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The inoculum effect and band-pass bacterial response to periodic antibiotic treatment.

Tan C, Smith RP, Srimani JK, Riccione KA, Prasada S, Kuehn M, You L - Mol. Syst. Biol. (2012)

Bottom Line: The inoculum effect (IE) refers to the decreasing efficacy of an antibiotic with increasing bacterial density.A critical requirement for this bistability is sufficiently fast degradation of ribosomes, which can result from antibiotic-induced heat-shock response.Our proposed mechanism for the IE may be generally applicable to other bacterial species treated with antibiotics targeting the ribosomes.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Duke University, Durham, NC, USA.

ABSTRACT
The inoculum effect (IE) refers to the decreasing efficacy of an antibiotic with increasing bacterial density. It represents a unique strategy of antibiotic tolerance and it can complicate design of effective antibiotic treatment of bacterial infections. To gain insight into this phenomenon, we have analyzed responses of a lab strain of Escherichia coli to antibiotics that target the ribosome. We show that the IE can be explained by bistable inhibition of bacterial growth. A critical requirement for this bistability is sufficiently fast degradation of ribosomes, which can result from antibiotic-induced heat-shock response. Furthermore, antibiotics that elicit the IE can lead to 'band-pass' response of bacterial growth to periodic antibiotic treatment: the treatment efficacy drastically diminishes at intermediate frequencies of treatment. Our proposed mechanism for the IE may be generally applicable to other bacterial species treated with antibiotics targeting the ribosomes.

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Delayed bacterial recovery from transient antibiotic treatment. (A) Recovery of a bacterial population after the removal of an antibiotic. For modeling studies, we defined recovery time (τlag) as the time from the removal of the antibiotic to the time when bacterial density starts to increase. (B) Recovery time increased much faster with fast degradation of ribosomes (black line, degradation rate=10−1) than with slow degradation (gray line, degradation rate=10−6). k0=10−6, k1=0.1, V1=0.2, ku=0.1, kf=1, kb=0.1, kin=3, kout=0.03, kr=0.02, and Aout=10 (which corresponds to an intermediate concentration). See Supplementary Equations S1–S5 and S16. (C) Population recovery after transient antibiotic treatment. We incubated bacteria in a flow system (Supplementary Figure S5A and B) in medium supplemented with either 10 μg/ml kanamycin or 10 μg/ml chloramphenicol. After treatment for a specific duration (i.e., treatment duration), we washed bacteria using fresh medium, tracked population growth and quantified recovery time as the time required for a population to increase above its initial density after antibiotic treatment. When treated with kanamycin, recovery time increased significantly with treatment duration (filled squares). In contrast, with chloramphenicol, recovery time stayed nearly constant (open squares). Lines of best fit, as determined visually, are shown. See Supplementary Figure S5 for additional data. Source data is available for this figure in the Supplementary Information.
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f5: Delayed bacterial recovery from transient antibiotic treatment. (A) Recovery of a bacterial population after the removal of an antibiotic. For modeling studies, we defined recovery time (τlag) as the time from the removal of the antibiotic to the time when bacterial density starts to increase. (B) Recovery time increased much faster with fast degradation of ribosomes (black line, degradation rate=10−1) than with slow degradation (gray line, degradation rate=10−6). k0=10−6, k1=0.1, V1=0.2, ku=0.1, kf=1, kb=0.1, kin=3, kout=0.03, kr=0.02, and Aout=10 (which corresponds to an intermediate concentration). See Supplementary Equations S1–S5 and S16. (C) Population recovery after transient antibiotic treatment. We incubated bacteria in a flow system (Supplementary Figure S5A and B) in medium supplemented with either 10 μg/ml kanamycin or 10 μg/ml chloramphenicol. After treatment for a specific duration (i.e., treatment duration), we washed bacteria using fresh medium, tracked population growth and quantified recovery time as the time required for a population to increase above its initial density after antibiotic treatment. When treated with kanamycin, recovery time increased significantly with treatment duration (filled squares). In contrast, with chloramphenicol, recovery time stayed nearly constant (open squares). Lines of best fit, as determined visually, are shown. See Supplementary Figure S5 for additional data. Source data is available for this figure in the Supplementary Information.

Mentions: Based on our proposed mechanism for IE, we would expect a profound difference in the recovery of bacterial populations after transient treatment by the two types of antibiotics. Indeed, our modeling analysis showed that fast degradation of C would considerably delay the recovery of bacterial populations (Figure 5A and B). With a faster degradation of C, the total concentration of C would drop drastically during antibiotic treatment. As such, after the removal of an antibiotic, bacteria would need a longer time to synthesize sufficient amount of C to re-initiate growth.


