Comparison of phenotypic methods and matrix-assisted laser desorption ionisation time-of-flight mass spectrometry for the identification of aero-tolerant Actinomyces spp. isolated from soft-tissue infections.

Aero-tolerant Actinomyces spp. are an under-recognised cause of cutaneous infections, in part because identification using conventional phenotypic methods is difficult and may be inaccurate. Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) is a promising new technique for bacterial identification, but with limited data on the identification of aero-tolerant Actinomyces spp. This study evaluated the accuracy of a phenotypic biochemical kit, MALDI-TOF MS and genotypic identification methods for the identification of this problematic group of organisms. Thirty aero-tolerant Actinomyces spp. were isolated from soft-tissue infections over a 2-year period. Species identification was performed by 16 s rRNA sequencing and genotypic results were compared with results obtained by API Coryne and MALDI-TOF MS. There was poor agreement between API Coryne and genotypic identification, with only 33% of isolates correctly identified to the species level. MALDI-TOF MS correctly identified 97% of isolates to the species level, with 33% of identifications achieved with high confidence scores. MALDI-TOF MS is a promising new tool for the identification of aero-tolerant Actinomyces spp., but improvement of the database is required in order to increase the confidence level of identification.

Bacterial contamination of hands and the environment in a microbiology laboratory.

This study investigated both the impact of glove usage on bacterial hand contamination of laboratory technicians and extent of environmental contamination of a microbiology laboratory with potential bacterial pathogens. Two groups of laboratory technologists participated in the study - one group who always used gloves when handling bacterial cultures and another group who did not. Semiquantitative bacterial sampling from technicians' hands was performed before and after a defined work period. Frequently touched areas of the laboratory were sampled over a four-week period and selective or chromogenic media utilised for the identification of meticillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Salmonella spp. and Enterobacteriaceae. Laboratory technicians who did not use gloves were at significantly greater risk of acquiring MRSA following their work periods but no protective effect was demonstrated for glove usage against acquisition of Enterobacteriaceae. Hand washing was equally effective at removing acquired bacterial pathogens in both groups of workers. Environmental sampling documented the presence of MRSA in one-fifth of sampled sites, with the most frequent recovery from computer keyboards. Enterobacteriaceae and P. aeruginosa were less commonly recovered from the environment. This study demonstrates that glove usage is protective against the acquisition of MRSA and that MRSA is the most frequently recovered bacterial pathogen from our microbiology laboratory environment.

Evaluation of disc susceptibility tests performed directly from positive blood cultures.

AIMS: To evaluate the accuracy of direct disc susceptibility testing performed from positive BACTEC blood culture vials, using a predetermined dilution protocol. METHODS: Direct susceptibility testing was performed from 432 positive blood culture vials, generating 3829 antibiotic-organism results. Results were compared with those obtained by standard disc susceptibility testing according to Clinical Laboratory Standards Institute (CLSI) methods. RESULTS: When results were compared with the reference method, no very major errors were detected. One (0.03%) major error and 89 (2.3%) minor errors were found. Error rates by organism group ranged from 1.3% for Pseudomonas aeruginosa to 8.2% for beta-haemolytic streptococci. CONCLUSIONS: Direct susceptibility testing provided accurate susceptibility results for most organism-antibiotic combinations, with the exception of the beta-haemolytic streptococci.