Designing phage cocktails to combat the emergence of bacteriophage-resistant mutants in multidrug-resistant Klebsiella pneumoniae.

IMPORTANCE: In this study, we aimed to design a novel and effective bacteriophage cocktail that can target both wild-type bacteria and phage-resistant mutants. To achieve this goal, we isolated four phages (U2874, phi_KPN_H2, phi_KPN_S3, and phi_KPN_HS3) that recognized different bacterial surface molecules using phage-resistant bacteria. We constructed three phage cocktails and tested their phage resistance-suppressing ability against multidrug-resistant Klebsiella pneumoniae. We argue that the phage cocktail that induces resensitization of phage susceptibility exhibited superior phage resistance-suppressing ability. Moreover, we observed trade-off effects that manifested progressively in phage-resistant bacteria. We hypothesize that such trade-off effects can augment therapeutic efficacy. We also recommend collating phage host range data against phage-resistant mutants in addition to wild-type bacteria when establishing phage banks to improve the efficiency of phage therapy. Our study underscores the importance of phage host range data in constructing effective phage cocktails for clinical use.

Nasal symbiont Staphylococcus epidermidis restricts the cellular entry of influenza virus into the nasal epithelium.

Our recent study presented that human nasal commensal Staphylococcus epidermidis could potentiate antiviral immunity in the nasal mucosa through interferon-related innate responses. Here, we found that human nasal commensal S. epidermidis promoted protease-protease inhibitor balance in favor of the host and prevented influenza A virus (IAV) replication in the nasal mucosa and lungs. A relatively higher induction of Serpine1 exhibited in S. epidermidis-inoculated nasal epithelium and S. epidermidis-induced Serpine1 significantly decreased the expression of serine proteases. Furthermore, the transcription of urokinase plasminogen activator (uPA) and Serpine1 was biologically relevant in S. epidermidis-inoculated nasal epithelium, and the induction of uPA might be related to the sequential increase of Serpine1 in human nasal epithelium. Our findings reveal that human nasal commensal S. epidermidis manipulates the cellular environment lacking serine proteases in the nasal epithelium through Serpine1 induction and disturbs IAV spread to the lungs at the level of the nasal mucosa.

Genome-wide association study of signature genetic alterations among pseudomonas aeruginosa cystic fibrosis isolates.

Pseudomonas aeruginosa (PA) is an opportunistic pathogen that causes diverse human infections including chronic airway infection in patients with cystic fibrosis (CF). Comparing the genomes of CF and non-CF PA isolates has great potential to identify the genetic basis of pathogenicity. To gain a deeper understanding of PA adaptation in CF airways, we performed a genome-wide association study (GWAS) on 1,001 PA genomes. Genetic variations identified among CF isolates were categorized into (i) alterations in protein-coding regions, either large- or small-scale, and (ii) polymorphic variation in intergenic regions. We introduced each CF-associated genetic alteration into the genome of PAO1, a prototype PA strain, and validated the outcomes experimentally. Loci readily mutated among CF isolates included genes encoding a probable sulfatase, a probable TonB-dependent receptor (PA2332~PA2336), L-cystine transporter (YecS, PA0313), and a probable transcriptional regulator (PA5438). A promoter region of a heme/hemoglobin uptake outer membrane receptor (PhuR, PA4710) was also different between the CF and non-CF isolate groups. Our analysis highlights ways in which the PA genome evolves to survive and persist within the context of chronic CF infection.

High-Fat-Diet-Induced Oxidative Stress Linked to the Increased Colonization of Lactobacillus sakei in an Obese Population.

