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PubMed2006

Phenotypic and molecular typing of Vibrio harveyi isolates and their pathogenicity to tiger shrimp larvae.

AIMS: The objective of the present study was to identify the biotype(s) and molecular type(s) of Vibrio harveyi associated with pathogenicity in tiger shrimp (Penaeus monodon) larvae. METHODS AND RESULTS: Five luminescent and four nonluminescent V. harveyi isolates were subjected to phenotyping and random amplified polymorphic DNA (RAPD) fingerprinting, and pathogenicity testing to P. monodon mysis. Four isolates induced 34-41% mortality of P. monodon mysis when challenged at the rate of 10(6) CFU ml(-1) within 60 h. Sucrose-fermenting biotypes of V. harveyi appeared to be associated with pathogenicity to larval shrimp. Higher temperature and salinity appeared to play a role on the onset of vibriosis and mortality in the challenged larval shrimp. Pathogenic isolates of V. harveyi could be demarcated as revealed by their clustering in the dendrogram constructed based on the RAPD fingerprints. CONCLUSIONS: Nonluminescent V. harveyi also appear to be important aetiological agents of vibriosis of shrimp larvae. Sucrose-fermenting biotypes are likely to be pathogenic. High temperature may trigger onset of vibriosis. SIGNIFICANCE AND IMPACT OF THE STUDY: Biotyping of V. harveyi isolates and looking for traits, such as ability to ferment sucrose may be helpful in identifying the pathogenic forms, and such approach requires to be investigated further with larger number of isolates.

Animals↗
PubMed2006

Predicting pathogen introduction: West Nile virus spread to Galáipagos.

Emerging infectious diseases are a key threat to conservation and public health, yet predicting and preventing their emergence is notoriously difficult. We devised a predictive model for the introduction of a zoonotic vector-borne pathogen by considering each of the pathways by which it may be introduced to a new area and comparing the relative risk of each pathway. This framework is an adaptation of pest introduction models and estimates the number of infectious individuals arriving in a location and the duration of their infectivity. We used it to determine the most likely route for the introduction of West Nile virus to Galápagos and measures that can be taken to reduce the risk of introduction. The introduction of this highly pathogenic virus to this unique World Heritage Site could have devastating consequences, similar to those seen following introductions of pathogens into other endemic island faunas. Our model identified the transport of mosquitoes on airplanes as the highest risk for West Nile virus introduction. Pathogen dissemination through avian migration and the transportation of day-old chickens appeared to be less important pathways. Infected humans and mosquitoes transported in sea containers, in tires, or by wind all represented much lower risk. Our risk-assessment framework has broad applicability to other pathogens and other regions and depends only on the availability of data on the transport of goods and animals and the epidemiology of the pathogen.

Animals↗
PubMed1997

Oligonucleotides specific for pathogenic and saprophytic leptospira occurring in water.

Sets of primers specific for both pathogenic (SPL) and saprophytic (SSL) Leptospira were designed from ribosomal 16S genes (rrs) available in databases. They were used as two sets of primer pairs for the PCR amplification of known pathogenic and saprophytic strains. It was possible to identify pathogenic strains by the use of SPL primers and saprophytic ones by SSL primers. Serovars from L. meyeri, of controversial pathogenicity status, confirmed the heterogeneity of the species representatives in this respect. Serovars ranarum, sofia and perameles were amplified by SPL and not SSL. Conversely, serovar semaranga was amplified by SSL and not SPL. In order to use SPL primers for the detection of pathogenic leptospires from a natural water environment, we set up an additional semi-nested PCR by employing a second internal primer which succeeded in detecting as few as 5 pathogenic leptospires per ml of water.

DNA, Bacterial↗
PubMed2001

Characterization of the mutS-proximal region of the Salmonella typhimurium SPI-1 identifies a group of pathogenicity island-associated genes.

