Escherichia coli adhesion to Saccharomyces cerevisiae and mammalian cells: role of piliation and surface hydrophobicity

Tuning interdomain conjugation to enable in situ population modification in yeasts

The ability to modify and control natural and engineered microbiomes is essential for biotechnology and biomedicine. Fungi are critical members of most microbiomes, yet technology for modifying the fungal members of a microbiome has lagged far behind that for bacteria. Interdomain conjugation (IDC) is a promising approach, as DNA transfer from bacterial cells to yeast enables in situ modification. While such genetic transfers have been known to naturally occur in a wide range of eukaryotes and are thought to contribute to their evolution, IDC has been understudied as a technique to control fungal or fungal-bacterial consortia. One major obstacle to the widespread use of IDC is its limited efficiency. In this work, we manipulated metabolic and physical interactions between genetically tractable Escherichia coli and Saccharomyces cerevisiae to control the incidence of IDC. We test the landscape of population interactions between the bacterial donors and yeast recipients to find that bacterial commensalism leads to maximized IDC, both in culture and in mixed colonies. We demonstrate the capacity of cell-to-cell binding via mannoproteins to assist both IDC incidence and bacterial commensalism in culture and model how these tunable controls can predictably yield a range of IDC outcomes. Furthermore, we demonstrate that these controls can be utilized to irreversibly alter a recipient yeast population, by both "rescuing" a poor-growing recipient population and collapsing a stable population via a novel IDC-mediated CRISPR/Cas9 system.IMPORTANCEFungi are important but often unaddressed members of most natural and synthetic microbial communities. This work highlights opportunities for modifying yeast microbiome populations through bacterial conjugation. While conjugation has been recognized for its capacity to deliver engineerable DNA to a range of cells, its dependence on cell contact has limited its efficiency. Here, we find "knobs" to control DNA transfer, by engineering the metabolic dependence between bacterial donors and yeast recipients and by changing their ability to physically adhere to each other. Importantly, we functionally validate these "knobs" by irreversibly altering yeast populations. We use these controls to "rescue" a failing yeast population, demonstrate the capacity of conjugated CRISPR/Cas9 to depress or collapse populations, and show that conjugation can be easily interrupted by disrupting cell-to-cell binding. These results offer building blocks toward in situ mycobiome editing, with significant implications for clinical treatments of fungal pathogens and other fungal system engineering.

Tuning Interdomain Conjugation Toward in situ Population Modification in Yeast

The ability to modify and control natural and engineered microbiomes is essential for biotechnology and biomedicine. Fungi are critical members of most microbiomes, yet technology for modifying the fungal members of a microbiome has lagged far behind that for bacteria. Interdomain conjugation (IDC) is a promising approach, as DNA transfer from bacterial cells to yeast enables in situ modification. While such genetic transfers have been known to naturally occur in a wide range of eukaryotes, and are thought to contribute to their evolution, IDC has been understudied as a technique to control fungal or fungal-bacterial consortia. One major obstacle to widespread use of IDC is its limited efficiency. In this work, we utilize interactions between genetically tractable Escherichia coli and Saccharomyces cerevisiae to control the incidence of IDC. We test the landscape of population interactions between the bacterial donors and yeast recipients to find that bacterial commensalism leads to maximized IDC, both in culture and in mixed colonies. We demonstrate the capacity of cell-to-cell binding via mannoproteins to assist both IDC incidence and bacterial commensalism in culture, and model how these tunable controls can predictably yield a range of IDC outcomes. Further, we demonstrate that these lessons can be utilized to lastingly alter a recipient yeast population, by both "rescuing" a poor-growing recipient population and collapsing a stable population via a novel IDC-mediated CRISPR/Cas9 system.

Impact of direct physical association and motility on fitness of a synthetic interkingdom microbial community

Mutualistic exchange of metabolites can play an important role in microbial communities. Under natural environmental conditions, such exchange may be compromised by the dispersal of metabolites and by the presence of non-cooperating microorganisms. Spatial proximity between members during sessile growth on solid surfaces has been shown to promote stabilization of cross-feeding communities against these challenges. Nonetheless, many natural cross-feeding communities are not sessile but rather pelagic and exist in turbulent aquatic environments, where partner proximity is often achieved via direct cell-cell adhesion, and cooperation occurs between physically associated cells. Partner association in aquatic environments could be further enhanced by motility of individual planktonic microorganisms. In this work, we establish a model bipartite cross-feeding community between bacteria and yeast auxotrophs to investigate the impact of direct adhesion between prokaryotic and eukaryotic partners and of bacterial motility in a stirred mutualistic co-culture. We demonstrate that adhesion can provide fitness benefit to the bacterial partner, likely by enabling local metabolite exchange within co-aggregates, and that it counteracts invasion of the community by a non-cooperating cheater strain. In a turbulent environment and at low cell densities, fitness of the bacterial partner and its competitiveness against a non-cooperating strain are further increased by motility that likely facilitates partner encounters and adhesion. These results suggest that, despite their potential fitness costs, direct adhesion between partners and its enhancement by motility may play key roles as stabilization factors for metabolic communities in turbulent aquatic environments.

Biochar filters as an on-farm treatment to reduce pathogens when irrigating with wastewater-polluted sources

Microbial contamination of vegetables due to irrigation with wastewater-polluted streams is a common problem around most cities in developing countries because wastewater is an available source of water and nutrients but wastewater treatment is often inadequate. On-farm treatment of polluted water is a feasible option to manage microbial risks in a multi-barrier approach. Current evidence indicates good suitability of biochar filters for microbe removal from wastewater using the hydraulic loading rate (HLR) designed for sand filters, but their suitability has not been tested under on-farm conditions. This study evaluated the combined effect of several variables on removal of microbial indicators from diluted wastewater by biochar filtration on-farm and the correlations between removal efficiency and HLR. Columns of biochar with three different effective particle diameters (d₁₀) were fed with diluted wastewater at 1x, 6x, and 12x the design HLR and two levels of water salinity (electrical conductivity, EC). Influent and effluent samples were collected from the columns and analyzed for bacteriophages (ɸX174 and MS2), Escherichia coli, Enterococcus spp., and Saccharomyces cerevisiae. Microbe removal decreased with increasing HLR, from 2 to 4 to 1 log₁₀ for bacteria and from 2 to 0.8 log₁₀ for viruses, while S. cerevisiae removal was unaffected. Effective particle diameter (d₁₀) was the main variable explaining microbe removal at 6x and 12x, while EC had no effect. Correlation analysis showed removal of 2 log₁₀ bacteria and 1 log₁₀ virus at 3x HLR. Thus biochar filters on-farm would not remove significant amounts of bacteria and viruses. However, the design HLR was found to be conservative. These results, and some technical and management considerations identified, can assist in the development of a scientific method for designing biochar filters for on-farm and conventional wastewater treatment.

