SPARFLOXACIN RESISTANCE IN CLINICAL ISOLATES OF STREPTOCOCCUS-PNEUMONIAE - INVOLVEMENT OF MULTIPLE MUTATIONS IN GYRA AND PARC GENES

Antimicrobial susceptibility testing revealed among 150 clinical isola tes of Streptococcus pneumoniae 4 pneumococcal isolates with resistanc e to fluoroquinolones (MIC of ciprofloxacin, greater than or equal to 32 mu g/ml; MIC of sparfloxacin, greater than or equal to 16 mu g/ml). Gene amplification and sequencing analysis of gyrA and parC revealed nucleotide changes leading to amino acid substitutions in both GyrA an d ParC of all four fluoroquinolone-resistant isolates. In the case of strains 182 and 674 for which sparfloxacin MICs were 16 and 64 mu g/ml , respectively, nucleotide changes were detected at codon 81 in gyrA a nd codon 79 in parC; these changes led to an Ser-->Phe substitution in GyrA and an Ser-->Phe substitution in ParC, Strains 354 and 252, for which sparfloxacin MICs were 128 mu g/ml, revealed multiple mutations in both gyrA and parC, These strains exhibited nucleotide changes at c odon 85 leading to a Glu-->Lys substitution in GyrA, in addition to Se r-79-->Tyr and Lys-137-->Asn substitutions in ParC, Moreover, strain 2 52 showed additional nucleotide changes at codon 93, which led to a Tr p-->Arg substitution in GyrA These results suggest that sparfloxacin r esistance could be due to the multiple mutations in GyrA and ParC, How ever, it is possible that other yet unidentified mutations may also be involved in the high-level resistance to fluoroquinolones in S. pneum oniae.