ANTIMICROBIAL SUSCEPTIBILITY TESTING

Antimicrobial Susceptibility Reference Testing - Confirmation of Resistant Organisms

Drug resistant organisms continue to increase in prevalence and antimicrobial resistance is one of the most significant infectious disease problems of the millenium.  Numerous resources related to Antimicrobial Resistance laboratory testing and treatment of resistant organisms are available online. 

In addition, WPHL's Bacteriology Laboratory does confirmation testing for state clinical laboratories on isolates that show antimicrobial resistance.  The WPHL Bacteriology Laboratory does not perform routine antimicrobial susceptibility testing, only isolates that have preliminary susceptibility patterns indicating antimicrobial resistance will be accepted for confirmation testing. Those isolates that can be referred for confirmation testing include the ones listed below. 

Methicillin-resistant Staphylococcus aureus (MRSA)
Vancomycin resistant Enterococci (VRE)
Drug resistant Streptococcus pneumoniae (DRSP)
Extended-spectrum beta lactamases (ESBL’s)
Vancomycin-resistant or intermediate Staphylococcus aureus (GISA/VISA)

REPORTABLE DISEASE AND AMR TESTING REQUIREMENTS
1. Drug-resistant Streptococcus pneumoniae isolates from sterile sites such as CSF and other body fluids are required to be sent to the WPHL.
2. Testing MRSA, VRE and ESBL isolates is strictly an epidemiological tool and prior consultation is required before isolates can be sent to WPHL for testing.
3. Any suspected case of Vancomycin-resistant or intermediate Staphylococcus aureus should be sent to the WPHL for confirmation before reporting to the physician.

Specimen Requirements
1. A pure isolate of the above-listed suspected drug-resistant organism is required.
2. Cultures should be accompanied by a bacteriology form.
3. Note on the form which drugs have been tested and by which method.

Shipment
Specimens should be shipped according to the federal postal regulations for infectious substances.

Criteria for rejection
1. Non-viable cultures.
2. Organisms other than the specified genus.
3. Contaminated cultures.

Reporting/Interpretation
1. The minimum inhibitory concentration as determined by E-test will be reported for each drug tested.
2. Interpretation will include "Resistant", "Susceptible" or "Intermediate".

 

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