Gaseous ligand binding to Porphyromonas gingivalis HmuY hemophore-like protein in complex with heme

Porphyromonas gingivalis is the main pathogenic player in the development of periodontitis. To acquire heme, being an essential source of iron and protoporphyrin IX, P. gingivalis utilizes TonB-dependent outer membrane heme receptor (HmuR) and heme-binding hemophore-like protein (HmuY) as the main system for heme uptake from host hemoproteins. In this work, we present an extensive spectroscopic characterization of the binding of exogenous gaseous ligands to the holo-form of the HmuY (HmuY-heme) to unravel the mechanistic basis of heme release. Our data are consistent with a scenario where heme release from HmuY-heme is a multistep process that requires the initial rupture of one of the two heme‑iron coordination bonds with endogenous histidines.

Berberine-Functionalized Bismuth-Doped Carbon Dots in a Pathogen-Responsive Hydrogel System: A Multifaceted Approach to Combating Periodontal Diseases

Periodontal disease, a global health burden linked to dysbiotic oral polymicrobial communities and disrupted immune-inflammatory responses, is critically mediated byPorphyromonas gingivalis(Pg)─the keystone pathogen that sabotages host immunity, triggers tissue inflammation and destruction, and disrupts microbiota balance. Effective therapies should combine antimicrobial action, immune modulation, virulence suppression, and microbiome restoration. Bismuth ions and berberine, which exhibit antimicrobial and epithelial barrier-protecting effects, show potential effectiveness in treating periodontal diseases but face practical limitations due to poor water solubility and bioavailability. To address this, we developed bismuth-doped carbon dots functionalized with structure-modified berberine (BiCD-Ber) as a multifunctional nanomedicine. BiCD-Ber eradicated Pg in various forms, restored Pg-perturbed immune responses in gingival fibroblasts, and preserved epithelial barrier integrity. The doped bismuth ions neutralized Pg virulence factors by blocking the catalytic sites of gingipains. To facilitate in vivo delivery, BiCD-Ber was encapsulated in a disulfide-modified hyaluronic acid hydrogel that degrades in response to Pg metabolites. This BiCD-Ber hydrogel system modulated subgingival microbiota, alleviated inflammation in gingiva, and thereby prevented alveolar bone loss. This approach to concurrently eliminating Pg, modulating inflammatory responses , suppressing virulence factors, and restoring microbiota showcases great potential in managing periodontitis effectively.

Complete genome sequence provides information on quorum sensing related spoilage and virulence of Aeromonas salmonicida GMT3 isolated from spoiled sturgeon

Foodborne bacteria can pose a threat to the public health due to their spoilage and virulence potential, which can be regulated by quorum sensing (QS) system. In the study, we isolated a spoilage bacteria strain Aeromonas salmonicida GMT3 from refrigerated sturgeon. The complete genome of A. salmonicida GMT3 was sequenced, and the QS related genes were assigned. QS signal molecules N-acyl-homoserine lactones (AHLs) and AI-2 were detected. Genes regulating the spoilage-related metabolic pathways, including protease and lipase secretion, amines metabolism, sulfur metabolism, motility and biofilm formation were analyzed. Furthermore, genes encoding for several virulence factors, e.g. hemolysin, aerolysin, type II secretion system (T2SS), type VI secretion system (T6SS), antibiotic and multidrug resistance were also identified. In addition, the spoilage and virulence phenotypes associated with QS including protease, swimming and swarming activity, biofilm and hemolytic activity were detected. This study provided new insights into spoilage and virulence mechanisms correlated with QS of A. salmonicida GMT3, which might promote development of new approaches for spoilage and virulence control based on QS target.

Fourier transform infrared spectroscopy and machine learning for Porphyromonas gingivalis detection in oral bacteria

Porphyromonas gingivalis, a Gram-negative anaerobic bacillus, is the primary pathogen in periodontitis. Herein, we cultivated strains of oral bacteria, including P. gingivalis and the oral commensal bacteria Actinomyces viscosus and Streptococcus mutans, and recorded the infrared absorption spectra of the gases released by the cultured bacteria at a resolution of 0.5 cm-1 within the wavenumber range of 500-7500 cm-1. From these spectra, we identified the infrared wavenumbers associated with characteristic absorptions in the gases released by P. gingivalis using a decision tree-based machine learning algorithm. Finally, we compared the obtained absorbance spectra of ammonia (NH3) and carbon monoxide (CO) using the HITRAN database. We observed peaks at similar positions in the P. gingivalis gases, NH3, and CO spectra. Our results suggest that P. gingivalis releases higher amounts of NH3 and CO than A. viscosus and S. mutans. Thus, combining Fourier transform infrared spectroscopy with machine learning enabled us to extract the specific wavenumber range that differentiates P. gingivalis from a vast dataset of peak intensity ratios. Our method distinguishes the gases from P. gingivalis from those of other oral bacteria and provides an effective strategy for identifying P. gingivalis in oral bacteria. Our proposed methodology could be valuable in clinical settings as a simple, noninvasive pathogen diagnosis technique.

