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PubMed2005

Emerging pathogens: the epidemiology and evolution of species jumps.

Novel pathogens continue to emerge in human, domestic animal, wildlife and plant populations, yet the population dynamics of this kind of biological invasion remain poorly understood. Here, we consider the epidemiological and evolutionary processes underlying the initial introduction and subsequent spread of a pathogen in a new host population, with special reference to pathogens that originate by jumping from one host species to another. We conclude that, although pathogen emergence is inherently unpredictable, emerging pathogens tend to share some common traits, and that directly transmitted RNA viruses might be the pathogens that are most likely to jump between host species.

Journal Article↗

PubMed2005

Community-based monitoring of diarrhea in urban Brazilian children: incidence and associated pathogens.

Community-based monitoring was conducted in order to investigate the occurrence of diarrhea in 'sentinel areas' of Salvador, Brazil, and to establish a preliminary profile of the most common pathogens present in children's diarrhea by screening stool samples. This report describes the results obtained from twice weekly home visits to identify and follow diarrhea episodes and testing of carer-requested stool sample collection over a 6-month period. Participants were selected from a large longitudinal study in 21 areas representing the city's poorer socioeconomic and sanitary conditions. Fecal samples were examined for the presence of pathogenic bacteria, viruses and protozoa. The mean incidence of diarrhea was 4.97 episodes per child-year, and longitudinal prevalence was 13.6 days per child-year (3.7%). Pathogens were found in 44% of the fecal samples examined. Bacteria were the most frequently encountered pathogens (isolated in 22% of samples), followed by protozoa (19.5%) and viruses (16%). Viral and bacterial pathogens were associated with episodes of severe diarrhea, while viral and protozoan pathogens were associated with longer episodes. The study demonstrated the importance of a public health monitoring system based on 'sentinel areas'.

Brazil↗

PubMed1996

Impact of changing pathogens and antimicrobial susceptibility patterns in the treatment of serious infections in hospitalized patients.

The selection of drug-resistant pathogens in hospitalized patients with serious infections such as pneumonia, urinary tract infections (UTI), skin and skin-structure infections, and primary or secondary bacteremia has generally been ascribed to the widespread use of antimicrobial agents. Issues of concern regarding gram-negative bacilli include the expression of extended spectrum beta-lactamase-producing Escherichia coli and Klebsiella pneumonias and constitutive resistance in some Enterobacteriaceae caused by Bush group 1 beta-lactamases. Current concerns with gram-positive pathogens are increasing multidrug resistance in methicillin-resistant Staphylococcus aureus, enterococci, and coagulase-negative staphylococci, and increasing incidence of penicillin-resistant Streptococcus pneumoniae. Contemporary treatment strategies for pneumonia in hospitalized patients mandate early empiric therapy for the most likely gram-positive and gram-negative pathogens. Newer beta-lactams, such as fourth-generation cephalosporins, may be useful in the treatment of pneumonia, including those cases associated with bacteremia. Combination beta-lactam/beta-lactamase inhibitor drugs, an aminoglycoside co-drug, or a carbapenem may also be indicated. The initial treatment of UTI in the hospital setting also may be empirically treated with the newer cephalosporins, combination broad-spectrum penicillins plus an aminoglycoside, a quinolone, or a carbapenem. Current problems in treating UTI include the emergence of extended spectrum beta-lactamase-producing Escherichia coli, the tendency of fluoroquinolones both to select for resistant strains of major UTI pathogens and to induce cross-resistance among different drug classes, and beta-lactam and vancomycin resistance of enterococci and coagulase-negative staphylococci. Treatment of skin and skin-structure infections is complicated by the coexistence of gram-positive and gram-negative infections, which may be drug resistant. Both fourth-generation beta-lactams and carbapenems may have in vitro activity against these pathogens; however, where these drugs--with their increased spectra and lower affinity for beta-lactamases and less susceptibility to beta-lactamase hydrolysis--fit into the therapeutic armamentarium remains to be determined. Initial clinical studies appear to be promising, nonetheless. The ability of both nosocomial and community-acquired pathogens to develop resistance to powerful broad-spectrum agents presents a great challenge for prescribing patterns and in the development of new drugs to be relatively resistant to inactivation.