Agglutination Typing of Vibrio anguillarum Isolates from Diseased Fish and from the Environment

Agglutinating activity was widely distributed among 101 Vibrio anguillarum strains of different origin and three Vibrio ordalii strains from salmonids. The spectrum of cells which were agglutinated comprised yeast cells and human (type O), poultry, guinea pig, and trout erythrocytes, whereas ovine, bovine, and tanned bovine erythrocytes were not affected. Mannose-sensitive hemagglutination, mannose-resistant hemagglutination, and non-agglutinating strains were recognized. The three V. ordalii strains showed mannose-resistant hemagglutination, whereas V. anguillarum exhibited either mannose-sensitive hemagglutination or was non-agglutinating. Among V. anguillarum, sensitivity to d-galactose and l-fucose occurred sporadically. An agglutination typing scheme was developed for strains of V. anguillarum based on the agglutination pattern of human, poultry, guinea pig, and trout erythrocytes and yeast cells. Eight different agglutination types (A through H) were defined. The distribution of these types among fish pathogenic and environmental V. anguillarum strains were studied. The application of the typing scheme in ecological and epidemiological studies and for preventive medical purposes is discussed.

Salmonella Sofia differs from other poultry-associated Salmonella serovars with respect to cell surface hydrophobicity

Salmonella enterica is one of the most important foodborne pathogens. Salmonella enterica subsp. II 4,12:b:- (Salmonella Sofia) is commonly found in Australian poultry. It has been suggested that physicochemical properties such as surface charge and hydrophobicity may affect bacterial attachment to surfaces and their ability to persist in food systems. A possible link between hydrophobicity cell surface charge and persistence of Salmonella from the poultry system was examined. Hydrophobicity of Salmonella Sofia (n = 14), Salmonella Typhimurium (n = 6), Salmonella Infantis (n = 3), and Salmonella Virchow (n = 2) was assayed using hydrophobic interaction chromatography, bacterial adherence to hydrocarbons (BATH), using xylene or hexadecane, and the contact angle method (CAM). Cellular surface charge (CSC) of the isolates was determined using zeta potential measurements. The majority (12 of 14) of Salmonella Sofia isolates were found to be hydrophobic when assayed using BATH with xylene, except isolates S1635 and S1636, and the other serovars were found to be hydrophilic. Salmonella Sofia isolates were not significantly different (P > 0.05) from isolates of other serovars as measured by hydrophobic interaction, BATH with hexadecane, or the CAM. No significant differences (P > 0.05) in zeta potential measurements were observed between isolates. Principal component analysis using results from all four measures of hydrophobicity allowed clear differentiation between isolates of the serovar Salmonella Sofia (except S1635 and S1636) and those of other Salmonella serovars. Differences in physicochemical properties may be a contributing factor to the Salmonella Sofia serovar's ability to attach to surfaces and persist in a food system.

Identification of antiadhesive fraction(s) in nonimmunized egg yolk powder: in vitro study

The presence of antiadhesive component(s) in the hen egg yolk against foodborne pathogens was anticipated from results of a previous animal study conducted by the authors. The previous work showed egg yolk powder without specific antibodies is effective in controlling Salmonella enteritidis,Salmonella typhimurium, and Escherichia coli O157:H7 colonization in laying hens. Therefore, this study was necessary to locate the activity and identify the effective component(s). In vitro experiments were conducted using confluent Caco-2 cell monolayers. S. enteritidis, S. typhimurium, and E. coli O157:H7 were investigated against the various extracted granule and plasma fractions in three different assays: adhesion elimination, adhesion prevention, and antimicrobial. This study revealed original findings and identified the protective yolk fraction against the foodborne pathogens as the granule component, high-density lipoproteins (HDL). The protective activity conveyed by HDL was confirmed to remain intact despite peptic and tryptic enzymatic digestion and to have antiadhesive but not antimicrobial effect.

Effect of 2,4-dichlorophenoxyacetic acid herbicide on escherichia coli growth, chemical composition, and cellular envelope

2,4-Dichlorophenoxyacetic acid (2,4-D) is a herbicide widely used in the world and mainly excreted by the renal route in exposed humans and animals. Herbicides can affect other nontarget organisms, such as Escherichia coli. We observed that a single exposure to 1 mM 2,4-D diminished growth and total protein content in all E. coli strains tested in vitro. In addition, successive exposures to 0.01 mM 2,4-D had a toxic effect decreasing growth up to early stationary phase. Uropathogenic E. coli adhere to epithelial cells mediated by fimbriae, adhesins, and hydrophobic properties. 2,4-D exposure of uropathogenic E. coli demonstrated altered hydrophobicity and fimbriation. Hydrophobicity index values obtained by partition in p-xylene/water were 300-420% higher in exposed cells than in control ones. Furthermore, values of hemagglutination titer, protein contents in fimbrial crude extract, and electron microscopy demonstrated a significant diminution of fimbriation in treated cells. Other envelope alterations could be detected, such as lipoperoxidation, evidenced by decreased polyunsaturated fatty acids and increased lipid degradation products (malonaldehyde), and motility diminution. These alterations decreased cell adherence to erythrocytes, indicating a diminished pathogenic capacity of the 2,4-D-exposed E. coli.

Occurrence of lectins and hydrophobicity of bacteria obtained from biofilm of hospital catheters and water pipes

Bacteria isolated from biofilms of water distribution pipes and colonized catheters from hospitalized patients were studied for their haemagglutination ability, expression of lectins and hydrophobicity. Higher haemagglutination ability of clinical strains for human red blood cells was demonstrated, which could be an expression of their adaptation to the human ecosystem. Environmental strains had higher hydrophobicity, possibly related to adaptation to a low nutritive ecosystem. Expression of lectins was relatively low and comparable in both bacterial populations, but carbohydrate specificities were very different, possibly related to a different implication of these structures in the two ecosystems.

