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Staphylococcus aureus but not Listeria monocytogenes adapt to triclosan and adaptation correlates with increased fabI expression and agr deficiency.

Nielsen LN, Larsen MH, Skovgaard S, Kastbjerg V, Westh H, Gram L, Ingmer H - BMC Microbiol. (2013)

Bottom Line: Also, they displayed decreased or no expression of the virulence associated agrC of the agr quorum sensing system.S. aureus displayed an intrinsically lower MIC for triclosan compared to L. monocytogenes but was easily adapted leading to the same MIC as L. monocytogenes.Thus, adaptation to triclosan by S. aureus appears to involve multiple genetic pathways.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Background: The ability of pathogens to adapt to the widely used biocide, triclosan, varies substantially. The purpose of the study was to examine bacterial adaptation over an extended period of time to low increments of triclosan concentrations. Focus was two human pathogens, S. aureus and L. monocytogenes that previously have displayed inherent high and low adaptability, respectively.

Results: Three strains of L. monocytogenes and two strains of S. aureus including the community-acquired USA300 were exposed to increasing, sub-lethal concentrations of triclosan in triclosan-containing agar gradients. Following 25 days of exposure on agar plates to sub-lethal concentrations of triclosan with a twofold concentration increase every second day, minimum inhibitory concentration (MIC) for S. aureus increased from 0.125 (8325-4) and 0.0625 (USA 300) mg/L to 4 mg/L. The MIC of all three L. monocytogenes strains was initially 4 mg/L and remained unaltered by the exposure. The adapted S. aureus isolates retained normal colony size but displayed increased expression of fabI encoding an essential enzyme in bacterial fatty acid synthesis. Also, they displayed decreased or no expression of the virulence associated agrC of the agr quorum sensing system. While most adapted strains of USA300 carried mutations in fabI, none of the adapted strains of 8325-4 did.

Conclusions: Adaptability to triclosan varies substantially between Gram positive human pathogens. S. aureus displayed an intrinsically lower MIC for triclosan compared to L. monocytogenes but was easily adapted leading to the same MIC as L. monocytogenes. Even though all adapted S. aureus strains over-expressed fabI and eliminated expression of the agr quorum sensing system, adaptation in USA300 involved fabI mutations whereas this was not the case for 8325-4. Thus, adaptation to triclosan by S. aureus appears to involve multiple genetic pathways.

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EtBr efflux activity in triclosan exposed S. aureus cells. Isolates were grown for 24 h at 37°C on TSA containing EtBr (1 μg/ml), followed by inspection for fluorescence under UV light as described previously. Wt (freeze stock), C1 and C2 (two controls passed on TSA without triclosan), A1-A7 (7 triclosan adapted strains). Strains JCM 16555 (qacA) and JCM 16556 (qacB) (lower left), that overexpress efflux pumps, were included as controls.
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Figure 1: EtBr efflux activity in triclosan exposed S. aureus cells. Isolates were grown for 24 h at 37°C on TSA containing EtBr (1 μg/ml), followed by inspection for fluorescence under UV light as described previously. Wt (freeze stock), C1 and C2 (two controls passed on TSA without triclosan), A1-A7 (7 triclosan adapted strains). Strains JCM 16555 (qacA) and JCM 16556 (qacB) (lower left), that overexpress efflux pumps, were included as controls.

Mentions: With the aim of determining if the adaptation processes are the same in the two strains of S. aureus, namely the laboratory strain 8325–4 and the clinical isolate USA300, the adapted isolates were characterized. Previously, enhanced expression of the AcrAB efflux pump has been associated with increased tolerance to triclosan in E. coli[27]. To address if efflux pump activity may be part of the adaptation process in S. aureus strains, the efflux activity was examined by monitoring extrusion of ethidium bromide [44]. As shown in Figure 1 noobvious differences in ethidium bromide staining of triclosan tolerant and adapted strains were observed indicating that they are equally able to extrude the compound. Transcription of norA and mepA were also measured and no differences between triclosan adapted strains and their controls were observed (data not shown).