Anti-Bacterial Agents↗

PubMed1980

Significance of bacteriuria with presumed non-pathogenic organisms.

The results of 2,793 clean catch midstream specimens submitted to the microbiology laboratory were examined to determine if the isolation of reputed non-pathogens such as Lactobacillus, Staphylococcus epidermidis. Micrococcus and diphtheroids represented poor collection technique, contaminant growth by failure to plate or refrigerate quickly or actual urinary tract infection. Eight per cent of the inpatient cultures and 18 per cent of the outpatient cultures had more than 10(5) colony-forming units per ml. of these non-pathogens. Of the outpatient cultures with more than 10(5) colony-forming units per ml. of non-pathogens 44 per cent had symptoms of urinary tract infection and more than 10 white blood cells per high power field in the urinary sediment, compared to 3 per cent of inpatients. In a prospective analysis of an outpatient population a second clean catch midstream specimen was collected within 2 hours of the first specimen with careful attention to sterile collection technique. Of 15 cases of significant bacteriuria with non-pathogens in the first specimen only 1 had significant bacteriuria with the same organism in the second specimen. In contrast, in the inpatient population 7 of 11 cases with pathogen significant bacteriuria in the first specimen had significant bacteriuria in the second specimen. These findings suggest that most episodes involving isolation of non-pathogens in greater than 10(5) colony-forming units per ml. from urine represent poor techniques of specimen collection rather than urinary tract infection.

Bacteria↗

PubMed1997

Insect-pathogen dynamics: stage-specific susceptibility and insect density dependence.

The control of insect pests by using insect pathogens as dynamic biological control agents is a recent effort. Model studies on insect-pathogen relations can help in the development of biocontrol programs. Except for the work of Briggs and Godfray [1], insect-pathogen models ignore the stage-specific susceptibility of insects. Moreover most models do not incorporate insect self-regulation. We develop stage-structured models of insect-pathogen relations incorporating insect-density dependence and disease transmitted through direct contact between susceptible and infective individuals. The models are analyzed by using steady-state and stability analysis. Numerical solutions are used as sources of further insight into the dynamics of the insect-pathogen systems. It is shown that there are major differences in the dynamics of adult- and juvenile-infecting diseases. Moreover, the interplay between insect-density dependence and stage-specific susceptibility has important consequences for the dynamics of insect-pathogen systems.

Agriculture↗

PubMed2002

Role of disinfection in suppressing the spread of pathogens with drinking water: possibilities and limitations.

Transmission of pathogens with drinking water is a widespread problem, which affects not only the countries with low hygienic standards but the industrialized countries as well. The pathogens are excreted by man or animals and are picked up orally. Chlorination of drinking water has been introduced to the water supply in the beginning of the 19th century in order to stop the spreading of pathogens especially typhoid fever by drinking water. Despite the worldwide use of chlorine for disinfection of drinking water, water-mediated disease outbreaks occur again and again. Disinfection of drinking water with chlorine has undoubtedly contributed to the reduction of typhoid fever mortality. However, it must be clear that other factors play an important role in the mortality drop. Filtration of water is a long-known and very effective process for eliminating pathogens from the drinking water. Pathogens in particles cannot be killed sufficiently by a chemical disinfectant. Even small fecal particles have to be eliminated reliably from the water by filtration. Disinfection of drinking water cannot replace filtration. The disinfection should be used to minimize the residual risk due to the presence of pathogens in the water but cannot be used for bringing fecally contaminated water into a hygienically sound condition.

Chlorine↗

PubMed2002

Microarray analysis of bacterial pathogenicity.

The DNA microarray, a surface that contains an ordered arrangement of each identified open reading frame of a sequenced genome, is the engine of functional genomics. Its output, the expression profile, provides a genome wide snap-shot of the transcriptome. Refined by array-specific statistical instruments and data-mined by clustering algorithms and metabolic pathway databases, the expression profile discloses, at the transcriptional level, how the microbe adapts to new conditions of growth--the regulatory networks that govern the adaptive response and the metabolic and biosynthetic pathways that effect the new phenotype. Adaptation to host microenvironments underlies the capacity of infectious agents to persist in and damage host tissues. While monitoring the whole genome transcriptional response of bacterial pathogens within infected tissues has not been achieved, it is likely that the complex, tissue-specific response is but the sum of individual responses of the bacteria to specific physicochemical features that characterize the host milieu. These are amenable to experimentation in vitro and whole-genome expression studies of this kind have defined the transcriptional response to iron starvation, low oxygen, acid pH, quorum-sensing pheromones and reactive oxygen intermediates. These have disclosed new information about even well-studied processes and provide a portrait of the adapting bacterium as a 'system', rather than the product of a few genes or even a few regulons. Amongst the regulated genes that compose this adaptive system are transcription factors. Expression profiling experiments of transcription factor mutants delineate the corresponding regulatory cascade. The genetic basis for pathogenicity can also be studied by using microarray-based comparative genomics to characterize and quantify the extent of genetic variability within natural populations at the gene level of resolution. Also identified are differences between pathogen and commensal that point to possible virulence determinants or disclose evolutionary history. The host vigorously engages the pathogen; expression studies using host genome microarrays and bacterially infected cell cultures show that the initial host reaction is dominated by the innate immune response. However, within the complex expression profile of the host cell are components mediated by pathogen-specific determinants. In the future, the combined use of bacterial and host microarrays to study the same infected tissue will reveal the dialogue between pathogen and host in a gene-by-gene and site- and time-specific manner. Translating this conversation will not be easy and will probably require a combination of powerful bioinformatic tools and traditional experimental approaches--and considerable effort and time.

Animals↗

PubMed2001

Rapid duplex PCR assay for the detection of pathogenic Yersinia enterocolitica strains.

For the detection of pathogenic Yersinia enterocolitica strains, a duplex PCR has been developed based on differences observed between the fingerprint profiles of pathogenic and non-pathogenic strains. The profiles were obtained by using a primer derived from the Enterobacterial Repetitive Intergenic Consensus (ERIC) sequences. From the sequence of one pathogen-specific amplified fragment, a discriminative primer has been designed bridging the sequence of the highly conserved core region and 3' end of the ERIC element. In combination with three other primers, all located within the detected open reading frame that resembled the sequence of the bipA gene, this primer was applied in a duplex PCR assay to simultaneously detect Y. enterocolitica and to discriminate between pathogenic and non-pathogenic strains. The same primer combinations were used in an on line rapid cycling real-time PCR assay. The used SYBR Green I format allowed for the easy translation of the PCR conditions and confirmation of the resulting amplicons. The time of analysis was reduced to approximately 60 min.

Amino Acid Sequence↗

PubMed2003

Towards a unified system for detecting waterborne pathogens.

Currently, there is no single method to collect, process, and analyze a water sample for all pathogenic microorganisms of interest. Some of the difficulties in developing a universal method include the physical differences between the major pathogen groups (viruses, bacteria, protozoa), efficiently concentrating large volume water samples to detect low target concentrations of certain pathogen groups, removing co-concentrated inhibitors from the sample, and standardizing a culture-independent endpoint detection method. Integrating the disparate technologies into a single, universal, simple method and detection system would represent a significant advance in public health and microbiological water quality analysis. Recent advances in sample collection, on-line sample processing and purification, and DNA microarray technologies may form the basis of a universal method to detect known and emerging waterborne pathogens. This review discusses some of the challenges in developing a universal pathogen detection method, current technology that may be employed to overcome these challenges, and the remaining needs for developing an integrated pathogen detection and monitoring system for source or finished water.

