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D F Welch

Publications and source records attributed to D F Welch.

71 records · Page 4Linked to original sources
PubMed1982

In vitro activity of antibiotics commonly used in the treatment of otitis media against Streptococcus pneumoniae isolates with different susceptibilities to penicillin.

Susceptibilities of 82 clinical isolates of Streptococcus pneumoniae, including 25 from the middle-ear fluid, were evaluated against antibiotics commonly used in the treatment of acute otitis media. Potentially significant resistance occurred in 6% of the isolates to erythromycin and an erythromycin-sulfisoxazole combination. The combination of trimethoprim and sulfamethoxazole was synergistic for 95% of the isolates. Only 2.5% of all of the isolates were resistant to both erythromycin-sulfisoxazole and trimethoprim-sulfamethoxazole. The presently used drug regimens should be effective against the majority of S. pneumoniae isolates in otitis media.

Anti-Bacterial Agents↗
PubMed1982

Cefoperazone: regression analysis, disk content, and disk susceptibility testing considerations.

Cefoperazone agar dilution minimal inhibitory concentration (MIC) susceptibility results were compared with zones of inhibition produced by disk diffusion susceptibility testing. Disks containing 30, 50, 75, and 100 micrograms of cefoperazone were tested for purposes of regression line comparisons and error rate-bounded analysis. Results suggest that if the MIC equivalent of susceptibility is 32 micrograms/ml, either a 50-micrograms disk with zone sizes of susceptibility (S) greater than or equal to 15 mm and resistance (R) less than or equal to 12 mm or a 75-micrograms disk with zone sizes of S greater than or equal to 17 mm and R less than or equal to 14 mm may be appropriate. If the MIC equivalent of susceptibility is 64 micrograms/ml, this would dictate use of a 75-micrograms disk with zone sizes of S greater than or equal to 17 mm and R less than or equal to 12 mm. Disks containing either less than or equal to 30 or greater than or equal to 100 micrograms of cefoperazone did not adequately discriminate among susceptible and resistant bacterial strains at either the 32- or 64-micrograms/ml MIC equivalent.

Anti-Bacterial Agents↗
PubMed1982

Differentiation of Haemophilus spp. in Respiratory isolate cultures by an indole spot test.

Indole spot tests using isolated, nonhemolytic colonies of Haemophilus species were positive for 90 of 151 (60%) respiratory isolates of Haemophilus influenzae, whereas 67 to 72 (93%) isolates of H. influenzae from cerebrospinal fluid and blood specimens were indole positive. Only 4 of 117 (3%) Haemophilus parainfluenzae isolates were positive for indole spot tests. Thus, indole-positive, nonhemolytic Haemophilus isolates in respiratory cultures can be presumptively identified as H. influenzae.

Bacteriological Techniques↗
PubMed1982

Evaluation of Bactogen and Phadebact for detection of Haemophilus influenzae type b antigen in cerebrospinal fluid.

Latex agglutination and coagglutination tests are commercially available as Bactogen and the Phadebact Haemophilus Test, respectively. We evaluated both for the detection of Haemophilus influenzae type b in cerebrospinal fluids. Both tests were positive in all of 51 culture-positive cases of meningitis caused by H. influenzae. Both were more sensitive than counterimmunoelectrophoresis. Antigen was also detected by Bactogen in seven of seven additional cerebrospinal fluid specimens (compared with four of seven by Phadebact) after 1 to 15 days of antimicrobial therapy. The cerebrospinal fluid of infants with meningitis owing to other common causative agents did not react with Bactogen or Phadebact. However, the cerebrospinal fluid of one patient with overwhelming infection owing to Proteus mirabilis reacted positively with Bactogen. Cost analysis revealed that Phadebact was less expensive to perform than Bactogen.

Agglutination Tests↗
PubMed1982

In vitro activity of moxalactam and cefoperazone against Streptococcus pneumoniae with differing susceptibilities to penicillin.