Oral microbiome as a co-mediator of halitosis and periodontitis: a narrative review

Objective

Halitosis or oral malodor is an unpleasant odor from the oral cavity. However, although patients with periodontitis often complain of halitosis, their relationship has not been fully elucidated. We reviewed previous literature based on the hypothesis that the relationship between halitosis and periodontitis is mediated by the oral microbiome.

Materials and methods

This narrative review sought to provide insight into the causative role of the oral microbiome in influencing halitosis and periodontitis. In addition, we tried to deepen knowledge related to the relationship between halitosis and periodontitis generated by the oral microbiome accumulated over the past 40 years.

Results

From 1984 to 2023, a total of 106 papers that carefully and scientifically dealt with halitosis and periodontitis were included in this narrative review. Based on previous results, halitosis and periodontitis were closely related. For decades, researchers have taken an intriguing approach to the question of whether there is a relationship between halitosis and periodontitis. Central factors in the relationship between halitosis and periodontitis include volatile sulfur compounds (VSCs), the oral microbiota that produce VSCs, and the inflammatory response.

Conclusions

Taken together, the more severe periodontitis, the higher the level of VSC in halitosis, which may be mediated by oral microbiome. However, the relationship between the occurrence, maintenance, and exacerbation of periodontitis and halitosis is not a necessary and sufficient condition for each other because they are complex interplay even in one individual.

Comparison of clinical indices with halitosis grading in chronic periodontitis: A randomized control trial

Background

Oral malodor is a major periodontal complaint, but the best method for assessing the halitosis grade is still undefined. The primary objective of the study was to detect the halitosis grade in the exhaled breath using the three distinct techniques and to compare the readings with different clinical indices to find out the best method of halitosis grading.

Materials and Methods

A total of 90 patients with chronic periodontitis having oral malodor were included in the study. The subjective assessment of the exhaled breath (halitosis grading) was done by three different methods; using a handheld portable Tanita FitScan sulfide monitor, by Halitox toxin assay, and by organoleptic (Sniff test) method. The findings were then compared with the clinical parameters of poor oral hygiene like plaque index (PI), gingival index (GI), gingival bleeding index (BI), and pocket depth (PD) to detect the best method of halitosis grading.

Results

The mean age of the patients included was 38.23 ± 8.83 (mean ± standard deviation) years. The median value of halitosis grading as obtained by Tanita FitScan was 3.0 (95% confidence interval as 2 and 4) which was then compared with clinical indices (PI, GI, BI, and PD) and the results were statistically significant (P < 0.05), whereas the other two techniques of halitosis grading gave insignificant results.

Conclusion

The results confirmed that the halitosis grading done using Tanita FitScan sulfide monitor is more appropriate with respect to clinical indices when compared with the other two techniques.

Antibiotic treatment and supplemental hemin availability affect the volatile organic compounds produced by P. gingivalis in vitro

We have measured the changes in the production of volatile organic compounds (VOCs) by the oral pathogen Porphyromonas gingivalis, when treated in vitro with the antibiotic amoxicillin. We have also measured the VOC production of P. gingivalis grown in the presence and absence of supplemental hemin. Planktonic bacterial cultures were treated with different amounts of amoxicillin in the lag phase of the bacterial growth. Planktonic bacteria were also cultured with and without supplemental hemin in the culture medium. Concentrations of VOCs were measured with proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) and further molecular identification was done with gas chromatography-mass spectrometry (GC-MS) using solid phase microextraction (SPME) for sampling. The cell growth of P. gingivalis in the cultures was estimated with optical density measurements at the wavelength of 600 nm (OD₆₀₀). We found that the production of methanethiol, hydrogen sulfide and several short- to medium-chain fatty acids was decreased with antibiotic treatment using amoxicillin. Compounds found to increase with the antibiotic treatment were butyric acid and indole. In cultures without supplemental hemin, indole and short- to medium-chain fatty acid production was significantly reduced. Acetic acid production was found to increase when supplemental hemin was not available. Our results suggest that the metabolic effects of both antibiotic treatment and supplemental hemin availability are reflected in the VOCs produced by P. gingivalis and could be used as markers for bacterial cell growth and response to threat. Analysis of these volatiles from human samples, such as the exhaled breath, could be used in the future to rapidly monitor response to antibacterial treatment.

