M.C. Beltrán

Evaluation of the Charm maximum residue limit β-lactam and tetracycline test for the detection of antibiotics in ewe and goat milk

The Charm maximum residue limit β-lactam and tetracycline test (Charm MRL BLTET; Charm Sciences Inc., Lawrence, MA) is an immunoreceptor assay utilizing Rapid One-Step Assay lateral flow technology that detects β-lactam or tetracycline drugs in raw commingled cow milk at or below European Union maximum residue levels (EU-MRL). The Charm MRL BLTET test procedure was recently modified (dilution in buffer and longer incubation) by the manufacturers to be used with raw ewe and goat milk. To assess the Charm MRL BLTET test for the detection of β-lactams and tetracyclines in milk of small ruminants, an evaluation study was performed at Instituto de Ciencia y Tecnologia Animal of Universitat Politècnica de València (Spain). The test specificity and detection capability (CCβ) were studied following Commission Decision 2002/657/EC. Specificity results obtained in this study were optimal for individual milk free of antimicrobials from ewes (99.2% for β-lactams and 100% for tetracyclines) and goats (97.9% for β-lactams and 100% for tetracyclines) along the entire lactation period regardless of whether the results were visually or instrumentally interpreted. Moreover, no positive results were obtained when a relatively high concentration of different substances belonging to antimicrobial families other than β-lactams and tetracyclines were present in ewe and goat milk. For both types of milk, the CCβ calculated was lower or equal to EU-MRL for amoxicillin (4 µg/kg), ampicillin (4 µg/kg), benzylpenicillin (≤ 2 µg/kg), dicloxacillin (30 µg/kg), oxacillin (30 µg/kg), cefacetrile (≤ 63 µg/kg), cefalonium (≤ 10 µg/kg), cefapirin (≤ 30 µg/kg), desacetylcefapirin (≤ 30 µg/kg), cefazolin (≤ 25 µg/kg), cefoperazone (≤ 25 µg/kg), cefquinome (20 µg/kg), ceftiofur (≤ 50 µg/kg), desfuroylceftiofur (≤ 50µg/kg), and cephalexin (≤ 50 µg/kg). However, this test could neither detect cloxacillin nor nafcillin at or below EU-MRL (CCβ >30 µg/kg). The CCβ for tetracyclines was also lower than EU-MRL for chlortetracycline (ewe milk: ≤ 50 µg/kg; goat milk: 75 µg/kg), oxytetracycline (≤ 50 µg/kg), and tetracycline (≤ 50 µg/kg). Regarding the 4-epimers of these tetracyclines only 4-epioxytetracycline was detected by the Charm MRL BLTET test below EU-MRL (ewe milk: 75 µg/kg; goat milk: ≤ 50 µg/kg). Acidiol had no effect on the performance of the test. The Charm MRL BLTET test could be used routinely with adapted test procedure for the fast screening of ewe and goat milk.

Detection of antibiotics in goat's milk: effect of detergents on the response of microbial inhibitor tests.

The aim of the study was to evaluate the interference of acid and alkaline detergents employed in the cleaning of milking equipment of caprine dairy farms on the performance of microbial tests used in antibiotic control (BRT MRL, Delvotest MCS, and Eclipse 100). Eight concentrations of commercial detergents, five acid (0-0.25%) and five alkaline (0-1%) were add to antimicrobial-free goats milk to evaluate the detergent effect on the response of microbial inhibitor tests. To evaluate the effect of detergents on the detection capability of microbial tests two detergents at 0.5 ml/l (one acid and one basic) and eight concentrations of four β-lactam antibiotics (ampicillin, amoxicillin, cloxacillin and benzylpenicillin) were used. Milk without detergents was used as control. The spiked samples were analysed twelve times by three microbial tests. The results showed that the presence of acid detergents did not affect the response of microbial tests for any of the concentrations tested. However, at concentrations equal to or greater than 2 ml/l alkaline detergents positive results were found in microbial tests (16.7-100%). The detection limits of the screening tests for penicillins were not modified substantially by the presence of detergents. In general, the presence of acid and alkaline detergents in goats milk did not produce a great interference in the microbial tests, only high concentrations of detergents could cause non-compliant results, but these concentrations are difficult to find in practice if proper cleaning procedures are applied in goat dairy farms.

