Rapid and effective method for preparation of fecal specimens for PCR assays

Epidemiology and antimicrobial resistance of toxin-producing Klebsiella oxytoca clinical isolates from children admitted to the oncology chemotherapy center in Mofid Children's Hospital in Tehran, Iran: A cross-sectional study

Background and Aims

Klebsiella oxytoca (K. oxytoca) is the second bacterial cause of nosocomial infections in the general population after K. pneumoniae. This study surveyed the frequency of cytotoxin-producing strains of K. oxytoca and their antibiotic susceptibility profile in a cohort of children admitted to a referral hospital with different malignancies.

Methods

The Stool samples of children admitted to the Cancer Chemotherapy Unit of the Mofid Children's Hospital, Tehran, Iran were analyzed using conventional biochemical tests and polymerase chain reaction targeting the pehX gene to identify K. oxytoca. The antibiotic susceptibility profile of isolated K. oxytoca against commonly prescribed antibiotics used in treating infection at the facility was determined using the Kirby-Bauer disk diffusion technique. Also, the prevalence of genes encoding toxins among K. oxytoca was identified by PCR assay.

Results

The Stool samples of 280 participants were taken for the study of which 38 samples [(55.3% (21/38) 42 males and 44.7% (17/38) females)] tested positive for various Klebsiella spp. Out of this, K. oxytoca was identified in 2.5% (7/280) stools using cultures and conventional biochemical tests. Also, the stools of 2.9% (8/280) of the participants tested positive for K. oxytoca using PCR assay. Using PCR, (2/7) of the K. oxytoca isolates tested positive for the npsA and npsB genes and were identified as toxigenic K. oxytoca strains.

Conclusion

The prevalence of toxin-producing K. oxytoca strains in stool samples of children diagnosed with cancer in Iran is relatively low. Most of the K. oxytoca isolates were susceptible to tested antibiotics. Globally, active surveillance of toxigenic K. oxytoca strains in patients with different malignancies or immunocompromised patients is recommended in healthcare settings.

Evaluation of a New Device for Simplifying and Standardizing Stool Sample Preparation for Viral Molecular Testing with Limited Hands-On Time

Sensitive molecular assays have greatly improved the diagnosis of viral gastroenteritis. However, the proper preparation of stool samples for clinical testing remains an issue. bioMérieux has developed a stool preprocessing device (SPD) that includes a spoon for calibrated sampling and a vial containing buffer, glass beads, and two filters. The resulting stool filtrate is used for nucleic acid extraction. The purpose of this study was to evaluate the performance of the SPD for the quantification of human adenovirus (HAdV) DNA in stool samples collected from hematopoietic stem cell transplant (HSCT) recipients. HAdV DNA was quantified with the Adenovirus R-gene kit. The suitability of the device to reproducibly quantify HAdV DNA in stools using different extraction platforms (easyMAG and QIAsymphony) was determined using archived HAdV-positive stool samples. Coefficients of variation of HAdV DNA quantifications ranged from 1.79% to 1.83%, and no difference in quantification was observed between the two extraction systems. The HAdV DNA limit of quantification using the SPD was 3.75 log10copies/g of stool. HAdV DNA quantification using the SPD was then compared to that of the routine preprocessing technique on 75 fresh stool samples collected prospectively from pediatric HSCT recipients at risk for HAdV infections. Thirty-eight samples were HAdV DNA positive with both the SPD and routine preprocessing methods. HAdV DNA loads were on average 1.14-log10copies/g of stool higher with the SPD (P< 0.0001) than with routine methods. This new device enabled a standardized preparation of stool samples in <5 min and a reproducible and sensitive quantification of HAdV DNA. The use of the SPD for the detection of other gastrointestinal infections warrants further evaluation.