Heavy Metals and Essential Metals Are Associated with Cerebrospinal Fluid Biomarkers of Alzheimer's Disease

Various metals have been associated with the pathogenesis of Alzheimer's disease (AD), principally heavy metals that are environmental pollutants (such as As, Cd, Hg, and Pb) and essential metals whose homeostasis is disturbed in AD (such as Cu, Fe, and Zn). Although there is evidence of the involvement of these metals in AD, further research is needed on their mechanisms of toxicity. To further assess the involvement of heavy and essential metals in AD pathogenesis, we compared cerebrospinal fluid (CSF) AD biomarkers to macro- and microelements measured in CSF and plasma. We tested if macro- and microelements' concentrations (heavy metals (As, Cd, Hg, Ni, Pb, and Tl), essential metals (Na, Mg, K, Ca, Fe, Co, Mn, Cu, Zn, and Mo), essential non-metals (B, P, S, and Se), and other non-essential metals (Al, Ba, Li, and Sr)) are associated with CSF AD biomarkers that reflect pathological changes in the AD brain (amyloid β1-42, total tau, phosphorylated tau isoforms, NFL, S100B, VILIP-1, YKL-40, PAPP-A, and albumin). We used inductively coupled plasma mass spectroscopy (ICP-MS) to determine macro- and microelements in CSF and plasma, and enzyme-linked immunosorbent assays (ELISA) to determine protein biomarkers of AD in CSF. This study included 193 participants (124 with AD, 50 with mild cognitive impairment, and 19 healthy controls). Simple correlation, as well as machine learning algorithms (redescription mining and principal component analysis (PCA)), demonstrated that levels of heavy metals (As, Cd, Hg, Ni, Pb, and Tl), essential metals (Ca, Co, Cu, Fe, Mg, Mn, Mo, Na, K, and Zn), and essential non-metals (P, S, and Se) are positively associated with CSF phosphorylated tau isoforms, VILIP-1, S100B, NFL, and YKL-40 in AD.

Genetic Determinants of Hydrogen Sulfide Biosynthesis in Fusobacterium nucleatum Are Required for Bacterial Fitness, Antibiotic Sensitivity, and Virulence

The Gram-negative anaerobe Fusobacterium nucleatum is a major producer of hydrogen sulfide (H₂S), a volatile sulfur compound that causes halitosis. Here, we dissected the genetic determinants of H₂S production and its role in bacterial fitness and virulence in this important member of the oral microbiome. F. nucleatum possesses four enzymes, CysK1, CysK2, Hly, and MegL, that presumably metabolize l-cysteine to H₂S, and CysK1 was previously shown to account for most H₂S production in vitro, based on correlations of enzymatic activities with gene expression at mid-log phase. Our molecular studies showed that cysK1 and megL were highly expressed at the late exponential growth phase, concomitant with high-level H₂S production, while the expression levels of the other genes remained substantially lower during all growth phases. Although the genetic deletion of cysK1 without supplementation with a CysK1-catalyzed product, lanthionine, caused cell death, the conditional ΔcysK1 mutant and a mutant lacking hly were highly proficient in H₂S production. In contrast, a mutant devoid of megL showed drastically reduced H₂S production, and a cysK2 mutant showed only minor deficiencies. Intriguingly, the exposure of these mutants to various antibiotics revealed that only the megL mutant displayed altered susceptibility compared to the parental strain: partial sensitivity to nalidixic acid and resistance to kanamycin. Most significantly, the megL mutant was attenuated in virulence in a mouse model of preterm birth, with considerable defects in the spread to amniotic fluid and the colonization of the placenta and fetus. Evidently, the l-methionine γ-lyase MegL is a major H₂S-producing enzyme in fusobacterial cells that significantly contributes to fusobacterial virulence and antibiotic susceptibility.

