Shrivastava S. M, Shukla S. K, Chaudhary M. In vitro microbial efficacy analysis of tobracef, a fixed dose combination of ceftazidime and tobramycin against Acinetobacter lwoffii, Morganella morganii, Enterobacter cloacae, Hafnia alvei, Citrobacter freundii & Serratia grimesii. Biomed. Pharmacol. J.2008;1(2)

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Manuscript received on :October 05, 2008
Manuscript accepted on :November 25, 2008
Published online on: 09-11-2015

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Sanjay Mohan Shrivastava*, Sanjeev Kumar Shukla and Manu Chaudhary.

Venus Medicine Research Center, Hill Top Industrial Estate, Jharmajri EPIP, Phase I (Extn) Bhatoli Kalan, Baddi - 173205 (India).

Abstract

Ceftazidime belongs to cephalosporin class of antibiotics with broad spectrum activity. Tobramycin is an aminoglycoside antibiotic used to treat various types of bacterial infections, particularly gram negative infections. In present study is an attempt to determine efficacy of ceftazidime, tobramycin and Tobracef, their Fixed Dose Combination (FDC) on some microorganisms. Efficacy was evaluated on the basis of Minimum Inhibitory Concentration (MIC) and Antibiotic Susceptibility Test (AST). In Acinetobacter lwoffii, Morganella morganii, Enterobacter cloacae, Hafnia alvei, Citrobacter freundii and Serratia grimesii. MIC were found to be 8µg/l, 4µg/l, 16µg/l, 4 µg/l, 2µg/l and 1µg/l for ceftazidime respectively. In a tobramycin alone the MIC were found to be 4 µg/l, 8 µg/l, 8 µg/l, 8 µg/l, 4 µg/l and 8 µg/l respectively whereas in tobracef MIC were found to be 2 µg/l, 2 µg/l, 4 µg/l, 2 µg/l, 1 µg/l and 0.5 µg/l. Results of AST also showed more lytic zone by Tobracef in all organisms when compared with ceftazidime and tobramycin alone. These results indicate that the Tobracef has better bactericidal activity in comparison to ceftazidime and tobramycin alone in organisms under study.

Keywords

Minimum Inhibitory Concentration (MIC); AST; Ceftazidime; Tobramycin; Tobracef

Introduction

Ceftazidime belongs to cephalosporin class of antibiotics with broad spectrum activity.^{1, 2} It is stable to both plasmid and chromosomal β – lactamase resistance  then other cephalosporins.^{3, 4} Ceftazidime is a third generation cephalosporin and is resistant to hydrolysis.  It is effective against a broad range of gram positive and gram negative bacteria and also against bacteria resistant to cephalosporins.

Tobramycin is an aminoglycoside antibiotic used to treat various types of bacterial infections, particularly gram  negative infections. It  is often used concomitantly with other antibacterials to extend its spectrum of efficacy or increases its effectiveness. Treatment with a combination of an aminoglycoside  with  a  β – lactam has showed  increased efficacy.

Combination therapy of cephalosporins and aminoglycosides is also used to broaden the antimicrobial spectrum in critically ill patients while awaiting a bacteriological diagnosis or  proven polymicrobial infection. Synergism appears to be maintained even at very  high  MIC  with drug  combinations within achievable therapeutic ranges.^{5, 6, 7, 8}

Ceftazidime and tobramycin combination therapy is considered by some clinicians to be the clinical standard.^[9] Antibacterial drugs have been highly successful in controlling the morbidity and mortality that accompany serious bacterial infections. Some of the exiting antibiotics may cause adverse effects in some patients. Some of  these side effect  may be significant enough to require that therapy should be discontinued.^{10, 11}

The fight against bacterial infection represents one of the highest point of the modern medicine. Since the development of  antibiotics, this powerful tool has saved millions of  lives. However, because of inappropriate and large use of antibiotics, many antibiotic resistant strains are growing in number. The resistant bacteria  pose a significant threat to human health and a challenge to researches^{12, 13} Keeping this in the view, the present study was planned  to evaluate efficacy  of  tobracef, FDC of ceftazidime and tobramycin against some clinically significant microorganisms.

Materials and Methods

Bacterial Strains

Following strains obtained from Microbial Type Collection Center of Institute of Microbial Technology, Chandigarh, India were  used for the study:

Acinetobacter lwoffii (MTCC No. 496), Morganella  morganii (MTCC No. 662 ), Enterobacter cloacae (MTCC No. 509), Hafnia alvei (MTCC No. 1426), Citrobacter freundii (MTCC No. 1658)  and  Serratia grimesii (MTCC No. 1887).