P-fimbriation and haemolysin production are the most important virulence factors in diabetic patients with Escherichia coli bacteraemia: a multivariate statistical analysis of seven bacterial virulence factors

Diabetic patients, as compared to non-diabetic subjects, run an increased risk of acquiring Gram-negative bacteraemia. We therefore studied the prevalence and coexpression of seven bacterial virulence markers of 69 Escherichia coli strains isolated from 64 bacteraemic patients with diabetes mellitus and 67 E. coli strains from faeces of healthy controls. The strains were analyzed for haemolysin (HLY) production, aerobactin-mediated iron uptake (AMI), cytotoxic necrotizing factor (CNF) production, expression of cell surface hydrophobicity, P-fimbriae, mannose-resistant haemagglutination (MRHA) and mannose-sensitive haemagglutination (MSHA). All bacterial properties were significantly more common among the bacteraemic strains (P < 0.02 vs. controls). Correlations between HLY and CNF (P < 0.0004) and between P-fimbriae and MRHA (P < 0.0001), MSHA (P < 0.0002) or AMI (P < 0.05), as well as between MRHA and MSHA (P < 0.0005) were observed. In patients with proteinuria, as sign of diabetic complications in the urinary tract, HLY-negative strains, P-fimbriae-negative strains, and strains which were both HLY-/CNF-negative, were more common (P = 0.04, P < 0.01 and P = 0.048, respectively). Using a multivariate statistical analysis, production of HLY and the expression of P-fimbriae were the two virulence factors with the highest discrimination between bacteraemic and control strains. In conclusion, all virulence factors studied were more prevalent in bacteraemic than in control strains, although HLY and P-fimbriae were shown to be of greatest and independent importance. Low virulent strains (P-fimbriae-, HLY- and CNF-negative) were more prevalent in diabetic patients with signs of renal complications.

Fimbriation, surface hydrophobicity and serum resistance in uropathogenic strains of Escherichia coli

A total of 80 Escherichia coli strains were examined for expression of P-fimbriae, mannose-sensitive haemagglutination (MSHA) and mannose-resistant haemagglutination (MRHA) of human group A erythrocytes and guinea pig erythrocytes, cell surface hydrophobicity and resistance to serum bactericidal activity. Isolates were obtained from urine of children and adults, either with acute pyelonephritis (n = 15 and n 12) or lower urinary tract infection (UTI) (n = 30 and n = 23, respectively). Results obtained showed that, in E. coli strains isolated both from children and adults with lower UTI, significant differences were not found concerning the incidence of P-fimbriae, cell surface hydrophobicity and serum resistance. In pyelonephritogenic E. coli isolated from children and adults, the incidence of P-fimbriae and cell surface hydrophobicity was associated more frequently with the former (87% vs. 42% and 100% vs. 67%, P < 0.05), while serum resistance was associated with the latter (47% vs. 67%, P < 0.05).

Environmental regulation of the fim switch controlling type 1 fimbrial phase variation in Escherichia coli K-12: effects of temperature and media

Expression of type 1 fimbriae in Escherichia coli K-12 is phase variable and associated with the inversion of a short DNA element (switch). The fim switch requires either fimB (on-to-off or off-to-on switching) or fimE (on-to-off switching only) and is affected by the global regulators leucine-responsive regulatory protein (Lrp), integration host factor (IHF), and H-NS. Here it is shown that switching frequencies are regulated by both temperature and media and that these effects appear to be independent. fimE-promoted on-to-off switching occurs far more rapidly than previously estimated (0.3 per cell per generation in defined rich medium at 37 degrees C) and faster at lower than at higher temperatures. In direct contrast, fimB-promoted switching increases with temperature, with optima between 37 and 41 degrees C. Switching promoted by both fimB and fimE is stimulated by aliphatic amino acids (alanine, isoleucine, leucine, and valine), and this stimulation requires lrp. Furthermore, lrp appears to differentially regulate fimB- and fimE-promoted switching in different media.

Type 1 fimbriation and fimE mutants of Escherichia coli K-12

We reexamined the influence of fimE, also referred to as hyp, on type 1 fimbriation in Escherichia coli K-12. We found that one strain used previously and extensively in the analysis of type 1 fimbriation, strain CSH50, is in fact a fimE mutant; the fimE gene of CSH50 contains a copy of the insertion sequence IS1. Using a recently described allelic exchange procedure, we transferred the fimE::IS1 allele from CSH50 to our present wild-type strain, MG1655. Characterization of this IS1-containing strain (AAEC137), together with another fimE mutant of MG1655 (AAEC143), led to two conclusions about the role of fimE. First, the formation of phase variant colony types, reported widely in strains of E. coli, depends on mutation of fimE, at least in K-12 strain MG1655. Here we showed that this phenomenon reflects the ability of fimE to stimulate the rapid inversion of the fim invertible element from on to off when the bacteria are grown on agar. Second, our analysis of fimE mutants, which is limited to chromosomal constructs, provided no evidence that they are hyperfimbriate. We believe that these results, which are at odds with a previous study using fim-containing multicopy plasmids, reflect differences in gene copy number.

Virulence factors in Escherichia coli urinary tract infection

Uropathogenic strains of Escherichia coli are characterized by the expression of distinctive bacterial properties, products, or structures referred to as virulence factors because they help the organism overcome host defenses and colonize or invade the urinary tract. Virulence factors of recognized importance in the pathogenesis of urinary tract infection (UTI) include adhesins (P fimbriae, certain other mannose-resistant adhesins, and type 1 fimbriae), the aerobactin system, hemolysin, K capsule, and resistance to serum killing. This review summarizes the virtual explosion of information regarding the epidemiology, biochemistry, mechanisms of action, and genetic basis of these urovirulence factors that has occurred in the past decade and identifies areas in need of further study. Virulence factor expression is more common among certain genetically related groups of E. coli which constitute virulent clones within the larger E. coli population. In general, the more virulence factors a strain expresses, the more severe an infection it is able to cause. Certain virulence factors specifically favor the development of pyelonephritis, others favor cystitis, and others favor asymptomatic bacteriuria. The currently defined virulence factors clearly contribute to the virulence of wild-type strains but are usually insufficient in themselves to transform an avirulent organism into a pathogen, demonstrating that other as-yet-undefined virulence properties await discovery. Virulence factor testing is a useful epidemiological and research tool but as yet has no defined clinical role. Immunological and biochemical anti-virulence factor interventions are effective in animal models of UTI and hold promise for the prevention of UTI in humans.

