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PubMed1980

Comparative in vitro appraisal of piperacillin, including its activity against Salmonella typhi.

Piperacillin was evaluated in vitro against 711 clinical isolates of aerobic and anerobic gram-positive and gram-negative bacteria, including 76 isolates of Salmonella typhi. Piperacillin minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were compared with those of a range of beta-lactam, aminoglycoside, and other antimicrobial agents, and inoculum size effects were considered. The relationship between dilution and disk diffusion tests was studied by regression analysis. In addition, piperacillin was assessed in combination with aminoglycoside and other beta-lactam drugs. This investigation has confirmed the activity of piperacillin against a broad range of bacteria, including Pseudomonas, Enterobacteriaceae, Neisseria, beta-lactamase-negative Haemophilus influenzae, and Staphylococcus aureus as well as enterococci, Bacteroides fragilis, and other anaerobes. All strains of Pseudomonas aeruginosa were inhibited by </=32 mug/ml or less, demonstrating again the potential usefulness of piperacillin in the treatment of pseudomonal infections. S. typhi proved susceptible to piperacillin, all isolates being inhibited by 1 mug/ml. Inoculum size experiments showed that inocula of 10(8) CFU resulted in MICs and MBCs appreciably higher than those resulting from inocula of 10(6) CFU, and inocula of 10(2) CFU resulted in MICs and MBCs appreciably lower than those resulting from inocula of 10(4) CFU. Piperacillin was active against all gentamicin-resistant pseudomonads tested, but not against gentamicin-resistant klebsiellas and enterobacters. Combinations of piperacillin with tobramycin and amikacin were consistently synergistic against Pseudomonas and Serratia isolates. Less consistent results were shown when piperacillin was combined with aminoglycosides or cephalothin against Klebsiella and indole-positive Proteus isolates, although synergy was observed in most cases. Occasional antagonistic reactions were encountered with piperacillin-cephalothin or piperacillin-tobramycin combinations against the latter isolates.

Anti-Bacterial Agents↗

PubMed1983

Differences among Nocardia spp. in susceptibility to aminoglycosides and beta-lactam antibiotics and their potential use in taxonomy.

Using disk diffusion and agar dilution methods, 109 clinical isolates of Nocardia were tested against 10 antimicrobial agents. A species difference in susceptibility was noted for cefamandole, carbenicillin, gentamicin, and kanamycin. These differences in susceptibility may be of use taxonomically as well as having some potential use clinically.

Aminoglycosides↗

PubMed1992

The activity of ceftiofur sodium for Aeromonas spp. isolated from ornamental fish.

Our objective was to determine the activity of ceftiofur sodium against Aeromonas hydrophila and A. sobria isolated from a variety of domestic and imported tropical fish. Twelve antimicrobial drugs were tested for effectiveness against these aeromonads using the Kirby-Bauer Disk Diffusion technique and minimum inhibitory concentration determinations. Ceftiofur sodium was highly effective in vitro against aeromonads isolated from ornamental fish. Of the 42 isolates of Aeromonas spp. tested, none were resistant to ceftiofur sodium; however, all isolates were resistant to ampicillin, and 71% were resistant to tetracycline.

Aeromonas↗

PubMed2000

Comparison of antioxidant and antimicrobial activities of tilia (Tilia argentea Desf ex DC), sage (Salvia triloba l.), and black tea (Camellia sinensis) extracts.

