Pyochelin biotransformation by Staphylococcus aureus shapes bacterial competition with Pseudomonas aeruginosa in polymicrobial infections

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Viscous medium promotes cooperation in the pathogenic bacterium Pseudomonas aeruginosa

There has been extensive theoretical debate over whether population viscosity (limited dispersal) can favour cooperation. While limited dispersal increases the probability of interactions occurring between relatives, which can favour cooperation, it can also lead to an increase in competition between relatives and this can reduce or completely negate selection for cooperation. Despite much theoretical attention, there is a lack of empirical research investigating these issues. We cultured Pseudomonas aeruginosa bacteria in medium with different degrees of viscosity and examined the fitness consequences for a cooperative trait—the production of iron-scavenging siderophore molecules. We found that increasing viscosity of the growth medium (i) significantly limited bacterial dispersal and the diffusion of siderophore molecules and (ii) increased the fitness of individuals that produced siderophores relative to mutants that did not. We propose that viscosity favours siderophore-producing individuals in this system, because the benefits of siderophore production are more likely to accrue to relatives (i.e. greater indirect benefits), and, at the same time, bacteria are more likely to gain direct fitness benefits by taking up siderophore molecules produced by themselves (i.e. the trait becomes less cooperative). Our results suggest that viscosity of the microbial growth environment is a crucial factor determining the dynamics of wild-type bacteria and siderophore-deficient mutants in natural habitats, such as the viscous mucus in cystic fibrosis lung.     

Occurrence of Staphylococcus aureus and Pseudomonas aeruginosa in Israeli coastal water

The occurrence of Pseudomonas aeruginosa and coagulase-positive Staphylococcus aureus in seawater from beaches of central Israel was investigated from June 1983 until June 1985. P. aeruginosa was monitored in 652 samples of seawater from 34 beaches, and S. aureus was monitored in 628 samples. P. aeruginosa was found in 44.8% of samples (6.5% with 1 bacterium per 100 ml of water), and S. aureus was recovered from 60.7% of samples (5.3% with 1 organism per 100 ml), compared with 91.6% of samples with total coliforms (TC) and 82.2% with fecal coliforms (FC). The correlation between the presence of P. aeruginosa to that of TC and FC was 99.1 and 98.3%, respectively, while S. aureus was found in 4.3 and 8% of samples where TC and FC, respectively, were absent. Monitoring of S. aureus as a supplementary indicator in populated beaches is recommended because it will add valuable information on the sanitary quality of the seawater.     

Anti-infective properties of Lactobacillus fermentum against Staphylococcus aureus and Pseudomonas aeruginosa

Surgical wounds and implant-associated Staphylococcus aureus and Pseudomonas aeruginosa infections are often difficult to treat because of limited susceptibility of several of these strains to conventional antibiotics. As a result, there is a constant need for new alternative drugs. The aim of this study was to investigate the antimicrobial properties of Lactobacillus fermentum, a probiotic bacterium, which we have isolated from colonic biopsies. The inhibition of S. aureus and P. aeruginosa growth was evaluated by coincubating with L. fermentum strains. Growth inhibition was tested for several of their clinical isolates using agar well diffusion assays. For biofilm assay S. aureus and P. aeruginosa were grown on the glass slides and in 96-well plates in presence of 2.5 μg/ml culture filtrate of L. fermentum. Biofilms were photographed using confocal microscope or stained with 0.1% crystal violet. Reduction in the cytotoxicity of S. aureus and P. aeruginosa was observed in presence of 2.5 μg/ml L. fermentum-spent media. Using in vitroexperiments, we showed that L. fermentum-secreted compound(s) inhibits the growth, cytotoxicity and biofilm formation of several S. aureus and P. aeruginosa strains. Compound(s) present in the culture supernatant of L. fermentum may have promising applications in treating hospital-acquired infections.     