The virulence properties of Salmonella enterica are largely encoded within a set of horizontally acquired gene blocks termed pathogenicity islands. One such pathogenicity island, SPI-1, located at centisome 63 of the Salmonella chromosome between the mutS and fhlA genes, encodes a type III protein secretion system and an iron uptake system. We have characterized the mutS-proximal border of this pathogenicity island and have identified two sets of genes, pigAB and pigCD. All four genes have homologs of unknown function in several bacteria that share the ability to establish an intimate association with higher eukaryotic hosts. The expression of at least two of these genes, pigA and pigB, is controlled by SprA, a transcription factor encoded within SPI-1 that controls the expression of genes associated with the type III secretion system of this island. In addition, we found that homologs of the pig genes are also found at different locations of the S. enterica chromosome in association with segments of DNA that exhibit features of pathogenicity islands. The presence of several apparently functional copies of these genes argues for an important role in the biology of this bacterial pathogen. Furthermore, they constitute a valuable tool to identify potential pathogenicity islands.

Animals↗
PubMed2002

Characterization of pathogenic and nonpathogenic strains of Xanthomonas axonopodis pv. manihotis by PCR-based DNA fingerprinting techniques.

Strains of Xanthomonas axonopodis pv. manihotis (Xam) were characterized for pathogenicity and for DNA polymorphism using different PCR-based techniques. Using amplified restriction fragment length polymorphism (AFLP), strains were distinguished from each other and also from other Xanthomonas strains. Cluster analysis showed a high correlation between DNA polymorphism and pathogenicity. Four Xam strains were further analyzed using three PCR-based techniques, AFLP, AFLP-pthB and RAPD-pthB. Various primer combinations were used including primers specific to a Xam pathogenicity gene (pthB) along with RAPD or AFLP primers. The AFLP primer combinations EcoRI+T/MseI+A and EcoRI+T/MseI+T were the most efficient to discriminate among pathogenic and nonpathogenic Xam strains. Polymorphic bands were excised from the gel, amplified and cloned. Sequences analysis showed significant homology with bacterial pathogenicity island, genes involved in pathogenic fitness and regulators of virulence. Three cloned AFLP fragments were used as probes in DNA blot experiments and two of them showed significant polymorphism.

Blotting, Southern↗
PubMedDate not supplied

Respiratory pathogen colonization of the dental plaque of institutionalized elders.

Although it has been established that aspiration of pharyngeal bacteria is the major route of infection in the development of nosocomial pneumonia, colonization of the pharyngeal mucosa by respiratory pathogens has been shown to be a transient phenomenon. It has been suggested that the dental plaque may constitute an additional, possibly more stable, reservoir of respiratory pathogens. The purpose of this study was to assess the prevalence of oral colonization by potential respiratory pathogens in a group of elderly (mean age = 75.9 yrs) chronic-care-facility residents (n = 28) and a group of age-, gender-, and race-matched outpatient control subjects (n = 30), with specific attention to plaque present on tooth, denture, and oral mucosal surfaces. Plaque scores on teeth and dentures were significantly higher in the chronic-care-facility (CCF) subjects than in the dental outpatient control (DOC) subjects (PII 2.3 vs. 1.2 and denture plaque 1.4 vs. 0.3). While no subjects in the DOC group were found to be colonized with respiratory pathogens (> 1.0% of the cultivable aerobic flora), 14.3% (4/28) of the CCF subjects were found to be colonized. Oral colonization with respiratory pathogens in CCF subjects was associated with the presence of chronic obstructive pulmonary disease (COPD) and higher plaque scores. These results suggest that deficient dental plaque control and the presence of COPD may be related to respiratory pathogen colonization of dental plaque in chronic-care-facility residents.

Aged↗
PubMed2002

[Four serotypes highly positive for pathogenic factor-related genes found among Escherichia coli isolates from sporadic diarrheal cases in Fukui Prefecture].

