Here we used Expectation Maximization (EM) clustering algorithm to divide the data on the basis of the biochemical test results. Since GDC-941 the precise pathogenic status of most Cronobacter strains is unknown, we considered the resulting clusters as being pathogenic or not on the basis of (a) the source from which the strains were isolated and/or (b) MLST types previously associated with pathogenic or non-pathogenic strains (see Materials and Methods) and reference [14]. The clustering of the biochemical test results was also examined for traits associated with pathogenicity. Results and Discussion Clustering the dataset for Test
1 with the number of clusters being 2, resulted in clusters 1 (p 1 = 0.26) and 2 (p 2 = 0.74) containing 25 and 65 strains respectively (L
= -3.119; Table 1) where p i (i = 1, 2) is the probability of cluster membership for a randomly chosen strain and L is the maximum log likelihood (see Materials and Methods). According to our hypothesis cluster 2 was most likely to contain pathogenic strains since all ST 4 strains were assigned to this cluster. It is known that ST 4 strains are associated with the most serious pathogenic states such as meningitis in infants [14]. Of the other MLST types, ST 1 and 3 were click here placed exclusively with the potentially non-pathogenic strains in cluster 1. ST 7 was split between two clusters with 7 of 11 strains in the non-pathogenic grouping. All except one ST 8 strain were predicted to be in the
pathogenic cluster, as were all of the ST 12 strains (Table 1). The group with CHIR-99021 concentration unspecified clinical source (22 strains) was divided between the two clusters, indicating that not all clinical isolates are likely to be pathogenic Palmatine and this feature (isolation of a strain from a clinical sample) alone by no means allows us to infer pathogenicity of a strain. For example, one clinical case, classified as non-pathogenic, was obtained from a breast abscess and it is plausible that this was a secondary infection although it is not known if another infectious agent was isolated. Thus this may indeed be a non-pathogenic strain. Two asymptomatic strains appeared in the pathogenic cluster; one of these strains is ST 12 and the other ST 13. Several ST 12 strains are from clinical sources and it is likely that all ST 12 strains will have similar pathogenic characteristics. Therefore, we can speculate that these strains could have caused an infection following a higher ingested dose or a lower immune status. Table 1 Clusters from Test 1 dataset Cronobacter species MLST type Cluster 1: potential non-pathogenic Source (number of strains) Cluster 2: potential pathogenic Source (number of strains) C. sakazakii 1 IF(4), C(1), MP(1), Faeces(1) IF(1) C. sakazakii 3 IF(1), EFT(2), FuF(4), U(1) C. sakazakii 4 C(9), IF(7), MP(1), Washing Brush(1), E(1), U(2) C. sakazakii 8 C(1) C(6), IF(1) C. sakazakii 12 C(3), U(1) C.