# An In Vitro Study on the Antibacterial Activity of Statins Against the Most Common Bacterial Pathogens Causing Respiratory Tract Infections in a Tertiary Care Hospital

## TL;DR

This study tested statins for antibacterial effects against common respiratory infection bacteria but found no significant activity.

## Contribution

The study provides empirical evidence that common statins lack antibacterial activity against major respiratory pathogens.

## Key findings

- Atorvastatin, rosuvastatin, and simvastatin showed no antibacterial activity against Staphylococcus aureus, Klebsiella pneumoniae, and Streptococcus pneumoniae.
- Amoxicillin and gentamicin demonstrated statistically significant microbial growth inhibition compared to statins.
- The zone of inhibition for statins was consistently less than 4 mm, indicating resistance.

## Abstract

Introduction

The vast pleiotropic effect of statins has intrigued many researchers to select them as potential candidates against bacterial infections. The role of statins against bacterial pathogens remains debatable. This study was undertaken to evaluate and compare the antibacterial effect of commonly available statins against the most frequently isolated bacterial pathogens causing respiratory tract infections in our tertiary care hospital using sputum as a sample.

Materials and methods

The study was conducted in the Microbiology Laboratory of our hospital. Drugs including atorvastatin, rosuvastatin, and simvastatin were purchased in pure form from Sigma Aldrich. Dimethylsulfoxide (DMSO) was used as a solvent for all three drugs. The positive controls used were gentamycin and amoxicillin for Gram-negative and Gram-positive bacteria, respectively.

Data regarding all the culture and sensitivity results of sputum samples of patients admitted to the Respiratory Intensive Care Unit over the past 12 months were analyzed. The most common bacterial pathogens Staphylococcus aureus, Klebsiella pneumoniae, and Streptococcus pneumoniae isolated from sputum specimens were taken for our study.

The antibacterial effect of statins was studied using two methods: the agar cup diffusion method and the broth dilution method. The zone of inhibition and minimum inhibitory concentration of the drugs were calculated and analyzed. Statistical analysis was performed using GraphPad Prism software version 10.2.0. A one-way ANOVA test was used to determine if there was any statistical difference between the different statins and antibiotic groups. An unpaired t-test was used to determine the statistical difference between the statins.

Results and discussion

For the agar cup diffusion method, our results displayed a lack of antibacterial activity of all three statins atorvastatin, rosuvastatin, and simvastatin against all three bacterial strains Staphylococcus aureus, Klebsiella pneumoniae, and Streptococcus pneumoniae after overnight incubation by agar cup method at concentrations of 3.125 μg/ml, 6.25 μg/ml, 12.5 μg/ml, 25 μg/ml and 50 μg/ml, respectively. The zone of inhibition observed was less than 4 mm (resistant) for all the serial dilutions of atorvastatin, rosuvastatin, and simvastatin.

For the broth dilution method, the ANOVA test showed amoxicillin and gentamicin to have high statistically significant microbial growth inhibitory activity (p-value < 0.005) compared to atorvastatin and rosuvastatin. Statistically, though atorvastatin showed significant antimicrobial activity compared to normal saline and rosuvastatin, this was not considered clinically significant as the antimicrobial activity shown by atorvastatin was very negligible compared to the controls used and did not correspond to the serial dilutions of the drug.

Conclusion

Atorvastatin, rosuvastatin, and simvastatin lacked antibacterial activity against all three bacterial strains isolated from sputum specimens: Staphylococcus aureus, Klebsiella pneumoniae, and Streptococcus pneumoniae. Hence, the use of statins as an antimicrobial drug for respiratory tract infections has limited applications.