About

Graciela Lorca is a Professor in the Department of Microbiology and Cell Science at the University of Florida, affiliated with the Institute of Food and Agricultural Sciences. Her research focuses on host-microbe interactions, particularly in the context of preventing Type I Diabetes through the regulation of gut microbiota. She has studied how commensal bacteria such as Lactobacillus and Bifidobacterium influence host processes and immune responses, with a specific interest in how these interactions can reduce inflammation and oxidative stress associated with diabetes development. Her work includes microbiota analyses in rodent models and pilot human studies to evaluate the safety and potential preventive effects of probiotic strains like L. johnsoniiN6.2. Additionally, she investigates molecular mechanisms involving small molecules that modulate transcription factor activity, utilizing small molecule screens to identify natural ligands and chemical modulators for various bacterial and pathogenic transcription factors. Her contributions extend to identifying compounds such as glyoxylate, pyruvate, novobiocin, kaempferol, and others as effectors or inhibitors of key regulatory proteins, with applications in microbiology and disease control, including citrus greening disease.

Research topics

• Biology
• Biochemistry
• Medicine
• Immunology
• Microbiology
• Endocrinology
• Molecular biology
• Botany
• Nursing
• Intensive care medicine
• Pediatrics
• Bioinformatics
• Food science
• Horticulture
• Cell biology

Selected publications

• Lactobacillus johnsonii N6.2 improves glycemia and reduces diabetes-induced organ injury in the db/db mice model

  Journal of Endocrinology · 2025-10-01 · 1 citations

  articleSenior author

  Diabetes mellitus is a complex metabolic disorder characterized by hyperglycemia and the associated comorbidities. Type 2 diabetes is also associated with the dysfunction of liver, kidney and nervous system. In addition, an altered microbiota is frequently observed in subjects with type 2 diabetes. In this study, a db/db (diabetic) mouse model of type 2 diabetes was used to elucidate the beneficial effects of the probiotic Lactobacillus johnsonii N6.2. To evaluate metabolic effects, we performed metabolomics on liver samples, and RNA-seq from the liver and visceral adipose tissue, followed by qRT-PCR validation. Using L. johnsonii N6.2 extracellular vesicles, we evaluated lipid accumulation in hepatocytes. Finally, the gut microbiome of db/db mice was profiled using 16S rRNA sequencing. We observed that administration of the probiotic improved glycemic levels and decreased diabetes scores and type 2 diabetes-associated injury to the pancreas, liver and kidneys. Liver metabolomic and transcriptome analyses identified biomarkers of L. johnsonii N6.2 activity, including modulation of the vitamin K pathway, upregulation of FGF21, a key regulator of glucose and lipid metabolism, and alternations in selected circadian genes. This study elucidates the beneficial effects of L. johnsonii N6.2, against the common symptoms of type 2 diabetes, highlighting its potential as an adjuvant therapeutic agent.

  PublisherDOI

• A critical evaluation of methodological and mechanistic insights on probiotic-derived extracellular vesicles

  Frontiers in Nutrition · 2025-08-29 · 4 citations

  reviewOpen accessSenior authorCorresponding

  Probiotic extracellular vesicles (pEVs) have emerged as promising postbiotics with potential applications in inflammatory diseases, infections, allergies, cancer treatment, autoimmune disorders, and even neurological and degenerative conditions. Yet despite the surge in research on pEVs, critical gaps and inconsistencies in study design, methodology, and mechanistic understanding hinder unlocking their full potential. This literature review provides a concise introduction to beneficial bacterial EVs, mechanistic insights into their role in interkingdom interactions, and current challenges in pEV research. We highlight methodological inconsistencies in model selection, control design, and effect measurement, discuss their consequences and provide recommendations to improve experimental rigor and comparability of results. These include methodological considerations like standardization strategies for pEV preparation, purification, formulation, and administration as well as general study design questions. Finally, we outline key avenues for future research, emphasizing the need for biomarkers to track pEV biodistribution, the identification of effector molecules, and a deeper understanding of their mechanistic targets, as well as their interactions with food components and their use as delivery systems, among others. By addressing these challenges, this review aims to provide a roadmap for advancing pEV research and facilitating their transition into clinical and biotechnological applications.