In vitro studies were performed to examine the potential usefulness of two new drugs, moxalactam and cefoperazone, for the treatment of infections caused by Streptococcus pneumoniae. 34 isolates of S. pneumoniae with differing susceptibilities to penicillin were examined by disk diffusion, agar and microbroth dilution methods. Isolates highly resistant to penicillin (MIC greater then 1 microgram/ml) were also resistant to moxalactam (MIC = 128 micrograms/ml) but were sensitive to cefoperazone (MIC = 2--4 micrograms/ml). All isolates relatively resistant to penicillin (MIC 0.25--0.5 micrograms/ml) were sensitive to cefoperazone (MIC 0.25--1 microgram/ml) and had moxalactam MICs of 4--16 micrograms/ml for 10/12 isolates. The disk diffusion test was unreliable for detecting strain relatively resistant to moxalactam. These studies showed that cefoperazone is more active than moxalactam in vitro against S. pneumoniae regardless of the penicillin susceptibility of these bacteria.

Cefoperazone↗
PubMed1981

Susceptibility of group A beta-hemolytic Streptococcus isolates to penicillin and erythromycin.

We have reevaluated the antibiotic susceptibilities of group A beta-hemolytic streptococci in view of recent reports of a high prevalence of erythromycin resistance in Japan and of an increase in penicillin treatment failures in the United States. A total of 474 isolates recovered during a 2- to 3-month period in 1980 were tested. All were susceptible by microtiter broth dilution to a penicillin concentration of less than or equal to 0.03 micrograms/ml (minimal inhibitory concentration), and 473 were killed by less than or equal to 0.06 micrograms/ml (minimal inhibitory concentration). Erythromycin minimal inhibitory concentrations showed a bimodal distribution: 95% were less than or equal to 0.06 micrograms/ml, and 5% were greater than or equal to 1 microgram/ml. Of the minimal bactericidal concentrations, 21% were greater than or equal to 1 microgram/ml and 3% were greater than or equal to 16 micrograms/ml. Group A beta-hemolytic streptococci remain susceptible to the inhibitory and bactericidal actions of penicillin, thus providing no in vitro explanation for the bacteriological relapses reported in some clinical studies. Unlike the Japanese experience, only 5% of our isolates were resistant to erythromycin (minimal inhibitory concentration, greater than or equal to 1 microgram/ml); however, 22% were tolerant (ratio of minimal inhibitory/bactericidal concentrations, greater than or equal to 32).

Erythromycin↗
PubMed1980

Antimicrobial susceptibility testing of Streptococcus pneumoniae by micro-broth dilution.

Thirty-three clinical isolates of Streptococcus pneumoniae were tested for susceptibility to penicillin and ampicillin by a standard agar dilution method. Results were compared to those obtained using a micro-broth dilution technique in which Mueller-Hinton broth was supplemented with 5% difibrinated whole sheep blood. Among the 33 strains, 2 were resistant (minimal inhibitory concentration, 8 micrograms/ml), 10 were relatively resistant (minimal inhibitory concentration, 0.12 to 0.5 micrograms/ml), and 20 were susceptible (minimal inhibitory concentration, less than or equal to 0.06 micrograms/ml) to penicillin by both methods. Only one stain showed a two-dilutional-step difference by micro-broth and agar dilution testing resulting in categorization as relatively resistant by the former method but susceptible by the latter. A 1-microgram oxacillin disk correctly identified 11 of the 12 resistant strains. The micro-broth dilution technique is a reliable, simple method for penicillin or ampicillin susceptibility testing of pneumococci and economically feasibile to perform manually or with a semiautomated system.

Ampicillin↗
PubMed1980

Use of preserved organisms for individual test-use quality control of bacterial typing antisera.

Bacterial antigens representing 14 of the most common clinical isolates requiring serological confirmation for identification were prepared. These antigens were stable for periods in excess of 5 months, readily available, and sero-specific. Use of these antigens for quality control of bacterial typing antisera increased the accuracy, reduced the technician time, and obviated the delay which otherwise occurred while stock isolates were subcultured to provide a sero-specific control for this procedure.

