A Gram-negative-selective antibiotic that spares the gut microbiome.

Infections caused by Gram-negative pathogens are increasingly prevalent and are typically treated with broad-spectrum antibiotics, resulting in disruption of the gut microbiome and susceptibility to secondary infections1-3. There is a critical need for antibiotics that are selective both for Gram-negative bacteria over Gram-positive bacteria, as well as for pathogenic bacteria over commensal bacteria. Here we report the design and discovery of lolamicin, a Gram-negative-specific antibiotic targeting the lipoprotein transport system. Lolamicin has activity against a panel of more than 130 multidrug-resistant clinical isolates, shows efficacy in multiple mouse models of acute pneumonia and septicaemia infection, and spares the gut microbiome in mice, preventing secondary infection with Clostridioides difficile. The selective killing of pathogenic Gram-negative bacteria by lolamicin is a consequence of low sequence homology for the target in pathogenic bacteria versus commensals; this doubly selective strategy can be a blueprint for the development of other microbiome-sparing antibiotics.

The quorum-sensing peptidic inhibitor rescues host immune system eradication: A novel infectivity mechanism.

Subverting the host immune system is a major task for any given pathogen to assure its survival and proliferation. For the opportunistic human pathogen Bacillus cereus (Bc), immune evasion enables the establishment of potent infections. In various species of the Bc group, the pleiotropic regulator PlcR and its cognate cell-cell signaling peptide PapR7 regulate virulence gene expression in response to fluctuations in population density, i.e., a quorum-sensing (QS) system. However, how QS exerts its effects during infections and whether PlcR confers the immune evading ability remain unclear. Herein, we report how interception of the QS communication in Bc obliterates the ability to affect the host immune system. Here, we designed a peptide-based QS inhibitor that suppresses PlcR-dependent virulence factor expression and attenuates Bc infectivity in mouse models. We demonstrate that the QS peptidic inhibitor blocks host immune system-mediated eradication by reducing the expression of PlcR-regulated major toxins similarly to the profile that was observed for isogenic strains. Our findings provide evidence that Bc infectivity is regulated by QS circuit-mediated destruction of host immunity, thus reveal a interesting strategy to limit Bc virulence and enhance host defense. This peptidic quorum-quenching agent constitutes a readily accessible chemical tool for studying how other pathogen QS systems modulate host immunity and forms a basis for development of anti-infective therapeutics.

Leveraging intracellular ALDH1A1 activity for selective cancer stem-like cell labeling and targeted treatment via in vivo click reaction.

Inhibition of overexpressed enzymes is among the most promising approaches for targeted cancer treatment. However, many cancer-expressed enzymes are "nonlethal," in that the inhibition of the enzymes' activity is insufficient to kill cancer cells. Conventional antibody-based therapeutics can mediate efficient treatment by targeting extracellular nonlethal targets but can hardly target intracellular enzymes. Herein, we report a cancer targeting and treatment strategy to utilize intracellular nonlethal enzymes through a combination of selective cancer stem-like cell (CSC) labeling and Click chemistry-mediated drug delivery. A de novo designed compound, AAMCHO [N-(3,4,6-triacetyl- N-azidoacetylmannosamine)-cis-2-ethyl-3-formylacrylamideglycoside], selectively labeled cancer CSCs in vitro and in vivo through enzymatic oxidation by intracellular aldehyde dehydrogenase 1A1. Notably, azide labeling is more efficient in identifying tumorigenic cell populations than endogenous markers such as CD44. A dibenzocyclooctyne (DBCO)-toxin conjugate, DBCO-MMAE (Monomethylauristatin E), could next target the labeled CSCs in vivo via bioorthogonal Click reaction to achieve excellent anticancer efficacy against a series of tumor models, including orthotopic xenograft, drug-resistant tumor, and lung metastasis with low toxicity. A 5/7 complete remission was observed after single-cycle treatment of an advanced triple-negative breast cancer xenograft (~500 mm3).

Membrane phospholipid remodeling modulates nonalcoholic steatohepatitis progression by regulating mitochondrial homeostasis.

