Update in tuberculosis 2008

Hsp65 phylogenetic assay for molecular diagnosis of nontuberculous mycobacteria isolated in Mexico

BACKGROUND AND AIMS

Nontuberculous mycobacteria (NTM) are mainly distributed as important emerging pathogens in patients with chronic or immunosuppressive diseases. Accurate identification of causative species is crucial for proper treatment and patient follow-up. However, several difficulties are associated with phenotypic and molecular diagnostic methods for precise identification at the species level due to shared metabolic and genetic characteristics. We undertook this study to evaluate the application of the phylogenetic method based on hsp65 gene into Telenti's PCR-restriction enzyme analysis (PRA) for molecular identification of NTM.

METHODS

The study population was comprised of 1646 Mycobacterium clinical isolates (AFB positive) collected from 2008-2011, of which 537 (32.6%) were MNT identified by PRA analysis. DNA sequencing of hsp65 in 53 isolates (10%) was performed. Sequence identification through NCBI-Basic Local Alignment Search Tool (BLAST) achieved correct identification in 23 isolates. Phylogenetic trees including hsp65 available GenBank sequences for all described genres of NTM and hsp65 obtained sequences were constructed using Mega 5.05 software. We compared sequence identification based on phylogenetic clustering and BLAST similarity search.

RESULTS

Phylogenetic clustering allowed more specific differentiation of closely related species and clearer identification in comparison with BLAST; 30 Mycobacterium species (this is the first report of isolation of some of these from clinical samples in Mexico) were identified in this way.

CONCLUSIONS

The proposed 440 bp hsp65 phylogenetic method allows a better identification tool to differentiate Mycobacterium species and is useful to complement diagnosis and epidemiological surveillance of NTM.

Hypoalbuminemia and lymphocytopenia are predictive risk factors for in-hospital mortality in patients with tuberculosis

OBJECTIVE

The aim of this study was to clarify the association between nutritional state on admission and in-hospital death in tuberculosis (TB) patients, including a high proportion of elderly patients.

METHODS

A retrospective cohort study of 246 TB patients was conducted. The serum albumin concentrations and peripheral blood lymphocyte counts were measured on admission, and the primary outcome of interest was in-hospital death. Patient mortality was categorized into two groups: TB death and non-TB death. A multivariate analysis was performed to evaluate the relationship between nutritional state on admission and in-hospital mortality in TB patients.

RESULTS

The median [interquartile range] patient age was 79 [69-83] years, and the in-hospital death rate was 20.73% (TB death: 26 patients; non-TB death: 25 patients). The multivariate analysis revealed that the serum albumin concentrations (OR: 0.21, 95% CI: 0.10-0.41; p<0.0001) and peripheral blood total lymphocyte counts (Category 2 [627.2-1,106.7/mm(3)] vs. 1 [<627.2/mm(3)]. OR: 0.28, 95% CI: 0.11-0.73; p=0.009, Category 3 [>1,106.7/mm(3)] vs. 1. OR: 0.24, 95% CI: 0.08-0.76, p=0.015) on admission were significantly associated with all in-hospital deaths in the TB patients. The serum albumin concentrations and peripheral blood total lymphocyte counts were also found to be associated with in-hospital deaths directly caused by TB.

CONCLUSION

Hypoalbuminemia and lymphocytopenia on admission are predictive risk factors for in-hospital mortality in TB patients. Nutritional defects should thus receive special attention in order to reduce TB patient mortality, particularly among elderly patients.

Prevalence of positive carriage of tuberculosis, methicillin-resistant Staphylococcus aureus, and vancomycin-resistant Enterococci in patients transported by ambulance: a single center observational study

OBJECTIVES

An ambulance can be a potential source of contagious or droplet infection of a community. We estimated the prevalence of positive carriage of tuberculosis (TB), methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococci (VRE) in patients transported by ambulance.

METHODS

This was a retrospective observational study. We enrolled all patients who visited a tertiary teaching hospital emergency department (ED). Blood, sputum, urine, body fluid, and rectal swab samples were taken from patients when they were suspected of TB, MRSA, or VRE in the ED. The patients were categorized into three groups: pre-hospital ambulance (PA) group; inter-facility ambulance (IA) group; and non-ambulance (NA) group. Adjusted odds ratio (OR) and 95% confidence intervals (CI) were calculated using a multivariable logistic regression model for the prevalence of each infection.

RESULTS

The total number of patients was 89206. Of these, 9378 (10.5%) and 4799 (5.4%) were in the PA and IA group, respectively. The prevalence of TB, MRSA, and VRE infection were 0.3%, 1.1%, and 0.3%, respectively. In the PA group, the prevalence of TB, MRSA, and VRE were 0.3%, 1.8%, and 0.4%. In the IA group, the prevalence of TB, MRSA, and VRE were 0.7%, 4.6%, and 1.5%, respectively. The adjusted ORs (95% CI) of the PA and IA compared to the NA group were 1.02 (0.69 to 1.53) and 1.83 (1.24 to 2.71) for TB, 2.24 (1.87 to 2.69) and 5.47 (4.63 to 6.46) for MRSA, 2.59 (1.78 to 3.77) and 8.90 (6.52 to 12.14) for VRE, respectively.

CONCLUSIONS

A high prevalence of positive carriage of TB, MRSA, and VRE in patients transported by metropolitan ambulances was found.

Resuscitation-promoting factors reveal an occult population of tubercle Bacilli in Sputum

RATIONALE

Resuscitation-promoting factors (Rpfs) are a family of secreted proteins produced by Mycobacterium tuberculosis (Mtb) that stimulate mycobacterial growth. Although mouse infection studies show that they support bacterial survival and disease reactivation, it is currently unknown whether Rpfs influence human infection. We hypothesized that tuberculous sputum might include a population of Rpf-dependent Mtb cells.

OBJECTIVES

To determine whether Rpf-dependent Mtb cells are present in human sputum and explore the impact of chemotherapy on this population.

METHODS

In tuberculous sputum samples we compared the number of cells detected by conventional agar colony-forming assay with that determined by limiting dilution, most-probable number assay in the presence or absence of Rpf preparations.

MEASUREMENTS AND MAIN RESULTS

In 20 of 25 prechemotherapy samples from separate patients, 80-99.99% of the cells demonstrated by cultivation could be detected only with Rpf stimulation. Mtb cells with this phenotype were not generated on specimen storage or by inoculating sputum samples with a selection of clinical isolates; moreover, Rpf dependency was lost after primary isolation. During chemotherapy, the proportion of Rpf-dependent cells was found to increase relative to the surviving colony-forming population.

CONCLUSIONS

Smear-positive sputum samples are dominated by a population of Mtb cells that can be grown only in the presence of Rpfs. These intriguing proteins are therefore relevant to human infection. The Rpf-dependent population is invisible to conventional culture and is progressively enhanced in relative terms during chemotherapy, indicating a form of phenotypic resistance that may be significant for both chemotherapy and transmission.