Identification and characterization of aerobic spore forming bacteria isolated from commercial camel’s milk in south of Algeria

Abstract

The aim of this study was to evaluate aerobic spore-forming species contamination levels in raw and pasteurized camel’s milk. The isolated strains were also identified by 16S rDNA sequencing and characterized for their heat resistance. Camel milk (8 samples of which 4 were pasteurized) were collected from farms and markets from different regions in south east Algeria’s (Laghouat, Ghardaïa and Ain Aminas). Aerobic spore counts had 2 logCFU/mL in the raw samples. The 16S rDNA sequencing enables the identification of a selection of 20 isolates: Bacillus licheniformis (Five strains), Bacillus cereus (Nine strains), Bacillus subtilis (Three strains), Bacillus pumilus (One strain), Bacillus sonorensis (One strain), Geobacillus stearothermophilus (One strain). All B. cereus strains belonged to the phylogenetic group III of B. cereus, according to the classification proposed by Guinebretière et al. (2008), and supposedly represent potential strains of pathogenic B. cereus.The heat resistance (D-value i.e. the decimal reduction time) and heat sensitivity (zT values i.e. the temperature increase that lead to a ten-fold reduction of the D value) of spores of B. cereus, B. licheniformis, B. pumilus, B. sonorensis, B. subtilis were determined. The D100°C-values were ranged 1.09–9.55min whereas the z-values 6.45–8.50°C.