Antigens, Bacterial↗
PubMed1980

Identification of toxigenic Clostridium difficile by counterimmunoelectrophoresis.

A counterimmunoelectrophoresis (CIE) technique which reacted positively with culture filtrates of Clostridium difficile was developed and compared with a cytotoxicity assay in human embryonic lung cell cultures. CIE, employing C. sordellii antitoxin, detected 17 of 17 C. difficile strains. Of those positive by CIE, 13 were cytotoxic in cell culture. Fourteen Clostridium species other than C. difficile, C. sordellii, and C. bifermentans were negative by CIE. C. sordellii and C. bifermentans gave positive CIE results but were not cytotoxic. Similar sensitivity of toxin detection was observed for both methods. Optimal conditions for performing CIE included use of 48-h chopped meat-glucose broth cultures as the antigen source, use of a 10x-concentrated U.S. Standard C. sordillii antitoxin, and electrophoresis for 1.5 h in 0.05 M tris(hydroxymethyl)aminomethane-barbital-sodium barbital, pH 8.8, at a constant current of 6 mA/slide. CIE appears to be a suitable alternative to the cytotoxicity assay and may serve as a means for presumptive identification of C. difficile.

Antitoxins↗
PubMed1980

Bactericidal activity of cefoperazone in comparison with other beta-lactam antibiotics and gentamicin.

Killing curves were employed to determine the in vitro bactericidal activity of cefoperazone against several aerobic bacterial species of clinical origin. Cefoperazone was bactericidal at concentrations equal to, or greater than, the minimal inhibitory concentration (MIC) but allowed regrowth of the organisms after four to six hours when tested in concentrations of one-fourth or one-half the MIC. Comparative studies with gentamicin, LY127935 (moxalactam), piperacillin, cefamandole, and cephalothin indicate that, in general, cefoperazone demonstrated similar killing activity as other beta-lactam compounds, with some strain differences noted. Gentamicin, as the representative aminoglycoside, demonstrated a greater rate of bactericidal activity than the beta-lactam compounds studied.

Cefoperazone↗
PubMed1979

Antimicrobial susceptibility testing of Mycobacterium fortuitum complex.

A total of 24 strains of the Mycobacterium fortuitum complex were tested for susceptibility to antimicrobial agents by the disk diffusion and agar dilution techniques. By comparing zones of inhibition obtained with the disk diffusion technique with results of minimal inhibitory concentration determinations, it was shown that disk diffusion results could predict in vitro susceptibility to selected antimicrobial agents. All of 17 strains of M. fortuitum were susceptible to </=1 mug of amikacin per ml. The corresponding average zone of inhibition around a 10-mug amikacin disk was 37 mm. Seven M. chelonei strains were more resistant to amikacin, with minimal inhibitory concentrations ranging from 1 to 32 mug/ml, and the corresponding average zone size was 21 mm. Susceptibility of both M. fortuitum and M. chelonei to tetracycline was variable and none of the M. chelonei strains was inhibited by polymyxin B, whereas M. fortuitum strains consistently had zones of inhibition around the polymyxin disk. It appears that identification to species of the M. fortuitum complex may be of importance with regard to antibiotic susceptibility. Separation of M. fortuitum and M. chelonei was readily accomplished in the present study by the nitrate reduction and 3-day arylsulfatase tests.

Aminoglycosides↗
PubMed1979

Relationship between superoxide dismutase and pathogenic mechanisms of Listeria monocytogenes.

