Bacteria-triggered release of antimicrobial agents.

Medical devices employed in healthcare practice are often susceptible to microbial contamination. Pathogenic bacteria may attach themselves to device surfaces of catheters or implants by formation of chemically complex biofilms, which may be the direct cause of device failure. Extracellular bacterial lipases are particularly abundant at sites of infection. Herein it is shown how active or proactive compounds attached to polymeric surfaces using lipase-sensitive linkages, such as fatty acid esters or anhydrides, may be released in response to infection. Proof-of-concept of the responsive material is demonstrated by the bacteria-triggered release of antibiotics to control bacterial populations and signaling molecules to modulate quorum sensing. The self-regulating system provides the basis for the development of device-relevant polymeric materials, which only release antibiotics in dependency of the titer of bacteria surrounding the medical device.

Clearance of Pseudomonas aeruginosa foreign-body biofilm infections through reduction of the cyclic Di-GMP level in the bacteria.

Opportunistic pathogenic bacteria can engage in biofilm-based infections that evade immune responses and develop into chronic conditions. Because conventional antimicrobials cannot efficiently eradicate biofilms, there is an urgent need to develop alternative measures to combat biofilm infections. It has recently been established that the secondary messenger cyclic diguanosine monophosphate (c-di-GMP) functions as a positive regulator of biofilm formation in several different bacteria. In the present study we investigated whether manipulation of the c-di-GMP level in bacteria potentially can be used for biofilm control in vivo. We constructed a Pseudomonas aeruginosa strain in which a reduction in the c-di-GMP level can be achieved via induction of the Escherichia coli YhjH c-di-GMP phosphodiesterase. Initial experiments showed that induction of yhjH expression led to dispersal of the majority of the bacteria in in vitro-grown P. aeruginosa biofilms. Subsequently, we demonstrated that P. aeruginosa biofilms growing on silicone implants, located in the peritoneal cavity of mice, dispersed after induction of the YhjH protein. Bacteria accumulated temporarily in the spleen after induction of biofilm dispersal, but the mice tolerated the dispersed bacteria well. The present work provides proof of the concept that modulation of the c-di-GMP level in bacteria is a viable strategy for biofilm control.

Extracellular DNA shields against aminoglycosides in Pseudomonas aeruginosa biofilms.

Within recent years, it has been established that extracellular DNA is a key constituent of the matrix of microbial biofilms. In addition, it has recently been demonstrated that DNA binds positively charged antimicrobials such as aminoglycosides and antimicrobial peptides. In the present study, we provide evidence that extracellular DNA shields against aminoglycosides in Pseudomonas aeruginosa biofilms. We show that exogenously supplemented DNA integrates into P. aeruginosa biofilms and increases their tolerance toward aminoglycosides. We provide evidence that biofilms formed by a DNA release-deficient P. aeruginosa quorum-sensing mutant are more susceptible to aminoglycoside treatment than wild-type biofilms but become rescued from the detrimental action of aminoglycosides upon supplementation with exogenous DNA. Furthermore, we demonstrate that exposure to lysed polymorphonuclear leukocytes, which are thought to be a source of extracellular DNA at sites of infections, increases the tolerance of P. aeruginosa biofilms toward aminoglycosides. Although biofilm-associated aminoglycoside tolerance recently has been linked to extracellular DNA-mediated activation of the pmr genes, we demonstrate that the aminoglycoside tolerance mediated by the presence of extracellular DNA is not caused by activation of the pmr genes in our P. aeruginosa biofilms but rather by a protective shield effect of the extracellular DNA.

The catabolite repression control protein Crc plays a role in the development of antimicrobial-tolerant subpopulations in Pseudomonas aeruginosa biofilms.

Bacteria form complex surface-attached biofilm communities in nature. Biofilm cells differentiate into subpopulations which display tolerance towards antimicrobial agents. However, the signal transduction pathways regulating subpopulation differentiation in biofilms are largely unelucidated. In the present study, we show that the catabolite repression control protein Crc regulates the metabolic state of Pseudomonas aeruginosa cells in biofilms, and plays an important role in the development of antimicrobial-tolerant subpopulations in P. aeruginosa biofilms.

