PCR and blood culture for detection of Escherichia coli bacteremia in rats

The era of molecular and other non-culture-based methods in diagnosis of sepsis

Sepsis, a leading cause of morbidity and mortality throughout the world, is a clinical syndrome with signs and symptoms relating to an infectious event and the consequent important inflammatory response. From a clinical point of view, sepsis is a continuous process ranging from systemic inflammatory response syndrome (SIRS) to multiple-organ-dysfunction syndrome (MODS). Blood cultures are the current "gold standard" for diagnosis, and they are based on the detection of viable microorganisms present in blood. However, on some occasions, blood cultures have intrinsic limitations in terms of sensitivity and rapidity, and it is not expected that these drawbacks will be overcome by significant improvements in the near future. For these principal reasons, other approaches are therefore needed in association with blood culture to improve the overall diagnostic yield for septic patients. These considerations have represented the rationale for the development of highly sensitive and fast laboratory methods. This review addresses non-culture-based techniques for the diagnosis of sepsis, including molecular and other non-culture-based methods. In particular, the potential clinical role for the sensitive and rapid detection of bacterial and fungal DNA in the development of new diagnostic algorithms is discussed.

A profile of drug resistance genes and integrons in E. coli causing surgical wound infections in the Faisalabad region of Pakistan

Escherichia coli are one of the leading causes of infection in wounds. Emerging multiple drug resistance among E. coli poses a serious challenge to antimicrobial therapy for wounds. This study was conducted to ascertain a baseline profile of antimicrobial resistance in E. coli isolates infecting surgical wounds. A total of 64 pus samples from hospitalized patients were screened and 29 (45.3%) were found to have E. coli, which were identified biochemically and confirmed by molecular methods. Using the disc diffusion method, antimicrobial resistance was observed toward tetracycline (100%), cefradine (100%), nalidixic acid (93.1%), ampicillin (86.2%), gentamicin (86.2%), cefixime (82.8%), ceftriaxone (82.8%), aztreonam (82.8%), ciprofloxacin (75.9%), streptomycin (72.4%), cefoperazone (65.5%), chloramphenicol (58.6%) and amikacin (58.6%). In an effort to find relevant genes, 11 different genes were targeted by PCR. Among these, the mutated gyrA gene was found to be the most prevalent (82.8%), followed by the TEM (72.4%), catP (68.9%), catA1 (68.9%), tetB (62.1%), blt (58.6%), bla(CTX-M-15) (27.6%), bla(TEM) (20.7%), bla(OXA) (17.2%), tetA (17.2%) and aadA1 (13.8%) genes. The presence of integrons was also studied among these isolates. The prevalence of class 1 integrons was the highest (44.8%), followed by class 2 (27.6%). Three (10.3%) isolates carried both class 1 and class 2 integrons (first report from E. coli infecting wounds). The high incidence of integrons points toward their facilitation for carriage of antimicrobial resistance genes; however, in nearly 37% isolates, no integrons were detected, indicating the significance of alternative mechanisms of gene transfer. Another salient finding was that all isolates were multidrug-resistant E. coli.

Detection of multiple-antimicrobial resistance and characterization of the implicated genes in Escherichia coli isolates from foods of animal origin in Tunis

Phenotypic and genotypic characterization of antimicrobial resistance was conducted for 98 Escherichia coli isolates recovered from 40 food samples of animal origin (poultry, sheep, beef, fish, and others) obtained in supermarkets and local butcheries in Tunis during 2004 and 2005. Susceptibility to 15 antimicrobial agents was tested by disk diffusion and agar dilution methods, the mechanisms of resistance were evaluated using PCR and sequencing methods, and the clonal relationship among isolates was evaluated using pulsed-field gel electrophoresis. High resistance was detected to tetracycline, sulphonamides, nalidixic acid, ampicillin, streptomycin, and trimethoprim-sulfamethoxazole (29 to 43% of isolates), but all isolates were susceptible to cefotaxime, ceftazidime, cefoxitin, azthreonam, and amikacin. One-third of the isolates had multiresistant phenotypes (resistance to at least five different families of antimicrobial agents). Different variants of blaTEM, tet, sul, dfrA, aadA, and aac(3) genes were detected in most of the strains resistant to ampicillin, tetracycline, sulphonamide, trimethoprim, streptomycin, and gentamicin, respectively. The presence of class 1 and class 2 integrons was studied in 15 sulphonamide-resistant unrelated E. coli strains, and 14 of these strains harbored class 1 integrons with five different arrangements of gene cassettes, and a class 2 integron with the dfrA 1 + sat + aadA 1 arrangement was found in one strain. This study revealed the high diversity of antimicrobial resistance genes, some of them included in integrons, in E. coli isolates of food origin.

