Lectin-mediated bacterial adhesion to human tissue

Glycosylated Lipopeptides-Synthesis and Evaluation of Antimicrobial Activity and Cytotoxicity

Ultrashort cationic lipopeptides (USCLs) are promising antimicrobial agents that may be used to combat pathogens such as bacteria and fungi. USCLs consist of a few basic amino acid residues and at least one lipid moiety, usually a fatty acid chain. Generally, USCLs are potent antimicrobials but their major shortcoming is a relatively high cytotoxicity and hemolytic activity. Glycopeptide antibiotics (e.g. vancomycin) are essential in combating bacterial infections and are popular in medicinal practice. However, literature concerning the effect of glycosylation of peptides on their antimicrobial activity is rather scarce. For the first time, this study highlights the effect of USCLs glycosylation on in vitro biological activity. The aim of this study was to evaluate the impact of glycosylation of a series of USCLs on antimicrobial activity, cytotoxicity and hemolytic activity. Straight-chain fatty acids (C14, C16, C18) were attached to the N-terminal amino group of tripeptides-SRR-NH₂, RSR-NH₂ and RRS-NH₂. Two groups of the lipopeptides were synthetized, the first with unmodified L-serine (USCLs) and the other with L-serine O-glycosylated by N-acetyl-β-d-glucosamine to produce new class of glycosylated ultrashort cationic lipopeptide (gUSCLs). Both USCLs and gUSCLs were tested against planktonic and biofilm cultures of ESKAPE strains (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp.) and Candida glabrata, and hemolytic activity on human erythrocytes and cytotoxicity against the HaCaT cell line was examined. Generally, USCLs and gUSCLs proved to be active against all the tested strains. The highest activity displayed was by lipopeptides containing the C18 fatty acid. Antimicrobial, hemolytic and cytotoxic activities were mainly correlated with amino acid sequence (position of serine/glycosylated serine) and hydrophobicity of molecule and were found to be highly strain-dependent. In general, glycosylation did not guarantee an increased antimicrobial activity or a decreased hemolytic and cytotoxic activities. However, in some cases, gUSCLs proved to be superior to their USCLs analogs. The most pronounced differences were found for peptides with C18 fatty acid and serine at the first and second position against both planktonic cells and biofilm of C. glabrata, as well as the second and third position against S. aureus. It is noteworthy that gUSCLs were also more active against biofilm than were USCLs.

Specific association of lectin LecB with the surface of Pseudomonas aeruginosa: role of outer membrane protein OprF

The fucose binding lectin LecB affects biofilm formation and is involved in pathogenicity of Pseudomonas aeruginosa. LecB resides in the outer membrane and can be released specifically by treatment of an outer membrane fraction with fucose suggesting that it binds to specific ligands. Here, we report that LecB binds to the outer membrane protein OprF. In an OprF-deficient P. aeruginosa mutant, LecB is no longer detectable in the membrane but instead in the culture supernatant indicating a specific interaction between LecB and OprF.

The vaccine potential of Streptococcus pneumoniae surface lectin- and non-lectin proteins

We have fractionated S. pneumoniae surface proteins into lectin and non-lectin fractions and tested their ability to elicit protective immune responses in the mouse model system. The total cell wall protein fraction (CW-T) was separated into lectin (CW-L), and non-lectin (CW-NL) fractions and used for immunization of mice. Immunized mice were challenged intranasally or intraperitoneally with S. pneumoniae strain WU2 (serotype 3). CW-T, CW-NL and CW-L and adjuvant only vaccination protected 55%, 43%, 44% and 0% of the intranasally challenged mice, respectively and 67%, 86%, 11% and 0% of mice challenged intraperitoneally, respectively. Immunogenic proteins in each fraction were sequenced and identified using MALDI-TOF. CW-L proteins provided a significantly better protection against intranasal inoculation and CW-NL proteins provided a significantly better protection from intraperitoneal inoculation. Proteins identified by sera from mice immunized with the cell-wall derived fractions may constitute candidates for future development of anti S. pneumoniae vaccines.

Use of specific sugars to inhibit bacterial adherence to equine endometrium in vitro

OBJECTIVE

To determine whether specific sugars inhibit adhesion of Streptococcus zooepidemicus, Pseudomonas aeruginosa, and Escherichia coli to equine endometrial epithelial cells in vitro.

SAMPLE POPULATION

Endometrial biopsy specimens collected during estrus from 7 healthy mares.

PROCEDURE

Endometrial specimens on glass slides were incubated for 30 minutes at 4 C with suspensions of S. zooepidemicus, P. aeruginosa, or E. coli in phosphate-buffered saline solution (PBSS) alone or with various concentrations of D-(+)-mannose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, D-(+)-glucose, galactose, or N-acetyl-neuraminic acid. Inhibition of bacterial adherence was determined by comparing adhesion of bacteria (i.e., percentage of glandular epithelial cells with adherent bacteria) suspended in each sugar solution with that of bacteria suspended in PBSS.