To evaluate the prevalence of pathogenic factor-related genes in 964 O-serotype Escherichia coli isolated from sporadic diarrhea cases at 2 hospitals in Fukui during 1997 to 2001, we checked all of these strains for H-serotype and examined them for 4 pathogenic factor-related genes (LT, ST, stx and invE) by PCR. Of these strains, 409 except for most of 9 serotypes which are usually low prevalence of pathogenic factor-related genes, and additional 16 strains isolated from other hospitals in Fukui Prefecture were also examined for 3 pathogenic factor-related genes (eaeA, astA and aggR) by PCR. It was found that 4 serotypes, O6:H16, O25:HNM, O111:H21 and O126:H27, were highly positive for pathogenic factor-related genes; O6:H16 (11/12 strains) positive for LT, ST, astA, O 25:HNM (10/14 strains) positive for ST and astA, O111:H21 (22/22 strains) positive for astA or aggR, and O126:H27 (8/9) positive for astA and aggR genes. According to the drug susceptibility test, these serotypes as O6:H16, O25:HNM, O111:H21 and O126:H27 showed a significant resistance to some drugs in 7/12, 4/14, 21/22 and 9/9 strains, respectively. Such results indicate that both O111 and O126-serotypes are highly positive for pathogenic factor-related genes and also drug-resistant, namely this fact suggests that the O-serotyping as laboratory screening is one of the useful measures of clinical management. Additionally, the pulsedfied gel electrophoresis patterns found in each of the 4 serotypes mentioned revealed that a part of E. coli in Fukui might be derived from the same source of infection.

Diarrhea↗
PubMed1995

Genetic Diversity among Xanthomonas campestris Strains Pathogenic for Small Grains.

A collection of 51 Xanthomonas campestris strains from throughout the world was studied to detect and assess genetic diversity among pathogens of small grains. Isolates from barley, bread wheat, bromegrass, canary grass, cassava, maize, orchard grass, rice, rough-stalked meadow grass, rye, timothy, and triticale were analyzed by pathogenicity tests on bread wheat cv. Alondra and barley cv. Corona, indirect immunofluorescence, and restriction fragment length polymorphism (RFLP). Three probes were used for the RFLP analysis. They were an acetylaminofluorene-labelled 16S+23S rRNA probe from Escherichia coli and two (sup32)P-labelled restriction fragments from either plasmidic (pBSF2) or chromosomal (pBS8) DNA of X. campestris pv. manihotis. Strains clustered in 9 and 20 groups with the rRNA probe and the pBSF2 DNA probe, respectively. Strains of X. campestris pv. graminis, X. campestris pv. phleipratensis, and X. campestris pv. poae are shown to be related but are also distinguishable by RFLP patterns, serology, and pathogenicity on bread wheat. Strains pathogenic only for barley and not for wheat grouped together. Another group is temporarily designated deviant X. campestris pv. undulosa. These South American isolates from bread wheat did not react by indirect immunofluorescence and produced atypical lesions in pathogenicity tests. The results stress the need to perform pathogenicity tests before strains are named at the pathovar level. The importance of the different probes used for epidemiological studies or phylogenetic studies of closely related strains is underlined.

Journal Article↗
PubMed2005

Monte Carlo simulation of pathogen behavior during the sprout production process.

Food-borne disease outbreaks linked to the consumption of raw sprouts have become a concern over the past decade. A Monte Carlo simulation model of the sprout production process was created to determine the most-effective points for pathogen control. Published literature was reviewed, and relevant data were compiled. Appropriate statistical distributions were determined and used to create the Monte Carlo model with Analytica software. Factors modeled included initial pathogen concentration and prevalence, seed disinfection effectiveness, and sampling of seeds prior to sprouting, sampling of irrigation water, or sampling of the finished product. Pathogen concentration and uniformity of seed contamination had a large effect on the fraction of contaminated batches predicted by the simulation. The model predicted that sprout sampling and irrigation water sampling at the end of the sprouting process would be more effective in pathogen detection than seed sampling prior to production. Day of sampling and type of sample (sprout or water) taken had a minimal effect on rate of detection. Seed disinfection reduced the proportion of contaminated batches, but in some cases it also reduced the ability to detect the pathogen when it was present, because cell numbers were reduced below the detection limit. Both the amount sampled and the pathogen detection limit were shown to be important variables in determining sampling effectiveness. This simulation can also be used to guide further research and compare the levels of effectiveness of different risk reduction strategies.

