Visions of Artificial Intelligence and Robots in Science Fiction: a computational analysis.

Driven by the rapid development of artificial intelligence (AI) and anthropomorphic robotic systems, the various possibilities and risks of such technologies have become a topic of urgent discussion. Although science fiction (SF) works are often cited as references for visions of future developments, this framework of discourse may not be appropriate for serious discussions owing to technical inaccuracies resulting from its reliance on entertainment media. However, these science fiction works could help researchers understand how people might react to new AI and robotic systems. Hence, classifying depictions of artificial intelligence in science fiction may be expected to help researchers to communicate more clearly by identifying science fiction elements to which their works may be similar or dissimilar. In this study, we analyzed depictions of artificial intelligence in SF together with expert critics and writers. First, 115 AI systems described in SF were selected based on three criteria, including diversity of intelligence, social aspects, and extension of human intelligence. Nine elements representing their characteristics were analyzed using clustering and principal component analysis. The results suggest the prevalence of four distinctive categories, including human-like characters, intelligent machines, helpers such as vehicles and equipment, and infrastructure, which may be mapped to a two-dimensional space with axes representing intelligence and humanity. This research contributes to the public relations of AI and robotic technologies by analyzing shared imaginative visions of AI in society based on SF works.

Anti-Inflammatory and Protective Effects of Juncus effusus L. Water Extract on Oral Keratinocytes.

Periodontitis is a chronic inflammatory disease caused by periodontopathogenic bacteria that form biofilms in periodontal pockets. The gingival epithelium acts as the first physical barrier in fighting attacks by periodontopathogenic pathogens, such as the primary etiological agent Porphyromonas gingivalis, and various exogenous chemicals, as well as regulates the local innate immune responses. Therefore, the development of novel oral care products to inhibit inflammatory reactions caused by bacterial infection and protect the gingival epithelium is necessary. Juncus effusus L. has generally been used as an indigenous medicine, such as a diuretic, an antipyretic, and an analgesic, in ancient practice. In this study, we examined the effects of a water extract from J. effusus L. on the inhibition of the inflammatory reaction elicited by bacterial infection and protection of the oral epithelium by chemical irritation. Pretreatment of oral epithelial cells with the water extract from J. effusus L. significantly reduced P. gingivalis or its lipopolysaccharide- (LPS-) mediated production of chemokines (interleukin-8 and C-C-chemokine ligand20) in a concentration-dependent manner with comparable to or greater effects than epigallocatechin gallate and protected oral epithelial cells from injury by chemical irritants, cetylpyridinium chloride, and benzethonium chloride. Moreover, the water extract from J. effusus L. in the presence of antimicrobial agents or antifibrinolytics already used as ingredients in mouthwash could significantly reduce the production of chemokines from P. gingivalis LPS-stimulated oral epithelial cells in a concentration-dependent manner. These findings suggest that the water extract from J. effusus L. is potentially useful for oral care to prevent oral infections, such as periodontal infections, and maintain oral epithelial function.

Therapeutic window for obtaining favorable remodeling after thoracic endovascular aortic repair of type B aortic dissection.

