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Comparative Effects of Intermittent vs. Constant Ceftiofur Hydrochloride Exposure on Staphylococcus aureus In Vitro
Junli Wang1, Chongyang Li1, Fanxi Guo1
1Laboratory of Veterinary Pharmacology and Toxicology, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing 210095, China.
Background/Objectives:
Ceftiofur hydrochloride (CEF) is a third-generation cephalosporin widely used in cattle to treat various disease. The recommended dosage was 1.1 to 2.2 mg/kg BW for 3 to 5 consecutive days by intramuscular or subcutaneous injection. Incomplete treatment, overuse, or misuse, often observed in clinical practice, are major contributors to resistance development. This study aims to explore how different concentrations, durations, and dosing frequencies affect susceptibility and bactericidal efficacy of Staphylococcus aureus to optimize CEF dosage regimens.
Methods:
First, CEF was intermittently administered at 1/2 × minimum inhibitory concentration (MIC), 2 × MIC, 6 × MIC, and 100 × MIC for 30 cycles. Second, CEF was continuously administered for 48, 72, 96, 120, 144, and 168 h. Bacterial susceptibility, regrowth, survival rate, and the emergence of persisters or tolerant phenotypes were assessed. Genetic mutations were identified by whole-genome resequencing. Membrane permeability, integrity, and efflux pump activity were analyzed to elucidate the mechanism of CEF.
Results:
After 30 cycles, the MIC increased eight-fold in the 2 × MIC group. No significant MIC increase was found in other groups, but a progression from susceptibility to persistence and then to tolerance was observed in the 100 × MIC intermittent group. The survival rate increased both in the 2 × MIC and 100 × MIC groups. With continuous exposure to ≥6 × MIC over 120 h, strains were completely eradicated without MIC increase. Resistance-associated single-nucleotide polymorphism (SNP) mutations were detected only in strains of the 2 × MIC and 100 × MIC intermittent groups. CEF altered the membrane hydrophobicity, damaging membrane integrity after 30 cycles.
Conclusions:
These findings suggest that high-dose, prolonged exposure is more effective for eliminating Staphylococcus aureus and avoiding resistance, whereas intermittent dosing may promote persistence, tolerance, and resistance evolution.
Insights
High-dose, prolonged ceftiofur hydrochloride (CEF) exposure effectively eliminates Staphylococcus aureus and prevents resistance. Intermittent dosing, however, can promote bacterial persistence, tolerance, and resistance evolution, highlighting the importance of optimized CEF dosage regimens.
Area of Science:
- Veterinary Pharmacology
- Antimicrobial Resistance
- Bacterial Pathogenesis
Background:
- Ceftiofur hydrochloride (CEF) is a crucial third-generation cephalosporin for treating cattle diseases.
- Suboptimal CEF administration (incomplete treatment, overuse, misuse) drives antimicrobial resistance.
- Optimizing CEF dosage is critical for effective treatment and resistance mitigation.
Purpose of the Study:
- To investigate the impact of varying CEF concentrations, durations, and dosing frequencies on Staphylococcus aureus susceptibility and bactericidal efficacy.
- To determine optimal CEF dosage regimens for minimizing resistance development and maximizing therapeutic outcomes.
Main Methods:
- Intermittent CEF administration at different multiples of the minimum inhibitory concentration (MIC) for 30 cycles.
- Continuous CEF exposure for extended durations (48–168 hours).
- Assessment of bacterial susceptibility, regrowth, survival, persistence, tolerance, and genetic mutations; analysis of membrane properties and efflux pump activity.
Main Results:
- Intermittent CEF at 2x MIC induced an eight-fold MIC increase, while 100x MIC led to persistence and tolerance.
- Continuous exposure to ≥6x MIC for ≥120 hours eradicated bacteria without increasing MIC.
- Resistance-associated mutations and membrane damage were observed in intermittent dosing groups.
Conclusions:
- High-dose, prolonged CEF exposure is superior for eradicating Staphylococcus aureus and preventing resistance.
- Intermittent CEF dosing strategies may inadvertently promote bacterial persistence, tolerance, and resistance evolution.
- Optimized CEF dosage regimens are essential for effective antimicrobial therapy in cattle.
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