Obesity is a major public health problem related to various chronic health conditions. Lactobacillus species has been reported in obese individuals; however, its role is unknown. We compared the abundance and composition of Lactobacillus species by analyzing feces from 64 healthy control subjects and 88 obese subjects. We isolated one Lactobacillus strain from the feces of a subject with obesity and further analyzed its genetic and molecular features. We found that an increased abundance and higher prevalence of Lactobacillus sakei distinguished the fecal microbiota of the obese group from that of healthy subjects and that it was related to the increased levels of reactive oxygen species (ROS) induced by higher fat intake. The L. sakei ob4.1 strain, isolated from the feces of a subject with obesity, showed high catalase activity, which was regulated by oxidative stress at the gene transcription level. L. sakei ob4.1 maintained colon epithelial cell adhesion ability under ROS stimulation, and treatment with saturated fatty acid increased colon epithelial ROS levels in a dose-dependent manner; however, L. sakei ob4.1 did not change the level of fat-induced colon epithelial ROS. Exposing mice to a high-fat diet revealed that high-fat-diet-induced colon ROS was associated with the increased colonization of L. sakei ob4.1 through catalase activity. Four-week supplementation with this strain in mice fed a high-fat diet did not change their body weights or ROS levels. A high-fat diet induces changes in the colon environment by increasing ROS levels, which provides a colonization benefit to an L. sakei strain with high catalase activity. IMPORTANCELactobacillus provides many health benefits; its various species are widely used as probiotics. However, an increased abundance of Lactobacillus has been reported in obesity, and the role of Lactobacillus strains in obesity remains unknown. We found a high abundance of the Lactobacillus sakei species in a group of obese subjects and examined its relationship with a high-fat diet and reactive oxygen species (ROS) in the feces. To find the underlying mechanism, we analyzed and characterized an L. sakei strain isolated from a severely obese individual. We found that higher gut oxidative stress could link high-fat-diet-induced obesity and L. sakei. This translational research identifies the roles of the host gut environment in the colonization and survival of L. sakei.

Chemical inhibitors of the conserved bacterial transcriptional regulator DksA1 suppressed quorum sensing-mediated virulence of Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen whose virulence is dependent on quorum sensing (QS). DksA1, an RNA polymerase-binding transcriptional regulator, plays a role in determining a number of phenotypes, including QS-mediated virulence. We therefore envisioned that DksA1 inhibitors may help to control P. aeruginosa infection. Here, we screened a library of 6970 chemical compounds and identified two compounds (henceforth termed Dkstatins) that specifically suppressed DksA1 activity. Treatment with these two compounds also substantially decreased the production of elastase and pyocyanin, dominant virulence determinants of P. aeruginosa, and protected murine hosts from lethal infection from a prototype strain of P. aeruginosa, PAO1. The Dkstatins also suppressed production of homoserine lactone (HSL)-based autoinducers that activate P. aeruginosa QS. The level of 3-oxo-C12-HSL produced by Dkstatin-treated wildtype PAO1 closely resembled that of the ΔdksA1 mutant. RNA-Seq analysis showed that transcription levels of QS- and virulence-associated genes were markedly reduced in Dkstatin-treated PAO1 cells, indicating that Dkstatin-mediated suppression occurs at the transcriptional level. Importantly, Dkstatins increased the antibiotic susceptibilities of PAO1, particularly to protein synthesis inhibitors, such as tobramycin and tetracycline. Co-immunoprecipitation assays demonstrated that these Dkstatins interfered with DksA1 binding to the ß subunit of RNA polymerase, pointing to a potential mechanism of action. Collectively, our results illustrate that inhibition of P. aeruginosa QS may be achieved via DksA1 inhibitors and that Dkstatins may serve as potential lead compounds to control infection.

IL-17C Protects Nasal Epithelium from Pseudomonas aeruginosa Infection.

IL-17 family cytokines are directly involved in host immune responses and the critical mediators for host defense against infection or inflammation. IL-17C is highly expressed in respiratory epithelium and is induced after acute bacterial lung infection. However, the definite function of IL-17C induced by Pseudomonas aeruginosa (PAO1 strain) is not fully understood, and our study was designed to demonstrate IL-17C-induced immune response against PAO1 infection in nasal epithelium. Passage-2 normal human nasal epithelial (NHNE) cells were infected with PAO1 and the relationship between IL-17C-related immune responses and the iron absorption of PAO1, depending on inoculation of recombinant human IL-17C (rhIL-17C), was assessed by measuring the siderophore activity of PAO1. Microarray data showed that IL-17C expression increased 34.7 times at 8 hours postinfection (hpi) in NHNE cells, and IL-17C mRNA levels increased until 48 hpi. The PAO1 colonies significantly increased from 8 hpi in NHNE cells, and siderophore activity of PAO1 was enhanced in the supernatants of PAO1-infected NHNE cells. Interestingly, PAO1 colonies were reduced in PAO1-infected NHNE cells treated with rhIL-17C, and supernatants from NHNE cells treated with rhIL-17C also exhibited decreased PAO1 colonies. We found that the siderophore activity of PAO1 was significantly reduced in the supernatants of NHNE cells treated with rhIL-17C where LCN2 expression was highly elevated. Our findings indicate that IL-17C mediates an antibacterial effect against PAO1 by inhibiting siderophore activity in nasal epithelium. We propose that IL-17C might be an efficient mediator to suppress PAO1 infection through disturbing iron absorption of PAO1 in nasal epithelium.

