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Biomedical subjects

E O Mason

Publications and source records attributed to E O Mason.

At least 55 records · Page 3Linked to original sources
PubMed1993

Use of intravenous rifampin in neonates with persistent staphylococcal bacteremia.

Ten neonates with persistent staphylococcal bacteremia (positive blood cultures for > or = 5 days despite appropriate antibiotic therapy) received intravenous (i.v.) rifampin in combination with vancomycin with or without aminoglycoside. Their mean birth weight and length of gestation were 900 g and 27 weeks, respectively. Their ages at the time of infection ranged from 6 to 64 days (mean, 26 days). The staphylococcal isolates were methicillin-resistant Staphylococcus aureus (five isolates), methicillin-susceptible S. aureus (two isolates), and coagulase-negative staphylococci (three isolates). The mean number of bacteremia days prior to administration of i.v. rifampin was 8.3 (range, 5 to 15 days), despite a mean peak vancomycin concentration of 33 micrograms/ml. The dosing of rifampin varied from 2.5 to 10 mg/kg of body weight every 12 h. The mean duration of the rifampin course was 9.7 days (range, 3 to 16 days). Of the 10 neonates, 8 (80%) had sterile blood cultures within 24 h, 1 (10%) had a sterile blood culture within 48 h, and 1 (10%) had a sterile blood culture within 5 days of being placed on i.v. rifampin. No adverse effects were noted in this small group of infants. Seven of the 10 neonates survived; three died from unrelated complications. The MIC ranges of amikacin, vancomycin, and rifampin for the isolates were 2.0 to 16, 0.5 to 2.0, and 0.0013 to 0.04 micrograms/ml, respectively. We also studied eight infants, with a mean age of 23 days, who were receiving i.v. or oral rifampin at a dose of 10 mg/kg/day. For i.v. administration, the peak serum concentration of rifampin (mean +/- standard deviation) was 4.02 +/- 1.22 microgram/ml. The mean trough level at 12 h postifution was 1.11 +/- 0.48 micrograms/ml. For oral administration, the concentrations of rifampin in serum ranged from 0.59 to 2.86 micrograms/ml (mean, 1.86 +/- 0.96 microgram/ml) at 2 h postingestion, increasing to a peak concentration of 2.8 micrograms/ml at 8 h postingestion. The mean 12-h postingestion level was 0.77 +/- 0.03 microgram/ml. From the study of this limited series of neonates, rifampin appears to be a safe and effective addition to therapy when staphylococcal bacteremia is persistent despite vancomycin treatment.

Amikacin↗
PubMed1993

Diffusion of rifampin and vancomycin through a Staphylococcus epidermidis biofilm.

Using an equilibrium dialysis chamber, we evaluated the penetration of vancomycin, rifampin, or both through a staphylococcal biofilm to simulate treatment of an infected biomedical implant. A biofilm of ATCC 35984 (slime-positive Staphylococcus epidermidis; vancomycin MIC and MBC, 1 and 2 micrograms/ml, respectively; rifampin MIC and MBC, 0.00003 and 0.00025 micrograms/ml, respectively) was established on the inner aspect of the dialysis membrane (molecular mass exclusion, 6,000 kDa). Serum containing vancomycin (40 micrograms/ml), rifampin (20 micrograms/ml), or a combination of both was introduced into the inner chamber of the dialysis unit (in direct contact with the biofilm), and serum alone was added to the outer chamber. Rifampin and vancomycin concentrations in both chambers were determined over a 72-h period. In the absence of rifampin, the concentration of vancomycin in the outer chamber exceeded the MBC for the organism after 24 h, and the MBC increased to nearly 8.0 micrograms/ml by 72 h, demonstrating that therapeutic levels of vancomycin can penetrate a staphylococcal biofilm. However, viable bacteria were recovered from the biofilm after 72 h of treatment with no apparent increase in the MIC or MBC of vancomycin. Similarly, concentrations of rifampin exceeding the MBC were detected in the outer chamber after 24 h of treatment, but viable organisms were recovered from the biofilm after 72 h of treatment. In this case, the rifampin MBCs for surviving organisms increased from 0.00025 to > 128 micrograms/ml. The combination of agents prevented the development of resistance to rifampin, improved the perfusion of vancomycin through the biofilm, and decreased the penetration of rifampin but did not sterilize the membrane. These observations provide evidence that bactericidal levels of vancomycin, rifampin, or both can be attained at the surface of an infected implant. Despite this, sterilization of the biofilm was not accomplished after 72 h of treatment.

Bacterial Adhesion↗
PubMed1993

Testing of Streptococcus pneumoniae for resistance to penicillin.

