Abstract
In Kenya there is currently no screening of antimicrobial drug residues in milk. This study evaluated the improved tube test as a possible screening method using seven representatives of the b-lactam antibiotics. The group comprises antimicrobials most frequently used to treat bacterial infections in dairy cows. Each antimicrobial was tested at five concentrations based on established codex alimentarius maximum residue limits (MRLs). Test parameters studied were practicability and limits of detection (LODs) compared to MRLs and repeatability. The LODs established using a logistic regression model were: penicillin G (2 µg /kg), ampicillin (2 µg /kg), amoxicillin (2 µg /kg), oxacillin (30 µg /kg), cefalexin(100 µg /kg), cephapirin(60 µg /kg) and ceftiofur(100 µg /kg) all within codex alimentarius MRLs. The cost per ten samples using the improved tube test was less than 1 USD compared with 5 USD for the Delvo test. The improved tube test is concluded to be an affordable method, which could be used for qualitative identification of residues in low-income countries dairies. Key words: Improved tube test, b-lactams, Kenyan milk, maximum residue limits.
Highlights
Antibiotics residues in bovine milk are a problem in Kenyan milk (Ombui et al, 1995; Shitandi and Sternesjö, 2001)
This study is aimed at evaluating the laboratory performances of the improved tube test method as a screening assay for commonly used β-lactam antimicrobials based on established codex alimentarius (1993 and 1994) maximum residue limits (MRLs)
Milk samples were collected from the Egerton University Njoro (Kenya) dairy farm and initially screened with the Beta STAR test (UCB Bioproducts, Belgium), which involves a specific β-lactam receptor linked to gold particles
Summary
Antibiotics residues in bovine milk are a problem in Kenyan milk (Ombui et al, 1995; Shitandi and Sternesjö, 2001). The β-lactam group of antimicrobials are in particular commonly utilised in lactating animals (Mandell and Perti, 1996; Mitchell et al, 1998). They are the most frequent contaminants in milk. It is important to avoid these residues because of toxicological and public health reasons (Honkanen and Reybroeck, 1997). The tests used include microbiological, spectrophotometric, thin-layer chromatographic and bioautographic, liquid chromatographic, high-performance liquid chromatographic, gas chromatographic, mass spectrometric, and immunochemical methods (Nakazawa et al, 1992; Honkanen - Buzalski and Reybroeck, 1997; Elliott et al, 1998). The main reason for not incorporating such tests in a control program is because they are expensive and cannot be sustained by the local dairy industries
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