Development of a PCR assay for the detection of Spironucleus muris

Spironucleus muris is a protozoan that can colonize the intestinal tract of many rodent species. Although its effects on animal health and research are debated, S. muris is often included on exclusion lists for rodent facilities. Common diagnostic tests for S. muris are insensitive and typically are performed at postmortem examination. We sought to develop a PCR-based diagnostic test with sufficient sensitivity and specificity for use on fecal samples from live rodents. We designed and optimized a PCR assay that targeted the 16S-like rRNA gene of S. muris. The assay was highly specific, given that samples from mice contaminated with S. muris were PCR positive, whereas samples from mice contaminated with other protozoa were negative. The assay also was highly sensitive, detecting as few as 5 template copies per microliter diluent. All mice positive for S. muris on postmortem exams also were positive by fecal PCR. Moreover, S. muris was detected by PCR in mice negative by postmortem examination but from colonies known to be contaminated as well as in rats and hamsters. To assess protozoal loads in mice of differing ages, the PCR assay was adapted to a quantitative format. Fecal loads of S. muris were highest in 4-wk-old mice and declined with age. The PCR assay developed promises to be a highly specific antemortem diagnostic assay with higher sensitivity than that of existing postmortem tests.

Comparison of selective agars recommended by method ISO 11290-1 and chromogenic agars for the isolation of Listeria sp. in refrigerated sausages

The aim of this study was to determine the prevalence of Listeria sp. in refrigerated sausages, and to compare the performance of the selective plating media employed in the ISO 11290-1 method (PALCAM and Oxford agars) with chromogenic agars (Chromogenic Listeria agars CM 1080 (OCLA) and CM 1084). The prevalence of Listeria sp. detected was 52.9%, comprising 13.7% L. monocytogenes strains. The efficacy of the four agars for the isolation of L. monocytogenes proved to be satisfactory. Despite differences in composition of the chromogenic media assessed, these disparities did not affect concordance among results. However, PALCAM agar was shown to suppress other microorganisms more effectively, being more applicable for detecting Listeria strains present in lower quantities. Based on these results, the use of PALCAM agar, in combination with a chromogenic media, is recommended for enhanced isolation of atypical Listeria sp. strains in meat products.

Simultaneous detection of Clostridium perfringens and Clostridium colinum by duplex-polymerase chain reaction

In this study, we provide a protocol for detection of Clostridium colinum and Clostridium perfringens by the single-tube duplex-PCR (dPCR) test for simultaneous and specific detection of both bacteria from pure cultures and fecal samples spiked with these pathogens. Specific primers for each pathogen were selected that amplified products of predicted sizes from bacteria in the dPCR as well as in the single-tube PCR (sPCR) assays. The sensitivity and specificity of dPCR assay were compared with those of the sPCR. No product amplification was obtained with DNA from reference strains belonging to the genus Clostridium (except C. colinum and C. perfringens) and isolates belonging to other genera using these primer sets. The dPCR assay was as sensitive as the sPCR assay because bacterial detection limits were similar in both assays. The detection limits of sPCR and dPCR in bacterial suspension were 20 and 25 cfu/mL for C. colinum and C. perfringens, respectively. Meanwhile, in the presence of feces the sensitivity of both assays decreased to a detection limit of 1.25 × 10(4) and 1.94 × 10(4) cfu/g of feces for C. colinum and C. perfringens, respectively. In summary, dPCR assay holds potential to be an economical and rapid diagnostic method for the simultaneous detection of C. colinum and C. perfringens in pure cultures and could be used to screen fecal samples for the presence of these pathogens.

Genetic analysis of H1N1 influenza virus from throat swab samples in a microfluidic system for point-of-care diagnostics

The ability to obtain sequence-specific genetic information about rare target organisms directly from complex biological samples at the point-of-care would transform many areas of biotechnology. Microfluidics technology offers compelling tools for integrating multiple biochemical processes in a single device, but despite significant progress, only limited examples have shown specific, genetic analysis of clinical samples within the context of a fully integrated, portable platform. Herein we present the Magnetic Integrated Microfluidic Electrochemical Detector (MIMED) that integrates sample preparation and electrochemical sensors in a monolithic disposable device to detect RNA-based virus directly from throat swab samples. By combining immunomagnetic target capture, concentration, and purification, reverse-transcriptase polymerase chain reaction (RT-PCR) and single-stranded DNA (ssDNA) generation in the sample preparation chamber, as well as sequence-specific electrochemical DNA detection in the electrochemical cell, we demonstrate the detection of influenza H1N1 in throat swab samples at loads as low as 10 TCID(50), 4 orders of magnitude below the clinical titer for this virus. Given the availability of affinity reagents for a broad range of pathogens, our system offers a general approach for multitarget diagnostics at the point-of-care.

