title: Differential expression of virulence genes and role of gyrA mutations in quinolone resistant and susceptible strains of Salmonella Weltevreden and Newport isolated from seafood.
abstract: OBJECTIVE
  To investigate the differential expression of virulence genes and role of gyrA mutations in quinolone resistant and susceptible strains of Salmonella isolated from seafood.
  
  
  RESULTS
  Forty Salmonella isolates from seafood were tested for antibiotic sensitivity. Minimal inhibitory concentration (MIC) was determined and two nalidixic acid-resistant isolates, viz Salmonella Weltevreden (SW9) and Salmonella Newport (SN36) were selected for identifying the mechanism of resistance. SW9 showed mutation in the gyrA gene at codon 83 (Ser to Tyr) while SN36 presented at codon 87 (Asp to Asn). Experimental induction of resistance to a sensitive Salm. Newport (SN71) showed point mutation at codon 87 (Asp to Gly) in the gyrA gene, and was designated SN71R. All the isolates resistant to nalidixic acid had a single mutation at different positions in the gyrA gene. However, induction of resistance to a sensitive Salm. Weltevreden (SW30) was exceptional in that it did not show any mutation in the gyrA region. Use of Phe-Arg-β-naphthylamide (PAβN) also could not reduce MIC below the Clinical and Laboratory Standards Institute guidelines revealing the absence of efflux mediated resistance. Thus, the resistance mechanism in SW30R is unknown. The growth rate of quinolone resistant isolates was slower than the susceptible ones. The resistant isolates showed decreased epithelial cell invasion and intracellular replication. The mRNA expression levels of some of the genes were significantly (P < 0·005) reduced in SN71R compared to the sensitive strain (SN71).
  
  
  CONCLUSIONS
  Nalidixic acid-resistant Salmonella strains are associated with lower virulence and pathogenicity than the sensitive strains.
  
  
  CONCLUSIONS
  This study provided valuable information on the difference in the growth, cytotoxicity, infectivity and expression of virulence genes in resistant and susceptible strains. Furthermore, the gyrA mutation was shown to be the main mechanism of quinolone resistance in Salmonella other than the overexpression of efflux pumps or the presence of plasmid mediated quinolone resistance genes.
authors.affiliation: Department of Biomedical Sciences, Nitte University Center for Science Education and Research, UNESCO MIRCEN for Marine Biotechnology, University Enclave, Mangalore-575018, India.
authors.forename: V K
authors.initials: VK
authors.lastname: Deekshit
authors.affiliation: Department of Biomedical Sciences, Nitte University Center for Science Education and Research, UNESCO MIRCEN for Marine Biotechnology, University Enclave, Mangalore-575018, India.
authors.forename: B K
authors.initials: BK
authors.lastname: Kumar
authors.affiliation: Department of Biomedical Sciences, Nitte University Center for Science Education and Research, UNESCO MIRCEN for Marine Biotechnology, University Enclave, Mangalore-575018, India.
authors.forename: P
authors.initials: P
authors.lastname: Rai
authors.affiliation: Department of Biomedical Sciences, Nitte University Center for Science Education and Research, UNESCO MIRCEN for Marine Biotechnology, University Enclave, Mangalore-575018, India.
authors.forename: I
authors.initials: I
authors.lastname: Karunasagar
authors.affiliation: Department of Biomedical Sciences, Nitte University Center for Science Education and Research, UNESCO MIRCEN for Marine Biotechnology, University Enclave, Mangalore-575018, India.
authors.forename: I
authors.initials: I
authors.lastname: Karunasagar
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D027081:DNA Gyrase / Q000235:genetics* / Q000378:metabolism; D027101:DNA Topoisomerase IV; D024881:Drug Resistance, Bacterial; D005506:Food Contamination / Q000032:analysis; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000235:genetics; D015363:Quinolones / Q000494:pharmacology*; D012475:Salmonella / Q000145:classification / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D017747:Seafood / Q000382:microbiology*; D037521:Virulence Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015363:Quinolones; D037521:Virulence Factors; D027101:DNA Topoisomerase IV; D027081:DNA Gyrase
keywords: Salmonella Newport; Salmonella Weltevreden; differential expression; quinolone resistance; virulence genes