OBJECTIVE: The purpose of the present study was to determine the most appropriate timing for thoracic endovascular aortic repair (TEVAR) of type B aortic dissection (TBAD) in terms of remodeling of the aorta. METHODS: A total of 41 patients who had undergone TEVAR for the treatment of aortic dissection were included in the present study. The patients were divided into two groups: those who had undergone TEVAR in the acute or subacute phase (group A) and those who had undergone TEVAR in the chronic phase (group B). The indications for TEVAR as the treatment of TBAD were the presence of aortic rupture or malperfusion of the aortic branches, a maximum aortic diameter of ≥40 mm on the initial diagnostic computed tomography scan, and/or expansion of the aorta of ≥5 mm within 3 months for acute and subacute TBAD. The indication was a maximum aortic diameter of ≥50 mm or expansion of the aorta of ≥5 mm within 1 year for chronic TBAD. The diameters of the aorta, true lumen, and false lumen were measured at the level of the most dilated part of the descending aorta (level M) and at the diaphragm (level D) on the computed tomography scan obtained before TEVAR and at the 2-year follow-up examination. RESULTS: The median interval between TEVAR and the onset of TBAD was 0.2 month (interquartile range, 0.03-0.7 month) in group A (n = 21) and 32 months (interquartile range, 4.7-35.2 months) in group B (n = 20). Except for the aortic diameter at level D in group B, favorable remodeling was obtained at both levels in both groups. The diameter change ratio of the aorta at level D was significantly greater in group A than in group B (P = .02). Receiver operating characteristic curve analysis of the interval for a significant decrease in the aortic diameter at level D yielded 4.2 months as the optimal threshold for performing TEVAR (area under the curve, 0.859; 95% confidence interval, 0.7-1.0). CONCLUSIONS: TEVAR for TBAD will result in favorable outcomes, irrespective of the timing of the procedure. However, it might be more effective to perform TEVAR within 4.2 months of the onset of TBAD, provided that the TEVAR procedure can be performed safely.

Iatrogenic Common Femoral Artery Occlusion Caused by a Suture-Mediated Closure System: A Case Report.

Vascular closure devices (VCDs) are useful for reducing bed rest time after percutaneous catheterization procedure without manual compression at the femoral puncture site. Occlusion of the common femoral artery (CFA) related to VCDs has rarely been reported. Although catheter treatment for CFA occlusion may be the first choice, it may be insufficient. Surgical treatment should be performed immediately when catheter treatment for artery occlusion is deemed difficult. We report a case of surgical angioplasty performed for femoral artery occlusion by using a suture-mediated device.

Aortic Valve Perforation During Endovascular Repair of an Abdominal Aortic Aneurysm-A Case Report.

Although complications associated with endovascular aneurysm repair (EVAR) of abdominal aortic aneurysms are rarely observed above the diaphragm, they could lead to catastrophic outcomes once they develop. Aortic valve perforation is one of those rare and major adverse events. In this report, we describe a case of an 82-year-old woman who suffered aortic valve perforation during EVAR caused by the wire-push technique. Her hemodynamics became unstable during the procedure and did not improve thereafter. Echocardiography performed 8 days after EVAR revealed aortic valve perforation. Surgical intervention was abandoned because her general condition was poor. The patient died 4 months after EVAR due to heart failure. It should be reminded that inadvertent manipulation of the wire can cause aortic valve perforation even during EVAR.

Clinical Significance of Carbapenem-Tolerant Pseudomonas aeruginosa Isolated in the Respiratory Tract.

We often come across difficult to treat infections-even after administering appropriate antibiotics according to the minimal inhibitory concentration of the causative bacteria. Antibiotic tolerance has recently started to garner attention as a crucial mechanism of refractory infections. However, few studies have reported the correlation between clinical outcomes and antibiotic tolerance. This study aims to clarify the effect of antibiotic tolerance on clinical outcomes of respiratory tract infection caused by Pseudomonas aeuginosa (P. aeruginosa). We examined a total of 63 strains isolated from sputum samples of different patients and conducted a retrospective survey with the medical records of 37 patients with imipenem-sensitive P. aeruginosa infections. Among them, we selected 15 patients with respiratory infections, and they were divided into high-tolerance minimal bactericidal concentration for adherent bacteria (MBCAD)/minimal inhibitory concentration for adherent bacteria (MICAD) ≥ 32 (n = 9) group and low-tolerance MBCAD/MICAD ≤ 16 (n = 6) group for further investigations. The findings indicated that the high-tolerance group consisted of many cases requiring hospitalization. Chest computed tomography findings showed that the disease was more extensive in the high-tolerance group compared to the low-tolerance group. Regarding the bacterial phenotypic characterization, the high-tolerance group significantly upregulated the production of the virulence factors compared to the low-tolerance group. Our study provided evidence that carbapenem tolerance level is a potent prognostic marker of P. aeruginosa infections, and carbapenem tolerance could be a potential target for new antimicrobial agents to inhibit the progression of persistent P. aeruginosa infections.