Flock-level prevalence of Clostridium colinum in broiler flocks with digestive disease in Jordan by polymerase chain reaction

A cross-sectional study was conducted from May to September of the year 2008 in broiler flocks in the southern and northern area of Jordan, to determine the flock-level prevalence of Clostridium colinum infection. Intestinal swabs were collected from 170 broiler flocks and tested by PCR. Among the study population, 20 flocks in both areas (11.8%, 95% confidence interval: 10 to 22%) were positive for C. colinum infection. The prevalence of positive intestinal samples in the southern and northern area of Jordan were 4.7 and 7.1%, respectively, which was statistically significant (chi(2) = 3.9 df = 1, P = 0.0482). It is recommended to conduct further epidemiologic studies to determine risk factors and to evaluate the economic consequences of the C. colinum infection in the region.

Flotation-A New Method to Circumvent PCR Inhibitors in the Diagnosis of Lawsonia intracellularis

The obligate intracellular bacterium Lawsonia intracellularis causes enteritis and poor growth in weaned pigs. Cultivation is difficult and diagnosis ante mortem is mainly based on techniques such as polymerase chain reaction. However, false negative results caused by the presence of PCR-inhibitory factors constitute a problem. This study aimed to develop and evaluate a new technique, flotation, to separate L. intracellularis from inhibitors in faeces prior to PCR. The technique was evaluated by comparison to two previously evaluated and commonly used methods, preparation by boiling lysate combined with nested PCR and preparation by a commercial kit combined with conventional PCR. Continuous density centrifugation of faecal samples containing L. intracellularis suggested the buoyant density of the microbe to be between 1.064 and 1.077 g/mL. Several flotation setups were tested to achieve optimal separation of the microbe from inhibitors and faecal particles. The finally selected setup floated whole L. intracellularis from the application site at the bottom to the upper part of the gradient while inhibitory components mainly remained in the bottom. PCR was performed directly on material recovered from the upper interphase. The method was evaluated on 116 clinical samples. As compared to sample preparation by boiling combined with nested PCR, fewer samples were inhibited but also fewer positives were identified. In comparison to preparation by a commercial kit combined with conventional PCR, presently used for routine diagnosis, similar results were obtained. However, the new method was comparably faster to perform. The new method, based on flotation of Lawsonia intracellularis combined with conventional PCR, was well suited for routine diagnosis.

Spread of infectious chronic bee paralysis virus by honeybee (Apis mellifera L.) feces

Knowledge of the spreading mechanism of honeybee pathogens within the hive is crucial to our understanding of bee disease dynamics. The aim of this study was to assess the presence of infectious chronic bee paralysis virus (CBPV) in bee excreta and evaluate its possible role as an indirect route of infection. Samples of paralyzed bees were (i) produced by experimental inoculation with purified virus and (ii) collected from hives exhibiting chronic paralysis. CBPV in bee heads or feces (crude or absorbed onto paper) was detected by reverse transcription-PCR. CBPV infectivity was assessed by intrathoracic inoculation of bees with virus extracted from feces and by placement of naive bees in cages previously occupied by contaminated individuals. CBPV RNA was systematically detected in the feces of naturally and experimentally infected bees and on the paper sheets that had been used to cover the floors of units containing bees artificially infected with CBPV or the floor of one naturally infected colony. Both intrathoracic inoculation of bees with virus extracted from feces and placement of bees in contaminated cages provoked overt disease in naive bees, thereby proving that the excreted virus was infectious and that this indirect route of infection could lead to overt chronic paralysis. This is the first experimental confirmation that infectious CBPV particles excreted in the feces of infected bees can infect naive bees and provoke overt disease by mere confinement of naive bees in a soiled environment.

Monitoring and characterization of extended-spectrum beta-lactamases in Escherichia coli strains from healthy and sick animals in Spain in 2003

Genes encoding CTX-M-14, CTX-M-9, CTX-M-1, CTX-M-32, SHV-12, TEM-52, or CMY-2 beta-lactamases were detected in 21 Escherichia coli strains recovered during 2003 from sick animals (11 of 459 [2.4%] strains) and healthy animals (10 of 158 [6.3%] strains) in Spain. Twelve of these strains harbored bla(CTX-M) genes and showed unrelated pulsed-field gel electrophoresis patterns.

