Pseudomonas aeruginosa infections

Structure-guided disruption of the pseudopilus tip complex inhibits the Type II secretion in Pseudomonas aeruginosa

Pseudomonas aeruginosa utilizes the Type II secretion system (T2SS) to translocate a wide range of large, structured protein virulence factors through the periplasm to the extracellular environment for infection. In the T2SS, five pseudopilins assemble into the pseudopilus that acts as a piston to extrude exoproteins out of cells. Through structure determination of the pseudopilin complexes of XcpVWX and XcpVW and function analysis, we have confirmed that two minor pseudopilins, XcpV and XcpW, constitute a core complex indispensable to the pseudopilus tip. The absence of either XcpV or -W resulted in the non-functional T2SS. Our small-angle X-ray scattering experiment for the first time revealed the architecture of the entire pseudopilus tip and established the working model. Based on the interaction interface of complexes, we have developed inhibitory peptides. The structure-based peptides not only disrupted of the XcpVW core complex and the entire pseudopilus tip in vitro but also inhibited the T2SS in vivo. More importantly, these peptides effectively reduced the virulence of P. aeruginosa towards Caenorhabditis elegans.

The Type II secretion system has been characterized as an important virulence factor translocation machine that secrets various toxic proteins from the periplasm into the extracellular milieu used by a wide spectrum of Gram-negative bacteria. Through the characterization of the structure of the pseudopilus tip complex by protein crystallography and small-angle X-ray scattering, we have identified a critical interaction interface in the core binary complex formed by two minor pseudopilins, XcpV and–W, in Pseudomonas aeruginosa. Based on the interaction interface, two inhibitory peptides were developed, which showed potency of disrupting the entire pseudopilus tip complex and further inhibited the Type II secretion system. When applied to Caenorhabditis elegans, these peptides prevent the killing of worms by the P. aeruginosa. Our work has represented the first successful research on the inhibition of the Type II secretion system based on the structure of the pseudopilus tip complex.

Chitin modulates innate immune responses of keratinocytes

BACKGROUND

Chitin, after cellulose the second most abundant polysaccharide in nature, is an essential component of exoskeletons of crabs, shrimps and insects and protects these organisms from harsh conditions in their environment. Unexpectedly, chitin has been found to activate innate immune cells and to elicit murine airway inflammation. The skin represents the outer barrier of the human host defense and is in frequent contact with chitin-bearing organisms, such as house-dust mites or flies. The effects of chitin on keratinocytes, however, are poorly understood.

METHODOLOGY/PRINCIPAL FINDINGS

We hypothesized that chitin stimulates keratinocytes and thereby modulates the innate immune response of the skin. Here we show that chitin is bioactive on primary and immortalized keratinocytes by triggering production of pro-inflammatory cytokines and chemokines. Chitin stimulation further induced the expression of the Toll-like receptor (TLR) TLR4 on keratinocytes at mRNA and protein level. Chitin-induced effects were mainly abrogated when TLR2 was blocked, suggesting that TLR2 senses chitin on keratinocytes.

CONCLUSIONS/SIGNIFICANCE

We speculate that chitin-bearing organisms modulate the innate immune response towards pathogens by upregulating secretion of cytokines and chemokines and expression of MyD88-associated TLRs, two major components of innate immunity. The clinical relevance of this mechanism remains to be defined.

Dietary marine lipid does not alter susceptibility of (NZBxNZW)F1 mice to pathogenic microorganisms

Female (NZBxNZW)F1 mice were fed for one month with a diet in which the sources of fat were either melted beef tallow or fish oil, the latter regimen being associated with a marked decrease in the expression of auto-immune disease in these animals. To test whether or not this beneficial effect was associated with an increased risk of infection, animals fed each of these diets were challenged intraperitoneally with graded doses of four different classes of microorganisms: a gram positive bacillus that is an intracellular parasite (Listeria monocytogenes), an exotoxin-producing gram negative bacillus (Pseudomonas aeruginosa), a yeast (Candida albicans), and a herpes group virus (murine cytomegalovirus). There was no difference in the susceptibility of the animals fed the two different diets to any of these infections as shown by either determinations of the LD50 for each organism or by assessment of the times of survival for those animals that did succumb. We conclude that the beneficial anti-inflammatory effects of fish oil diets in these mice are not associated with an increased risk of infection with a variety of microbial agents.

The serum sensitivity, colonial morphology, serogroup specificity, and outer membrane protein of Pseudomonas aeruginosa strains isolated from several clinical sites

Ninety-three strains of Pseudomonas aeruginosa, isolated from 68 patients hospitalized with respiratory tract infections, burns, urinary tract infections, and other illnesses, were examined for: 1) sensitivity to the bactericidal activity of fresh normal human serum (FHS); 2) colonial morphology; 3) serogroup designation; and 4) outer membrane protein (OMP) profile. The purpose of this study was to determine if there was any relationship between any of these microbial characteristics and the propensity of this microorganism to infect a specific clinical site or tissue. The results of this study can be summarized as follows: 1) slime-producing strains were generally more serum-sensitive than non-slime producers, although serum sensitivity was not related to slime production per se; 2) CF strains were much more serum-sensitive than non-CF strains; 3) the clinical isolation site appeared to be the predominant determinant of a strain's sensitivity to FHS; 4) the ability of P. aeruginosa to colonize/infect a specific clinical site or resist the bactericidal activity of FHS was generally unrelated to serogroup specificity; and 5) whereas the OMP profile of a particular strain does not appear to correlate with its response to the bactericidal effect of FHS, it does appear to be related to its clinical isolation site.

