The rate of recovery and time to the detection of mycobacteria in clinical specimens were measured in traditional egg-based media cultures and on Middlebrook 7H11 agar plate cultures using microcolony detection. In the 5438 specimens processed, a total of 293 (5.4%) clinically relevant mycobacterial isolates were detected (Mycobacterium tuberculosis, n = 231; Mycobacterium avium complex, n = 60; Mycobacterium kansasii, n = 2). Of these, 227 (77%) and 237 (81%) isolates were detected on Lowenstein-Jensen medium and Coletsos medium, respectively, and 265 (90%) isolates were detected on Middlebrook 7H11 plates examined microscopically. The detection time was shorter with the microcolony detection method. While the Lowenstein-Jensen and Coletsos media required an average of 23 and 25 days, respectively, for first detection of mycobacteria, microcolony detection on Middlebrook 7H11 required an average of only 12 days. For acid-fast, stain-positive specimens that were culture positive for Mycobacterium tuberculosis, the average interval to positivity was nine days for the microcolony method compared with 20 and 21 days for the Lowenstein-Jensen and Coletsos media, respectively. Microscopic detection on Middlebrook 7H11 agar plates is a rapid, accurate and inexpensive method of detecting Mycobacterium tuberculosis and other clinically important mycobacteria.

RESUMENEl arsénico se encuentra en estado natural en rocas, suelo, agua, aire y es liberado al ambiente mediante fenómenos naturales tales como erupciones volcánicas, erosión de las rocas e incendios forestales, donde los microorganismos son esenciales para el ecosistema por su participación en diferentes procesos naturales. El objetivo del trabajo fue aislar bacterias resistentes a arsénico, desde muestras de rocas provenientes de la Quebrada Camarones, región Parinacota, Chile. Las rocas fueron cultivadas en un medio mineral adicionado con arsenito (500 ug/ml) durante 7 días a temperatura ambiente y con agitación. Las cepas fueron aisladas en diferentes medios e identificadas mediante el sistema Rapid™NF plus. La capacidad de oxidar arsénico fue realizada mediante el ensayo cualitativo con nitrato de plata y la detección de genes aox, mediante RT-PCR. La reducción de arsénico fue evaluada mediante la amplificación de los genes ars por PCR. Se aislaron bacilos Gram negativos, no fermentadores, identificados como Pseudomonas alcaligenes y Wautersia solanacearum todas ellas capaces de tolerar concentraciones igual o mayor a 8 mM de As(III). Los análisis mediante RT-PCR demuestran la presencia de genes aox, que codifica para una enzima oxidante que cataliza la oxidación de As(III) a As(V). La capacidad de oxidar arsenito de las cepas aisladas, favorecería la colonización de otras especies no tolerantes a arsénico importantes en los ciclos biogeoquímicos. PALABRAS CLAVES: Arsenito, arseniato, Wautersia solanacearum, Pseudomonas alcaligenes. ABSTRACTArsenic is naturally present in rocks, soil, water, and air, being released to the environment by natural processes such as volcanic eruptions, and erosion rock. Microorganisms are known to play an important role in the Arsenic natural cycle. The aim of this work was isolate arsenic resistant bacteria to volcanic rocks, from Quebrada Camarones, Parinacota Region, Chile. Rocks were cultured in an arsenite conditioned mineral broth (500 ug/mL) over 7 days at ambient temperature, under stirring. Strains were isolated using different medium and identified by Rapid™NF plus system. The arsenic oxidation capacity was assayed with silver nitrate, and aox genes were detected by RT-PCR. Arsenic reduction was evaluated means ars gene amplification by PCR. Gram negative no fermentative bacillum, identified as Pseudomonas alcaligenes and Wautersia solanacearum able to tolerate concentrations above 8 mM As(III) were isolated. RT-PCR analysis showed the presence of aox, genes; these codify an oxidant enzyme that catalyses As(III) oxidation to As(V). The Arsenic oxidation capacity of the isolated seeds would favor colonization by other non tolerant species participating in biogeochemical cycles.