Candida albicans: Molecular interactions with Pseudomonas aeruginosa and Staphylococcus aureus

The fields of mycology and bacteriology have traditionally functioned independently of each other despite the fundamental actuality that fungi and bacteria not only co-exist but also interact within several niches. In the clinical context, these interactions commonly occur within biofilms, which can be composed of single-species communities or mixed-species populations and recent studies have shown that the properties of mixed-species populations differ from those of their individual components. The interacting bacteria and fungi can exert effects on microbial behavior, dissemination, survival, the response to antimicrobials and, ultimately, patient prognosis. Microbes within biofilms exhibit increased resistance to antimicrobial agents, and a significant amount of research has thus focused on gaining an understanding of how inter-domain interactions affect biofilm formation and the response to antimicrobial therapies. Candida albicans, a commensal and opportunistic pathogen of humans, is among the fungi most frequently identified in mixed-species biofilms. Here, we review interactions between C. albicans and bacterial species with which it is commonly isolated, namely Pseudomonas aeruginosa and Staphylococcus aureus in order to look into the spectrum of biologically relevant fungal–bacterial interactions that have been described.     

Occurrence of Staphylococcus aureus and Pseudomonas aeruginosa in Israeli coastal water.

The occurrence of Pseudomonas aeruginosa and coagulase-positive Staphylococcus aureus in seawater from beaches of central Israel was investigated from June 1983 until June 1985. P. aeruginosa was monitored in 652 samples of seawater from 34 beaches, and S. aureus was monitored in 628 samples. P. aeruginosa was found in 44.8% of samples (6.5% with 1 bacterium per 100 ml of water), and S. aureus was recovered from 60.7% of samples (5.3% with 1 organism per 100 ml), compared with 91.6% of samples with total coliforms (TC) and 82.2% with fecal coliforms (FC). The correlation between the presence of P. aeruginosa to that of TC and FC was 99.1 and 98.3%, respectively, while S. aureus was found in 4.3 and 8% of samples where TC and FC, respectively, were absent. Monitoring of S. aureus as a supplementary indicator in populated beaches is recommended because it will add valuable information on the sanitary quality of the seawater.     

Pattern differentiation in co-culture biofilms formed by Staphylococcus aureus and Pseudomonas aeruginosa

Biofilm infections may not simply be the result of colonization by one bacterium, but rather the consequence of pathogenic contributions from several bacteria. Interspecies interactions of different organisms in mixed-species biofilms remain largely unexplained, but knowledge of these is very important for understanding of biofilm physiology and the treatment of biofilm-related infectious diseases. Here, we have investigated interactions of two of the major bacterial species of cystic fibrosis lung microbial communities -Pseudomonas aeruginosa and Staphylococcus aureus- when grown in co-culture biofilms. By growing co-culture biofilms of S. aureus with P. aeruginosa mutants in a flow-chamber system and observing them using confocal laser scanning microscopy, we show that wild-type P. aeruginosa PAO1 facilitates S. aureus microcolony formation. In contrast, P. aeruginosa mucA and rpoN mutants do not facilitate S. aureus microcolony formation and tend to outcompete S. aureus in co-culture biofilms. Further investigations reveal that extracellular DNA (eDNA) plays an important role in S. aureus microcolony formation and that P. aeruginosa type IV pili are required for this process, probably through their ability to bind to eDNA. Furthermore, P. aeruginosa is able to protect S. aureus against Dictyostelium discoideum phagocytosis in co-culture biofilms.     

铜绿假单胞菌抗菌物质对耐甲氧西林金黄色葡萄球菌的抑菌活性研究

目的观察铜绿假单胞菌抗菌物质对耐甲氧西林金黄色葡萄球菌(methicillin-resistant Staphylococcusaureus,MRSA)的体外抑菌活性。方法用交叉划线接种方法进行铜绿假单胞菌对32株耐甲氧西林金葡菌的体外抗菌活性的测定。结果铜绿假单胞菌抗菌物质对MRSA的体外抑菌活性良好,产生色素的菌株的抗菌活性最好,15株铜绿假单胞菌中,7株产蓝绿色色素的铜绿假单胞菌,对MRSA的抑制率均达到了100%,平均抑菌带的宽度为37.7 mm。结论铜绿假单胞菌抗菌物质对32株MRSA具有较强的抗菌活性,无疑对MRSA感染的抗菌药物研制方面开辟了一条新的途径。这是国内的首次研究报道。     

