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C N Baker

Publications and source records attributed to C N Baker.

15 recordsLinked to original sources
PubMed1992

The E-Test and Campylobacter jejuni.

The E-Test is a recently introduced method for performing antimicrobial susceptibility tests. We compared the E-Test to the broth microdilution test and to the standard agar dilution test by using five antimicrobial agents tested against 55 clinical isolates of Campylobacter jejuni from 11 locations in USA (group 1). Later, we selected 30 strains (group 2), which were more resistant than the original survey isolates. Erythromycin, tetracycline, and ciprofloxacin were tested on both groups of organisms. When the three test methods were compared with each other at +/- 1 log2 dilution, the E-test gave the best overall agreement, with 85% of all strains being within acceptable limits. Category interpretation of erythromycin (drug of choice) results was a problem using current NCCLS guideline breakpoints. For the E-Test and the agar dilution method, 82% of the strains were in the intermediate category; but with the broth microdilution method, only 16.4% of the isolates were interpreted as intermediate. If the susceptible category breakpoint was raised to less than or equal to 2 micrograms/ml, then only 3% of the C. jejuni isolates would be interpreted as intermediate by any of the three methods. Our preference for antimicrobial susceptibility testing of C. jejuni is either E-Test or agar dilution at 42 degrees C for 16 hr.

Anti-Bacterial Agents↗
PubMed1992

In vitro susceptibilities of aerotolerant Campylobacter isolates to 22 antimicrobial agents.

We evaluated the in vitro activities of 22 antimicrobial agents against 78 human and animal isolates belonging to two aerotolerant Campylobacter species, C. cryaerophila and C. butzleri, using a broth microdilution technique. An additional 10 antimicrobial agents were included at concentrations found in selective Campylobacter media. Strains of C. cryaerophila belonged to two DNA hybridization groups: DNA hybridization group 1A, which includes the type strain of C. cryaerophila, and DNA hybridization group 1B. The aminoglycosides, fluoroquinolones, and one tetracycline (minocycline) demonstrated the most activity against all DNA hybridization groups (C. cryaerophila DNA groups 1A and 1B and C. butzleri). Most isolates were resistant to cephalosporin antibiotics, with the exception of cefotaxime, and were variably susceptible to trimethoprim-sulfamethoxazole. C. cryaerophila DNA hybridization group 1A isolates were generally susceptible to the tetracyclines, chloramphenicol, nalidixic acid, azithromycin, erythromycin, and roxithromycin and moderately susceptible to clindamycin, trimethoprim-sulfamethoxazole, ampicillin, and ampicillin-sulbactam. The MICs of tetracyclines were higher for C. butzleri and C. cryaerophila DNA hybridization group 1B isolates than for C. cryaerophila DNA hybridization group 1A isolates, but most strains were still susceptible to doxycycline and tetracycline; all isolates were susceptible to minocycline. C. butzleri and C. cryaerophila DNA hybridization group 1B isolates were generally resistant to the macrolide antibiotics (including erythromycin), chloramphenicol, clindamycin, nalidixic acid, ampicillin, and trimethoprim-sulfamethoxazole. Differences in antimicrobial susceptibility between aerotolerant Campylobacter species and more common Campylobacter species, e.g., C. jejuni, suggest that different treatment strategies may be necessary. Strains of all three DNA hybridization groups of aerotolerant Campylobacter isolates were susceptible to colistin, polymyxin B, and rifampin at concentrations commonly used in selective media. These results suggest that primary isolation methods for Campylobacter species may need to be modified to include aerotolerant Campylobacter strains.

Animals↗
PubMed1992

Interpretive criteria and quality control parameters for testing susceptibility of Haemophilus influenzae to enoxacin, ofloxacin, and temafloxacin.

Haemophilus influenzae isolates were uniformly susceptible to enoxacin, ofloxacin, and temafloxacin. Zone diameter and MIC interpretive criteria were proposed to define susceptible populations so that mutants with diminished susceptibility might be detected when and if they appear in clinical specimens. Additional collaborative quality control studies defined MIC and zone size limits for tests with H. influenzae ATCC 49247.

Anti-Infective Agents↗
PubMed1992

Accuracy of the E test for determining antimicrobial susceptibilities of staphylococci, enterococci, Campylobacter jejuni, and gram-negative bacteria resistant to antimicrobial agents.

We compared the results of the E test MIC method with the results of agar dilution susceptibility testing for 18 antimicrobial agents against 324 strains of gram-positive and gram-negative bacteria, including 99 strains of staphylococci, 101 strains of antimicrobial-resistant gram-negative bacteria, 40 strains of enterococci, and 84 isolates of Campylobacter jejuni. Overall agreement of MICs (+/- 1 log2 dilution) was 97.3% for staphylococci, 94.6% for gram-negative bacilli, and 100.0% for enterococci. The MIC results for C. jejuni showed an overall agreement of only 82.9%. This was due primarily to a number of offscale values that limited the number of comparisons with clindamycin, trimethoprim-sulfamethoxazole, and tetracycline. Interpretative criteria for the results of the two test methods, however, were similar. Overall, the E test produced MIC results comparable to those of agar dilution when multiresistant organisms were tested. However, it was necessary to add 2% NaCl to the agar when testing oxacillin against staphylococci for both the E test and agar dilution to obtain results comparable to those of the broth microdilution method.

