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PubMedDate not supplied

Antibacterial activity of cefotaxime, desacetylcefotaxime, and the combination of the two.

Cefotaxime (CTX) is metabolized to desacetylcefotaxime (dCTX), which is antibacterially active. The combination of CTX and dCTX is synergistic in a 1:1 ratio, but in this study, a combination of CTX:dCTX in a fixed ratio of 5:1 was not found synergistic when tested on 120 recently isolated clinical strains. Zone diameters of disks containing pure CTX or dCTX 30 micrograms or the combination of CTX/dCTX in micrograms: 25/5, 20/10, 15/15, and 10/20, were compared. The correlation between the zone size of the pure CTX disk and the 25/5, 20/10, and 15/15 disks were high with correlation coefficients (r) 0.98 to 0.96. Regardless of the metabolism and the potential synergy, no differences were found in the zone sizes comparing the pure CTX disk with the combination with a ratio from 5:1 to 1:1. The clinical microbiological laboratory can go on using the pure 30 micrograms CTX disk for routine susceptibility testing.

Bacteria↗
PubMed1977

Susceptibility of anaerobic bacteria to metronidazole, ornidazole, and tinidazole and routine susceptibility testing by standardized methods.

A total of 114 strains of anaerobic bacteria were examined for their susceptibility to metronidazole, ornidazole, and tinidazole by measuring the minimum inhibitory concentration (MIC) and minimum bactericidal concentration in different media. All strains, with the exception of the isolates of Propionibacterium acnes, were inhibited by 3.1 mug each and killed by 6.3 mug each of all three nitroimidazole compounds per ml. No significant differences in MIC values were found among metronidazole, ornidazole, and tinidazole. Only minor differences were detected by comparing MIC values obtained in brain heart infusion agar with and without sheep blood, brucella agar, and Mueller-Hinton agar (both containing blood). When the strains were tested by the modified broth-disk method proposed by the Anaerobe Laboratory of the Virginia Polytechnic Institute (VPI), there was good correlation with the MIC values (97.4% agreement for metronidazole and 94.7% for ornidazole and tinidazole). For routine testing, use of a 30-mug-class disk of either nitroimidazole derivative is proposed for the broth-disk method, resulting in a final concentration of 6 mug/ml in the test tubes, a concentration easily attainable in body fluids. In contrast to the broth-disk method, there was very poor correlation between inhibition zone diameters by the standardized VPI agar diffusion test and MIC values.

Anaerobiosis↗
PubMed1979

Comparative study of anti-pseudomonas activity of azlocillin, mezlocillin, and ticarcillin.

The anti-pseudomonas activities of azlocillin and mezlocillin were compared with that of ticarcillin. We measured the minimal inhibitory and minimal bactericidal concentrations of the three drugs against 20 different strains of Pseudomonas aeruginosa and found significantly lower values for azlocillin than for the other two drugs. We then infused 5 g of each drug into 10 volunteers on three consecutive days and determined the serum levels of the three antibiotics at 1-h intervals from 1 to 6 h after injection. The levels of azlocillin were significantly higher than those of mezlocillin and ticarcillin (at 1 h: 236.55 mug/ml +/- 12.9 for azlocillin, 192.45 mug/ml +/- 28.8 for mezlocillin, and 131.5 mug/ml +/- 10.9 for ticarcillin). The inhibitory and bactericidal activities of the sera obtained 1 and 6 h after the injection against the same 20 strains of P. aeruginosa demonstrated a significantly greater anti-pseudomonas activity of azlocillin when compared with mezlocillin and ticarcillin; mezlocillin and ticarcillin had approximately the same activity. The mean values for bactericidal activity against the strains tested were 1/32 for azlocillin, 1/8 for mezlocillin, and 1/8 for ticarcillin. Azlocillin thus appears to be a promising anti-pseudomonas drug and should be tested in clinical trials.

Humans↗
PubMed1983

Comparative in vitro activity of semisynthetic penicillins against Proteeae.

The in vitro susceptibilities of 181 isolates of precisely identified Proteeae species to five semisynthetic penicillins were determined with low and high inocula. Significant differences in susceptibility patterns among various Proteeae species to the penicillins examined were demonstrated. Providencia stuartii was clearly distinguished from Providencia alcalifaciens by its greater resistance to the antibiotics tested.

Microbial Sensitivity Tests↗
PubMed1974

Susceptibility of 1,500 isolates of Pseudomonas aeruginosa to gentamicin, carbenicillin, colistin, and polymyxin B.

