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Intended use: etest® is a manual, quantitative technique for the determination of antimicrobial susceptibility of non-fastidious gram-negative and gram-positive aerobic bacteria and fastidious bacteria.The system comprises a predefined antibiotic gradient which is used to determine the minimum inhibitory concentration (mic, in g/ml) of different antimicrobial agents against microorganisms tested on agar media after overnight incubation.Description: a biomérieux investigation determined that a customer in canada may have obtained false susceptible trimethoprim/sulfamethoxazole (sxt) results for staphylococcus aureus in association with the etest® trim/sulfa 1/10 ts 32 ww s30 (ref412481).The investigation ( inv-15607 ) was initiated to determine the cause for potential false resistant trimethoprim/sulfamethoxazole (sxt) results for staphylococcus aureus strains in association with the vitek® 2 ast-gp67 test kit (ref 22226, lot 1322363503) compared to etest, which obtained susceptible results ((b)(4)).The investigation compared the vitek 2 and etest test methods to the broth macrodilution method, which was the reference method used to develop the formulation of sxt found on the ast-gp67 cards and determined that the expected sxt result for the 4 strains submitted for investigational testing was resistant.There is no indication or report from the customer that the etest results they obtained during the initial testing led to or contributed to death, serious injury, or serious deterioration in the state of health for any patient.Ref 412481 is not sold/marketed in the united states ,however an equivalent product (ref 412480) is sold/marketed in the united states and is registered with the fda (k983027).
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An investigation was initiated in response to a customer complaint of obtaining potential false susceptible trimethoprim/sulfamethoxazole (sxt) results for staphylococcus aureus in association with the etest® trim/sulfa 1/10 ts 32 ww s30 (ref (b)(4)).Investigation: complaint trend analysis: global customer service (gcs) performed a complaint trend analysis and did not identify the customer's issue as a trend for the etest trim/sulfa 1/10 ts 32 ww s30 (ref (b)(4)).Retained samples analysis: biomérieux retains samples of every lot number released to the market.As the lot numbers 1008493080 and 1008695840 were expired, these two lots were not tested during the investigation.The retained samples from lot numbers 1009195020 and 1009773320 were tested in parallel with one internal lot number used as a reference lot (reference (b)(4), lot 1010000830).The tests were performed by using the quality control (qc) strains escherichia coli atcc 25922, enterococcus faecalis atcc 29212, staphylococcus aureus atcc 29213, haemophilus influenzae atcc 49247 and streptococcus pneumoniae atcc 49619 according to the qc protocol used for the release of each lot number.The qc results obtained for the five strains tested are within the expected range for the three etest lots tested.For each strain tested, the minimum inhibitory concentration (mic) values obtained did not show any difference of results between these three etest lots tested.Tests on strains returned: tests were performed with the four returned staphylococcus aureus patient strains.A°) etest ts 32 and reference method.The four strains were tested with strips from the etest ts 32 lot numbers 1009195020 and 1009773320 related to the complaints, and from the etest ts 32 lot number 1010000830 used as a reference lot.These four patient strains were tested in parallel with the reference method agar dilution (ad) since ad was the reference method used for the development of etest ts 32.For each strain tested, the mic values obtained were the following : - ad method : 20 (1/19) ¿g/ml.- etest ts 32, all strips : 10 (0,5/9,5) ¿g/ml.Following clsi breakpoints 2023 for staphylococcus spp: (s= 40 (2/38) ¿ r = 80 (4/76)), the mic values obtained with ad reference method and etest ts 32 strips are interpreted as susceptible (s).The etest ts 32 mics are within essential agreement compared to the reference method ad mics whatever the strain and the etest ts 32 lots tested without category error.As etest ts 32 strips results (s results) are in agreement with the reference method ad and as the investigation realized on vitek 2 (showing r results) was also in agreement with its reference method (broth macro dilution), additional testing was needed to understand those gaps between the two reference methods.B°) strains characterization.The four strains were characterized by whole genome sequencing (wgs), tested with trimethoprim alone (etest trimethoprim tr strips) and tested with sulfamethoxazole alone (diffusion disks of sulfamethoxazole).These tests showed that the four strains are resistant against trimethoprim and susceptible against sulfamethoxazole.At the state of the art, only the isolates resistant to both single agents (trimethoprim and sulfamethoxazole) are classified consistently as trimethoprim/sulfamethoxazole (sxt) resistant.If the strain is susceptible to sulfamethoxazole, even if the strain is resistant to trimethoprim, the final result to sxt should be susceptible.C°) complementary tests on reference methods and etest ts 32.Broth micro dilution (bmd), broth macrodilution and etest ts 32 by using mhf media were performed with the four strains.Bmd results showed variable results for a same strain.Depending on the replicate tested, the result is susceptible or resistant.The mic values obtained are between 10 mg/l and 640 mg/l.These results allow to suspect an hetero-resistance.With broth macrodilution, three strains showed susceptible results with a mic value at 40 mg/l and the fourth one showed resistant result with a mic value at 80mg/l.Following these results, the strains can be considered as borderline strains for trimethoprim/sulfamethoxazole.Etest ts 32 strips tested with mhf medium showed micro and macro-colonies in the inhibition zone beyond 32 ¿g/ml for the four strains after 48 hours of incubation.These results confirm the suspicion of hetero-resistance for the four strains.Conclusion: the investigation did not identify any product performance issues for the etest® trim/sulfa 1/10 ts 32 ww s30 (ref (b)(4)).It was determined that the four returned staphylococcus aureus patient strains are borderline for trimethoprim/sulfamethoxazole and may present hetero-resistance characteristics.Such observations may explain the differences observed in between the several phenotypic methods tested.
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