In vitro effect of new antibiotics against Clinical isolates of Salmonella enterica subspecies enterica

Abstract

Background: Typhoid fever is caused by Salmonella enterica serovar Typhi (S, Typhi, T is capital because Typhi is serotype and not species) a gram negative bacterium (1). It continues to be a global health problem with over 21.6 million cases and more than 200,000 deaths occurring annually (2;3). Most of these deaths occur in Asia (4). Salmonella enterica serotype Paratyphi is traditionally associated with relatively milder illness as compared to Salmonella enterica serotype Typhi. Aim & Objectives: The aim of this study was to determine in vitro MIC patterns of various therapeutic alternatives available for the treatment of enteric fever and non-typhoidal salmonellae in an endemic region reporting a recent increase in ciprofloxacin resistance. Study design: It is a cross sectional research carried out at Armed Forces Institute of Pathology Rawalpindi. Research was conducted from June 2011 to May 2013. Materials and Methods: Samples of blood, bone marrow, pus, urine, stool and fluids were collected from suspected cases of salmonella infections. Standard protocols were observed during collection and transportation. Culture was applied on Bactec 9050 special and/or standard media. Suspected salmonella colonies were tested by API 20E and confirmed by serology. The isolates were also tested for resistance to antibiotics ampicillin, cotrimoxazole, ciprofloxacin, ceftriaxone, doripenem, imipenem, ertapenem, aztreonam, moxifloxacin, cefpirome, cefepime, gatifloxacin, and chloramphenicol by Kirby-Bauer disc diffusion method (5). MIC (Minimum Inhibitory concentration) was done on MDR and ciprofloxacin intermediate or resistant cases by E-strips. Results: 316 isolates of Salmonella were recovered from 2230 specimens. Resistance by disk diffusion technique was determined, for Salmonella Typhi 11 against Ampicillin 72%, Chloramphenicol 62%, Cotrimoxazole 41.2%, ceftriaxone 2.4%, ciprofloxacin 8%, cefpodoxime 4.7%, doripenem 2.3%, ertapenem 3.5%, aztreonam 3.5%, and moxifloxacin 3.5%. No resistance was noted for imipenem, cefepime and gatifloxacin. Resistance noted in Salmonella Paratyphi A was ampicillin 60%, chloramphenicol 40%, cotrimoxazole 38%, ceftriaxone 7.9%, ciprofloxacin 8%, cefpodoxime 7.9%, imipenem and ertapenem 2.6%, aztreonam 1.3%, moxifloxacin 6.6%, and gatifloxacin1.3%. No resistance was noted for doripenem and cefepime. For non-typhoidal salmonellae resistance was noted only against cotrimoxazole 66.6% and ciprofloxacin 7%. For S. Typhi imipenem MIC90 was 0.38 and MIC50 was 0.25. For cefpirome MIC90 was 0.64 and MIC50 was 0.09. For aztreonam MIC90 was 0.12 and MIC50 was 0.09. For cefpodoxime MIC90 was 0.75 and MIC50 was 0.38. For azithromycin these values were 16.0 and 7.0 and for tigecycline they were 0.25 and 0.09