Animals↗

PubMed2004

In vitro growth characteristics of five candidate aquaculture probiotics and two fish pathogens grown in fish intestinal mucus.

The selection of probiotics for aquaculture is usually based on their antagonism towards pathogens. However, other criteria such as growth, attachment to intestinal mucus and production of beneficial compounds should also be considered. We suggest a protocol for the isolation and selection of potential probiotic bacteria based on their in vitro growth characteristics and propose a ranking index (RI) to screen potential aquaculture probionts. We suggest that the lag period and doubling time are the most important criteria for the comparison of growth curves, hence the RI is based on the doubling time (t(d)) and lag period (lambda) obtained from the growth profile of each bacterium. Bacteria were isolated from the gut of the common clownfish, Amphiprion percula, and screened for antagonistic activity towards seven aquatic pathogens. All five candidate probiotics showed antagonism to various aquatic pathogens. When grown in intestinal fish mucus no probiotic had a RI higher than the two tested pathogens (Aeromonas hydrophila and Vibrio alginolyticus). However, candidate probiont AP1 had a faster specific growth rate (micro) (0.05) than the pathogens (0.049 and 0.047 respectively), while AP5 grown in marine broth had a shorter lag period than the pathogens. Strategies to increase probiotic concentration include the inoculation of high concentrations and the preconditioning of these bacteria to reduce the lag period. It should be tested whether or not such strategies will allow the probiotic bacteria to dominate initially and thereby gain a competitive advantage. This could become an important aspect under in vivo conditions where both attachment and nutrient supply differ from that found in in vitro studies.

Aeromonas↗

PubMedDate not supplied

Pathogenicity of mollicutes for insects: possible use in biological control.

Acholeplasmas, spiroplasmas and other non-helical sterol-requiring mycoplasmas of unknown phylogenetic affinity inhabit insects. Of these, only spiroplasmas are known to be pathogenic. Group I-2 spiroplasmas, or Spiroplasma apis, especially in combination with other organisms, reduce honey-bee longevity. Plant pathogenic mycoplasma-like organisms are often found intracellularly in insects. Spiroplasmas are found predominantly in the gut lumen or haemolymph (or both) of their insect hosts. Pathogenicity of mycoplasmas is usually altered by extended passage in unusual hosts, in only one of two alternate hosts, or in culture media. Enhancement of experimental pathogenicity may occur with extended cultural passages, but maintenance of natural pathogenicity must be accomplished by continuous exposure to the usual host. Recent data provide new information on the ecology of pathogenicity. Spiroplasmas from unique habitats also tend to be unique. Spiroplasmas isolated from flowers appear to be adapted to insect species that frequent floral surfaces. Group IV spiroplasmas have been isolated from members of 4 holometabolous insect orders (including Lepidoptera), all of which visit flowers. Social or predatory insects, or insects with an "aggregation" phase in their life histories, also appear to be prone to spiroplasma infection. Some insect species which harbor spiroplasmas also carry infections of other mollicutes, some of which involve the haemolymph. Appearance of spiroplasmas in adult insects in nature is strongly affected by seasonality. Extensive tests of the host ranges of the new insect mollicutes will be required before their suitability for biological control can be evaluated.