Bacteria↗
PubMed1992

Haemophilus influenzae ATCC 49766, an alternative quality control strain for monitoring broth microdilution susceptibility tests with selected beta-lactams.

A beta-lactamase-negative, ampicillin-resistant strain of Haemophilus influenzae is currently used for quality control of broth microdilution tests performed with Haemophilus test medium (HTM). Studies with eight lots of HTM broth documented the fact that MIC limits for some antimicrobial agents are unrealistically stringent; i.e., only three of eight lots of HTM broth were satisfactory for testing cefaclor. An alternative, ampicillin-susceptible strain of H. influenzae (ATCC 49766) was found to provide much more reproducible results with five problematic drugs (cefaclor, cefuroxime, cefamandole, loracarbef, and cefonicid). Multilaboratory studies defined MIC control limits for both control strains tested against 12 antimicrobial agents.

Ampicillin↗
PubMed1992

Proposed interpretive criteria and quality control parameters for testing susceptibility of Neisseria gonorrhoeae to beta-lactam-clavulanate combinations.

To support future clinical studies, in vitro susceptibility tests were examined to determine whether Neisseria gonorrhoeae could be tested reliably against two beta-lactam-clavulanate combinations. All isolates that were tested appeared to be susceptible to amoxicillin and ticarcillin in combination with clavulanic acid. In the absence of resistant isolates, only a breakpoint for a susceptible category could be defined for agar dilution tests with amoxicillin-clavulanic acid (MIC of less than or equal to 2.0/1.0 micrograms/ml is tentatively proposed). For disk diffusion tests, a corresponding breakpoint zone diameter of greater than or equal to 28 mm is suggested. The validity of the breakpoints for penicillinase-negative penicillin-resistant strains awaits clinical data. Proposed quality control limits for testing amoxicillin-clavulanic acid by agar dilution and disk diffusion methods are a MIC of 0.25/0.125 to 1.0/0.5 micrograms/ml and zones of 30 to 40 mm in diameter for N. gonorrhoeae ATCC 49226, a MIC of 0.125/0.06 to 0.5/0.25 micrograms/ml for Staphylococcus aureus ATCC 29213, and zones of 30 to 38 mm for S. aureus ATCC 25923. Ticarcillin-clavulanate is currently tested against other species by preparing doubling dilutions of ticarcillin with a constant 2 micrograms of clavulanate per ml. By that method, all gonococci were susceptible to low concentrations. However, the amount of clavulanic acid that is included (2 micrograms/ml) will, by itself, inhibit many strains of N. gonorrhoeae. Consequently, the role of ticarcillin in the combination cannot be determined, and such tests are not recommended.

Amoxicillin↗
PubMed1991

Meningococcal disease in the United States--1986. Meningococcal Disease Study Group.

Active surveillance for invasive meningococcal disease was conducted during 1986 and 1987 in six areas of the United States with a total population of approximately 34 million persons. The incidence of meningococcal disease was 1.3:10(5). The highest incidence of disease among the surveillance areas was in Los Angeles County (1.65:10(5). Neisseria meningitidis serogroups B and C caused about equal amounts of disease, which reflects a recent increase in the incidence of group C disease. Group C caused more than half of the cases of meningococcal disease in Los Angeles and Tennessee but less than one-third of the cases in Missouri and Oklahoma. Multilocus enzyme electrophoresis demonstrated that a group of closely related isolates of N. meningitidis was prevalent in Los Angeles during the surveillance period and was associated with an increased incidence of meningococcal disease there.

Adolescent↗
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

Characterization and identification of 95 diphtheroid (group JK) cultures isolated from clinical specimens.

Ninety-five cultures of group JK bacteria isolated from clinical specimens were characterized morphologically and biochemically. The microorganisms were isolated primarily from blood cultures. The bacterial cultures produced positive reactions when tested for catalase, Tween hydrolysis, and carbohydrate fermentation. Glucose and galactose were fermented by more than 90% of the organisms. Gas-liquid chromatography of trimethylsilyl derivatives of whole-cell hydrolysates of some of the group JK cultures yielded nearly identical elution profiles. The group JK microorganisms were susceptible to vancomycin but were resistant to most of the other 17 antimicrobial agents tested. A method is presented for differentiating the group JK microorganisms from other similar bacteria encountered in clinical specimens. Although these bacteria rarely occur in clinical specimens, they are capable of producing fatal infections (endocarditis and sepsis) in humans.

