PMID:20660686

Citation	Singh, R, Ledesma, KR, Chang, KT and Tam, VH (2010) Impact of recA on levofloxacin exposure-related resistance development.Antimicrob. Agents Chemother. 54:4262-8
Abstract	Genetic mutations are one of the major mechanisms by which bacteria acquire drug resistance. One of the known mechanisms for inducing mutations is the SOS response system. We investigated the effect of disrupting recA, an inducer of the SOS response, on resistance development using an in vitro hollow-fiber infection model. A clinical Staphylococcus aureus isolate and a laboratory wild-type strain of Escherichia coli were compared to their respective recA-deleted isogenic daughter isolates. Approximately 2 × 10(5) CFU/ml of bacteria were subjected to escalating levofloxacin exposures for up to 120 h. Serial samples were obtained to ascertain simulated drug exposures and total and resistant bacterial burdens. Quinolone resistance determining regions of gyrA and grlA (parC for E. coli) in levofloxacin-resistant isolates were sequenced to confirm the mechanism of resistance. The preexposure MICs of the recA-deleted isolates were 4-fold lower than those of their respective parents. In S. aureus, a lower area under the concentration-time curve over 24 h at steady state divided by the MIC (AUC/MIC) was required to suppress resistance development in the recA-deleted mutant (an AUC/MIC of >23 versus an AUC/MIC of >32 was necessary in the mutant versus the parent isolate, respectively), and a prominent difference in the total bacterial burden was observed at 72 h. Using an AUC/MIC of approximately 30, E. coli resistance emergence was delayed by 24 h in the recA-deleted mutant. Diverse mutations in gyrA were found in levofloxacin-resistant isolates recovered. Disruption of recA provided additional benefits apart from MIC reduction, attesting to its potential role for pharmacologic intervention. The clinical relevance of our findings warrants further investigations.
Links	PubMed Online version:10.1128/AAC.00168-10
Keywords	Anti-Bacterial Agents; Bacterial Proteins; Chromatography, High Pressure Liquid; Escherichia coli; Microbial Sensitivity Tests; Mutation; Ofloxacin; Rec A Recombinases; Staphylococcus aureus
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Phenotype of	Taxon Information	Genotype Information (if known)	Condition Information	OMP ID	OMP Term Name	ECO ID	ECO Term Name	Notes	Status
a mutation or genetic difference within a strain	Taxon: Escherichia coli Strain: K-12 Substrain: M86227	Genotype of Reference Strain: recA Genotype of Experimental Strain : deltaRecA	Reference Condition:					The deletion of the recA gene caused only a marginal change in the growth rate compared to the wild type when both were exposed to the same concentration of levofloxacin.
a mutation or genetic difference within a strain	Taxon: Escherichia coli Strain: K-12 Substrain: M86227	Genotype of Reference Strain: recA Genotype of Experimental Strain : deltaRecA	Reference Condition:					Once the recA gene was deleted only a marginal difference in the level of resistance was detected comparable to the wild type strain when exposed to the same concentration of levofloxacin.
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