BACKGROUND AND AIMS: NASH, characterized by inflammation and fibrosis, is emerging as a leading etiology of HCC. Lipidomics analyses in the liver have shown that the levels of polyunsaturated phosphatidylcholine (PC) are decreased in patients with NASH, but the roles of membrane PC composition in the pathogenesis of NASH have not been investigated. Lysophosphatidylcholine acyltransferase 3 (LPCAT3), a phospholipid (PL) remodeling enzyme that produces polyunsaturated PLs, is a major determinant of membrane PC content in the liver. APPROACH AND RESULTS: The expression of LPCAT3 and the correlation between its expression and NASH severity were analyzed in human patient samples. We examined the effect of Lpcat3 deficiency on NASH progression using Lpcat3 liver-specific knockout (LKO) mice. RNA sequencing, lipidomics, and metabolomics were performed in liver samples. Primary hepatocytes and hepatic cell lines were used for in vitro analyses. We showed that LPCAT3 was dramatically suppressed in human NASH livers, and its expression was inversely correlated with NAFLD activity score and fibrosis stage. Loss of Lpcat3 in mouse liver promotes both spontaneous and diet-induced NASH/HCC. Mechanistically, Lpcat3 deficiency enhances reactive oxygen species production due to impaired mitochondrial homeostasis. Loss of Lpcat3 increases inner mitochondrial membrane PL saturation and elevates stress-induced autophagy, resulting in reduced mitochondrial content and increased fragmentation. Furthermore, overexpression of Lpcat3 in the liver ameliorates inflammation and fibrosis of NASH. CONCLUSIONS: These results demonstrate that membrane PL composition modulates the progression of NASH and that manipulating LPCAT3 expression could be an effective therapeutic for NASH.

Signal recognition particle RNA is critical for genetic competence and virulence of Streptococcus pneumoniae.

Streptococcus pneumoniae (pneumococcus) causes a wide range of important human infectious diseases, including pneumonia, pneumonia-derived sepsis, otitis media, and meningitis. Pneumococcus produces numerous secreted proteins that are critical for normal physiology and pathogenesis. The membrane targeting and translocation of these secreted proteins are partly mediated by the signal recognition particle (SRP) complex, which consists of 4.5S small cytoplasmic RNA (ScRNA), and the Ffh, and FtsY proteins. Here, we report that pneumococcal ∆scRNA, ∆ffh, and ∆ftsY mutants were significantly impaired in competence induction, competence pili production, exogenous DNA uptake, and genetic transformation. Also, the ∆scRNA mutant was significantly attenuated in the mouse models of bacteremia and pneumonia. Interestingly, unlike the ∆scRNA, both ∆ffh and ∆ftsY mutants had growth defects on Todd-Hewitt Agar, which were alleviated by the provision of free amino acids or serum. Differences in nutritional requirements between ∆ffh and ∆ftsY vs ∆scRNA suggest that Ffh and FtsY may be partially functional in the absence of ScRNA. Finally, the insertase YidC2, which could functionally rescue some SRP mutations in other streptococcal species, was not essential for pneumococcal genetic transformation. Collectively, these results indicate that ScRNA is crucial for the successful development of genetic competence and virulence in pneumococcus. IMPORTANCE: Streptococcus pneumoniae (pneumococcus) causes multiple important infectious diseases in humans. The signal recognition particle (SRP) complex, which comprised 4.5S small cytoplasmic RNA (ScRNA), and the Ffh and FtsY proteins, mediates membrane targeting and translocation of secreted proteins in all organisms. However, the role of SRP and ScRNA has not been characterized during the induction of the competence system for genetic transformation and virulence in pneumococcus. By using a combination of genetic, biochemical, proteomic, and imaging approaches, we demonstrated that the SRP complex plays a significant role in membrane targeting of competence system-regulated effectors important for genetic transformation, virulence during bacteremia and pneumonia infections, and nutritional acquisition.

Antibacterial efficacy of an ultra-short palmitoylated random peptide mixture in mouse models of infection by carbapenem-resistant Klebsiella pneumoniae.