Colony Count, Microbial↗
PubMed2005

Potential role of Diploscapter sp. strain LKC25, a bacterivorous nematode from soil, as a vector of food-borne pathogenic bacteria to preharvest fruits and vegetables.

Diploscapter, a thermotolerant, free-living soil bacterial-feeding nematode commonly found in compost, sewage, and agricultural soil in the United States, was studied to determine its potential role as a vehicle of Salmonella enterica serotype Poona, enterohemorrhagic Escherichia coli O157:H7, and Listeria monocytogenes in contaminating preharvest fruits and vegetables. The ability of Diploscapter sp. strain LKC25 to survive on agar media, in cow manure, and in composted turkey manure and to be attracted to, ingest, and disperse food-borne pathogens inoculated into soil or a mixture of soil and composted turkey manure was investigated. Diploscapter sp. strain LKC25 survived and reproduced in lawns of S. enterica serotype Poona, E. coli O157:H7, and L. monocytogenes on agar media and in cow manure and composted turkey manure. Attraction of Diploscapter sp. strain LKC25 to colonies of pathogenic bacteria on tryptic soy agar within 10, 20, 30, and 60 min and 24 h was determined. At least 85% of the worms initially placed 0.5 to 1 cm away from bacterial colonies migrated to the colonies within 1 h. Within 24 h, > or =90% of the worms were embedded in colonies. The potential of Diploscapter sp. strain LKC25 to shed pathogenic bacteria after exposure to bacteria inoculated into soil or a mixture of soil and composted turkey manure was investigated. Results indicate that Diploscapter sp. strain LKC25 can shed pathogenic bacteria after exposure to pathogens in these milieus. They also demonstrate its potential to serve as a vector of food-borne pathogenic bacteria in soil, with or without amendment with compost, to the surface of preharvest fruits and vegetables in contact with soil.

Animals↗
PubMed2005

Validity of the indicator organism paradigm for pathogen reduction in reclaimed water and public health protection.

The validity of using indicator organisms (total and fecal coliforms, enterococci, Clostridium perfringens, and F-specific coliphages) to predict the presence or absence of pathogens (infectious enteric viruses, Cryptosporidium, and Giardia) was tested at six wastewater reclamation facilities. Multiple samplings conducted at each facility over a 1-year period. Larger sample volumes for indicators (0.2 to 0.4 liters) and pathogens (30 to 100 liters) resulted in more sensitive detection limits than are typical of routine monitoring. Microorganisms were detected in disinfected effluent samples at the following frequencies: total coliforms, 63%; fecal coliforms, 27%; enterococci, 27%; C. perfringens, 61%; F-specific coliphages, approximately 40%; and enteric viruses, 31%. Cryptosporidium oocysts and Giardia cysts were detected in 70% and 80%, respectively, of reclaimed water samples. Viable Cryptosporidium, based on cell culture infectivity assays, was detected in 20% of the reclaimed water samples. No strong correlation was found for any indicator-pathogen combination. When data for all indicators were tested using discriminant analysis, the presence/absence patterns for Giardia cysts, Cryptosporidium oocysts, infectious Cryptosporidium, and infectious enteric viruses were predicted for over 71% of disinfected effluents. The failure of measurements of single indicator organism to correlate with pathogens suggests that public health is not adequately protected by simple monitoring schemes based on detection of a single indicator, particularly at the detection limits routinely employed. Monitoring a suite of indicator organisms in reclaimed effluent is more likely to be predictive of the presence of certain pathogens, and a need for additional pathogen monitoring in reclaimed water in order to protect public health is suggested by this study.

