Comparison of Automated and Nonautomated Systems for Identification of Burkholderia pseudomallei

Abstract

The identification of Burkholderia pseudomallei, the causative agent of melioidosis, is usually not difficult in laboratories in areas where it is endemic. With the increase in international travel and the threat of bioterrorism, it has become more likely that laboratories in areas where it is not endemic could encounter this organism. The increase in the use of and dependence upon automated identification systems makes accurate identification of uncommonly encountered organisms such as B. pseudomallei critically important. This study compares the manual API 20NE and 20E identification systems with the automated Vitek 1 and 2 systems. A total of 103 B. pseudomallei isolates were tested and correctly identified in 98%, 99%, 99%, and 19% of cases, respectively. The failure of the Vitek 2 to correctly identify B. pseudomallei was largely due to differences in the biochemical reactions achieved compared to expected values in the database. It is suggested that this deficiency in the Vitek 2 may be due to the large number of uncertain results reported for these isolates. These results reduce the discriminating ability of the instrument to distinguish between uncommonly encountered isolates such as those of B. pseudomallei.Burkholderia pseudomallei, the causative agent of melioidosis, is endemic in regions of southeast Asia and northern Australia (8, 10, 13). Within Australia, disease is particularly prevalent in north Queensland and the Northern Territory, with peaks of disease usually associated with high levels of rainfall in the wet season. (2,11,14,15). Three forms of the disease are recognized, acute, subacute, and chronic. Infection occurs via ingestion, inoculation, or inhalation. Acute melioidosis commonly presents as a fulminant septicemia, often resulting in death within a few days of exposure. Mortality rates for acute septicemic melioidosis remain high despite antibiotic therapy (6, 18; J. Warner, D. Learoyd, B. Pelowa, J. Koehler, and R. G. Hirst, Abstr. Ann. Sci. Meet. Med. Soc. Papua New Guinea, p. 38, 1998). Chronic infection often remains asymptomatic and may persist for years (5,13,14). Reactivation of chronic infection to an acute form can occur when the host is immunocompromised (13,14,16).The laboratory diagnosis of melioidosis is best made with a culture of the appropriate clinical material. Serology has a role in the diagnosis of this condition, particularly in patients from areas where it is not endemic who travel to an area where it is endemic and develop a suggestive clinical condition. Serum samples from patients resident in areas where it is endemic can be positive in the absence of clinical disease. This would represent previous exposure and does not necessarily imply current disease. Other diagnostic methods that have been used include latex agglutination for detection of antigen in urine (17) and molecular detection (3).With the increase in international travel, melioidosis is increasingly likely to show up in regions where it is not normally endemic (7). For the routine diagnostic labo...

Melioidosis: an important cause of pneumonia in residents of and travellers returned from endemic regions

“…Identification of B. pseudomallei can be made by combining the commercial API 20NE or 20E biochemical kit with a simple screening system involving Gram stain, the oxidase reaction, typical growth characteristics and resistance to certain antibiotics [108,109]. Some commercial identification systems are poor at identifying B. pseudomallei [110]. Any confirmed culture of B. pseudomallei should be considered to represent active infection, although the rare possibility of sputum colonisation in people with chronic lung disease such as CF has recently been noted [59,106].…”

Development of Real-Time PCR Assays and Evaluation of Their Potential Use for Rapid Detection of Burkholderia pseudomallei in Clinical Blood Specimens

“…B. pseudomallei-specific antigen detection methods using monoclonal antibodies such as the latex agglutination assay and direct immunofluorescence appear to be useful for rapid identification of B. pseudomallei in Thailand, but these tests are not commercially available (21,24,33). Commercially available biochemical tests such as API 20NE have been reported to misidentify B. pseudomallei as a number of other bacterial species (12,16).…”

PCR-based identification of Burkholderia pseudomallei

“…Previous evaluations of B. pseudomallei identification methods have relied on assumptions about the sensitivity and specificity of the reference method or the culture collection used to validate the identification approach taken 4,10 . In our recent evaluation of confirmatory phenotypic methods, we regarded the semi-nested PCR protocol used during assembly of the B. pseudomallei culture collection as 100% reliable.…”