Phenotypic differences and characteristics of pyelonephritogenic strains of Escherichia coli isolated from children and adults

We examined the frequency of bacterial strains expressing cell surface hydrophobicity, P-fimbriae, mannose-resistant haemagglutination (MRHA), type I fimbriae, production of aerobactin, haemolysin synthesis (Hly), production of cytotoxic necrotising factor (CNF) and HeLa cell adherence in 126 strains of Escherichia coli isolated from children (n = 65) and women (n = 61) with acute non-obstructive pyelonephritis. Previous investigations have shown that pyelonephritogenic strains of E. coli more often express hydrophobic properties, P-fimbriae, MRHA, aerobactin-mediated iron uptake, Hly and CNF production than strains isolated from the faecal flora of healthy persons. The objective of the present study was to examine phenotypic differences between strains of E. coli obtained from children with their first episode of acute pyelonephritis and strains from women with non-obstructive acute pyelonephritis. Of the pyelonephritogenic strains of E. coli isolated from children, 98% expressed cell surface hydrophobic properties compared to 82% isolated from adults (P = 0.004). Strains from children and adults had the same ability to assimilate iron and equally often expressed P-fimbriae, MRHA and type I fimbriae. Strains from children with acute pyelonephritis more significantly expressed Hly (72%) and CNF (58%) than did pyelonephritogenic strains from adults (49 and 37% respectively, P = 0.013 and P = 0.028 respectively). The frequency of HeLa cell adherence was similar and low in both groups. The phenotype aerobactin+ Hly+ and Hly+CNF+ was found significantly more often in pyelonephritogenic strains from children than in strains from adults (P = 0.006 and P = 0.028 respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Cell surface hydrophobicity, adherence to HeLa cell cultures and haemagglutination pattern of pyelonephritogenic Escherichia coli strains

Cell surface hydrophobicity, haemagglutination pattern and adherence to HeLa cells were examined in 230 strains of Escherichia coli collected from women (n = 61 strains) and children (n = 65 strains) with non-obstructive acute pyelonephritis and in 104 faecal control strains of E. coli from healthy adults (n = 71 strains) and children (n = 33 strains). Pyelonephritogenic E. coli strains showed a significantly increased incidence of hydrophobic properties (90%) and mannose resistant haemagglutination (MRHA) of human erythrocytes (83%) than faecal control strains (64 and 23% respectively, P less than 0.001 in both cases). Mannose sensitive haemagglutination (MSHA) was observed in 48% of the pyelonephritogenic E. coli strains and in 50% of the faecal control strains (NS). The incidence of adherence to HeLa cells was low both in pyelonephritogenic and faecal control strains, 6 and 7% respectively (NS). The bacterial phenotypes MRHA + MSHA + and MRHA + MSHA- appeared significantly more often in pyelonephritogenic E. coli strains (35 and 48% respectively) than in faecal control strains (5 and 17% respectively, P less than 0.001 in both cases). The phenotype MRHA- MSHA + occurred significantly more often in control strains (45%) than in pyelonephritogenic strains (13%, P less than 0.001). Eighty-three per cent of the pyelonephritogenic E. coli strains expressing hydrophobic properties showed MRHA and 50% of the hydrophobic strains showed MSHA. There were no significant correlations between cell surface hydrophobic properties and haemagglutination pattern or adherence to HeLa cells in pyelonephritogenic E. coli strains nor in faecal control strains.

Mouse model for colonization and disease caused by enterohemorrhagic Escherichia coli O157:H7

Enterohemorrhagic Escherichia coli O157:H7 isolates produce Shiga-like toxins and carry a 60-megadalton plasmid which encodes an adhesin for Henle 407 intestinal cells. A streptomycin-treated mouse model was used to compare the intestinal colonizing capacity of E. coli O157:H7 strain 933 with that of its 60-megadalton plasmid-cured derivative, strain 933cu. When fed individually to mice, both 933 and 933cu maintained a stable number of organisms per gram of feces, and the greatest numbers of 933 or 933cu were isolated from cecal and proximal colonic epithelial cells. When 933 and 933cu were simultaneously fed to mice, 933cu was unable to maintain a stable level of colonization in about two-thirds of the mice tested. However, in one-third of the mice, the number of 933cu in feces began to increase rapidly until a stable level of co-colonization with 933 was attained. The isolate from these mice, 933cu-rev, was excreted in high numbers when fed alone to mice and was found on epithelial cells throughout the entire large bowel and distal small intestine. Moreover, 933cu-rev grew in mucus from all segments of the intestine and at higher levels than strain 933 or 933cu. Only mice fed strain 933cu-rev died. Histopathological studies confirmed that mice fed 933cu-rev died from bilateral renal cortical tubular necrosis consistent with toxic insult, perhaps due to Shiga-like toxins. The virulence of 933cu-rev may reflect its ability to grow well in mucus and colonize the small as well as large bowel.

Characteristics of binding of Escherichia coli serotype O157:H7 strain CL-49 to purified intestinal mucin

Purified rat intestinal mucin was used as a model mucin to study the binding of Escherichia coli serotype O157:H7, a human pathogen associated with outbreaks of hemorrhagic colitis and hemolytic uremic syndrome. Of six O157:H7 strains, only one strain (designated CL-49) bound to rat (and other) intestinal mucins by a specific and saturable process. Binding was observed only after the bacteria were serially passaged to promote the expression of type 1 pili (fimbriae). Several other type 1-piliated E. coli strains, however, did not bind to mucin. Binding of E. coli CL-49 was inhibited by D-mannose and short oligomannosyl derivatives, particularly Man-alpha-1,3-Man, Man-alpha-1,2-Man, and Man-alpha-1,3-Man-beta-1,4-N-acetylglucosamine. Other inhibitors of binding included p-nitrophenol (10(-4) M), heating at 60 degrees C (to remove pili), an antibody to type 1 pili, and purified type 1 pili of E. coli CL-49 used as hapten inhibitors. A comparison of the hydrophobicity of piliated E. coli CL-49 with other type 1-piliated E. coli strains indicated that the former strain was much more hydrophobic than the others. These findings indicate that highly purified intestinal mucins possess specific mannosyl receptor sites for bacterial type 1 pili on E. coli CL-49, but that strong hydrophobic interactions between the mucin and the pili stabilize the mannose-dependent binding process. We speculate that the mucin receptors for type 1 pili reside in oligosaccharides of the 118-kilodalton "link" glycopeptide, since this is the only mucin component known to contain mannose.

