Prevalence of disseminated Mycobacterium avium complex infection in Thai AIDS patients.

Infections caused by nontuberculous mycobacteria (NTM), although rare in immuno-competent individuals, can potentially produce problems in immunocompromised patients such as those with acquired immunodeficiency syndrome (AIDS). In this study, hemocultures for mycobacteria using radiometric BACTEC 13A media were taken from 334 patients with known human immunodeficiency virus infection admitted to four referral hospitals with fever of unknown site of infection and negative blood cultures for pathogenic bacteria. The mycobacterial hemocultures were positive for Mycobacterium avium complex (MAC) in 58 patients (17.4%) and positive for Mycobacterium tuberculosis in 34 patients (10.2%). The results of this study have proved that MAC infection, indeed, exists among Thai AIDS patients. The prevalence of MAC infection in Thailand is very high and comparable to that in the western countries. Physicians taking care of AIDS patients in Thailand should be aware of potential MAC infection, particularly in advanced cases. Considering the high prevalence of infection, primary prophylaxis against MAC infection in advanced AIDS patients is recommended.

Kat G mutations in isoniazid resistant Mycobacterium tuberculosis isolates from Thai patients.

Isoniazid resistant mechanisms in Mycobacterium tuberculosis have been shown to involve at least two genes, kat G and inh A. Alteration in the kat G gene has been found in a great number of resistant isolates. Percentage of resistant isolates harboring alteration in this gene varied among laboratories suggesting that different mutations were presented in different geographic areas. Fourteen isoniazid resistant and five multidrug resistant isolates from the Central Chest Hospital, Thailand, were examined for the kat G gene mutations in the region between base position 17 to 299. No different pattern of mutations were found between these two groups. Among nineteen isolates, there were nine isolates which showed point mutations and five isolates with base insertions of the kat G gene. The remaining five isolates revealed gene deletion. Heteroduplex formation technique also confirmed base alterations in these nine mutants.

Analysis of RNA polymerase gene mutation in three isolates of rifampicin resistant Mycobacterium tuberculosis.

Drug resistance in tuberculosis (TB) has become a major public health threat, particularly when the disease cannot be 100% controlled by BCG vaccination. In Thailand, resistance to rifampicin, a major component of multidrug regimens of treatment, is the common cause of tuberculosis recurrence. The mechanism of rifampicin resistance involves alterations of the RNA polymerase subunit beta (rpo B) gene. Mutations in rpo B gene were often found to cluster within a region of 23 amino acids starting from amino acid residue 511 to residue 533. Direct PCR sequencing was utilized to compare base changes in rpo B gene in three rifampicin resistant phenotypes of M. tuberculosis isolated from Thai patients. The sequences showed one base substitution at codon 531 resulting in an amino acid change from serine (TCG) to leucine (TTG) in a multidrug resistant isolate compared to that of a sensitive isolate, whereas a point mutation at codon 516 causing a change from aspartic acid (GAC) to tyrosine (TAC) was detected in a multidrug resistant isolate from a HIV positive patient. In an isolate resistant only to rifampicin a double mutation at codon 531 changing serine (TCG) to phenylalanine (TTT) was found. No mutations were observed in the same region in streptomycin, ethambutol or isoniazid resistant isolates. This finding reports two new types of mutation (GAC to TAC at codon 516 and TCG to TTT at codon 531) and confirms a direct correlation between rpo B gene alteration and rifampicin resistant phenotype in M. tuberculosis.

Prevalence of drug resistance in Thai human immunodeficiency virus seropositive tuberculosis patients.

The emergence of drug resistant tuberculosis has been reported from many countries which have had epidemics of human immunodeficiency virus (HIV) infection. This study was conducted at the Central Chest Hospital, Thailand in order to determine the prevalence of drug resistance before treatment in Thai HIV-infected tuberculosis patients. From the Statistics and Registration Unit, pulmonary tuberculosis patients with HIV seropositivity were matched in terms of age and gender with control cases who attended the tuberculosis clinic on the same day. Results of sensitivity test were obtained from record cards in the Microbiology Section. The method for determining the sensitivity test was absolute concentration. During the study period from January 1988 to December 1993, 798 patients were registered as having tuberculosis and HIV infection. Only 406 sensitivity tests were available before treatment and resisted to Isoniazid 56 (13.8%), rifampicin 36 (8.9%), ethambutol 6 (1.5%), streptomycin 64 (15.8%) and Multidrug resistant (MDR)- TB 11 (2.7%). In the control group, 475 tests were available and resisted to isoniazid 61 (12.8%), rifampicin 52 (10.9%), ethambutal 2 (0.4%), streptomycin 46 (9.7%) and MDR-TB 13 (2.7%). The prevalence of resistance to each drug was not significantly different except for streptomycin. We concluded that the prevalence of antituberculous drug resistance among Thai HIV-infected tuberculosis patients was not higher than among general tuberculosis patients.