Antibiotic

Tobracef, ceftazidime and tobramycin used in study were provided by manufacturer, Venus Remedies Limited, India.

Medium

Mueller- Hinton (MH) media supplemented with calcium (25 mg/l) and Magnesium (1.25 mg/l) was used for MIC and susceptibility tests experiments. Colony counts were determined with MH agar plates.

Susceptibility Testing

The MIC of ceftazidime and tobramycin alone and in a Tobracef against A. lwoffii, M. morganii, E. cloacae, H. alvei, C. freundii  and  S. grimesii were determined by broth micro dilution method as per the standard National Committee for Clinical Laboratory Standards.¹⁴ Overnight MH broth cultures were used to prepare inocula of  10⁵  CFU/ml. The MIC was defined as the lowest concentration of antimicrobial  agent that prevented  turbidity after 24 h of  incubation at 37 ⁰C.

Results

MIC studies

In case  of A. lwoffii, M. morganii, E. cloacae, H. alvei, C. freundii  and  S. grimesii  MIC were found to be 8 µg/l, 4 µg/l, 16 µg/l 4 µg/l 2 µg/l and 1 µg/l for ceftazidime respectively. In  a  tobramycin  alone the  MIC  was found to be  4 µg/l, 8 µg/l, 8 µg/l 8 µg/l 4 µg/l and 8 µg/l  respectively and Tobracef  MIC was found to be 2 µg/l, 2 µg/l, 4 µg/l, 2 µg/l, 1 µg/l and 0.5 µg/l.

The MIC of all microbial strains under study resulted in significant reduction in ceftazidime, tobramycin  alone  and Tobracef. (Table-1)

Table 1: Minimum Inhibitory Concentrations determination of ceftazidime, tobramycin  and Tobracef with  A. lwoffii, M. morganii,  E. cloacae, H. alvei, C. freundii  and S. grimesii.

MIC of  all microbial strain under study resulted in reduction in Tobracef when compared with ceftazidime and tobramycin alone. (Table – 2).

Table 2 ;Results of comparative Antimicrobial Susceptibility Test  studies of ceftazidime,  tobramycin and Tobracef.

Average ±  standard deviation

Susceptibility studies

Discussion

A synergistic interaction between the two antibiotics is one reason for using this combination.¹⁵ A further indication for antibiotic combinations is to prevent emergence of resistance.¹⁶ Antibiotic combinations have long been used to provide antibacterial activity against  multiple potential pathogen for initial empirical treatment of critically ill patients. Several studies of antibiotic combination therapy  for gram  negative infection conducted from the 1970s  to the 1990s. The consensus  is that combination therapy is probably more effective than mono therapy only for infections. Gram negative bacterial species typically have a higher degree of antibiotic resistance than gram positive bacteria. This is largely in part due to the presence of a selectively permeable outer membrane which restricts the entrance of small hydrophobic molecules, including many available antibiotics.¹⁷  Aminoglycoside class antibiotic exert a killing effect by binding to bacterial ribosomes and inhibiting bacterial protein synthesis.

Useful antibiotic classes based  on  a  β – lactam structure include broad  penicillins, cephalosporins, carbapenems, all of which inhibit bacterial cell wall synthesis. β – lactamase enzymes that rapidly degrade the cephalosporins  β – lactam ring have a primary bacterial resistance mechanism against this class of drug since the commencement of clinical cephalosporins use in the 1940s. Because of  this, most cephalosporins derived antibiotics still clinically used  are formulated to include a  β – lactamase  inhibitor  in order to increase the drug’s effectiveness. Cephalosporins also contain a  β – lactam ring, but are structurally more resistance  to  β – lactamase  degradation.

Ceftazidime is a third generation cephalosporins, with good antibacterial activity.^{2, 18} Clinically administration of two or more antibiotics in the treatment of infections is usually rationalized with the knowledge that multiple antibiotics often exert additive or synergistic effects, increasing the likelihood of pathogen eradication. In comparison with older cephalosporins, it crosses the bacterial outer cell membrane faster and has advantages of rapid penetration in periplasmic space as well as of extended spectrum of the activity that include gram positive and gram negative organisms.

Tobracef has lower MIC than ceftazidime and tobramycin alone against A. lwoffii, M. morganii, E. cloacae, H. alvei, C. freundii and S. grimesii. AST studies also showed  that  bacterial   lytic zone was more under influence of  Tobracef   than  ceftazidime and tobramycin alone.

This investigation indicated that Tobracef has better efficacy as compared to ceftazidime and tobramycin alone  in organisms under  study.

References

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