Acholeplasma↗

PubMed1998

Genetics of plant-pathogen interactions

Progress has occurred in understanding the function of disease-resistance genes that govern the resistance of plants to pathogens, and pathogen-produced molecules, called elicitors, that resistance genes key on. Data support the elicitor-receptor model wherein resistant plants contain receptors for pathogen elicitors. This recognition may be complex, however, involving delivery of elicitors to plant cells by specialized pathogen secretion systems and their processing prior to perception. Furthermore, elicitor receptors may not be the resistance gene proteins that govern specificity of the system. It is now also recognized that many elicitors function as virulence factors for the pathogen but have been co-opted by plants as triggers for active resistance. Major recent advances in the cloning and sequencing of clustered plant disease-resistance genes are providing information on the basis of their recognitional specificities and offer the opportunity to engineer new genes that recognize refractory pathogens or exhibit increased efficacy and durability. In combination with the transformation of cloned disease-resistance genes into new plant species, these approaches should facilitate disease control strategies in practical agriculture.

Journal Article↗

PubMed1999

Novel detection techniques for human pathogens that contaminate poultry.

Poultry products are presumed to be a major contributor to human foodborne illness due to their high frequency of contamination with pathogens Salmonella spp. and Campylobacter spp. This has stimulated the development of more sensitive and rapid methods for identifying pathogens present in poultry. These new methods include immunomagnetic separation of pathogen, PCR amplification of pathogen-specific sequences, pathogen-specific DNA and RNA probes, and identification of pathogen-specific ions by mass spectrometry.

Animals↗

PubMed2002

Sources of pathogens causing pleuropulmonary infections after lung cancer resection.

OBJECTIVE: The source of pathogens responsible for pleuropulmonary complications after lung resection is not yet completely understood, yet knowing this source is very important for proper perioperative use of antibiotics in lung surgery. We studied prospectively the value of sputum samples -- collected 3 days before and 3 days after surgery -- and of intraoperative bronchial swabs in the diagnosis of infective pulmonary complications following lung cancer resection. METHODS: In a prospective trial, we studied 194 patients (18 women and 176 men, age range 34-79 years, mean 57 years) who were operated on for lung cancer. The infection screen consisted of intraoperative bronchial swabs, and sputum samples obtained prior to and 3 days after surgery. Before the operation, all patients were free of clinical signs of respiratory infection. In patients with postoperative infection, causative pathogens were identified from sputum, tracheal aspirate, thoracic puncture and thoracic drainage fluids. RESULTS: Thirty-four patients suffered from 32 pleuropulmonary infections, and two from wound infection. Pathogenic organisms were isolated from preoperative and postoperative sputum samples and from intraoperative bronchial swabs in 50, 64 and 27% of patients, respectively. Postoperative infective complications were caused by gram-negative bacteria and Candida albicans in 75% of patients. These potential pathogens were recovered from preoperative sputum samples and from intraoperative bronchial swabs in only 18 and 13% of cases, but from postoperative sputum samples in 63% of cases. A strong correlation in identified pathogens was found between the postoperative sputum samples and the samples collected for microbiological diagnosis of subsequent postoperative infective complications (P<0.01). CONCLUSIONS: Our results indicate that pathogens that cause pleuropulmonary infective complications are probably acquired postoperatively from the patient's oral cavity, pharynx and hypopharynx. Appropriate antibiotic prophylaxis is discussed.

Adult↗

PubMed2002

Caenorhabditis elegans as a host for the study of host-pathogen interactions.

Recently, pathogenicity models that involve the killing of the genetically tractable nematode Caenorhabditis elegans by human pathogens have been developed. From the perspective of the pathogen, the advantage of these models is that thousands of mutagenized bacterial clones can be individually screened for avirulent mutants on separate petri plates seeded with C. elegans. The advantages of using C. elegans to study host responses to pathogen attack are the extensive genetic and genomic resources available and the relative ease of identifying C. elegans mutants that exhibit altered susceptibility to pathogen attack. The use of Caenorhabditis elegans as the host for a variety of human pathogens is discussed.

Actinomycetales↗

PubMed2006

Occurrence of infected amoebae in cooling towers compared with natural aquatic environments: implications for emerging pathogens.