Animals↗
PubMed2006

Recovery, bioaccumulation, and inactivation of human waterborne pathogens by the Chesapeake Bay nonnative oyster, Crassostrea ariakensis.

The introduction of nonnative oysters (i.e., Crassostrea ariakensis) into the Chesapeake Bay has been proposed as necessary for the restoration of the oyster industry; however, nothing is known about the public health risks related to contamination of these oysters with human pathogens. Commercial market-size C. ariakensis triploids were maintained in large marine tanks with water of low (8-ppt), medium (12-ppt), and high (20-ppt) salinities spiked with 1.0 x 10(5) transmissive stages of the following human pathogens: Cryptosporidium parvum oocysts, Giardia lamblia cysts, and microsporidian spores (i.e., Encephalitozoon intestinalis, Encephalitozoon hellem, and Enterocytozoon bieneusi). Viable oocysts and spores were still detected in oysters on day 33 post-water inoculation (pwi), and cysts were detected on day 14 pwi. The recovery, bioaccumulation, depuration, and inactivation rates of human waterborne pathogens by C. ariakensis triploids were driven by salinity and were optimal in medium- and high-salinity water. The concentration of human pathogens from ambient water by C. ariakensis and the retention of these pathogens without (or with minimal) inactivation and a very low depuration rate provide evidence that these oysters may present a public health threat upon entering the human food chain, if harvested from polluted water. This conclusion is reinforced by the concentration of waterborne pathogens used in the present study, which was representative of levels of infectious agents in surface waters, including the Chesapeake Bay. Aquacultures of nonnative oysters in the Chesapeake Bay will provide excellent ecological services in regard to efficient cleaning of human-infectious agents from the estuarine waters.

Animals↗
PubMed2003

Production of eicosanoids and other oxylipins by pathogenic eukaryotic microbes.

Oxylipins are oxygenated metabolites of fatty acids. Eicosanoids are a subset of oxylipins and include the prostaglandins and leukotrienes, which are potent regulators of host immune responses. Host cells are one source of eicosanoids and oxylipins during infection; however, another potential source of eicosanoids is the pathogen itself. A broad range of pathogenic fungi, protozoa, and helminths produce eicosanoids and other oxylipins by novel synthesis pathways. Why do these organisms produce oxylipins? Accumulating data suggest that phase change and differentiation in these organisms are controlled by oxylipins, including prostaglandins and lipoxygenase products. The precise role of pathogen-derived eicosanoids in pathogenesis remains to be determined, but the potential link between pathogen eicosanoids and the development of TH2 responses in the host is intriguing. Mammalian prostaglandins and leukotrienes have been studied extensively, and these molecules can modulate Th1 versus Th2 immune responses, chemokine production, phagocytosis, lymphocyte proliferation, and leukocyte chemotaxis. Thus, eicosanoids and oxylipins (host or microbe) may be mediators of a direct host-pathogen "cross-talk" that promotes chronic infection and hypersensitivity disease, common features of infection by eukaryotic pathogens.

Animals↗
PubMed2002

Isocitrate lyase is essential for pathogenicity of the fungus Leptosphaeria maculans to canola (Brassica napus).

