Differentiation of Mycobacterium tuberculosis from other mycobacteria with rho-nitrobenzoic acid using MGIT960.

SETTING: Mycobacteria growth in media with the addition of inhibitory substances has been used in species identification. Growth of the Mycobacterium tuberculosis complex (MTC) is inhibited by rho-nitrobenzoic acid (PNB), whereas non-tuberculous mycobacteria (NTM) are resistant. OBJECTIVE: To develop a rapid PNB test using the automated BACTEC MGIT960 system and to evaluate its usefulness in the screening of mycobacterial isolates. DESIGN: PNB tests were performed in 93 MTC strains and 61 NTM strains from the Instituto Adolfo Lutz Culture Collection. PNB was added to Löwenstein-Jensen (LJ) medium and to BACTEC MGIT960 medium. RESULTS: The MTC strains were all PNB-susceptible, confirming the original identification. Among 10 NTM species, all were found to be resistant to PNB, except for one strain of M. kansasii and another of M. marinum. The median time to obtain presumptive identification of MTC by inhibition test in the BACTEC MGIT960 system was 6.3 days and for NTM it was 2.5 days. The presumptive identification of MTC in LJ was mostly obtained after day 20. CONCLUSION: The key finding of this analysis was the possibility of combining the traditionally accepted method proposed by Tsukamura and Tsukamura in 1964 with the modern, safe and rapid BACTEC MGIT960 methodology.

Drug resistance of strains of Mycobacterium tuberculosis isolated in Brazil.

Tuberculosis remains a serious public health problem, worsened by an increased frequency of multidrug-resistant Mycobacterium tuberculosis. We report here a retrospective study of resistance to antituberculosis drugs of 170 strains of M. tuberculosis isolated from the state of Rio Grande do Sul, Brazil. The frequency of resistance to at least one drug was 34%, while 22% were resistant to more than one drug. Among the strains isolated from patients without a history of previous treatment for tuberculosis, patients with positive serology for HIV and patients with previous treatment for tuberculosis, the resistance to at least one drug was 14, 27 and 73%, respectively. Multidrug-resistant tuberculosis, defined as resistant to at least rifampicin (RMP) and isoniazid (INH), was found in the groups of patients without previous treatment, HIV co-infected and with previous treatment for tuberculosis at 10, 17 and 44%, respectively. With the purpose of evaluating whether the sensitivity test to INH and RMP would be a good marker to indicate resistance to other antituberculosis drugs, sensitivity tests were performed with four more drugs in 32 strains, initially classified as resistant to INH, RMP or both. Of 18 strains resistant to INH and RMP simultaneously, 89% showed resistance to four more drugs.

Typing of Staphylococcus aureus from surgical site infections: comparison of pulsed-field gel electrophoresis (PFGE) and PCR technique using repetitive extragenic palindromic (rep) and Tn916-Shine-Dalgarno (TnSD) target sequences.

Staphylococcus aureus continues to be the main cause of surgical site infections. DNA typing is useful for studying this type of infection and establishing control programs within hospitals. In this study 19 S. aureus strains were isolated from surgical site infections of 19 patients, between August and December 1994 at the Rio de Janeiro University Hospital. The strains were typed by pulsed-field gel electrophoresis (PFGE) and by two polymerase chain reaction techniques targeting the repetitive extragenic palindromic and Tn916-Shine Dalgarno sequences. Analysis of the PFGE patterns divided the collection into 15 types, while PCR techniques identified 11 distinct strain patterns. There were two clusters, 1 of four strains and 1 of two strains with related PFGE and PCR patterns. Of the remaining strains, 10 were clustered in 5 PCR patterns but their PFGE patterns showed 4 to 6 different bands, and they were considered to be possibly related. The comparison of the S. aureus typing systems in the present study indicated that the PCR methods are useful for initial screening of genetically related isolates, but strains with identical PCR fingerprint need to be typed with PFGE for detailed strain differentiation.

Multiple isolates from aids patients: aspects of an analysis by a genotypic marker and antimicrobial susceptibilities variations.

Twenty-one Mycobacterium avium multisolates, from ten human immunodeficiency virus-infected patients, were typed by restriction fragment length polymorphism using as marker the IS1245 and characterized by minimum inhibitory concentration for nine different antibiotics. Two out of four patients harboring multisolates with different fingerprint profile, were therefore considered as having a polyclonal infection, since their isolates were taken from sterile site. This result confirms that polyclonal infection caused by M. avium occurs with a nonnegligenciable frequency. Analyzing the multisolates susceptibility profile of each patient it was observed that most of them were infected with strains having appreciably different antimicrobial susceptibility patterns, no matter what the genotypic pattern of the strains was. These results have strong implication for the treatment of the patients.

Emergence of high-level mupirocin resistance in methicillin-resistant Staphylococcus aureus isolated from Brazilian university hospitals.

Surveillance for methicillin-resistant Staphylococcus aureus (MRSA) was implemented in Rio de Janeiro and Uberlândia University Hospitals, which had different policies on use of mupirocin. One hundred fourteen multiresistant MRSA strains were isolated from 62 patients. Mupirocin resistance was observed in 63% of strains in Rio de Janeiro, where there was extensive use of topical mupirocin, and 6.1% in Uberlândia, where its use was rare.

Use of the 2,3-diacyl-trehalose and the purified protein derivative in the serodiagnosis of tuberculosis in AIDS.

The effect of the human immunodeficiency virus (HIV) infection on IgG production against purified protein derivative (PPD) and 2,3-diacil-trehalose (SL-IV) was investigated by an enzyme-linked immunosorbent assay (ELISA) test. Comparison between the antigens showed that immunocompetent patients produce preferentially antibodies to SL-IV than to PPD (73.3% versus 63.3%). Combination of these results showed an increase of the sensitivity to 80%, which decreased over the spectrum of immunodepression caused by HIV. In the tuberculous HIV seropositive group the sensitivities of SL-IV and PPD were 36.4% versus 40% and 0% versus 22.2% in the tuberculosis/acquired immunodeficiency syndrome (TB/AIDS) group. Combination of these results gave respectively 54.5% and 20%, showing that serological tests have limited value for diagnosis of tuberculosis in HIV infected patients. High antibody levels were observed in HIV seropositive asymptomatic group, but only two individuals were positive for both antigens. In the follow up, one of them developed tuberculous lymphadenitis, indicating that further work is needed to access the value of serological tests in predicting tuberculosis in HIV infected individuals.