Test Description
Identification (First Step)
After culture on agar, an analysis using MALDI-TOF mass spectrometry is performed. The result of this initial analysis is reported immediately. Depending on the nature of the microorganism, identification may reach the genus or species level.
Randomly Amplified Polymorphic DNA Typing (RAPD)
Strains are typed using the RAPD technique to quickly assess whether there is similarity with previous isolates of the same species from the same patient.
Antibiotic Susceptibility Testing
Microdilution is used to determine the isolate’s susceptibility to antibiotics based on the species. The tested antibiotics include:
Temocillin; Piperacillin; Piperacillin/tazobactam; Aztreonam; Ceftazidime; Ceftazidime/avibactam; Ceftolozane/tazobactam; Cefiderocol; Meropenem; Ciprofloxacin; Levofloxacin; Tobramycin; Amikacin; Tigecycline; Eravacycline; Trimethoprim/sulfamethoxazole; Colistin
Antibiotics for which there is known intrinsic resistance are reported as resistant without performing a test.
Interpretation of antibiotic susceptibility is based on PK/PD data or Pseudomonas spp. breakpoints from EUCAST, or in some cases, CLSI critical values are used with provisional interpretation.
Purpose of the Test
The objective of these tests is to quickly obtain a preliminary identification of inert Gram-negative bacilli. Antibiotic susceptibility testing is intended to help guide antimicrobial therapy. It should be noted that there are few guidelines for the clinical interpretation of the susceptibility of these bacteria, and results should be interpreted with caution.
Criteria for Performing This Test in the Context of Reference Activities
- Patients with Cystic Fibrosis: Laboratories are advised to refer up to two respiratory isolates per patient per year per bacterial species to the National Reference Center (NRC).
- Other Patients: Only with well-documented justification (e.g., outbreak investigation, unusual clinical presentation).
Sample Collection
Specimen
Bacterial isolates from cultures of respiratory secretions of a cystic fibrosis patient or relevant specimens from other patients.
Storage
Not applicable.
Transport
Isolates are transported to the NRC without refrigeration. The NRC does not provide transport materials; the referring laboratory uses its own (e.g., tubes with nutrient medium or Petri dishes) for transport according to UN3373 standards.
Unacceptable Requests
Indications
- Isolates without clinical relevance.
- Isolates of Pseudomonas aeruginosa or Acinetobacter spp.
- Environmental isolates (unless under a specific agreement for exceptional circumstances, such as an outbreak investigation).
- Isolates without a completed request form.
- A maximum of two isolates per species per patient per calendar year are accepted.
Sample Collection
The NRC does not accept primary clinical samples.
Turnaround Time
- Preliminary Identification: 2 working days. A first MALDI-TOF MS analysis is generally possible after overnight incubation, with results reported the following day.
- Antibiotic Susceptibility Testing: 5 days.
- RAPD Typing: 14 days.
Result Transmission
- By mail.
- Via Medibridge for laboratories and prescribers registered with UZ Brussel.