Inappropriateness of Quinolone in Scrub Typhus Treatment Due to gyrA Mutation in Orientia tsutsugamushi Boryong Strain

The use of quinolone for treatment of rickettsial diseases remains controversial. Recent clinical studies suggest that quinolone is not as effective as others in patients with rickettsial diseases including scrub typhus, although the mechanism is not well understood. In this study, we evaluated the mutation in gyrA associated with quinolone resistance. We prospectively enrolled scrub typhus patients, collected blood samples and clinical data from October, 2010 to November, 2011. Among the 21 patients enrolled, one initially received ciprofloxacin for 3 days but was switched to doxycycline due to clinical deterioration. We obtained the gyrA gene of Orientia tsutsugamushi from 21 samples (20 Boryong strain, 1 Kato strain) and sequenced the quinolone resistance-determining region. All of 21 samples had the Ser83Leu mutation in the gyrA gene, which is known to be associated with quinolone resistance. This suggests that quinolones may be avoided for the treatment of serious scrub typhus.

The Bacterial Surface Expression of SARS Viral Epitope using Salmonella typhi Cytolysin A

The cytolysin A (ClyA) is a 34 kDa pore-forming cytotoxic protein and expressed by some enteric bacteria including Salmonella typhi. This toxin is transported on the bacterial surface and secreted without posttranslational modification. Using the surface display of ClyA, the expression vectors for 193-aa immunogenic antigen of spike protein (termed S1E) from severe acute respiratory syndrome coronavirus (SARS-CoV) were constructed. The vectors carried a gene encoding S. typhi ClyA conjugated to S1E at the C terminus (termed ClyA-S1E) and asd gene in pGEM-T and pBR322, named pGApLCS1E and pBApLCS1E, respectively. An asd-mutated E. coli transformed with these vectors could grow without diaminopimelic acid (DAP), indicating that they were stably maintained in such mutants. ClyA-S1E recombinant proteins from these vectors were expressed on the surface of the attenuated S. typhimurium deficient of global virulence gene regulator, ppGpp. However, they did not show the hemolytic activity on the blood agar plate and cytotoxicity against HeLa cells. To examine whether bacteria expressing ClyA-S1E induced the immune response against S1E, S. typhimurium deficient of ppGpp and Asd was transformed with these vectors and orally immunized in mice. In the western blotting against GST-conjugated S1E using the immunized mouse sera, it was shown that the significant band was detected in the mouse serum by the bacteria transformed with pGApLCS1E but not with pBApLCS1E. It indicates that the immune response producing antibody was dependent on the expression level of ClyA-S1E. Therefore, ClyA delivery system can be used for SARS vaccine development.