  PublisherOA PDFDOI

• Lactobacillus johnsonii N6.2 Phospholipids Induce T Cell Anergy upon Cognate Dendritic Cell Interactions

  Metabolites · 2025-04-22 · 1 citations

  articleOpen access

  Background/Objectives: Lactobacillus johnsonii N6.2 is a gut symbiont with probiotic properties. L. johnsonii N6.2 delayed the progression of type 1 diabetes (T1D) in diabetic-prone rats. The probiotic intake demonstrated immune cell modulation in healthy volunteers, leading to improved wellness and fewer reported symptoms like headaches and abdominal pain. These systemic immune-modulating benefits are attributed to L. johnsonii N6.2’s bioactive fractions, including extracellular vesicles (EVs) and purified phospholipids (PLs). We have previously shown that L. johnsonii N6.2 PLs modulate dendritic cell (DC) function towards a regulatory-like phenotype. Here, we further characterize the immune regulatory effects of L. johnsonii N6.2 PLs on adaptive immunity, specifically upon DC and T cell interactions. We hypothesized that PL-stimulated DCs suppress T cell-mediated responses to maintain tolerance in intra- and extra-intestinal sites. Methods: Bone marrow-derived dendritic cells (BMDCs) were generated from Sprague-Dawley rats and stimulated with L. johnsonii N6.2 PLs. Isogenic T cells were isolated from PBMCs obtained via terminal exsanguination. In vitro cellular assays, co-culture experiments, gene expression analysis by qRT-PCR, and flow cytometry assays were conducted to assess the immune regulatory effects of L. johnsonii N6.2 PLs. Results: The PL-stimulated BMDCs upregulated DC regulatory markers and exhibited an immature-like phenotype with reduced surface expression of maturation markers but increased surface migratory molecules (ICAM-1). These BMDCs presented immunosuppressive functions upon cognate T cell interactions and in the presence of TCR stimulation. Specifically, PL-stimulated BMCDs suppressed Th1 effector function and induced the expression of T cell anergy-related genes after co-culturing for 72 h. Conclusions: This study highlights the immune regulatory capacity of L. johnsonii N6.2’s bioactive components on adaptive immunity, specifically that of purified PLs on DC:T cell-mediated responses leading to immunosuppression. Our findings suggest that L. johnsonii N6.2-purified PLs play a role in regulating adaptive immunity, offering potential benefits for managing immune-related diseases like T1D.

  PublisherOA PDFDOI

• Bile promotes Lactobacillus johnsonii N6.2 extracellular vesicle production with conserved immunomodulatory properties

  Scientific Reports · 2024-05-28 · 12 citations

  articleOpen accessSenior author

  Recently, Lactobacillus johnsonii N6.2-derived extracellular vesicles (EVs) were shown to reduce apoptosis in human beta cell lines and stimulate insulin secretion in human islets. Our goal was to identify a physiologically relevant environmental condition that induces a hypervesiculation phenotype in L. johnsonii N6.2 and to evaluate if transcriptional changes are involved in this process. Culturing this strain in the presence of 0.2% bovine bile, which mimics a stressor encountered by the bacterium in the small intestine, resulted in approximately a 100-fold increase in EVs relative to cells grown in media without bile. Whole transcriptome analysis of cells grown with bile revealed upregulation of several peptidoglycan hydrolases as well as several genes involved in fatty acid utilization. These results suggest that the hypervesiculation phenotype may be the result of increased cell wall turnover combined with increased accumulation of phospholipids, in agreement with our previous proteomic and lipidomics results. Additionally, EVs isolated from L. johnsonii N6.2 grown in presence of bile maintained their immunomodulatory properties in host-derived βlox5 pancreatic and THP-1 macrophage cell lines. Our findings suggest that in L. johnsonii N6.2 vesiculogenesis is significantly impacted by the expression of cell wall modifying enzymes and proteins utilized for exogenous fatty acid uptake that are regulated at the transcriptional level. Furthermore, this data suggests that vesiculogenesis could be stimulated in vivo using small molecules thereby maximizing the beneficial interactions between bacteria and their hosts.

