Validación de un software electrónico para el conteo de unidades formadoras de colonias y determinación de sensibilidad bacteriana en muestras de leche cruda

Abstract

The aim of this work was to evaluate a software of the Escuela Superior Politécnica de Chimborazo for the reading of colony-forming units (CFUs) and inhibition halos in microbial cultures, in order to comply with the appropriate protocol for the evaluation of mesophilic aerobes in raw milk and the antimicrobial susceptibility of Staphylococcus aureus. Mesophilic aerobes were determined in 18 samples of raw milk sold in three markets of Riobamba - Chimborazo, using the spread plate method. For antimicrobial susceptibility, the Kirby-Bauer method was used on S. aureus isolates in Baird Parker Agar. The software evaluation was not achieved due to its inability to read "real" in vitro culture plates, although the software was previously tested with plate imaging and some culture plates. However, manual reading of the results indicated that 28% (5/18) of the examined milk samples exceed the limit of the Ecuadorian regulation 1.5 x 10e6 CFU / mL of mesophilic aerobes, 72% (13/18) are found within the permissible limits with values between 4x10e5 and 6.9 x 10e6 CFU/mL, without ruling out the activity of bacterial inhibitors. S aureus, in the antimicrobial susceptibility test, showed 100% susceptibility against Oxacillin, Ampicillin, Erythromycin, Tetracycline, Gentamicin, Ciprofloxacin, Chloramphenicol, Rifampicin, while one isolate was intermediate against Vancomycin and 100% of the isolates were resistant to Ceftazidimide, representing a reservoir for horizontal resistance transmission. It is concluded that the software deserves further review in order to comply with its intended use. In addition, sale of raw milk reveals contamination problems putting public health at risk. It is recommended to carry out an investigation from the moment of milking to the commercialization of the milk.