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Nanobiotechnica Universale Vol. 2(2), 39-45 (2011).
In vitro assessment of some antibacterial combinations
against Clinical Isolates of Staphylococcus aureus
Zafar Ahmed*, Shaukat Saeed Khan, Shazia Siddiqui and Mahnaaz Khan
Department of Microbiology, Saifia Science College, Bhopal – 462001 (M.P.) ABSTRACT
Different antibiotics exercise their inhibitory activity against a number of pathogenic microorganisms either by killing them, an actionreferred to as microbicidal or by arresting the cell growth, a microbistaticactivity. The impact of antibiotic on a pathogen is specific which differsfrom pathogen to pathogen and vice-versa. The aim of this study was toinvestigate in vitro antibiotic synergism of combination of β-lactamsand β-lactam - aminoglycoside against clinical isolates of Staphylococcusaureus. S. aureus is responsible for causing a number of infections. It isone of the five most common causes of nosocomial infections and israpidly increasing as multidrug resistant strain worldwide. In the presentstudy synergy was determined by checkerboard double dilution method.
The combination of streptomycin & ceftriaxone was found mostsynergistic (84.48%), followed by ampicillin & ceftriaxone (79.31%) andamoxicillin and cefaclor (72.41%) against S. aureus isolates. Furtheractions are needed to characterize the possible interaction mechanismbetween these antibiotics. Moreover, the combination of streptomycinand ceftriaxone may lead to the development of new and vitalantimicrobial against simultaneous infections of S. aureus. Key words: Synergism, microbicidal, microbistatic, antibiotics,
infections are due to antibiotic resistantstrains1, 10.
that a number of people are becoming infected Staphylococcus aureus is responsible with nosocomial infections leading to numerous for causing a range of illnesses from minor deaths annually worldwide and to heavy economic skin infections, such as pimples, impetigo, boils burden on both developed and developing world8.
(furuncles), cellulitis folliculitis, carbuncles, Emerging trends in nosocomial infections signal scalded skin syndrome, and abscesses, to life- pathogens. Studies show that 70% of nosocomial meningitis, osteomyelitis, endocarditis, toxic *Senior Research Technologist, Analytical Science Center, 402/403/1098, Urawade, At. Pirangut, shock syndrome (TSS), chest pain, bacteremia, collection of the Vishakha Clinical Microbiology and sepsis. Its incidence is from skin, soft tissue, Laboratory, Nagpur, India. The clinical isolates respiratory, bone, joint, endovascular to wound were from different specimens like pus, swab, infections. It is still one of the five most common sputum, blood and wound discharge of patients causes of nosocomial infections, often causing attending the health centres of Nagpur district.
postsurgical wound infections. In an increasing number of microbial infections of man, treatment biochemical tests including catalase, coagulase, with single antibiotics fails to cure. Some of and by growth characteristics on Mannitol salt these infections, however, respond favourably to combined treatment with two antibioticdrugs. Certain pairs of these drugs have proved Antimicrobial agents :
successful in a limited number of clinical situations.
The clinical significance of in vitro synergism Antimicrobial agents, namely amoxicillin, has not yet been defined in the treatment of cephotaxime, cefaclor and streptomycin were procured from Himedia Laboratories Pvt. Ltd.,Mumbai, cephalexin and ceftriaxone sodium to investigate the effectiveness of combinations of antibiotics against clinical isolates of S. Ranbaxy. All drugs were dissolved in their aureus which are synergistic in vitro. It will be respective solvents and diluted in deionized shown that the use of two antibiotics that are water and filtered through 0.22µ Millipore filter.
synergistic in vitro against the microorganism responsible for the infection may be associatedwith a significantly better outcome than that MIC and FICI Determination :
achieved with a combination which is notsynergistic for the offending microorganism.
In vitro checkerboard studies on the Synergistic activity of antimicrobials cannot be activity of antibiotics alone and in combination assumed and should be tested for, prior to were performed in Muller Hinton broth (Himedia Ltd.) in tube dilution. Two-fold dilutions (0.125- regimen9. It is therefore thought imperative to 256 µg ml-1) of each drug or drug combination assess the in vitro synergy of antibiotics were tested in two rows. One row was inoculated amoxicillin, ampicillin, cefaclor, ceftriaxone, with 105 organisms/ml test organism and the second row with the control organism. Results against fifty eight clinical isolates of S. aureus.
were read after tubes were incubated at37±2°C for 18 hours. MIC (Minimum inhibitory Material and Methods
concentration) is determined as the lowest Staphylococcus aureus isolates :
concentration of the drugs (alone or incombination) that inhibit growth. The fractional A total of fifty eight S. aureus isolates inhibitory concentration index (FICI) is defined included in present study were taken from as the sum of the MIC of each drug when used in combination divided by the MIC of the drug against 1.72% isolate. The combination of used alone. Synergistic effect was recorded amoxicillin and cephalexin against S. aureus was when FIC indexes 0.5; partial synergy when found synergistic against 18.97% isolates, partial FIC >0.5 but <1.0; additive when FIC =1.0; synergistic against 22.41% isolates, additive indifferent when FIC >1.0 but <4.0 and against 3.45% isolates, indifferent against 55.17% isolates and no antagonism found against anyisolate. The combination of amoxicillin and cephotaxime against S. aureus was foundsynergistic against 55.17% isolates, partial synergistic against 25.86%, additive against cefaclor against S. aureus was found synergistic 5.17% isolates, indifferent against 12.07% against 72.41% isolates, partial synergistic against isolates and antagonistic against 1.72% isolate.