In vitro trials of some antimicrobial combinations against Staphylococcus aureus and Pseudomonas aeruginosa

Staphylococcus aureus and Pseudomonas aeruginosa are rapidly increasing as multidrug resistant strains worldwide. In nosocomial settings because of heavy exposure of different antimicrobials, resistance in these pathogens turned into a grave issue in both developed and developing countries. The aim of this study was to investigate in vitro antibiotic synergism of combinations of β-lactam–β-lactam and β-lactam–aminoglycoside against clinical isolates of S. aureus and P. aeruginosa. Synergy was determined by checkerboard double dilution method. The combination of amoxicillin and cefadroxil was found to be synergistic against 47 S. aureus isolates, in the FICI range of 0.14–0.50 (81.03%) followed by the combination of streptomycin and cefadroxil synergistic against 44 S. aureus isolates in the FICI range of 0.03–0.50 (75.86%). The combination of streptomycin and cefadroxil was observed to be synergistic against 39 P. aeruginosa isolates in the FICI range of 0.16–0.50 (81.28%). Further actions are needed to characterize the possible interaction mechanism between these antibiotics. Moreover, the combination of streptomycin and cefadroxil may lead to the development of a new and vital antimicrobial against simultaneous infections of S. aureus and P. aeruginosa.     

Specific ion effects on the growth rates of Staphylococcus aureus and Pseudomonas aeruginosa

Motivated by recent advances in the physical and chemical basis of the Hofmeister effect, we measured the rate cell growth of S. aureus--a halophilic pathogenic bacterium--and of P. aeruginosa, an opportunistic pathogen, in the presence of different aqueous salt solutions at different concentrations (0.2, 0.6 and 0.9 M). Microorganism growth rates depend strongly on the kind of anion in the growth medium. In the case of S. aureus, chloride provides a favorable growth medium, while both kosmotropes (water structure makers) and chaotropes (water structure breakers) reduce the microorganism growth. In the case of P. aeruginosa, all ions affect adversely the bacterial survival. In both cases, the trends parallel the specific ion, or Hofmeister, sequences observed in a wide range of physico-chemical systems. The correspondence with specific ion effect obtained in other studies, on the activities of a DNA restriction enzyme, of horseradish peroxidase, and of Lipase A (Aspergillus niger) is particularly striking. This work provides compelling evidence for Hofmeister effects, physical chemistry in action, in these organisms.     

Effect of temperature on antibacterial activity of lidocaine to Staphylococcus aureus and Pseudomonas aeruginosa

The effect of temperature on the antibacterial activity of lidocaine to Staphylococcus aureus and Pseudomonas aeruginosa was investigated in vitro. At 10 C at which S. aureus organisms do not grow and might be metabolically inactive, the antibacterial activity of lidocaine to S. aureus was not observed in a concentration of 1%, which was quite antibacterial to S. aureus at 37 C. On the other hand, at 40 C a conspicuously increased antibacterial activity to S. aureus of lidocaine was observed in a concentration of 0.25% which was not antibacterial to S. aureus organisms at 37 C. Similar results were obtained when P. aeruginosa organisms were examined in place of S. aureus, although P. aeruginosa was found to be less susceptible to lidocaine than S. aureus. The clinical significance of the thermal effect on the antibacterial activity of lidocaine was discussed in brief.     

Alteration of protein homeostasis mediates the interaction of Pseudomonas aeruginosa with Staphylococcus aureus

Intracellular protein degradation is essential for the survival of all organisms, but its role in interspecies interaction is unknown. Here, we show that the ClpXP protease of Pseudomonas aeruginosa suppresses its antimicrobial activity against Staphylococcus aureus, a common pathogen co-isolated with P. aeruginosa from polymicrobial human infections. Using proteomic, biochemical, and molecular genetic approaches, we found that this effect is due to the inhibitory effects of ClpXP on the quorum sensing (QS) of P. aeruginosa, mainly by degrading proteins (e.g., PhnA, PhnB, PqsR, and RhlI) which are critical for the production of QS signal molecules PQS and C4-HSL. We provide evidence that co-culturing with S. aureus induces a decrease in the activity of ClpXP in P. aeruginosa, an effect which was also achieved by the treatment of P. aeruginosa with N-acetylglucosamine (GlcNAc), a widespread chemical present on the surface of diverse cell types from bacteria to humans. These findings extend the range of biological events governed by proteolytic machinery to microbial community structure, thus also suggesting that a chemical-induced alteration of protein homeostasis is a mechanism for interspecies interactions.     