The antioxidant activity of the water extract of Tilia argentea Desf ex DC was determined by the thiocyanate method. The antioxidant activity of the water extract increased with the increasing amount of lyophilized extract (50-400 microg) added into the linoleic acid emulsion. Statistically significant effect was determined in 100 microg and higher amounts. Antioxidant activities of water extracts of tilia (Tilia argentea Desf ex DC), sage (Salvia triloba L.), and two Turkish black teas commercially called Rize tea and young shoot tea (Camellia sinensis) were compared. For comparison studies, 100 microg portions of extracts were added into test samples. All samples were able to show statistically significant antioxidant effect. Both of the tea extracts showed highest antioxidant activities, nevertheless, differences between tilia and sage and tilia and tea were not statistically significant (for both cases p > 0.05). Like antioxidant activity, the reducing power of water extract of Tilia argentea Desf ex DC was also concentration dependent. Even in the presence of 50 microg of extract, the reducing power was significantly higher than that of the control (p < 0.05) in which there was no extract. Unlike antioxidant activity, the highest reducing power activity was shown by sage extract. Among the tea extracts, young shoot extract was the most effective one, however, it had significantly lower activity than sage (p < 0.05). Although tea flower had the lowest reducing power activity, it was higher than that of tilia. But this difference was not statistically significant (p > 0.05). From these results, we could suggest that although the reducing power of a substance may be an indicator of its potential antioxidant activity, there may not always be a linear correlation between these two activities. In addition, antimicrobial activities of each of the above extracts were studied by disk diffusion methods on different test microorganisms. None of the extracts showed antibacterial activity on the studied microorganisms.

Anti-Bacterial Agents↗

PubMed1987

Clinical limitations of in vitro testing of microorganism susceptibility.

General concepts in evaluating the clinical importance of discrepancies between in vitro susceptibility tests of microorganisms and in vivo results are reviewed, and four problematic antibacterial-bacterial combinations are discussed. The three most common in vitro testing systems--agar disk diffusion, agar dilution, and broth dilution--are designed to detect the minimum inhibitory concentration (MIC) of an antimicrobial agent. However, agar and broth systems cannot include all of the biologic variables found within the human body. Factors affecting the reliability of in vitro testing systems include the limitations in interpreting MIC data, because in vitro test conditions cannot duplicate the host environment; the variability of testing media (e.g., acidic versus alkaline, differences in cation content); and the limiting effect of protein binding on an antimicrobial agent. In vitro testing systems do not consider the pharmacokinetics of the antimicrobial agent or the postantibiotic effect, whereby microbial growth is suppressed even when the antibiotic concentration falls below the MIC. The variability in drug distribution to infection sites within the body is also not considered. The following antimicrobial agent-bacterial combinations present specific problems to the clinician: trimethoprim-sulfamethoxazole and Group D enterococcus, cephalosporins and methicillin-resistant Staphylococcus aureus, aminoglycosides and Staph. aureus, and aminoglycosides and Pseudomonas aeruginosa. Despite the limitations of currently available systems, in vitro testing of the susceptibility of microorganisms can be an invaluable tool in selecting antimicrobial therapy when it is used in conjunction with data regarding the clinical course of the infected patient.

Aminoglycosides↗

PubMed2005

The fixed combination of fortified vancomycin and amikacin ophthalmic solution--VA solution: in vitro study of the potency and stability.

PURPOSE: We compared the in vitro potency and stability of a fixed combination of vancomycin and amikacin solution (VA solution) with amikacin or vancomycin solution. METHODS: Solutions of 2% amikacin (20 mg/mL) and of 5% vancomycin (50 mg/mL) and VA solution (each 1 mL contained 20 mg of amikacin and 50 mg of vancomycin) were prepared from parenteral antibiotics by reconstituting them with sterile injection water and refrigerated (4 degrees C) in the dark. Triplicate 5-mL portions of each solution were tested before storage and 7 and 14 days after preparation for potency of antimicrobial activity by the disk diffusion method and for stability. RESULTS: There were no significant differences in the diameter of zones of inhibition of VA solution compared with amikacin or vancomycin solution within a 2-week period. Visual inspection revealed that all solutions remained clear, colorless, and particle-free at 4 degrees C throughout the study period. For osmolarity, the VA solution was much higher than that of either amikacin or vancomycin solution at all tested times and more near the well-tolerated range of human eyes. There were no significant differences at days 0, 7, or 14 for either vancomycin, amikacin, or VA solution. For pH, the VA solution was higher than that of vancomycin solution (nearly equal to that of amikacin solution) at each time and more near the level of normal tear film. The pH did not differ significantly for either vancomycin, amikacin, or VA solution at all tested times. CONCLUSIONS: The vancomycin and amikacin ophthalmic solutions can be mixed together with the same potency and stable physical properties. It may be useful in the treatment of bacterial keratitis pending clinical trials to determine its effectiveness and safety.