Genotypes and phenotypes of Shiga toxin producing-Escherichia coli isolated from healthy cattle in Thailand

Shiga toxin producing-Escherichia coli (STEC) has not yet been identified as an important aetiologic agent of human disease in Thailand. To evaluate the potential for STEC to contribute to human disease in Thailand, 139 fecal samples were collected from healthy cattle from five different provinces and analysed by genotypic and phenotypic methods for STEC. Of 139 samples, 27 (19.4%) were positive for stx1 and/or stx2 by multiplex polymerase chain reaction, or for O157 lipopolysaccharide (LPS) by immunoassay. Isolates positive for stx and/or O157 were subdivided into 49 strains that varied in the presence of the virulence determinants stx1+/stx2+ (22 strains), stx2+ (22 strains), stx1+ (4 strains), and O157 LPS (1 strain). Within these 49 distinguishable strains, other virulence determinants varied as follows: hlyA+ (77.6%), eae+ and tir+ (4.1%), and katP+ (6.12%). The most predominant profile (22 isolates) was stx1+/stx2+, eae-, tir-, etpD-, hlyA+, katP-. For further characterization of the isolated strains by two molecular typing assays, plasmid profiles and ERIC PCR were performed. The results suggest that the genetic and phenotypic profiles of STEC associated with human disease are not prevalent at this time in cattle in Thailand.

Evaluation of four DNA extraction methods for the detection of Mycobacterium avium subsp. paratuberculosis by polymerase chain reaction

Polymerase chain reaction (PCR) has been widely used due to its high specificity, sensitivity, and rapid turn-around time. However, inhibitory factors may be co-extracted with the target nucleic acid that will hinder the performance of PCR. In this study, DNA extraction methods for Mycobacterium avium subsp. paratuberculosis were evaluated including rapid lysis, organic extraction, silica-based and magnetic particle-based (MagaZorb) technologies on bacterial cells, and spiked bovine feces. Efficiency of the extraction was determined by PCR end point titration with primers targeting the insertion sequence, IS900. Results of the end point titrations are identical for bacterial cells and spiked feces. Inhibition was observed in PCR with DNA isolated from spiked feces, and a 1/100 dilution was able to alleviate this problem with DNA extracted by MagaZorb. A 1/1000 dilution was required for the other three methods. MagaZorb proved to be more efficient at removing inhibitory factors and required the least labor and completion time. Further evaluation is required for its utilization in other clinical specimens.

Evaluation of PCR for detection of Campylobacter in a national broiler surveillance programme in Denmark

AIMS

To develop and evaluate a rapid and sensitive PCR method for detection of Campylobacter spp. directly from chicken faeces.

METHODS AND RESULTS

DNA was isolated from faecal swabs using magnetic beads followed by PCR using a prealiquoted PCR mixture, which had been stored in the freezer. The result could be obtained in <6 h. The method was evaluated on 1282 samples from the Danish surveillance programme for Campylobacter in broilers by comparing with conventional culture. The diagnostic specificity was calculated to be 0.99. The detection limits of the PCR method and of the conventional culture were compared using spiked control material. For both methods the detection limit was 36 CFU ml-1.

CONCLUSIONS

It was concluded that the PCR proved useful for detection of Campylobacter in pooled cloacal swabs from broilers.

SIGNIFICANCE AND IMPACT OF THE STUDY

By taking cloacal samples in the broiler flocks the technique can be used as an important tool for planning and directing the broiler slaughtering process. This will be a great help in minimizing the risk of contaminating Campylobacter-free flocks at the abattoir.

Primary fecal culture used as template for PCR detection of diarrheagenic E. coli virulence factors

The PCR technique applied to primary fecal cultures (PFC-PCR) was compared to the usual method employing isolated colonies (IC-PCR) in order to assess its sensitivity in the detection of virulence markers of diarrheagenic Escherichia coli in fecal samples obtained from children with diarrhea. Among the 149 samples analysed, PFC-PCR detected 81(54.4%) samples presenting one or two virulence markers, while IC-PCR detected only 59 (39.6%) positive samples. The markers detected in order of frequency were: pAA, LT-I, eaeA, ST-I, daaE, and ipaH. The PFC-PCR method of detection of diarrheagenic E. coli virulence markers proved to be reliable and more sensitive (p<0.05) than the usual method employing isolated colonies. It has also the advantage of being faster and less expensive than the detection methods in current use.

