Short Communication - (2021) Volume 12, Issue 5
Shilpakala Sainath Rao1* , Malathi Raghunathan1, Rathna Durga Manian2, Ramesh E2 and Raghunathan R2
1Department of Genetics, Dr. ALMPGIBMS, University of Madras, Taramani Campus, Chennai, Tamilnadu, India
2Department of Organic Chemistry , University of Madras, Tamilnadu, India
Received Date: August 25, 2021; Accepted Date: September 08, 2021; Published Date: September 15, 2021
Citation: Rao SS, Raghunathan M, Manian RD, Ramesh E, Raghunathan R (2021) In vitro Activity of The Quinoline Derivatives RD-3 and ER-2 Against Clinical Isolates of C. pneumoniae. Arch Clin Microbial Vol.12 No.5: 173.
Description
RD-3 and ER-2 are both, investigational quinoline derivative drugs that have previously shown potent activity against Grampositive and Gram-negative organisms [1], and clinical isolates of M. pneumoniae [2,3]. C. pneumoniae is an obligate intracellular pathogen that causes respiratory tract infections and communityacquired pneumonia, in adults and children [4]. Antibiotics that are commonly used to treat C. pneumoniae are macrolides, quinolones and tetracycline. In this study we examined the activity of RD-3 and ER-2 against clinical isolates and standard strain AR-39 of C. pneumoniae and compared the activities against azithromycin, doxycycline, moxifloxacin, levofloxacin.
Twenty one C. pneumoniae strains were used in this study. AR-39 was obtained from the Washington Research Foundation, Seattle WA, USA. Wild type strains were isolated from nasopharyngeal swabs specimens collected from patients with acute respiratory tract infections at different hospitals in Chennai. The clinical isolates were stained with C. pneumoniae specific monoclonal antibody.
The comparator agents, azithromycin, doxycycline, moxifloxacin, and levofloxacin were from Sigma-Aldrich (St. Louis, MO,USA).
Antimicrobial powders were used according to the manufacturer’s protocol. Working dilutions of the drugs were prepared fresh on the day of the assay.
Susceptibility testing of C. pneumoniae was performed as described [5]. The HEp-2 cells were grown in 96 well microfiber plates containing Eagle's essential medium and 10% heatinactivated fetal calf serum. The wells were inoculated with 0.1 ml of the test strain that was diluted to yield 103 to 104 Inclusion forming units per ml. The plates were centrifuged at 1,700 × g for 1 hr and incubated at 35°C for 1 hr. The wells were aspirated and 0.2 ml of media containing 1microgram of cycloheximide per ml was dispensed into each well with serial two fold dilution of the test drug. After incubation in 5% CO2 at 35°C for 72 h, the cultures were stained with fluorescent isothiocyanate-conjugated monoclonal antibody (Bio-Rad, Hercules, CA. Minimum Inhibitory Concentration (MIC) was defined as the lowest concentration at which no inclusions were found. Minimum Bactericidal Concentration (MBC) was determined by aspirating the antibiotic containing medium, washing wells twice with phosphate-buffered saline and adding antibiotic-free medium. The infected cells were frozen at 70°C, thawed and then passed onto new cells incubated for 72 h, fixed and then stained as described above. MBC was the lowest antibiotic concentration which showed no inclusions after passage. All tests were performed in triplicates. The MIC and MBC of C. pneumoniae against different drugs are given in (Table 1). RD-3 was most active with an MIC90 and MBC90 of 0.125 mg/L (range 0.03-0.125 mg/L). ER-2 was better than doxycycline and azithromycin with an MIC90 of 0.25mg/L and MBC90 of 0.25mg/L. Doxycycline and azithromycin were superior to moxifloxacin and levofloxacin with an MIC90 of 0.25mg/L (range 0.06-0.25 mg/L), and MBC90 of 0.25 mg/L (range 0.06-0.25 mg/L).
Table 1: Activities of RD-3 and other antibiotics against clinical isolates of C. pneumoniae.
| MICs mg/L | MBCs mg/L | ||||
|---|---|---|---|---|---|
| Range | MIC50 | MIC90 | Range | MBC90 | |
| RD-3 | 0.03-0.125 | 0.06 | 0.125 | 0.03-0.125 | 0.125 |
| ER-2 | 0.06-0.125 | 0.06 | 0.25 | 0.06-0.25 | 0.25 |
| Doxycycline | 0.06-0.25 | 0.125 | 0.25 | 0.06-0.5 | 0.25 |
| Azithromycin | 0.06-0.25 | 0.125 | 0.25 | 0.06-0.6 | 0.25 |
| Moxifloxacin | 0.125-0.5 | 0.25 | 0.5 | 0.25-0.5 | 0.5 |
| Levofloxacin | 0.25-0.5 | 0.25 | 0.5 | 0.5-1 | 1 |
Due to the rise in antimicrobial resistance in alarming speed there is a need for alternative drugs [6,7].
Conclusion
The results presented in this study and our previous studies indicate that RD-3 and ER-2 could be effective in the treatment of C. pneumoniae infections; however its clinical application will depend on its toxicity and pharmacokinetic properties.
Acknowledgement
This study was funded partially by University of Madras. Azithromycin, levofloxacin and moxifloxacin were gifts from Department of Microbiology, University of Madras.
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