  PublisherOA PDFDOI

• Erucic acid utilization by Lactobacillus johnsonii N6.2

  Frontiers in Microbiology · 2024-11-25 · 2 citations

  articleOpen accessSenior authorCorresponding

  A multivariate nutritional analysis indicated that the consumption of erucic acid-rich food, a fatty acid (FA) found primarily in rapeseed and mustard oil, was positively correlated with higher counts of lactic acid bacteria (LAB). Furthermore, we showed Lactobacillus johnsonii N6.2, as well as other species of LAB tested from the former Lactobacillus genus, were able to efficiently use erucic acid (EA) as the source of FA. In this work, we identified significant changes induced in the FA profiles of L. johnsonii cultured with EA as the source of FA. We performed global transcriptomics to identify genes and pathways involved in EA utilization. It was found that L. johnsonii incorporates external fatty acids via a FakA/FakB and the plsX/plsY/plsC pathway for phosphatidic acid synthesis. It was found that cells grown in MRS with EA (MRS-E) significantly upregulated fakB2 and fakB4 when compared to cells grown in standard MRS with tween 80 as the source of FA. Additionally, in MRS-E, L. johnsonii N6.2 induced the expression of plsY2, plsC2 and plsC4 while the expression of pslX was constitutive during short term EA exposure. LC–MS analyses revealed that L. johnsonii N6.2 rapidly incorporates EA and synthesizes a variety of long chain fatty acids, including the health-relevant omega-9 monounsaturated fatty acids such as nervonic and gondoic acids.

  PublisherOA PDFDOI

• The Sdp-SH3b2 domain contained in Lactobacillus johnsonii N6.2-derived extracellular vesicles inhibit murine norovirus replication

  Frontiers in Immunology · 2024-12-05 · 9 citations

  articleOpen accessSenior author

  The internalization of Lactobacillus johnsonii N6.2 extracellular vesicles (EVs) by cells results in a significant induction of the 2’,5’-oligoadenylate synthetase (OAS) pathway. It also induces expression of IFI44L, MX1, MX2 and DDX60 . In this work, we evaluated whether the antiviral response induced by L. johnsonii N6.2-derived EVs, has an inhibitory effect on an RNA viral insult using murine norovirus (MNV-1) as the viral infection model. We found that RAW 264.7 Macrophages treated with EVs significantly decreased the levels of MNV-1 genome. These results were consistent with an increase in expression of Oas1b, Oas2, Oasl, Mx1, Mx2 and Ifi44l (6 hours post infection). Out of six proteins enriched in EVs, we found that SH3b2 domain of Sdp was the only protein effector molecule able to recapitulate the activation of the OAS pathway. In C57BL6 mice, the administration of live L. johnsonii N6.2, EVs, and Sdp-SH3b2/liposomes significantly decreased MNV-1 titers in the distal ileum, in contrast to the controls with PBS and liposomes alone that did not affect MNV-1. These results establish that the SH3b2 domain of Sdp, which is enriched in L. johnsonii derived EVs, is an effector molecule in EVs that can orchestrate the control of viral infections in vivo .

  PublisherDOI

• A Scoping Review of the Oral Microbiome in Preterm Infants

  American Journal of Perinatology · 2023-10-31 · 1 citations

  reviewOpen access

  The purpose of this scoping review was to examine the oral microbiome composition in preterm infants, sampling and collection methods, as well as exposures associated with oral microbiome composition and health implications. We conducted a scoping review of the literature using the Arskey and O'Malley framework. We identified a total of 13 articles which met our inclusion criteria and purpose of this scoping review. Articles included in this review compared the oral microbiome in preterm infants to term infants, examined alterations to the oral microbiome over time, compared the oral microbiome to different body site microbiomes, and explored associations with clinically relevant covariates and outcomes. Exposures associated with the diversity and composition of the oral microbiome in preterm infants included delivery mode, oral feeding, oropharyngeal care, skin-to-skin care, and antibiotics. Day of life and birth weight were also associated with oral microbiome composition. The oral microbiome may be associated with the composition of the tracheal and gut microbiomes, likely due to their proximity. Alpha and beta diversity findings varied across studies as well as the relative abundance of taxa. This is likely due to the different sampling techniques and timing of collection, as well as the wide range of infant clinical characteristics. Multiple factors may influence the composition of the oral microbiome in preterm infants. However, given the heterogeneity of sampling techniques and results within this review, the evidence is not conclusive on the development as well as short- and long-term implications of the oral microbiome in preterm infants and needs to be explored in future research studies. KEY POINTS: · Day of life is a critical factor in oral microbiome development in preterm infants.. · The oral microbiome may be associated with tracheal and gut microbiome colonization.. · Future research should examine sampling methodology for examining the oral microbiome.. · Future research should explore associations with the oral microbiome and adverse health outcomes..

