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D M Citron

Publications and source records attributed to D M Citron.

At least 73 records · Page 4Linked to original sources
PubMed1994

Characterization of a beta-lactamase from Clostridium clostridioforme.

A beta-lactamase-producing strain of Clostridium clostridioforme isolated from human peritoneal fluid was examined by MIC testing and enzyme characterization. MICs of penicillins (64-512 mg/L) were higher than those of cephalosporins (8-128 mg/L); the strain was susceptible to cefoxitin (8 mg/L) and imipenem (1 mg/L). No enhancement of cephalosporin activity occurred when clavulanate was also added, but a limited degree of enhancement of penicillin activity (resulting in beta-lactam MICs higher than available NCCLS breakpoints) occurred when clavulanate, sulbactam or tazobactam was added simultaneously. By contrast, addition of BRL 42715 with amoxycillin, ticarcillin or piperacillin led to a drop in beta-lactam MICs from 512 to < or = 1 mg/L, with a drop from 64 to 1 mg/L when BRL 42715 was added with cefotaxime. All inhibitors were added at fixed concentrations of 2 mg/L. As determined spectrophotometrically, the enzyme hydrolysed penicillin G, cloxacillin and piperacillin (Vmax values (%) 372, 1816, 1001, respectively relative to cephaloridine) more efficiently than cephalosporins (69-191, with cephaloridine as 100%). Km values (microM) varied between 30-308 microM (penicillins) and 2-20 microM (cephalosporins). Relative enzyme efficiency (relative Vmax/Km with cephaloridine as 100) varied from 21-100 (cephalosporins) and 8-77 (penicillins). IC50 values (microM) with nitrocefin, piperacillin and penicillin G substrates (concentrations 20, 100 and 20 microM, respectively) were > 1000, 7, 3.5 (clavulanate); > 1000, 300, 59 (sulbactam), > 1000, 29, 7.7 (tazobactam); 0.0004, 0.001, 0.0018 (BRL 42715). The enzyme was not inhibited by EDTA, cefoxitin, cloxacillin or aztreonam, but was inhibited by pCMB.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Bacterial Agents↗
PubMed1993

Empyema due to Bacteroides gracilis: case report and in vitro susceptibilities to eight antimicrobial agents.

We describe a patient with empyema due to Bacteroides gracilis and a viridans streptococcus. Therapy with both cefoxitin and imipenem failed, and the patient remained symptomatic even after thoracotomy was performed. Clinical response occurred after initiation of clindamycin therapy. The susceptibilities of the patient's isolate, other clinical strains, and the reference strain were determined by an agar dilution method. The isolates were generally susceptible to all the agents tested; however, some strains were resistant to clindamycin (MIC, 8 micrograms/mL), penicillin G (MIC90, 16 micrograms/mL), and metronidazole (MIC90, 64 micrograms/mL). The B. gracilis isolate from our patient was susceptible to all agents tested, including cefoxitin and imipenem.

Adult↗
PubMed1993

How far should a clinical laboratory go in identifying anaerobic isolates, and who should pay?

Identification of anaerobic bacteria in specimens from sites of infection due to mixed organisms can be time-consuming and expensive. Laboratories should limit anaerobic workups by testing only those specimens that have been properly collected and transported to the laboratory. Use of selective and differential media for initial processing can provide rapid and relevant information to the clinician. Anaerobes isolated from normally sterile sites and sites of serious infection should always be completely identified. Group- or genus-level identifications may suffice in other instances. The Bacteroides fragilis group of organisms should always be identified because of their virulence and resistance to many antimicrobial agents. Some of the other organisms that warrant identification include Clostridium septicum (associated with gastrointestinal malignancy); Clostridium ramosum, Clostridium innocuum, and Clostridium clostridioforme (which are resistant to antibiotics); Clostridium perfringens (a cause of potentially serious infection); anaerobic cocci (which may be resistant to metronidazole and clindamycin); and fusobacteria (which may be virulent and resistant to clindamycin and penicillin).