Interference of non-specific detergents in microbial inhibitor test results for screening antibiotics in goat's milk

ABSTRACT Cleaning and disinfection of dairy equipment is essential to ensure the hygienic quality of milk. Occasionally, some farmers use washing-up liquids and disinfectants for home use, especially when cleaning procedures are carried out manually. Residues of detergents and disinfectants in milk may interfere with the response of microbial inhibitor tests used for screening antibiotics in milk. Therefore, the aim of this study was to evaluate the interference of non-specific detergents in screening tests (BRT MRL; Delvotest SP-NT MCS; Eclipse 100) for goats milk. Twelve replicates of eight concentrations of five washing-up liquids (0–1%) and one disinfectant (0–1%) were analysed. The results showed that the presence of washing-up liquids at concentrations of ≥1 ml/l leads to positive results in microbial tests. In particular, the product containing sodium laureth sulphate and ethanol produced the largest number of positive outcomes. The presence of disinfectant based on sodium hypochlorite did not affect the test response. The detection capabilities of microbial inhibitor tests for penicillins were also studied in milk with and without cleaning products, calculating the dose–response curve with eight concentrations of amoxicillin, ampicillin, benzylpenicillin and cloxacillin, respectively. The detection limits of the screening tests for penicillins were not modified substantially by the cleaning product based on sodium laureth sulphate and ethanol. Residues of cleaning agents in milk can be avoided when specific detergents and disinfectants for milking equipment are used and good cleaning practices are applied.

Influence of enrofloxacin on the coagulation time and the quality parameters of goat's milk yoghurt

1 Three batches of yoghurts were made from goat’s milk with different enrofloxacin 2 concentrations (0, 50, 100 and 150 μg/kg). Quality parameters were analysed at 1, 7, 14 and 3 28 days at 5oC. Drug residues were also quantified by HPLC. Coagulation time and most 4 yoghurt properties remained unaffected by the presence of enrofloxacin in goat’s milk. 5 However, quality parameters were affected by the storage period. 74.9-99.2% of 6 enrofloxacin initially added to goat’s milk remained in the yoghurt throughout its entire 7 shelf life, potentially posing a risk to consumer health. Therefore, an enrofloxacin 8 Maximum Residue Limit in yoghurt should be established. 9

Short communication: Drug residues in goat milk after prophylactic use of antibiotics in intravaginal sponges for estrus synchronization

The aim of this study was to determine whether the prophylactic use of antibiotics in intravaginal sponges used for estrus synchronization in goats may result in the presence of inhibitors in milk and, therefore, of positive results by microbial screening tests. Ninety-eight Murciano-Granadina goats were used, divided into 7 groups of 14 animals. Intravaginal sponges were placed in 6 groups using 2 concentrations of 3 different antibiotics: doxycycline, oxytetracycline, and sulfathiazole-framycetin. The sponges of the control group were placed without antibiotics. Milk samples were collected daily until 7 d posttreatment and analyzed using 3 microbial tests. Positive samples were retested by specific receptor-binding assays to confirm the positive results. Vaginal status was evaluated by visual assessment of the external aspect of the sponges after removal. The microbial test response was not affected by either day posttreatment or dose of antibiotic used, except for oxytetracycline at the higher concentration. Moreover, no positive results were obtained using receptor-binding assays, suggesting that residues, if present in milk, did not exceed the regulatory (safety) levels established for these drugs. The occurrence of soiled sponges was higher in the control group. With respect to the dose of antibiotics used, no significant differences were found for the lower dose administered. However, a significant increase in the percentage of clean sponges was observed for the higher dose of doxycycline. We conclude that the prophylactic use of low doses of doxycycline, oxytetracycline, or sulfathiazole in intravaginal sponges used for synchronization of estrus helps to reduce clinical vaginitis in dairy goats and does not seem to be the cause of positive results in microbial inhibitor tests used to detect antibiotics in goat milk.