Listeria monocytogenes was examined for superoxide dismutase(SOD) activity. Two catalase-negative strains possessed at least twofold greater SOD activities than the catalase-positive L. monocytogenes strains examined. Growth conditions such as aeration and iron concentration influenced the specific activity of SOD obtained from cells cultured in defined media. L. monocytogenes SOD from crude extracts and after partial purification was analyzed by polyacrylamide gel electrophoresis. Iron was associated with the single band of SOD activity detected in the gels. SOD activity appeared to be primarily extracytoplasmic. Survival of organisms in a superoxide-generating medium was studied, with photoactivation of riboflavin used as the source of free radical formation. Virulent, catalase-positive L. monocytogenes strains were relatively resistant to killing in a pH 7 superoxide-containing medium. An intact-cell assay for SOD was developed, which used the superoxide-generating system and employed the superoxide-dependent oxidation of sulfite, added to the medium, and inhibition of this oxidation by SOD. Maximal SOD activites of intact cells were observed when 100 to 400 micrograms (dry weight) of viable Listeria cells per ml was added to the medium. A possible role for SOD in the pathogenesis of listeric infection is discussed.

Fungal Proteins↗
PubMed1979

Sputum screening by Nomarski interference contrast microscopy.

Gram-stained smears of specimens submitted for sputum cultures were compared with direct wet mounts examined by Nomarski interference contrast microscopy (NIM) for enumeration of squamous epithelial cells (EPC) and leukocytes (WBC). The results obtained by the two methods were comparable, but specimens were more rapidly screened and cell types were more readily differentiated by NIM. Specimens submitted for sputum culture over a 3-month period were examined for EPC and WBC by NIM. Twenty-two percent of the specimens had greater than 25 EPC/field or a predominance of EPC (class I), 30% had greater than 25 EPC and greater than 25 WBC/field (class II), and 48% had greater than 25 WBC/field or a predominance of WBC (class III). The clinical relevance of the culture results was determined by reviewing the records of patients whose specimens were included in the study. Class I specimens provided only 30% clinically relevant culture results. Specimens in class II provided useful culture results in 63% of the patients, and 96% of those in class III provided clinically relevant information. The results confirm the value of sputum screening and demonstrate that NIM provides a rapid, simple, and accurate method for sputum screening.

Diagnosis, Differential↗
PubMedDate not supplied

Comparison of lysis-direct plating and broth methods for pediatric blood cultures: clinical relevance and cost effectiveness.

To determine the clinical significance and therapeutic impact of pediatric blood cultures, we analyzed 1650 cultures comparing conventional broth and direct plating methods. The rate of positive cultures was 5.8%. Of 96 positive cultures 68 were deemed clinically significant. The mean time to detection was 23.8 and 33.7 hours, and the sensitivity was 89 and 83% in the Isolator and broth systems, respectively. The overall rate of insignificant isolates was 1.7% and was similar for both methods. Clinical interventions based on blood culture results occurred in 39 patients, primarily those with pneumococcal and staphylococcal bacteremia. Only six of 28 clinically insignificant isolates had negative impact. Use of the pediatric Isolator permitted earlier institution of appropriate therapies and shorter duration of unneeded or toxic therapies without frequent negative impact. Since direct costs were comparable the Isolator system may be a clinically valuable and cost effective alternative to conventional methodology.

Bacterial Infections↗
PubMedDate not supplied

Microbiology of recently treated acute otitis media compared with previously untreated acute otitis media.

Isolates were obtained from 169 middle ear aspirates of 148 children with recently treated acute otitis media (RTOM) and from 123 aspirates of 84 children with previously untreated acute otitis media (UOM). In RTOM Streptococcus pneumoniae and Group A streptococcus (P less than 0.02) were recovered less frequently whereas Staphylococcus aureus (P less than 0.001) and Haemophilus influenzae (P less than 0.02) were recovered more frequently than in UOM. Patients with RTOM had more beta-lactamase-producing organisms and multiple isolates. Bilateral sterile aspirates were more common in RTOM although bilateral otitis media was more common in UOM. In RTOM most Branhamella catarrhalis isolates were co-pathogens whereas Staphylococcus epidermidis were always isolated in pure culture. Amoxicillin was the antimicrobial most frequently (83.9%) received for the recently treated episode of otitis media. In RTOM 62.4% of isolates were susceptible to previously prescribed antibiotics, suggesting that factors other than antimicrobial susceptibility are also important in the occurrence of RTOM.

Acute Disease↗