High levels of mecA DNA detected by a quantitative real-time PCR assay are associated with mortality in patients with methicillin-resistant Staphylococcus aureus bacteremia

Persistent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is known to be a poor prognostic factor. While several PCR assays for the detection of MRSA in various clinical samples were recently reported, the possibility that a quantitative PCR assay could be used to quantify and monitor MRSA bacteremia has not been explored. In this study, we established a quantitative real-time PCR assay for the mecA gene using known copy numbers of a plasmid containing mecA DNA as a standard and the previously described mecA-specific primers and probe (P. Francois et al., J. Clin. Microbiol. 41:254-260, 2003). We employed this assay to examine 250 sequential whole-blood samples from 20 adult patients, including 13 survivors and 7 nonsurvivors, with culture-proven MRSA bacteremia at the intensive care units of National Taiwan University Hospital between 1 July 2006 and 31 January 2007. The levels of mecA DNA in the nonsurvivors were significantly higher than those in the survivors during the three periods of bacteremia examined (days 0 to 2, 3 to 5, and 6 to 8) (P = 0.003 by two-tailed Mann-Whitney U test). Moreover, the nonsurvivors had higher mecA DNA levels than the survivors after 3 days and 7 days of anti-MRSA therapy (medians for nonsurvivors and survivors at 3 days, 5.86 and 4.30 log copies/ml, respectively; medians for nonsurvivors and survivors at 7 days, 5.21 and 4.36 log copies/ml, respectively; P = 0.02 and P = 0.04, respectively, by two-tailed Mann-Whitney U test). Together, these findings suggest that the level of mecA DNA in blood could potentially be used to monitor MRSA bacteremia and evaluate responses to therapy.

Use of cultivation-dependent and -independent techniques to assess contamination of central venous catheters: a pilot study

Background

Catheters are the most common cause of nosocomial infections and are associated with increased risk of mortality, length of hospital stay and cost. Prevention of infections and fast and correct diagnosis is highly important.

Methods

In this study traditional semiquantitative culture-dependent methods for diagnosis of bacteria involved in central venous catheter-related infections as described by Maki were compared with the following culture-independent molecular biological methods: Clone libraries, denaturant gradient gel electrophoresis, phylogeny and fluorescence in situ hybridization.

Results

In accordance with previous studies, the cultivation of central venous catheters from 18 patients revealed that S. epidermidis and other coagulase-negative staphylococci were most abundant and that a few other microorganisms such as P. aeruginosa and K. pneumoniae occasionally were found on the catheters. The molecular analysis using clone libraries and sequencing, denaturant gradient gel electrophoresis and sequencing provided several important results. The species found by cultivation were confirmed by molecular methods. However, many other bacteria belonging to the phyla Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes were also found, stressing that only a minor portion of the species present were found by cultivation. Some of these bacteria are known to be pathogens, some have not before been described in relation to human health, and some were not closely related to known pathogens and may represent new pathogenic species. Furthermore, there was a clear difference between the bacterial species found in biofilm on the external (exluminal) and internal (luminal) side of the central venous catheter, which can not be detected by Maki's method. Polymicrobial biofilms were observed on most of the catheters and were much more common than the cultivation-dependent methods indicated.

Conclusion

The results show that diagnosis based on molecular methods improves the detection of microorganisms involved in central catheter-related infections. The importance of these microorganisms needs to be investigated further, also in relation to contamination risk from improper catheter handling, as only in vivo contaminants are of interest. This information can be used for development of fast and more reliable diagnostic tools, which can be used in combination with traditional methods.

