Rapid method for testing susceptibility of Mycobacterium tuberculosis by using DNA probes.

The increasing number of multidrug-resistant Mycobacterium tuberculosis strains has stimulated the interest of investigators in finding a rapid method for susceptibility testing. We used commercially available rRNA DNA-bioluminescence-labelled probes (Accu-Probe, Gen Probe, Inc. San Diego, Calif.) for this purpose. The study was performed in three chronological steps. (i) We studied the correlation between the photometric light units (PLUs) given by the hybridization method, the numbers of CFU per milliliter, and turbidity as nephelometric units for six different inocula of an M. tuberculosis strain over 14 days. A good correlation (c > 0.9; P < 0.05) was found from the third day for all concentrations used. (ii) Over a period of 14 days we studied the evolution of the PLUs for 20 strains growing in medium with 0.2 microl of isoniazid (H) per ml and 18 strains in medium with 1 microl of rifampin (R) per ml to standardize the method. Susceptible and resistant strains were used according to the reference proportions method in Middlebrook 7H10, and the MICs were determined in solid and liquid media. The final inoculum of a 10(-2) dilution from a McFarland no. 1 standard and reading at 3 and 5 days provided the best results. A quotient was established to find a cutoff point between resistant and susceptible strains. (iii) We used the standardized parameters in 117 tests with H and R. On day 3, the sensitivity, specificity, positive predictive value, and negative predictive value for detecting resistant strains were 86.8, 100, 100, and 90.1%, respectively, and on day 5 they were 96.2, 100, 100, and 94%, respectively. We concluded that the method is readily available, is easy to perform, and could be useful for screening resistant M. tuberculosis strains.

[Serologic study in patients with streptococcal infective endocarditis]. / Estudio serológico en pacientes con endocarditis infecciosa estreptocócica.

BACKGROUND: Infective endocarditis is a systemic disease in which there are a continuously antigenic stimulation of immunologic system. Streptococcus is still the most frequent cause of infective endocarditis. PATIENTS AND METHODS: We investigated the presence of antibody (AB), total and IgM by indirect immune fluorescence technique, in four groups of population: streptococcal infective endocarditis (SIE), streptococcal bacteraemia (SB), Staphylococcus aureus endocarditis, and healthy people. Antigens used were: 1) their own strain isolated from the blood of patients with SIE and SB ¿homologous AB¿, and; 2) seven species of Streptococcus: Streptococcus intermedius, Streptococcus salivarius, Streptococcus bovis, Streptococcus sanguis I, Streptococcus sanguis II, nutritional dependent streptococci and Enterococcus faecalis (heterologous AB). RESULTS: Homologous antibodies: titers > or = 1/512 were found in all patients with SIE and only in 2 with SB (sensitivity 100% and specificity 93%). IgM titer (threshold 1/32) was positive only in patients with SIE (sensitivity 75,5% and specificity 100%). The fall of the AB titer was continuous and slow, despite the good clinical evolution of patients. (AB titers were > or = 1/512 and IgM > or = 1/64 in 30% of patients 1 year later). Heterologous AB: in spite of statistically significant difference found in SIE versus the other groups, sensitivity of this test (threshold 1/256) is low, confidence interval include expected random value (50%), specificity is 88%. CONCLUSIONS: The utility of homologous AB for diagnosing infective endocarditis is demonstrated. On the contrary for heterologous AB, antigenic common fractions must be found in the different species.

[Bite wound infections: study of 22 hospitalized patients]. / Infecciones en heridas por mordedura: estudio de 22 pacientes hospitalizados.

BACKGROUND: To study the characteristics of bite wounds with unfavorable evolution, developing infectious complications that requires hospital admission. METHODS: The data from 22 patients admitted to the Ciudad Sanitaria Vall d'Hebron hospital for the above mentioned reason over the last 5 years were reviewed. RESULTS: The patients (8 males, 8 females and 6 children) were bitten by 10 dogs, 6 cats, and 6 men with predominance of the wound site being in the upper limb (10) followed by the lower limbs (6), head or face (5) and exceptionally on the breast (1). The most frequent clinical manifestation was abscess and/or cellulitis (13) and adenopathies or lymphangitis (4); 5 patients presented osteoarticular involvement including 3 bone fractures due to human aggression. With regard to the etiology of infection, the common bucal flora bacteria were isolated in all the cases; Pasteurella multocida in 15/16 animal bites, Eikenella corrodens associated to streptococcus in 5/6 human bites, Fusobacterium spp. (5), Bacteroides spp. (3) and Peptococcus sp. (1). The most frequently administered antibiotics were gentamycin (15), penicillin (13), cloxacillin (5) and clindamycin (4). The evolution was favorable, although slow in many cases, with sequelae in 3 patients. CONCLUSIONS: It is very difficult to foresee in which cases infectious complications will develop in bite wounds. According to the authors' experience, in the case of deep wounds the bacteria implied come from the mouth of the aggressor. Careful cleansing, rapid administration of an adequate antibiotic and clinical control being the most recommendable procedure.

[Bacteremia caused by Mycobacterium tuberculosis and/or Mycobacterium avium detected by the non-radiometric Bactec system]. / Bacteriemia por Mycobacterium tuberculosis y/o Mycobacterium avium detectada con el sistema Bactec no radiométrico.

BACKGROUND: To assess the utility of Bactec non-radiometric system in detecting disseminated mycobacteremia. METHODS: Blood cultures are processed using the Bactec NR 660/HPS system. Incubation of the NR6A vials, from HIV infected patients, is prolonged for 6 weeks and read once a week. After the 14th day of incubation a growth value > or = 30 is considered positive. RESULTS: Mycobacteria were recovered from 80 blood cultures from 32 human immunodeficiency virus infected patients. The mean time required to detect growth was 37.8 days (range 20-45). Mycobacterium tuberculosis was isolated from 18 patients and Mycobacterium avium from 14. In 12 patients (37.5%) blood culture was the first or the only positive specimen. CONCLUSIONS: Prolonged incubation of NR6A medium has proved to be a suitable method for detecting mycobacteremia.