Suppressive effects of 2-methacryloyloxyethyl phosphorylcholine (MPC)-polymer on the adherence of Candida species and MRSA to acrylic denture resin.

OBJECTIVES: The effects of 2-methacryloyloxyethyl phosphorylcholine (MPC)-polymer on the adherence of microorganisms such as non-Candida albicans Candida (NCAC) and methicillin-resistant Staphylococcus aureus (MRSA), frequently detected in oral infections in immunocompromised and/or elderly people, to denture resin material, are still unclear. Here, we report the effects of MPC-polymer on the adherence of C. albicans, NCAC, and MRSA to acrylic denture resin. METHODS: Sixteen strains of C. albicans, seven strains of C. glabrata, two strains of C. tropicalis, one strain of C. parapsilosis, and six strains of MRSA were used. We cultured the fungal/bacterial strains and examined the cell growth and adherence of fungi/bacteria to mucin-coated acrylic denture resin plates (ADRP) with or without MPC-polymer coating, by scanning electron microscopy. The cell surface hydrophobicity of the fungal/bacterial strains was measured by the adsorption to hydrocarbons. RESULTS: MPC-polymer did not affect the growth of all strains of Candida species and MRSA, but significantly suppressed adherence to ADRP in most strains of C. albicans and all strains of NCAC and MRSA. A significant positive correlation was found between cell hydrophobicity and the reduction rates of microbial adherence to ADRP treated with 5% of MPC-polymer. CONCLUSIONS: MPC-polymer treatment for acrylic resin material suppresses the adherence of C. albicans, NCAC and MRSA via their hydrophilicity interaction. CLINICAL SIGNIFICANCE: The application of MPC-polymer for denture hygiene is potent to prevent oral candidiasis, denture stomatitis and opportunistic infection, caused by Candida species and MRSA, via suppressing the adherence of those fungus/bacteria.

Anti-inflammatory effects of olanexidine gluconate on oral epithelial cells.

BACKGROUND: Periodontitis is a biofilm-induced chronic inflammatory condition of the periodontium. Chemokines produced by the innate and acquired immune responses play a significant role in disease progression. Reducing biofilm formation and inflammatory response caused by chemokines is vital for preventing and treating periodontitis. Previously, we observed that treatment with 0.1% olanexidine gluconate (OLG) inhibited biofilm formation on saliva-coated hydroxyapatite. This study aimed to evaluate the anti-inflammatory effect of OLG on oral epithelial cells. METHODS: We examined if OLG could inhibit the inflammatory responses caused by Porphyromonas gingivalis (P. gingivalis) lipopolysaccharide (LPS) and heat-killed P. gingivalis in immortalized human oral keratinocytes (RT7). RESULTS: Treatment of RT7 with non-cytotoxic OLG concentrations significantly inhibited the production of inflammatory chemokines such as interleukin 8 (IL-8), C-C motif ligand 20 (CCL20), and growth-related oncogene protein-α (GRO-α), which are stimulated by P. gingivalis LPS in a concentration-dependent manner. Moreover, the inhibitory effects were observed regardless of the treatment time with P. gingivalis LPS (6, 12, or 24 h). OLG also significantly inhibited chemokine production stimulated by heat-killed P. gingivalis. CONCLUSIONS: The findings of this study suggest that treatment with OLG inhibits chronic inflammatory reactions in oral mucosal cells, such as periodontitis, caused by oral bacteria.

The Pathogenic Factors from Oral Streptococci for Systemic Diseases.