A series of 1,500 strains of Pseudomonas aeruginosa was collected from a variety of sources to provide a group of strains which would truly represent the species. All of them were pyocine typed, and a wide range of types was included among the isolates from each source. The gentamicin, carbenicillin, colistin, and polymyxin minimal inhibitory concentration of each strain was measured by the agar dilution method employing the Steers inocula replicator. Over 99% of strains were inhibited by 8 mug of gentamicin per ml, by 256 mug of carbenicillin per ml, and by 4 mug of colistin per ml. The small number of strains more resistant to each antibiotic comprised a variety of different pyocine types. Few strains were found to be susceptible to tetracycline, chloramphenicol, kanamycin, or streptomycin at the single concentration tested.

Carbenicillin↗
PubMed1988

Inadequate mixing in microdilution wells during preparation of antimicrobial dilutions for susceptibility testing.

An equation representing a twofold series of antibiotic dilutions was derived. The theoretical results were then validated with experimental observations of piperacillin against Pseudomonas aeruginosa. Insufficient mixing leads to an erroneously low MIC. It is concluded that maintaining antibiotic concentration equilibrium during microdilution is required for accurate microdilution susceptibility tests.

Microbial Sensitivity Tests↗
PubMed1998

Unreliability of disc diffusion test for screening for reduced penicillin susceptibility in Neisseria meningitidis.

The 2-U penicillin and microgram oxacillin discs proposed for screening meningococci for susceptibility to penicillin were evaluated by using MICs measured by the E test. The discs yielded unacceptably high frequencies of misclassification of susceptibility category and should be abandoned in favor of MIC estimations. An agreed breakpoint for reduced penicillin susceptibility in meningococci is needed for the E test.

Humans↗
PubMed1994

Antimicrobial susceptibility testing and blood cultures.

Susceptibility testing of microorganisms isolated from blood cultures should follow the guidelines of the NCCLS in the selection of antimicrobial agents and the method for testing. Standardized testing can be performed on isolated colonies from pure subcultures of the blood/broth mixture. Direct susceptibility testing can provide results up to 24 hours sooner, but the techniques for testing have not been standardized. The disk diffusion and agar dilution techniques do not utilize automated testing techniques and seem to provide reliable results. Limited studies of direct susceptibility testing using automated procedures have been published, but the results are not conclusive. The number of discrepancies with direct automated procedures in comparison with standardized techniques is low, and most investigators agree that direct testing is appropriate given the rapidity with which the results are available. New resistance patterns for microorganisms are appearing regularly, and the technology for automated procedures is changing rapidly. New clinical evaluations of direct susceptibility testing with larger numbers of microorganisms that include some of the recently described resistant microorganisms would help to clarify the accuracy and reliability of current procedures. Standardized direct susceptibility testing guidelines should be established so that reliability and accuracy can be improved. There is general consensus that repeat testing by standardized techniques is advisable, although the decision as to whether to repeat the test using a standardized method rests with the individual laboratory director based on his or her expertise and experience with the procedures. Each laboratory director should compare the advantages and limitations of direct antimicrobial susceptibility testing with the methodology currently in use and determine the need for repeat testing by standardized techniques.

Autoanalysis↗
PubMedDate not supplied

Neonatal bacteremia due to high level aminoglycoside resistant (HLAR) enterococci.

A study was conducted to determine the drug resistance pattern of enterococci isolated from cases of neonatal bacteremia. A total of 41 strains of enterococci were isolated of which 35 (85.4%) were Enterococcus faecalis and 6 (14.6%) were Enterococcus faecium. A total of 3 (8.6%) strains of E. faecalis and 2 (33.3%) E. faecium strains showed high level aminoglycoside resistance (HLAR). None of the enterococci tested were vancomycin resistant. Drug resistance was more common among E. faecium strains. All clinically significant isolates of enterococci should be tested for their antibiotic sensitivity pattern including HLAR, and for treatment, antibiotics are selected based on in vitro antibiotic sensitivity test results.

Aminoglycosides↗
PubMed1997

Susceptibility of vancomycin-resistant enterococci to environmental disinfectants.

