title: Antibiotic resistance of Salmonella enterica serovar Paratyphi A in India: emerging and reemerging problem.
abstract: BACKGROUND
  Antibiotic resistance pattern and R-plasmid of Salmonella enterica serovar Paratyphi A isolates from Kolkata, India are not well documented.
  
  
  OBJECTIVE
  To determine the trend of antibiotic resistance of S. paratyphi A isolates.
  
  
  METHODS
  A retrospective study was carried out using blood culture isolates of S. paratyphi A (1991 to 2005) obtained from patients of enteric fever from Asansol and Kolkata and its suburbs (India).
  
  
  METHODS
  Antibiotic susceptibility pattern, using seven antibiotics, for the isolates was determined following agar dilution and disk diffusion methods. Transferability of multidrug resistance to ampicillin (Am), chloramphenicol (Chl), cotrimoxazole (Cot) and tetracycline (Tet) among the isolates was determined by in vitro conjugation. The multi-drug resistant (MDR) and antibiotic susceptible S. paratyphi A strains and the trans-conjugants were screened for the presence of plasmid.
  
  
  METHODS
  The t test was used to compare the difference between mean minimum inhibitory concentration values of ciprofloxacin (Cp) for nalidixic acid (Nx)-resistant and Nalidixic acid (Nx)-susceptible isolates.
  
  
  RESULTS
  Among 13 outbreak causing isolates in 1991, 9 (69.23%) showed AmChlCotTet-resistance, while 4 (30.77%) Cot-resistance only. During 1992-1994, all 13 isolates were susceptible to Am, Chl, Cot and Tet. During 1995-2005, isolates demonstrated different resistance patterns and emergence of nalidixic acid (Nx)-resistance. A transferable plasmid conferring AmChlCotTet-resistance was detected among MDR isolates. All the isolates were susceptible to ceftriaxone (Ctx) and ciprofloxacin (Cp). Association between Nalidixic acid (Nx)-resistance and reduced susceptibility to ciprofloxacin (Cp) among 59 S. paratyphi A isolates was noticed (P < 0.001).
  
  
  CONCLUSIONS
  Vigilance for R-plasmid and surveillance of antibiotic susceptibility among S. paratyphi A isolates in and around Kolkata, India, are mandatory in order to combat antibiotic resistance of the isolates in this part of the world.
authors.affiliation: Department of Bacteriology and Serology, Calcutta School of Tropical Medicine, C. R. Avenue, Kolkata 700073, India. samtropmed@rediffmail.com
authors.forename: Shyamapada
authors.initials: S
authors.lastname: Mandal
authors.forename: M D
authors.initials: MD
authors.lastname: Mandal
authors.forename: N K
authors.initials: NK
authors.lastname: Pal
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial; D024901:Drug Resistance, Multiple, Bacterial; D006801:Humans; D007194:India; D008826:Microbial Sensitivity Tests; D011815:R Factors; D012189:Retrospective Studies; D012482:Salmonella paratyphi A / Q000187:drug effects* / Q000302:isolation & purification*; D013997:Time Factors; D014435:Typhoid Fever / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents