The present work compared 2 culture methods and the combinations of pre-enrichment and enrichment culture methods with PCR assays [buffered peptone water-PCR and tetrathionate-PCR or modified semisolid Rappaport-Vassiliadis (MSRV)-PCR] for motile and nonmotile Salmonella strain detection using artificially contaminated poultry feces. The specificity and positive predictive values were equal to one in both culture methods. Specificity and positive predictive values, accuracy, sensitivity, and negative predictive values were higher for motile than nonmotile Salmonella strains in culture methods. Only Salmonella enterica serovar Gallinarum was detected by the MSRV method with low accuracy, sensitivity, and negative predictive value. The detection level of motile strains was 2 ×10(0) to 22 × 10(2) cfu per 25 g for these methods, whereas it was 6.9 × 10(2) cfu per 25 g in culture methods for Salmonella Gallinarum. Extending the incubation time of the enrichment medium to 6 d in the TT method did not improve the isolation rates. In general, all selective plating media did not show any statistical differences in the parameters of performance studied. On the other hand, accuracy and sensitivity values were higher in MSRV-PCR and tetrathionate-PCR methods than in the buffered peptone water-PCR method. Specificity and positive predictive values were equal to one in most of the cases. In terms of detection limits, motile Salmonella strains were recovered from 5 × 10(0) cfu per 25 g in MSRV-PCR and tetrathionate-PCR methods, whereas the detection limit was better for nonmotile Salmonella in MSRV-PCR methods than in the tetrathionate-PCR method. Kappa coefficients showed that there was a very good agreement between tetrathionate and MSRV methods for motile Salmonella strains, whereas these methods did not show any concordance for nonmotile Salmonella strains. When buffered peptone water-PCR was compared with both tetrathionate-PCR and MSRV-PCR, agreement was poor for motile Salmonella strains and slight to fair for nonmotile Salmonella strains. The difference in isolation rate obtained with the methods used for motile and nonmotile Salmonella strains must be taken into account when a poultry fecal sample is considered negative for the presence of Salmonella.

Bacillus cereus is an endospore-forming, Gram-positive bacterium able to cause foodborne diseases. Lactic acid bacteria (LAB) are known for their ability to synthesize organic acids and bacteriocins, but the potential of these compounds against B. cereus has been scarcely documented in food models. The present study has examined the effect of the metabolites produced by Lactobacillus johnsonii CRL1647 and Enterococcus faecium SM21 on the viability of select B. cereus strains. Furthermore, the effect of E. faecium SM21 metabolites against B. cereus strains has also been investigated on a rice food model. L. johnsonii CRL1647 produced 128 mmol/L of lactic acid, 38 mmol/L of acetic acid and 0.3 mmol/L of phenyl-lactic acid. These organic acids reduced the number of vegetative cells and spores of the B. cereus strains tested. However, the antagonistic effect disappeared at pH 6.5. On the other hand, E. faecium SM21 produced only lactic and acetic acid (24.5 and 12.2 mmol/L, respectively) and was able to inhibit both vegetative cells and spores of the B. cereus strains, at a final fermentation pH of 5.0 and at pH 6.5. This would indicate the action of other metabolites, different from organic acids, present in the cell-free supernatant. On cooked rice grains, the E. faecium SM21 bacteriocin(s) were tested against two B. cereus strains. Both of them were significantly affected within the first 4 h of contact; whereas B. cereus BAC1 cells recovered after 24 h, the effect on B. cereus 1 remained up to the end of the assay. The LAB studied may thus be considered to define future strategies for biological control of B. cereus.

No abstract

To detect Salmonella gallinarum or Salmonella pullorum in artificially contaminated poultry feed, 9 culture combinations were compared, including 3 preenrichment/enrichment methods (tryptic soy broth plus ferrous sulfate/tetrathionate Hajna, tryptic soy broth plus ferrous sulfate/selenite cystine broth, and Salmosyst) in combination with 3 selective agars (xylose lysine desoxicholate agar added with tergitol 4, EF-18, and Önöz), respectively. Additionally, a single PCR technique was applied combined with 2 different preenrichment media (tryptic soy broth plus ferrous sulfate and Salmosyst). The specificity and positive predictive value were 1 for all methods. There were some differences among Salmonella strains for sensitivity and accuracy in the culture and Salmosyst-PCR methods. The sensitivity and accuracy values were less than 0.60 and 0.64, respectively, whereas the negative predictive values were between 0.12 and 0.23. Two PCR methods did not show any difference in the parameters of performance evaluated. Kappa coefficients showed good agreement between both methods. None of the culture combinations was able to detect S. gallinarum or S. pullorum when the inoculum was less than 3 × 10² cfu/25 g, except the Salmosyst broth method, which could recover S. gallinarum from 3 × 10¹ cfu/25 g onward. Overall, there were differences in the detection limits among the strains and methods used. In general, the 3 selective plating media did not show any significant difference in the parameters of performance studied for each strain. On the other hand, the agreements were slight to fair when culture methods were compared among them and with both PCR methods. The differences in the detection levels that were obtained using these methods and the difficulty in detecting S. gallinarum or S. pullorum in feed represent a potential problem when a poultry feed sample is considered to be negative. It is highly recommended to use at least 2 methods to increase the chances of detecting S. gallinarum or S. pullorum in poultry feed.