Nasal commensal Staphylococcus epidermidis enhances interferon-λ-dependent immunity against influenza virus.

BACKGROUND: Staphylococcus epidermidis is one of the most abundant colonizers of healthy human mucosa including that in the respiratory tract. As the respiratory microbiome has been linked to host immune responses, this study sought to determine the role of nasal mucosa-associated S. epidermidis in innate immune responses against the influenza A virus (IAV). S. epidermidis strains were isolated from nasal mucus samples of healthy individuals. The effects of these mucosa-derived commensal strains on interferon (IFN)-dependent innate immunity and IAV infection dynamics were tested in vitro using normal human nasal epithelial (NHNE) cells and human turbinate mucosa. The effects of S. epidermidis on antiviral immunity were also tested in vivo using an acute IAV infection mouse model. RESULTS: Exposure of NHNE cells to nasal mucosa-derived S. epidermidis increased IFN-λ mRNA and secreted protein levels in the absence of viral stimulation. In the context of IAV infection, NHNE exposure to S. epidermidis prevented an increase in the viral burden, as revealed by IAV PA mRNA abundance, IAV nucleoprotein levels, and viral titers. S. epidermidis also enhanced transcription of IFN-stimulated genes independently of Toll-like receptor 2 and further induced IFN-λ production in IAV-infected cells by promoting phosphorylation of interferon regulatory factor 7. In a murine infection model, S. epidermidis prevented the spread of IAV to the lungs by stimulating IFN-λ innate immunity and suppressing IAV replication in the nasal mucosa. CONCLUSION: The human nasal commensal S. epidermidis mediates front-line antiviral protection against IAV infection through modulation of IFN-λ-dependent innate immune mechanisms in the nasal mucosa, thereby demonstrating the role of host-bacterial commensalism in shaping human antiviral responses.

Cleaved Cochlin Sequesters Pseudomonas aeruginosa and Activates Innate Immunity in the Inner Ear.

In the inner ear, endolymph fluid surrounds the organ of Corti, which is important for auditory function; notably, even slight environmental changes mediated by trauma or infection can have significant consequences. However, it is unclear how the immune response is modulated in these tissues. Here, we report the local immune surveillance role of cleaved cochlin LCCL (Limulus factor C, Cochlin, and Lgl1) during Pseudomonas aeruginosa infection in the cochlea. Upon infection, the LCCL domain is cleaved from cochlin and secreted into the perilymph. This cleaved fragment sequesters infiltrating bacteria in the scala tympani and subsequently recruits resident immune cells to eliminate the bacteria. Importantly, hearing loss in a cochlin knockout mouse model is remedied by treatment with a cochlin LCCL peptide. These findings suggest cleaved cochlin LCCL constitutes a critical factor in innate immunity and auditory function and may be a potential therapeutic target to treat chronic otitis media-induced hearing loss.

Risk factors for mortality in patients with Pseudomonas aeruginosa pneumonia: Clinical impact of mucA gene mutation.

OBJECTIVES: Pseudomonas aeruginosa frequently colonizes the lungs of chronic obstructive pulmonary disease (COPD) patients. Mucoid conversion is a hallmark of chronic P. aeruginosa infection, which is mediated by mucA gene mutations. The aim of this study is to identify predictive factors for mortality and the influence of mucA gene mutation in COPD patients with P. aeruginosa pneumonia. METHODS: This study assessed 75 COPD patients with P. aeruginosa pneumonia at two university hospitals. The clinical and laboratory data were collected, and the P. aeruginosa isolates analyzed for the presence of mucA gene mutations. RESULTS: MucA gene mutation of P. aeruginosa was an independent predictor of mortality (odds ratio [OR] 10.43, 95% confidence interval [CI]: 1.53-70.90, p = 0.017). In addition, the APACHE II score and C-reactive protein/Albumin (CA) ratio were independent predictive factors for mortality (OR 1.25, 95% CI: 1.07-1.46, p = 0.004; and OR 1.06, 95% CI: 1.02-1.10, p = 0.003, respectively). The optimal cutoff value of CA ratio for the greatest sensitivity and specificity was calculated as 31.27 (sensitivity, 85.7%; specificity, 80.3%). CONCLUSIONS: CA ratio and mucA gene mutation of P. aeruginosa could be used as predictors to identify poor prognosis in COPD patients with P. aeruginosa pneumonia.