The effect of subinhibitory concentrations of some antibiotics on the hydrophobicity of gram-negative bacteria

Cell surface hydrophobicity is currently regarded as an important factor in promoting bacterial adherence to a wide variety of surfaces. This feature was investigated in some Gram-negative bacteria isolated from urinary tract infections and the extent to which their surface characteristics were affected by subinhibitory concentrations of some antibiotics was assayed. Surface properties were evaluated using the salting-out technique (SAT) and bacterial absorption to n-hexadecane (BATH). SAT showed that all except 3 Escherichia coli strains were autoaggregating. BATH detected more hydrophobic characteristics in the stationary phase of bacterial growth. Pretreatment with antibiotics generally reduced hydrophobicity and thus affected the initial reversible phase of attachment of bacteria to eukaryotic cells.

Adherence of uropathogenic E. coli to differentiated human uroepithelial cells grown in vitro

A quantitative in vitro model to measure E. coli adherence to differentiated human uroepithelial cells has been developed. Primary cultures of uroepithelial cells were initiated from normal ureteral epithelium. Adherence of uropathogenic 3H-labelled Escherichia coli to postconfluent human uroepithelial cells was directly related to the bacteria:epithelial cell ratio during incubation. Bacterial attachment was inhibited either by mannose or by urine containing anti-E. coli antibodies. Transmission electron microscopy showed that epithelial cells differentiated in vitro to resemble normal uroepithelium in vivo. Furthermore, electron microscopy showed specific adherence of bacteria to the glycocalyx of microvilli of the superficial uroepithelial cells in vitro in a manner which closely mimics the in vivo interaction. This model of bacterial adherence permits in vitro analysis of adhesin-receptor interactions between uropathogenic E. coli and a layer of viable uroepithelial cells similar to those lining the bladder.

Hydrophobic properties of Escherichia coli causing acute pyelonephritis

Cell surface hydrophobic properties and expression of P-fimbriae were examined in 130 strains of Escherichia coli derived from women (n = 66) and children (n = 64) with acute non-obstructive pyelonephritis and in 170 faecal strains of E. coli from healthy adults (n = 103) and children (n = 67) by use of the salt aggregation test and the P-fimbriae-specific particle agglutination test. The strains of E. coli isolated were aggregated in salt solutions of varying molarity (0.001-1.6 M final concentration). Patients with predisposing medical or urological conditions in the urinary tract were excluded. Pyelonephritic strains of E. coli from the women and children had a higher degree of cell surface hydrophobicity (80 and 98% respectively) than faecal strains from healthy adults and children (57 and 82% respectively, P less than 0.01 and P less than 0.01). Both pyelonephritic and faecal strains of E. coli from the children were more often salt aggregation positive (hydrophobic) than faecal strains of E. coli from healthy adults (P less than 0.01 and P less than 0.001, respectively). Pyelonephritic strains of E. coli from women and children were more often P-fimbriated (79 and 84% respectively) than faecal control strains from women and children (15 and 33%, P less than 0.001 and P less than 0.001, respectively) but there was no significant correlation between expression of P-fimbriae and cell surface hydrophobicity.

Isolation and characterization of the alpha-galactosyl-1,4-beta-galactosyl-specific adhesin (P adhesin) from fimbriated Escherichia coli

The alpha-galactosyl-1,4-beta-galactosyl-specific adhesin (P adhesin) was isolated from the fimbria-adhesin complex (FAC) of recombinant Escherichia coli strains expressing the F7(1), F8, or F13 fimbrial antigens. Separation into fimbriae and adhesin was achieved by heating the FAC to 80 degrees C in the presence of Zwittergent 3-16. After removal of the fimbriae by precipitation with lithium chloride, the adhesin was purified by anion-exchange fast protein liquid chromatography in the presence of 4 M urea. The purified adhesins from the three strains had pIs of 4.8 to 5.0 and molecular weights of approximately 35,000. The fimbrillins were smaller, their molecular weights being different with different F antigens. The amino-terminal amino acid sequence of the F7(1)- and F13-derived adhesins were different, that of the F13-derived adhesin being identical to that extrapolated from the DNA sequence of the papG gene (B. Lund, G. Lindberg, B.-I. Marklund, and S. Normark, Proc. Natl. Acad. Sci. USA 84:5898-5902). An antiadhesive monoclonal antibody which reacted with the three P adhesins was prepared. The FAC and the purified adhesins but not the fimbriae from which the adhesins had been removed agglutinated erythrocytes and galactose-galactose-coated latex beads. The adhesion of erythrocytes to the surface-fixed adhesins could be specifically inhibited with alpha-galactosyl-1,4-beta-galactosyl-1,4-glucosyl. The results indicate that the P adhesin(s) of uropathogenic E. coli represents a group of related proteins with conserved receptor recognition domains. The F13-derived P adhesin is the PapG protein postulated by Normark and his colleagues (Lund et al., Proc. Natl. Acad. Sci. USA 84:5898-5902; B. Lund, F. Lindberg, and S. Normark, J. Bacteriol. 170:1887-1894).

Study of Vibrio anguillarum strains from different sources with emphasis on ecological and pathobiological properties

A total of 317 Vibrio anguillarum strains were isolated from water, sediment, and diseased as well as healthy rainbow trout at a Danish mariculture farm and from feral fish caught close to the farm. All strains were examined serologically. Ten sera permitted determination of the O group in 66.7% of the strains from diseased rainbow trout. Furthermore, the O group could be determined in 45.1 to 65.4% of the strains from mucus, gills, and intestinal contents of healthy rainbow trout, while only 22.2 to 28.8% of the isolates from water, sediment, and gills or mucus of feral fish were groupable. Serogroup O1 and to some extent O2 appeared to be associated with trout. Strains from these serogroups were selected for analyses of hemagglutinating activity and surface hydrophobicity. Serogroup O1 comprised hemagglutinating as well as nonhemagglutinating strains; from cases of vibriosis, all O1 strains were nonhemagglutinating. The strains belonging to serogroup O2 were generally hemagglutinating. Examinations of surface hydrophobicity by salt aggregation and hydrophobic interaction chromatography suggested that the O1 strains were more hydrophobic than the O2 strains. In pathogenicity tests, O1 strains isolated from gills and mucus of healthy rainbow trout killed all trout in the test groups. A strain from the intestinal contents of healthy rainbow trout did not produce significant mortality. This strain could, however, be frequently reisolated from the pronephros of fish in the test group concerned. After challenge with strains from eel mucus and seawater, mortality was not produced, and furthermore, these strains could not be reisolated from the pronephros.

