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Biomedical subjects

R E Badal

Publications and source records attributed to R E Badal.

17 recordsLinked to original sources
PubMed1983

Influence of inoculum growth phase on microdilution susceptibility tests.

Two types of commercially available microdilution trays were inoculated with log-phase cultures, stationary-phase cultures, and direct suspensions of 18- to 24-h colonies, with essentially comparable results. Direct pick-up of colonies was also tested with two Prompt inoculation systems (3M Co.); they were found to be convenient and reliable methods for standardizing inocula without preincubation in broth and without turbidity adjustment.

Ampicillin↗
PubMed1982

Direct comparison of two mechanized systems for identification of gram-negative bacilli. Autobac ID system versus the auto microbic system (with EBC plus).

The Auto Microbic System (AMS) is an almost completely automated system, capable of identifying Enterobacteriaceae after 8 hours, and some glucose nonfermenters after 13 hours of incubation. The Autobac ID system is a mechanized, computer-assisted system capable of identifying Enterobacteriaceae and many nonfermentative gram-negative bacilli within 3-6 hours. The present report combines the results of two independent studies, both of which evaluated the AMS and the Autobac ID system compared with standard reference tests. Among the 1,510 isolates that were tested, both systems reported equivocal identifications (low confidence values) with 5-6% of the strains. AMS produced fewer erroneous identifications (3.8% vs. 4.9%) but more equivocal test results (5.7% vs. 4.9%). Reproducibility of the two systems was compared by triplicate testing of 88 selected strains in both laboratories. AMS was somewhat more reproducible than the Autobac ID system. The AMS was capable of identifying more species with greater accuracy and reproducibility, but the Autobac ID system was more rapid. Both systems demonstrated excellent accuracy and reproducibility and both could be used efficiently in the clinical laboratory.

Bacterial Infections↗
PubMed1982

Identification of Enterobacteriaceae by the automicrobic system: Enterobacteriaceae biochemical cards versus Enterobacteriaceae-plus biochemical cards.

Enterobacteriaceae Biochemical Cards (EBC) may be used in the AutoMicrobic system for identification of enteric bacilli. Recently, the card has been modified to permit identification of enteric and certain nonenteric bacilli. Also, minor modifications have been in the computer program used for interpretation of tests with the new cards (EBC+). The two types of cards (EBC and EBC+) were tested in parallel and found to be in agreement with 97% of 650 Enterobacteriaceae. Most of the discrepancies were resolved when selected strains were retested on 3 separate days. A lack of absolute reproducibility with either system was demonstrated and explained most of the initial discrepancies. Approximately 97% of the AutoMicrobic system identifications agreed with those obtained from standard reference methods, after equivocal AutoMicrobic system results (P less than 0.80) were excluded. Equivocal responses occurred with 4% of our EBC tests and 7% of our EBC+ tests; additional tests are needed before such strains can be identified with confidence.

Bacteriological Techniques↗
PubMed1982

Sensitivity, specificity, and reproducibility of the automicrobic system (with the Enterobacteriaceae-plus biochemical card) for identifying clinical isolates of Gram- negative bacilli.

Two independent laboratories tested 1,743 clinical isolates by using the Enterobacteriaceae-plus Biochemical Card in the AutoMicrobic system (AMS) and identical standard reference methods. Included were 55 isolates representing 11 species that cannot be identified by the enterobacteriaceae-plus Biochemical Card computer program; 3 or these isolates were incorrectly identified as Pseudomonas cepacia. With the other 1,688 isolates, 5% of the AMS identifications were considered to be equivocal (probability value, less than 0.80), and the remaining test were 97% accurate (sensitive), Difficulty was observed in the ability of the AMS to identify some H2S-negative Citrobacter freundii species. An AMS response of P. cepacia was also considered nonspecific, because several other organisms were misidentified at P. cepacia. Reproducibility of the system was documented by testing 125 strains on 3-separate days; only 6 strains produced significantly variable results. The AMS (with the Enterobacteriaceae-plus Biochemical Card) was a very satisfactory, automated system for accurately identifying most gram-negative bacilli within 8 to 13 h.

Aeromonas↗
PubMed1982

Tentative interpretive standards for agar disk diffusion antimicrobial susceptibility testing of cefoperazone.