The oral cavity is suggested as the reservoir of bacterial infection, and the oral and pharyngeal biofilms formed by oral bacterial flora, which is comprised of over 700 microbial species, have been found to be associated with systemic conditions. Almost all oral microorganisms are non-pathogenic opportunistic commensals to maintain oral health condition and defend against pathogenic microorganisms. However, oral Streptococci, the first microorganisms to colonize oral surfaces and the dominant microorganisms in the human mouth, has recently gained attention as the pathogens of various systemic diseases, such as infective endocarditis, purulent infections, brain hemorrhage, intestinal inflammation, and autoimmune diseases, as well as bacteremia. As pathogenic factors from oral Streptococci, extracellular polymeric substances, toxins, proteins and nucleic acids as well as vesicles, which secrete these components outside of bacterial cells in biofilm, have been reported. Therefore, it is necessary to consider that the relevance of these pathogenic factors to systemic diseases and also vaccine candidates to protect infectious diseases caused by Streptococci. This review article focuses on the mechanistic links among pathogenic factors from oral Streptococci, inflammation, and systemic diseases to provide the current understanding of oral biofilm infections based on biofilm and widespread systemic diseases.

2-Methacryloyloxyethyl phosphorylcholine (MPC)-polymer suppresses an increase of oral bacteria: a single-blind, crossover clinical trial.

OBJECTIVES: The biocompatible 2-methacryloyloxyethyl phosphorylcholine (MPC)-polymers, which mimic a biomembrane, reduce protein adsorption and bacterial adhesion and inhibit cell attachment. The aim of this study is to clarify whether MPC-polymer can suppress the bacterial adherence in oral cavity by a crossover design. We also investigated the number of Fusobacterium nucleatum, which is the key bacterium forming dental plaque, in clinical samples. MATERIALS AND METHODS: This study was a randomized, placebo-controlled, single-blind, crossover study, with two treatment periods separated by a 2-week washout period. We conducted clinical trial with 20 healthy subjects to evaluate the effect of 5% MPC-polymer mouthwash after 5 h on oral microflora. PBS was used as a control. The bacterial number in the gargling sample before and after intervention was counted by an electronic bacterial counter and a culture method. DNA amounts of total bacteria and F. nucleatum were examined by q-PCR. RESULTS: The numbers of total bacteria and oral streptcocci after 5 h of 5% MPC-polymer treatment significantly decreased, compared to the control group. Moreover, the DNA amounts of total bacteria and F. nucleatum significantly decreased by 5% MPC-polymer mouthwash. CONCLUSIONS: We suggest that MPC-polymer coating in the oral cavity may suppress the oral bacterial adherence. CLINICAL RELEVANCE: MPC-polymer can be a potent compound for the control of oral microflora to prevent oral infection.

Antifungal and Mechanical Properties of Tissue Conditioner Containing Plant-Derived Component: An In Vitro Study.

PURPOSE: To evaluate the antifungal activity and mechanical properties of a novel antifungal tissue conditioner containing Juncus powder. MATERIALS AND METHODS: Juncus powder was mixed with GC tissue conditioner at concentrations of 2.5%, 5.0%, and 10.0% by mass. The cylindrical specimens of Juncus-mixed tissue conditioner (dimensions: 10 mm in diameter and 2 and 6 mm in height for antimicrobial and mechanical tests, respectively) were prepared. The specimens placed on the bottom of the 24-well tissue culture plate were cultured with Candida albicans CAD1 for 2 and 4 days. The proliferation of the C. albicans in the wells was determined by measuring the optical density of fungal culture, and the surface of the specimens were also observed by scanning electron microscopy (SEM). To assess the mechanical properties of the specimens, the fluidity and hardness of Juncus-mixed tissue conditioner were measured using the methods certified according to ISO 10139-1. RESULTS: Juncus-mixed tissue conditioner significantly exhibited growth inhibitory effect in a Juncus concentration-dependent manner after both 2- and 4- day cultures. SEM observation showed that the amount of C. albicans on Juncus-mixed specimens drastically decreased, and biofilm formation was markedly inhibited. Moreover, both mechanical properties were found to be within the ranges regulated and specified by ISO. CONCLUSION: These findings demonstrated that the tissue conditioner including Juncus powder has a significant growth inhibitory effect against C. albicans, and it is suggested that the application of Juncus-mixed tissue conditioner may prevent denture stomatitis and oral candidiasis in denture wearers.