Actinomycetales↗
PubMed1978

In vitro activity of antimicrobial agents on Legionnaires disease bacterium.

Six isolates of Legionnaires disease bacteria were tested for their susceptibility to 22 antimicrobial agents. The most active agent was rifampin (minimal inhibitory concentration, </=0.01 mug/ml). On the basis of minimal inhibitory concentration breakpoints that have been used to categorize susceptibility for most of these drugs, the organisms were susceptible to rifampin, cefoxitin, erythromycin, the aminoglycosides, minocycline and doxycycline, chloramphenicol, ampicillin, penicillin G, carbenicillin, colistin, and sulfamethoxazole-trimethoprim (19:1 ratio); sensitive to intermediate in susceptibility to tetracycline, methicillin, cefamandole, cephalothin, and clindamycin; and resistant to vancomycin. More clinical data must be obtained before an optimal therapeutic regimen can be recommended.

Anti-Bacterial Agents↗
PubMed1978

Inhibition of beta-lactamase in Neisseria gonorrhoeae by sodium clavulanate.

Sodium clavulanate at subinhibitory concentrations affected the activity of penicillin G, ampicillin, or amoxicillin on beta-lactamase-positive strains of Neisseria gonorrhoeae as demonstrated by marked reduction in the minimal inhibitory concentrations of the drugs for the organisms. The compound did not affect the activity of these penicillins on beta-lactamase-negative strains of N. gonorrhoeae. It also had no effect on the activity of cefoxitin against either beta-lactamase-negative or -positive strains. The reduction in minimal inhibitory concentrations of the penicillins for the beta-lactamase-positive organisms brought about by sodium clavulanate is probably due to inhibition of the beta-lactamase by the compound.

Anti-Bacterial Agents↗
PubMed1976

Susceptibility of ampicillin-resistant Haemophilus influenzae to seven penicillins.

Sixty-seven clinical isolates of Haemophilus influenzae from various sections of the United States, England, and Germany were tested for susceptibility to penicillin, ampicillin, amoxicillin, epicillin, carbenicillin, ticarcillin, and methicillin. Fifty-three of the strains had previously been judged to be ampicillin resistant and 14 had been determined to be ampicillin susceptible. Fifty-two of the 53 resistant strains produced beta-lactamase, but none of the susceptible strains produced it. On the basis of minimal inhibitory concentrations, the most active compounds were ticarcillin and carbenicillin. Whether this greater activity is useful clinically has not been established.

Ampicillin↗
PubMed1976

Halophilic Vibrio species isolated from blood cultures.

The Special Bacteriology Section of the Center for Disease Control has received 38 cultures of a halophilic bacterium which apparently unnamed. On the basis of the minimal characteristics of Vibrio species proposed by Hugh and Sakazaki, this bacterium belongs to the genus Vibrio. The unnamed species can be differentiated from Vibro parahaemolyticus by a lower tolerance for sodium chloride (NaC1) and the fermentation of lactose. The failure to ferment sucrose is an additional characteristic which differentiates these organisms from V. alginolyticus. Of 33 unnamed species strains tested, all were sensitive to penicillin, ampicillin, carbenicillin, cephalothin, chlorapmphenicol, gentamicin, tetracycline, rifampin, nitrofurantoin, and sulfisoxazole by agar diffusion and agar dilution tests. The sources of isolation of the cultures of the unnamed species suggest that it is a clinically important organism. Twenty strains were isolated remaining cultures were isolated from localized infections of the extremities. In contrast, only 2 of 60 cultures of V. parahaemolyticus and V. alginolyticus received in our laboratory as human isolates from extra-intestinal sources were isolated from blood.

Anti-Bacterial Agents↗
PubMed1975

Effect of calcium and magnesium ions on the susceptibility of Pseudomonas species to tetracycline, gentamicin polymyxin B, and carbenicillin.

The effect of calcium and magnesium on the susceptibility of 13 species of Pseudomonas to tetracycline, gentamicin, polymyxin B, and carbenicillin was measured. The majority of the minimum inhibitory concentrations (MICs) of these antibiotics was increased if these cations were added to the test media. The increases in MICs caused by calcium or magnesium were similar, but the combination of both ions generally caused a greater change than either alone. Although the MIC of polymyxin B was most affected by calcium and magnesium, its interpretive susceptibilities (i.e., whether susceptible or resistant) were least changed. Susceptibility tests on Pseudomonas species probably should be done with Muller-Hinton broth supplemented with physiological concentrations of calcium and magnesium to better approximate the in vivo activity of these antibiotics. When the susceptibility tests were performed with Mueller-Hinton agar, the MICs were slightly less than those obtained with Mueller-Hinton broth supplemented with both cations but greater than those obtained with Mueller-Hinton broth supplemented with individual cations.

Calcium↗