  PublisherOA PDFDOI

• Pasteurization of human milk affects the miRNA cargo of EVs decreasing its immunomodulatory activity

  Scientific Reports · 2023-06-21 · 20 citations

  articleOpen accessSenior author

  Abstract In this report, we evaluated the effect of the pasteurization (P) process of mother’s own milk (MOM) on the miRNA content of extracellular vesicles (EVs) and its impact on innate immune responses. Differences in size or particle number were not observed upon pasteurization of MOM (PMOM). However, significant differences were observed in the EV membrane marker CD63 and miRNA profiles. miRNA sequencing identified 33 differentially enriched miRNAs between MOM EV and PMOM EV . These changes correlated with significant decreases in the ability of PMOM EV to modulate IL-8 secretion in intestinal Caco2 cells where only MOM EV were able to decrease IL-8 secretion in presence of TNFα. While EVs from MOM EV and PMOM EV were both able to induce a tolerogenic M2-like phenotype in THP-1 macrophages, a significant decrease in the transcript levels of IL-10 and RNA sensing genes was observed with PMOM EV . Together, our data indicates that pasteurization of MOM impacts the integrity and functionality of MOM EV , decreasing its EVs-mediated immunomodulatory activity. This data provides biomarkers that may be utilized during the optimization of milk processing to preserve its bioactivity.

  PublisherOA PDFDOI

• Editorial: Women in microbial physiology and metabolism: 2022

  Frontiers in Microbiology · 2023-08-14

  editorialOpen access1st authorCorresponding

  There is still a gender imbalance in the field of STEM research. According to the UNESCO Institute for Statistics, only 33% of the world's researchers are women. They continue to be underrepresented in the highest academic positions, with only 26% of full professor positions held by women. As highlighted by UNESCO, science and gender equality are essential to ensure sustainable development. The present Research Topic highlights recent work performed by female researchers across the entire breadth of Microbial Physiology and Metabolism. It covers recent insights into the physiology of bacteria that are pathogenic to humans or plants, the prevalence of antimicrobial resistance genes in different environments, the molecular mechanisms of microbial light harvesting systems, and novel application potential of microbial metabolism in biotechnology.Pseudomonas aeruginosa is an opportunistic pathogen often associated with nosocomial infections. Its ability to form robust biofilms is related with enhanced virulence and antibiotic resistance. Though structural modeling and site directed mutagenesis, the authors show that the 90 phycoerythrobilin isomerization activity of MpeV is modulated depending on the amino acid that is 91 located at position 141 within its phycoerythrin-I β-subunit substrate. These results in combination 92 with structural models led the authors to propose that identity of the residue at this position in the β-93 subunits may be used to predict which phycobilin is bound on both PEI and PEII. 94

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• Oral Care in Critically Ill Infants and the Potential Effect on Infant Health: An Integrative Review

  Critical Care Nurse · 2023 · 5 citations

  • Medicine
  • Intensive care medicine
  • Pediatrics

  BACKGROUND: Critically ill infants admitted to the neonatal intensive care unit are at risk for ventilator-associated pneumonia and abnormal oral colonization. Adherence to evidence-based guidelines for oral care in critically ill adults is associated with improved short- and long-term health outcomes. However, oral care guidelines for critically ill infants admitted to the neonatal intensive care unit have not been established, possibly increasing their risk of ventilator-associated pneumonia and other health complications. OBJECTIVE: To describe and summarize the evidence regarding oral care for critically ill infants admitted to the neonatal intensive care unit and to identify gaps needing further investigation. METHODS: The MEDLINE (through PubMed) and CINAHL databases were searched for observational studies and randomized controlled trials investigating the effect of oral care on oral colonization, ventilator-associated pneumonia, and health outcomes of infants in the neonatal intensive care unit. RESULTS: This review of 5 studies yielded evidence that oral care may promote a more commensal oral and endotracheal tube aspirate microbiome. It may also reduce the risk of ventilator-associated pneumonia and length of stay in the neonatal intensive care unit. However, the paucity of research regarding oral care in this population and differences in oral care procedures, elements used, and timing greatly limit any possible conclusions. CONCLUSIONS: Oral care in critically ill infants may be especially important because of their suppressed immunity and physiological immaturity. Further appropriately powered studies that control for potential covariates, monitor for adverse events, and use recommended definitions of ventilator-associated pneumonia are needed to make clinical recommendations.

  PublisherDOI

Recent grants

• NIH Grant R03AI078001

  NIH · $146k · 2012

Frequent coauthors

• Claudio F. González

  University of Florida

  52 shared

• Fernando A. Pagliai

  University of Florida

  19 shared

• Christopher L. Gardner

  Simon Fraser University

  16 shared

• Leslie A. Parker

  Florida College

  15 shared

• Josef Neu

  University of Florida

  15 shared

• Graciela Font de Valdez

  14 shared

• Natalie A. Harrison

  University of Florida

  10 shared

• Mark A. Atkinson

  University of Florida

  8 shared

Labs

• MCS Lorca LabPI

  Not provided