Many species of bacteria pathogenic to humans, such as Legionella, are thought to have evolved in association with amoebal hosts. Several novel unculturable bacteria related to Legionella have also been found in amoebae, a few of which have been thought to be causes of nosocomial infections in humans. Because amoebae can be found in cooling towers, we wanted to know whether cooling tower environments might enhance the association between amoebae and bacterial pathogens of amoebae in order to identify potential "hot spots" for emerging human pathogens. To compare occurrence of infected amoebae in natural environments with those in cooling towers, 40 natural aquatic environments and 40 cooling tower samples were examined. Logistic regression analysis determined variables that were significant predictors of the occurrence of infected amoebae, which were found in 22 of 40 cooling tower samples but in only 3 of the 40 natural samples. An odds ratio showed that it is over 16 times more likely to encounter infected amoebae in cooling towers than in natural environments. Environmental data from cooling towers and natural habitats combined revealed dissolved organic carbon (DOC) and pH were predictors of the occurrence of the pathogens, however, when cooling tower data alone were analyzed, no variables accounted for the occurrence. Several bacteria have novel rRNA sequences, and most strains were not culturable outside of amoebae. Such pathogens of amoebae may spread to the environment via aerosols from cooling towers. Studies of emerging infectious diseases should strongly consider cooling towers as a source of amoeba-associated pathogens.

Air Conditioning↗

PubMed2006

Hydrologic modeling of pathogen fate and transport.

A watershed-scale fate and transport model has been developed for Escherichia coli and several waterborne pathogens: Cryptosporidiumspp., Giardiaspp., Campylobacter spp, and E. coli O157:H7. The objectives were to determine the primary sources of pathogenic contamination in a watershed used for drinking water supply and to gain a greater understanding of the factors that most influence their survival and transport. To predict the levels of indicator bacteria and pathogens in surface water, an existing hydrologic model, WATFLOOD, was augmented for pathogen transport and tested on a watershed in Southwestern Ontario, Canada. The pathogen model considered transport as a result of overland flow, subsurface flow to tile drainage systems, and in-stream routing. The model predicted that most microorganisms entering the stream from land-based sources enter the stream from tile drainage systems rather than overland transport. Although the model predicted overland transport to be rare, when it occurred, it corresponded to the highest observed and modeled microbial concentrations. Furthermore, rapid increases in measured E. coli concentrations during storm events suggested that the resuspension of microorganisms from stream sediments may be of equal or greater importance than land-based sources of pathogens.

Animals↗

PubMed2002

Toxicity of (+)- and (-)-gossypol to the plant pathogen, Rhizoctonia solani.

The dimeric sesquiterpene gossypol occurs naturally in cottonseed and other parts of the cotton plant. Gossypol exists as enantiomers because of the restricted rotation around the central binaphthyl bond. The (-)-enantiomer is toxic to nonruminant animals while the (+)-enantiomer exhibits little, if any, toxicity to these animals. Developing cotton plants with low levels of the (-)-gossypol could expand the use of cottonseed as a feed source. Gossypol also may play a role in protecting the plant from pathogens. The relative toxicity of (+)- and (-)-gossypol to plant pathogens has not been reported. We measured the concentration of (+)- and (-)-gossypol in roots from cotton seedlings that were treated with the biocontrol agent Trichoderma virens that induces biosynthesis of gossypol and related terpenoids in cotton roots. (-)-Gossypol was the minor enantiomer in control and treated roots, but levels were slightly higher in roots from T. virens-treated seed. We also determined the toxicity of the gossypol enantiomers and the racemate to the seedling disease pathogen Rhizoctonia solani. The (+)- and (-)-enantiomers of gossypol and the racemate are equally effective in inhibiting growth of this pathogen. The lethal doses of the gossypols required to kill the pathogen appeared to be similar, but their toxicities are significantly less than those of related cotton and kenaf sesquiterpenes. The results indicate that altering the enantiomeric ratio in cotton roots will not adversely affect the resistance of seedlings to the seedling pathogen R. solani.

Gossypium↗