Indiscriminate use of antibiotics has imposed a selective pressure for the rapid rise in bacterial resistance, creating an urgent need for novel therapeutics for managing bacterial infectious diseases while counteracting bacterial resistance. Carbapenem-resistant Klebsiella pneumoniae strains have become a major challenge in modern medicine due to their ability to cause an array of severe infections. Recently, we have shown that the 20-mer random peptide mixtures are effective therapeutics against three ESKAPEE pathogens. Here, we evaluated the toxicity, biodistribution, bioavailability, and efficacy of the ultra-short palmitoylated 5-mer phenylalanine:lysine (FK5P) random peptide mixtures against multiple clinical isolates of carbapenem-resistant K. pneumoniae and K. oxytoca. We demonstrate the FK5P rapidly and effectively killed various strains of K. pneumoniae, inhibited the formation of biofilms, and disrupted mature biofilms. FK5P displayed strong toxicity profiles both in vitro and in mice, with prolonged favorable biodistribution and a long half-life. Significantly, FK5P reduced the bacterial burden in mouse models of acute pneumonia and bacteremia and increased the survival rate in a mouse model of bacteremia. Our results demonstrate that FK5P is a safe and promising therapy against Klebsiella species as well as other ESKAPEE pathogens.

Designing cyclic competence-stimulating peptide (CSP) analogs with pan-group quorum-sensing inhibition activity in Streptococcus pneumoniae.

Streptococcus pneumoniae is an opportunistic human pathogen that utilizes the competence regulon, a quorum-sensing circuitry, to acquire antibiotic resistance genes and initiate its attack on the human host. Interception of the competence regulon can therefore be utilized to study S. pneumoniae cell-cell communication and behavioral changes, as well as attenuate S. pneumoniae infectivity. Herein we report the design and synthesis of cyclic dominant negative competence-stimulating peptide (dnCSP) analogs capable of intercepting the competence regulon in both S. pneumoniae specificity groups with activities at the low nanomolar range. Structural analysis of lead analogs provided important insights as to the molecular mechanism that drives CSP receptor binding and revealed that the pan-group cyclic CSPs exhibit a chimeric hydrophobic patch conformation that resembles the hydrophobic patches required for both ComD1 and ComD2 binding. Moreover, the lead cyclic dnCSP, CSP1-E1A-cyc(Dap6E10), was found to possess superior pharmacological properties, including improved resistance to enzymatic degradation, while remaining nontoxic. Lastly, CSP1-E1A-cyc(Dap6E10) was capable of attenuating mouse mortality during acute pneumonia caused by both group 1 and group 2 S. pneumoniae strains. This cyclic pan-group dnCSP is therefore a promising drug lead scaffold against S. pneumoniae infections that could be administered individually or utilized in combination therapy to augment the effects of current antimicrobial agents.

AB569, a nontoxic chemical tandem that kills major human pathogenic bacteria.

Antibiotic-resistant superbug bacteria represent a global health problem with no imminent solutions. Here we demonstrate that the combination (termed AB569) of acidified nitrite (A-NO2-) and Na2-EDTA (disodium ethylenediaminetetraacetic acid) inhibited all Gram-negative and Gram-positive bacteria tested. AB569 was also efficacious at killing the model organism Pseudomonas aeruginosa in biofilms and in a murine chronic lung infection model. AB569 was not toxic to human cell lines at bactericidal concentrations using a basic viability assay. RNA-Seq analyses upon treatment of P. aeruginosa with AB569 revealed a catastrophic loss of the ability to support core pathways encompassing DNA, RNA, protein, ATP biosynthesis, and iron metabolism. Electrochemical analyses elucidated that AB569 produced more stable SNO proteins, potentially explaining one mechanism of bacterial killing. Our data implicate that AB569 is a safe and effective means to kill pathogenic bacteria, suggesting that simple strategies could be applied with highly advantageous therapeutic/toxicity index ratios to pathogens associated with a myriad of periepithelial infections and related disease scenarios.