Rapid methods for diagnosis of bloodstream infections

Direct detection technologies for pathogenic microorganisms are emerging to be applied in the diagnosis of serious bloodstream infections and infections at sterile body sites, as well as for quality control measures prior to the release of sterile blood products and to ascertain microbial safety of food. Standard blood cultures as the current gold standard for detection of bacteraemia/sepsis and other culture-based microbiological identification procedures are comparatively slow and have limited sensitivity for fastidious or slow-growing microorganisms. Rapid nucleic acid-based technologies with PCR amplification or hybridisation probes for specific pathogens, broad-range bacterial or fungal assays, flow cytometry, as well as protein-based characterisation by mass spectrometry, aim at identification of pathogenic microorganisms within minutes to hours. Interpretation of direct detection of panbacterial or panfungal nucleic acids instead of living microorganisms in blood is complex, given the risk of contamination, the ubiquitous presence of bacterial and fungal DNA, and the lack of a gold standard. Since many of the infections at sterile sites, particularly sepsis, are medical emergencies requiring immediate therapeutic responses, rapid technologies could contribute to reduction of morbidity, mortality, and of the economic burden. This review summarises the currently available data on rapid non-culture-based technologies and outlines the potential clinical usefulness in infectious disease diagnosis.

Validation criteria for nucleic acid amplification techniques for bacterial infections

Nucleic acid techniques (NATs), such as species-specific and universal polymerase chain reactions (PCRs), are finding ever wider use in the diagnosis of bacterial infection. However, although universal PCR assays, in particular, approach a type of modern Petri dish, they have a number of limitations which restrict their applicability. The sensitivity of universal PCR is lower than that of many species-specific PCRs, and the contamination of samples and PCR reagents with irrelevant DNA from various sources remains a problem. Thus, NATs in general and universal PCR assays in particular require careful validation to be of value for the diagnosis of infection. Validation includes sampling, DNA extraction/isolation, template amplification and visualisation of the results. Furthermore, it implies the establishment of measures of asepsis, the inclusion of positive and negative controls, techniques to optimise the release of DNA from bacterial cells, adequate repetition of the amplification reaction, and routine testing of reagent negative and inhibition controls. Finally, it entails the comparison of results obtained by NATs with those obtained by conventional microbiological methods and matching with clinical evidence of infection. Validation of NATs in clinical diagnosis remains an ongoing challenge. Because of these limitations, NATs can only serve as adjunct tools for the diagnosis of infection in selected cases; they cannot replace conventional culturing techniques.

A real-time polymerase chain reaction for the detection of Streptococcus pneumoniae in blood using a mouse model: a potential new "gold standard"

Better diagnostics for pneumococcal disease are urgently needed. In a murine model, real-time polymerase chain reaction was superior to conventional culture in detecting pneumococcus in blood, particularly in early disease and after antibiotic administration, and could distinguish between commensalism and infection.

Quantitative detection of Staphylococcus aureus and Enterococcus faecalis DNA in blood to diagnose bacteremia in patients in the intensive care unit

Direct detection of bacterial DNA in blood offers a fast alternative to blood culture and is presumably unaffected by the prior use of antibiotics. We evaluated the performance of two real-time PCR assays for the quantitative detection of Staphylococcus aureus bacteremia and for Enterococcus faecalis bacteremia directly in blood samples, without prior cultivation. Whole-blood samples for PCR were obtained simultaneously with blood cultures from patients admitted to the intensive care unit of our hospital. After the extraction of DNA from 200 mul of blood, real-time PCR was performed for the specific detection and quantification of S. aureus and E. faecalis DNA. The sensitivity for bacteremia of the S. aureus PCR was 75% and that of the E. faecalis PCR was 73%, and both tests had high specificity values (93 and 96%, respectively). PCR amplification reactions were positive for S. aureus for 10 (7%) blood samples with negative blood cultures, and 7 (4%) PCR reactions were positive for E. faecalis. The majority of these PCR results were likely (50%) or possibly (42%) related to infection with the specific microorganism, based on clinical data and radiological and microbiological investigations. PCR results were concordant for 95% of paired whole-blood samples, and blood culture results were concordant for 97% of the paired samples. We conclude that the detection of S. aureus and E. faecalis DNA in blood by real-time PCR enables a rapid diagnosis of bacteremia and that a positive DNAemia is related to proven or possible infection with the specific microorganism in the majority of patients with negative blood cultures.

