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PubMed2002

Transfer of the core region genes of the Yersinia enterocolitica WA-C serotype O:8 high-pathogenicity island to Y. enterocolitica MRS40, a strain with low levels of pathogenicity, confers a yersiniabactin biosynthesis phenotype and enhanced mouse virulence.

The high-pathogenicity island (HPI) of yersiniae encodes an iron uptake system represented by its siderophore yersiniabactin (Ybt). The HPI is present in yersiniae with high levels of pathogenicity--i.e., Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica biogroup (BG) 1B--but absent in Y. enterocolitica strains with low (BG 2 to 5) and no (BG 1A) levels of pathogenicity and has been shown to be an important virulence factor. Comparison of the HPI in Y. enterocolitica (Yen-HPI) and that in Y. pestis and Y. pseudotuberculosis revealed that, in contrast to genes of the variable region, genes of the core region (genes irp9 to fyuA) are highly homologous. In the present work the Yen-HPI core genes were rescued from the chromosome of Y. enterocolitica WA-C (BG 1B, serotype O:8) using the FRT-FLP recombinase system. Transfer of the resulting plasmid pCP1 into the siderophore-deficient strain Y. enterocolitica NF-O (BG 1A) led to no halo on siderophore indicator chrome azurol S (CAS) agar. Transfer of pCP1 into the Y. enterocolitica strain MRS40 (serotype O:9, BG 2; phenotype, CAS negative) led to a CAS halo larger than that of parental strain WA-C, indicating high Ybt production. pCP1 was highly unstable in iron-deficient medium, and no enhanced mouse virulence conferred by MRS40 carrying pCP1 could be detected. To overcome the problem of instability, pCP1 was integrated into the chromosome of MRS40, leading to the formation of a CAS halo comparable to that seen with WA-C and correspondingly to increased mouse virulence. Thus, the core genes of Yen-HPI are sufficient to confer a positive CAS phenotype and mouse virulence to Y. enterocolitica MRS40, BG 2, but are insufficient to confer this phenotype to Y. enterocolitica NF-O, BG 1A.

Animals↗

PubMed2003

Role of virulence factors in resistance of avian pathogenic Escherichia coli to serum and in pathogenicity.

In chickens, colibacillosis is caused by avian pathogenic Escherichia coli (APEC) via respiratory tract infection. Many virulence factors, including type 1 (F1A) and P (F11) fimbriae, curli, aerobactin, K1 capsule, and temperature-sensitive hemagglutinin (Tsh) and plasmid DNA regions have been associated with APEC. A strong correlation between serum resistance and virulence has been demonstrated, but roles of virulence factors in serum resistance have not been well elucidated. By using mutants of APEC strains TK3, MT78, and chi7122, which belong to serogroups O1, O2, and O78, respectively, we investigated the role of virulence factors in resistance to serum and pathogenicity in chickens. Our results showed that serum resistance is one of the pathogenicity mechanisms of APEC strains. Virulence factors that increased bacterial resistance to serum and colonization of internal organs of infected chickens were O78 lipopolysaccharide of E. coli chi7122 and the K1 capsule of E. coli MT78. In contrast, curli, type 1, and P fimbriae did not appear to contribute to serum resistance. We also showed that the iss gene, which was previously demonstrated to increase resistance to serum in certain E. coli strains, is located on plasmid pAPEC-1 of E. coli chi7122 but does not play a major role in resistance to serum for strain chi7122.

Animals↗

PubMed2003

Pathogenic potential of environmental Vibrio cholerae strains carrying genetic variants of the toxin-coregulated pilus pathogenicity island.

The major virulence factors of toxigenic Vibrio cholerae are cholera toxin (CT), which is encoded by a lysogenic bacteriophage (CTXPhi), and toxin-coregulated pilus (TCP), an essential colonization factor which is also the receptor for CTXPhi. The genes for the biosynthesis of TCP are part of a larger genetic element known as the TCP pathogenicity island. To assess their pathogenic potential, we analyzed environmental strains of V. cholerae carrying genetic variants of the TCP pathogenicity island for colonization of infant mice, susceptibility to CTXPhi, and diarrheagenicity in adult rabbits. Analysis of 14 environmental strains, including 3 strains carrying a new allele of the tcpA gene, 9 strains carrying a new allele of the toxT gene, and 2 strains carrying conventional tcpA and toxT genes, showed that all strains colonized infant mice with various efficiencies in competition with a control El Tor biotype strain of V. cholerae O1. Five of the 14 strains were susceptible to CTXPhi, and these transductants produced CT and caused diarrhea in adult rabbits. These results suggested that the new alleles of the tcpA and toxT genes found in environmental strains of V. cholerae encode biologically active gene products. Detection of functional homologs of the TCP island genes in environmental strains may have implications for understanding the origin and evolution of virulence genes of V. cholerae.