Treatment of Infected Aneurysm with Combined Endovascular Aneurysm Repair and Abscess Drainage.

PURPOSE: To evaluate the clinical utility of combination therapy with endovascular aneurysm repair (EVAR) and abscess drainage for the treatment of infected aneurysms. MATERIALS AND METHODS: Between July 2009 and May 2015, 8 patients underwent combination therapy with EVAR and abscess drainage. There were 5 men and 3 women, with a mean age of 75 years ± 7. Aneurysms were of the thoracic aorta in 5 patients, the abdominal aorta in 2, and the internal iliac artery in 1. Four patients had concurrent infection, including pyelonephritis in 2, pelvic abscess in 1, and suppurative knee arthritis in 1. Three patients had ruptured aneurysms. Abscess drainage was performed percutaneously under computed tomographic guidance in 5 patients, thoracoscopic guidance in 2, and both in 1. RESULTS: Six patients (75%) were discharged without additional intervention except for antibiotic therapy, and the other 2 patients (25%) underwent open repair to control infection and to repair endoleak, respectively. There were no in-hospital deaths. During the mean follow-up period of 48 months ± 22, all patients were alive except for 1 patient who died of recurrence of rectal cancer at 51 months. There were no aorta- or artery-related adverse events. Overall survival rates at 1 and 5 years were 100% and 80%, respectively. Aneurysm-related event-free rates at 1 and 5 years were 75%. CONCLUSIONS: Combination therapy with EVAR and abscess drainage for the treatment of infected aneurysms seems to be a promising strategy as an alternative or "bridge" to open surgery.

Antibiofilm and Anti-Inflammatory Activities of Houttuynia cordata Decoction for Oral Care.

Dental biofilms that form in the oral cavity play a critical role in the pathogenesis of several infectious oral diseases, including dental caries, periodontal disease, and oral candidiasis. Houttuynia cordata (HC, Saururaceae) is a widely used traditional medicine, for both internal and external application. A decoction of dried HC leaves (dHC) has long been consumed as a health-promoting herbal tea in Japan. We have recently reported that a water solution of HC poultice ethanol extract (wHCP) exerts antimicrobial and antibiofilm effects against several important oral pathogens. It also exhibits anti-inflammatory effects on human keratinocytes. In our current study, we examined the effects of dHC on infectious oral pathogens and inflammation. Our results demonstrated that dHC exerts moderate antimicrobial effects against methicillin-resistant Staphylococcus aureus (MRSA) and other oral microorganisms. dHC also exhibited antibiofilm effects against MRSA, Fusobacterium nucleatum (involved in dental plaque formation), and Candida albicans and inhibitory effects on interleukin-8, CCL20, IP-10, and GROα productions by human oral keratinocytes stimulated by Porphyromonas gingivalis lipopolysaccharide (a cause of periodontal disease), without cytotoxic effects. This suggests that dHC exhibits multiple activities in microorganisms and host cells. dHC can be easily prepared and may be effective in preventing infectious oral diseases.

Royal Jelly Inhibits Pseudomonas aeruginosa Adherence and Reduces Excessive Inflammatory Responses in Human Epithelial Cells.

Pseudomonas aeruginosa is a Gram-negative bacterium and causes respiratory infection especially in elderly patients. Royal jelly has been used worldwide as a traditional remedy and as a nutrient; however, the effect against P. aeruginosa is unclear. The aim of this study was to analyze antibacterial, antiadherent, and anti-inflammatory effects of royal jelly against P. aeruginosa. Wild-type strain PAO1 and clinical isolates of P. aeruginosa were used for antibacterial assay and antiadherent assay to abiotic surface and epithelial cells, which are pharynx (Detroit 562) and lung (NCI-H292) epithelial cells. In anti-inflammatory assay, epithelial cells were pretreated with royal jelly before bacterial exposure to investigate its inhibitory effect on interleukin (IL-8) and macrophage inflammatory protein-3α/CCL20 overproduction. Although royal jelly did not have antibacterial activity at concentration of 50% w/v, antiadherent activity was confirmed on the abiotic surface and epithelial cells under concentration of 25%. Pretreatment with royal jelly significantly inhibited overproduction of IL-8 and CCL20 from both cells. These results demonstrated that royal jelly inhibits P. aeruginosa adherence and protects epithelial cells from excessive inflammatory responses against P. aeruginosa infection. Our findings suggested that royal jelly may be a useful supplement as complementary and alternative medicine for preventing respiratory infection caused by P. aeruginosa.