Identification of human pathogens isolated from blood using microarray hybridisation and signal pattern recognition

Background

Pathogen identification in clinical routine is based on the cultivation of microbes with subsequent morphological and physiological characterisation lasting at least 24 hours. However, early and accurate identification is a crucial requisite for fast and optimally targeted antimicrobial treatment. Molecular biology based techniques allow fast identification, however discrimination of very closely related species remains still difficult.

Results

A molecular approach is presented for the rapid identification of pathogens combining PCR amplification with microarray detection. The DNA chip comprises oligonucleotide capture probes for 25 different pathogens including Gram positive cocci, the most frequently encountered genera of Enterobacteriaceae, non-fermenter and clinical relevant Candida species. The observed detection limits varied from 10 cells (e.g. E. coli) to 10⁵ cells (S. aureus) per mL artificially spiked blood. Thus the current low sensitivity for some species still represents a barrier for clinical application. Successful discrimination of closely related species was achieved by a signal pattern recognition approach based on the k-nearest-neighbour method. A prototype software providing this statistical evaluation was developed, allowing correct identification in 100 % of the cases at the genus and in 96.7 % at the species level (n = 241).

Conclusion

The newly developed molecular assay can be carried out within 6 hours in a research laboratory from pathogen isolation to species identification. From our results we conclude that DNA microarrays can be a useful tool for rapid identification of closely related pathogens particularly when the protocols are adapted to the special clinical scenarios.

Detection and identification by PCR of a highly virulent phylogenetic subgroup among extraintestinal pathogenic Escherichia coli B2 strains

Closely related Escherichia coli B2 strains O1:K1, O2:K1, O18:K1, and O45:K1 constitute a major subgroup causing extraintestinal infections. A DNA pathoarray analysis was used to develop a PCR specific for this subgroup that was included in the multiplex phylogenetic-grouping PCR method. Our PCR may serve to identify this virulent subgroup among different ecological niches.

Bacteraemia following periodontal procedures

INTRODUCTION

Transient bacteraemias are frequently detected following dental manipulation. Infective endocarditis (IE) can arise in susceptible individuals and antibiotic prophylaxis is routinely performed for certain procedures considered to be "at risk" of IE. Evidence is emerging that periodontal disease may be a significant risk factor for the development of certain systemic diseases such as cardiovascular disease. These systemic conditions could be initiated or detrimentally influenced by the repeated entry of bacteria into the bloodstream.

MATERIALS AND METHODS

The present study comprised a single blind parallel study of 2 weeks duration. A baseline blood sample was obtained from 30 volunteers with untreated periodontal disease following which a periodontal probing depth chart was collected. A further blood sample was taken following this procedure, and each subject was recalled 2 weeks later. A blood sample was collected, the subject carried out toothbrushing and a further blood sample taken. Full-mouth ultrasonic scaling was then performed and a final blood sample taken. Blood samples were analysed for bacteraemia using conventional microbiological culture and polymerase chain reaction (PCR) using universal bacterial primers that target the 16S ribosomal RNA gene of the vast majority of bacteria.

RESULTS

Using culture methods, the incidence of bacteraemias was as follows: following ultrasonic scaling (13%), periodontal probing (20%) and toothbrushing (3%). PCR analysis revealed bacteraemia incidences following ultrasonic scaling, periodontal probing and toothbrushing of 23%, 16% and 13%, respectively.

CONCLUSION

These findings suggest that detectable dental bacteraemias induced by periodontal procedures are at a lower level than previously reported.

