We employ the latter, with final dilution factors of 10_l,10, and 10-5 (Fig 2), similar to the method used for quantitative PSB cultures. Contaminants generally grow at a concentration ^lO cfu/ml and pathogens at a concentration ^lO cfu/ml, frequently ^lO.-* In practice, the quantitative method at one dilution (10 ~ dilution) obtained by plating 0.001 ml, similar to the handling of a urine culture, may be equally reliable (personal observation). ampicillin antibiotic
The methods used to diagnose mycobacterial infection include both acid-fast stains and culture. We perform both fluorescent auramine-rhodamine and Kinyoun or Ziehl-Neelsen stains because some mycobacteria, other than tuberculosis, may fail to stain well with the former. The diagnostic yield for BAL stains is, in our hands, generally low (22 percent for culture-positive BAL vs 60 percent for sputum), and diagnosis relies heavily on culture. For optimal isolation of M tuberculosis and other species, both conventional agar media (Lowenstein-Jensen or Middlebrook formulations) and liquid radiometric media (Bactec, Becton, Dickinson, Sparks, MD) should be used. The Bactec method has been shown to significantly increase the recovery of mycobacteria, particularly nontuberculous isolates, and to reduce time for culture positivity.
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