A pathogenicity gene has been identified in Leptosphaeria maculans, the ascomycetous fungus that causes blackleg disease of canola (Brassica napus). This gene encodes isocitrate lyase, a component of the glyoxylate cycle, and is essential for the successful colonization of B. napus. It was identified by a reverse genetics approach whereby a plasmid conferring hygromycin resistance was inserted randomly into the L. maculans genome. Twelve of 516 transformants tested had reduced pathogenicity on cotyledons of B. juncea and B. napus, and 1 of these 12 had a deletion of the isocitrate lyase gene, as well as an insertion of the hygromycin resistance gene. This mutant was unable to grow on fatty acids, including monolaurate, and the isocitrate lyase transcript was not detected. When the wild-type gene was reintroduced into the mutant, growth on monolaurate was restored and pathogenicity was partially restored. L. maculans isocitrate lyase is produced during infection of B. napus cotyledons, while the plant homologue is not. When 2.5% glucose was added to the inoculum of the isocitrate lyase mutant, lesions of sizes similar to those caused by wild-type isolate M1 developed on B. napus cotyledons. These findings suggest that the glyoxylate pathway is essential for disease development by this plant-pathogenic fungus, as has been shown recently for a fungal and bacterial pathogen of animals and a bacterial pathogen of plants. Involvement of the glyoxylate pathway in pathogenesis in animals and plants presents potential drug targets for control of diseases.

Amino Acid Sequence↗
PubMed1984

Atrophic rhinitis in swine: correlation of Pasteurella multocida pathogenicity with membrane protein and lipopolysaccharide patterns.

Cell envelope proteins and lipopolysaccharides (LPS) of Pasteurella multocida strains associated with atrophic rhinitis in swine were compared by using sodium dodecyl sulfate gel electrophoresis. Among 34 strains, three different types of cell envelope protein patterns, named I (16 strains), II (3 strains), and III (15 strains), could be distinguished. These differences were based on the electrophoretic mobility of the major protein, designated as protein H. Comparison of cell envelope protein type and pathogenicity of the strain, the latter property predicted by the guinea pig skin test, revealed that all type I strains, 6 of 15 type III strains, and none of the type II strains were pathogenic. Although pathogenicity has been correlated with extracellular toxin activity, no protein could be detected in either the cell envelopes or in the extracellular fluid that absolutely correlated with pathogenic strains. Electrophoretic analysis of the LPS revealed that all strains possessed low-molecular-weight LPS, which is inconsistent with the presence of a classical O antigen. The method allowed the detection of at least six types of LPS, which often coincided with a certain cell envelope protein type and with the presence or absence of the pathogenic character of the strain. These results strongly suggest that the sampled swine carry a limited number of P. multocida clones, in each of which the patterns of cell envelope proteins and LPS, as well as the presence or absence of the ability to produce extracellular toxin, are well conserved. Therefore, the possibility is discussed that sodium dodecyl sulfate gel electrophoresis of cell envelope proteins and LPS may be used for the prediction of the pathogenic character of part of the strains. Finally, the typing of strains based on cell envelope protein patterns might contribute to the development of vaccines containing outer membrane proteins as protective antigens.

Animals↗
PubMed1989

Effect of streptomycin administration on association of enteric pathogens with cecal tissue of mice.

The effect of streptomycin on the ability of Shigella sonnei 3SR and enterotoxigenic Escherichia coli 2SR to associate with cecal tissue of mice in vivo and in vitro was examined. After orogastric challenge, both pathogens associated in significantly greater numbers (P less than or equal to 0.05) with the cecal tissue of streptomycin-treated mice than with the tissue of untreated mice. The population levels of the pathogens were also significantly greater (P less than or equal to 0.05) in the cecal contents of streptomycin-treated mice than in untreated mice. When excised cecal tissues from the two groups of mice were exposed to the pathogens in vitro, the extent of the association of the pathogens was markedly greater with tissues from streptomycin-treated mice than with tissues from untreated mice. There was also a positive correlation between the numbers of the pathogens in the suspending fluid and the extent of the tissue associations. The population size of fusiform organisms, which are the major components of the mucus layer of the ceca of mice, was reduced 100-fold by streptomycin administration. This was determined by microscopic count. Sections of cecal tissue obtained from the mice and stained with hematoxylin and eosin demonstrated that streptomycin administration greatly decreased the number of fusiform bacteria present in the mucosal microbial layer. We speculate that the partial elimination of fusiform organisms from this layer by streptomycin administration provides available association sites for pathogens so that they can successfully colonize the mouse cecum.

