Novel method for processing respiratory specimens for detection of mycobacteria by using C18-carboxypropylbetaine: blinded study.
A novel method for processing respiratory specimens to improve culture and acid-fast staining of mycobacteria is introduced. This new method utilized N,N-dimethyl-N-(n-octadecyl)-N-(3-carboxypropyl)ammonium inner salt (Chemical Abstract Service no. 78195-27-4), also known as C18-carboxypropylbetaine (CB-18). In a blinded, five-center study, CB-18-based processing was compared to the standard method combining NALC and NaOH (NALC/NaOH). A total of 573 respiratory specimens were tested. Individual specimens were split approximately equally; the host institutions processed half of each specimen by the NALC/NaOH method, while the other half was processed with CB-18 at Quest Diagnostics--Baltimore. A total of 106 specimens were culture positive for acid-fast bacilli (AFB). Replacement of the primary decontamination agent with CB-18 caused changes in all diagnostic parameters. Aggregate culture sensitivity improved by approximately 43% (P < 0.01), and smear sensitivity improved by approximately 58% (P < 0.01). The sensitivity of smear relative to that of M. tuberculosis isolates exceeded 93% (P < 0.01) when specimens were processed with CB-18. The average times to a positive result were reduced by 7.3 days in liquid culture (P < 0.01) and 5.3 days on solid media (P < 0.05); however, the CB-18 method had a 20.8% contamination rate in liquid culture versus a rate of approximately 7.5% with NALC/NaOH processing. There were also unusual reductions in liquid culture sensitivity and smear specificity among CB-18-processed specimens. The characteristics of the latter parameters suggested that refinement of the CB-18 processing method should allow further improvements in culture sensitivity. This study showed that the CB-18 method has the potential to improve both smear and culture detection for these important human pathogens.
Thornton
C G
CG
Department of Molecular Biology and Genetics, Quest Diagnostics--Baltimore, Maryland 21227, USA. thornton@msmail.mml.com
MacLellan
K M
KM
Brink
T L
TL
Lockwood
D E
DE
Romagnoli
M
M
Turner
J
J
Merz
W G
WG
Schwalbe
R S
RS
Moody
M
M
Lue
Y
Y
Passen
S
S
D001431:Bacteriological Techniques; D001622:Betaine / Q000031:analogs & derivatives*; D001980:Bronchi / Q000382:microbiology; D004396:Coloring Agents; D003470:Culture Media; D005069:Evaluation Studies as Topic; D006801:Humans; D009161:Mycobacterium / Q000145:classification / Q000254:growth & development / Q000302:isolation & purification*; D009165:Mycobacterium Infections, Nontuberculous / Q000175:diagnosis / Q000382:microbiology; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification*; D009170:Nontuberculous Mycobacteria / Q000302:isolation & purification*; D011933:Reagent Kits, Diagnostic; D012680:Sensitivity and Specificity; D016037:Single-Blind Method; D013048:Specimen Handling; D013183:Sputum / Q000382:microbiology*; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000382:microbiology
C114390:C(18)-carboxypropylbetaine; D004396:Coloring Agents; D003470:Culture Media; D011933:Reagent Kits, Diagnostic; D001622:Betaine