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Background <p>Key mechanisms contributing to antibacterial resistance include efflux pump overexpression and enzymatic drug inactivation. Levofloxacin, a widely prescribed fluoroquinolone, demonstrates potent activity against Gram-positive pathogens, such as <i>Streptococcus pneumoniae</i>, and Gram-negative pathogens, such as <i>Pseudomonas aeruginosa</i>. However, the increasing prevalence of multidrug resistance (MDR) continues to compromise its clinical utility. To date, there is a paucity of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) data of levofloxacin against previously characterised MDR isolates with defined resistance mechanisms.</p> Methods <p>Using agar well diffusion and agar dilution techniques, this experimental study evaluated the antibacterial activity, MIC, and MBC of levofloxacin against 20 bacterial isolates, comprising 18 previously characterised clinical MDR isolates and 2 American Type Culture Collection (ATCC) reference strains. Antimicrobial susceptibility testing was performed according to Clinical and Laboratory Standards Institute (CLSI) guidelines. <i>Escherichia coli</i> (ATCC 25922) and <i>Staphylococcus aureus</i> (ATCC 25923) served as drug-susceptible quality control strains. Data were expressed as mean ± standard deviation (SD), and <i>p</i> &lt; 0.05 was considered statistically significant.</p> Results <p>Three of eight <i>Klebsiella pneumoniae</i> isolates were non-susceptible to levofloxacin across four tested concentrations ranging from 6.25 to 50&#xa0;µg/mL. One <i>Staphylococcus aureus</i> isolate (ES 44), previously characterised as multidrug resistant, exhibited high-level resistance (MIC: 8&#xa0;µg/mL). MIC values ranged from 0.0625 to 8&#xa0;µg/mL for Gram-positive and 0.015625–1&#xa0;µg/mL for Gram-negative organisms. MBC values ranged from 0.125 to 8&#xa0;µg/mL for Gram-positive and 0.015625–8&#xa0;µg/mL for Gram-negative isolates. <i>Micrococcus</i> spp. exhibited high susceptibility (inhibition zone at 50&#xa0;µg/mL: 37.33 ± 0.58&#xa0;mm; MIC: 0.125&#xa0;µg/mL). Overall, levofloxacin exhibited significantly higher inhibitory activity against Gram-negative (72.73%) than Gram-positive isolates (55.56%) (<i>p</i> &lt; 0.05).</p> Conclusion <p>This study demonstrates variability in levofloxacin MIC and MBC values among previously characterised MDR bacterial isolates at Lagos University Teaching Hospital. While levofloxacin retains activity against several pathogens, reduced susceptibility among some MDR isolates highlights the need for informed prescribing, continuous resistance surveillance, and strengthened antimicrobial stewardship efforts in Nigeria.</p>

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Experimental evaluation of levofloxacin efficacy against multidrug-resistant bacterial isolates at the Lagos University Teaching Hospital, Nigeria

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月26日

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  • Abubakar Sadiq Abdullahi,
  • Gloria Abiodun Ayoola,
  • Adebowale Olufemi Adeluola,
  • David Blessing Orojuekun,
  • Sunday N. Okafor,
  • David Kehinde Adeyemi,
  • Modupe Oluyemisi Ologunagba,
  • Oluwatosin Oladele Johnson,
  • Usman Abdulrahman

摘要

Background

Key mechanisms contributing to antibacterial resistance include efflux pump overexpression and enzymatic drug inactivation. Levofloxacin, a widely prescribed fluoroquinolone, demonstrates potent activity against Gram-positive pathogens, such as Streptococcus pneumoniae, and Gram-negative pathogens, such as Pseudomonas aeruginosa. However, the increasing prevalence of multidrug resistance (MDR) continues to compromise its clinical utility. To date, there is a paucity of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) data of levofloxacin against previously characterised MDR isolates with defined resistance mechanisms.

Methods

Using agar well diffusion and agar dilution techniques, this experimental study evaluated the antibacterial activity, MIC, and MBC of levofloxacin against 20 bacterial isolates, comprising 18 previously characterised clinical MDR isolates and 2 American Type Culture Collection (ATCC) reference strains. Antimicrobial susceptibility testing was performed according to Clinical and Laboratory Standards Institute (CLSI) guidelines. Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923) served as drug-susceptible quality control strains. Data were expressed as mean ± standard deviation (SD), and p < 0.05 was considered statistically significant.

Results

Three of eight Klebsiella pneumoniae isolates were non-susceptible to levofloxacin across four tested concentrations ranging from 6.25 to 50 µg/mL. One Staphylococcus aureus isolate (ES 44), previously characterised as multidrug resistant, exhibited high-level resistance (MIC: 8 µg/mL). MIC values ranged from 0.0625 to 8 µg/mL for Gram-positive and 0.015625–1 µg/mL for Gram-negative organisms. MBC values ranged from 0.125 to 8 µg/mL for Gram-positive and 0.015625–8 µg/mL for Gram-negative isolates. Micrococcus spp. exhibited high susceptibility (inhibition zone at 50 µg/mL: 37.33 ± 0.58 mm; MIC: 0.125 µg/mL). Overall, levofloxacin exhibited significantly higher inhibitory activity against Gram-negative (72.73%) than Gram-positive isolates (55.56%) (p < 0.05).

Conclusion

This study demonstrates variability in levofloxacin MIC and MBC values among previously characterised MDR bacterial isolates at Lagos University Teaching Hospital. While levofloxacin retains activity against several pathogens, reduced susceptibility among some MDR isolates highlights the need for informed prescribing, continuous resistance surveillance, and strengthened antimicrobial stewardship efforts in Nigeria.