Bacteria, Anaerobic↗
PubMed1993

Comparative susceptibility of the Bacteroides fragilis group species and other anaerobic bacteria to meropenem, imipenem, piperacillin, cefoxitin, ampicillin/sulbactam, clindamycin and metronidazole.

The in-vitro activity of meropenem, imipenem, piperacillin, cefoxitin, ampicillin/sulbactam, clindamycin and metronidazole was determined against 395 strains of strict and facultative anaerobes, including Gardnerella vaginalis, Lactobacillus spp. and Mobiluncus spp. The activities of meropenem and imipenem were within one dilution of their MIC50 and MIC90 values. One isolate of Bacteroides fragilis, two of Bacteroides distasonis, and two of Bacteroides ovatus showed resistance or diminished susceptibility to meropenem and imipenem. Metronidazole was active against almost all obligate anaerobic isolates. Some non-spore-forming Gram-positive bacilli and lactobacilli were resistant. Ampicillin/sulbactam inhibited almost all isolates at < or = 16/8 mg/L. The activity of clindamycin and cefoxitin was relatively good, but some strains of non-fragilis B. fragilis group species were resistant. Piperacillin was the least active agent tested.

Ampicillin↗
PubMed1993

Methods for testing the susceptibility of anaerobic bacteria to two fluoroquinolone compounds, PD 131628 and clinafloxacin.

The susceptibility of anaerobic bacteria to two new fluoroquinolones, PD 131628 (the bioactive form of PD 131112 or CI-990) and clinafloxacin (CI-960 or PD 127391), was determined with the agar dilution procedures and two media, and one broth microdilution procedure. Sparfloxacin and ciprofloxacin were also tested by the broth microdilution method. One hundred anaerobic isolates and four control strains were tested by the three methods which gave minimum inhibitory concentrations (MICs) that were essentially comparable, but not identical. With the broth microdilution method, the relative potency of the four fluoroquinolones was: clinafloxacin > PD 131628 > sparfloxacin > ciprofloxacin. For the latter three drugs but not clinafloxacin, the MIC values were often near the proposed interpretive breakpoint concentrations, and thus minor methodological differences frequently influenced the interpretive categories. Replicate agar dilution tests in five laboratories established MIC control limits for each of four control strains: those MIC limits could also be used to define the expected performance of the two alternative methods.

Anti-Infective Agents↗
PubMed1993

Comparative susceptibilities of 173 aerobic and anaerobic bite wound isolates to sparfloxacin, temafloxacin, clarithromycin, and older agents.

The in vitro activities of sparfloxacin, temafloxacin, ciprofloxacin, ofloxacin, clarithromycin, erythromycin, tetracycline, cephalothin, penicillin G, and amoxicillin-clavulanic acid against 173 recent clinical bite wound isolates were determined by agar dilution. Sparfloxacin was active against all strains (MIC for 90% of strains tested, < or = 1 micrograms/ml) except for most fusobacteria and one-third of the Prevotella spp. The other fluoroquinolones had similar activities but higher MICs, especially for streptococci. Clarithromycin was more active against many isolates including Pasteurella multocida than erythromycin, with MICs of < or = 2 micrograms/ml (versus 4 micrograms/ml for erythromycin).

Animals↗
PubMed1992

Comparative activity of ciprofloxacin, ofloxacin, sparfloxacin, temafloxacin, CI-960, CI-990, and WIN 57273 against anaerobic bacteria.

The in vitro activities of seven fluoroquinolones against 290 anaerobes were determined by agar dilution. CI-960 and WIN 57273 inhibited greater than 95% of the strains at less than or equal to 2 micrograms/ml. CI-990 required less than or equal to 16 micrograms/ml. Clustering around 2 to 4 micrograms/ml was noted for Bacteroides fragilis group organisms with CI-990, sparfloxacin, and temafloxacin. Temafloxacin and sparfloxacin inhibited most strains at less than or equal to 2 micrograms/ml. B. fragilis was more susceptible to all quinolones than were the other B. fragilis group strains.

