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The Salmonella genus is currently divided into 2 species, Salmonella bongori and Salmonella enterica, the latter being classified into 6 subspecies, S. enterica subsp. enterica, salamae, arizonae, diarizonae, houtenae, and indica (1). Most salmonellae possess two flagellin genes, fliC and fljB, encoding the so-called phase 1 and phase 2 flagellins, respectively. Only one flagellin type is expressed at a time in a Salmonella cell. Isolates are termed biphasic, monophasic, or nonmotile if they can express both, one, or no flagellar phases, respectively. Expression of the two genes is under the control of a switch mechanism called "phase inversion." The switch mechanism consists of the DNA inversion of a sequence segment, the so-called invertible region, by recombination of the two flanking sites, hixL and hixR, mediated by an invertase encoded by the hin gene included in this segment (2). The promoter of the fljBA operon is born on this invertible region. The fljBA operon encodes the FljB flagellin and FljA, a repressor of the fliC gene. The orientation of the invertible region determines whether the fljBA operon or the fliC gene will be expressed (2).Characterization of Salmonella spp. below the subspecies level is traditionally obtained by serotyping based on the KauffmannWhite-Le Minor scheme (1). Serovars are determined following agglutination of entire bacteria with specific sera to identify variants of the somatic (O) and flagellar (H) antigens. Serotyping results in an antigenic formula, indicating the O, H1, and H2 antigens separated by colons. The different O and H antigens are named by numbers, alphabetical characters, or both. Some O antigens can be present or absent without interfering with serovar identification. These antigens are interesting only as epidemiological markers within a given serovar. These accessory O antigens are underlined when their presence is linked to the integration of a prophage. O or H antigens are written within square brackets if they may be present or absent without relation to phage conversion. The 1,4,[5],12:i:1,2 antigenic formula, corresponding to S. enterica serovar Typhimurium, therefore indicates that (i) the O4 and O12 antigens are always present in this serovar, (ii) the O1 antigen can be present or absent due to phage conversion, (iii) the O5 antigen can be present or absent without relation to phage conversion, and (iv) the H1 antigen "i" and the H2 antigens "1" and "2" are always present. If no H1 or H2 antigen can be detected,

Despite recent norovirus (NoV) outbreaks related to consumption of fruit products, little is known regarding the NoV load on these foods. Therefore, 75 fruit products were screened for NoV presence by using an evaluated in-house NoV detection methodology consisting of a NoV extraction method and a reverse transcription quantitative PCR assay. Additionally, the fruit samples were screened for bacterial pathogens and bacterial hygiene indicators. Results of the NoV screening showed that 18 of 75 samples tested positive for GI and/or GII NoV despite a good bacteriological quality. The recovery of murine norovirus 1 virus particles acting as process control was successful in 31 of 75 samples with a mean recovery efficiency of 11.32% ± 6.08%. The level of detected NoV genomic copies ranged between 2.5 and 5.0 log per 10 g. NoV GI and/or GII were found in 4 of 10, 7 of 30, 6 of 20, and 1 of 15 of the tested raspberries, cherry tomatoes, strawberries, and fruit salad samples, respectively. However, confirmation of the positive quantitative PCR results by sequencing genotyping regions in the NoV genome was not possible. Due to the nature of the method used (reverse transcription quantitative PCR) for detection of genomic material, no differentiation was possible between infectious and noninfectious viral particles. No NoV outbreaks related to the tested fruit product types were reported during the screening period, which hampers a conclusion as to whether these unexpected high numbers of NoV-positive results should be perceived as a public health threat. These results, however, may indicate a prior NoV contamination of the tested food samples throughout the fresh produce chain.

A comparative study of lag phases and growth rates of healthy, stressed, and sublethally injured Escherichia coli O157 cells in 10 enrichment broths was performed. The evaluation of enrichment protocols was validated by different end point detection methods (two PCR and two combined capture-plate methods). Tryptic soy broth b [TSB (b)] provided the fastest growth (max = 1.00 1 0.06 h- ) but failed to recover oxidative-stressed E. coli O157. TSB (a), TSB-yeast extract medium, TSB supplemented with 8 mg/liter novobiocin plus 16 mg/liter vancomycin (TSB+), buffered peptone water (BPW), and BPW supplemented with 8 mg/liter vancomycin (BPW+V) enabled resuscitation of E. coli O157 cells independent from precultural conditions. Modified TSB plus 10 mg/liter novobiocin (mTSB+N), EC medium, EC reduced bile salts medium (ECred), TSB (b), and TSB supplemented with 8 mg/liter novobiocin plus 16 mg/liter vancomycin plus 2 mg/liter rifampin plus 1 mg/liter K-Telluriet plus 1.5 g/liter bile salts no. 3 (TSB++) all failed to recover E. coli O157 cells for at least one type of stress. The use of TSB (a), TSB+, BPW, and BPW+V was compared with that of mTSB+N (International Organization for Standardization reference broth) for reliable detection of low numbers of healthy, stressed, and sublethally injured E. coli O157 (approximately 10 CFU/10 g) from foods (sprouted seeds, fermented sausage, raw milk, and raw ground beef). When low numbers of healthy cells were inoculated, BPW, BPW+V, TSB, TSB+, and mTSB+N enabled growth until detectable numbers within 6 h of enrichment at 41.5 degrees C. Results showed that mTSB+N failed to recover to detectable numbers E. coli O157 cells sublethally injured by freeze and food stresses, in contrast to what was obtained with BPW and BPW+V. This study highlights that using mTSB+N for recovery of E. coli O157 from foods may yield false-negative results.

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