Colonization of the streptomycin-treated mouse large intestine by a human fecal Escherichia coli strain: role of growth in mucus

The relative colonizing abilities of Escherichia coli F-18, isolated from the feces of a healthy human, and E. coli F-18col-, a strain derived from it which does not make the E. coli F-18 colicin, were studied. In a previous report, it was shown that when each strain was fed individually to streptomycin-treated mice, at approximately 10(10) CFU per mouse, each colonized the large intestine at between 10(7) and 10(8) CFU/g of feces indefinitely. However, when simultaneously fed to mice, although E. coli F-18 colonized at about 10(8) CFU/g of feces, E. coli F-18col- dropped to a level of 10(3) CFU/g of feces within 3 to 5 days. In the present investigation, we show that when given enough time to establish a state of colonization, E. coli F-18col- persists in feces in high numbers despite subsequent challenge by E. coli F-18. Therefore, a major defect in the ability of E. coli F-18col- to colonize in the presence of E. coli F-18 appears to be in initiating that state. In addition, when mucus was scraped from the cecal wall and, without further treatment, was inoculated with E. coli F-18 or F-18col-, both strains grew well. However, when cecal mucus was inoculated with both strains simultaneously, E. coli F-18 grew far more rapidly than E. coli F-18col-. Moreover, neither strain grew in cecal luminal contents. Together, these data suggest the possibility that both E. coli F-18 and F-18col- must grow in mucus to colonize the streptomycin-treated mouse large intestine, that E. coli F-18col- is eliminated by E. coli F-18 because it does not grow in mucus as well as E. coli F-18, and that E. coli F-18col- can resist elimination by E. coli F-18 if it is allowed enough time to establish itself within the mucus layer.

Tamm Horsfall glycoprotein interferes with bacterial adherence to human kidney cells

The effect of Tamm Horsfall protein (THP) of 18 healthy subjects and 14 diabetics on adherence of Escherichia coli (06:K13) 2699 strain to human kidney cells (HUK) was studied. Adhesion of bacteria (without additions: 100 bacteria per cell) was reduced dose-dependently by THP, half maximal inhibition occurring with 250 micrograms THP ml-1. Maximal inhibition (-84% at 1000 micrograms ml-1) exceeded inhibition by alpha-methyl-mannoside (36% at 50 mM), was specific (not reproduced by other glycoproteins, e.g. ovalbumin, mucin or thyroglobulin) and reversible (abolished by washing THP off HUK cells). Anti-adherence property of THP was not abolished by neuraminidase treatment. No significant difference of anti-adherence activity of THP was found between controls and diabetics, despite altered carbohydrate composition of THP in diabetes.

Adhesion properties of E. coli cells in the presence of promethazine

Some E. coli strains were tested for adsorption to HEp-2 cells and on aluminium hydroxide gel. The adhesiveness of E. coli to HEp-2 cells was inhibited by promethazine. MRHA (mannose-resistant haemagglutinating activity) positive plasmid-carrying E. coli strains were found to be adsorbed to tissue culture cells more effectively than the MRHA-negative strains. Fifty percent of the clinical isolates contained antibiotic resistance plasmids, but only 40% of these strains were able to transfer the antibiotic resistance properties to E. coli as recipient. It is presumed that the hydrophobic adsorption of bacteria depends on the fimbriae, while aluminium hydroxide gel adsorption correlates with surface properties other than the fimbriae.

Surface properties of the Vero cytotoxin-producing Escherichia coli O157:H7

Strains of Escherichia coli serotype O157:H7 are Vero cytotoxin-producing enteric pathogens which have been associated with sporadic cases and outbreaks of hemorrhagic colitis and with the hemolytic uremic syndrome in humans. In addition to toxin production, adherence of many pathogenic bacteria to intestinal mucosal surfaces is a critical primary step in the pathogenesis of diarrheal diseases. Although E. coli serotype O157:H7 organisms adhere to intestinal epithelia of orally infected animals in a pattern morphologically identical to that previously described in adherent, effacing E. coli infections, the mechanisms of bacterial adherence are not known. To determine the cell surface adhesins which mediate attachment of E. coli O157:H7 to epithelial surfaces, we evaluated the surface properties of these organisms. Five strains isolated from children with the hemolytic uremic syndrome were grown both in broth cultures and on agar media. Adherence and invasion of E. coli O157:H7 in Intestine 407 and HEp-2 epithelial cell lines was quantitated using an enteroinvasive E. coli strain (serotype O164:NM) as a control. Cell surface properties of E. coli O157:H7 were evaluated by agglutination of a series of erythrocytes, transmission electron microscopy, DEAE-ion-exchange chromatography, and hydrophobic interaction chromatography. E. coli O157:H7 strains adhered to but did not invade either Intestine 407 or HEp-2 cells. Homologous O157:H7 rabbit antiserum blocked attachment of bacteria to tissue culture cells, in contrast to heterologous antiserum and preimmune rabbit serum, which did not inhibit attachment of E. coli O157:H7. None of the five O15:H7 isolates mediated mannose-resistant hemagglutination under any of the in vitro culture conditions. One isolate mediated mannose-sensitive hemagglutination after serial passage in broth cultures. Pili and fibrillae were not visualized by electron microscopy on nonhemagglutinating organisms, but pili were demonstrated on the one isolate which mediated mannose-sensitive hemagglutination. All O157:H7 strains demonstrated high anionic surface charge (DEAE) but low surface hydrophobicity properties (hydrophobic interaction chromatography). The findings suggest that surface structures other than pili can mediate attachment of serotype O157:H7 bacteria to epithelial cells in vitro.