The increasing prevalence of penicillin-resistant Streptococcus pneumoniae requires antibiotic susceptibility tests that can be done with greater ease and reliability. We measured the MIC of penicillin for pneumococci by the tube macrodilution method with Mueller-Hinton broth (MHB), Haemophilus Test Medium (HTM), Todd-Hewitt broth with 0.5% yeast extract (THY), and MHB with 3% lysed horse blood (LHB). Eight (19%) and 6 (14%) of 42 pneumococcal isolates failed to generate turbid growth in MHB and HTM, respectively, whereas all pneumococcal isolates did so in THY and LHB. For those strains that replicated to turbidity, the mean MICs of penicillin were lower in MHB and HTM than in THY and LHB, with differences being significant (P < 0.05) for comparisons with LHB. Four isolates appeared to be penicillin susceptible in HTM but were actually moderately resistant in THY and LHB, and two isolates appeared to be moderately resistant but were resistant. A similar failure to detect resistance was seen with MHB. S. pneumoniae ATCC 49619, a moderately penicillin-resistant strain that has been proposed for quality control testing, gave variable results in MHB or THM and appeared to be susceptible to penicillin in some assays, whereas the MICs for S. pneumoniae ATCC 49619 in THY or LHB fell within a twofold dilution range, with geometric means of 0.16 and 0.18 micrograms/ml, respectively. Pneumococcal isolates thus may appear falsely susceptible to penicillin when tested in MHB or HTM. LHB remains the standard medium; however, because THY is an easily prepared clear medium that can be used in automated systems and appears to yield results similar to those obtained with LHB, THY deserves consideration for routine use.

Culture Media↗
PubMed1993

Penicillin-resistant systemic pneumococcal infections in children: a retrospective case-control study.

OBJECTIVE: To determine whether there are any risk factors that differentiate children with systemic infections due to Streptococcus pneumoniae relatively or fully resistant (minimum inhibitory concentration > 0.1 microgram/mL) to penicillin from those children with infections due to S pneumoniae susceptible to penicillin. DESIGN: Retrospective case-control study. SETTING: A large children's hospital. PARTICIPANTS: Forty-three children with systemic penicillin-resistant S pneumoniae infections identified at Texas Children's Hospital over the 51-month period from January 1989 through March 1993. Each case had one or two controls matched only for age and date of S. pneumoniae infection. Sixty-six controls were selected from a group of 341 children with susceptible isolates. OUTCOME MEASURES: Variables compared included gender, race, diagnosis, underlying conditions, past hospitalization, geographic area of residence, antibiotic use in past month, amoxicillin-clavulanic acid use in past month, and outcome. RESULTS: Thirty-seven patients (86%) had relatively resistant isolates (minimum inhibitory concentration range 0.125 to 1.0 microgram/mL) and six patients (15%) had fully resistant isolates (minimum inhibitory concentration range 2.0 to 8.0 micrograms/mL). Thirty-three percent of the cases vs 36% of the controls had underlying conditions. Seventy-one percent of the cases vs 39% of the controls had received antibiotics in the previous month. Compared with their matched controls, the patients with penicillin-resistant systemic pneumococcal infections were more likely (P = .02) to have received a course of antibiotics within the month prior to their infection. CONCLUSION: The only identified associated risk factor in children who developed a systemic penicillin-resistant pneumococcal infection appears to have been the use of antibiotics within the month prior to their infection.

Case-Control Studies↗
PubMed1992

Immunogenicity of Haemophilus influenzae type b polysaccharide-tetanus protein conjugate vaccine in children with sickle hemoglobinopathy or malignancies, and after systemic Haemophilus influenzae type b infection.

To determine the immunogenicity of Haemophilus influenzae type b polysaccharide-tetanus protein conjugate vaccine in specific populations at risk, we administered vaccine to children with sickle cell anemia (n = 19; mean age, 18.3 months, malignancies (n = 18; mean age, 43.1 months), or a recent history of systemic H. influenzae type b infection (n = 17; mean age, 11.9 months). After one dose of polyribosylribitol phosphate-tetanus toxoid conjugate vaccine the geometric mean titers for polyribosylribitol phosphate antibody were 4.8 micrograms/ml (14/19 greater than 1 microgram/ml), 1.4 micrograms/ml (9/18 greater than 1 microgram/ml), and 5.6 micrograms/ml (15/17 greater than 1 microgram/ml) in these three groups, respectively. Children with sickle cell anemia or a recent history of systemic H. influenzae type b infection had polyribosylribitol phosphate antibody levels comparable to those of normal children of similar age after one or two doses of polyribosylribitol phosphate-tetanus toxoid conjugate vaccine. We conclude that this vaccine is immunogenic in children with underlying conditions associated with an increased risk of H. influenzae type b infection.