Pulmonary Mycosis Drives Forkhead Box Protein A2 Degradation and Mucus Hypersecretion through Activation of the Spleen Tyrosine Kinase-Epidermal Growth Factor Receptor-AKT/Extracellular Signal-Regulated Kinase 1/2 Signaling.

Pulmonary mycoses are difficult to treat and detrimental to patients. Fungal infections modulate the lung immune response, induce goblet cell hyperplasia and metaplasia, and mucus hypersecretion in the airways. Excessive mucus clogs small airways and reduces pulmonary function by decreasing oxygen exchange, leading to respiratory distress. The forkhead box protein A2 (FOXA2) is a transcription factor that regulates mucus homeostasis in the airways. However, little is known whether pulmonary mycosis modulates FOXA2 function. Herein, we investigated whether Blastomyces dermatitidis and Histoplasma capsulatum-infected canine and feline lungs and airway epithelial cells could serve as higher animal models to examine the relationships between fungal pneumonia and FOXA2-regulated airway mucus homeostasis. The results indicate that fungal infection down-regulated FOXA2 expression in airway epithelial cells, with concomitant overexpression of mucin 5AC (MUC5AC) and mucin 5B (MUC5B) mucins. Mechanistic studies reveal that B. dermatitidis infection, as well as ß-glucan exposure, activated the Dectin-1-SYK-epidermal growth factor receptor-AKT/extracellular signal-regulated kinase 1/2 signaling pathway that inhibits the expression of FOXA2, resulting in overexpression of MUC5AC and MUC5B in canine airway cells. Further understanding of the role of FOXA2 in mucus hypersecretion may lead to novel therapeutics against excessive mucus in both human and veterinary patients with pulmonary mycosis.

Streptococcus pneumoniae Elaborates Persistent and Prolonged Competent State during Pneumonia-Derived Sepsis.

The competence regulon of pneumococcus regulates both genetic transformation and virulence. However, competence induction during host infection has not been examined. By using the serotype 2 strain D39, we transcriptionally fused the firefly luciferase (luc) to competence-specific genes and spatiotemporally monitored the competence development in a mouse model of pneumonia-derived sepsis. In contrast to the universally reported short transient burst of competent state in vitro, the naturally developed competent state was prolonged and persistent during pneumonia-derived sepsis. The competent state began at approximately 20 h postinfection (hpi) and facilitated systemic invasion and sepsis development and progressed in different manners. In some mice, acute pneumonia quickly led to sepsis and death, accompanied by increasing intensity of the competence signal. In the remaining mice, pneumonia lasted longer, with the competence signal decreasing at first but increasing as the infection became septic. The concentration of pneumococcal inoculum (1 × 106 to 1 × 108 CFU/mouse) and postinfection lung bacterial burden did not appreciably impact the kinetics of competence induction. Exogenously provided competence stimulating peptide 1 (CSP1) failed to modulate the onset kinetics of competence development in vivo The competence shutoff regulator DprA was highly expressed during pneumonia-derived sepsis but failed to turn off the competent state in mice. Competent D39 bacteria propagated the competence signal through cell-to-cell contact rather than the classically described quorum-sensing mechanism. Finally, clinical pneumococcal strains of different serotypes were also able to develop natural competence during pneumonia-derived sepsis.

Gram-Negative Antibiotic Active Through Inhibition of an Essential Riboswitch.

Multidrug-resistant Gram-negative (GN) infections for which there are few available treatment options are increasingly common. The development of new antibiotics for these pathogens is challenging because of the inability of most small molecules to accumulate inside GN bacteria. Using recently developed predictive guidelines for compound accumulation in Escherichia coli, we have converted the antibiotic Ribocil C, which targets the flavin mononucleotide (FMN) riboswitch, from a compound lacking whole-cell activity against wild-type GN pathogens into a compound that accumulates to a high level in E. coli, is effective against Gram-negative clinical isolates, and has efficacy in mouse models of GN infections. This compound allows for the first assessment of the translational potential of FMN riboswitch binders against wild-type Gram-negative bacteria.