Animals↗

PubMed2005

Molecular characterization of a widespread, pathogenic, and antibiotic resistance-receptive Enterococcus faecalis lineage and dissemination of its putative pathogenicity island.

Enterococcus faecalis, a common cause of endocarditis and known for its capacity to transfer antibiotic resistance to other pathogens, has recently emerged as an important, multidrug-resistant nosocomial pathogen. However, knowledge of its lineages and the potential of particular clones of this species to disseminate and cause disease is limited. Using a nine-gene multilocus sequence typing (MLST) scheme, we identified an evolving and widespread clonal complex of E. faecalis that has caused outbreaks and life-threatening infections. Moreover, this unusual clonal complex was found to contain isolates of unexpected relatedness, including the first known U.S. vancomycin-resistant enterococcus (E. faecalis strain V583), the first known penicillinase-producing (Bla(+)) E. faecalis isolate, and the previously described widespread clone of penicillinase producers, a trait found in <0.1% of E. faecalis isolates. All members of this clonal cluster (designated as BVE for Bla(+) Van(r) endocarditis) were found to contain a previously described putative pathogenicity island (PAI). Further analysis of this PAI demonstrated its dissemination worldwide, albeit with considerable variability, confirmed its association with clinical isolates, and found a common insertion site in different clonal lineages. PAI deletions, MLST, and the uncommon resistances were used to predict the evolution of the BVE clonal cluster. The finding of a virulent and highly successful clonal complex of E. faecalis with different members resistant to the primary therapies of choice, ampicillin and vancomycin, has important implications for the evolution of virulence and successful lineages and for public health monitoring and control.

Bacterial Proteins↗

PubMed1976

Attenuation of pathogenicity of fowl plague virus by recombination with other influenza A viruses nonpathogenic for fowl: nonexculsive dependence of pathogenicity on hemagglutinin and neuraminidase of the virus.

A number of antigenic hybrids of influenza A viruses were produced possessing either the hemagglutinin or the neuraminidase of fowl plague virus and the corresponding antigen derived from another influenza A virus. Other recombinants were obtained carrying both surface antigens of fowl plague virus but differing from the parent in certain biological properties. None of the recombinants isolated were pathogenic for adult chickens. Most recombinants obtained after crosses between reciprocal recombinants carrying both fowl plague virus surface antigens were also apathogenic for chickens. Using the same parent recombinants for double infection some of the progeny "back-recombinants" were pathogenic, whereas others were not. From these results it is concluded that the surface components do not by themselves determine the pathogenicity of influenza A viruses.

Animals↗

PubMed1995

Antibiotic susceptibility of the sputum pathogens and throat swab pathogens isolated from the patients undergoing treatment in twenty-one private clinics in Japan.

Bacteriology of the respiratory isolates from 2,539 patients with respiratory infections in 21 primary care clinics was documented. Of a total of 1,887 strains of potential pathogens recovered from 1,507 patients, 996 were gram-positive and 891 were gram-negative. Major pathogens were Staphylococcus aureus, Haemophilus influenzae, Streptococcus pneumoniae and Streptococcus pyogenes. The MIC's against microbial isolates of six antimicrobial agents were determined. Ciprofloxacin and ofloxacin were more active against S. aureus, Moraxella catarrhalis and Pseudomonas aeruginosa, and ampicillin and cefteram were more active against S. pnuemoniae and S. pyogenes than four other antimicrobials tested, respectively, in this experiment. New quinolones and new generation cephems were active against H. influenzae and Enterobacteriaceae. Only one strain of S. aureus was methicillin-resistant. As regards other pathogens, 6.5% of S. pneumoniae and 14.9% of H. influenzae were resistant to ampicillin, and 26.7% of H. influenzae were beta-lactamase-positive. MRSA was found infrequently. But ampicillin-resistant S. pneumoniae and H. influenzae were found in primary care clinics almost as frequently as in intensive-medication-oriented clinics.

Adolescent↗

PubMed2005

Pathogenic bacteria isolated from disease outbreaks in shellfish hatcheries. First description of Vibrio neptunius as an oyster pathogen.