Guanosine tetra- and pentaphosphate increase antibiotic tolerance by reducing reactive oxygen species production in Vibrio cholerae.

The pathogen Vibrio cholerae is the causative agent of cholera. Emergence of antibiotic-resistant V. cholerae strains is increasing, but the underlying mechanisms remain unclear. Herein, we report that the stringent response regulator and stress alarmone guanosine tetra- and pentaphosphate ((p)ppGpp) significantly contributes to antibiotic tolerance in V. cholerae We found that N16961, a pandemic V. cholerae strain, and its isogenic (p)ppGpp-overexpressing mutant ΔrelAΔspoT are both more antibiotic-resistant than (p)ppGpp0 (ΔrelAΔrelVΔspoT) and ΔdksA mutants, which cannot produce or utilize (p)ppGpp, respectively. We also found that additional disruption of the aconitase B-encoding and tricarboxylic acid (TCA) cycle gene acnB in the (p)ppGpp0 mutant increases its antibiotic tolerance. Moreover, expression of TCA cycle genes, including acnB, was increased in (p)ppGpp0, but not in the antibiotic-resistant ΔrelAΔspoT mutant, suggesting that (p)ppGpp suppresses TCA cycle activity, thereby entailing antibiotic resistance. Importantly, when grown anaerobically or incubated with an iron chelator, the (p)ppGpp0 mutant became antibiotic-tolerant, suggesting that reactive oxygen species (ROS) are involved in antibiotic-mediated bacterial killing. Consistent with that hypothesis, tetracycline treatment markedly increased ROS production in the antibiotic-susceptible mutants. Interestingly, expression of the Fe(III) ABC transporter substrate-binding protein FbpA was increased 10-fold in (p)ppGpp0, and fbpA gene deletion restored viability of tetracycline-exposed (p)ppGpp0 cells. Of note, FbpA expression was repressed in the (p)ppGpp-accumulating mutant, resulting in a reduction of intracellular free iron, required for the ROS-generating Fenton reaction. Our results indicate that (p)ppGpp-mediated suppression of central metabolism and iron uptake reduces antibiotic-induced oxidative stress in V. cholerae.

Molecular Determinants of the Thickened Matrix in a Dual-Species Pseudomonas aeruginosa and Enterococcus faecalis Biofilm.

Biofilms are microbial communities that inhabit various surfaces and are surrounded by extracellular matrices (ECMs). Clinical microbiologists have shown that the majority of chronic infections are caused by biofilms, following the introduction of the first biofilm infection model by J. W. Costerton and colleagues (J. Lam, R. Chan, K. Lam, and J. W. Costerton, Infect Immun 28:546-556, 1980). However, treatments for chronic biofilm infections are still limited to surgical removal of the infected sites. Pseudomonas aeruginosa and Enterococcus faecalis are two frequently identified bacterial species in biofilm infections; nevertheless, the interactions between these two species, especially during biofilm growth, are not clearly understood. In this study, we observed phenotypic changes in a dual-species biofilm of P. aeruginosa and E. faecalis, including a dramatic increase in biofilm matrix thickness. For clear elucidation of the spatial distribution of the dual-species biofilm, P. aeruginosa and E. faecalis were labeled with red and green fluorescence, respectively. E. faecalis was located at the lower part of the dual-species biofilm, while P. aeruginosa developed a structured biofilm on the upper part. Mutants with altered exopolysaccharide (EPS) productions were constructed in order to determine the molecular basis for the synergistic effect of the dual-species biofilm. Increased biofilm matrix thickness was associated with EPSs, not extracellular DNA. In particular, Pel and Psl contributed to interspecies and intraspecies interactions, respectively, in the dual-species P. aeruginosa and E. faecalis biofilm. Accordingly, targeting Pel and Psl might be an effective part of eradicating P. aeruginosa polymicrobial biofilms.IMPORTANCE Chronic infection is a serious problem in the medical field. Scientists have observed that chronic infections are closely associated with biofilms, and the vast majority of infection-causing biofilms are polymicrobial. Many studies have reported that microbes in polymicrobial biofilms interact with each other and that the bacterial interactions result in elevated virulence, in terms of factors, such as infectivity and antibiotic resistance. Pseudomonas aeruginosa and Enterococcus faecalis are frequently isolated pathogens in chronic biofilm infections. Nevertheless, while both bacteria are known to be agents of numerous nosocomial infections and can cause serious diseases, interactions between the bacteria in biofilms have rarely been examined. In this investigation, we aimed to characterize P. aeruginosa and E. faecalis dual-species biofilms and to determine the molecular factors that cause synergistic effects, especially on the matrix thickening of the biofilm. We suspect that our findings will contribute to the development of more efficient methods for eradicating polymicrobial biofilm infections.