Anti-inflammatory response is associated with mortality and severity of infection in sepsis

Using a murine model of sepsis, we found that the balance of tissue pro- to anti-inflammatory cytokines directly correlated with severity of infection and mortality. Sepsis was induced in C57BL/6 mice by cecal ligation and puncture (CLP). Liver tissue was analyzed for levels of IL-1beta, IL-1 receptor antagonist (IL-1ra), tumor necrosis factor (TNF)-alpha, and soluble TNF receptor 1 by ELISA. Bacterial DNA was measured using quantitative real-time PCR. After CLP, early predominance of proinflammatory cytokines (6 h) transitioned to anti-inflammatory predominance at 24 h. The elevated anti-inflammatory cytokines were mirrored by increased tissue bacterial levels. The degree of anti-inflammatory response compared with proinflammatory response correlated with the bacterial concentration. To modulate the timing of the anti-inflammatory response, mice were treated with IL-1ra before CLP. This resulted in decreased proinflammatory cytokines, earlier bacterial load, and increased mortality. These studies show that the initial tissue proinflammatory response to sepsis is followed by an anti-inflammatory response. The anti-inflammatory phase is associated with increased bacterial load and mortality. These data suggest that it is the timing and magnitude of the anti-inflammatory response that predicts severity of infection in a murine model of sepsis.

New developments in the diagnosis of bloodstream infections

New techniques have emerged for the detection of bacteria in blood, because the blood culture as gold standard is slow and insufficiently sensitive when the patient has previously received antibiotics or in the presence of fastidious organisms. DNA-based techniques, hybridisation probes, and PCR-based detection or protein-based detection by mass spectroscopy are aimed at rapid identification of bacteria and provide results within 2 h after the first signal of growth in conventional blood cultures. Also, detection of microorganisms directly in blood by pathogen-specific or broad-range PCR assays (eubacterial or panfungal) shows promising results. Interpretation is complex, however, because of detection of DNA rather than living pathogens, the risk of interfering contamination, the presence of background DNA in blood, and the lack of a gold standard. As these techniques are emerging, clinical value and cost-effectiveness have to be assessed. Nevertheless, molecular assays are expected eventually to replace the current conventional microbiological techniques for detection of bloodstream infections.

Effect of comprehensive validation of the template isolation procedure on the reliability of bacteraemia detection by a 16S rRNA gene PCR

The influence of the DNA extraction method on the sensitivity and specificity of bacteraemia detection by a 16S rRNA gene PCR assay was investigated. The detection limit of the assay was 5 fg with purified DNA from Escherichia coli or Staphylococcus aureus, corresponding to one bacterial cell. However, with spiked blood samples, the detection limits were 10(4) and 10(6) CFU/mL, respectively. The sensitivity of the S. aureus assay was improved to the level of the E. coli test with the addition of proteinase K to the commercial DNA extraction kit protocol. Ten (16.6%) of 60 amplification reactions were positive with templates isolated from sterile blood, while PCR reagent controls were negative, thereby indicating contamination during the DNA extraction process. Blood samples were spiked with serial dilutions of E. coli and S. aureus cells, and six PCR results were obtained from three extractions for each blood sample. A classification threshold system was devised, based on the number of positive reactions for each sample. Samples were deemed positive if at least four positive reactions were recorded, making it possible to avoid false-positive results caused by contamination. These results indicate that a comprehensive validation procedure covering all aspects of the assay, including DNA extraction, can improve considerably the validity of PCR assays for bacteraemia, and is a prerequisite for the meaningful detection of bacteraemia by PCR in the clinical setting.

Antibiotics delay but do not prevent bacteremia and lung injury in murine sepsis

OBJECTIVES

To investigate the effect of antibiotics on infection, lung injury, and mortality rate in polymicrobial sepsis and to determine whether an association exists between infection and lung injury and mortality rate. To circumvent the effect of antibiotics on cultures, we used polymerase chain reaction to detect bacteria.

DESIGN

Prospective, randomized, controlled laboratory trial.

SETTING

University research laboratory.

SUBJECTS

C57/BL6 mice.

INTERVENTIONS

Mice underwent cecal ligation and puncture without antibiotics (CLP) or with imipenem (CLP + Abx).

MEASUREMENTS AND MAIN RESULTS

CLP resulted in 50% mortality rate at 48 hrs and 100% mortality rate at 84 hrs. Antibiotics delayed these time points to 72 and 120 hrs, respectively. Lung injury occurred before mortality in both groups. Polymerase chain reaction detected bacteria in the blood and lungs of all CLP mice by 24 hrs. Antibiotics delayed but did not prevent infection in CLP + Abx mice. Serum tumor necrosis factor-alpha and lung endotoxin were elevated to similar concentrations in both CLP and CLP + Abx mice.