Animals↗
PubMed1990

Pathogenic and nonpathogenic strains of Entamoeba histolytica can be differentiated by monoclonal antibodies to the galactose-specific adherence lectin.

Entamoeba histolytica infection results in either asymptomatic colonization or invasive colitis and liver abscess. E. histolytica isolates from patients with invasive disease have characteristic isoenzyme profiles (pathogenic zymodemes), suggesting a role for parasite factors in determining the severity of infection. A galactose-specific cell surface lectin from a pathogenic zymodeme was shown to mediate in vitro adherence to human colonic mucins and contact-dependent killing of target cells. Six nonoverlapping antigenic determinants were identified on the 170-kilodalton heavy subunit of the pathogenic lectin. Anti-lectin monoclonal antibodies (MAb) directed against epitopes 1 and 2 enhanced adherence whereas MAb to epitopes 3 through 6 either inhibited or had no effect on adherence. We tested 50 pathogenic and nonpathogenic strains for reactivity to these anti-lectin MAb by radioimmunoassay. MAb to epitopes 1 through 6 reacted in the radioimmunoassay with all 16 pathogenic zymodeme strains tested. In contrast, only MAb to epitopes 1 and 2 bound to the lectin from nonpathogenic strains. Western immunoblots with anti-lectin antibodies showed that the 170-kilodalton heavy subunit was present in the nonpathogenic amebae. Adherence of the nonpathogenic SAW 760 strain to human erythrocytes was enhanced by MAb to epitope 1 and blocked by galactose, confirming the presence of a functionally active lectin. A lectin radioimmunoassay based on MAb to epitopes 1 and 3 proved to be a simple and rapid method to distinguish pathogenic from nonpathogenic amebae in culture. Further exploration of the functional consequences of the antigenic differences demonstrated for the lectin may lead to a better understanding of its role in pathogenesis.

Animals↗
PubMed1996

Outer membrane differences between pathogenic and environmental Yersinia enterocolitica biogroups probed with hydrophobic permeants and polycationic peptides.

Sensitivities to polycationic peptides and EDTA were compared in Yersinia enterocolitica pathogenic and environmental biogroups. As shown by changes in permeability to the fluorescent hydrophobic probe N-phenylnaphthylamine (NPN), the outer membranes (OMs) of pathogenic and environmental strains grown at 26 degrees C in standard broth were more resistant to poly-L-lysine, poly-L-ornithine, melittin, cecropin P1, polymyxin B, and EDTA than Escherichia coli OMs. At 37 degrees C, OMs of pathogenic biogroups were resistant to EDTA and polycations and OMs of environmental strains were resistant to EDTA whereas E. coli OMs were sensitive to both EDTA and polycations. Similar results were found when testing deoxycholate sensitivity after polycation exposure or when isogenic pairs with or without virulence plasmid pYV were compared. With bacteria grown without Ca++ available, OM permeability to NPN was drastically increased in pathogenic but not in environmental strains or E. coli. Under these conditions, OMs of pYV+ and pYV- cells showed small differences in NPN permeability but differences in polycation sensitivity could not be detected by fluorimetry. O:1,6 (environmental type) lipopolysaccharide (LPS), but not O:3 or O:8 LPS, was markedly rough at 37 degrees C, and this could explain the differences in polycation sensitivity. LPSs from serotypes O:3 and O:8 grown at 37 degrees C were more permeable to NPN than O:1,6 LPS, and O:8 LPS was resistant to polycation-induced permeabilization. These data suggest that LPSs relate to some but not all the OM differences described. It is hypothesized that the different OM properties of environmental and pathogenic biogroups reflect the adaptation of the latter biogroups to pathogenicity.

Bacterial Outer Membrane Proteins↗