Controlling chronic Pseudomonas aeruginosa infections by strategically interfering with the sensory function of SagS.

The hybrid sensor SagS plays a central role in the formation of Pseudomonas aeruginosa biofilms, by enabling the switch from the planktonic to the biofilm mode of growth and by facilitating the transition of biofilm cells to a highly tolerant state. In this study, we examined the importance of the SagS key amino acid residues associated with biofilm formation (L154) and antibiotic tolerance (D105) in P. aeruginosa virulence. Recombinant P. aeruginosa ΔsagS and ΔsagS chromosomally expressing wild-type sagS, or its two variants D105A and L154A, were tested for their potential to form biofilms and cause virulence in plants and mouse models of acute and chronic pneumonia. Although mutation of sagS did not alter P. aeruginosa virulence during acute infections, a significant difference in pathogenicity of sagS mutants was observed during chronic infections, with the L154A variant showing reduced bacterial loads in the chronic pneumonia model, while interference with the D105 residue enhanced the susceptibility of P. aeruginosa biofilms during tobramycin treatment. Our findings suggest that interference with the biofilm or tolerance regulatory circuits of SagS affects P. aeruginosa pathogenicity in chronic but not acute infections, and reveal SagS to be a promising new target to treat P. aeruginosa biofilm infections.

FOXA2 depletion leads to mucus hypersecretion in canine airways with respiratory diseases.

Because of exposure to environmental pollutants, infectious agents, and genetic predisposition, companion animals develop respiratory illnesses similar to those in humans. Older dogs of smaller breeds develop canine infectious respiratory disease, chronic bronchitis, and chronic obstructive pulmonary disease, with chronic lung infection, airway goblet cell hyperplasia and metaplasia, and mucus hypersecretion. Excessive mucus clogs airways, reduces gas exchanges, disables the mucociliary clearance, and reduces drug penetration. The Forkhead box protein A2 (FOXA2) is a key transcriptional regulator that maintains airway mucus homeostasis. Prior studies have shown that FOXA2 expression is frequently depleted in diseased human airways. Unfortunately, FOXA2 depletion has not been examined in dogs. Our current study indicated that both single bacterial infection by Pseudomonas aeruginosa and Bordetella bronchiseptica and polymicrobial infection by viral/bacterial pathogens depleted FOXA2 in canine airways, resulting in goblet cell hyperplasia and metaplasia and excessive mucus production. Furthermore, P. aeruginosa virulence factor pyocyanin activated the antagonistic STAT6 and epidermal growth factor receptor signalling pathways to inhibit FOXA2. Unravelling the mechanism of FOXA2 inactivation will hasten the development of non-antibiotic therapeutics to improve mucociliary clearance of pathogens in canine airway.

DprA-Dependent Exit from the Competent State Regulates Multifaceted Streptococcus pneumoniae Virulence.

Streptococcus pneumoniae (pneumococcus) causes multiple infectious diseases. The pneumococcal competence system facilitates genetic transformation, spreads antibiotic resistance, and contributes to virulence. DNA-processing protein A (DprA) regulates the exit of pneumococcus from the competent state. Previously, we have shown that DprA is important in both bacteremia and pneumonia infections. Here, we examined the mechanisms of virulence attenuation in a ΔdprA mutant. Compared to the parental wild-type D39, the ΔdprA mutant enters the competent state when exposed to lower concentrations of the competence-stimulating peptide CSP1. The ΔdprA mutant overexpresses ComM, which delays cell separation after division. Additionally, the ΔdprA mutant overexpresses allolytic factors LytA, CbpD, and CibAB and is more susceptible to detergent-triggered lysis. Disabling of the competent-state-specific induction of ComM and allolytic factors compensated for the virulence loss in the ΔdprA mutant, suggesting that overexpression of these factors contributes to virulence attenuation. Finally, the ΔdprA mutant fails to downregulate the expression of multiple competence-regulated genes, leading to the excessive energy consumption. Collectively, these results indicate that an inability to properly exit the competent state disrupts multiple cellular processes that cause virulence attenuation in the ΔdprA mutant.

