Comparison of livestock-associated and community-associated Staphylococcus aureus pathogenicity in a mouse model of skin and soft tissue infection

Industrial Hog Operation Workers' Perspectives on Occupational Exposure to Zoonotic Pathogens: A Qualitative Pilot Study in North Carolina, USA

Industrial hog operation (IHO) workers face a range of occupational hazards, including exposure to zoonotic pathogens such as livestock-associated antimicrobial-resistant Staphylococcus aureus and swine-origin influenza viruses with epidemic or pandemic potential. To better understand this population's occupational exposure to zoonotic pathogens, we conducted a community-driven qualitative research study in eastern North Carolina. We completed in-depth interviews with ten IHO workers and used thematic analysis to identify and analyze patterns of responses. Workers described direct and indirect occupational contact with hogs, with accompanying potential for dermal, ingestion, and inhalation exposures to zoonotic pathogens. Workers also described potential take-home pathways, wherein they could transfer livestock-associated pathogens and other contaminants from IHOs to their families and communities. Findings warrant future research, and suggest that more restrictive policies on antimicrobials, stronger health and safety regulations, and better policies and practices across all IHOs could afford greater protection against worker and take-home zoonotic pathogen exposures.

γδ T cell-intrinsic IL-1R promotes survival during Staphylococcus aureus bacteremia

Staphylococcus aureus is a leading cause of bacteremia, further complicated by the emergence of antibiotic-resistant strains such as methicillin-resistant S. aureus (MRSA). A better understanding of host defense mechanisms is needed for the development of host-directed therapies as an alternative approach to antibiotics. The levels of IL-1, IL-17, and TNF-α cytokines in circulation have been associated with predictive outcomes in patients with S. aureus bacteremia. However, their causative role in survival and the cell types involved in these responses during bacteremia is not entirely clear. Using a mouse model of S. aureus bacteremia, we demonstrated that IL-17A/F and TNF-α had no significant impact on survival, whereas IL-1R signaling was critical for survival during S. aureus bacteremia. Furthermore, we identified that T cells, but not neutrophils, monocytes/macrophages, or endothelial cells were the crucial cell type for IL-1R-mediated survival against S. aureus bacteremia. Finally, we determined that the expression of IL-1R on γδ T cell, but not CD4+ or CD8+ T cells was responsible for survival against the S. aureus bacteremia. Taken together, we uncovered a role for IL-1R, but not IL-17A/F and TNF-α in protection against S. aureus bacteremia. Importantly, γδ T cell-intrinsic expression of IL-1R was crucial for survival, but not on other immune cells or endothelial cells. These findings reveal potential cellular and immunological targets for host-directed therapies for improved outcomes against S. aureus bacteremia.

Toward Optimization of a Rabbit Model of Staphylococcus aureus (USA300) Skin and Soft Tissue Infection

Staphylococcus aureus remains a leading cause of skin and soft tissue infections (SSTIs) globally. In the United States, many of these infections are caused by isolates classified as USA300. Our understanding of the success of USA300 as a human pathogen is due in part to data obtained from animal infection models, including rabbit SSTI models. These animal models have been used to study S. aureus virulence and pathogenesis and to gain an enhanced understanding of the host response to infection. Although significant knowledge has been gained, the need to use a relatively high inoculum of USA300 (1 × 108 to 5 × 108 CFU) is a caveat of these infection models. As a step toward addressing this issue, we created mutations in USA300 that mimic those found in S. aureus strains with naturally occurring rabbit tropism-namely, single nucleotide polymorphisms in dltB and/or deletion of rot. We then developed a rabbit SSTI model that utilizes an inoculum of 106 USA300 CFU to cause reproducible disease and tested whether primary SSTI protects rabbits against severe reinfection caused by the same strain. Although there was modest protection against severe reinfection, primary infection and reinfection with rabbit-tropic USA300 strains failed to increase the overall level of circulating anti-S. aureus antibodies significantly. These findings provide additional insight into the host response to S. aureus. More work is needed to further develop a low-inoculum infection model that can be used to better test the potential of new therapeutics or vaccine target antigens. IMPORTANCE Animal models of S. aureus infection are important for evaluating bacterial pathogenesis and host immune responses. These animal infection models are often used as an initial step in the testing of vaccine antigens and new therapeutics. The extent to which animal models of S. aureus infection approximate human infections remains a significant consideration for translation of results to human clinical trials. Although significant progress has been made with rabbit models of S. aureus infection, one concern is the high inoculum needed to cause reproducible disease. Here, we generated USA300 strains that have tropism for rabbits and developed a rabbit SSTI model that uses fewer CFU than previous models.

