Dissemination of a highly virulent pathogen: tracking the early events that define infection

The series of events that occurs immediately after pathogen entrance into the body is largely speculative. Key aspects of these events are pathogen dissemination and pathogen interactions with the immune response as the invader moves into deeper tissues. We sought to define major events that occur early during infection of a highly virulent pathogen. To this end, we tracked early dissemination of Yersinia pestis, a highly pathogenic bacterium that causes bubonic plague in mammals. Specifically, we addressed two fundamental questions: (1) do the bacteria encounter barriers in disseminating to draining lymph nodes (LN), and (2) what mechanism does this nonmotile bacterium use to reach the LN compartment, as the prevailing model predicts trafficking in association with host cells. Infection was followed through microscopy imaging in addition to assessing bacterial population dynamics during dissemination from the skin. We found and characterized an unexpected bottleneck that severely restricts bacterial dissemination to LNs. The bacteria that do not pass through this bottleneck are confined to the skin, where large numbers of neutrophils arrive and efficiently control bacterial proliferation. Notably, bottleneck formation is route dependent, as it is abrogated after subcutaneous inoculation. Using a combination of approaches, including microscopy imaging, we tested the prevailing model of bacterial dissemination from the skin into LNs and found no evidence of involvement of migrating phagocytes in dissemination. Thus, early stages of infection are defined by a bottleneck that restricts bacterial dissemination and by neutrophil-dependent control of bacterial proliferation in the skin. Furthermore, and as opposed to current models, our data indicate an intracellular stage is not required by Y. pestis to disseminate from the skin to draining LNs. Because our findings address events that occur during early encounters of pathogen with the immune response, this work can inform efforts to prevent or control infection.

The earliest stage of any infection takes place when a pathogen enters the body (inoculation) at an initial site of contact. From this point, the pathogen can spread into deeper tissues where the pathogen itself and the immune responses against it cause disease. Very little is known about the events that follow inoculation and how pathogens move from the initial site of contact into deeper tissues. A better understanding of this process can potentially result in strategies to control or prevent disease. We studied the highly infectious bacterium that causes bubonic plague (Yersinia pestis) and how it spreads inside the body, from the skin into lymph nodes. We found that movement from the skin is highly restricted as only a small fraction of the bacteria that are deposited into this tissue are found in lymph nodes. While it is currently thought that Y. pestis spreads from the skin inside trafficking cells of the innate immune response, our work suggests these cells are not required for the bacteria to move into lymph nodes. Our findings can influence vaccine development efforts as these strategies are based on the study of early pathogen interactions with cells of the immune response.

Skin own bacteria may aggravate inflammatory and occlusive changes in atherosclerotic arteries of lower limbs

AIM

Seroepidemiological studies have given rise to the hypothesis that microorganisms like Chlamydia pneumoniae (CP), Helicobacter pylori (HP), cytomegalovirus (CMV), HCV types 1 and 2, and bacteria involved in dental or other unspecified infection sites may initiate or maintain the atherosclerotic process in lower limb arteries. However, not much attention has been attached to the patient's own limb skin and deep tissues bacterial flora, activated in ischemic tissues. This flora may enhance the inflammatory and thrombotic process in the atherosclerotic arteries. Lower limb tissues are exposed to microorganisms from the environment (foot) and microbes on floating epidermal cells from the perineal and anal regions. The aim of this paper was to identify microbial cells and their DNA in perivascular tissues and arterial walls of lower limbs.

METHODS

Bacterial cultures and PCR method for detection of 16sRNA and immunohistopathological staining for identification of immune cells infiltrating vascular bundles.

RESULTS

1) specimens of atherosclerotic calf and femoral arteries contained bacterial isolates and/or their DNA, whereas, in control normal cadaveric organ donors' limb arteries or patients' carotid arteries and aorta bacteria they were detected only sporadically; 2) lower limb lymphatics contained bacterial cells in 76% of specimens, whereas controls only in 10%; 3) isolates from limb arteries and lymphatics belonged in majority to the coagulase-negative staphylococci and S.aureus, however, other highly pathogenic strains were also detected; 4) immunohistopathological evaluation arterial walls showed dense focal infiltrates of granulocytes and macrophages.

CONCLUSION

Own bacterial isolates can be responsible for dense neutrophil and macrophage inflitrates of atherosclerotic walls and periarterial tissue in lower limbs and aggravate the ischemic changes.

Pulmonary lymphatics are primary sites of Mycobacterium tuberculosis infection in guinea pigs infected by aerosol

Mycobacterium tuberculosis causes a lymphatic vasculitis in the lungs of guinea pigs infected by a low-dose aerosol. This observation suggests that in addition to being a direct conduit from the lungs to the regional lymph nodes, pulmonary lymphatics are themselves sites of infection and could be the site of latent infection.

Endolymphatic infusion: human surgical investigation and application

The ability to influence changes within the lymphatic system, and to exert a therapeutic influence on the composition and quality of the lymph, may have a substantial impact on the therapeutic outcome in disease interventions. This report concerns our experience with endolymphatic infusion (ELI) of drugs, an approach that we have utilized in a surgical context to destroy bacteria within lymphatic vessels and lymph nodes. Experimentally, we have demonstrated that a variety of antibiotics will temporarily decrease the contractile activity of the lymphatic vessels and reduce the volume of lymph flow. Based on our initial observations, we have applied endolymphatic infusion to clinical care. ELI was evaluated in the treatment of 330 patients, utilizing protocols to alter the characteristics of lymph flow.