Molecular fingerprinting of Clostridium difficile isolates: pulsed-field gel electrophoresis versus amplified fragment length polymorphism

Two molecular fingerprinting techniques, pulsed-field gel electrophoresis (PFGE) and amplified fragment length polymorphism (AFLP), were used to investigate the epidemiological relatedness among Clostridium difficile isolates from suspected outbreaks in three general hospitals. Analysis by PFGE yielded inconclusive data as a result of extensive DNA degradation. Although this degradation could be prevented to a certain extent by the inclusion of thiourea in the electrophoresis buffer, the weak DNA banding patterns obtained in this way were still far from optimal. AFLP data were obtained by using fluorescently labeled PCR primers and analysis on an ABI PRISM automated DNA analysis platform. AFLP analysis yielded high resolution and highly reproducible DNA fingerprinting patterns from which the epidemiological relatedness among the isolates could easily be determined. AFLP results could be readily obtained within 24 h, whereas 3 to 4 days were routinely required to complete the lengthy PFGE protocol. AFLP clearly proved to be a much more fail-safe fingerprinting method for C. difficile isolates, especially for those isolates for which a standard PFGE procedure yielded inconclusive results due to DNA degradation.

Evaluation of a PCR/DNA probe colorimetric membrane assay for identification of Campylobacter spp. in human stool specimens

DNA was extracted from 50 human stool specimens using the QIAamp DNA stool minikit. PCR amplification was followed by post-PCR hybridization to DNA probes specific for the Campylobacter genus, Campylobacter jejuni, and Campylobacter coli in a colorimetric membrane assay. Thirty-two of 38 culture-positive specimens were PCR/DNA probe positive for C. jejuni. The assay is rapid and simple and can be applied to stool specimens for the detection of Campylobacter.

Comparison of cultivation and PCR-hybridization for detection of Salmonella in porcine fecal and water samples

A total of 150 fecal and water samples from four swine farms were tested for the presence of Salmonella enterica using different enrichment techniques as follows: (i) 92 fecal samples from nursery and farrowing barns at three swine farms were preenriched overnight in tryptic soy broth (TSB) at 37 degrees C followed by overnight enrichment in Rappaport-Vassiliadis 10 broth (RV10) at 42 degrees C; (ii) 24 water samples from the third farm were preenriched overnight in 3MC broth at 37 degrees C followed by overnight enrichment in RV10 at 42 degrees C; and (iii) 34 fecal samples from a fourth farm, a finishing farm, were enriched overnight in RV10 at 42 degrees C with no additional enrichment. Following each of the enrichment techniques, samples were subcultured onto modified semisolid Rappaport-Vassiliadis (MSRV) agar prior to transfer to Hektoen Enteric agar plates for the recovery of viable Salmonella bacteria. Presumptive Salmonella isolates were biochemically and serologically confirmed. For the PCR detection of Salmonella, a 1-ml portion was removed from each sample after the first overnight enrichment and the DNA was extracted using a Sepharose CL-6B spin column. Amplicons (457 bp) derived from primers to the invA and invE genes were confirmed as Salmonella specific on ethidium bromide-stained agarose gels by Southern hybridization with a 20-mer oligonucleotide probe specific for the Salmonella invA gene. Neither the standard microbiological method nor the molecular method detected all of the 65 samples that tested positive by both methods or either method alone. Salmonella bacteria were detected by both cultivation and PCR-hybridization in 68% (17 of 25) of the positive samples that were preenriched in TSB, in 73% (11 of 15) of the positive samples preenriched in 3MC broth, and in 24% (6 of 25) of the positive samples enriched in RV10. Agreement between Salmonella detection using cultivation with preenrichment and detection by PCR was 76% using the kappa statistic. However, agreement between Salmonella detection using cultivation without preenrichment and detection by PCR was about 6%; the PCR assay detected 80% (20 of 25) of the 25 positive samples, while Salmonella bacteria were recovered from only 44% (11 of 25) by cultivation. Our results indicate that the PCR-hybridization approach is equivalent to or better than cultivation for detecting Salmonella in swine feces or water samples from swine farms when using the medium combinations evaluated in this study.

