Delvotest

The system discussed, commercially known as the Delvotest (9-11), utilizes a strain of stearothermophilus which grows at a very rapid rate and produces acid from the nutrients in the medium in the absence of inhibitory substances. When inhibitory substances such as the 3-lactam antibiotics are present, acid production is inhibited. By incorporating bromcresol purple in the medium, it is easy to observe acid production, a change from purple to yellow. Incubation is performed at 65 C for approximately 3 h. 

Table IV. Limits of Detection of 3-Lactams in Milk Using the Delvotest System...

Application of Delvotest or the disc assay systems to detecting other antibiotics in milk has not been successful. Only the receptor assay system appears to be versatile and potentially applicable to determine the presence of different antibiotic residues in different matrices. 

Results showed a total of 2.8% of the samples (n 2972) to be inhibitor positive by the Delvotest SP test further examination identified 1.7% as -lactam antibiotics, and 1.1 % as sulfonamides and dapsone. The percentage of chloramphenicol suspicious samples determined by the Charm II test was amazingly high however, tests for confirmation were not available and contamination of the samples by residues of the chloramphenicol-based preservative azidiol could not be excluded with certainty. Low concentrations of streptomycins were also detected in 5.7% of the samples (n 1221), but the MRL was not exceeded. Macrolide and tetracycline residues were not found in significant levels. Model trials with commercially applied yoghurt cultures confirmed how important the compliance to MRLs can be to dairy industry compared to antibiotic-free milk, a pH of 5.0 was reached with a delay of 15 min in the case of contamination with cloxacillin 30 min in the case of penicillin, spiramycin, and tylosin and 45 min in the case of oxytetracycline contamination. 

In 1989, an experimental study designed by the International Dairy Federation in 53 laboratories of 22 different countries to achieve deeper insight into state of proficiency of routinely applied tests showed that the most frequently used microbial inhibitor screening tests were the disc assays with Bacillus stearo-tliermopliilus, Delvotest-P, Brilliant black reduction test, acidification test, CHARM II test, and the Penzyme test (32), Currently available microbial inhibitor tests for screening of residual antibacterials in milk and milk products are presented in Table 27.1. 

Delvotest P/SP/ Direct assay B. ste rothermophilus 2.5 h at 64 C into Bromocresol Penicillineise 130 ... 

The Delvotest-P-Multitest is a modification of the original Delvotest-P test (50). This is not an ampoule test but a polystyrene plate-based test with cups similar in principle to the original version. Its main advantage is that it permits up to 96 test cups to be used at one time. Following a collaborative study (51), both tests have been adopted by the Association of Official Analytical Chemists (AOAC) as official tests for the detection of -lactams in milk and milk products. 

The Delvotest-P test (84), which was originally designed for rapid detection of penicillins in milk, has also been successfully employed for the detection of oxytetracycline residues in chicken tissues. In this method samples of liver, kidney, and muscle tissue are homogenized with distilled water, and the homogenates... 

Since its original development in the 1970s the DelvoTest has been further refined to meet the customers requirements in terms of both detection capabilities and presentation of the test format. The current commercially available versions of the test are described below ... 

DelvoTest SP. This test has enhanced sensitivity to the sulfonamide class, as well as the ability to detect... 

Marker Residue) Milk (p.g/kg) Eclipse 100 DelvoTest SP DelvoTest SP-NT CMT Blue Yellow II Cowside II... 

More recently, the DelvoTest Accelerator system for the combined incubation and measurement of the DelvoTest SP-NT ampoules and multi-plates (Section 5.2.3) has been launched by DSM Food Specialties. The test ampoules or multi-plates are placed directly onto the scanner glass top plate the glass plate is heated to 63°C to perform the incubation step. The Accelerator system can run up to 100 individual ampoules or four 96-well multi-plates (potential for 384 samples) in parallel. A scanner measurement is taken every minute until the test end-point is reached, which is determined automatically via the software control system. The incubation time is shorter than the conventional system, at around 100 min. Once the end-point is reached, the test is automatically terminated and the results stored for subsequent assessment, meaning that the tests can be performed out of the normal working hours. 

DelvoTest Ampoule Format DelvoTest Multiplate Format Radial axis = Fraction of the EU milk MRL Log scale... 

Figure 5.2 Radar plot showing the DelvoTest (SP-NT ampoules and multi-plate formats) lowest limit of detection for 10 antimicrobial compounds in bovine milk expressed as a fraction of the current EU MRLs.

The DelvoTest Accelerator system in combination with the DelvoTest SP-NT ampoules and multi-plates were validated in milk in accordance to the requirements of the International Dairy Federation. The estimated detection limits of the DelvoTest SP-NT ampoules and multi-plates are expressed as a fraction of the current EU MRLs (Fig. 5.2). With the exceptions of oxytetracycline and neomycin, all the analytes included in the study were detected at or below the EU MRL by both test formats. This finding reflects the degree of susceptibility of the microorganism employed in the test to the range of antimicrobial compounds tested. 

Gibbons-Burgener et al. " evaluated the performance of the rapid SNAPBL, DelvoTest SP, and Penzyme milk test-kits for testing raw milk samples from individual cows. 

Stead SL, Ashwin H, Richmond SF, Sharman M, Langeveld PC, Barendse JP, Stark J, Keely BJ, Evaluation and validation according to international standards of the Delvotest SP-NT screening assay for antimicrobial drugs in milk, Int-natl. Dairy J. 2008 18 3-11. 

Le Breton MH, Savoy-Perroud MC, Diserens JM, Vahdation and comparison of the Copan milk test and Delvotest SP-NT for the detection of antimicrobials in milk. Anal. Chim. Acta 2007 586(l-2) 280-283. 

Antimicrobial (class) Penzyme Delvotest P Three-plate Six-plate Charm II... 

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