Shellfish hatcheries are often affected by disease outbreaks. Three such episodes were investigated in different Galician hatcheries in order to establish the relationship between present microbiota and mortalities. Isolates were obtained from various parts of the hatcheries. Experimental tests for pathogenicity were carried out in microscale experiments using selected strains on Ostrea edulis larvae. The pathogenicity of 1 strain from each outbreak was demonstrated and shown to cause high mortalities (ranging from 98.5 to 100%) in 72 to 96 h after inoculation of larval cultures. All 3 strains belong to the genus Vibrio. One of the strains was identified as Vibrio neptunius and is the first description of this species as a molluscan pathogen. The other 2 strains showed low similarity with the Vibrio species analysed and may constitute new species within this genus.

Animals↗

PubMed1992

Protecting workers from pathogens. Employers must act now to comply with OSHA's new standard on bloodborne pathogens.

A new standard set forth by the Occupational Safety and Health Administration (OSHA) requires healthcare employers to implement sweeping new controls in areas such as record keeping, engineering, hazard prevention, and work practice. Through the bloodborne pathogen standard, which went into effect on March 6, OSHA acknowledges that healthcare workers face significant health risks as a result of occupational exposure to blood and other infectious materials. Although most prudent healthcare providers already adhere to the Centers for Disease Control's universal precautions, the OSHA regulations include several additional mandatory measures that are more specific and stringent. The additional measures include the development of an exposure control plan, procedures for responding to an employee's exposure to bloodborne pathogens, the implementation of certain engineering and work practice controls to eliminate or minimize on-the-job exposure risks, and the provision of personal protective equipment and information and training programs. OSHA estimates that the greatest cost component of implementing procedures to bring a facility into compliance is attributable to the purchase of personal protective equipment. Although the costs of compliance are substantial, OSHA has estimated that these costs represent less than 1 percent of the healthcare industry's annual revenues. Violation of the bloodborne pathogen standard may result in penalties of up to $70,000, depending on the severity of the infraction. Criminal penalties are also possible for willful violations that result in worker death.

Blood↗

PubMed1999

[Genetic control of Vibrio cholerae pathogenicity: the temperate filamentous phage CTX, coding for cholera toxin and the "island of pathogenicity"].

Reviews modern data on the genetic control of the key factors of Vibrio cholerae pathogenicity: cholera toxin and toxin-coregulated adhesion pili. Pays special attention to the temperate filamentous CTX bacteriophage, whose genome contains structural genes of cholera toxin, and the "pathogenicity island" carrying tcp genes responsible for the most important factor of the human small intestine colonization with V. cholerae. Discusses the mechanism of coordinated regulation of the activity of the main genes of V. cholerae pathogenicity genes.

Bacteriophages↗

PubMed2002

Effects of aerobic and anaerobic digestion systems on pathogen and pathogen indicator reduction in municipal sludge.

In this study, the effectiveness of anaerobic treatment systems in reducing pathogenic density levels was evaluated under the US EPA municipal sludge rule (40 CFR Part 503 Rule). Wastewater and sludge samples were analyzed for both pathogens and pathogenic indicator organisms from six different existing wastewater treatment systems. The results indicate that Class B sludge requirements under the US 503 Rule are reasonable and can be achievable by the existing treatment systems while Class A sludge requirements under the same rule may not be easily achieved by the existing treatment systems. The effects of volatile solids loading rates on anaerobic digester performance were investigated. Under anaerobic digestion conditions, it appears that the log reductions in fecal coliform and fecal streptococcus appeared to be dependent on VSS loading rates. On the other hand, Salmonella sp. density reductions did not appear to be dependent on VSS loading rates.

Bacteria, Aerobic↗

PubMed2005

Biofilms in an urban water distribution system: measurement of biofilm biomass, pathogens and pathogen persistence within the Greater Stockholm Area, Sweden.

Distribution pipe biofilms can provide sites for the concentration of a wide range of microbial pathogens, thereby acting as a potential source of continual microbial exposure and furthermore can affect the aesthetic quality of water. In a joint project between Stockholm Water, the MISTRA "Sustainable Urban Water" program, the Swedish Institute for Infectious Disease Control and the Royal Technical University, Stockholm, the aim of the current study was to investigate biofilms formed in an urban water distribution system, and quantify the impact of such biofilms on potential pathogen accumulation and persistence within the Greater Stockholm Area, Sweden. When used for primary disinfection, ultra-violet (UV) treatment had no measurable influence on biofilm formation within the distribution system when compared to conventional chlorination. Biofilms produced within a model pilot-plant were found to be representative to those that had formed within the larger municipal water distribution system, demonstrating the applicability of the novel pilot-plant for future studies. Polystyrene microspheres (1.0 microm) and Salmonella bacteriophages demonstrated their ability to accumulate and persist within the model pilot-plant system, where the means of primary disinfection (UV-treatment, chlorination) had no influence on such phenomena. With the exception of aeromonads, potential pathogens and faecal indicators could not be detected within biofilms from the Stockholm water distribution system. Results from this investigation may provide information for water treatment and distribution management strategies, and fill key data gaps that presently hinder the refinement of microbial risk models.