Anti-Infective Agents↗
PubMed1992

National hospital survey of anaerobic culture and susceptibility testing methods: results and recommendations for improvement.

The methods for performing anaerobic bacterial isolation and identification continue to change and improve. Anaerobic susceptibility testing has become controversial, and method-dependent variability has been noted. To assess the status of clinical anaerobic bacteriology in the United States, we surveyed, by means of a questionnaire, 120 hospitals, selected at random, with bed capacities of 200 to 1,000, and we received responses from 88 (73%). All hospitals performed cultures for anaerobes. The media and methods used for transport, initial processing, incubation, and identification varies between the different regions in the United States. Thirty percent of laboratories did not perform susceptibility studies, 16% used a reference laboratory, and 54% performed them in house. For half the laboratories, susceptibility testing was performed on isolates depending on the source; in this case, blood cultures were tested by 97% of the laboratories, serious infections were tested by 60%, sterile body sites were tested by 73%, pure cultures were tested by 47%, and tests were done by physician request by 39%. For laboratories doing testing, the broth disk method, no longer sanctioned by the National Committee for Clinical Laboratory Standards, was used most often (56%), followed by microdilution (33%), beta-lactamase testing (25%), macrotube dilution (2%), and agar dilution (2%). The antimicrobial agents tested were as follows: penicillin-ampicillin, 94%; clindamycin, 94%, metronidazole, 90%; chloramphenicol, 80%; cefoxitin, 76%; tetracyclines, 51%; and erythromycin, 45%. All other agents were tested by less than or equal to 25% of laboratories; the methods used could be improved to make the results more timely and consequently more clinically relevant.

Bacteria, Anaerobic↗
PubMed1992

Escherichia coli resistant to ampicillin/sulbactam.

Escherichia coli strains resistant to ampicillin/sulbactam from hospitals in 4 different geographic locations were examined with respect to type and amount of beta-lactamase produced. A total of 5 strains was examined from each region. The isoelectric points of all of the involved beta-lactamases were 5.4, corresponding to TEM-1. Km and Vmax values of the beta-lactamases among the clinical isolates resembled those from the control TEM-1 strain. In an 18-hour broth culture the highly resistant isolates produced 3 times more beta-lactamase as compared to the ampicillin/sulbactam-susceptible isolates. However, the highly resistant strains contained approximately the same amount of plasmid DNA (size of > 6,500 bp) as the susceptible isolates. In transformation experiments, both the resistance and the degree of resistance appeared to have been transferable by plasmids. The mechanism for resistance is likely to be a baseline overproduction of TEM-1 beta-lactamase due to either an alteration in the control of gene expression or simply to an increase in the number of copies of the beta-lactamase gene in the plasmids.

Ampicillin↗
PubMed1991

Antibacterial activity of crotalid venoms against oral snake flora and other clinical bacteria.

Despite heavy oral and fang contamination of crotalid species with a wide variety of potentially pathogenic bacteria, crotalid envenomation is associated with a low incidence of bacterial infection. Minimal inhibitory and bactericidal concentrations of venoms from three crotalid species were determined against six aerobic and eight anaerobic reference and oral crotalid microorganisms. All anaerobic isolates were resistant to greater than 20,480 micrograms/ml, whereas variable activity (range, 5-20,480 micrograms/ml) was observed for aerobic strains. Further studies against other aerobic clinical isolates demonstrated that venom had the greatest activity (MIC, less than or equal to 80 micrograms/ml) against staphylococci, Pseudomonas aeruginosa, and Enterobacter, Citrobacter, Proteus, and Morganella species. Inhibitory activity was lost with prolonged incubation for many gram-negative species. Crotalid venoms are broadly active against aerobic gram-negative and -positive bacteria. This activity may play a role in the low incidence of infection after envenomation injuries.

Animals↗
PubMed1991

A selective medium for Fusobacterium spp.