Anemia, Sickle Cell↗
PubMed1992

Interaction of Citrobacter diversus strains with HEp-2 epithelial and human umbilical vein endothelial cells.

More than 75% of neonates with Citrobacter diversus meningitis develop brain abscesses. Interaction of C. diversus strains with HEp-2 and human umbilical vein endothelial cells (HUVEC) was studied to examine mechanisms related to brain abscess formation. Two of 9 strains invaded HEp-2 cells and 0 of 6 invaded HUVEC better than the others. C. diversus survived at least 20 h within HEp-2 cells (in decreasing numbers). Adhesion to HEp-2 cells was increased in 3 of 4 strains expressing type 1 fimbriae, but this did not correlate with increased invasion. Inhibition of RNA or protein synthesis blocked invasion but not adhesion. Thus, invasion requires ongoing protein synthesis, and adhesion to and invasion of HEp-2 cells by type-1-fimbriated strains are independent steps. Invasion was inhibited by cytochalasin D. A 32-kDa protein found in cerebrospinal fluid isolates of C. diversus was not related to invasion of either cell line. Ability to invade HEp-2 cells was not increased among strains isolated from central nervous system sources.

Bacterial Adhesion↗
PubMed1992

Increased rate of isolation of penicillin-resistant Streptococcus pneumoniae in a children's hospital and in vitro susceptibilities to antibiotics of potential therapeutic use.

The isolation of Streptococcus pneumoniae with both high and intermediate resistance to penicillin has increased in our institution since 1989 to an average of 12.1% of all isolates. We determined the susceptibilities of 95 isolates (34 susceptible to penicillin, 42 intermediate in resistance to penicillin, and 19 resistant to penicillin) to 16 antimicrobial agents of potential use in the treatment of disease caused by S. pneumoniae. Susceptibility to penicillin was determined by broth macrodilution with Mueller-Hinton broth supplemented with 5% lysed horse blood. Isolates were classified as highly resistant when the MIC was greater than or equal to 2.0 micrograms/ml, intermediate in resistance when the MIC was between 0.1 and 1.0 microgram/ml, and susceptible when the MIC was less than 0.1 microgram/ml. Fifteen of 19 isolates found to be highly resistant to penicillin were recovered from the middle ear of children. None of the isolates recovered from cerebrospinal fluid was highly resistant to penicillin. Fifteen of these isolates highly resistant to penicillin were found to be serogroup 6. Susceptibilities to other antibiotics were determined by the agar dilution method with Mueller-Hinton agar containing 5% lysed horse blood and an inoculum of 10(4) CFU per spot delivered by a replicator device. The MIC for 90% of isolates increased with increasing penicillin resistance for all antibiotics tested, except chloramphenicol, ciprofloxacin, rifampin, and vancomycin. Regardless of the classification of penicillin resistance, all isolates were classified as susceptible to cefotaxime, cefpirome, cefpodoxime, clarithromycin, imipenem, rifampin, and vancomycin on the basis of National Committee for Clinical Laboratory Standards interpretive guidelines. Interpretation of susceptibilities on the basis of currently available guidelines is difficult in that susceptibility guidelines applicable specifically to S. pneumoniae are not available.

Anti-Bacterial Agents↗
PubMed1992

Systemic infections due to Streptococcus pneumoniae relatively resistant to penicillin in a children's hospital: clinical management and outcome.

Streptococcus pneumoniae isolates relatively (0.1 microgram/mL < minimum inhibitory concentration < or = 1.0 microgram/mL) resistant to penicillin (RRP) have been recovered worldwide, but reports of therapy and outcome of systemic infections due to these strains are limited. This retrospective study of prospectively identified patients reviews the clinical features, management, and outcome of 19 children with systemic infections due to S pneumoniae. From January 1, 1989 to December 31, 1991, 13 of 244 blood (5.3%) and 4 of 32 cerebrospinal fluid (12.5%) pneumococcal isolates were relatively resistant to penicillin. The serotypes were as follows: 14 (12 isolates), 6 (4 isolates), 19 (2 isolates), 23 (1 isolates). One peritoneal fluid isolate and one joint fluid isolate were also relatively resistant to penicillin. The mean age of the 19 patients was 30 months (range 5 to 104 months), and five children had underlying disorders. Eleven children (nine inpatients) were treated initially with a parenteral cephalosporin. Six patients were treated as outpatients, and all had (occult) bacteremia. Three of these patients received ceftriaxone intramuscularly in the emergency department; five were treated with amoxicillin/clavulanic acid, and one received amoxicillin. Seven of 13 children treated in the hospital became afebrile in 48 hours. Three others were afebrile from the time of admission. Repeat blood cultures obtained within 24 to 48 hours after therapy was initiated were sterile in 10 children. All but one child responded to initial therapy. The recovery of S pneumoniae isolates relatively resistant to penicillin has increased in our hospital during the last 3 years.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Bacterial Agents↗
PubMed1991

Hematogenous pneumococcal meningitis in the infant rat: description of a model.