Development of a Dominant Negative Competence-Stimulating Peptide (dnCSP) that Attenuates Streptococcus pneumoniae Infectivity in a Mouse Model of Acute Pneumonia.

Streptococcus pneumoniae (pneumococcus) is a prevalent human pathogen responsible for a variety of diseases, including pneumonia, bacteremia, sepsis, meningitis and otitis media, with a death toll of >22 000 a year in the United States alone. Pneumococcus uses the competence regulon and its associated signaling peptide, the competence stimulating peptide (CSP), to initiate its attack on the host and establish an infection. In this work, we set out to: 1) develop a pan-group quorum sensing inhibitor that could effectively interact with both the pneumococcus ComD1 and ComD2 receptors; and 2) evaluate the utility of dominant-negative CSPs (dnCSPs) in attenuating pneumococcus infectivity. Our results highlight the potential of inhibiting the competence regulon as a therapeutic approach to combat pneumococcus infections.

HtrA Is Important for Stress Resistance and Virulence in Haemophilus parasuis.

Haemophilus parasuis is an opportunistic pathogen that causes Glässer's disease in swine, with polyserositis, meningitis, and arthritis. The high-temperature requirement A (HtrA)-like protease, which is involved in protein quality control, has been reported to be a virulence factor in many pathogens. In this study, we showed that HtrA of H. parasuis (HpHtrA) exhibited both chaperone and protease activities. Finally, nickel import ATP-binding protein (NikE), periplasmic dipeptide transport protein (DppA), and outer membrane protein A (OmpA) were identified as proteolytic substrates for HpHtrA. The protease activity reached its maximum at 40°C in a time-dependent manner. Disruption of the htrA gene from strain SC1401 affected tolerance to temperature stress and resistance to complement-mediated killing. Furthermore, increased autoagglutination and biofilm formation were detected in the htrA mutant. In addition, the htrA mutant was significantly attenuated in virulence in the murine model of infection. Together, these data demonstrate that HpHtrA plays an important role in the virulence of H. parasuis.

Deletion analysis of Streptococcus pneumoniae late competence genes distinguishes virulence determinants that are dependent or independent of competence induction.

The competence regulon of Streptococcus pneumoniae (pneumococcus) is crucial for genetic transformation. During competence development, the alternative sigma factor ComX is activated, which in turn, initiates transcription of 80 'late' competence genes. Interestingly, only 16 late genes are essential for genetic transformation. We hypothesized that these late genes that are dispensable for competence are beneficial to pneumococcal fitness during infection. These late genes were systematically deleted, and the resulting mutants were examined for their fitness during mouse models of bacteremia and acute pneumonia. Among these, 14 late genes were important for fitness in mice. Significantly, deletion of some late genes attenuated pneumococcal fitness to the same level in both wild-type and ComX-null genetic backgrounds, suggesting that the constitutive baseline expression of these genes was important for bacterial fitness. In contrast, some mutants were attenuated only in the wild-type genetic background but not in the ComX-null background, suggesting that specific expression of these genes during competence state contributed to pneumococcal fitness. Increased virulence during competence state was partially caused by the induction of allolytic enzymes that enhanced pneumolysin release. These results distinguish the role of basal expression versus competence induction in virulence functions encoded by ComX-regulated late competence genes.

Disentangling competence for genetic transformation and virulence in Streptococcus pneumoniae.

Horizontal gene transfer mediated by the competence regulon is a major driver of genome plasticity in Streptococcus pneumoniae. When pneumococcal cells enter the competent state, about 6% of the genes in the genome are up-regulated. Among these, some genes are essential for genetic transformation while others are dispensable for the process. Exhaustive deletion analyses show that some up-regulated genes dispensable for genetic transformation contribute to pneumococcal-mediated pneumonia and bacteremia infections. Interestingly, virulence functions of such genes are either dependent or independent of the competent state. Among the competent-state-dependent genes are those mediating allolysis, a process where small fraction of non-competent cells within the pneumococcal population are lysed by their competent counterparts, releasing DNA presumably for transformation. Inadvertently, the pore-forming toxin pneumolysin is also released during allolysis, contributing to virulence. In this review, we discuss recent advances in our understanding of pneumococcal virulence processes mediated by the competence regulon. We proposed that coupling of competence induction and bacterial fitness drives the natural selection to favor an intact competence regulon, which in turn, provides the long-term benefits of genetic plasticity.