Volatile composition of the morning breath

We have measured the composition of volatile organic compounds (VOCs) in the morning breath of 30 healthy individuals before and after tooth brushing. The concentrations of VOCs in the breath samples were measured with proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) and further identification was performed with a combination of solid phase microextraction (SPME) and offline gas chromatography-mass spectrometry (GC-MS). We hypothesize that compounds, whose concentrations significantly decreased in the breath after tooth brushing are largely of microbial origin. In this study, we found 35 such VOCs. Out of these, 33 have been previously connected to different oral niches, such as salivary and subgingival bacteria. We also compared the concentrations of the 35 VOCs found in increased amounts in the morning breath to their respective odor thresholds to evaluate their ability to cause odor. Compounds that could contribute to the breath odor include many volatile sulfur compounds, such as methanethiol, hydrogen sulfide, dimethyl sulfide, and 2-methyl-1-propanethiol, but also other VOCs, such as acetic acid, butyric acid, valeric acid, acetaldehyde, octanal, phenol, indole, ammonia, isoprene, and methyl methacrylate.

Role of Hydrogen Sulfide in Oral Disease

Oral diseases are among the most common human diseases yet less studied. These diseases affect both the physical, mental, and social health of the patients resulting in poor quality of life. They affect all ages, although severe stages are mostly observed in older individuals. Poor oral hygiene, genetics, and environmental factors contribute enormously to the development and progression of these diseases. Although there are available treatment options for these diseases, the recurrence of the diseases hinders their efficiency. Oral volatile sulfur compounds (VSCs) are highly produced in oral cavity as a result of bacteria activities. Together with bacteria components such as lipopolysaccharides, VSCs participate in the progression of oral diseases by regulating cellular activities and interfering with the immune response. Hydrogen sulfide (H2S) is a gaseous neurotransmitter primarily produced endogenously and is involved in the regulation of cellular activities. The gas is also among the VSCs produced by oral bacteria. In numerous diseases, H2S have been reported to have dual effects depending on the cell, concentration, and donor used. In oral diseases, high production and subsequent utilization of this gas have been reported. Also, this high production is associated with the progression of oral diseases. In this review, we will discuss the production of H2S in oral cavity, its interaction with cellular activities, and most importantly its role in oral diseases.

Mesenchymal Stromal/Stem Cells-Derived Exosomes as an Antimicrobial Weapon for Orodental Infections

The oral cavity as the second most various microbial community in the body contains a broad spectrum of microorganisms which are known as the oral microbiome. The oral microbiome includes different types of microbes such as bacteria, fungi, viruses, and protozoa. Numerous factors can affect the equilibrium of the oral microbiome community which can eventually lead to orodental infectious diseases. Periodontitis, dental caries, oral leukoplakia, oral squamous cell carcinoma are some multifactorial infectious diseases in the oral cavity. In defending against infection, the immune system has an essential role. Depending on the speed and specificity of the reaction, immunity is divided into two different types which are named the innate and the adaptive responses but also there is much interaction between them. In these responses, different types of immune cells are present and recent evidence demonstrates that these cell types both within the innate and adaptive immune systems are capable of secreting some extracellular vesicles named exosomes which are involved in the response to infection. Exosomes are 30-150 nm lipid bilayer vesicles that consist of variant molecules, including proteins, lipids, and genetic materials and they have been associated with cell-to-cell communications. However, some kinds of exosomes can be effective on the pathogenicity of various microorganisms and promoting infections, and some other ones have antimicrobial and anti-infective functions in microbial diseases. These discrepancies in performance are due to the origin of the exosome. Exosomes can modulate the innate and specific immune responses of host cells by participating in antigen presentation for activation of immune cells and stimulating the release of inflammatory factors and the expression of immune molecules. Also, mesenchymal stromal/stem cells (MSCs)-derived exosomes participate in immunomodulation by different mechanisms. Ease of expansion and immunotherapeutic capabilities of MSCs, develop their applications in hundreds of clinical trials. Recently, it has been shown that cell-free therapies, like exosome therapies, by having more advantages than previous treatment methods are emerging as a promising strategy for the treatment of several diseases, in particular inflammatory conditions. In orodental infectious disease, exosomes can also play an important role by modulating immunoinflammatory responses. Therefore, MSCs-derived exosomes may have potential therapeutic effects to be a choice for controlling and treatment of orodental infectious diseases.