Burkholderia type VI secretion systems have distinct roles in eukaryotic and bacterial cell interactions.

Bacteria that live in the environment have evolved pathways specialized to defend against eukaryotic organisms or other bacteria. In this manuscript, we systematically examined the role of the five type VI secretion systems (T6SSs) of Burkholderia thailandensis (B. thai) in eukaryotic and bacterial cell interactions. Consistent with phylogenetic analyses comparing the distribution of the B. thai T6SSs with well-characterized bacterial and eukaryotic cell-targeting T6SSs, we found that T6SS-5 plays a critical role in the virulence of the organism in a murine melioidosis model, while a strain lacking the other four T6SSs remained as virulent as the wild-type. The function of T6SS-5 appeared to be specialized to the host and not related to an in vivo growth defect, as ΔT6SS-5 was fully virulent in mice lacking MyD88. Next we probed the role of the five systems in interbacterial interactions. From a group of 31 diverse bacteria, we identified several organisms that competed less effectively against wild-type B. thai than a strain lacking T6SS-1 function. Inactivation of T6SS-1 renders B. thai greatly more susceptible to cell contact-induced stasis by Pseudomonas putida, Pseudomonas fluorescens and Serratia proteamaculans-leaving it 100- to 1000-fold less fit than the wild-type in competition experiments with these organisms. Flow cell biofilm assays showed that T6S-dependent interbacterial interactions are likely relevant in the environment. B. thai cells lacking T6SS-1 were rapidly displaced in mixed biofilms with P. putida, whereas wild-type cells persisted and overran the competitor. Our data show that T6SSs within a single organism can have distinct functions in eukaryotic versus bacterial cell interactions. These systems are likely to be a decisive factor in the survival of bacterial cells of one species in intimate association with those of another, such as in polymicrobial communities present both in the environment and in many infections.

Influence of putative exopolysaccharide genes on Pseudomonas putida KT2440 biofilm stability.

We report a study of the role of putative exopolysaccharide gene clusters in the formation and stability of Pseudomonas putida KT2440 biofilm. Two novel putative exopolysaccharide gene clusters, pea and peb, were identified, and evidence is provided that they encode products that stabilize P. putida KT2440 biofilm. The gene clusters alg and bcs, which code for proteins mediating alginate and cellulose biosynthesis, were found to play minor roles in P. putida KT2440 biofilm formation and stability under the conditions tested. A P. putida KT2440 derivative devoid of any identifiable exopolysaccharide genes was found to form biofilm with a structure similar to wild-type biofilm, but with a stability lower than that of wild-type biofilm. Based on our data, we suggest that the formation of structured P. putida KT2440 biofilm can occur in the absence of exopolysaccharides; however, exopolysaccharides play a role as structural stabilizers.

Silver-palladium surfaces inhibit biofilm formation.

Undesired biofilm formation is a major concern in many areas. In the present study, we investigated biofilm-inhibiting properties of a silver-palladium surface that kills bacteria by generating microelectric fields and electrochemical redox processes. For evaluation of the biofilm inhibition efficacy and study of the biofilm inhibition mechanism, the silver-sensitive Escherichia coli J53 and the silver-resistant E. coli J53[pMG101] strains were used as model organisms, and batch and flow chamber setups were used as model systems. In the case of the silver-sensitive strain, the silver-palladium surfaces killed the bacteria and prevented biofilm formation under conditions of low or high bacterial load. In the case of the silver-resistant strain, the silver-palladium surfaces killed surface-associated bacteria and prevented biofilm formation under conditions of low bacterial load, whereas under conditions of high bacterial load, biofilm formation occurred upon a layer of surface-associated dead bacteria.

Cultural differences in the development of a preference for scarce objects.

