Antibiotic susceptibility including tigecycline and MALDITOFMS of E.coli and S.aureus isolates

Abstract number: R2183


1To test tigecycline against ESBL producing E coli and MRSA isolates and compare results to those of the E-test programme

2To carry out antibiotic susceptibility to commonly used antibiotics using the Vitek 2 analyser

3To carry out MALDI-TOF-MS on the isolates and evaluate its potential in discriminating organisms

Methods: A total of 50 MSSA, 50 MRSA, 50 ESBL-producing E. coli and 20 non-ESBL producing E. coli isolates were obtained from Northampton hospital and county, from various specimen types. Presumptive identification of isolates was on chromogenic agar (Oxoid). Confirmation of MRSA and E. coli isolates identification and assessment of antimicrobial susceptibility was by Vitek 2 analysis. Tigecycline E-test was carried out on confirmed ESBL E. coli and MRSA isolates according to manufacturer's instructions (AB Biodisk, Solna, Sweden). For MALDI analysis, organisms were grown on Columbia blood agar plates with 5% horse blood overnight. Direct inoculation technique was carried out by emulsifying a single isolated colony using a 5ml loop onto a MALDI target well. This was left to dry before addition of 0.5 ml of CHCA matrix. MALDI-TOF-MS analysis was carried out using 95% laser power, a maximum of 120 profiles per minute and 5 shots per profile.

Results: MSSA was sensitive to most of the antibiotics, with reduced susceptibility to penicillin. MRSA isolates showed increased resistance to antibiotics e.g. ciprofloxacin but were sensitive to vancomycin, teicoplanin and linezolid. ESBL producing-E. coli isolates were 100% sensitive to meropenem and ertapenem, and 97% sensitive to piperacillin/tazobactam. Tigecycline exhibited 100% potency against 50 MRSA and 50 ESBL producing E. coli isolates with mic values of less than 1 mg/l. Tigecycline results were comparable to those of the E-test programme, e.g. Spain and Canada.

The MALDI fingerprints derived from 120 isolates produced rich peaks with high reproducibility. Hierarchical cluster analysis categorized the MALDI spectra precisely into groups according to the antibiotic sensitivity patterns of S. aureus and E. coli isolates as well as b-lactamase production.

Conclusion: This study highlighted the problem of antibiotic resistance and potency of tigecycline against resistant isolates. Furthermore, MALDI-TOF-MS was shown as a rapid method for identification of bacteria at species and subspecies level and useful for characterization according to antibiotic susceptibility pattern.

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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