PCR detection of Brachyspira aalborgi and Brachyspira pilosicoli in human faeces

Previously-developed PCR protocols specific for the 16S rRNA gene of the intestinal spirochaetes Brachyspira aalborgi and Brachyspira pilosicoli were adapted for the detection of these species in human faeces, following DNA extraction and purification using mini-prep columns. The limits of detection in seeded faeces for B. aalborgi and B. pilosicoli respectively were 2x10(2) and 7x10(3) cells per PCR reaction, equivalent to 5x10(4) and 1x10(5) cells per g of faeces. The PCR techniques were applied to faecal samples from two patients with histological evidence of intestinal spirochaetosis. In the first patient, in whom B. aalborgi had been identified by 16S rDNA PCR from colonic biopsies, a positive amplification for B. aalborgi only was obtained from the faeces. The organism could not be isolated from these faeces. In the second patient, both colonic biopsies and faeces were PCR positive for B. pilosicoli only, and B. pilosicoli was isolated from the faeces. These new faecal PCR protocols should be valuable for future studies on the epidemiology of intestinal spirochaete infections in human populations, particularly as it is not currently possible to isolate B. aalborgi from faeces.

PCR detection of Escherichia coli O157:H7 directly from stools: evaluation of commercial extraction methods for purifying fecal DNA

Rapid identification of Escherichia coli O157:H7 is important for patient management and for prompt epidemiological investigations. We evaluated one in-house method and three commercially available kits for their ability to extract E. coli O157:H7 DNA directly from stool specimens for PCR. Of the 153 stool specimens tested, 107 were culture positive and 46 were culture negative. The sensitivities and specificities of the in-house enrichment method, IsoQuick kit, NucliSens kit, and QIAamp kit were comparable, as follows: 83 and 98%, 85 and 100%, 74 and 98%, and 86 and 100%, respectively. False-negative PCR results may be due to the presence of either inherent inhibitors or small numbers of organisms. The presence of large amounts of bacteria relative to the amount of the E. coli O157:H7 target may result in the lower sensitivities of the assays. All commercial kits were rapid and easy to use, although DNA extracted with the QIAamp kit did not require further dilution of the DNA template prior to PCR.

Application of nucleic acid amplification in clinical microbiology

The use of nucleic acid amplification methods in routine clinical microbiology laboratories is becoming increasingly widespread. The theory of polymerase chain reaction is described, including discussion of suitable microbal targets, extraction of nucleic acid from clinical samples, choice of primers, optimization of the process, laboratory design, contamination, and other problems as well as quality control. Other nucleic acid amplification methods such as ligase chain reaction, self-sustained sequence replication, strand displacement amplification, and branched DNA signal amplification are described and the choice of technology is discussed.

Strain-specific identification of probiotic Lactobacillus rhamnosus with randomly amplified polymorphic DNA-derived PCR primers

In the present work, strain-specific PCR primers for Lactobacillus rhamnosus Lc 1/3 are described. The randomly amplified polymorphic DNA (RAPD) technique was used to produce potential strain-specific markers. They were screened for specificity by hybridization with DNA from 11 L. rhamnosus strains. A 613-bp RAPD marker found to be strain-specific was sequenced, and a primer pair specific to L. rhamnosus Lc 1/3 was constructed based on the sequence. The primer pair was tested with 11 Lactobacillus species and 11 L. rhamnosus strains and was found to be strain specific. The nucleotide sequence of the specific RAPD marker was found to contain part of a protein encoding region which showed significant similarity to several transposases for insertion sequence elements of various bacteria, including other lactic acid bacterium species.

Diarrheagenic Escherichia coli

Escherichia coli is the predominant nonpathogenic facultative flora of the human intestine. Some E. coli strains, however, have developed the ability to cause disease of the gastrointestinal, urinary, or central nervous system in even the most robust human hosts. Diarrheagenic strains of E. coli can be divided into at least six different categories with corresponding distinct pathogenic schemes. Taken together, these organisms probably represent the most common cause of pediatric diarrhea worldwide. Several distinct clinical syndromes accompany infection with diarrheagenic E. coli categories, including traveler's diarrhea (enterotoxigenic E. coli), hemorrhagic colitis and hemolytic-uremic syndrome (enterohemorrhagic E. coli), persistent diarrhea (enteroaggregative E. coli), and watery diarrhea of infants (entero-pathogenic E. coli). This review discusses the current level of understanding of the pathogenesis of the diarrheagenic E. coli strains and describes how their pathogenic schemes underlie the clinical manifestations, diagnostic approach, and epidemiologic investigation of these important pathogens.