Amikacin↗

PubMedDate not supplied

Prevalence of antimicrobial resistance in eighty clinical isolates of Helicobacter pylori.

We studied the in vitro susceptibility of 80 Helicobacter pylori clinical isolates to several antimicrobials commonly used to treat the infection, using the Epsilometer test (E-test). We also compared E-test and disk diffusion test in determining H. pylori susceptibility to the same antibiotics. We found a high prevalence of H. pylori strains resistant to metronidazole (23.7%), whereas the prevalence of H. pylori strains resistant to clarithromycin was 10%. Also, a significant correlation was found between MICs obtained with the disk diffusion test and E-test for metronidazole and clarithromycin. In conclusion, our study confirms a high prevalence of metronidazole- or clarithromycin-resistant H. pylori strains. Also, our data suggest that the E-test is a single, reliable, and cost-effective method to assess in vitro susceptibility of H. pylori to antimicrobial agents commonly used to eradicate the infection.

Adult↗

PubMed1998

Evaluation of the BIOMIC video reader system for determining interpretive categories of isolates on the basis of disk diffusion susceptibility results.

The BIOMIC System (Giles Scientific, New York, N.Y.) includes software and a video-assisted plate reader that functions with a personal computer to automate, speed read, and interpret standard antibiotic disk diffusion test plates. The video reader helps standardize endpoints, speeds quantitative measurements by 40 to 90%, and reduces fatigue and transcription and interpretation errors (H. Wei-Fang, Am. Clin. Lab. 13:28-29, 1994). Organisms tested were isolated from patient specimens collected at Primary Children's Medical Center and included rapidly growing gram-positive and gram-negative strains that fulfill the National Committee for Clinical Laboratory Standards guidelines for disk diffusion susceptibility testing. A comparison of the plate reader-determined zones and visually measured zones for 3,339 organism-antimicrobial agent combinations was performed. The results demonstrated 0.1% (4 of 3,339) false-susceptible reads and 0.2% (6 of 3,339) false-resistant reads by the video reader compared with visual reads. Minor discrepancies (4.7% [156 of 3339]), resulting in category interpretation changes of intermediate to resistant or susceptible or changes of resistant or susceptible to intermediate, were also encountered. Of the discrepant results, 80.8% (139 of 172) resulted from a 3-mm or less zone diameter difference between the two different techniques. We conclude that the video-assisted plate reader is a reliable system for determining interpretative categories from zone diameters of standard antibiotic disk diffusion test plates.

Diffusion↗

PubMed1990

Antimicrobial susceptibility of vancomycin-resistant Leuconostoc, Pediococcus, and Lactobacillus species.

Eighty-five strains of vancomycin-resistant gram-positive bacteria from three genera, Leuconostoc, Pediococcus, and Lactobacillus, were tested to determine susceptibility to 24 antimicrobial agents by broth microdilution and to 10 agents by disk diffusion. The MICs of vancomycin and teicoplanin ranged from 64 to greater than 512 micrograms/ml; however, the MICs of daptomycin, a new lipopeptide, were all less than or equal to 0.25 micrograms/ml. None of the organisms were resistant to imipenem, minocycline, chloramphenicol, gentamicin, or daptomycin. The MICs of penicillin were in the moderately susceptible range for all but three strains. Susceptibility to the other agents varied by genus and, in some cases, by species. When disk diffusion results were compared with MICs for drugs recommended for streptococci by the National Committee for Clinical Laboratory Standards, Villanova, Pa., few very major or major errors were obtained, but the number of minor errors was 19.3%. Therefore, we recommended that MIC testing be used instead of disk diffusion testing for these organisms.