RESULTS

Mannose and N-acetyl-D-galactosamine inhibited adhesion of E. coli and P. aeruginosa to epithelial cells, whereas only mannose inhibited adhesion of S. zooepidemicus. The other sugars did not affect bacterial adherence.

CONCLUSIONS AND CLINICAL RELEVANCE

Mannose and N-acetyl-D-galactosamine appear to play a role in adhesion of S. zooepidemicus, P. aeruginosa, and E. coli to equine endometrium. In horses with uterine infections, use of sugars to competitively displace bacteria from attachment sites on cells may provide an adjunct to antibiotic treatment.

Problems and priorities for controlling opportunistic pathogens with new antimicrobial strategies; an overview of current literature

An International Study Group on New Antimicrobial Strategies (ISGNAS) has been formed in response to the recognition that development of microbial resistance to antibiotics is becoming a serious, world-wide problem. The group met in 1993 for the first time to discuss the feasibility of developing rational alternatives to the use of antibiotics and prepared, as a result, a comprehensive overview of normal (physiological) mechanisms involved in the control of potentially pathogenic (oppotunistic) microorganisms. One objective of ISGNAS is to understand the conditions which allow opportunistic microbes present among the symbionts to cause an infection. There is a need for more coherent information concerning the habitat, growth requirements and host and pathogen properties which allow opportunistic pathogens to cause life-threatening infections. In particular, information is urgently being sought to understand the complexity of the interactions between the vast number of microbial species, and the interactions between the microbes and their host. Another goal is to inspire and enable basic and clinical research that will lead to the development of new therapies for regulating colonization, translocation and infection by opportunistic micro-organisms in patients during periods of decreased resistance. With a sufficient amount of knowledge of how healthy individuals keep opportunistic micro-organisms under control, it may become feasible for physicians to maintain host resistance and inter-microbial factors involved in the containment of opportunistic microbes. Therapies aimed at boostering natural resistance mechanisms will be of critical importance to individuals whose resistance has been compromised as a result of another clinical condition.

Blood group phenotype determines lectin-mediated adhesion of Pseudomonas aeruginosa to human outer ear canal epithelium

Pseudomonas aeruginosa is the most frequent bacterial pathogen causing acute diffuse otitis externa. In a recent prospective phase II study we demonstrated that lectin-mediated bacterial adhesion can be blocked by receptor-analogue carbohydrates in patients suffering from Pseudomonas aeruginosa-induced acute otitis externa. In this investigation, human ABO blood group antigens were analysed on outer ear canal epithelial cells with standard routine histological procedures by monoclonal antibodies for the blood groups A and B, and with Ulex europaeus I lectin for the blood group O, respectively. In all cases (n = 20) the blood groups could be shown immunohistologically. P. aeruginosa-specific adhesion and inhibition assays were performed in the presence of N-acetylgalactosamine (GalNAc), N-acetylglucosamine (GlcNAc), D-mannose and A-like substance. Outer ear canal tissue sections were incubated with P. aeruginosa (strain PA 60), presenting lectin-specificity for GalNAc. Sections from patients presenting with blood group A were closely settled with bacteria in the presence of non-specific GlcNAc, D-mannose and PBS however, GalNAc and A-like substance inhibited the microbial adhesion. Amongst others, P. aeruginosa present adhesion molecules (lectins) with specificity for GalNAc. Thus, the correlation between blood group A phenotype and P. aeruginosa-induced acute diffuse otitis externa was investigated. Statistical evaluation proved a highly significant association. These data support the hypothesis that P. aeruginosa lectins with GalNAc specificity apparently adhere to GalNAc moieties, representing the terminal blood group A-determinant and further indicate that patients presenting with blood group A may have a genetic disposition for this form of otitis externa.

Adhesion of fimbriated and non-fimbriated Klebsiella strains to synthetic polymers

Adherence of three fimbriated and non-fimbriated Klebsiella strains to polyetherurethane was investigated in order to assess the possible role of fimbriae in the adhesion of Klebsiella to synthetic polymers. Fimbriated strains with type 1 and type 1.3 fimbriae adhere significantly stronger to polyurethane than the same strains lacking fimbriae, whereas a strain with type 3 fimbriae shows no different adherence compared with the non-fimbriated variant. Analysis of adhesion kinetics and isotherms reveals that adherence of fimbriated Klebsiella strains is proceeded by the formation of multicellular bacterial layers on the polymer surface. Measurements of the relative hydrophobicity of the strains and adherence experiments under exclusion of unspecific interactions point out that fimbriae obviously play a more important role in adhesion than relative hydrophobicity. The demonstration of reduction of bacterial adherence to polyetherurethane by blocking fimbrial action with fimbriae-specific sugars supports this further.

