This study was done in order to assess the incidence of Staphylococcus species from milk of cows with subclinical mastitis and their antimicrobial sensitivity in some selected antibiotics and Usnea barbata lichen extracts. The study was conducted in two different commercial dairy farms. Staphylococcus species isolates were identified using several biochemical tests which included Gram’s staining test, catalase test and oxidase test. A commercial API® staph kit (bioMerieux, France) was used to confirm the bacterial organisms to their species level. The antimicrobial sensitivity of individual species was determined according to the Clinical Laboratory Standard Institute (CLSI) for the selected antibiotics. Agar well diffusion method and the broth micro-dilution technique were used to determine the sensitivity of Staphylococcus species in U. barbata extracts. A total of 467 milk samples were screened for bacterial identification from the two farms. Fifteen different Staphylococcus species isolates were identified from all milk samples that were examined. The most frequently isolated species included Staphylococcus xylosus (54.34%), Staphylococcus hominis (24.78%), Staphylococcus aureus (16.38%), Staphylococcus saprophyticus (16.12%) and Staphylococcus haemolyticus (11.63%). Most Staphylococcus species were resistant to Penicillin (75.35%), Nalidixic acid (72.55%) and Ampicillin (63%). Furthermore, the bacterial sensitivity evaluation of U. barbata lichen extracted with methanol and ethyl-acetate against selected Staphylococcus species isolates showed 92.31% and 53.85% susceptibility, respectively. The minimum inhibitory concentration (MIC) of the methanol and ethyl-acetate extracts ranged between 0.0390 to 10 mg/ml. There was a relatively high incidence of Staphylococcus species identified in milk of cows with subclinical mastitis from both farms. Conversely, Staphylococcus species isolates were resistant to antibiotics (mostly penicillin and ampicillin) commonly used in the farms. Furthermore, the study investigated the antimicrobial sensitivity of U. barbata extract in-vitro which may validate its use in traditional medicine for treatment of cows with mastitis.

An environmentally friendly, rapid and cost effective analytical procedure based on dispersive liquid-liquid microextraction was developed for the determination of six tetracyclines (TCs) in meat destined for human consumption. Meat extracts were analyzed for TCs using a sensitive and selective analytical technique, liquid chromatography tandem mass spectrometry. Various influencing factors on the extraction, separation and determination of TCs such as pH of mobile phases, type and volume of disperser solvent, type and volume of extraction solvent and sample pH were optimized. Validation parameters such as calibration function, limit of detection (LOD), limit of quantification (LOQ), detection capability (CCα), decision limit (CCβ), accuracy and precision were established according to EU commission decision 2002/657/EC. Linearity in the range of 25-200 μg kg-1 was obtained with regression coefficients ranging from 0.9991 to 0.9998. Recoveries of spiked blank muscle samples at three levels (i.e. 50, 100 and 150 μg kg-1) ranged from 80 to 101% and reproducibility was between 2 and 7%. The LODs and LOQs ranged from 2.22 to 3.59 μg kg-1 and from 7.38 to 11.49 μg kg-1 respectively. The CCα ranged from 105 to 111 μg kg-1 while CCβ ranged from 107 to 122 μg kg-1. The proposed method compared well with the dispersive solid phase extraction method and was successfully applied to the determination of TCs in meat samples. Some of the thirty bovine muscle samples obtained from local abattoirs and butcheries were found to contain two tetracycline antibiotics residues (chlortetracycline and oxytetracycline) with oxytetracycline being the most commonly detected. The concentration levels of the TC residues detected in the eleven bovine muscle samples were between 12.4 and 68.9 μg kg-1, levels that are lower than the European Union set maximum residue level (MRL) of 100 μg kg-1 hence the meat was fit for human consumption. / Chemistry / M. Sc. (Chemistry)