Multi-locus sequence typing of Bartonella henselae isolates from three continents reveals hypervirulent and feline-associated clones

Abstract

Bartonella henselae is a zoonotic pathogen and the causative agent of cat scratch disease and a variety of other disease manifestations in humans. Previous investigations have suggested that a limited subset of B. henselae isolates may be associated with human disease. In the present study, 182 human and feline B. henselae isolates from Europe, North America and Australia were analysed by multi-locus sequence typing (MLST) to detect any associations between sequence type (ST), host species and geographical distribution of the isolates. A total of 14 sequence types were detected, but over 66% (16/24) of the isolates recovered from human disease corresponded to a single genotype, ST1, and this type was detected in all three continents. In contrast, 27.2% (43/158) of the feline isolates corresponded to ST7, but this ST was not recovered from humans and was restricted to Europe. The difference in host association of STs 1 (human) and 7 (feline) was statistically significant (P< or =0.001). eBURST analysis assigned the 14 STs to three clonal lineages, which contained two or more STs, and a singleton comprising ST7. These groups were broadly consistent with a neighbour-joining tree, although splits decomposition analysis was indicative of a history of recombination. These data indicate that B. henselae lineages differ in their virulence properties for humans and contribute to a better understanding of the population structure of B. henselae.

Figure 1. Geographical distribution of B. henselae STs in different continents.

The lower panel shows the ST distribution in European countries that were represented by at least 10 isolates.

Figure 2. Frequency of feline and human B. henselae isolates within each ST in correlation with the geographic origin of the isolates.

Figure 3. Phylogenetic relationship between different B. henselae STs as determined by eBURST.

A clonal complex contains STs that have 7 out of 8 alleles in common. ST7 is assigned as a singleton since it differed in 3–7 alleles from all other STs. The size of the circles relates to the frequency of the corresponding ST, and illustrates that the assigned primary founder of the major clonal complex (ST5) is a common clone.

Figure 4. Neighbour-joining tree of the concatenated sequences of B. henselae STs as reconstructed by MEGA4.

1,000 bootstrap replicates were used to examine the confidence in the tree. The only node to score above 60 is the one leading to Group 1 (75%, as indicated), indicating that the delineation of Group 1 represents a real division in the B. henselae population.

Figure 5. Splits decomposition was used to detect evidence for a past history of recombination in the sequences.

The extensive reticulation suggests that recombination has occurred relatively frequently. However, Group 1 remains distinct (as indicated by the filled oval).