Staphylococcus aureus and Pseudomonas aeruginosa Express and Secrete Human Surfactant Proteins

Surfactant proteins (SP), originally known from human lung surfactant, are essential to proper respiratory function in that they lower the surface tension of the alveoli. They are also important components of the innate immune system. The functional significance of these proteins is currently reflected by a very large and growing number of publications. The objective goal of this study was to elucidate whether Staphylococcus aureus and Pseudomonas aeruginosa is able to express surfactant proteins. 10 different strains of S. aureus and P. aeruginosa were analyzed by means of RT-PCR, Western blot analysis, ELISA, immunofluorescence microscopy and immunoelectron microscopy. The unexpected and surprising finding revealed in this study is that different strains of S. aureus and P. aeruginosa express and secrete proteins that react with currently commercially available antibodies to known human surfactant proteins. Our results strongly suggest that the bacteria are either able to express ‘human-like’ surfactant proteins on their own or that commercially available primers and antibodies to human surfactant proteins detect identical bacterial proteins and genes. The results may reflect the existence of a new group of bacterial surfactant proteins and DNA currently lacking in the relevant sequence and structure databases. At any rate, our knowledge of human surfactant proteins obtained from immunological and molecular biological studies may have been falsified by the presence of bacterial proteins and DNA and therefore requires critical reassessment.     

Siderophore-mediated cooperation and virulence in Pseudomonas aeruginosa

Why should organisms cooperate with each other? Helping close relatives that are likely to share the same genes (kin selection) is one important explanation that is likely to apply across taxa. The production of metabolically costly extracellular iron-scavenging molecules (siderophores) by microorganisms is a cooperative behaviour because it benefits nearby conspecifics. We review experiments focusing on the production of the primary siderophore (pyoverdin) of the opportunistic bacterial pathogen, Pseudomonas aeruginosa, which test kin selection theories that seek to explain the evolution of cooperation. First, cooperation is indeed favoured when individuals interact with their close relatives and when there is competition between groups of cooperators and noncooperators, such that the benefit of cooperation can be realized. Second, the relative success of cheats and cooperators is a function of their frequencies within populations. Third, elevated mutation rates can confer a selective disadvantage under conditions when cooperation is beneficial, because high mutation rates reduce how closely bacteria are related to each other. Fourth, cooperative pyoverdin production is also shown to be favoured by kin selection in vivo (caterpillars), and results in more virulent infections. Finally, we briefly outline ongoing and future work using this experimental system.     

Effects of staphylolytic enzymes from Pseudomonas aeruginosa on the growth and ultrastructure of Staphylococcus aureus

Pseudomonas aeruginosa produces two extracellular staphylolytic enzymes able to lyse Staphylococcus aureus cells when they are added to liquid cultures of S. aureus. In addition, when cultivation was carried out in the presence of both lytic enzymes and 1 M sucrose, the staphylococci either lacked cell walls or showed damaged walls. Lytic activity-resistant cells of S. aureus were also detected.     

Epidemiological study of the associations of Staphylococcus aureus and Pseudomonas aeruginosa in the pulmonology clinic

The results of the five-year study of S. aureus and P. aeruginosa associations isolated from the sputa of pulmonological patients are presented. The incidence rate of these bacteria in monocultures and associations is estimated. The results of the phage typing and serotyping of S. aureus and P. aeruginosa strains suggest that the formation of the associations of these organisms occurs mainly due to the tendency of P. aeruginosa hospital strains to associate with S. aureus cultures present in the patients.