The present work compared 2 culture methods and a PCR assay applied with 2 enrichment methods for the detection of motile and nonmotile Salmonella strains using artificially contaminated egg content. The specificity (Sp) was 1 in all methods. The sensitivity (Se), accuracy (Ac), positive predictive value (PPV), and negative predictive value (NPV) were 1 in both culture methods for motile and nonmotile strains. In reference to the PCR methods, Se and PPV were between 0 and 1, whereas Ac and NPV were between 0.14 and 1. The detection level of motile and nonmotile strains was 5 to 54 cfu per 25 mL for both culture methods, but some strains could not be detected by the PCR methods. Extending incubation time of the enrichment medium to 5 d in the tetrathionate broth (TT), and Muller-Kauffmann tetrathionate-novobiocin broth (MKTTn) methods did not improve the isolation rates. All selective plating media did not show any statistical differences in the parameters of performance studied. Kappa coefficients showed that there was an excellent agreement between the bacteriological methods for all Salmonella strains. The agreement was very good and good between the PCR methods, for motile and nonmotile strains, respectively. However, there was a poor agreement when the PCR and bacteriological methods were compared for motile and nonmotile Salmonella strains. The TT and MKTTn methods are similar in terms of Ac, Se, Sp, PPV, and NPV for different Salmonella strains in egg content. The use of the PCR method cannot improve the same parameters, described before, in this matrix. So, further studies are needed to improve the performance parameters and limit of detection in egg content for the PCR methods, so that test can be used in poultry and food industry.

The performance of detection methods (culture methods and polymerase chain reaction assay) and plating media used in the same type of samples were determined as well as the specificity of PCR primers to detected Salmonella spp. contamination in layer hen farms. Also, the association of farm characteristics with Salmonella presence was evaluated. Environmental samples (feces, feed, drinking water, air, boot-swabs) and eggs were taken from 40 layer hen houses. Salmonella spp. was most detected in boot-swabs taken around the houses (30% and 35% by isolation and PCR, respectively) follow by fecal samples (15.2% and 13.6% by isolation and PCR, respectively). Eggs, drinking water, and air samples were negative for Salmonella detection. Salmonella Schwarzengrund and S. Enteritidis were the most isolated serotypes. For plating media, relative specificity was 1, and the relative sensitivity was greater for EF-18 agar than XLDT agar in feed and fecal samples. However, relative sensitivity was greater in XLDT agar than EF-18 agar for boot-swab samples. Agreement was between fair to good depending on the sample, and it was good between isolation and PCR (feces and boot-swabs), without agreement for feed samples. Salmonella spp. PCR was positive for all strains, while S. Typhimurium PCR was negative. Salmonella Enteritidis PCR used was not specific. Based in the multiple logistic regression analyses, categorization by counties was significant for Salmonella spp. presence (P-value = 0.010). This study shows the importance of considering different types of samples, plating media and detection methods during a Salmonella spp. monitoring study. In addition, it is important to incorporate the sampling of floors around the layer hen houses to learn if biosecurity measures should be strengthened to minimize the entry and spread of Salmonella in the houses. Also, the performance of some PCR methods and S. Enteritidis PCR should be improved, and biosecurity measures in hen farms must be reinforced in the region of more concentrated layer hen houses to reduce the probability of Salmonella spp. presence.

The present work compared 2 culture methods and PCR assay for the detection of motile and non-motile Salmonella strains using artificially contaminated poultry feed. The specificity was 1 in all methods. The accuracy and sensitivity were between 0.5 and 1 for motile Salmonella strains, whereas these parameters were between 0 and 0.6 for non-motile Salmonella strains. The positive predictive value was 1 for tetrathionate (TT), PCR, and modified semisolid Rappaport-Vassiliadis (MSRV) methods in most of the strains studied. The negative predictive value of each method was very low for non-motile Salmonella strains. The detection level of motile strains was 8 to 20 cfu/25 g for all methods, whereas it was ≥10(4) cfu/25 g in culture methods for non-motile Salmonella strains. In general, the PCR method detected lower non-motile Salmonella contamination levels in feed than did culture methods. Extending incubation time of the enrichment medium to 6 d in the TT method did not improve the isolation rates. All selective plating media did not show any statistical differences in the parameters of performance studied. Kappa coefficients showed that there was good agreement between TT and MSRV methods, and MSRV and PCR methods for motile Salmonella strains in poultry feed samples. The agreement was fair between TT and PCR methods for these strains. For non-motile Salmonella strains, there was poor (TT and MSRV methods), slight (PCR and TT methods), and fair (MSRV and PCR methods) agreement. The TT, MSRV, and PCR methods are similar in terms of accuracy, sensitivity, specificity, positive predictive value, and negative predictive value for different motile Salmonella strains in poultry feed. For non-motile Salmonella strains, the use of the PCR method improves the same parameters, described before, in this matrix. The difference in detection levels obtained with the methods used for motile and nonmotile Salmonella strains and the difficulty to detect these last strains represent a potential problem, when a poultry feed sample is considered negative for the presence of Salmonella.

No abstract