A genome-wide screen in macrophages identifies PTEN as required for myeloid restriction of Listeria monocytogenes infection.

Listeria monocytogenes (Lm) is an intracellular foodborne pathogen which causes the severe disease listeriosis in immunocompromised individuals. Macrophages play a dual role during Lm infection by both promoting dissemination of Lm from the gastrointestinal tract and limiting bacterial growth upon immune activation. Despite the relevance of macrophages to Lm infection, the mechanisms underlying phagocytosis of Lm by macrophages are not well understood. To identify host factors important for Lm infection of macrophages, we performed an unbiased CRISPR/Cas9 screen which revealed pathways that are specific to phagocytosis of Lm and those that are required for internalization of bacteria generally. Specifically, we discovered the tumor suppressor PTEN promotes macrophage phagocytosis of Lm and L. ivanovii, but not other Gram-positive bacteria. Additionally, we found that PTEN enhances phagocytosis of Lm via its lipid phosphatase activity by promoting adherence to macrophages. Using conditional knockout mice lacking Pten in myeloid cells, we show that PTEN-dependent phagocytosis is important for host protection during oral Lm infection. Overall, this study provides a comprehensive identification of macrophage factors involved in regulating Lm uptake and characterizes the function of one factor, PTEN, during Lm infection in vitro and in vivo. Importantly, these results demonstrate a role for opsonin-independent phagocytosis in Lm pathogenesis and suggest that macrophages play a primarily protective role during foodborne listeriosis.

Shifts in the Skin Bacterial and Fungal Communities of Healthy Children Transitioning through Puberty.

Previous cross-sectional studies have shown that skin microbiomes in adults are distinct from those in children. However, the human skin microbiome in individuals as they sexually mature has not been studied as extensively. We performed a prospective, longitudinal study to investigate the puberty-associated shifts in skin microbiota. A total of 12 healthy children were evaluated every 6-18 months for up to 6 years. Using 16S ribosomal RNA (V1-V3) and internal transcribed spacer 1 amplicon sequencing analyzed with Divisive Amplicon Denoising Algorithm 2, we characterized the bacterial and fungal communities of five different skin and nares sites. We identified significant alterations in the composition of skin microbial communities, transitioning toward a more adult microbiome, during puberty. The microbial shifts were associated with Tanner stages (classification method for the degree of sexual maturation) and showed noticeable sex-specific differences. Over time, female children demonstrated a predominance of Cutibacterium with decreasing diversity. Among fungi, Malassezia predominated at most skin sites in more sexually mature subjects, which was more pronounced in female children. The higher relative abundances of these lipophilic taxa-C. acnes and M. restricta-were strongly associated with serum sex hormone concentrations with known influence on sebaceous gland activity. Taken together, our results support the relationship between sexual maturation, skin physiology, and the skin microbiome.

Alterations of human skin microbiome and expansion of antimicrobial resistance after systemic antibiotics.

Although systemic antibiotics are critical in controlling infections and reducing morbidity and mortality, overuse of antibiotics is presumed to contribute to negative repercussions such as selection of antimicrobial-resistant organisms and collateral damage to commensal microbes. In a prospective, randomized study of four clinically relevant antibiotic regimens [doxycycline (20 mg or 100 mg), cephalexin, or trimethoprim/sulfamethoxazole], we investigated microbial alterations on skin after administration of systemic antibiotics to healthy human volunteers. Samples from different skin and oral sites, as well as stool, were collected before, during, and up to 1 year after antibiotic use, and shotgun metagenomic sequencing was performed. Taxonomic analysis showed that subjects receiving doxycycline 100 mg and trimethoprim/sulfamethoxazole (TMP/SMX) exhibited greater changes to their skin microbial communities, as compared to those receiving other regimens or untreated controls. Oral and stool microbiota also demonstrated fluctuations after antibiotics. Bacterial culturing in combination with whole-genome sequencing revealed specific emergence, expansion, and persistence of antibiotic-resistant staphylococci harboring tetK or tetL and dfrC or dfrG genes in all subjects who received doxycycline 100 mg or TMP/SMX, respectively. Last, analysis of metagenomic data revealed an increase of genes involved in gene mobilization, indicating stress responses of microbes to antibiotics. Collectively, these findings demonstrate direct, long-lasting effects of antibiotics on skin microbial communities, highlighting the skin microbiome as a site for the development and persistence of antibiotic resistance and the risks of overprescribing.

Investigating the Roles of Listeria monocytogenes Peroxidases in Growth and Virulence.

Bacteria have necessarily evolved a protective arsenal of proteins to contend with peroxides and other reactive oxygen species generated in aerobic environments. Listeria monocytogenes encounters an onslaught of peroxide both in the environment and during infection of the mammalian host, where it is the causative agent of the foodborne illness listeriosis. Despite the importance of peroxide for the immune response to bacterial infection, the strategy by which L. monocytogenes protects against peroxide toxicity has yet to be illuminated. Here, we investigated the expression and essentiality of all the peroxidase-encoding genes during L. monocytogenes growth in vitro and during infection of murine cells in tissue culture. We found that chdC and kat were required for aerobic growth in vitro, and fri and ahpA were each required for L. monocytogenes to survive acute peroxide stress. Despite increased expression of fri, ahpA, and kat during infection of macrophages, only fri proved necessary for cytosolic growth. In contrast, the proteins encoded by lmo0367, lmo0983, tpx, lmo1609, and ohrA were dispensable for aerobic growth, acute peroxide detoxification, and infection. Together, our results provide insight into the multifaceted L. monocytogenes peroxide detoxification strategy and demonstrate that L. monocytogenes encodes a functionally diverse set of peroxidase enzymes. IMPORTANCE Listeria monocytogenes is a facultative intracellular pathogen and the causative agent of the foodborne illness listeriosis. L. monocytogenes must contend with reactive oxygen species generated extracellularly during aerobic growth and intracellularly by the host immune system. However, the mechanisms by which L. monocytogenes defends against peroxide toxicity have not yet been defined. Here, we investigated the roles of each of the peroxidase-encoding genes in L. monocytogenes growth, peroxide stress response, and virulence in mammalian cells.

Bacterial endosymbionts influence host sexuality and reveal reproductive genes of early divergent fungi.

Many heritable mutualisms, in which beneficial symbionts are transmitted vertically between host generations, originate as antagonisms with parasite dispersal constrained by the host. Only after the parasite gains control over its transmission is the symbiosis expected to transition from antagonism to mutualism. Here, we explore this prediction in the mutualism between the fungus Rhizopus microsporus (Rm, Mucoromycotina) and a beta-proteobacterium Burkholderia, which controls host asexual reproduction. We show that reproductive addiction of Rm to endobacteria extends to mating, and is mediated by the symbiont gaining transcriptional control of the fungal ras2 gene, which encodes a GTPase central to fungal reproductive development. We also discover candidate G-protein-coupled receptors for the perception of trisporic acids, mating pheromones unique to Mucoromycotina. Our results demonstrate that regulating host asexual proliferation and modifying its sexual reproduction are sufficient for the symbiont's control of its own transmission, needed for antagonism-to-mutualism transition in heritable symbioses. These properties establish the Rm-Burkholderia symbiosis as a powerful system for identifying reproductive genes in Mucoromycotina.