Application of Markov models to predict changes in nasal carriage of Staphylococcus aureus among industrial hog operations workers

Industrial hog operation (IHO) workers can be occupationally exposed to Staphylococcus aureus and may carry the bacteria in their nares. Workers may persistently carry S. aureus or transition between different states of nasal carriage over time: no nasal carriage, nasal carriage of a human-associated strain, and nasal carriage of a livestock-associated strain. We developed a mathematical model to predict the proportion of IHO workers in each nasal carriage state over time, accounting for IHO worker mask use. We also examined data sufficiency requirements to inform development of models that produce reliable predictions. We used nasal carriage data from a cohort of 101 IHO workers in North Carolina, sampled every 2 weeks for 4 months, to develop a three-state Markov model that describes the transition dynamics of IHO worker nasal carriage status over the study period and at steady state. We also stratified models by mask use to examine their impact on worker transition dynamics. If conditions remain the same, our models predicted that 49.1% of workers will have no nasal carriage of S. aureus, 28.2% will carry livestock-associated S. aureus, and 22.7% will carry human-associated S. aureus at steady state. In stratified models, at steady state, workers who reported only occasional mask (<80% of the time) use had a higher predicted proportion of individuals with livestock-associated S. aureus nasal carriage (39.2%) compared to workers who consistently (≥80% of the time) wore a mask (15.5%). We evaluated the amount of longitudinal data that is sufficient to create a Markov model that accurately predicts future nasal carriage states by creating multiple models that withheld portions of the collected data and compared the model predictions to observed data. Our data sufficiency analysis indicated that models created with a small subset of the dataset (approximately 1/3 of observed data) perform similarly to models created using all observed data points. Markov models may have utility in predicting worker health status over time, even when limited longitudinal data are available.

Spatiotemporal land use change and environmental degradation surrounding CAFOs in Michigan and North Carolina

Concentrated Animal Feeding Operations (CAFOs) have arisen and expanded in the U.S. and globally to address efficiencies in livestock production. CAFOs tend to cluster in space for logistical purposes. Efficient distribution of concentrated manures produced by these operations is often not economically feasible, which may lead to accumulation on land near CAFOs, potentially resulting in local environmental changes. Moreover, as CAFOs are established or expand, they may need more lands to apply their manures, likely driving land use changes even after their establishment. Studies have yet to investigate these spatiotemporal impacts of CAFOs. We investigated whether the presence of regulated liquid waste CAFOs is associated with land use change over time and space as well as degraded environmental conditions surrounding those facilities. We used MODIS (Moderate Resolution Imaging Spectrometer) images from 2000 to 2018 to examine these questions in Michigan and North Carolina- states with varied CAFO establishment histories. We found that cropland extent increased while savanna and forest decreased near CAFOs. Similar observations did not occur outside of areas influenced by CAFOs. We also found evidence of environmental degradation, including decreased evapotranspiration and increased day and nighttime land surface temperatures in North Carolina. This study advances our understanding of environmental impacts surrounding CAFOs. Our findings can support policy changes and highlight the need to better understand these globally increasing entities.

The Relevance of IL-1-Signaling in the Protection against Gram-Positive Bacteria

Previous studies performed using a model of group B streptococcus (GBS)-induced peritoneal inflammation indicate that the interleukin-1 receptor (IL-1R) family plays an important role in the innate host defense against this encapsulated Gram-positive bacteria. Since the role of IL-1-dependent signaling in peritoneal infections induced by other Gram-positive bacteria is unknown, in the present study we sought to investigate the contribution of IL-1R signaling in host defenses against Streptococcus pyogenes (group A streptococcus or GAS) or Staphylococcus aureus, two frequent and global human Gram-positive extracellular pathogens. We analyzed here the outcome of GAS or S. aureus infection in IL-1R-deficient mice. After inoculated intraperitoneal (i.p.) inoculation with group A Streptococcus or S. aureus, all the wild-type (WT) control mice survived the challenge, while, respectively, 63% or 50% of IL-1-defective mice died. Lethality was due to the ability of both bacterial species to replicate and disseminate to the target organs of IL-1R-deficient mice. Moreover, the experimental results indicate that IL-1 signaling promotes the production of leukocyte attractant chemokines CXCL-1 and CXCL-2 and recruitment of neutrophils to bacterial infection sites. Accordingly, the reduced neutrophil recruitment in IL-1R-deficient mice was linked with decreased production of neutrophil chemokines. Collectively, our findings indicate that IL-1 signaling, as previously showed in host defense against GBS, plays a fundamental role also in controlling the progression and outcome of GAS or S. aureus disease.

Comparative Genomics of Plasmid-Bearing Staphylococcus aureus Strains Isolated From Various Retail Meats

Food poisoning due to the consumption of Staphylococcus aureus contaminated food is a major health problem worldwide. In this study, we sequenced the genomes of ten plasmid-bearing S. aureus strains isolated from retail beef, chicken, turkey, and pork. The chromosomes of the strains varied in size from 2,654,842 to 2,807,514 bp, and a total of 25 plasmids were identified ranging from 1.4 to 118 kb. Comparative genomic analysis revealed similarities between strains isolated from the same retail meat source, indicating an origin-specific genomic composition. Genes known to modulate attachment, invasion, and toxin production were identified in the 10 genomes. Strains from retail chicken resembled human clinical isolates with respect to virulence factors and genomic islands, and retail turkey and pork isolates shared similarity with S. aureus from livestock. Most chromosomes contained antimicrobial resistance, heavy metal resistance, and stress response genes, and several plasmids contained genes involved in antimicrobial resistance and virulence. In conclusion, the genomes of S. aureus strains isolated from retail meats showed an origin-specific composition and contained virulence and antimicrobial resistance genes similar to those present in human clinical isolates.