Detection and identification of Mycobacterium avium in the blood of AIDS patients by the polymerase chain reaction

Mycobacterium avium complex infection in patients with human immunodeficiency virus: A systematic review and meta-analysis

BACKGROUND

Mycobacterium avium-intracellulare complex (MAC) is one of the leading causes of death among people living with human immunodeficiency virus (HIV). The current study was aimed to determine the frequency of MAC infection in patients infected with HIV.

METHODS

Embase, PubMed, and Web of Science were searched for relevant studies. All statistical analyses were performed by STATA version 14.

RESULTS

From 6,627 retrieved articles, 23 were included in the final analysis. A total of 18,463 patients with HIV were included in the analysis. The frequency of MAC infection in patients with HIV was found to be 10.6% (95% confidence interval, 6.9-14.2).

CONCLUSION

The relatively large fractions of HIV-infected patients were coinfected with MAC, which may poses significant public health problems. Continued progress in the development of rapid diagnostic methods and preventive therapy for MAC should lead to further improvements in survival and quality of life in patients with HIV.

Selective enrichment and detection of mycobacterial DNA in paucibacillary specimens

A major challenge for tuberculosis control is mycobacterial detection in paucibacillary disease, particularly in pediatric, extrapulmonary and smear-negative pulmonary infections. We developed a simple and efficient DNA extraction and real-time quantitative PCR (qPCR) protocol for mycobacterial detection and quantification in paucibacillary specimens. The method was refined using an in vitro model mimicking blood specimens which are characterized by the presence of numerous qPCR inhibitors. Mycobacterial DNA detection in blood is of interest given the high sensitivity we previously reported using conventional PCR in blood of patients with tuberculosis lymphadenitis. Mechanical lysis of mycobacteria in the presence of an organic solvent provided the highest sensitivity. Mycobacterial DNA amplification was compromised when the human:bacterial genome ratio was at least 190:1. Separation of the specimen into bacterial- and host-rich fractions prior to DNA extraction improved mycobacterial DNA detection by 30%. Preliminary testing of our protocol in smear-negative, culture-positive specimens (gastric and lymph node aspirates, pleural and cerebrospinal fluid, and blood) confirmed the applicability of our technique to a range of paucibacillary specimens for the detection, quantification and speciation (M. tuberculosis versus M. avium) of mycobacteria, several weeks before culture results were available. Our protocol provides a novel, efficient and simple strategy to improve the performance of qPCR in paucibacillary specimens, including those with excess human DNA background. This tool is useful to study the pathophysiology of early pulmonary or occult tuberculosis, and for more rapid and accurate diagnosis in difficult to diagnose infections.

Culture of Mycobacterium avium subspecies paratuberculosis from the blood of patients with Crohn's disease

BACKGROUND

Crohn's disease, a form of inflammatory bowel disease, resembles some aspects of tuberculosis, leprosy, and paratuberculosis. The role of Mycobacterium avium subspecies paratuberculosis (MAP) in Crohn's disease is controversial.

METHODS

We tested for MAP by PCR and culture in buffy coat preparations from 28 individuals with Crohn's disease, nine with ulcerative colitis, and 15 without inflammatory bowel disease.

FINDINGS

MAP DNA in uncultured buffy coats was identified by PCR in 13 (46%) individuals with Crohn's disease, four (45%) with ulcerative colitis, and three (20%) without inflammatory bowel disease. Viable MAP was cultured from the blood of 14 (50%) patients with Crohn's disease, two (22%) with ulcerative colitis, and none of the individuals without inflammatory bowel disease. Current use of immunosuppressive medication did not correlate with a positive MAP culture. Sequencing of PCR products from MAP cultures confirmed the presence of the MAP-specific IS900 fragment. Among 11 MAP isolates assessed, we identified nine strains that were not identical.

INTERPRETATION

We detected viable MAP in peripheral blood in a higher proportion of individuals with Crohn's disease than in controls. These data contribute to the evidence that MAP might be a cause of Crohn's disease.