CONCLUSIONS

In this model of sepsis, antibiotics delay but do not prevent acute lung injury and mortality. Even in the presence of antibiotics, acute lung injury is strongly associated with bacteremia and bacteria within the lungs.

Mechanisms of antibiotic resistance in Escherichia coli isolates obtained from healthy children in Spain

Antibiotic resistance and mechanisms involved were studied in Escherichia coli isolates from fecal samples of healthy children. Fifty fecal samples were analyzed, and one colony per sample was recovered and identified by biochemical and molecular tests. Forty-one E. coli isolates were obtained (82%). MIC testing was performed by agar dilution with 18 antibiotics, and the mechanisms of resistance were analyzed. Ampicillin resistance was detected in 24 isolates (58.5%), and blaTEM, blaSHV, and blaOXA type genes were studied by PCR and sequencing. The following beta-lactamases were detected (number of isolates): TEM (20), SHV-1 (1), and OXA-30 (1). The number of aminoglycoside-resistant isolates detected was as follows: streptomycin (15), tobramycin (1), gentamicin (1), and kanamycin (4). The aac(3)-IV gene was detected in the only gentamicin-resistant isolate. Nine (22%) and 2 (5%) isolates showed nalidixic acid (NALR) and ciprofloxacin resistance (CIPR), respectively. Mutations in GyrA and ParC proteins were shown in both NAL(R)-CIP(R) isolates and were the following: (1) GyrA (S83L + D87N), ParC (S801); and (2) GyrA (S83L + A84P), ParC (S80I + A108V). A single mutation in the S83 codon of the gyrA gene was found in the remaining seven NAL(R)-CIP(S) isolates. Tetracycline resistance was identified in 21 isolates (51%) and the following resistance genes were found (number of isolates): tetA (12), tetB (5), and tetD (1). Chloramphenicol resistance was detected in five isolates (12%). These results show that the intestinal tract of healthy children constitutes a reservoir of resistant bacteria and resistance genes.

Flow cytometric detection of beta-D-glucuronidase gene in wild-type bacterial cells using in-situ PCR

An in situ PCR-based flow cytometry method useful for monitoring the presence or absence of the beta-D-glucuronidase gene in Escherichia coli has been developed. A single-step fixation and permeabilization procedure, which maintained cell integrity at the elevated temperatures used during thermal cycling in the presence of PCR reagents, was demonstrated. We have chosen a shorter DNA sequence of length 147 bp for the PCR. Cells subjected to in situ PCR using fluorescein-12-dUTP as a label, showed the presence of uid both in epifluorescence microscopic examination and flow cytometric analysis. Multi-parametric analysis of flow cytometric profiles revealed that the efficiency of labeling was found to be high. The potential of in situ PCR for the detection of uid in intact coliform cells was then successfully tested with a fecal coliform isolated from the coastal waters of Singapore.

DNase pretreatment of master mix reagents improves the validity of universal 16S rRNA gene PCR results

DNase I pretreatment of 16S rRNA gene PCR reagents was tested. The DNase I requirement for the elimination of false-positive results varied between 0.1 and 70 IU per master mix depending on the applied Taq polymerase. PCR sensitivity was mostly maintained when 0.1 IU of DNase I was used.

Detection of Escherichia coli O157:H7 using immunomagnetic separation and absorbance measurement

