Abstract

Method for the microbiological determination of traces of antibiotics in low volume biological samples, which comprises determining the minimum inhibitory concentration (MIC) of an antibiotic selected from among minocycline, ciprofloxacin, kanamycin, tetracycline and oxacillin against Staphylococcus aureus. The bacteria are grown in Mueller-Hinton broth (MHB) overnight, said cultures subsequently being diluted to 0.5 McFarland standard (1.5 x 108 cells/mL). Said antibiotics are subsequently added to 96-well plates in a final volume of 200 µL and incubated at 37°C for 18 hours. Absorbency is determined and the results are expressed as the percentage of inhibition relative to the control containing the biological sample, in turn selected from urine, blood, synovial fluid, aqueous humour of the eye or cerebro spinal fluid (CSF), and the bacterial culture. The curve representing the percentage of inhibition of bacterial growth versus concentration of antibiotic is obtained, and is adjusted by the "Four Parameter Logistic Curve (4PL)", yielding the concentration values ​​of the antibiotics in the biological sample. The method determines amounts of antibiotic in the biological sample even at ng/mL level.