Progress in Oral Microbiome Related to Oral and Systemic Diseases: An Update

The human oral microbiome refers to an ecological community of symbiotic and pathogenic microorganisms found in the oral cavity. The oral cavity is an environment that provides various biological niches, such as the teeth, tongue, and oral mucosa. The oral cavity is the gateway between the external environment and the human body, maintaining oral homeostasis, protecting the mouth, and preventing disease. On the flip side, the oral microbiome also plays an important role in the triggering, development, and progression of oral and systemic diseases. In recent years, disease diagnosis through the analysis of the human oral microbiome has been realized with the recent development of innovative detection technology and is overwhelmingly promising compared to the previous era. It has been found that patients with oral and systemic diseases have variations in their oral microbiome compared to normal subjects. This narrative review provides insight into the pathophysiological role that the oral microbiome plays in influencing oral and systemic diseases and furthers the knowledge related to the oral microbiome produced over the past 30 years. A wide range of updates were provided with the latest knowledge of the oral microbiome to help researchers and clinicians in both academic and clinical aspects. The microbial community information can be utilized in non-invasive diagnosis and can help to develop a new paradigm in precision medicine, which will benefit human health in the era of post-metagenomics.

Fungal and host protein persulfidation are functionally correlated and modulate both virulence and antifungal response

Aspergillus fumigatus is a human fungal pathogen that can cause devastating pulmonary infections, termed "aspergilloses," in individuals suffering immune imbalances or underlying lung conditions. As rapid adaptation to stress is crucial for the outcome of the host-pathogen interplay, here we investigated the role of the versatile posttranslational modification (PTM) persulfidation for both fungal virulence and antifungal host defense. We show that an A. fumigatus mutant with low persulfidation levels is more susceptible to host-mediated killing and displays reduced virulence in murine models of infection. Additionally, we found that a single nucleotide polymorphism (SNP) in the human gene encoding cystathionine γ-lyase (CTH) causes a reduction in cellular persulfidation and correlates with a predisposition of hematopoietic stem cell transplant recipients to invasive pulmonary aspergillosis (IPA), as correct levels of persulfidation are required for optimal antifungal activity of recipients' lung resident host cells. Importantly, the levels of host persulfidation determine the levels of fungal persulfidation, ultimately reflecting a host-pathogen functional correlation and highlighting a potential new therapeutic target for the treatment of aspergillosis.

Hydrogen sulfide: An endogenous regulator of the immune system

Hydrogen sulfide (H₂S) is now recognized as an endogenous signaling gasotransmitter in mammals. It is produced by mammalian cells and tissues by various enzymes - predominantly cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST) - but part of the H₂S is produced by the intestinal microbiota (colonic H₂S-producing bacteria). Here we summarize the available information on the production and functional role of H₂S in the various cell types typically associated with innate immunity (neutrophils, macrophages, dendritic cells, natural killer cells, mast cells, basophils, eosinophils) and adaptive immunity (T and B lymphocytes) under normal conditions and as it relates to the development of various inflammatory and immune diseases. Special attention is paid to the physiological and the pathophysiological aspects of the oral cavity and the colon, where the immune cells and the parenchymal cells are exposed to a special "H₂S environment" due to bacterial H₂S production. H₂S has many cellular and molecular targets. Immune cells are "surrounded" by a "cloud" of H₂S, as a result of endogenous H₂S production and exogenous production from the surrounding parenchymal cells, which, in turn, importantly regulates their viability and function. Downregulation of endogenous H₂S producing enzymes in various diseases, or genetic defects in H₂S biosynthetic enzyme systems either lead to the development of spontaneous autoimmune disease or accelerate the onset and worsen the severity of various immune-mediated diseases (e.g. autoimmune rheumatoid arthritis or asthma). Low, regulated amounts of H₂S, when therapeutically delivered by small molecule donors, improve the function of various immune cells, and protect them against dysfunction induced by various noxious stimuli (e.g. reactive oxygen species or oxidized LDL). These effects of H₂S contribute to the maintenance of immune functions, can stimulate antimicrobial defenses and can exert anti-inflammatory therapeutic effects in various diseases.