Bacterial Secretant from Pseudomonas aeruginosa Dampens Inflammasome Activation in a Quorum Sensing-Dependent Manner.

Inflammasome signaling can contribute to host innate immune defense against bacterial pathogens such as Pseudomonas aeruginosa. However, bacterial evasion of host inflammasome activation is still poorly elucidated. Quorum sensing (QS) is a bacterial communication mechanism that promotes coordinated adaptation by triggering expression of a wide range of genes. QS is thought to strongly contribute to the virulence of P. aeruginosa, but the molecular impact of bacterial QS on host inflammasome defense is completely unknown. Here, we present evidence that QS-related factors of the bacterial secretant (BS) from P. aeruginosa can dampen host inflammasome signaling in mouse bone marrow-derived macrophages. We found that BS from QS-defective ΔlasR/rhlR mutant, but not from wild-type (WT) P. aeruginosa, induces robust activation of the NLRC4 inflammasome. P. aeruginosa-released flagellin mediates this inflammasome activation by ΔlasR/rhlR secretant, but QS-regulated bacterial proteases in the WT BS impair extracellular flagellin to attenuate NLRC4 inflammasome activation. P. aeruginosa-secreted proteases also degrade inflammasome components in the extracellular space to inhibit the propagation of inflammasome-mediated responses. Furthermore, QS-regulated virulence factor pyocyanin and QS autoinducer 3-oxo-C12-homoserine lactone directly suppressed NLRC4- and even NLRP3-mediated inflammasome assembly and activation. Taken together, our data indicate that QS system of P. aeruginosa facilitates bacteria to evade host inflammasome-dependent sensing machinery.

A Genetic Screen Reveals Novel Targets to Render Pseudomonas aeruginosa Sensitive to Lysozyme and Cell Wall-Targeting Antibiotics.

Pseudomonas aeruginosa is capable of establishing airway infections. Human airway mucus contains a large amount of lysozyme, which hydrolyzes bacterial cell walls. P. aeruginosa, however, is known to be resistant to lysozyme. Here, we performed a genetic screen using a mutant library of PAO1, a prototype P. aeruginosa strain, and identified two mutants (ΔbamB and ΔfabY) that exhibited decrease in survival after lysozyme treatment. The bamB and fabY genes encode an outer membrane assembly protein and a fatty acid synthesis enzyme, respectively. These two mutants displayed retarded growth in the airway mucus secretion (AMS). In addition, these mutants exhibited reduced virulence and compromised survival fitness in two different in vivo infection models. The mutants also showed susceptibility to several antibiotics. Especially, ΔbamB mutant was very sensitive to vancomycin, ampicillin, and ceftazidime that target cell wall synthesis. The ΔfabY displayed compromised membrane integrity. In conclusion, this study uncovered a common aspect of two different P. aeruginosa mutants with pleiotropic phenotypes, and suggests that BamB and FabY could be novel potential drug targets for the treatment of P. aeruginosa infection.

A single gene of a commensal microbe affects host susceptibility to enteric infection.

Indigenous microbes inside the host intestine maintain a complex self-regulating community. The mechanisms by which gut microbes interact with intestinal pathogens remain largely unknown. Here we identify a commensal Escherichia coli strain whose expansion predisposes mice to infection by Vibrio cholerae, a human pathogen. We refer to this strain as 'atypical' E. coli (atEc) because of its inability to ferment lactose. The atEc strain is resistant to reactive oxygen species (ROS) and proliferates extensively in antibiotic-treated adult mice. V. cholerae infection is more severe in neonatal mice transplanted with atEc compared with those transplanted with a typical E. coli strain. Intestinal ROS levels are decreased in atEc-transplanted mice, favouring proliferation of ROS-sensitive V. cholerae. An atEc mutant defective in ROS degradation fails to facilitate V. cholerae infection when transplanted, suggesting that host infection susceptibility can be regulated by a single gene product of one particular commensal species.