Staphylococcus aureus but not Listeria monocytogenes adapt to triclosan and adaptation correlates with increased fabI expression and agr deficiency.

Nielsen LN, Larsen MH, Skovgaard S, Kastbjerg V, Westh H, Gram L, Ingmer H - BMC Microbiol. (2013)

EtBr efflux activity in triclosan exposed S. aureus cells. Isolates were grown for 24 h at 37°C on TSA containing EtBr (1 μg/ml), followed by inspection for fluorescence under UV light as described previously. Wt (freeze stock), C1 and C2 (two controls passed on TSA without triclosan), A1-A7 (7 triclosan adapted strains). Strains JCM 16555 (qacA) and JCM 16556 (qacB) (lower left), that overexpress efflux pumps, were included as controls.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3733935&req=5

Figure 1: EtBr efflux activity in triclosan exposed S. aureus cells. Isolates were grown for 24 h at 37°C on TSA containing EtBr (1 μg/ml), followed by inspection for fluorescence under UV light as described previously. Wt (freeze stock), C1 and C2 (two controls passed on TSA without triclosan), A1-A7 (7 triclosan adapted strains). Strains JCM 16555 (qacA) and JCM 16556 (qacB) (lower left), that overexpress efflux pumps, were included as controls.
Mentions: With the aim of determining if the adaptation processes are the same in the two strains of S. aureus, namely the laboratory strain 8325–4 and the clinical isolate USA300, the adapted isolates were characterized. Previously, enhanced expression of the AcrAB efflux pump has been associated with increased tolerance to triclosan in E. coli[27]. To address if efflux pump activity may be part of the adaptation process in S. aureus strains, the efflux activity was examined by monitoring extrusion of ethidium bromide [44]. As shown in Figure 1 noobvious differences in ethidium bromide staining of triclosan tolerant and adapted strains were observed indicating that they are equally able to extrude the compound. Transcription of norA and mepA were also measured and no differences between triclosan adapted strains and their controls were observed (data not shown).

Bottom Line: Also, they displayed decreased or no expression of the virulence associated agrC of the agr quorum sensing system.S. aureus displayed an intrinsically lower MIC for triclosan compared to L. monocytogenes but was easily adapted leading to the same MIC as L. monocytogenes.Thus, adaptation to triclosan by S. aureus appears to involve multiple genetic pathways.

View Article: PubMed Central - HTML - PubMed

ABSTRACT

Background: The ability of pathogens to adapt to the widely used biocide, triclosan, varies substantially. The purpose of the study was to examine bacterial adaptation over an extended period of time to low increments of triclosan concentrations. Focus was two human pathogens, S. aureus and L. monocytogenes that previously have displayed inherent high and low adaptability, respectively.

Results: Three strains of L. monocytogenes and two strains of S. aureus including the community-acquired USA300 were exposed to increasing, sub-lethal concentrations of triclosan in triclosan-containing agar gradients. Following 25 days of exposure on agar plates to sub-lethal concentrations of triclosan with a twofold concentration increase every second day, minimum inhibitory concentration (MIC) for S. aureus increased from 0.125 (8325-4) and 0.0625 (USA 300) mg/L to 4 mg/L. The MIC of all three L. monocytogenes strains was initially 4 mg/L and remained unaltered by the exposure. The adapted S. aureus isolates retained normal colony size but displayed increased expression of fabI encoding an essential enzyme in bacterial fatty acid synthesis. Also, they displayed decreased or no expression of the virulence associated agrC of the agr quorum sensing system. While most adapted strains of USA300 carried mutations in fabI, none of the adapted strains of 8325-4 did.

Conclusions: Adaptability to triclosan varies substantially between Gram positive human pathogens. S. aureus displayed an intrinsically lower MIC for triclosan compared to L. monocytogenes but was easily adapted leading to the same MIC as L. monocytogenes. Even though all adapted S. aureus strains over-expressed fabI and eliminated expression of the agr quorum sensing system, adaptation in USA300 involved fabI mutations whereas this was not the case for 8325-4. Thus, adaptation to triclosan by S. aureus appears to involve multiple genetic pathways.

Show MeSH
Related in: MedlinePlus