Multiple enzymes can make hydrogen sulfide from cysteine in Treponema denticola

Treponema denticola is a spirochete that is involved in causing periodontal diseases. This bacterium can produce H2S from thiol compounds found in the gingival crevicular fluid. Determining how H2S is made by oral bacteria is important since this molecule is present at high levels in periodontally-diseased pockets and the biological effects of H2S can explain some of the pathologies seen in periodontitis. Thus, it is of interest to identify the enzyme, or enzymes, involved in the synthesis of H2S by T. denticola. We, and others, have previously identified and characterized a T. denticola cystalysin, called HlyA, which hydrolyzes cysteine into H2S (and pyruvate and ammonia). However, there have been no studies to show that HlyA is, or is not, the only pathway that T. denticola can use to make H2S. To address this question, allelic replacement mutagenesis was used to make a deletion mutant (ΔhlyA) in the gene encoding HlyA. The mutant produces the same amount of H2S from cysteine as do wild type spirochetes, indicating that T. denticola has at least one other enzyme that can generate H2S from cysteine. To identify candidates for this other enzyme, a BLASTp search of T. denticola strain 33520 was done. There was one gene that encoded an HlyA homolog so we named it HlyB. Recombinant His-tagged HlyB was expressed in E. coli and partially purified. This enzyme was able to make H2S from cysteine in vitro. To test the role of HlyB in vivo, an HlyB deletion mutant (ΔhlyB) was constructed in T. denticola. This mutant still made normal levels of H2S from cysteine, but a strain mutated in both hly genes (ΔhlyA ΔhlyB) synthesizes significantly less H2S from cysteine. We conclude that the HlyA and HlyB enzymes perform redundant functions in vivo and are the major contributors to H2S production in T. denticola. However, at least one other enzyme can still convert cysteine to H2S in the ΔhlyA ΔhlyB mutant. An in silico analysis that identifies candidate genes for this other enzyme is presented.

Thymoquinone inhibits biofilm formation and virulence properties of periodontal bacteria

OBJECTIVES

To evaluate the effects of thymoquinone (TQ) on biofilm formation, hemolysis, hydrogen sulfide (H₂S) production and expression of virulence factors of Fusobacterium nucleatum and Porphyromonas gingivalis.

MATERIALS AND METHODS

Reference strains of F. nucleatum ATCC 25586 and P. gingivalis A7436 were tested in our study. The minimum inhibitory concentration (MIC) of TQ was determined by broth microdilution method. The impacts of TQ on virulence properties of the periodontal bacteria including biofilm formation, hemolysis and H₂S activities were studied. Quantitative RT-PCR was performed to evaluate the expression levels of key virulence factors including outer membrane proteins (aim-1, fadA) in F. nucleatum as well as cysteine proteinases or gingipains (rgpA, rgpB, kgp) and fimbriae (fimA, mfa1) in P. gingivalis.

RESULTS

The MIC of TQ were 12.5 and 1.56 μg/mL in F. nucleatum and P. gingivalis, respectively. The sub-MIC concentrations of TQ could prevent biofilm formation and hemolysis activities of both bacteria. TQ also inhibited H₂S production which is highly associated with oral malodour. Scanning electron microscopy revealed that TQ could disrupt bacterial membrane and led to cell lysis. Furthermore, TQ reduced the expression of major virulence factors tested in F. nucleatum and P. gingivalis.

CONCLUSIONS

The TQ had potent antibacterial effect and could attenuate virulence properties of F. nucleatum and P. gingivalis. Therefore, TQ has the potential to be developed and used in periodontal treatments, especially to prevent the progression of periodontitis.

The Mycoplasma pneumoniae HapE alters the cytokine profile and growth of human bronchial epithelial cells

Mycoplasma pneumoniae is one of the most common pathogenic causes of community-acquired pneumonia. Hydrogen sulfide, alanine, and pyruvate producing enzyme (HapE) is a recently discovered M. pneumoniae virulence factor that can produce H₂S to promote erythrocyte lysis. However, other cytotoxic effects of HapE have not been explored. The present study examined the effects of this enzyme on normal human bronchial epithelial (NHBE) cells, in an attempt to identify additional mechanisms of M. pneumoniae pathogenesis. Recombinant HapE was purified for use in downstream assays. MTT and colony formation assays were conducted to determine the effects of HapE on cell viability and growth, while flow cytometry was used to examine changes in cell proliferation and cell cycle function. ELISA was performed to examine changes in the cytokine profile of HapE-treated cells. HapE treatment arrested NHBE cells in S phase and inhibited cell proliferation in a concentration-dependent manner. The anti-inflammatory factors interleukin (IL)-4 and IL-6 were significantly enhanced following HapE treatment. Increased secretion of pro-inflammatory factors was not observed. The effects of HapE on the respiratory epithelium may have an impact on the efficiency of host immune surveillance and pathogen elimination, and contribute to the pathogenesis of M. pneumoniae.