An assay system for detection of Escherichia coli O157:H7 was developed based on immunomagnetic separation of the target pathogen from samples and absorbance measurement of p-nitrophenol at 400 nm from p-nitrophenyl phosphate hydrolysis by alkaline phosphatase (EC 3.1.3.1) on the "sandwich" structure complexes (antibodies coated onto micromagnetic beads--E. coli O157:H7-antibodies conjugated with the enzyme) formed on the microbead surface. The effects of immunoreaction time, phosphate buffer concentration, pH and temperature on the immunomagnetic separation of E. coli O157:H7 from samples were determined and the conditions used for the separation were 1-h reaction time, 1.0 x 10(-2) M PBS, pH 8.0 and 33 degrees C in this system. The effects of MgCl(2) concentration, Tris buffer concentration, pH and temperature on the activity of alkaline phosphatase conjugated on the immuno-"sandwich" structure complexes were investigated after immunomagnetic separation of the target pathogen and the conditions used for the enzymatic amplification were 1.0 x 10(-4) M MgCl(2), 1.0 M Tris buffer, pH 8.0, 28 degrees C and 30-min reaction time during the assay. The selectivity of the system was examined and no interference from the other pathogens including Salmonella typhimurium, Campylobacter jejuni and Listeria monocytogenes was observed. Its working range was from 3.2 x 10(2) to 3.2 x 10(4) CFU/ml, and the relative standard deviation was 2.5-9.9%. The total detection time was less than 2 h.

An antibody-immobilized capillary column as a bioseparator/bioreactor for detection of Escherichia coil O157:H7 with absorbance measurement

A capillary-column-based bioseparator/bioreactor was developed for detection of Escherichia coli O157:H7 by chemically immobilizing anti-E. coli O157:H7 antibodies onto the inner wall of the column, forming the "sandwich" immunocomplexes (immobilized antibody-E. coli O157: H7-enzyme-labeled antibody) after the sample and the enzyme-labeled antibody passed through the column and detecting the absorbance of the product in the bioreactor with an optical detector. The effects of the blocking agent, flow rate of samples and substrates, buffer, MgCl2, and pH on the detection of E. coli O157:H7 were investigated. The parameters, 2% BSA in 1.0 x 10-2 M, pH 7.4, PBS as the blocking agent, 0.5 mL/h as the sample flow rate, 1.0 x 10(-2) M MgCl2, and 2.0 x 10(-4) M p-nitrophenyl phosphate in 1.0 M, pH 9.0 Tris buffer as the substrate for the enzymatic reaction, and 1.0 mL/h as the substrate flow rate, were used in the bioseparator/bioreactor system for detection of E. coli O157:H7. The selectivity of the system was checked, and other pathogens, including Salmonella typhimurium, Campylobacterjejuni, and Listeria monocytogenes, had no interference with the detection of E. coli O157:H7. Its working range was from 5.0 x 10(2) to 5.0 x 10(6) cfu/mL, and the total assay time was < 1.5 h without any enrichment. The relative standard deviation was approximately 2.0-7.3%.

Polymerase Chain Reaction for the Detection of Bacteremia

Analysis of blood by polymerase chain reaction (PCR) is a more rapid and sensitive method to detect bacteremia than blood culture. The PCR was performed on blood obtained from patients during blood culture draws and on blood from normal volunteers. Eighty-seven patients provided 125 blood samples for blood culture comparison with PCR. Specific PCR primers for Staphylococcus aureus and Escherichia coli that targeted conserved regions common to Gram-positive and Gram-negative bacteria were used. Selective stringency conditions identified other Gram-positive and Gram-negative bacteria. The blood culture agreed with the PCR in 93 of the 125 patient specimens (74%). In 29 of these specimens the PCR was positive yet the blood culture was negative. When clinical information was included with positive blood culture to define sepsis in these patients and their specimens were added to the positive blood cultures the statistical accuracy of PCR was 93 per cent. Only three of the 78 specimens with negative PCR had positive blood cultures. The PCR was negative in all but one of the 50 volunteers. PCR is more sensitive than blood culture, and it can quickly rule out bacteremia.

Quantitation of Pseudomonas aeruginosa in wound biopsy samples: from bacterial culture to rapid 'real-time' polymerase chain reaction

STATEMENT OF FINDINGS: We developed a real-time detection (RTD) polymerase chain reaction (PCR) with rapid thermal cycling to detect and quantify Pseudomonas aeruginosa in wound biopsy samples. This method produced a linear quantitative detection range of 7 logs, with a lower detection limit of 103 colony-forming units (CFU)/g tissue or a few copies per reaction. The time from sample collection to result was less than 1h. RTD-PCR has potential for rapid quantitative detection of pathogens in critical care patients, enabling early and individualized treatment.