17.24% isolates, additive against 3.45% isolates, The combination of amoxicillin and streptomycin indifferent against 6.90% isolates and no against S. aureus was found synergistic against antagonism was found against any isolate. The 44.83% isolates, partial synergistic against combination of amoxicillin and ceftriaxone against S. aureus was found synergistic against indifferent against 27.59% isolates and no 18.97% isolates, partial synergistic against antagonism was found against any isolate (Figure indifferent against 41.38% isolates and antagonistic Figure 1: Amoxicillin interaction with cephalosporins and streptomycin antibiotics against S. (Am = Amoxicillin, Cj = Cefaclor, Ci = Ceftriaxone, Cp = Cephalexin, Ce = Cephotaxime,
additive against 27.59% isolates, indifferent cefaclor against S. aureus was found synergistic against 43.10% isolates and antagonistic against against 13.79% isolates, partial synergistic against 1.72% isolate. The combination of ampicillin and 31.03%, additive against 34.48% isolates, cephotaxime against S. aureus was found indifferent against 20.69% isolates and antagonistic synergistic against 53.45% isolates, partial against 6.90% isolates. The combination of synergistic against 31.03%, no additive was found ampicillin and ceftriaxone against S. aureus was against any isolate, indifferent against 12.07% found synergistic against 79.31% isolates, partial isolates and antagonistic against 3.45% isolates.
synergistic against 17.24%, additive against The combination of ampicillin and streptomycin 1.72% isolates, indifferent against 1.72% isolates against S. aureus was found synergistic against and no antagonism was found against any isolate.
55.17% isolates, partial synergistic against The combination of ampicillin and cephalexin 24.14%, additive against 10.34% isolates, against S. aureus found synergistic against indifferent against 8.62% isolates and antagonism 5.17% isolates, partial synergistic against 22.41%, was found against 3.45% isolates (Figure 2).
Figure 2: Ampicillin interaction with cephalosporins and streptomycin against (A= Ampicillin, Cj = Cefaclor, Ci = Ceftriaxone, Cp = Cephalexin, Ce = Cephotaxime,
3.45% isolates, indifferent against 6.90% isolates cefaclor against S. aureus was found synergistic and no antagonistic effect was observed against against 46.55% isolates, partial synergistic against any isolate. The combination of streptomycin and 41.38%, additive against 3.45% isolates, indifferent cephalexin against S. aureus was found synergistic against 8.62% isolates and no antagonism found against 25.86% isolates, partial synergistic against against any isolate. The combination of strep- 22.41% isolates, additive against 15.52% isolates, tomycin and ceftriaxone against S. aureus was indifferent against 36.21% isolates and no found synergistic against 84.48% isolates, partial antagonism was found against any isolate. The synergistic against 5.17% isolates, additive against combination of streptomycin and cephotaxime against S. aureus was found synergistic against cefaclor (72.41%) synergism against S. aureus 74.14% isolates, partial synergistic against 20.69%, additive against 3.45% isolates, indifferentagainst 1.72% isolates and no antagonistic effect DISCUSSION
observed against any isolate (Figure 3).
widespread emergence of antibiotic resistance of streptomycin & ceftriaxone was found most against nosococomial infecting microorganisms synergistic (84.48%), followed by ampicillin & is continuously striking. Despite this understanding Figure 3: Streptomycin interaction with cephalosporins against S. aureus isolates (Cj = Cefaclor, Ci = Ceftriaxone, Cp = Cephalexin, Ce = Cephotaxime, S = Streptomycin)
synergistic approaches will be the powerful and the results were encouraging in the control tools for the development of new therapeutic of S. aureus. They concluded that in view of strategies. In the present study we observed that its toxicity, baicalin offers potential for development the combination of streptomycin and ceftriaxone of a valuable adjunct to beta-lactam treatments was very effective against S. aureus, followed against otherwise resistant microorganisms.
by ampicillin & ceftriaxone and amoxicillin and Cai and his associates2 investigated antibacterial cefaclor. Other combinations showed partial activity of Allicin (isolated from garlic) in synergism, additive and indifferent effects, combination with three beta lactams (cefazolin, antagonistic behaviour was negligible. Likewise, oxicillin and cefoperazone) against S. aureus, a flavone baicalin (isolated from herb) has been S. epidermidis and Pseudomonas aeruginosa.
found effective antibacterial by Liu et al.,6 but Their studies concluded that almost in all the in combination with benzyl penicillin, amoxicillin, cases synergism was observed and therefore methicillin and cefotaxime was highly synergistic these strains of bacteria can be controlled by the combination of drugs instead of using the surpassed their individual inhibitory effects.
particular disease in vitro experiments should be synergistic and antagonistic efficacy of various carried out with various antibiotics and their antibiotics against 12 clinical isolates of combination so that a right combination may be Staphylococcus aureus having the ability of administered to the patient for early and safe biofilm formation. The synergism result was recovery from a specific ailment. All the investigated by the comparison of MBIC and combinations do not produce synergistic effect and therefore a number of combinations are the combination of β – lactam antibiotics (ampicillin + penicillin and ampicillin + cloxacillin) REFERENCES
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