Parallel placement of Excluder legs for treatment of type IIIb endoleaks caused by fabric tear after endovascular aneurysm repair.

A total of 576 patients underwent endovascular aneurysm repair using main body devices for treatment of abdominal aortic aneurysms or iliac artery aneurysms. During follow-up, type IIIb endoleaks caused by fabric tear occurred in six patients (1.0% [6/576]). The device used was Zenith (Cook Medical, Bloomington, Ind) in five cases and Talent (Medtronic, Santa Rosa, Calif) in one case. All endoleaks were close to the flow divider of the main body devices. The distance between the lower renal artery and the top end of the contralateral leg was 53 ± 14 mm. Bell-bottom-shaped Excluder (W. L. Gore & Associates, Flagstaff, Ariz) legs were placed parallel from the top of the main body device through both legs to treat these endoleaks. In two patients, coil embolization was required to treat gutter endoleaks. Postoperative computed tomography showed the obliteration of type IIIb endoleaks in all patients. Our technique may be an acceptable method for treatment of type IIIb endoleaks, especially when they occur near the flow divider.

Synthesis and evaluation of c-di-4'-thioAMP as an artificial ligand for c-di-AMP riboswitch.

Cyclic-di-adenosine monophosphate (c-di-AMP) is a bacterial second messenger that binds to an RNA receptor called riboswitch and regulates its downstream genes involving cell wall metabolism, ion transport, and spore germination. Therefore, the c-di-AMP riboswitch can be a novel target of antibiotics. In this study, we synthesized c-di-4'-thioAMP (1), which possesses a sulfur atom instead of an oxygen atom in the furanose ring, as a candidate of a bioisoster for natural c-di-AMP. The resulting 1 bound to the c-di-AMP riboswitch with a micromolar affinity (34.8µM), and the phosphodiesterase resistance of 1 was >12-times higher than that of c-di-AMP. Thus, 1 can be considered to be a stable ligand against a c-di-AMP riboswitch.

Effects of an autoinducer analogue on antibiotic tolerance in Pseudomonas aeruginosa.

Objectives: Antibiotic tolerance causes chronic, refractory and persistent infections. In order to advance the development of a new type of drug for the treatment of infectious diseases, we herein investigated the effects of a newly synthesized analogue of the Pseudomonas aeruginosa quorum-sensing autoinducer named AIA-1 ( a uto i nducer a nalogue) on antibiotic tolerance in P. aeruginosa . Methods: A P. aeruginosa luminescent strain derived from PAO1 was injected into neutropenic ICR mice and bioluminescence images were acquired for a period of time after treatments with antibiotics and AIA-1. In vitro susceptibility testing and killing assays for the planktonic and biofilm cells of PAO1 were performed using antibiotics and AIA-1. The expression of quorum-sensing-related genes was examined using real-time PCR. Results: In vivo and in vitro assays showed that AIA-1 alone did not exert any bactericidal effects and also did not affect the MICs of antibiotics. However, the combined use of AIA-1 and antibiotics exerted markedly stronger therapeutic effects against experimental infection than antibiotics alone. The presence of AIA-1 also enhanced the killing effects of antibiotics in planktonic and biofilm cells. Although AIA-1 did not inhibit the expression of lasB and rhlA genes, which are directly regulated by quorum sensing, it clearly suppressed expression of the rpoS gene. Conclusions: The new compound, AIA-1, did not alter the antibiotic susceptibility of P. aeruginosa by itself; however, its addition enhanced the antibacterial activity of antibiotics. AIA-1 did not inhibit quorum sensing, but reduced the antibiotic tolerance of P. aeruginosa by suppressing rpoS gene expression.

