Validation of the βeta-s.t.a.r. 1 + 1 for rapid screening of residues of β-lactam antibiotics in milk

Figures & data

Table 1. Repeatability of the reader (dry and wet dipsticks) and repeatability of the βeta-s.t.a.r. 1 + 1 test at different ratios.

Milk	Compound and concentration	Number of samples	Mean ratio	^a s r	CV (%)^b
Reader repeatability–wet dipsticks
Blank milk		30	4.08	0.30	0.52
Positive milk	Penicillin G; 4 µg kg^−1	30	0.12	0.04	0.13
	Ampicillin; 6 µg kg^−1	30	0.33	0.04	0.13
	Cloxacillin; 12 µg kg^−1	30	0.05	0.02	0.04
Reader repeatability–dry dipsticks
Blank milk		10	2.40	0.02	0.06
Positive milk	Penicillin G; 1 µg kg^−1	10	1.89	0.10	0.09
	Penicillin G; 2 µg kg^−1	10	1.94	0.06	0.05
	Penicillin G; 2.5 µg kg^−1	10	0.85	0.03	0.03
	Penicillin G; 3 µg kg^−1	10	0.35	0.03	0.03
	Penicillin G; 4 µg kg^−1	10	0.17	0.01	0.01
Test repeatability
Blank milk		20	4.35	0.33	0.55
Positive milk	Penicillin G; 4 µg kg^−1	20	0.10	0.05	0.09
	Ampicillin; 6 µg kg^−1	20	0.34	0.09	0.14
	Cloxacillin; 12 µg kg^−1	20	0.05	0.03	0.04
Notes: ^a s r, standard deviation of repeatability.
^bCV (%), relative standard deviation.

Table 2. Detection capabilities in raw cows’ milk of the βeta-s.t.a.r. 1+1 instrumental reading with a cut-off ratio of 1.00^a in comparison to the βeta-s.t.a.r.

Group	Compound	MRL^b (µg kg^−1)	Detection capability
			βeta-s.t.a.r. 1 + 1 protocol	βeta-s.t.a.r.^c,d
Penicillins	Penicillin G	4	3	3
	Ampicillin	4	7	4
	Amoxicillin	4	8	4
	Oxacillin	30	11	6
	Cloxacillin	30	9	6
	Dicloxacillin	30	8	5
	Nafcillin	30	36	14
	Penethamate	4	80	n.d.^e
Cephalosporins	Ceftiofur	100	500	110
	Cefquinome	20	28	10
	Cefazolin	50	175	60
	Cephapirin	60	28	12
	Cefacetrile	125	100	40
	Cefoperazone	50	7	6
	Cefalexin	100	6000	>1000
	Cefalonium	20	4	4
Notes: ^aDetection capability is defined as the lowest concentration tested giving a minimum of 19 positive results out of 20.
^bMRL, maximum residue limit (European Commission 2009, European Union 2010).
^c3 + 2 classic protocol.
^dReybroeck and Ooghe (2004) and unpublished data.
^en.d., No data available.

Figure 1. Ratios for normal and abnormal blank milk (

, mean;

, lowest;

, highest) and normal and abnormal milks containing 12 µg kg⁻¹ cloxacillin (

, mean;

, lowest;

, highest). Milks were of normal composition (1) or with: (2) a high somatic cell count; (3) a high bacterial count; (4) a low fat content; (5) a high fat content; (6) a low protein content; (7) a high protein content; (8) a low pH; and (9) a high pH. The horizontal line at a ratio of 1.00 gives the cut-off between a negative and a positive result.

Figure 2. Ratios for normal and abnormal milks containing 6 µg kg⁻¹ ampicillin (

, mean;

, lowest;

, highest). Milks were of normal composition (1) or with; (2) a high somatic cell count; (3) a high bacterial count; (4) a low fat content; (5) a high fat content; (6) a low protein content; (7) a high protein content; (8) a low pH; and (9) a high pH. The horizontal line at a ratio of 1.00 gives the cut-off between a negative and a positive result.

