ABSTRACT
OBJECTIVE To explore the gene gyrA mutation in nalidixic acid-resistant Salmonella paratyphi A(SPA) in Shaoxing area.METHODS Fifty-two strains of SPA gene were assessed by amplification and purification and the PCR products were detected by two directional sequencing methods.The sequences of DNA gyrase A were compared and analyzed with the OMIGA2.0 software,and the gene gyrA mutation was identified.RESULTS The mutation in nalidixic acid-resistant SPA was discovered in No.83 or No.87 animo acid site of gyrA quinolones resistant determinate region(QRDR),and the mutation of 51 strains occurred in No.83 site,1 strain occurred in No.87 site.The simultaneous mutation of two sites was not discovered,No mutations were found in other sites of gyrA QRDR.CONCLUSIONS No.83 site mutations of gene gyrA has a direct relation to nalidixic acid-resistant SPA.No.87 site mutation of gene gyrA might also cause nalidixic acid-resistantce.The nalidixic acid-resistant SPA is mainly mutated in No.83 site by TCC→TTC(Ser→Phe) in Shaoxing area.
ABSTRACT
Twenty-six nalidixic acid-resistant Shigella sonnei strains isolated from 1982 to 2001 and 56 nalidixic acid-resistant mutants induced by quinolone drugs from susceptible wild strains were analyzed by sequencing the gyrA gene. All the 22 nalidixic acid-resistant isolates from 1998 to 2001 showed identical amino acid substitution of Ser to Leu (TCG --> TTG) at codon 83 while 7 different mutation types were detected in artificially induced nalidixic acid-resistant mutants. Asp87 (GGC) type was observed most commonly among mutants induced by nalidixic acid while Ser83 (TTG) type was common among mutants induced by ciprofloxacin or norfloxacin. All the isolates collected between 1998 and 2001 showed identical or nearly identical pulsed-field gel electrophoresis pattern. These results suggest that the explosive increase of S. sonnei infection after 1998 was mainly due to the spread of restricted number of clones resistant to nalidixic acid.