BdlA, DipA and induced dispersion contribute to acute virulence and chronic persistence of Pseudomonas aeruginosa.

The human pathogen Pseudomonas aeruginosa is capable of causing both acute and chronic infections. Differences in virulence are attributable to the mode of growth: bacteria growing planktonically cause acute infections, while bacteria growing in matrix-enclosed aggregates known as biofilms are associated with chronic, persistent infections. While the contribution of the planktonic and biofilm modes of growth to virulence is now widely accepted, little is known about the role of dispersion in virulence, the active process by which biofilm bacteria switch back to the planktonic mode of growth. Here, we demonstrate that P. aeruginosa dispersed cells display a virulence phenotype distinct from those of planktonic and biofilm cells. While the highest activity of cytotoxic and degradative enzymes capable of breaking down polymeric matrix components was detected in supernatants of planktonic cells, the enzymatic activity of dispersed cell supernatants was similar to that of biofilm supernatants. Supernatants of non-dispersing ΔbdlA biofilms were characterized by a lack of many of the degradative activities. Expression of genes contributing to the virulence of P. aeruginosa was nearly 30-fold reduced in biofilm cells relative to planktonic cells. Gene expression analysis indicated dispersed cells, while dispersing from a biofilm and returning to the single cell lifestyle, to be distinct from both biofilm and planktonic cells, with virulence transcript levels being reduced up to 150-fold compared to planktonic cells. In contrast, virulence gene transcript levels were significantly increased in non-dispersing ΔbdlA and ΔdipA biofilms compared to wild-type planktonic cells. Despite this, bdlA and dipA inactivation, resulting in an inability to disperse in vitro, correlated with reduced pathogenicity and competitiveness in cross-phylum acute virulence models. In contrast, bdlA inactivation rendered P. aeruginosa more persistent upon chronic colonization of the murine lung, overall indicating that dispersion may contribute to both acute and chronic infections.

Type IV pilus glycosylation mediates resistance of Pseudomonas aeruginosa to opsonic activities of the pulmonary surfactant protein A.

Pseudomonas aeruginosa is a major bacterial pathogen commonly associated with chronic lung infections in cystic fibrosis (CF). Previously, we have demonstrated that the type IV pilus (Tfp) of P. aeruginosa mediates resistance to antibacterial effects of pulmonary surfactant protein A (SP-A). Interestingly, P. aeruginosa strains with group I pilins are O-glycosylated through the TfpO glycosyltransferase with a single subunit of O-antigen (O-ag). Importantly, TfpO-mediated O-glycosylation is important for virulence in mouse lungs, exemplified by more frequent lung infection in CF with TfpO-expressing P. aeruginosa strains. However, the mechanism underlying the importance of Tfp glycosylation in P. aeruginosa pathogenesis is not fully understood. Here, we demonstrated one mechanism of increased fitness mediated by O-glycosylation of group 1 pilins on Tfp in the P. aeruginosa clinical isolate 1244. Using an acute pneumonia model in SP-A+/+ versus SP-A-/- mice, the O-glycosylation-deficient ΔtfpO mutant was found to be attenuated in lung infection. Both 1244 and ΔtfpO strains showed equal levels of susceptibility to SP-A-mediated membrane permeability. In contrast, the ΔtfpO mutant was more susceptible to opsonization by SP-A and by other pulmonary and circulating opsonins, SP-D and mannose binding lectin 2, respectively. Importantly, the increased susceptibility to phagocytosis was abrogated in the absence of opsonins. These results indicate that O-glycosylation of Tfp with O-ag specifically confers resistance to opsonization during host-mediated phagocytosis.