Enterobacteriaceae in raw goat milk: isolation and characterization

Goat milk has been shown to be an option for cow milk, due to lower allergenicity and better digestibility. The milk of several mammals in general has a high nutritional value and therefore tends to be an excellent culture medium for deteriorating and pathogenic microorganisms and presents a great variety of Gram-negative bacteria, especially Enterobacteriaceae. The objective of this study was to detect and characterize enterobacteria in 21 samples of raw goat milk commercialized informally in several cities of the State of Rio de Janeiro. The isolates were obtained by plating the samples in Violet Red Bile Glucose Agar (VRBG), which were later identified by mass spectrometry (matrix assisted laser desorption/ionization - MALDI-TOF). The characterization took place through the evaluation of lipolytic activity (skim milk agar), proteolytic (spirit blue modified agar) and biofilm producer (red congo agar). In addition, enzyme-producing phenotypes that hydrolyze antibiotics, ESBL and KPC, have been found to occur by inoculation in chromogenic culture media. In the microbial population of raw goat milk, mainly composed of Pseudomonas sp., 59 isolates of the Enterobacteriaceae family were identified, most of them Enterobacter (48%), Serratia (14%) and Klebsiella (11%). Most (90%) of the isolates were biofilm producers, while about 20% presented deteriorating enzyme producing activity, being the majority of the Serratia genus. About 60% of the isolates presented as ESBL and KPC producers. These results point to the important role of this group of pathogens in the food area, especially in dairy products, besides showing the seriousness of the problem of informal trade in raw milk, with the possible transmission of microorganisms with ESBL+ and KPC+.