The inoculum effect and band-pass bacterial response to periodic antibiotic treatment.

Tan C, Smith RP, Srimani JK, Riccione KA, Prasada S, Kuehn M, You L - Mol. Syst. Biol. (2012)

Delayed bacterial recovery from transient antibiotic treatment. (A) Recovery of a bacterial population after the removal of an antibiotic. For modeling studies, we defined recovery time (τlag) as the time from the removal of the antibiotic to the time when bacterial density starts to increase. (B) Recovery time increased much faster with fast degradation of ribosomes (black line, degradation rate=10−1) than with slow degradation (gray line, degradation rate=10−6). k0=10−6, k1=0.1, V1=0.2, ku=0.1, kf=1, kb=0.1, kin=3, kout=0.03, kr=0.02, and Aout=10 (which corresponds to an intermediate concentration). See Supplementary Equations S1–S5 and S16. (C) Population recovery after transient antibiotic treatment. We incubated bacteria in a flow system (Supplementary Figure S5A and B) in medium supplemented with either 10 μg/ml kanamycin or 10 μg/ml chloramphenicol. After treatment for a specific duration (i.e., treatment duration), we washed bacteria using fresh medium, tracked population growth and quantified recovery time as the time required for a population to increase above its initial density after antibiotic treatment. When treated with kanamycin, recovery time increased significantly with treatment duration (filled squares). In contrast, with chloramphenicol, recovery time stayed nearly constant (open squares). Lines of best fit, as determined visually, are shown. See Supplementary Figure S5 for additional data. Source data is available for this figure in the Supplementary Information.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3472685&req=5

f5: Delayed bacterial recovery from transient antibiotic treatment. (A) Recovery of a bacterial population after the removal of an antibiotic. For modeling studies, we defined recovery time (τlag) as the time from the removal of the antibiotic to the time when bacterial density starts to increase. (B) Recovery time increased much faster with fast degradation of ribosomes (black line, degradation rate=10−1) than with slow degradation (gray line, degradation rate=10−6). k0=10−6, k1=0.1, V1=0.2, ku=0.1, kf=1, kb=0.1, kin=3, kout=0.03, kr=0.02, and Aout=10 (which corresponds to an intermediate concentration). See Supplementary Equations S1–S5 and S16. (C) Population recovery after transient antibiotic treatment. We incubated bacteria in a flow system (Supplementary Figure S5A and B) in medium supplemented with either 10 μg/ml kanamycin or 10 μg/ml chloramphenicol. After treatment for a specific duration (i.e., treatment duration), we washed bacteria using fresh medium, tracked population growth and quantified recovery time as the time required for a population to increase above its initial density after antibiotic treatment. When treated with kanamycin, recovery time increased significantly with treatment duration (filled squares). In contrast, with chloramphenicol, recovery time stayed nearly constant (open squares). Lines of best fit, as determined visually, are shown. See Supplementary Figure S5 for additional data. Source data is available for this figure in the Supplementary Information.
Mentions: Based on our proposed mechanism for IE, we would expect a profound difference in the recovery of bacterial populations after transient treatment by the two types of antibiotics. Indeed, our modeling analysis showed that fast degradation of C would considerably delay the recovery of bacterial populations (Figure 5A and B). With a faster degradation of C, the total concentration of C would drop drastically during antibiotic treatment. As such, after the removal of an antibiotic, bacteria would need a longer time to synthesize sufficient amount of C to re-initiate growth.

Bottom Line: The inoculum effect (IE) refers to the decreasing efficacy of an antibiotic with increasing bacterial density.A critical requirement for this bistability is sufficiently fast degradation of ribosomes, which can result from antibiotic-induced heat-shock response.Our proposed mechanism for the IE may be generally applicable to other bacterial species treated with antibiotics targeting the ribosomes.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Duke University, Durham, NC, USA.

ABSTRACT
The inoculum effect (IE) refers to the decreasing efficacy of an antibiotic with increasing bacterial density. It represents a unique strategy of antibiotic tolerance and it can complicate design of effective antibiotic treatment of bacterial infections. To gain insight into this phenomenon, we have analyzed responses of a lab strain of Escherichia coli to antibiotics that target the ribosome. We show that the IE can be explained by bistable inhibition of bacterial growth. A critical requirement for this bistability is sufficiently fast degradation of ribosomes, which can result from antibiotic-induced heat-shock response. Furthermore, antibiotics that elicit the IE can lead to 'band-pass' response of bacterial growth to periodic antibiotic treatment: the treatment efficacy drastically diminishes at intermediate frequencies of treatment. Our proposed mechanism for the IE may be generally applicable to other bacterial species treated with antibiotics targeting the ribosomes.

Show MeSH
Related in: MedlinePlus