Anti-Bacterial Agents↗

PubMed1995

Direct antimicrobial susceptibility testing for acute urinary tract infections in women.

Despite its theoretical advantages, direct antimicrobial susceptibility testing (DST) of urine specimens remains controversial largely because of concerns regarding its accuracy, particularly with mixed cultures. To evaluate the performance of DST in the setting of acute urinary tract infection (UTI), we performed DST using 25 traditional and contemporary antimicrobial agents on urine specimens from 162 women with suspected acute uncomplicated UTI, and compared these results with the results of standardized disk diffusion susceptibility tests done on the same specimens. Direct tests were interpretable for 129 specimens, i.e., 80% of all specimens and 85% of the 152 specimens that met the culture criteria for UTI. Of the 2,983 individual comparisons between the direct and standard tests, 0.8% represented very major errors, 0.6% represented major errors, 3.1% represented minor errors, and 95.5% were in agreement. Errors were more common in association with older antimicrobial agents and agents with a high prevalence of antimicrobial resistance, non-Escherichia coli strains, low urine bacterial concentrations, sparse or mixed growth in the direct test, and the presence of multiple significant organisms in urine. The urine leukocyte concentration was > or = 15/mm3 in all subjects and did not differentiate between specimens that gave an interpretable direct test and those that did not. Calculation of the sensitivity of DST in identifying antimicrobial resistance supplemented conventional error rate analysis. We conclude that when used selectively and interpreted carefully, DST of urine specimens offers an efficient, rapid, and accurate method for antimicrobial susceptibility determination for acute UTI, particularly when the urine bacterial concentration is > 10(5) CFU/ml.

Acute Disease↗

PubMed1995

Comparison of E-test with broth microdilution and disk diffusion for susceptibility testing of coryneform bacteria.

The susceptibilities of 135 coryneform bacteria isolated from clinical samples to ampicillin (AMP), cephalothin (CR), cefoxitin (FOX), cefotaxime (CTX), erythromycin (E), ciprofloxacin (CIP), tetracycline (TE), amikacin (AK), vancomycin (VA), and rifampin (R) were determined by disk diffusion, broth microdilution, and the E-test. The following species (number of isolates in parentheses) were included: Corynebacterium urealyticum (30), Corynebacterium minutissimum (20), coryneform CDC group ANF-1 (20), Corynebacterium striatum (20), Corynebacterium jeikeium (15), coryneform CDC group I2 (8), Listeria monocytogenes (7), Corynebacterium xerosis (5), and other coryneform bacteria (10). Agreement within one twofold dilution between the E-test and broth microdilution was 31% (VA), 64% (AK), 71% (CTX), 77% (FOX and CIP), 79% (TE), 84% (AMP), 87% (E), and 88% (CR and R). For the 1,350 combinations of microorganisms and antimicrobial agents, 85 (6.3%) discrepancies in interpretive category were found (4.2% minor, 1.2% major, and 0.9% very major). Seventy (5.1%) disagreements in interpretive category were found between disk diffusion and the E-test (3.8% minor, 0.4% major, and 0.9% very major), and 85 (6.3%) disagreements were found between microdilution (reference method) and disk diffusion (4.2% minor, 0.5% major, and 1.5% very major). MICs obtained with the E-test were highly reproducible. No category discrepancy was observed for VA, despite quantitative results. Considering interpretive categories, there is a good overall agreement between the three methods studied here, but further evaluation of current methodologies for susceptibility testing is required when considering coryneform bacteria and determination of quantitative activity of antimicrobial agents.

Actinomycetales↗

PubMed1978

Haemophilus influenzae susceptibility testing within four hours by a modification of the Autobac I system.