Cefoperazone is a new cephalosporin with a very wide spectrum of activity, including activity against Pseudomonas aeruginosa. It has less activity on enterococci and Acinetobacter. Of the 459 selected bacterial strains tested in this study, only 1.5% (7 strains and 6 genera) had minimum inhibitory concentrations of greater than or equal to 128 micrograms/ml. For a minimum inhibitory concentration breakpoint of less than or equal to 32 micrograms/ml (susceptible), we recommend that the disk diffusion test be done with a 75-micrograms disk and breakpoints of greater than or equal to 18 mm for susceptible, 15 to 17 mm for intermediate, and less than or equal to 14 mm for resistant. Diffusion tests using these criteria yielded only 1.1% very major or major errors.

Acinetobacter↗
PubMed1982

Reliability of early identifications obtained with Enterobacteriaceae-plus biochemical cards in the automicrobic system.

The AutoMicrobic system (AMS) is capable of identifying most Enterobacteriaceae within 8 h and many glucose-nonfermenting, gram-negative bacilli after 13 h of incubation. Early preliminary results can be readily obtained from the computer as the tests incubate. Data with 1,023 bacterial isolates were reviewed to determine the relative accuracy of 4-, 6-, 8-, 10-, and 13-h identifications. All AutoMicrobic system identifications with probability (P) values of less than 0.80 were considered equivocal responses which needed supplementary tests before a final report could be issued. Analysis of our data suggests that early identifications of Morganella morganii, Acinetobacter sp., Yersinia spp., Salmonella spp. (other than Salmonella typhi), Shigella spp. (other than Shigella sonnei), Enterobacter agglomerans, Pseudomonas spp. (other than Pseudomonas aeruginosa or Pseudomonas maltophilia), Klebsiella spp. (other than Klebsiella pneumoniae or Klebsiella oxytoca), Citrobacter amalonauticus, Serratia liquefaciens, or Vibrio spp. Should be considered nonspecific responses, even when P greater than or equal to 0.80. Other identifications reported after 4 h were 96% accurate. At least half of our isolates (60% of our Enterobacteriaceae) could be identified reliably within 4 h, the remaining isolates required longer incubation.

Bacteria↗
PubMed1982

Quality control limits for the agar overlay disk diffusion antimicrobial susceptibility test.

Replicate control tests were performed with the agar overlay and Kirby-Bauer techniques, using two sources of Mueller-Hinton agar. Mean zones observed with the two methods differed by 1 to 3 mm. Despite the minor differences between methods, National Committee for Clinical Laboratory Standards quality control limits which were established for the Kirby-Bauer method could also be used for the agar overlay technique.

Anti-Bacterial Agents↗
PubMed1981

Antibacterial activity of fortimicin A compared with those of five other aminoglycosides, and factors affecting susceptibility tests.

Fortimicin A, a pseudodisaccharide aminoglycoside, was found to have broad-spectrum activity against most clinically important aerobic and facultatively anaerobic bacteria, except Pseudomonas aeruginosa, some other Pseudomonas species, and streptococci. It was comparable to amikacin in its level of activity (minimum inhibitory concentrations) and spectrum of activity (except for the lack of activity on P. aeruginosa). Fortimicin A was bactericidal and was affected by cations when tested against P. aeruginosa. Minimum inhibitory concentrations were affected by the inoculum used in the susceptibility test. The drug was resistant to most aminoglycoside-inactivating enzymes, but probably is not active against permeability mutants.

Aminoglycosides↗
PubMed1980

Comparison of in vitro activity of Sch 21420, a gentamicin B derivative, with those of amikacin, gentamicin, netilmicin, sisomicin, and tobramycin.

