In vitro Assessment of Selected Antibiotics, Crude Extract of Dalbergia latifolia Leaf and Their Combination on MDR Salmonella enterica Strain.

Aims: To investigate the susceptibility pattern Salmonella enterica strains to selected antibiotics and extract of Dalbergia latifolia as well as their combinatory effect on (multi-drug resistant) MDR salmonella.  Place and Duration of Study: Faculty of Pharmacy, University of Ibadan, Nigeria from October 2012-May 2013. Methodology: In this study, a total of 11 clinical isolates of Salmonella enterica strains were screened in vitro against five antibiotics (ampicillin, amoxycillin, chloramphenicol, cotrimoxazole and ceftriaxone) for their antimicrobial susceptibility patterns, and against methanolic extracts of Dalbergia latifolia leaves. The isolates were also screened in vitro against the combined antibiotics and  plant  extracts  using  the  agar  well  diffusion  method  and  their  MICs  determined.  Phytochemical screening  was  done  to  determine  the  secondary  metabolites  present  in  the  plant  extracts. Salmonella  enterica  serovar  Typhimurium  ATCC  14028,  a  type  strain,  was  used  as  a  reference standard  in  the  identification  of  the  isolates.  The  isolates  were  collected  across  hospitals  in  South West  Nigeria.   Results:  All  the  isolates  were  multidrug  resistance  (with  each  showing  resistance  to  at  least  two  of the  antibiotics),  with  the  exception  of  one  susceptible  isolate.  All  the  isolates  were  resistant  to chloramphenicol  (100%),  while  the  highest  susceptible  numbers  of  isolates  were  observed  against ceftriaxone  (27.27%),  18.18%  were  susceptible  to  each  of  ampicillin  and  amoxycillin,  while  9.09% were  susceptible  to  cotrimoxazole.  MIC  values  ranged  from  of  30  µg/mL  to  >100  µg/mL.  All  the isolates  were  susceptible  to  the  extracts  of  Dalbergia  latifolia  leaves  with  a  zone  of  diameters equating  the  CSLI  recommendation  except  for  two  isolates  at  a  concentration  of  25  mg/mL showing  lesser  activities.  The  MIC  values  ranged  between  3.125  mg/mL  to  75  mg/mL. Conclusion:  The  combined  antibiotics  and  plant  extracts  showed  a  potentiative  and  synergistic effects  with  Fractional  Inhibitory  Concentration  (FIC)  values  ranging  between  0.45-0.75.  Among  the 11  isolates,  4  isolates  (36.36%)  showed  an  additional  effect  to  the  combined  activities  of  the antibiotics  and  plant  extracts  with  a  reduced  MIC  value.  From  the  in  vitro  study,  the  diameter  of  the zone  of  inhibition  of  the  combined  halved-MICs  (MIC*)  of  both  the  plant  and  antibiotics  increased significantly  than  their  individual  results.  The  result  of  this  study  showed  that  the  extract  of Dalbergia  latifolia  has  antimicrobial  properties  against  MDR  Salmonella  enterica  strain.