By adding an XV strip to the eugonic broth or substituting Levinthal broth, the standard Autobac I susceptibility testing system may be used to determine susceptibility of Haemophilus influenzae to antimicrobial agents. Complete concordance was attained in testing 30 strains (5 resistant) by Autobac I, disk diffusion, and broth dilution methods. Autobac I results were available within 4 h after isolation of the organism.

Evaluation Studies as Topic↗

PubMed1978

Simultaneous nosocomial outbreaks caused by multiply resistant Klebsiella pneumoniae types 2 and 30.

Two simultaneous Klebsiella pneumoniae outbreaks resistant to multiple antibiotics are reported. The closely related strains were distinguished by comparing the zone diameters obtained by disk diffusion susceptibility testing but not by interpretations of susceptible, resistant, or intermediate. Similar conclusions were made when minimal inhibitory concentrations were considered. The separation was subsequently confirmed by capsular serotyping into types 2 and 30. The data presented suggest that routine antimicrobial susceptibility patterns obtained from disk diffusion and/or minimal inhibitory concentrations may serve as an inexpensive and reliable typing system for epidemiological investigations.

Amikacin↗

PubMed1979

Antimicrobial susceptibility testing of pneumococci: determination of Kirby-Bauer breakpoints for penicillin G, erythromycin, clindamycin, tetracycline, chloramphenicol, and rifampin.

Antimicrobial susceptibility testing of pneumococci is now essential to monitor for the presence of resistance to agents such as the penicillins, macrolides, lincomycins, chloramphenicol, and tetracycline. In this study, clinical isolates of a selection of resistant South African strains were tested for antimicrobial susceptibility by minimal inhibitory concentration (MIC) determination and by a modified Kirby-Bauer disk diffusion technique, using Mueller-Hinton medium supplemented with 5% horse blood. Disk diffusion breakpoints were determined for penicillin G, erythromycin, clindamycin, tetracycline, chloramphenicol, and rifampin. Reliable results were obtained on disk diffusion for all these agents except for penicillin G. With 6-mug penicillin G disks, zones of strains with intermediate penicillin susceptibility overlapped those of sensitive and resistant strains. With 5-mug methicillin disks, clearer separation of strains based on susceptibility to penicillin G occurred. Strains with zones of <35 mm around penicillin G disks and <25 mm around methicillin disks should have penicillin G MICs determined to confirm their resistance to penicillin G. In view of the potential for pneumococci to be resistant to the agents used in this study, antimicrobial susceptibility of all clinically significant isolates should be determined.

Chloramphenicol↗

PubMed2004

Salmonella contamination during production of cantaloupe: a binational study.

Six cantaloupe farms and packing plants in South Texas (950 cantaloupe, 140 water, and 45 environmental samples), including the Rio Grande Valley area, and three farms in Colima State, Mexico (300 cantaloupe, 45 water, and 15 environmental samples), were sampled to evaluate cantaloupe contamination with Salmonella and Escherichia coli during production and processing. Samples collected from external surfaces of cantaloupes, water, and the environments of packing sheds on cantaloupe farms were examined for the presence of Salmonella and E. coli. Of a total of 1,735 samples collected, 31 (1.8%) tested positive for Salmonella. Fifteen Salmonella serotypes were isolated from samples collected in Texas, and nine from samples collected in Colima. Two serotypes (Poona and Oranienburg) that have been associated with three large Salmonella outbreaks in the United States and Canada linked to the consumption of contaminated cantaloupe were found in water samples collected at four farms (three from the United States). Susceptibility of Salmonella isolates to 10 antimicrobials was evaluated by disk diffusion. Eighty-eight percent of the isolates from the United States and Mexico were pansusceptible to the antimicrobials tested; eight isolates from the United States demonstrated an intermediate susceptibility to streptomycin and only two isolates were resistant to the same antimicrobial. From Mexico, four isolates showed an intermediate susceptibility to streptomycin and one isolate was resistant to nalidixic acid and streptomycin. Repetitive sequence-based PCR analysis of Salmonella isolates helped to trace potential sources of Salmonella contamination in source water and in subsequent water samples obtained after the filtration systems of U.S. and Mexican cantaloupe farms. No differences could be seen between the levels of Salmonella contamination in melons from both countries.