An assessment of a multiplex PCR assay for differentiating clinically important mycobacteria based on pncA gene variation

The pncA genes in mycobacteria are responsible for the production of pyrazinamidase (PZase). In Mycobacterium tuberculosis, PZase hydrolyses pyrazinamide (PZA) to pyrazonic acid, a compound that possesses bactericidal activity against tubercle bacilli. Nucleotide sequences of pncA genes found within mycobacteria where aligned in an effort to ascertain the significance of any variability in sequence. Three sets of primers (one degenerate and five consensus sequences) were designed and employed in a multiplex PCR assay to amplify the pncA region in seven clinically common mycobacteria. The banding patterns generated from each species in conjunction with PZase activity tests demonstrated that the mycobacterial species examined could be clearly identified and differentiated from one another. Although not yet tested with clinical isolates, the combination of these two assays has provided a promising discriminatory tool for the identification of commonly encountered clinical mycobacteria species.

PCR-hybridization assay for Mycobacterium avium complex: optimization of detection in peripheral blood from humans

We evaluated the sensitivity of a DNA amplification test for the detection of Mycobacterium avium in blood samples using different blood components and different DNA extraction methods. M. avium-inoculated blood samples were processed to obtain separate blood components: peripheral blood mononuclear cells (PBMCs), polymorphonuclear cells (PMNCs), and whole-blood sodium dodecyl sulfate (SDS)-lysate pellets. The sensitivity for the detection of the lowest mycobacterial load (1 CFU/ml) was significantly greater (P < 0.01) with DNA extracted from SDS-lysate pellets than with DNA extracted from PBMCs or PMNCs. Subsequently, DNA extraction methods based on guanidine NaOH, and proteinase were compared. The sensitivity of the guanidine-based method was significantly greater (P < 0.01) than those of the others.

Identification and semiquantitation of Mycobacterium avium using a competitive PCR method

A competitive PCR method with standard DNA (MIMIC) was developed for the rapid detection and semiquantitation of Mycobacterium avium (M. avium) using primers specific for the alpha antigen sequence of the bacteria. DNA from both M. avium and Mycobacterium marinum was amplified by polymerase chain reaction (PCR), but only M. avium could be detected by subsequent blotting confirmation with a probe specific for the bacteria. With the PCR and subsequent dot blot hybridization, as little as 10 fg of the M. avium DNA could be detected, equivalent to about 2 cells of the mycobacteria. In addition, we could distinguish 10(5) CFUs of M. avium from 10(4) CFUs or less by competitive PCR using a MIMIC. The present competitive PCR test enabled rapid identification and semiquantitation of M. avium, and could be used clinically to monitor disease severity and response to treatment of human M. avium disease.

Evaluation of IS1245-based PCR for detection of mycobacterium avium bacteraemia in AIDS patients

A PCR method based on the repetitive IS1245 sequence was evaluated for the detection of Mycobacterium avium bacteraemia in AIDS patients. Two blood preparation methods were applied: lysis of erythrocytes using a hypotonic buffer and Ficoll density centrifugation. Results were compared with culture and PCR amplification of the non-repetitive pMav22 sequence. Fifty-one of 251 tested samples grew M. avium. Bacterial densities lower than 10 cfu/ml blood were frequent, they occurred in 59% of blood samples from patients with mycobacteraemia. Inhibitory substances were detected more frequently with the lysis method (36%) than the Ficoll processed samples (19%). While specificity of PCR was high, sensitivities varied according to the methods used and the load of infection in the bloodstream. False-negative PCR results were attributable to low level bacteraemia and inhibition of PCR. Moreover, 1 of 186 and 9 of 51 M. avium strains investigated lacked the IS1245 and the pMav22 sequence, respectively. Sensitivities of culture, IS1245- and pMav22-based PCR were 88, 64 and 58%, within the lysis processed samples and 95, 86 and 50% using Ficoll prepared samples, respectively. Thus, we conclude that IS1245-based PCR is a rapid and specific method for diagnosing M. avium bacteraemia and shows a higher sensitivity than single copy gene targets, but that the sensitivity is inferior to culture.