Simple model for the study of Pseudomonas aeruginosa infections in leukopenic mice

A simple, reproducible model of fatal Pseudomonas aeruginosa sepsis in mice during immunosuppression was developed. Mice were rendered leukopenic (less than or equal to 800 leukocytes per mm3 of blood) for a period of 5 days by multiple injections of cyclophosphamide. Mice were challenged at the onset of leukopenia by instilling the bacteria onto a 0.5-mm incision made into the back. The mean lethal dose (LD50) for P. aeruginosa PA220 and M-2 was less than 20 bacteria. The mean time to death for these strains ranged from 46 to 59 h. Leukopenic mice were comparatively resistant when challenged with Klebsiella pneumoniae (LD50 = 1.5 x 10(6)) or Staphylococcus aureus (LD50 greater than 10(6)). Infection with P. aeruginosa was characterized by rapid bacterial multiplication in the skin at the site of infection, producing ecthyma gangrenosum. Bacteremia and colonization of the liver were pronounced 21 h postinfection. This model should prove to be a useful tool for studying the pathogenesis of P. aeruginosa infections under immunosuppressed conditions.

Protection against experimental Pseudomonas aeruginosa infection in mice by active immunization with exotoxin A toxoids

The immunoprophylactic effect of chemically inactivated Pseudomonas aeruginosa exotoxin A in experimental pseudomonas infections was studied. Exotoxin A toxoids were prepared by Formalin (f-TXD) or glutaraldehyde (g-TXD) treatment. Immunization of mice with three or four doses (10 micrograms each) of f-TXD and the synthetic adjuvant N-acetylmuramyl-L-alanyl-D-isoglutamine (50 micrograms) induced high levels of antiexotoxin A antibodies as measured by passive hemagglutination assay and enzyme-linked immunosorbent assay. Immunization with toxoid alone did not elicit antitoxin. A significant increase in survival time and survival rate (P less than 0.01) was seen in immunized (f-TXD) and in burned and infected mice (50 to 85%) as compared with control mice immunized with formalinized bovine serum albumin (6 to 20%). Virtually 100% survival was obtained when preinfection immunization weas combined with single-dose gentamicin treatment within 24 h of infection. Immunization with g-TXD increased survival time (P less than 0.01) but did not consistently increase survival rate, and the results were not as satisfactory as those with formalinized exotoxin. The data presented indicate that active immunization with formalinized exotoxin A toxoid and adjuvant induced protective immunity to various degrees against infections in mice and could be potentially useful in prophylaxis of P. aeruginosa infections.

Aberrant form of Pseudomonas aeruginosa in sputum and cerebrospinal fluid causing infection in a compromised patient

A patient with non-Hodgkin's lymphoma developed meningitis due to an aberrant form of Pseudomonas aeruginosa observed on Gram stain. The organism was grown on primary isolation media without needing hypertonic media. The significance of aberrant forms in body fluids is discussed.

Membrane filter method for the isolation and enumeration of Pseudomonas aeruginosa from swimming pools

A membrane filter technique using black membrane filters, MacConkey agar and fluorescence under ultraviolet (UV) light was investigated for the quantitative isolation of Pseudomonas aeruginosa from swimming pools. Three thousand four hundred forty-five samples were collected from public swimming pools and enumerated by this method over a 6-month period. Fluorescent cultures were isolated from 222 specimens. Seventy-seven of these fluorescent cultures were selected for biochemical screening, with 75 (97%) being verified as P. aeruginosa. To further assess the specificity and sensitivity of this UV screening technique, a comparative study was made of some morphological and biochemical characteristics of fluorescent pseudomonads obtained from different sources. The sensitivity of the method was unimpaired by either colony types or biochemical variations of P. aeruginosa. The failure of the other two fluorescent species, P. fluorescens and P. putida, to grow and/or fluoresce on MacConkey agar at 37 C illustrates the specificity of this technique. Further studies are needed to compare the viability of P. aeruginosa on MacConkey agar to that of efficacious nonselective media.

Rapid method for detection of Pseudomonas aeruginosa on MacConkey agar under ultraviolet light

A simple screening technique for the detection of Pseudomonas aeruginosa colonies by their fluorescence on MacConkey agar under ultraviolet light is proposed. From 306 nonlactose fermenting cultures screened under the ultraviolet light, 108 fluorescent isolates were obtained. These were screened biochemically, with 103 (94.8%) being verified as P. aeruginosa. From the 198 nonfluorescing cultures, only one suspected P. aeruginosa was isolated.