4. AOACRIMicroMethods-2018Awards

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C rowley et al .: J ournal of AOAC I nternational V ol . 97, N o . 2, 2014  449

Table 2. Heat-stress injury results Matrix (LMX test portion size)

Test organism a

CFU/OXA (selective agar) CFU/TSA (nonselective agar) Degree injury, %

5.0 × 10 8 2.9 × 10 8

1.3 × 10 9 9.0 × 10 8

62 68

Queso fresco LMX – 25 g Queso fresco LMX – 125 g

L. monocytogenes ATCC 19115 L. monocytogenes ATCC 19115

a  ATCC = American Type Culture Collection.

(including five uninoculated control replicates) that produced non- L. monocytogenes profiles, with five of the test portions producing questionable API profiles of L. grayi . Colonies on these plates contained one or more of the following biochemical reactions not typically associated with L. monocytogenes : Gram- negative, non-beta-hemolytic, and catalase negative. Based on the preliminary biochemical tests conducted, the test portions should not have been carried through for final biochemical identification on API Listeria strips which resulted in the misidentification of the test portion as Listeria spp. The selective agar plates for these test portions were sent to the coordinating laboratory for further examination. The coordinating laboratory verified the supplementary results (Gram stain, hemolysis, and catalase reaction) reported by the participating laboratory and were not able to identify any Listeria species. The results from this laboratory were excluded from statistical analysis. The MPN levels obtained for this test portion, with 95% confidence intervals, were 0.59 CFU/test portion (0.46, 0.74) for the low level and 5.41 CFU/test portion (3.53, 8.30) for the high level. For VIDAS LMX test portions, no differences were observed between confirmation of samples using the proprietary chromogenic ALOA and the reference method agar. For the high-level, 144 out of 144 test portions were reported as positive by VIDAS LMX with all test portions confirming positive. For the low level, 70 out of 144 test portions were reported as positive by VIDAS LMX with all 70 test portions confirming positive. For the uninoculated controls, 0 out of 144 samples produced a presumptive positive result by VIDAS LMX and no samples confirmed positive. For test portions analyzed by AOAC 993.12 , 144 out of 144 high inoculum and 69 out of 144 low inoculum test portions confirmed positive. For the uninoculated controls, 0 out of 144 test portions confirmed positive. For the low-level inoculum, dLPOD C values of 0.01 (–0.10, 0.13) were obtained between AOAC 993.12 and VIDAS LMX. The confidence intervals obtained for dLPOD C indicated no significant difference between the two methods. dLPOD CP values of 0.00 (–0.12, 0.12) were obtained between presumptive and confirmed VIDAS LMX results. The confidence intervals obtained for dLPOD CP indicated no significant difference between the presumptive and confirmed results using either confirmation process. For the high-level inoculum, dLPOD C values of 0.00 (–0.03, 0.03) were obtained between AOAC 993.12 and VIDAS LMX. The confidence intervals obtained for dLPOD C indicated no significant difference between the two methods. dLPOD CP values of 0.00 (–0.03, 0.03) were obtained between presumptive and confirmed VIDAS LMX results. The confidence intervals obtained for dLPOD CP indicated no significant difference between the presumptive and confirmed results. Detailed results of the POD statistical analysis are presented in Table  2013.11B ,

the participating laboratory and were not able to identify any Listeria species. Laboratory 11 also reported one uninoculated control portion positive for L. monocytogenes. Testing at the coordinating laboratory verified this result, which indicated cross contamination with that sample. The results from this laboratory were excluded from statistical analysis. The MPN obtained for this matrix, with 95% confidence intervals, were 0.55 CFU/test portion (0.43, 0.70) for the low inoculum level and 3.81 CFU/test portion (3.06, 5.48) for the high inoculum level. For VIDAS LMX test portions, no difference was observed between confirmation of samples using the proprietary chromogenic ALOA agar and OXA required by the reference method. For the high inoculum level, 156 out of 156 test portions were reported as positive by the VIDAS LMX method with all test portions confirming positive. For the low inoculum level, 77 out of 156 test portions were reported as positive by the VIDAS LMX method with 75 test portions confirming positive, indicating two false-positive results. For the uninoculated controls, 0 out of 156 samples produced a presumptive positive result by the VIDAS LMX method with no samples confirming positive. For test portions analyzed by AOAC 993.12 , 153 out of 156 high inoculum test portions and 69 out of 156 low inoculum test portions confirmed positive. For the uninoculated controls, 0 out of 156 test portions confirmed positive. For the low-level inoculum, a dLPOD C value of 0.04 (–0.08, 0.15) was obtained between AOAC 993.12 and VIDAS LMX. The confidence intervals obtained for dLPOD C indicated no significant difference between the two methods. A dLPOD CP of 0.01 (–0.10, 0.13) was obtained between presumptive and confirmedVIDAS LMX results for both confirmation procedures. The confidence intervals obtained for dLPOD CP indicated no significant difference between the presumptive and confirmed results. For the high-level inoculum, a dLPOD C value of 0.02 (–0.01, 0.06) was obtained betweenAOAC 993.12 andVIDASLMX. The confidence intervals obtained for dLPOD C indicated no significant difference between the two methods. A dLPOD CP of 0.00 (–0.02, 0.02) was obtained between presumptive and confirmed VIDAS LMX results. The confidence intervals obtained for dLPOD CP indicated no significant difference between the presumptive and confirmed results. Results of the POD statistical analysis are presented in Table 2013.11A , Tables 2A–B, and Figures 1A–D as supplemental data on the J. AOAC Int. website. Queso fresco test portions were inoculated at a low and high level and analyzed (Table 4) for the detection of L. monocytogenes . Uninoculated controls were included in each sample set. Fourteen laboratories participated in the analysis of this matrix and the results of 12 laboratories were included in the statistical analysis. Laboratory 2 did not report any data for this matrix. Laboratory 11 reported 10 reference method test portions 03/10/2019 Queso Fresco (125 g Test Portions)