Adults value scarce objects, such as rare precious stones and limited edition items. This valuation may derive from an understanding of market forces and sociological considerations, but it may also be related to more basic cognitive and motivational processes. The present studies addressed these possibilities by investigating the development and cross-cultural prevalence of a preference for scarce objects. Children (N = 366) from Israel and Taiwan, ranging from 4 to 11 years of age, were given a choice between a scarce and an abundant reward. We found that whereas a preference for the scarce appeared among Israelis by age 7, it never appeared among the Taiwanese. These findings indicate that a scarcity preference emerges already at age 7, but only among children living in a culture that emphasizes self-individuality. These findings are discussed in light of cultural accounts of the development of self-motivations. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Enumeration of collective entities by 5-month-old infants.

Recent findings suggest that infants are capable of distinguishing between different numbers of objects, and of performing simple arithmetical operations. But there is debate over whether these abilities result from capacities dedicated to numerical cognition, or whether infants succeed in such experiments through more general, non-numerical capacities, such as sensitivity to perceptual features or mechanisms of object tracking. We report here a study showing that 5-month-olds can determine the number of collective entities -- moving groups of items -- when non-numerical perceptual factors such as contour length, area, density, and others are strictly controlled. This suggests both that infants can represent number per se, and that their grasp of number is not limited to the domain of objects.

The metabolically active subpopulation in Pseudomonas aeruginosa biofilms survives exposure to membrane-targeting antimicrobials via distinct molecular mechanisms.

Biofilms are reported to be inherently refractory toward antimicrobial attack and, therefore, cause problems in industrial and medical settings. Pseudomonas aeruginosa biofilms contain subpopulations that exhibit high metabolic activity and subpopulations that exhibit low metabolic activity. We have found that membrane-targeting antimicrobials such as colistin, EDTA, SDS, and chlorhexidine specifically kill the inactive subpopulation in P. aeruginosa biofilms, whereas the active subpopulation survives exposure to these compounds. Because treatment of P. aeruginosa biofilms with the membrane-targeting compounds colistin, EDTA, SDS, and chlorhexidine resulted in the same spatial distribution of live and dead bacteria, we investigated whether tolerance to these compounds originated from the same molecular mechanisms. Development of colistin-tolerant subpopulations was found to depend on the pmr genes encoding lipopolysaccharide modification enzymes, as well as on the mexAB-oprM, mexCD-oprJ, and muxABC-opmB genes encoding antimicrobial efflux pumps, but does not depend on the mexPQ-opmE efflux pump genes. Development of chlorhexidine-tolerant subpopulations was found to depend on the mexCD-oprJ genes, but does not depend on the pmr, mexAB-oprM, mexPQ-opmE, or muxABC-opmB genes. Tolerance to SDS and EDTA in P. aeruginosa biofilms is linked to metabolically active cells, but does not depend on the pmr, mexAB, mexCD, mexPQ, or muxABC genes. Our data suggest that the active subpopulation in P. aeruginosa biofilms is able to adapt to exposure to membrane-targeting agents through the use of different genetic determinants, dependent on the specific membrane-targeting compound.

Lexical association and false memory for words in two cultures.

This study examined the relationship between language experience and false memory produced by the DRM paradigm. The word lists used in Stadler, et al. (Memory & Cognition, 27, 494-500, 1999) were first translated into Chinese. False recall and false recognition for critical non-presented targets were then tested on a group of Chinese users. The average co-occurrence rate of the list word and the critical word was calculated based on two large Chinese corpuses. List-level analyses revealed that the correlation between the American and Taiwanese participants was significant only in false recognition. More importantly, the co-occurrence rate was significantly correlated with false recall and recognition of Taiwanese participants, and not of American participants. In addition, the backward association strength based on Nelson et al. (The University of South Florida word association, rhyme and word fragment norms, 1999) was significantly correlated with false recall of American participants and not of Taiwanese participants. Results are discussed in terms of the relationship between language experiences and lexical association in creating false memory for word lists.