Molecular characterization of ciprofloxacin-resistant Salmonella enterica serovar Typhi and Paratyphi A causing enteric fever in India.
OBJECTIVE
To define the genetic characteristics and resistance mechanisms of clinical isolates of Salmonella enterica serovar Typhi (S. Typhi) and S. enterica serovar Paratyphi A (S. Paratyphi A) exhibiting high-level fluoroquinolones resistance.


METHODS
Three S. Typhi and two S. Paratyphi A ciprofloxacin-resistant isolates (MICs > 4 mg/L) were compared with isolates with reduced susceptibility to ciprofloxacin (MICs 0.125-1 mg/L) by PFGE, plasmid analysis, presence of integrons and nucleotide changes in topoisomerase genes.


RESULTS
In S. Typhi and Paratyphi A, a single gyrA mutation (Ser-83-->Phe or Ser-83-->Tyr) was associated with reduced susceptibility to ciprofloxacin (MICs 0.125-1 mg/L); an additional mutation in parC (Ser-80-->Ile, Ser-80-->Arg, Asp-69-->Glu or Gly-78-->Asp) was accompanied by an increase in ciprofloxacin MIC (> or = 0.5 mg/L). Three mutations conferred ciprofloxacin resistance: two in gyrA (Ser-83-->Phe and Asp-87-->Asn or Asp-87-->Gly) and one in parC. This is the first report of parC mutations in S. Typhi. Ciprofloxacin-resistant S. Typhi and S. Paratyphi A differed in their MICs and mutations in gyrA and parC. Moreover S. Typhi harboured a 50 kb transferable plasmid carrying a class 1 integron (dfrA15/aadA1) that confers resistance to co-trimoxazole and tetracycline but not to ciprofloxacin. PFGE revealed undistinguishable XbaI fragment patterns in ciprofloxacin-resistant S. Typhi as well as in S. Paratyphi A isolates and showed that ciprofloxacin-resistant S. Typhi have emerged from a clonally related isolate with reduced susceptibility to ciprofloxacin after sequential acquisition of a second mutation in gyrA.


CONCLUSIONS
To our knowledge this is the first report of molecular characterization of S. Typhi with full resistance to ciprofloxacin. Notably, the presence of a plasmid-borne integron in ciprofloxacin-resistant S. Typhi may lead to a situation of untreatable enteric fever.
Gaind
R
R
Department of Microbiology, Safdarjung Hospital and Assoc VMMC, New Delhi, India.
Paglietti
B
B
Murgia
M
M
Dawar
R
R
Uzzau
S
S
Cappuccinelli
P
P
Deb
M
M
Aggarwal
P
P
Rubino
S
S
D019943:Amino Acid Substitution; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002939:Ciprofloxacin / Q000494:pharmacology*; D027081:DNA Gyrase / Q000235:genetics; D027101:DNA Topoisomerase IV / Q000235:genetics; D026942:DNA Topoisomerases; D004269:DNA, Bacterial / Q000235:genetics; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D016521:Electrophoresis, Gel, Pulsed-Field; D006801:Humans; D007194:India; D032023:Integrons; D008826:Microbial Sensitivity Tests; D020125:Mutation, Missense; D010284:Paratyphoid Fever / Q000382:microbiology*; D010957:Plasmids; D012482:Salmonella paratyphi A / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D012485:Salmonella typhi / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D017422:Sequence Analysis, DNA; D013752:Tetracycline / Q000494:pharmacology; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000494:pharmacology; D014435:Typhoid Fever / Q000382:microbiology*
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D002939:Ciprofloxacin; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; C025580:endodeoxyribonuclease XBAI; D015252:Deoxyribonucleases, Type II Site-Specific; D027101:DNA Topoisomerase IV; D026942:DNA Topoisomerases; D027081:DNA Gyrase; D013752:Tetracycline