Impact of air humidity on the tenacity of different agents in bioaerosols.

Despite the variety of pathogens that are transmitted via the airborne route, few data are available on factors that influence the tenacity of airborne pathogens. In order to better understand and thus control airborne infections, knowledge of these factors is important. In this study, three agents, S. aureus, G. stearothermophilus spores and the MS2 bacteriophage, were aerosolized at relative humidities (RH) varying between 30% and 70%. Air samples were then analyzed to determine the concentration of the agents. S. aureus was found to have significantly lower survival rate in the aerosol at RH above 60%. It showed the lowest recovery rates of the three agents, ranging from 0.13% at approximately 70% RH to 4.39% at 30% RH. G. stearothermophilus spores showed the highest tenacity with recovery rates ranging from 41.85% to 61.73% with little effect of RH. For the MS2 bacteriophage, a significantly lower tenacity in the aerosol was observed with a recovery rate of 4.24% for intermediate RH of approximately 50%. The results of this study confirm the significant influence of the RH on the tenacity of airborne microorganisms depending on the specific agent. These data show that the behavior of microorganism in bioaerosols is varies under different environmental conditions.

Low airborne tenacity and spread of ESBL-/AmpC-producing Escherichia coli from fertilized soil by wind erosion.

ESBL-/AmpC-producing Escherichia coli from organic fertilizers were previously detected on soil surfaces of arable land and might be emitted by wind erosion. To investigate this potential environmental transmission path, we exposed ESBL-/AmpC-positive chicken litter, incorporated in agricultural soils, to different wind velocities in a wind tunnel and took air samples for microbiological analysis. No data exist concerning the airborne tenacity of ESBL-/AmpC-producing E. coli. Therefore, we explored the tenacity of two ESBL/AmpC E. coli strains and E. coli K12 in aerosol chamber experiments at different environmental conditions. In the wind tunnel, ESBL/AmpC-producing E. coli were detected in none of the air samples (n = 66). Non-resistant E. coli were qualitatively detected in 40.7% of air samples taken at wind velocities exceeding 7.3 m s-1 . Significantly increased emission of total viable bacteria with increasing wind velocity was observed. In the aerosol chamber trials, recovery rates of airborne E. coli ranged from 0.003% to 2.8%, indicating a low airborne tenacity. Concluding, an emission of ESBL/AmpC E. coli by wind erosion in relevant concentrations appears unlikely because of the low concentration in chicken litter compared with non-resistant E. coli and their low airborne tenacity, proven in the aerosol chamber trials.

The domestic pig as human-relevant large animal model to study adaptive antifungal immune responses against airborne Aspergillus fumigatus.

Pulmonary mucosal immune response is critical for preventing opportunistic Aspergillus fumigatus infections. Although fungus-specific CD4+ T cells in blood are described to reflect the actual host-pathogen interaction status, little is known about Aspergillus-specific pulmonary T-cell responses. Here, we exploit the domestic pig as human-relevant large animal model and introduce antigen-specific T-cell enrichment in pigs to address Aspergillus-specific T cells in the lung compared to peripheral blood. In healthy, environmentally Aspergillus-exposed pigs, the fungus-specific T cells are detectable in blood in similar frequencies as observed in healthy humans and exhibit a Th1 phenotype. Exposing pigs to 106 cfu/m3 conidia induces a long-lasting accumulation of Aspergillus-specific Th1 cells locally in the lung and also systemically. Temporary immunosuppression during Aspergillus-exposure showed a drastic reduction in the lung-infiltrating antifungal T-cell responses more than 2 weeks after abrogation of the suppressive treatment. This was reflected in blood, but to a much lesser extent. In conclusion, by using the human-relevant large animal model the pig, this study highlights that the blood clearly reflects the mucosal fungal-specific T-cell reactivity in environmentally exposed as well as experimentally exposed healthy pigs. But, immunosuppression significantly impacts the mucosal site in contrast to the initial systemic immune response.

Influence of Immune Status on the Airborne Colonization of Piglets with Methicillin-Resistant Staphylococcus aureus (MRSA) Clonal Complex (CC) 398.

Colonized vertebrates including humans and pigs are to date the main reservoirs of livestock-associated Methicillin-resistant Staphylococcus aureus (LA-MRSA). Currently, the mechanisms underlying colonization of pigs are not fully understood. We investigated the influence of piglet pre-immune status on airborne MRSA colonization. Three groups of MRSA-negative piglets were primed and exposed to airborne LA-MRSA (104 colony forming units (cfu)/m3) in an aerosol chamber for 24 h. One group was treated intramuscularly with dexamethasone (1 mg/kg body weight) to imitate weaning stress. The second group was exposed to bacterial endotoxin containing MRSA aerosol. Both conditions play a role in the development of multifactorial diseases and may promote MRSA colonization success. The third group served as control. The piglets' MRSA status was monitored for 21 days via swab samples. At necropsy, specific tissues and organs were analyzed. Blood was collected to examine specific immunological parameters. The duration of MRSA colonization was not extended in both treated groups compared to the control group, indicating the two immune-status influencing factors do not promote MRSA colonization. Blood sample analysis confirmed a mild dexamethasone-induced immune suppression and typical endotoxin-related changes in peripheral blood. Of note, the low-dose dexamethasone treatment showed a trend of increased MRSA clearance.

Persistent and Transient Airborne MRSA Colonization of Piglets in a Newly Established Animal Model.

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) was first found in 2005 and is up to date widespread in animal husbandry reservoir - focusing on pig farming. The regular detectability of MRSA in the air of pigsties as well as in exhaust air of pig farms (mean count: 102 cfu/m3) poses the question whether an airborne spread and, therefore, a MRSA colonization of animals via the airborne route exists. To answer this question, we exposed three groups of nine MRSA-negative tested piglets each to a defined airborne MRSA concentration (102, 104, and 106 cfu/m3) in our aerosol chamber for 24 h. In the following observation period of 21 days, the MRSA status of the piglets was monitored by taking different swab samples (nasal, pharyngeal, skin, conjunctival, and rectal swab). At the end of the experiment, we euthanized the piglets and investigated different tissues and organs for the spread of MRSA. The data of our study imply the presence of an airborne MRSA colonization route: the animals exposed to 106 cfu/m3 MRSA in the air were persistent colonized. The piglets exposed to an airborne MRSA concentration of 104 cfu/m3 were transient, and the piglets exposed to an airborne MRSA concentration of 102 cfu/m3 were not colonized. Consequently, a colonization via the airborne route was proven.