Detection of cytomegalovirus-infected cells by flow cytometry and fluorescence in suspension hybridisation (FLASH) using DNA probes labeled with biotin by polymerase chain reaction

Applications of flow cytometry to clinical microbiology

Classical microbiology techniques are relatively slow in comparison to other analytical techniques, in many cases due to the need to culture the microorganisms. Furthermore, classical approaches are difficult with unculturable microorganisms. More recently, the emergence of molecular biology techniques, particularly those on antibodies and nucleic acid probes combined with amplification techniques, has provided speediness and specificity to microbiological diagnosis. Flow cytometry (FCM) allows single- or multiple-microbe detection in clinical samples in an easy, reliable, and fast way. Microbes can be identified on the basis of their peculiar cytometric parameters or by means of certain fluorochromes that can be used either independently or bound to specific antibodies or oligonucleotides. FCM has permitted the development of quantitative procedures to assess antimicrobial susceptibility and drug cytotoxicity in a rapid, accurate, and highly reproducible way. Furthermore, this technique allows the monitoring of in vitro antimicrobial activity and of antimicrobial treatments ex vivo. The most outstanding contribution of FCM is the possibility of detecting the presence of heterogeneous populations with different responses to antimicrobial treatments. Despite these advantages, the application of FCM in clinical microbiology is not yet widespread, probably due to the lack of access to flow cytometers or the lack of knowledge about the potential of this technique. One of the goals of this review is to attempt to mitigate this latter circumstance. We are convinced that in the near future, the availability of commercial kits should increase the use of this technique in the clinical microbiology laboratory.

Applications of flow cytometry to clinical microbiology

Classical microbiology techniques are relatively slow in comparison to other analytical techniques, in many cases due to the need to culture the microorganisms. Furthermore, classical approaches are difficult with unculturable microorganisms. More recently, the emergence of molecular biology techniques, particularly those on antibodies and nucleic acid probes combined with amplification techniques, has provided speediness and specificity to microbiological diagnosis. Flow cytometry (FCM) allows single- or multiple-microbe detection in clinical samples in an easy, reliable, and fast way. Microbes can be identified on the basis of their peculiar cytometric parameters or by means of certain fluorochromes that can be used either independently or bound to specific antibodies or oligonucleotides. FCM has permitted the development of quantitative procedures to assess antimicrobial susceptibility and drug cytotoxicity in a rapid, accurate, and highly reproducible way. Furthermore, this technique allows the monitoring of in vitro antimicrobial activity and of antimicrobial treatments ex vivo. The most outstanding contribution of FCM is the possibility of detecting the presence of heterogeneous populations with different responses to antimicrobial treatments. Despite these advantages, the application of FCM in clinical microbiology is not yet widespread, probably due to the lack of access to flow cytometers or the lack of knowledge about the potential of this technique. One of the goals of this review is to attempt to mitigate this latter circumstance. We are convinced that in the near future, the availability of commercial kits should increase the use of this technique in the clinical microbiology laboratory.

Flow cytometric detection of EBV (EBER snRNA) using peptide nucleic acid probes

The application of peptide nucleic acid (PNA) probes for detection of Epstein-Barr Virus (EBV) snRNA in fixed cells is described. Fluorescein labelled PNA probes were used to detect EBER1 and EBER2 snRNA in Raji, Daudi and HS-Sultan cells. The fixation and permeabilization of cells were optimized. The optimal fixation was found to be 5% acetic acid plus 4% paraformaldehyde in PBS and the optimal permeabilization 0.5% Tween 20 in PBS whereas no proteolytic digestion was needed. The hybridization time needed with the PNA probes was only 1 h. When running mixed samples of Ramos (EBV neg.) Raji, Daudi and HS-Sultan (EBV pos.) cells in flow cytometry a strong fluorescence signal was seen in Raji, Daudi and HS-Sultan cells whereas no fluorescence signal was seen in the Ramos cells. In total 0.5% EBER positive Raji cells could easily be identified in a mixture of Raji and Ramos cells. The results were verified by fluorescence microscopy. It is concluded that PNA probes can be used for in situ hybridization in solution and the analysis can be done using flow cytometry or fluorescence microscopy. PNA probes therefore may facilitate and enhance the potential use of the in situ hybridization/flow cytometry combination.

Antiviral susceptibility testing-flow cytometric analysis (AST-FCA) for the detection of cytomegalovirus drug resistance

Antiviral susceptibility testing-flow cytometric analysis (AST-FCA), an application of flow cytometry in conjunction with cell culture, was developed to identify susceptibility of cytomegalovirus (CMV) isolates to the antiviral drugs ganciclovir (GCV) and foscarnet (PFA). The viral isolates used in this study were obtained from peripheral blood of AIDS patients. Among GCV-susceptible strains, the mean 50% inhibitory concentration (IC50) using AST-FCA was 18 microns (SI50 = 1.4). Among GCV resistant strains, the mean IC50 was 47 microns (SI50 = 3.6). For PFA, the mean IC50 was 80 microns (SI50 = 1.0) for susceptible strains. IC50s for strains resistant to PFA, showed no significant reduction of infectivity at the highest drug concentration (i.e., 200 microns PFA) tested. Additional analyses confirmed the accuracy of AST-FCA by parallel testing using plaque reduction assay. AST-FCA is a novel, nonisotopic, and relatively simple to perform laboratory procedure for the identification of CMV drug-resistant strains.

Molecular diagnosis of gastrointestinal infections associated with HIV infection

Developments in medical microbiology in the past 20 years have had a profound impact on our understanding of infectious diseases and have led the way in the development of new diagnostic techniques. Molecular diagnostic techniques are generally more sensitive, specific, and rapid than conventional methods by which infectious agents are detected. For many of the opportunistic infectious agents of the gastrointestinal tract found in HIV-infected individuals, the application of molecular diagnostic techniques to the clinical laboratory is in its infancy. In this article, methods by which these techniques can be evaluated are demonstrated, and the current status and potential future application of these techniques for each gastrointestinal opportunistic pathogen are described.

Three T-cell epitopes within the C-terminal 265 amino acids of the matrix protein pp65 of human cytomegalovirus recognized by human lymphocytes

Although a T-cell response in human cytomegalovirus (HCMV)-immune individuals exists against the most abundantly expressed protein pp65 of the virus matrix, less is known about the determinants that evoke this response. The aim of the study was to identify regions within HCMV pp65 (ppUL83) that contain sequences for the cellular immune response by the use of three recombinant overlapping beta-galactosidase pp65 fusion proteins (C74, C35, and C47), covering the C-terminal 265 amino acids of the entire pp65 sequence. Two T-cell epitope determinants were recognized by human lymphocytes of healthy, HCMV-seropositive, human leukocyte antigen (HLA)-typed individuals. One T-cell determinant (amino acids [aa] 303-388) was localized in the mid-region of the entire pp65 sequence and a second T-cell determinant (aa 477-561) within the C-terminal region. By fine mapping with synthetic hexadecamer peptides three T-cell epitopes were identified within these two regions: P10-I (aa 361-376) in the mid-region, P3-II (aa 485-499), and P6-II (aa 509-524) in the C-terminal region. Inhibition studies with monoclonal antibodies to HLA class I or class II revealed a class II restricted response to peptides P10-I or P6-II, respectively. P10-I responders shared the HLA-DR11 allele and P6-II responders the -DR3 allele. Therefore, these T-cell epitopes of HCMV pp65 might be presented in association with particular HLA class II alleles.

Detection of respiratory syncytial virus infection in nasal aspirate samples by flow cytometry

Hypotheses: (i) Flow cytometry has the potential for rapid detection of respiratory viral antigens. (ii) This technique can be applied to viral diagnosis in clinical samples.

Objectives and study design: (i) To study the identification of six common respiratory viral pathogens by flow cytometry, in virus infected and uninfected cultured cells, as models of positive and negative clinical samples. (ii) To compare flow cytometry with the established techniques of viral isolation and immunofluorescent microscopy in the diagnosis of respiratory syncytial virus infection in 68 naso-pharyngeal aspirates taken from children and sent to the virology laboratory for routine virological diagnosis.

Results: (i) For each virus analysed, populations of infected and non-infected cells were clearly discernable, confirming potential for this method in rapid viral diagnosis in clinical samples. (ii) Two definitions were employed for a sample to be positive by flow cytometry, these were compared with the combined established techniques. The sensitivity, specificity, positive and negative predictive values of flow cytometry were 41%, 98%, 92% and 71% for the first definition and 74%, 88%, 80% and 84% for the second definition respectively.

Conclusions: As tested in this study, flow cytometry is less sensitive than established techniques as well as recently developed rapid diagnostic techniques for the diagnosis of respiratory syncytial virus infection. Further evaluation of the potential of flow cytometry in rapid viral diagnosis is warranted.