Aeromonadaceae↗

PubMed1990

[Pneumonia in AIDS: pathogen spectrum and diagnostic value of various fiberoptic bronchoscopy methods for the detection of pathogens].

39 fibre-bronchoscopic examinations were performed prospectively in 29 AIDS-patients with pneumonia. Specimens were obtained from the central bronchial system with a protected brush and by suction, from the infiltrated peripheral area by catheter suction, protected brush, bronchoalveolar lavage (BAL) and transbronchial biopsy in randomized order. In patients with non-bacterial pneumonia, pneumocystis carinii (n = 20) was the most frequent pathogen. In this group BAL had a significantly higher rate of pathogen detection than other techniques. In patients with bacterial pneumonia (n = 10) the pathogens were found in all cases by suction from the central bronchial system. Fibre-bronchoscopy in patients with AIDS and pneumonia should include specimens from the central bronchial system and a bronchoalveolar lavage.

Acquired Immunodeficiency Syndrome↗

PubMed1987

Superiority of the chimpanzee animal model to study the pathogenicity of known Mycoplasma pneumoniae and reputed mycoplasma pathogens.

As far as we know, humans are the only known natural hosts for M. pneumoniae disease. Whereas volunteer studies have provided useful data on the pathogenesis of disease and efficacy of vaccines, experimentally inducing disease in humans raises serious ethical questions and has become increasingly difficult to defend. Thus, there is a genuine need for a satisfactory animal model to study M. pneumoniae disease. Using the cotton rat and developing chick embryo models, Eaton and co-workers (9-13) have clearly shown that the infectious "Eaton agent" was the cause of primary atypical pneumonia. After the causative agent was identified as M. pneumoniae (14), more definite and quantitative studies were possible. The hamster animal model has provided most of our information on the pathogenicity of strains, the pathogenesis of disease and the potency of inactivated vaccines. However, protective data obtained in hamsters immunized with the TS mutant vaccines did not correlate with data obtained in humans, raising concern regarding the use of the hamster animal model to evaluate the potency of live TS vaccines. The chimpanzee animal model has a number of advantages. Chimpanzees become clinically ill, show positive X-ray findings, and develop cold agglutinin titers. In fact, the experimentally induced disease in chimpanzees is remarkably similar to naturally occurring primary atypical pneumonia in patients. Because of the close genomic relationship, immunologic reagents prepared and used for human studies can also be used successfully in chimpanzee studies. The chimpanzee model also has some serious disadvantages. They are expensive to house and maintain and are generally not available to the scientific community. Nonetheless, chimpanzees are probably the best, most meaningful animal models established thus far to examine the infectious process, the immune response and the pathogenesis of this disease and to determine approaches to effective therapy and immunization of diseases produced by known pathogens, like M. pneumoniae, as well as reputed mycoplasma pathogens, such as M. genitalium and M. hominis.

Animals↗

PubMed1996

A conceptual framework to assess the risks of human disease following exposure to pathogens. ILSI Risk Science Institute Pathogen Risk Assessment Working Group.

Currently, risk assessments of the potential human health effects associated with exposure to pathogens are utilizing the conceptual framework that was developed to assess risks associated with chemical exposures. However, the applicability of the chemical framework is problematic due to many issues that are unique to assessing risks associated with pathogens. These include, but are not limited to, an assessment of pathogen/host interactions, consideration of secondary spread, consideration of short- and long-term immunity, and an assessment of conditions that allow the microorganism to propagate. To address this concern, a working group was convened to develop a conceptual framework to assess the risks of human disease associated with exposure to pathogenic microorganisms. The framework that was developed consists of three phases: problem formulation, analysis (which includes characterization of exposure and human health effects), and risk characterization. The framework emphasizes the dynamic and iterative nature of the risk assessment process, and allows wide latitude for planning and conducting risk assessments in diverse situations, each based on the common principles discussed in the framework.

Disease↗

PubMed1998

Differentiation of pathogenic and non-pathogenic Entamoeba: has the question been answered?