Sch 21420 is a new aminoglycoside synthesized from gentamicin B. Susceptibility tests with Sch 21420, amikacin, gentamicin, netilmicin, sisomicin, and tobramycin were performed on a variety of bacterial species including 44 with known mechanisms of resistance to aminoglycosides. Sch 21420 and amikacin had similar effects on all except Haemophilus influenzae and Neisseria species, which were more susceptible to amikacin. Except with some strains of Serratia marcescens, the drugs used were bactericidal. Sch 21420 and amikacin were more stable than the other four aminoglycosides in the presence of the inactivating enzymes produced by some strains. Strains which were very resistant to Sch 21420 and emikacin either were permeability mutants or produced AAC (6')-I inactivating enzyme. The effect of cations on the susceptibilities of these strains to Sch 21420 and amikacin was seen mostly with Pseudomonas aeruginosa and to Sch 21420 with Acinetobacter. Cations did not affect the susceptibilities of other Pseudomonas species, Enterobacteriaceae, Staphylococcus aureus, or Streptococcus faecalis to Sch 21420 or amikacin.

Amikacin↗
PubMed1980

Compound A49759, the 3-O-demethyl derivative of fortimicin A: in vitro comparison with six other aminoglycoside antibiotics.

O-Demethylfortimicin A (compound A49759) was tested against 445 bacteria, and the results were compared with those obtained with fortimicin A, amikacin, gentamicin, netilmicin, sisomicin, and tobramycin. A49759 was found to be active and bactericidal against the Enterobacteriaceae, nonfermentative gram-negative bacilli, and Staphylococcus aureus. A49759 was two- to fourfold more active than fortimicin A against most species tested, but generally fourfold less active than amikacin against this population of Pseudomonas aeruginosa (85% inhibited at less than or equal to 16 microgram of amikacin per ml and 85% inhibited at less than or equal to 64 microgram of A49759 per ml). Only amikacin and A49759 were resistant to most aminoglucoside-inactivating enzymes and also had significant antipseudomonal activity. Amikacin was inactivated by aminoglycoside 6'-acetyltransferase, and A49759 was inactivated by aminoglycoside 3-acetyltransferase. The minimal inhibitory concentrations of all tested aminoglycosides were increased by augmenting the inoculum size.

Aminoglycosides↗
PubMed1979

Piperacillin susceptibility tests by the single-disk agar diffusion technique.

Piperacillin is a new semisynthetic penicillin with a spectrum of activity broader than that of carbenicillin or ticarcillin. Studies were performed to establish standards for agar diffusion susceptibility tests with piperacillin disks. Tests with 100-, 150-, and 200-micrograms piperacillin disks and with 100-micrograms carbenicillin disks were evaluated. With both penicillins, 100-micrograms disks were satisfactory, in spite of the fact that piperacillin is a larger molecule and diffuses at a slower rate. With both carbenicillin and piperacillin disks, resistant strains of Staphylococcus aureus produced zones less than or equal to 28 mm and susceptible strains gave zones greater than or equal to 29 mm in diameter. When testing other microorganisms, zone standards of less than or equal to 13 mm for resistant (minimal inhibitory concentration, greater than or equal to 256 micrograms/ml) and greater than or equal to 17 mm for susceptible (minimal inhibitory concentration, less than or equal to 64 micrograms/ml) are recommended for tests with 100-micrograms piperacillin disks. Similar zone standards are currently recommended for carbenicillin and ticarcillin disk tests.

Bacteria↗
PubMed1979

Rapid identification of Enterobacteriaceae with the micro-ID system versus API 20E and conventional media.

The Micro-ID system for rapid (4 h) identification of Enterobacteriaceae was evaluated by testing 433 enteric bacilli and 9 other gram-negative bacilli. Each isolate was identified with conventional tubed media and was also tested in the Micro-ID and API 20E systems. The overall accuracy of both systems was 97%. Micro-ID tests for the Voges-Proskauer reaction, indole and H2S production, and ornithine and lysine decarboxylase all demonstrated a 97 to 99% correlation with conventional methods. Only 86% of the Micro-ID urease tests agreed with Christenson urea agar. Two inoculum densities were tested in Micro-ID panels, with 157 stock cultures. Over 90% of the tests were unaffected by changes in inoculum density. Tests with four control strains suggested that the Micro-ID system was more reproducible when a light inoculum was used. The Micro-ID system was found to be a very convenient method for rapid, accurate, and precise identification of the Enterobacteriaceae.

Bacteriological Techniques↗
PubMed1979

Identification of Enterobacteriaceae in frozen microdilution trays prepared by Micro-Media Systems.