Isolation and characterization of the alpha-sialyl-beta-2,3-galactosyl-specific adhesin from fimbriated Escherichia coli

The alpha-sialyl-beta-2,3-galactosyl-specific adhesin (S adhesin) was isolated from cells of a recombinant Escherichia coli K-12 strain expressing the S-fimbrial adhesin complex. A crude cell extract was partially dissociated into fimbriae and an adhesin-enriched fraction by heating to 70 degrees C. From the latter, adhesin was purified to apparent homogeneity (by fast protein liquid chromatography, immunoblot, and NaDodSO4/PAGE) by differential ammonium sulfate precipitation, dissociation in 8 M guanidine hydrochloride, and high-resolution anion-exchange chromatography in 8 M urea. The purified adhesin formed an aggregate of Mr approximately 10(6) that was made up of one type of 12-kDa polypeptide (fimbrillin is 16.5 kDa). It had pI value of 4.7 (fimbriae has a pI value of 6). Adhesin and fimbrillin had different amino acid compositions. The purified adhesins agglutinated human and bovine erythrocytes with the same specificity as the whole bacteria; purified fimbriae were not adhesive. Monoclonal anti-adhesin and anti-fimbriae antibodies were obtained. Monoclonal anti-adhesin, but none of the anti-fimbriae, antibodies inhibited the agglutination of erythrocytes. The anti-adhesive antibodies were used in immuno-gold electron microscopy to localize adhesin exclusively on the fimbriae, with a possible preference to their tips.

Haemagglutinins and adherence properties to HeLa and intestine 407 cells of Klebsiella pneumoniae and Klebsiella oxytoca isolates

The occurrence of haemagglutination (HA) and adherence properties were examined in 50 strains of K. pneumoniae and 17 K. oxytoca strains isolated from humans. All isolates except three exhibited HA activity. Mannose-sensitive haemagglutinins (MSHA) were expressed by the majority of K. pneumoniae strains, but only by one K. oxytoca isolate. Mannose-resistant haemagglutination (MRHA) to human or guinea pig erythrocytes could not be detected; haemagglutinins of the MR/K type were found in both species with similar frequencies. Adhesive properties could be demonstrated in K. pneumoniae as often as in K. oxytoca: About half of the strains adhered to two human cell lines: HeLa and Intestine 407. The incidence of HA activity was similar in adhering and nonadhering strains. A correlation between MSHA, MR/K-HA and adherence to tissue-cultured cells could not be detected.

Interaction of beta-lactam antibiotics with the bactericidal activity of leukocytes against Escherichia coli

The effect of beta-lactam antibiotics on phagocytosis and intracellular killing of four isogenic Escherichia coli strains differing in their 0- and K antigens was studied by adopting the rat polyvinyl-sponge model. The penicillins mezlocillin, ticarcillin and piperacillin rendered all four isogenic E. coli strains more susceptible to intraleukocyte killing; the cefalosporins tested exhibited inhomogenous effects; lamoxactam was marginally effective, whereas cefoxitin was completely ineffective; cefotaxime caused an increase in intracellular killing of the capsule-defective mutant only. The beta-lactam promoted increase in intracellular killing could be inhibited by alpha-methylmannoside but not by alpha-methylglucoside. Free-flow electrophoretic separation of mezlocillin-treated bacteria and guinea pig erythrocytes revealed that co-migration of E. coli and erythrocytes respectively could be inhibited by alpha-methylmannoside but not by alpha-methylglucoside. These data indicate that mezlocillin interferes with the mannose sensitive adhesins of E. coli.

Identification and characterization of two Campylobacter jejuni adhesins for cellular and mucous substrates

Campylobacter jejuni is able to colonize the human intestinal mucosa and cause disease. For this reason, it was important to investigate mechanisms by which C. jejuni adheres to epithelial cells and intestinal mucus gel. All strains of C. jejuni used were able to adhere to INT 407 epithelial cells and mucus, but high adherence to one substrate did not necessarily indicate comparable adherence to the other. The adherence of C. jejuni to cells was inhibited partially by treating the bacterial cells with proteases or glutaraldehyde or by adding a certain carbohydrate (fucose or mannose) to the medium. The flagellum of C. jejuni was identified as a potential adhesin by comparing adherence of flagellated and aflagellated variants. Shearing of the bacterial cells to remove the flagella reduced bacterial adhesion, whereas immobilization of the flagellum with KCN increased adhesion. Purified flagella showed specific, fucose-resistant binding to epithelial cells but not to intestinal mucus. The presence of a second, nonproteinaceous adhesin was suggested because no single treatment of the bacteria completely inhibited adhesion. Lipopolysaccharide (LPS) was identified as another C. jejuni adhesin. [3H]LPS specifically bound to epithelial cells, and this phenomenon was inhibited by periodate oxidation of the LPS or glutaraldehyde fixation of the epithelial cells. LPS, unlike flagella, was fucose sensitive and inhibited binding of whole bacterial cells to INT 407 cells. LPS was also able to bind to intestinal mucus gel. These data indicate that both flagella and LPS are important in adhesion to the mucosal surface.

Microbial and host factors that influence adherence of Escherichia coli to kidney epithelium

The adherence of Escherichia coli 06K13H1 to punch biopsy specimens of rabbit renal pelvic tissue and isolated epithelial cells was examined quantitatively. Organisms with pili adhered readily to kidney tissue, whereas organisms without pili (nonpiliated or grown in glucose-containing media) had significantly less adherence. Adherence was inhibited by antibody to pili antigen but not by mannose (a determinant of adherence to buccal mucosal cells). Studies were done to evaluate adherence under conditions operative in the renal medulla. The combination of hypertonic salt or urea solutions in acid pH interfered with adherence of the mannose-resistant strain. In additional studies of kidneys from humans, a similar effect of antipili serum and mannose was seen. These studies provide further evidence that pili are important in the initiation of upper urinary tract infection and define host factors that may inhibit initiation of infection.

Cell surface hydrophobicity of pigmented and nonpigmented clinical Serratia marcescens strains

The cell surface hydrophobicity of 10 pigmented and 4 nonpigmented clinical Serratia marcescens strains was studied, based on the ability of the strains to adhere to hydrocarbons and to polystyrene. The cell surface hydrophobicity depended greatly on growth temperature; all of the strains tested were adherent following growth at 30 degrees C, whereas none was adherent following growth at 38 degrees C. In previous studies, the pigment prodigiosin has been cited as responsible for cell surface hydrophobicity in various Serratia strains. However, the observed ability of the nonpigmented strains to adhere to the test hydrocarbons and to polystyrene indicates that Serratia strains can possess hydrophobic surface properties in the absence of this pigment. Moreover, strain 1785 cells were adherent whether they were grown at 30 or 36.5 degrees C, even though pigment was not synthesized at the higher temperature. In Escherichia coli correlations have been noted between increased cell surface hydrophobicity and the presence of mannose-specific adhesins; no such relationship was found in the S. marcescens strains tested. The expression of cell surface hydrophobicity in clinical S. marcescens strains at 30 degrees C and the loss of hydrophobicity at host temperatures raise the possibility that infective cells from the environment are initially hydrophobic, but lose this property upon subsequent proliferation within a host.

