mainly attributed to anatomic immaturity of the urinary tract.
Assuntos
Células Epiteliais/metabolismo , Escherichia coli/metabolismo , Rim/citologia , Rim/imunologia , Fatores Etários , Animais , Cálcio/metabolismo , Sinalização do Cálcio/fisiologia , Células Cultivadas , Criança , Células Epiteliais/imunologia , Células Epiteliais/microbiologia , Humanos , Técnicas In Vitro , Interleucina-6/imunologia , Interleucina-6/metabolismo , Rim/metabolismo , Rim/microbiologia , Receptores de Lipopolissacarídeos/imunologia , Receptores de Lipopolissacarídeos/metabolismo , Lipopolissacarídeos/metabolismo , Glicoproteínas de Membrana/imunologia , Glicoproteínas de Membrana/metabolismo , Ratos , Ratos Sprague-Dawley , Receptores de Superfície Celular/imunologia , Receptores de Superfície Celular/metabolismo , Receptor 4 Toll-Like , Receptores Toll-LikeRESUMO
Although the mucosal linings continuously are exposed to microbes, the microbes rarely induce disease. This is because mucosal surfaces are protected by a first line of host defence termed the innate immunity system. The innate immune response is an outcome of the complex interplay between microbes and host target cells, and leads to the activation of inflammatory processes. Although inflammation is essential for clearing out infectious agents, it can also be harmful to the host and is therefore subjected to control at multiple levels. We recently discovered that alpha-haemolysin, a toxin secreted by uropathogenic E. coli induces constant, low-frequency Ca2+ oscillations in renal epithelial cells (Uhlén et al., Nature 405, 694-696 (2000)). Ca2+ oscillation at a specific periodicity of 12 min was found to affect gene expression in target epithelial cells, as the proinflammatory cytokine IL-6 and chemokine IL-8 were specifically induced by alpha-haemolysin-induced Ca2+ oscillations. This demonstrates a novel feature of bacterial toxin effects on host target cells: as inducers of second messenger responses which fine-tune gene expression in target epithelial cells into pathways leading to e. g. a pro-inflammatory response.
Assuntos
Toxinas Bacterianas/metabolismo , Cálcio/metabolismo , Células Epiteliais/metabolismo , Escherichia coli/patogenicidade , Animais , Células Epiteliais/microbiologia , Escherichia coli/metabolismo , Regulação da Expressão Gênica , Proteínas Hemolisinas/metabolismo , Humanos , Interleucina-6/genética , Interleucina-6/metabolismo , Interleucina-8/genética , Interleucina-8/metabolismo , RimRESUMO
The ClyA protein is a pore-forming cytotoxin expressed by Escherichia coli and some other enterobacteria. It confers cytotoxic activity toward mammalian cells, but it has remained unknown how ClyA is surface exposed and exported from bacterial cells. Outer-membrane vesicles (OMVs) released from the bacteria were shown to contain ClyA protein. ClyA formed oligomeric pore assemblies in the OMVs, and the cytotoxic activity toward mammalian cells was considerably higher than that of ClyA protein purified from the bacterial periplasm. The redox status of ClyA correlated with its ability to form the oligomeric pore assemblies. In bacterial cells with a defective periplasmic disulphide oxidoreductase system, the ClyA protein was phenotypically expressed in a constitutive manner. The results define a vesicle-mediated transport mechanism in bacteria, and our findings show that the localization of proteins to OMVs directly may contribute to the activation and delivery of pathogenic effector proteins.