To investigate genetic relatedness among different H. acinonychis isolates, we compared 16S rRNA genes and RAPD fingerprint typing patterns of our five isolates (SB-1 and SB-5) with those of two other H. acinonychis strains from a Sumatran tiger maintained in captivity in a German zoo [61]. RFLP of the 16S rRNA PCR products yielded identical fragment patterns (Fig. S4A–D). The nucleotide sequence of the 16S rRNA gene was also highly similar between isolates from Bengal and Sumatran tigers (accession number AF057163) (Fig. 3, bottom). Thus, we next scored RAPD fingerprint patterns, which are more effective than the focused analysis of individual genes at discriminating between related strains. The RAPD patterns were also almost identical between our five strains and those from the Bengal and Sumatran tigers (Fig. S5A–C), indicating that very closely related H. acinonychis strains have colonized different tiger subspecies from very different geographic locations.
Next, we compared the RAPD fingerprint patterns of our H. acinonychis strain SB-1 with those of strains from other big cats: namely three cheetahs from a US zoo, two lions, one lion-tiger hybrid and another tiger housed at a European circus (Table 1). The results show that the fingerprinting patterns of our isolates from the Bengal tiger are also very similar to those of the cheetah and lion isolates, which were categorised in group I [33], while are distinct from those of the lion-tiger hybrid and other tiger isolates, classified as group II H. acinonychis (Fig. 4C and Fig. S6A–C) [33].