A new selective medium (JVN) for the isolation of Fusobacterium spp. from clinical material is described. The medium incorporates josamycin, vancomycin and norfloxacin (at 3, 4 and 1 microgram/ml, respectively) as the selective agents, plus 5% defibrinated horse blood in Fastidious Anaerobe Agar Base (Lab M). This formula allowed luxuriant growth of all 82 strains (eight recognized species) of fusobacteria tested, while significantly inhibiting 51/51 (100%) strains of facultative anaerobes and 45/51 (88%) strains of other obligate anaerobes. JVN medium allowed the successful isolation of strains of Fusobacterium naviforme, F. nucleatum and F. necrophorum from the gingivae of 9/16 healthy volunteers, and strains of F. varium and F. mortiferum from faecal suspensions seeded with these organisms.

Culture Media↗
PubMed1991

Susceptibility of anaerobic bacteria isolated from intra-abdominal infections to ofloxacin and interaction of ofloxacin with metronidazole.

The in vitro activities of ofloxacin alone and in combination with metronidazole against 177 anaerobic bacteria isolated from intra-abdominal infections, as determined by broth microdilution, showed that some Bacteroides fragilis strains were susceptible and that most other B. fragilis group species strains were resistant to ofloxacin. Isolates of other anaerobic species and genera, including those causing female genital tract disease, were generally susceptible to ofloxacin. Ofloxacin in combination with metronidazole usually showed an additive or indifferent interaction but no antagonism.

Abdomen↗
PubMed1991

Comparison of the inoculum effects of members of the family Enterobacteriaceae on cefoxitin and other cephalosporins, beta-lactamase inhibitor combinations, and the penicillin-derived components of these combinations.

We compared the inoculum effects of 105 recent clinical isolates of the family Enterobacteriaceae on cefoxitin, other cephalosporins, aztreonam, and three beta-lactamase inhibitors (clavulanic acid, sulbactam, and tazobactam) and their penicillin-derived components. Piperacillin and aztreonam showed the largest inoculum effect, and cefoxitin showed the smallest. The other cephalosporins tested (cefotetan, ceftizoxime, and ceftriaxone) showed an intermediate inoculum effect. In general, the inoculum effect was of greater magnitude for the penicillin and beta-lactamase inhibitor combinations than for the cephalosporins tested. Bactericidal activity was assayed and morphologic changes were monitored for selected strains exhibiting a large inoculum effect. MICs correlated with bactericidal activity at an inoculum level of 10(5) CFU/ml, while activity at 10(8) CFU/ml was variable. Cefoxitin demonstrated the least filamentous transformation and the most rapid bactericidal activity. Aztreonam showed the most marked filamentous transformation and was no longer bactericidal at 10(8) CFU/ml. The beta-lactamase inhibitor combinations showed variable bactericidal activity, and regrowth occurred with a number of strains with all three agents tested.

Anti-Bacterial Agents↗
PubMed1991

Comparison of the inoculum effect of cefoxitin and other cephalosporins and of beta-lactamase inhibitors and their penicillin-derived components on the Bacteroides fragilis group.

We compared the inoculum effects for 109 recent clinical isolates of the Bacteroides fragilis group of cefoxitin, cefotetan, ceftizoxime, ceftriaxone, and three beta-lactamase inhibitors (clavulanic acid, sulbactam, and tazobactam) and their penicillin-derived components. Bactericidal activity was assayed and morphologic changes were monitored for selected strains exhibiting a large inoculum effect. Ceftizoxime demonstrated the largest inoculum effect, followed by cefotetan and ceftriaxone. The large inoculum effect of ceftizoxime and ceftriaxone was correlated with filamentous transformation at the high inoculum (10(8) CFU/ml) and lack of bactericidal activity suggesting drug destruction or inactivation. Cefotetan was bactericidal for B. fragilis isolates but not for other members of the B. fragilis group. Cefoxitin showed the least inoculum effect and was consistently bactericidal at high (10(8) CFU/ml), standard (10(6) CFU/ml), and low (10(4) CFU/ml) inocula, followed by ampicillin-sulbactam. Piperacillin-tazobactam and ticarcillin-clavulanic acid showed an intermediate inoculum effect. The degree of inoculum effect observed generally correlated with bactericidal activity at all inocula.