OBJECTIVE: To determine the susceptibilities of vancomycin-resistant and -sensitive enterococci (VRE and VSE) to various concentrations of commonly used, commercial, hospital-grade disinfectants. DESIGN: A microbial suspension test using inocula of 10(8) cells per mL in a disinfectant test dilution was used to determine inactivation kinetics of the test strains. In each test, 1-mL aliquots were removed from the cell-disinfectant mixtures at 15 and 30 seconds and then at 1-minute intervals for 5 minutes and neutralized. Appropriate serial dilutions were plated on agar medium for enumeration of survivors. RESULTS: VRE and VSE challenge inocula (in the absence of any additional protein or serum challenge) were below the limit of detection (5 colony-forming units/mL) after 15 seconds' exposure to the manufacturers' suggested use-dilutions of quaternary ammonium, phenolic, or iodophor germicidal detergents. In subsequent tests, when the disinfectants were diluted far beyond-the recommended use-dilutions (extended dilution), no differences were demonstrated between the susceptibilities of VRE and VSE. CONCLUSIONS: VRE and VSE are sensitive to a spectrum of commonly used environmental disinfectants and have parallel inactivation rates when challenged with extended dilutions of these products. Our findings did not demonstrate a relationship between antibiotic and germicide resistance. Routine disinfection and housekeeping protocols presently used in hospitals need not be altered due to concerns about the potential for environmentally mediated transmission of antibiotic-resistant microorganisms.

Anti-Bacterial Agents↗
PubMed1978

[Comparison of two methods of antibiotic sensitivity test: gel diffusion and automatic method using ABAC apparatus. II. Study on 399 strains isolated in hospital (author's transl)].

The authors compared for routine use, the results obtained on 399 strains of Gram negative bacilli by two technics of antibiotic sensitivity: the technic of gel diffusion with imprenated discs and an automatic method (ABAC apparatus). Among the antibiotics used as a routine in our laboratory by the diffusion method and the 16 studied with the ABAC apparatus, 11 are common to both methods and were compared. The concordance of the results was greater than 90% for colistine (94.5%), oxolinic acid (93.5%), tobramycin (91.7%). It lies between 80 and 90% in the case of carbenicillin (89.1%), nalidixic acid (87.5%), kanamycin (87.2%). It is less in the case of gentamicin (77.9%), ampicillin (77.3%, chloramphenicol (76%), streptomycin (70.3%), minocycline with 55.9% gave the lowest results. The percentage of uninterpretable responses by ABAC was 0.7% for all 11 antibiotics. The correlations were good for the Enterobacteriaceae: Serratia (75.4%), Eschericia coli (87.5%). They are less in the case of Pseudomonas aeruginosa (71.6%). The ABAC makes sensitivity test automatic and appears a reliable method.

Anti-Bacterial Agents↗
PubMed1989

Radiometric studies on the use of selective inhibitors in the identification of Mycobacterium spp.

Radiometric selective inhibition tests were developed and evaluated for the rapid differentiation of Mycobacterium spp. Both a p-nitrobenzoic acid (PNB) test and a commercially-prepared p-nitro-alpha-acetylamino-beta-hydroxypropiophenone (NAP) test successfully differentiated M. tuberculosis and M. bovis from "atypical" mycobacteria or mycobacteria other than tubercle bacilli (MOTT). Thiophene-2-carboxylic acid hydrazide (TCH) readily distinguished human M. tuberculosis strains from M. bovis, irrespective of resistance to isoniazid. Both PNB and TCH tests were utilised in a routine radiometric susceptibility testing scheme over a period of 1 year in which 110 isolates of M. tuberculosis, 10 of M. bovis and one isolate of BCG were correctly differentiated from 10 isolates of MOTT. The rapidity, sensitivity and specificity of these radiometric tests can play a useful role in mycobacterial identification.

Drug Resistance, Microbial↗
PubMed1987

A simple broth-disk elution test for screening methicillin-resistant (heteroresistant) staphylococci.

Forty-six strains of Staphylococcus aureus and 47 strains of unspeciated coagulase-negative staphylococci were inoculated in tubes containing a cation-supplemented Mueller-Hinton broth with 4% (wt/vol) NaCl. A critical concentration of methicillin (10 micrograms/ml) or oxacillin (6 micrograms/ml) was achieved in each tube by adding the appropriate number of antibiotic disks. Growth was interpreted as resistance. Results obtained with fully resistant or fully sensitive strains showed complete agreement with the reference method. Four strains with intermediate sensitivity (two S. aureus and two coagulase-negative staphylococci) were classified as resistant by the broth-disk elution test.

Methicillin↗