UK standards for microbiology investigations of ear infection (SMI B1) are inadequate for the recovery of fungal pathogens and laboratory diagnosis of otomycosis: A real-life prospective evaluation.

BACKGROUND: We evaluated the recovery of fungal pathogens from clinical external ear samples from patients with otitis externa (OE) using the UK national Standard Microbiology Investigations of ear infection (SMI B1). METHOD: The UK SMI B1 protocol including a single Sabouraud dextrose agar with chloramphenicol (SABC) incubated at 37°C for 48 hours was compared with a standard fungal-specific culture method using two SABC agar plates incubated at 28 and 37°C for 2 weeks with an extra Candida chromogenic agar incubated at 37°C for 5 days. This real-life evaluation was undertaken on ear samples from patients with OE from January 2020 to December 2020. RESULTS: Altogether, 304 individual patient ear swabs were prospectively examined. The positivity rate of UK standard was 14% (42/304) versus 26% (79/304) for the fungal-specific protocol (p < .05). The standard protocol identified seven compared with 17 species using the fungal-specific protocol. A total of 93 fungal isolates were recovered; nine different yeasts and eight filamentous fungal species. Candida parapsilosis (38/304; 13%), C. albicans (10/304; 3%) and C. orthopsilosis (6/304; 2%) were common yeast species. Aspergillus niger complex (16/304; 5%) was the most common mould, followed by A. fumigatus complex (3/304; 1%). Many less common and emerging yeasts and moulds were only isolated from samples cultured using a fungal-specific protocol. CONCLUSION: Our results suggest that the UK SMI B1 media and procedures are inadequate to detect all fungal agents causing otomycosis. Fungal-specific culture protocols increase the recovery rate and diversity of fungal pathogens isolated from external ear samples.

Comparative evaluation of matrix-assisted laser desorption ionisation-time of flight mass spectrometry and conventional phenotypic-based methods for identification of clinically important yeasts in a UK-based medical microbiology laboratory.

AIMS: Performance of matrix-assisted laser desorption ionisation-time of flight mass spectrometry (MALDI-TOF MS) was compared in a side-by side-analysis with conventional phenotypic methods currently in use in our laboratory for identification of yeasts in a routine diagnostic setting. METHODS: A diverse collection of 200 clinically important yeasts (19 species, five genera) were identified by both methods using standard protocols. Discordant or unreliable identifications were resolved by sequencing of the internal transcribed spacer region of the rRNA gene. RESULTS: MALDI-TOF and conventional methods were in agreement for 182 isolates (91%) with correct identification to species level. Eighteen discordant results (9%) were due to rarely encountered species, hence the difficulty in their identification using traditional phenotypic methods. CONCLUSIONS: MALDI-TOF MS enabled rapid, reliable and accurate identification of clinically important yeasts in a routine diagnostic microbiology laboratory. Isolates with rare, unusual or low probability identifications should be confirmed using robust molecular methods.