RpoN Promotes Pseudomonas aeruginosa Survival in the Presence of Tobramycin.

Pseudomonas aeruginosa has developed diverse strategies to respond and adapt to antibiotic stress. Among the factors that modulate survival in the presence of antibiotics, alternative sigma factors play an important role. Here, we demonstrate that the alternative sigma factor RpoN (σ54) promotes survival in the presence of tobramycin. The tobramycin-sensitive phenotype of logarithmic phase ΔrpoN mutant cells is suppressed by the loss of the alternative sigma factor RpoS. Transcriptional analysis indicated that RpoN positively regulates the expression of RsmA, an RNA-binding protein, in the P. aeruginosa stationary growth phase in a nutrient-rich medium. The loss of RpoS led to the upregulation of gacA expression in the nutrient-limited medium-grown stationary phase cells. Conversely, in the logarithmic growth phase, the ΔrpoS mutant demonstrated lower expression of gacA, underscoring a regulatory role of RpoS for GacA. Supplementation of tobramycin to stationary phase ΔrpoN mutant cells grown in nutrient-rich medium resulted in decreased expression of gacA, relA, and rpoS without altering the expression of rsmA relative to wild-type PAO1. The observed downregulation of gacA and relA in the ΔrpoN mutant in the presence of tobramycin could be reversed through the mutation of rpoS in the ΔrpoN mutant background. The tobramycin-tolerant phenotype of the ΔrpoNΔrpoS mutant logarithmic phase cells may be associated with the expression of relA, which remained unresponsive upon addition of tobramycin. The logarithmic phase ΔrpoS and ΔrpoNΔrpoS mutant cells demonstrated increased expression of gacA in response to tobramycin. Together, these results suggest that a complex regulatory interaction between RpoN, RpoS, the Gac/Rsm pathway, and RelA modulates the P. aeruginosa response to tobramycin.

Role of psl Genes in Antibiotic Tolerance of Adherent Pseudomonas aeruginosa.

Bacteria attached to a surface are generally more tolerant to antibiotics than their planktonic counterparts, even without the formation of a biofilm. The mechanism of antibiotic tolerance in biofilm communities is multifactorial, and the genetic background underlying this antibiotic tolerance has not yet been fully elucidated. Using transposon mutagenesis, we isolated a mutant with reduced tolerance to biapenem (relative to that of the wild type) from adherent cells. Sequencing analysis revealed a mutation in the pslL gene, which is part of the polysaccharide biosynthesis operon. The Pseudomonas aeruginosa PAO1ΔpslBCD mutant demonstrated a 100-fold-lower survival rate during the exposure of planktonic and biofilm cells to biapenem; a similar phenotype was observed in a mouse infection model and in clinical strains. Transcriptional analysis of adherent cells revealed increased expression of both pslA and pelA, which are directly regulated by bis-(3',5')-cyclic dimeric GMP (c-di-GMP). Inactivation of wspF resulted in significantly increased tolerance to biapenem due to increased production of c-di-GMP. The loss of pslBCD in the ΔwspF mutant background abolished the biapenem-tolerant phenotype of the ΔwspF mutant, underscoring the importance of psl in biapenem tolerance. Overexpression of PA2133, which can catalyze the degradation of c-di-GMP, led to a significant reduction in biapenem tolerance in adherent cells, indicating that c-di-GMP is essential in mediating the tolerance effect. The effect of pslBCD on antibiotic tolerance was evident, with 50- and 200-fold-lower survival in the presence of ofloxacin and tobramycin, respectively. We speculate that the psl genes, which are activated by surface adherence through elevated intracellular c-di-GMP levels, confer tolerance to antimicrobials.