Frozen microdilution trays, with 20 different biochemical test media for identification of Enterobactericeae, were evaluated. The test panels were those provided by Micro-Media Systems (MMS), who also provided a code book for interpretation of the test results. The interpretations of the MMS test system and of the Analytab API 20E test system were compared with those obtained from tests with conventional media. Tests with 468 Enterobacteriaceae demonstrated nearly comparable results with the two commercial systems. About 6% (API) and 7% (MMS) of the isolates could not be identified without additional tests, and another 3% (MMS) to 4% (API) of the isolates gave test patterns that were not found in the code books. One to three percent of the isolates were misidentified. It was concluded that the MMS Enteric Quad Panels provide an efficient, relatively inexpensive, and reasonably accurate method for identification of the Enterobacteriaceae.

Bacteriological Techniques↗
PubMed1979

Piperacillin (T-1220), a new semisynthetic penicillin. II. In vitro antimicrobial activity and synergy comparison with carbenicillin and gentamicin.

Piperacillin, a new semisynthetic penicillin, was found to have potent antimicrobial activity against nearly all (405) tested bacterial species. Piperacillin was consistently 4 approximately 16-fold more active than carbenicillin against the Enterobacteriaceae, 16 approximately 32-fold against Pseudomonas aeruginosa and Pseudomonas species, and 16-fold against Streptococcus faecalis. Carbenicillin and piperacillin were equally effective against Staphylococcus aureus, but inactivated by beta-lactamase. A 38% overall synergy rate for the piperacillin-gentamicin combination was identified, a finding similar to that for carbenicillin-gentamicin. Highest incidences of synergy were found for both antibiotic pairs tested on gentamicin-resistant isolates (Ps. aeruginosa and Providencia). In vitro findings suggest that piperacillin alone or in combination with aminoglycosides may be highly efficacious in the treatment of most serious bacterial infections.

Bacteria↗
PubMed1977

Reliability of the microdilution technic for detection of methicillin-resistant strains of staphylococcus aureus.

To determine whether the microdilution technic for antimicrobic susceptibility testing could detect the hetero-resistance of "methicillin"-resistant Staphylococcus aureus, 100 stock cultures (54 methicillin-susceptible and 46 methicillin-resistant) were tested against methicillin, oxacillin, nafcillin and cephalothin. Each drug was diluted in Mueller-Hinton broth and in Mueller-Hinton broth with 5% NaCl. Minimum inhibitory concentration (MIC) determinations were made after 20-24 hours at 35 C and again after 48 hours of incubation. With one exception, methicillin resistance was detected in Mueller-Hinton broth when the trays were reincubated and read after 48 hours. Earlier detection of methicillin resistance was possible when the penicillinase-stable penicillins were diluted in broth containing 5% NaCl. Further studies suggest that the addition of NaCl to the broth medium might improve the stabilities of methicillin, oxacillin, and nafcillin during storage of the frozen microdilution trays. Either nafcillin or oxacillin would appear to be the best representative of the penicillinase-stable penicillins. Standardized disk-diffusion tests with cephalothin disks indicated that most methicillin-resistant strains are susceptible to cephalothin. However, there is reason to believe that such in-vitro test results might be inappropriate. With microdilution tests, most methicillin-resistant isolates were more resistant to cephalothin than were the methicillin-susceptible strains, but the MIC's for both types of staphylococci were generally within the range of concentrations that can be obtained during therapy. The addition of NaCl to the microdilution tests with cephalothin did not alter the test results significantly.

Indicator Dilution Techniques↗
PubMed1976

Short-term storage of six penicillins and cephalothin in microdilution trays for antimicrobial susceptibility tests.

To perform microdilution antimicrobial susceptibility tests efficiently, broth dilutions of the antimicrobial drugs should be prepared in large batches and stored frozen until needed. Studies were carried out to document the stability of ampicillin, benzylpenicillin, carbenicillin, methicillin, oxacillin, nafcillin, and cephalothin in microdilution trays during storage at -20 and -60 C. No significant deterioration was noted after 21 days of storage, as detected by bioassay and by replicate minimal inhibitory concentration determinations with control organisms. No significant differences were noted moreover between trays stored for three weeks at -20 C and those stored at -60 C. The microdilution technique was found to be a highly reproducible method for quantitative determination of antimicrobial susceptibility.

Biological Assay↗