Cronobacter spp. are opportunistic pathogens associated with serious infections in neonates. The increased stress tolerance, including thermoresistance, of some Cronobacter strains can promote their survival in production facilities and thus raise the possibility of contamination of dried infant milk formula, which has been identified as a potential source of infection. In this study, we characterized a DNA region which is present in some Cronobacter strains and which contributes to their prolonged survival at 58°C. The 18 kbp long region containing 22 open reading frames was sequenced in Cronobacter sakazakii ATCC 29544. The major feature of the region contained a cluster of conserved genes, most of them having significant homologies with bacterial proteins involved in some type of stress response, including heat, oxidation and acid stress. The same thermoresistance DNA region was detected in strains belonging to the genera Cronobacter, Enterobacter, Citrobacter and Escherichia and its presence positively correlated with increased thermotolerance.

The aim of this study was to identify and characterize Cronobacter spp. isolated from a range of foods. A total of 71 Cronobacter strains were isolated from 602 foods in our laboratory. The highest contamination was observed in foods of plant origin, e.g. spices, teas, chocolate, nuts, pastries and vegetables. On the basis of genus and species identification performed using genus-specific PCR, 16S rRNA sequencing and AFLP genotyping, most of the strains belonged to Cronobacter sakazakii. Biochemical profiling by the tests included in API 20E, complemented with relevant additional tests, classified the strains into 13 biogroups. AFLP genotyping facilitated discrimination of six main groups at the 70% similarity level and strain grouping correlated clearly with species identification. Our results indicate that molecular typing by AFLP may be applied as a useful tool not only for direct comparison of Cronobacter isolates, providing traceability, but also for the reliable species classification. Moreover, tracing of these bacteria in a wider variety of foods should be important to enhance the knowledge of their transmission.

After the enrichment, the PCR detection is more convenient than the standard one as PCR detection is not compromised by other present microflora.

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Aims:  The aim of this study was to develop a 5′‐nuclease polymerase chain reaction (PCR) for the rapid detection and quantification of Listeria monocytogenes. Methods and Results:  Specific primers and a fluorogenic probe were designed, which target a specific sequence of the actA gene encoding for a protein involved in the actin filament assembly. The PCR system was highly sensitive and specific for L. monocytogenes (inclusivity, 100%; exclusivity, 100%), which was determined using 46 L. monocytogenes and 28 non‐L. monocytogenes strains. Detection limits of 104 cfu ml−1 after 35 cycles and 102 cfu ml−1 after 45 cycles were achieved by PCR in both real‐time and end‐point fluorescence measurement modes. Linear calibration lines were obtained in the range from 102 to 109 cfu ml−1 for three L. monocytogenes strains in real‐time PCR with 45 cycles. Conclusions:  The developed 5′‐nuclease PCR of the actA gene provides a new target for the rapid detection and quantification of L. monocytogenes. Significance and Impact of the Study:  In conjunction with enrichment or with an appropriate quantitative sample preparation technique, the method is suitable for food safety applications.