Anti-Bacterial Agents↗

PubMed1982

Methicillin-resistant Staphylococcus aureus susceptibility testing with Abbott MS-2 system.

The antimicrobial susceptibilities of 100 methicillin=resistant Staphylococcus aureus strains were concurrently determined by the Abbott MS-2 System and by the standard disk diffusion method. Agreement between the two methods was 94% or greater for all of the antibiotics tested except for methicillin and gentamicin. This study indicates that the Abbott MS-2 cannot be relied upon for detection of methicillin resistance in clinical S. aureus isolates.

Anti-Bacterial Agents↗

PubMed1997

Critical evaluation of the Vitek GNS F6 card results compared to standardized, reference susceptibility test methods.

A large number of Enterobacteriaceae (291 unselected and 30 clinical challenge isolates) were used to evaluate the accuracy of the Vitek GNS-F6 susceptibility testing card for 10 antimicrobial agents (ampicillin, ampicillin/sulbactam, aztreonam, ciprofloxacin, imipenem, mezlocillin, ofloxacin, piperacillin, ticarcillin, and ticarcillin/clavulanate). Results were compared to reference broth microdilution and disk diffusion methods. Highest interpretive error on initial processing were observed with ticarcillin/clavulanate (very major false-susceptible error, 3.4%), imipenem (major false-resistant error, 1.9%), and ampicillin/sulbactam (minor error, 15.9%). Repeat testing resolved many very major errors (21 of 41 results), and the overall accuracy rate was improved from 92.1 to 93.4%. Analysis of all minor interpretive errors demonstrated that the trend for Vitek was to report slightly lower MICs (6 of 10 drugs; 97 of 159 results) in comparison to the reference test results. If a heavy inoculum was used in the Vitek cards, false resistance was observed more frequently with aztreonam and penicillins. These data demonstrate that susceptibility testing accuracy with Vitek GNS-F6 card based on categorical agreement varies from 83.2% (ampicillin/sulbactam) to 99.4% (ciprofloxacin) when testing enteric bacilli. Some antimicrobial agents (beta-lactamase inhibitor/penicillin combinations, antipseudomonal penicillins) may require slight modification of interpretive software. Finally, the overall accuracy of the Vitek System was greater than 91% for 9 of 10 drugs tested with a very low, acceptable rate of false-susceptible error (0.8%).

Anti-Bacterial Agents↗

PubMedDate not supplied

Susceptibility testing interpretive criteria and drug stability for cefdinir, cefetamet, and cefpodoxime against Neisseria gonorrhoeae.

Cefdinir, cefetamet, and cefpodoxime, three orally administered cephalosporins, were tested against 100 strains of Neisseria gonorrhoeae having various antimicrobial susceptibility patterns. Triplicate testing of each organism strain was performed for all agar dilution and disk diffusion tests. Cefdinir was the most active compound (MIC90) micrograms/ml) especially against gonococci with chromosomal-mediated resistance to penicillin. The recommended susceptible interpretive criteria were as follows: for the 5-micrograms cefdinir disk, > or = 31 mm (MIC correlate, < or = 0.25 microgram/ml); for the 10-micrograms cefetament disk, > or = 29 mm (MIC correlate, < or = 0.5 microgram/ml; for the 30-micrograms cefetamet disk, > or = 31 mm (MIC correlate, < or = 0.5 microgram/ml); and for the 10-micrograms cefpodoxime disk, > or = 29 mm (MIC correlate, < or = 0.5 microgram/ml). No organisms resistant to these new cephalosporins were detected. Cefdinir, cefetamet, and defpodoxime were stable in GC agar medium for at least 21 days when stored at 2 degrees-5 degrees C.

Cefdinir↗