Anti-Bacterial Agents↗
PubMed1991

Evaluation of the E test for susceptibility testing of anaerobic bacteria.

The susceptibilities of 105 clinical isolates of anaerobic bacteria were determined by a new method, the E test (AB Biodisk, Solna, Sweden), and were compared with the MICs for these organisms obtained by the reference agar dilution method by using supplemented brucella and Wilkins-Chalgren agars. The E test is a plastic strip with a predefined antibiotic gradient immobilized on one side and a MIC interpretive scale printed on the other side. Strips with cefoxitin, cefotaxime, imipenem, penicillin, metronidazole, and clindamycin were used in this study. A suspension of the test strain equal to the visual turbidity of a no. 0.5 McFarland standard was prepared and swabbed onto a 150-mm-diameter plate. The strips were applied in a radial fashion, and the plates were incubated under anaerobic conditions. After growth had occurred, an ellipse of inhibition was seen around each strip. At the point of intersection of the ellipse with the strip, the MIC was read from the interpretive scale. For most antibiotic-organism combinations, the ellipse was clear and the endpoint was sharp. The E-test MICs were interpreted after overnight and 48-h incubation for 58 of the strains. After overnight incubation, 87% of the E-test MICs were within 1 dilution of the agar dilution MICs, and 98% were within 2 dilutions. After 48 h of incubation, agreement was 86 and 97% respectively. E-test MICs obtained for the Bacteroides fragilis group after overnight incubation were more comparable than those obtained after 48 h of incubation to agar dilution MICs determined at 48 h for all drugs except clindamycin. On brucella agar, there was a 2% categorical discrepancy rate between the E-test MICs and agar dilution MICs, which occurred mostly with cefoxitin. The E test is easy to perform and read, is suitable for all anaerobes, can be used to test single patient isolates as needed, and offers the laboratory a reliable method for susceptibility testing of anaerobic bacteria.

Bacteria, Anaerobic↗
PubMed1990

Fastidious anaerobe agar compared with Wilkins-Chalgren agar, brain heart infusion agar, and brucella agar for susceptibility testing of Fusobacterium species.

Fastidious anaerobe agar supported the growth of 82 strains of fusobacteria better than brain heart infusion agar, brucella agar, and Wilkins-Chalgren agar. Fastidious anaerobe agar showed less hazing and fewer tailing endpoints with beta-lactam antibiotics. Whole-blood supplementation improved the performance of all media. Wilkins-Chalgren agar without blood failed to support the growth of 17% of the strains. All Fusobacterium ulcerans strains were resistant to clindamycin.

Agar↗
PubMed1990

Short prereduced anaerobically sterilized (PRAS) biochemical scheme for identification of clinical isolates of bile-resistant Bacteroides species.

The rapid identification of isolates of bile-resistant Bacteroides species has clinical and therapeutic relevance because of differences in their patterns of susceptibility and virulence. Five hundred twenty-one strains of bile-resistant Bacteroides species that were previously identified by conventional biochemical methods were reexamined to determine the minimum essential parameters necessary for correct identification. Rapid tests for bile resistance, indole production, and catalase were combined with a novel scheme for biochemical determination of saccharolytic activity on arabinose, trehalose, rhamnose, and/or xylan that included the postincubation addition of bromthymol blue for visual pH determination. Organisms were inoculated into prereduced anaerobically sterilized (PRAS) carbohydrates directly from plates, and identification was complete within 24 h of obtaining a pure culture. Ninety-three percent of bile-resistant Bacteroides species from routine clinical specimens were identified correctly by this scheme; a small number of other indole-positive strains, B. splanchnicus, B. eggerthii, and B. stercoris, were misidentified as B. uniformis.

Anaerobiosis↗