Microbiological quality of selected ready-to-eat leaf vegetables, sprouts and non-pasteurized fresh fruit-vegetable juices including the presence of Cronobacter spp.

Bacteria of the genus Cronobacter are emerging food-borne pathogens. Foods contaminated with Cronobacter spp. may pose a risk to infants or adults with suppressed immunity. This study was aimed at determining the microbiological quality of ready-to-eat (RTE) plant-origin food products available on the Polish market with special emphasis on the prevalence of Cronobacter genus bacteria. Analyses were carried out on 60 samples of commercial RTE type plant-origin food products, including: leaf vegetables (20 samples), sprouts (20 samples) and non-pasteurized vegetable, fruit and fruit-vegetable juices (20 samples). All samples were determined for the total count of aerobic mesophilic bacteria (TAMB) and for the presence of Cronobacter spp. The isolates of Cronobacter spp. were subjected to genetic identification and differentiation by 16S rDNA sequencing, PCR-RFLP analysis and RAPD-PCR and evaluation of antibiotic susceptibility by the disk diffusion assay. The TAMB count in samples of lettuces, sprouts and non-pasteurized fruit, vegetable and fruit-vegetable juices was in the range of 5.6-7.6, 6.7-8.4 and 2.9-7.7 log CFU g-1, respectively. The presence of Cronobacter spp. was detected in 21 (35%) samples of the products, including in 6 (30%) samples of leaf vegetables (rucola, lamb's lettuce, endive escarola and leaf vegetables mix) and in 15 (75%) samples of sprouts (alfalfa, broccoli, small radish, lentil, sunflower, leek and sprout mix). No presence of Cronobacter spp. was detected in the analyzed samples of non-pasteurized fruit, vegetable and fruit-vegetable juices. The 21 strains of Cronobacter spp. isolated from leaf vegetable and sprouts included: 13 strains of C. sakazakii, 4 strains of C. muytjensii, 2 strains of C. turicensis, one strain of C. malonaticus and one strain of C. condimenti. All isolated C. sakazakii, C. muytjensii, C. turicensis and C. malonaticus strains were sensitive to ampicillin, cefepime, chloramphenicol, gentamycin, streptomycin, tetracycline, ciprofloxacin and cotrimoxazol, whereas the C. condimenti isolate showed intermediate resistance to streptomycin and cotrimoxazole.