Figure 3. Ratios for normal and abnormal milks containing 4 µg kg⁻¹ penicillin G (

, mean;

, lowest;

, highest). Milks were of normal composition (1) or with: (2) a high somatic cell count; (3) a high bacterial count; (4) a low fat content; (5) a high fat content; (6) a low protein content; (7) a high protein content; (8) a low pH; and (9) a high pH. The horizontal line at a ratio of 1.00 gives the cut-off between a negative and a positive result.

Figure 4. Ratios for blank milk (

, mean;

, lowest;

, highest) and different milks containing 12 µg kg⁻¹ cloxacillin (

, mean;

, lowest;

, highest). Raw cows’ milk (1) compared with: (2) UHT milk; (3) sterilized milk; (4) reconstituted milk powder; (5) thawed milk; (6) goats’ milk; (7) ewes’ milk; and (8) mares’ milk. The horizontal line at a ratio of 1.00 gives the cut-off between a negative and a positive result.

Figure 5. Ratios for different milks containing 6 µg kg⁻¹ ampicillin (

, mean;

, lowest;

, highest). Raw cows’ milk (1) compared with: (2) UHT milk; (3) sterilized milk; (4) reconstituted milk powder; (5) thawed milk; (6) goats’ milk; (7) ewes’ milk; and (8) mares’ milk. The horizontal line at a ratio of 1.00 gives the cut-off between a negative and a positive result.

Figure 6. Ratios for different milks containing 4 µg kg⁻¹ penicillin G (

, mean;

, lowest;

, highest). Raw cows’ milk (1) compared with: (2) UHT milk; (3) sterilized milk; (4) reconstituted milk powder; (5) thawed milk; (6) goats’ milk; (7) ewes’ milk; and (8) mares’ milk. The horizontal line at a ratio of 1.00 gives the cut-off between a negative and a positive result.

Table 3. Ratios obtained when testing the same positive and negative milk samples with βeta-s.t.a.r. reagents from different batches.

Tested	Lot 70405					Lot 70213^a
	Ratio			Number		Ratio			Number
	Mean	Minimum	Maximum	Positive	Negative	Mean	Minimum	Maximum	Positive	Negative
Blank	3.67	3.20	4.04	0	20	3.06	2.63	3.70	0	20
Penicillin G at 4 µg kg^−1	0.04	0.00	0.15	20	0	0.09	0.00	0.19	20	0
Ampicillin at 6 µg kg^−1	0.24	0.01	0.42	20	0	0.96	0.79	1.36	14	6
Cloxacillin at 12 µg kg^−1	0.15	0.10	0.25	20	0	0.35	0.29	0.42	20	0
Cephapirin at 28 µg kg^−1	0.80	0.41	1.06	19	1	1.03	0.77	1.44	11	9
Note: ^aExcept for cephapirin, which was tested using Lot 70205.

Figure 7. Ratios obtained for 29 dairy control samples with blank milk (

) and milks containing (

) 4 µg kg⁻¹ penicillin G, (

), 6 µg kg⁻¹ ampicillin or (

) 12 µg kg⁻¹ cloxacillin. The horizontal line at a ratio of 1.00 gives the cut-off between a negative and a positive result.

European Commission. 2009. Council Regulation (EC) No. 470/2009 of the European Parliament and of the Council of 6 May 2009 laying down Community procedures for the establishment of residue limits of pharmacologically active substances in foodstuffs of animal origin, repealing Council Regulation (EEC) No. 2377/90 and amending Directive 2001/82/EC of the European Parliament and of the Council and Regulation (EC) No. 726/2004 of the European Parliament and of the Council laying down a Community procedure for the establishment of maximum residue limits of veterinary medicinal products in foodstuffs of animal origin. Off J Eur Union. L152:11–22.

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European Commission. 2010. Commission Regulation (EU) No. 37/2010 of 22 December 2009 on pharmacologically active substances and their classification regarding maximum residue limits in foodstuffs of animal origin. Off J Eur Union. L15:1–72.

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Reybroeck W, Ooghe S. 2004. Rapid screening for residues of antibiotics in milk at the factory. Paper presented at: IDF/FAO International Symposium on Dairy Safety and Hygiene. A Farm-to-Table Approach for Emerging and Developed Dairy Countries; 2–5 March 2003; Cape Town, South Africa.

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