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ABSTRACTSalmonella entericaserovar Typhimurium is one of the leading causes of gastroenteritis in humans. Phage typing has been used for the epidemiological surveillance of S. Typhimurium for over 4 decades. However, knowledge of the evolutionary relationships between phage types is very limited. In this study, we used single nucleotide polymorphisms (SNPs) as molecular markers to determine the relationships between common S. Typhimurium phage types. Forty-four SNPs, including 24 identified in a previous study and 20 from 6 available whole-genome sequences, were used to analyze 215 S. Typhimurium isolates belonging to 45 phage types. Altogether, 215 isolates and 6 genome strains were differentiated into 33 SNP profiles and four distinctive phylogenetic clusters. Fourteen phage types, including DT9, one of the most common phage types in Australia, were differentiated into multiple SNP profiles. These SNP profiles were distributed into different phylogenetic clusters, indicating that they have arisen independently multiple times. This finding suggests that phage typing may not be useful for long-term epidemiological studies over long periods (years) and diverse localities (different countries or continents). SNP typing provided a discriminative power similar to that of phage typing. However, 12 SNP profiles contained more than one phage type, and more SNPs would be needed for further differentiation. SNP typing should be considered as a replacement for phage typing for the identification of S. Typhimurium strains.

ABSTRACTFluorescent amplified fragment length polymorphism (AFLP) was applied to 46 Salmonella entericaserovar Typhimurium isolates of Australian origin comprising nine phage types, by using the restriction enzymes MseI and EcoRI and all 16 possible MseI +1-EcoRI +1 primer pair combinations. AFLP in the present study showed a very good discrimination power with a Simpson index of diversity of 0.98, and 35 different AFLP patterns were observed in the 46 isolates. AFLP grouped most serovar Typhimurium isolates by phage type and enabled differentiation of phage types. Furthermore, 84 phage-type-specific polymorphic AFLP fragments, for which presence or absence correlated with phage type (including 25 with one exception to phage type specificity) were observed in the 46 strains studied. Eighteen phage-type-specific AFLP fragments were cloned and sequenced. Fifteen are of known genes or have a homologue in the databases. Three sequences are plasmid related, eight are phage related, and four relate to chromosomal genes. Twelve of the 18 fragments are polymorphic because the DNA is present or absent as indicated by Southern hybridization, and we see good potential to use sequences of these fragments as the basis for multiplex PCR and development of a microarray-based molecular phage-typing method for serovar Typhimurium.

ABSTRACTThe seventh cholera pandemic started in 1961 and continues today. A collection of 45 seventh pandemic isolates of V. choleraesampled over a 33-year period were analyzed by amplified fragment length polymorphism (AFLP) fingerprinting. All but four pairs and one set of three isolates were distinguished. AFLP revealed far more variation than ribotyping, which was until now the most useful method of revealing variation within the pandemic clone. Unfortunately, the ribotype variation observed is mainly due to recombination between the multiple copies of the rrngenes (R. Lan and P. R. Reeves, Microbiology 144:1213–1221, 1998), which makes changes susceptible to repeat occurrences and reversion. This AFLP study shows that particularly for the common ribotypes G and H, such events have indeed occurred. AFLP grouped most of the 45 isolates into two clusters. Cluster I consists mainly of strains from the 1960s and 1970s, while cluster II contains mainly strains from the 1980s and 1990s, revealing a temporal pattern of change in the clone. This is best seen in the relationships of the strains from Africa, which correlate with the epidemiology of epidemics on that continent. The data confirm independent introductions to Africa during the 1970s outbreak and reveal several other African introductions. In the 1991 cholera upsurge, isolates from the Southern and Eastern African epidemic focus are markedly different from those from the West African epidemic focus. An isolate from 1987 in Algeria was identical to the West epidemic isolates, suggesting that the strain was present in Africa at least 3 years before causing large outbreaks. These observations have major implications for our understanding of cholera epidemiology.

ABSTRACTFlagellar (H) antigens are mostly encoded by genes at thefliClocus in E. coli. We have sequenced 11 H7fliCgenes from Escherichia colistrains that belong to seven O serotypes. These sequences, together with those of nine other H7 fliCgenes (from strains of three different O serotypes) sequenced recently (S. D. Reid, R. K. Selander, and T. S. Whittam, J. Bacteriol. 181:153–160, 1999), include 10 different sequences. The differences between these 10 sequences range from 0.06 to 3.12%. By comparison with other E. coliflagellin genes, we have identified primer length sequences specific for H7 genes in general and others specific for H7 genes of O157 and O55 strains: the specificity was confirmed by PCR testing the type strains for all 53 E. coliH types. We have previously identified genes specific for the E. coliO157 antigen, and use of the combination of O157- and H7-specific primers allows the sensitive and rapid detection of O157:H7 E. colistrains, which cause the majority of hemorrhagic colitis cases.

ABSTRACTShiga toxin (Stx)-producing Escherichia colistrains of serogroup O111 are the most frequently isolated non-O157 strains causing outbreaks of gastroenteritis with hemolytic-uremic syndrome. The O111 O-antigen gene cluster had been cloned and about half of it has been sequenced; we have now sequenced the remainder of the gene cluster, which is 12.5 kb in length and which comprises 11 genes. On the basis of sequence similarity, we have identified all the O-antigen genes expected, including five sugar biosynthetic pathway genes, three transferase genes, the O-unit flippase gene, and the O-antigen polymerase gene. By PCR testing with E. colistrains representing all 166 O-antigen forms, some randomly selected gram-negative bacteria, and Salmonella entericaserovar Adelaide, we showed that four O-antigen genes are highly specific to O111. This work provides the basis for a sensitive test for the rapid detection of E. coliO111. This is important both for decisions related to patient care, because early treatment may reduce the risk of life-threatening complications, and for the detection of sources of contamination.