Adherence of Actinobacillus pleuropneumoniae to porcine tracheal epithelial cells and frozen lung sections

The ability of 23 different Actinobacillus pleuropneumoniae isolates to adhere in vitro to porcine tracheal epithelial cells and to porcine frozen lung sections was examined. It was found that A. pleuropneumoniae adhered poorly to isolated tracheal epithelial cells. On the other hand, A. pleuropneumoniae adhered to frozen lung sections and marked variations were observed between and within serotypes. Adherence to lung sections did not seem related to the hemagglutinating activity of the isolate. Two noncapsulated variants adhered to lung sections in greater numbers than their capsulated parent strains. Adherence to lung sections was not inhibited by the extracellular matrix components tested namely, laminin, fibronectin, and collagen, but was inhibited by homologous serotype-specific antiserum. The data indicated that the A. pleuropneumoniae isolates tested possess the ability to adhere to porcine lung tissue, a property which did not seem to be related to the serotype and did not seem to involve the capsular material or the hemagglutinins of the isolates.

Biological properties of staphylococcal lipoteichoic acid and related macromolecules

Lipoteichoic acids (LTAs) and related macromolecules (e.g. cell surface substance, CSS; cell surface antigen, CSA; cell surface complex, CSC) are a group of phosphate-containing polymers associated with the cell walls of Gram-positive bacteria (32). They may be considered as surface-reactive antigens (immunogens, biological response modyfiers) as well as membrane components which mediate the attachment of certain bacteria (S. saprophyticus, S. aureus, group A streptococci) to host cell tissues.

Type of fimbriation determines adherence of Klebsiella bacteria to human epithelial cells

Clinical isolates of three Klebsiella strains (encapsulated and nonencapsulated mutants) with type 1 (mannose-sensitive, MS+MR-), type 3 (mannose-resistant, MS-MR+) and type 1 and 3 (MS+MR+) fimbriae were investigated for their ability to adhere to epithelial cells. Considerable adhesion to human buccal, tracheal, pulmonary and uroepithelial cells could be demonstrated. Independent of encapsulation and type of epithelial cells, adhesion of MS+MR+ (type 1.3) fimbriated Klebsiella bacteria was significantly stronger than adhesion of microorganisms carrying only type 1 (MS+MR-) or type 3 (MS-MR+) fimbriate, respectively. Adherence of nonencapsulated type 1 and 3 (MS+MR+) fimbriated Klebsiella bacteria to mammalian cells was significantly inhibited in the presence of D-mannose. Certain carbohydrates (D-glucose, D-galactose) did not interfere with this adhesion process.

Evidence for lectin-mediated adherence of S. saprophyticus and P. aeruginosa to polymers

By hemagglutination tests surface lectins on S. saprophyticus strain S 1 with N-acetylgalactosamine (GalNac) and N-acetylglucosamine (GlcNac) specificity and on P. aeruginosa ATCC strain 27853 with N-acetylneuraminic acid (NANA) specificity could be demonstrated. To elucidate the role of bacterial surface lectins for the specific adhesion, polyether urethane discs were preincubated for 15 h at 4 degrees C in human serum or urine. Adhesion studies with S. saprophyticus S1 and P. aeruginosa ATCC 27853 onto precoated polymers revealed that microbial lectins may play a role in the colonization of prosthetic devices since lectin-blocking with competitive glycoconjugates significantly decreased bacterial adherence to the coated surfaces. Non-specific carbohydrates did not inhibit the adherence demonstrating specificity of this process.

Respiratory and pericardial lesions in turkeys infected with avian or mammalian strains of Chlamydia psittaci

Three groups of turkeys were inoculated with strains of C. psittaci (B577, VS1, TT3) from different restriction endonuclease groups. Turkeys were necropsied at 15 times through post-inoculation day 70. Birds infected with the TT3 strain were lethargic and had decreased body weight. After forced exercise, dyspnea was seen in VS1-infected turkeys. Pericarditis was the most severe lesion in TT3-infected birds. Airsacculitis and bronchopneumonia were the most severe lesions in VS1-infected turkeys. Lateral nasal adenitis was in both VS1- and TT3-infected birds. Only mild peribronchial pneumonia was in B577-infected turkeys. Chlamydial antigen, identified by light microscopy using an immunoperoxidase technique, was seen from post-inoculation days 9 through 50 in the lateral nasal gland and at earlier times in other tissue from VS1- and TT3-infected turkeys. No chlamydial antigen was detected in tissue from B577-infected birds. These studies showed that chlamydial strains from different restriction endonuclease groups are associated with distinct disease syndromes in turkeys.