Monoclonal antibodies against the nonhemagglutinating fimbrial antigen 1C (pseudotype 1) of Escherichia coli

Hybridoma-derived monoclonal antibodies were produced with fimbrial preparations from Escherichia coli 20025 (04:K12:H-) with fimbrial (F) antigens 1C, 13, one related to 12, and one preliminarily termed y and from E. coli 2980 (018ac:K5:H-) with F antigens 1C and 8. Two clones of subclonal hybrid cells were studied which produced monoclonal antibodies (mc-20025-F2b, immunoglobulin G2b [IgG2b]; mc-2980-F2, IgG1) that were reactive with E. coli 20025, 2980, and a number of additional strains which exhibited the F1C antigen. Results of enzyme-linked immunosorbent assay and Western blot analysis indicated that the antibodies had F1C specificity, and competitive enzyme-linked immunosorbent assay with 125I-labeled antibodies showed that they recognized different epitopes on the fimbrial subunit. Neither of the antibodies agglutinated F1C-fimbriated E. coli but bound to the bacteria. There was no binding to E. coli without F1C fimbriae.

Urinary pathogenicity of Proteus mirabilis strains isolated from faeces or urine

Urinary and faecal isolates of Proteus mirabilis were studied with respect to a number of bacterial properties as possible virulence factors in the pathogenesis of urinary tract infections: experimental virulence in a mouse model, haemolysin production, haemagglutinating properties, hydrophobicity of the bacterial surface, sensitivity to the bactericidal effect of human serum, serotype and cell invasiveness. Urinary isolates were slightly more virulent than faecal isolates in the mouse model. No other significant differences were found between both groups. So urinary strains seem to be selected from the faecal reservoir mainly on the basis of their prevalence in the faeces and not on the basis of the possession of particular virulence factors.

Functional heterogeneity of intestinal Escherichia coli strains expressing type 1 somatic pili (fimbriae): assessment of bacterial adherence to intestinal membranes and surface hydrophobicity

Although the role of host-specific, nonmannose-sensitive pilus adhesins in the intestinal adherence of pathogenic Escherichia coli is well established, a similar role for mannose-sensitive type 1 or common pili is less clear, since these structures can be expressed by most E. coli, even nonpathogens. We first examined whether type 1 pili, expressed by the rabbit-effacing, adherent, enteropathogenic E. coli strain RDEC-1, mediated interactions with intestinal membranes of several species and compared these interactions with those mediated by the nonmannose-sensitive adhesin of RDEC-1. We next grew a series of E. coli intestinal strains in static broth to promote type 1 pilus expression and determined whether E. coli expressing type 1 pili differed in their affinity for intestinal membranes (as measured by phase-contrast microscopy and aggregometry), hydrophobic surface properties, net negative surface charge (as measured by hydrophobic interaction chromatography and salt aggregation), and hemagglutination patterns. In contrast to the species-specific attachment to rabbit brush borders of RDEC-1 expressing its nonmannose-sensitive adhesin, type 1 pili on RDEC-1 mediated mannose-sensitive attachment to intestinal membranes of all four species tested. Expression of type 1 pili on other E. coli strains resulted in varying degrees of nonspecies-specific, mannose-sensitive attachment to intestinal membranes. This attachment correlated with increasing surface hydrophobicity rather than with hemagglutination patterns. These results indicate that various E. coli strains expressing type 1 pili are functionally heterogeneous and suggest that some type 1 pili might contribute to in vivo enteroadherence.

Adhesion of a human fecal Escherichia coli strain to mouse colonic mucus

Escherichia coli F-18 isolated from the feces of a healthy human is an excellent colonizer of the CD-1 mouse colon. In the present investigation, adhesion of E. coli F-18 to CD-1 mouse colonic mucus and bovine serum albumin (BSA), immobilized on polystyrene, was studied. Adhesion of E. coli F-18 to mucus was two- to sixfold greater than to either BSA or polystyrene. E. coli F-18 lipopolysaccharide specifically blocked adhesion of E. coli F-18 to mucus and mimicked adhesion of E. coli F-18 to mucus, BSA, and polystyrene. Purified capsule also blocked adhesion of E. coli F-18 to mucus, but this inhibition was found to be entirely nonspecific. The specific E. coli F-18 receptor in mucus appeared to be a glycoprotein, containing sugars normally found in mucins and having a maximum molecular weight of between 1.25 X 10(5) and 2.5 X 10(5).

Effect of monosaccharides and ethyleneglycol on the interaction between Escherichia coli bacteria and Octyl-Sepharose

Combined effects of monosaccharides and reduced surface tension of the medium were studied in relation to the hydrophobic binding of Escherichia coli bacteria, with and without mannose-specific structures. Hydrophobic binding was analyzed by hydrophobic interaction chromatography on Octyl-Sepharose. The results showed that ethyleneglycol, as well as mannose, reduced the hydrophobic interaction of the bacteria with mannose-specific structures. This effect was potentiated by combining ethyleneglycol and mannose. No other monosaccharides tested (galactose and fucose) had any effect on the hydrophobic interaction of bacteria with mannose-specific structures. These results further strengthen the hypothesis that the mannose-specific interaction of Escherichia coli bacteria is, at least in part, mediated by hydrophobic forces.

Mechanisms of antibacterial immunity of mucous membranes

A survey based on both literary data and the authors own results, concerning the mechanisms of sIgA-mediated antibacterial immunity, is presented. Secretory IgA is characterized as a specific component of the immune system of mucous membranes, which can recognize harmful bacterial and distinguish them from indigenous microflora physiologically colonizing the mucous membranes, to fix them to the mucous membrane surface and to direct further factors, such as mucin, lysozyme, etc. (which form the effector component of the mucous membrane immunity system) for their final inactivation and neutralization.