Pathogenic and non-pathogenic Entamoeba have been separated into two distinct species. Recently, the non-pathogenic E. dispar has been cultivated axenically. However, the genetic variability among different clones from the same strain, experimental production of hybrid clones which may differ from their parents, and the possibility of invasiveness of E. dispar, are some phenomena which may indicate that the last word on distinctiveness of the species has not yet been said.

Animals↗

PubMed1992

The pathogenicity of Ab4p, the sequenced strain of equine herpesvirus-1, in specific pathogen-free foals.

The sequencing of the genome of equine herpesvirus-1 (EHV-1) is reported in Elizabeth A. R. Telford, Moira S. Watson, Kathryn McBride, and Andrew J. Davison, 1992, Virology, 189, 304-316. The sequence was derived using a plaque-purified clone of EHV-1 strain Ab4 (designated Ab4p). To ensure that Ab4p shares the pathogenic characteristics of parental Ab4 (hereafter Ab4), both were inoculated intranasally into foals, specifically free from EHV-1 and EHV-4. Clinical signs, including rectal temperature, were similar for both viruses. In addition, nasal shedding of virus was observed over a 1- to 2-week period postinfection, and viremia was established with both Ab4 and Ab4p. Isolation of virus from one foal following intravenous administration of steroids indicates that Ab4p can establish latency and undergo reactivation. Finally, retinal lesions were observed and these were similar to those seen with Ab4. In conclusion, several pathogenic characteristics of Ab4 are retained in the plaque-purified clone, Ab4p.

Animals↗

PubMed1998

Evaluation of day-old specific pathogen-free chicks as an experimental model for pathogenicity testing of intestinal spirochaete species.

Specific pathogen-free chicks aged 1 day were challenged per os with strains of five different species of intestinal spirochaete originally isolated from pigs or human beings. A virulent strain of Serpulina hyodysenteriae (WA 15) colonized chicks, causing retarded growth rate and histological changes, including caecal atrophy, epithelial and goblet cell hyperplasia, and crypt elongation. A further strain of S. hyodysenteriae (SA3), which was apparently avirulent for pigs, and a strain of Serpulina intermedia (889) colonized fewer chicks, caused less severe lesions and did not significantly depress growth rate. Strains of Serpulina murdochii and Brachyspira aalborgi failed to colonize or cause histological changes. Four strains of Serpulina pilosicoli (Kar, Rosie-2299 and GAP 401, isolated from human beings, and 3295, isolated from a pig) colonized chicks, and large numbers showed polar attachment to the caecal epithelium; all strains, apart from Rosie-2299, caused watery diarrhoea and wet litter, but did not significantly retard growth. Variation both in the degree of spirochaetal attachment and the resulting development of lesions was observed between S. pilosicoli strains as well as between individual chicks infected with the same strain. The study indicated that chicks may be useful in studying the pathogenicity of strains of S. hyodysenteriae, S. intermedia and S. pilosicoli.

Animals↗

PubMed1993

Pathogenicity of a thymidine kinase-deficient mutant of equine herpesvirus 1 in mice and specific pathogen-free foals.

Both intranasal (i.n.) and intracerebral (i.c.) inoculation of mice with wild-type equine herpesvirus type 1 (wt EHV-1) caused clinical signs and mortality. Virus could be recovered from target organs (turbinates, lungs and blood) for several days. By contrast, the thymidine kinase (TK)-deficient deletion mutant PR1 produced markedly less clinical disease following both i.n. and i.c. inoculation, and, in particular, no mortality occurred. PR1 did, however, establish productive infections following either route of inoculation. High titres of virus were recovered from target organs although virus did not persist for as long as wt EHV-1 and no viraemia was detected. Primary i.n. infection of mice with either wt EHV-1 or PR1 protected against subsequent challenge with wt EHV-1 5 weeks later. I.n. inoculation of specific pathogen-free (EHV-free) foals with PR1 produced results similar to those observed after infection of mice. Clinical signs were milder than for wt EHV-1 and pyrexia was short-lived or absent. PR1 could be recovered from nasal mucus at high titres but it persisted for only 5 days post-infection compared to 11 days in the case of wt EHV-1. No viraemia was detected in foals infected with PR1. On challenge with wt EHV-1, foals given a primary infection with the mutant were partially protected; but a viraemia with a TK+ EHV-1 was observed. These results demonstrate that our TK- mutant PR1 is markedly less pathogenic than wt EHV-1, despite being able to replicate in the host. The use of TK-deficient mutants of EHV-1 as potential vaccines in the horse is discussed.

Animals↗