Rapid Tool Detects Most Common Bacterial Pathogens

A novel microarray-based assay was developed to detect over 60 of the most common Gram-positive and Gram-negative bacterial species including detection of mecA, vanA and vanB resistance genes directly from osteoarticular samples.

An assessment has been made of the performance of the diagnostic platform on primarily culture positive samples by comparing its results to bacterial culture and an in-house broad-range bacterial polymerase chain reaction (PCR). The extensive evaluation included not only samples of osteoarticular origin but also samples from other primary sterile body sites.

Clinical microbiologists at the University Hospital Basel (Switzerland) collected clinical samples from January to May 2012 from in-patients. Out of 200 samples, 120 were obtained from the osteoarticular apparatus (65 biopsies, 42 implants, and 13 aspirates), and 80 other samples from body sites like pleura, ascites, cerebrospinal fluid (CSF), lung, pancreas, gallbladder, heart valve as well as intracardial or breast prosthetic devices (40 biopsies, 27 aspirates, 6 implants, 5 CSF samples, and 2 others).

Aerobic and anaerobic bacterial cultures were carried out following standard protocols including enrichment culture using thioglycolate medium. Broad-range bacterial PCR was performed and samples producing visible PCR products were sequenced on the ABI 3130 Capillary Sequencer (Applied Biosystems; Foster City, USA). DNA extracts were tested with the Prove-it Bone&Joint Assay (Mobidiag; Helsinki, Finland).

In 129/176 (73.3%) one microorganism was isolated, monomicrobial samples, and in 47/176 (26.7%) more than one microorganism were isolated, polymicrobial samples. The sensitivity of Prove-it Bone&Joint assay in monomicrobial osteoarticular samples was 62.6% and in non-osteoarticular, it was 52.2%. When only samples containing species covered by the panel were included in the calculation, the sensitivities of both sample types were 72.2% and 68.6%, respectively. The Prove-it assay correctly predicted methicillin resistance/susceptibility in all 66 samples where phenotypical susceptibility testing was performed. In two samples, a positive signal for Staphylococcus aureus and mecA gene was detected. One sample contained a true methicillin-resistant S. aureus (MRSA) strain, while the other sample contained methicillin-sensitive S. aureus and methicillin-resistant Staphylococcus epidermidis.

The authors concluded that concluded that the Prove-it Bone&Joint assay is a highly rapid diagnostic tool providing early information on the identity of the most common pathogens present not only in osteoarticular but also in other primary sterile samples while awaiting definitive results of the culture. Although this assay can only detect a limited number of bacterial species present in the Prove-it panel, it may serve as an alternative for broad-range bacterial PCR in laboratories that are not capable of performing this sequence-based molecular analysis. The study was published in the December 2014 issue of the Journal of Microbiological Methods.

Related Links:
University Hospital Basel
Applied Biosystems 
Mobidiag