The ferrichrome receptor A as a new target for Pseudomonas aeruginosa virulence attenuation.

Pseudomonas aeruginosa is an opportunistic pathogen, known to develop robust biofilms. Its biofilm development increases when antibiotics are presented at subminimal inhibitory concentrations (MICs) for reasons that remain unclear. In order to identify genes that affect biofilm development under such a sublethal antibiotic stress condition, we screened a transposon (Tn) mutant library of PAO1, a prototype P. aeruginosa strain. Among ∼5000 mutants, a fiuA gene mutant was verified to form very defective biofilms in the presence of sub-MIC carbenicillin. The fiuA gene encodes ferrichrome receptor A, involved in the iron acquisition process. Of note, biofilm formation was not decreased in the ΔpchΔpvd mutant defective in the production of pyochelin and pyoverdine, two well-characterized P. aeruginosa siderophore molecules. Moreover, ΔfiuA, a non-polar fiuA deletion mutant, produced a significantly decreased level of elastase, a major virulence determinant. Mouse airway infection experiments revealed that the mutant expressed significantly less pathogenicity. Our results suggest that the fiuA gene has pleiotropic functions that affect P. aeruginosa biofilm development and virulence. The targeting of FiuA could enable the attenuation of P. aeruginosa virulence and may be suitable for the development of a drug that specifically controls the virulence of this important pathogen.

Cholera Toxin Production Induced upon Anaerobic Respiration is Suppressed by Glucose Fermentation in Vibrio cholerae.

The causative agent of pandemic cholera, Vibrio cholerae, infects the anaerobic environment of the human intestine. Production of cholera toxin (CT), a major virulence factor of V. cholerae, is highly induced during anaerobic respiration with trimethylamine N-oxide (TMAO) as an alternative electron acceptor. However, the molecular mechanism of TMAO-stimulated CT production is not fully understood. Herein, we reveal that CT production during anaerobic TMAO respiration is affected by glucose fermentation. When the seventh pandemic V. cholerae O1 strain N16961 was grown with TMAO and additional glucose, CT production was markedly reduced. Furthermore, an N16961 Δcrp mutant, devoid of cyclic AMP receptor protein (CRP), was defective in CT production during growth by anaerobic TMAO respiration, further suggesting a role of glucose metabolism in regulating TMAO-mediated CT production. TMAO reductase activity was noticeably decreased when grown together with glucose or by mutation of the crp gene. A CRP binding region was identified in the promoter region of the torD gene, which encodes a structural subunit of the TMAO reductase. Gel shift assays further confirmed the binding of purified CRP to the torD promoter sequence. Together, our results suggest that the bacterial ability to respire using TMAO is controlled by CRP, whose activity is dependent on glucose availability. Our results reveal a novel mechanism for the regulation of major virulence factor production by V. cholerae under anaerobic growth conditions.

A novel siderophore system is essential for the growth of Pseudomonas aeruginosa in airway mucus.

Pseudomonas aeruginosa establishes airway infections in Cystic Fibrosis patients. Here, we investigate the molecular interactions between P. aeruginosa and airway mucus secretions (AMS) derived from the primary cultures of normal human tracheal epithelial (NHTE) cells. PAO1, a prototype strain of P. aeruginosa, was capable of proliferating during incubation with AMS, while all other tested bacterial species perished. A PAO1 mutant lacking PA4834 gene became susceptible to AMS treatment. The ΔPA4834 mutant was grown in AMS supplemented with 100 µM ferric iron, suggesting that the PA4834 gene product is involved in iron metabolism. Consistently, intracellular iron content was decreased in the mutant, but not in PAO1 after the AMS treatment. Importantly, a PAO1 mutant unable to produce both pyoverdine and pyochelin remained viable, suggesting that these two major siderophore molecules are dispensable for maintaining viability during incubation with AMS. The ΔPA4834 mutant was regrown in AMS amended with 100 µM nicotianamine, a phytosiderophore whose production is predicted to be mediated by the PA4836 gene. Infectivity of the ΔPA4834 mutant was also significantly compromised in vivo. Together, our results identify a genetic element encoding a novel iron acquisition system that plays a previously undiscovered role in P. aeruginosa airway infection.

(p)ppGpp, a Small Nucleotide Regulator, Directs the Metabolic Fate of Glucose in Vibrio cholerae.

When V. cholerae encounters nutritional stress, it activates (p)ppGpp-mediated stringent response. The genes relA and relV are involved in the production of (p)ppGpp, whereas the spoT gene encodes an enzyme that hydrolyzes it. Herein, we show that the bacterial capability to produce (p)ppGpp plays an essential role in glucose metabolism. The V. cholerae mutants defective in (p)ppGpp production (i.e. ΔrelAΔrelV and ΔrelAΔrelVΔspoT mutants) lost their viability because of uncontrolled production of organic acids, when grown with extra glucose. In contrast, the ΔrelAΔspoT mutant, a (p)ppGpp overproducer strain, exhibited better growth in the presence of the same glucose concentration. An RNA sequencing analysis demonstrated that transcriptions of genes consisting of an operon for acetoin biosynthesis were markedly elevated in N16961, a seventh pandemic O1 strain, but not in its (p)ppGpp(0) mutant during glucose-stimulated growth. Transposon insertion in acetoin biosynthesis gene cluster resulted in glucose-induced loss of viability of the ΔrelAΔspoT mutant, further suggesting the crucial role of acetoin production in balanced growth under glucose-rich environments. Additional deletion of the aphA gene, encoding a negative regulator for acetoin production, failed to rescue the (p)ppGpp(0) mutant from the defective glucose-mediated growth, suggesting that (p)ppGpp-mediated acetoin production occurs independent of the presence of AphA. Overall, our results reveal that (p)ppGpp, in addition to its well known role as a stringent response mediator, positively regulates acetoin production that contributes to the successful glucose metabolism and consequently the proliferation of V. cholerae cells under a glucose-rich environment, a condition that may mimic the human intestine.

A drug-repositioning screening identifies pentetic acid as a potential therapeutic agent for suppressing the elastase-mediated virulence of Pseudomonas aeruginosa.

Pseudomonas aeruginosa, a Gram-negative bacterium of clinical significance, produces elastase as a predominant exoprotease. Here, we screened a library of chemical compounds currently used for human medication and identified diethylene triamine penta-acetic acid (DTPA, pentetic acid) as an agent that suppresses the production of elastase. Elastase activity found in the prototype P. aeruginosa strain PAO1 was significantly decreased when grown with a concentration as low as 20 µM DTPA. Supplementation with Zn(2+) or Mn(2+) ions restored the suppressive effect of DTPA, suggesting that the DTPA-mediated decrease in elastase activity is associated with ion-chelating activity. In DTPA-treated PAO1 cells, transcription of the elastase-encoding lasB gene and levels of the Pseudomonas quinolone signal (PQS), a molecule that mediates P. aeruginosa quorum sensing (QS), were significantly downregulated, reflecting the potential involvement of the PQS QS system in DTPA-mediated elastase suppression. Biofilm formation was also decreased by DTPA treatment. When A549 alveolar type II-like adenocarcinoma cells were infected with PAO1 cells in the presence of DTPA, A549 cell viability was substantially increased. Furthermore, the intranasal delivery of DTPA to PAO1-infected mice alleviated the pathogenic effects of PAO1 cells in the animals. Together, our results revealed a novel function for a known molecule that may help treat P. aeruginosa airway infection.

Nonmucoid conversion of mucoid Pseudomonas aeruginosa induced by sulfate-stimulated growth.

Alginate-overproducing mucoid Pseudomonas aeruginosa, responsible for chronic airway infections in cystic fibrosis (CF) patients, is resistant to antibiotic treatments and host immune clearance. In this study, we performed a phenotype microarray screen and identified sulfate ion as a molecule that can suppress alginate production. When a mucoid P. aeruginosa strain CM21 and additional mucoid isolates were grown with 5% sodium sulfate, significantly decreased levels of alginate were produced. Suppression of alginate production was also induced by other sulfate salts. Expression of a reporter gene fused to the algD promoter was considerably decreased when grown with sulfate. Furthermore, bacterial cell shape was abnormally altered in CM21, but not in PAO1, a prototype nonmucoid strain, suggesting that sulfate-stimulated cell shape change is associated with transcriptional suppression of the alginate operon. Finally, a CM21 lpxC mutant defective in lipid A biosynthesis continued to produce alginate and maintained the correct cell shape when grown with sulfate. These results suggest a potential involvement of lipoploysaccharide biosynthesis in the sulfate-induced reversion to nonmucoid phenotype. This study proposes a novel strategy that can be potentially applied to treat persistent infection by recalcitrant mucoid P. aeruginosa.