Sensorineural deafness occurs in 20%-30% of children after Streptococcus pneumoniae meningitis. An infant rat model of S. pneumoniae meningitis was developed to study the pathogenesis of inner ear invasion by S. pneumoniae. S. pneumoniae type 6 was administered intraperitoneally (inoculum: 1-10 x 10(8) cfu) every 24 h for 3 days to 5-day-old rats. Bacteremia (12 [50%] of 24) and meningitis (11 [46%] of 24) were detected most frequently 4 days after the three doses. The mean cerebrospinal fluid (CSF) white blood count for rats with positive CSF cultures was 7271/mm3 (range, 81-20,475). Hematoxylin-eosin-stained brain tissue from the 11 rats with positive CSF cultures showed inflammation in the meninges and scala tympani in 9 each (82%), and scala vestibuli in 6 (55%), but none in the scala media. Gram's-stained brain and inner ear sections from the same 11 rats showed organisms in the meninges in 5 (45%) and scala tympani or vestibuli in 2 (18%). Perilymphatic inflammation occurred significantly (P less than .001) more than did endolymphatic inflammation.

Animals↗
PubMed1991

Effect of dexamethasone or HWA-138 in combination with antibiotics in experimental Haemophilus influenzae type b infection.

Modulation of the host's inflammatory response in bacterial meningitis may be beneficial. In this study, the effects of dexamethasone and HWA-138, an analog of pentoxifylline, on CSF cultures and cochlear inflammation in an infant rat model of Haemophilus influenzae type b were studied. Five-day-old infant rats were inoculated once intraperitoneally with 1 x 10(4) to 10 x 10(4) CFU of H. influenzae type b (strain 1406). Twenty-four hours later, infant rats were treated intraperitoneally with one dose of ampicillin (0.1 mg/g of body weight), cefotaxime (0.05 mg/g), or cefuroxime (0.05 mg/g) alone or in combination with one dose of dexamethasone (0.00015 mg/g) or HWA-138 (0.005 mg/g). Twenty-four hours after treatment with cefuroxime plus dexamethasone, animals had a significantly (P less than or equal to 0.04) greater incidence of bacteremia and meningitis (eight of nine animals) than that in animals of the other treatment groups. Overall, dexamethasone was associated with less inflammation (P less than 0.04) of the cochlear nerve compared with that from antibiotic treatment alone. In this model, when suboptimal antimicrobial therapy is administered, anti-inflammatory agents may be beneficial with respect to reducing cochlear inflammation. However, dexamethasone and cefuroxime lead to a higher rate of positive blood and cerebral spinal fluid cultures than cefuroxime alone.

Ampicillin↗
PubMed1991

A randomized clinical trial of ampicillin, gentamicin and clindamycin versus cefotaxime and clindamycin in children with ruptured appendicitis.

This prospective, randomized, double-blind study compares the efficacy, safety and cost-effectiveness of ampicillin, gentamicin and clindamycin (AGC) or cefotaxime and clindamycin (CC) for the treatment of children with complicated appendicitis. Ninety-seven children were randomized. Forty-seven were assigned to the AGC regimen and 50 received CC. Forty-two patients in the AGC group had an appropriate therapeutic outcome, whereas 48 of 50 children who received CC completed the trial successfully (p = NS). There were no differences between the groups with reference to the duration of antibiotic administration, fever, leukocytosis or length of hospitalization. Complications of therapy were uncommon and neither regimen demonstrated a significant advantage from an economic standpoint. We concluded that, in childhood, complicated appendicitis can be treated with either CC or AGC with equal efficacy.

Adolescent↗
PubMed1991

A preliminary report of ticarcillin and clavulanate versus triple antibiotic therapy in children with ruptured appendicitis.

Standard therapy for childhood ruptured appendicitis includes combination antibiotic therapy with ampicillin, gentamicin and clindamycin. Complicated dosing schedules and the possibility of aminoglycoside toxicity make alternatives desirable. One such alternative is Timentin (a combination agent of ticarcillin disodium and clavulanate potassium). This agent has a more convenient dose schedule than standard therapy and eliminates the possibility of aminoglycoside ototoxicity and nephrotoxicity. It is active in vitro against most pathogens associated with ruptured appendicitis in children. The preliminary results of an ongoing prospective, open label, randomized trial comparing ticarcillin and clavulanate with ampicillin, gentamicin and clindamycin in childhood ruptured appendicitis are reported herein. While further evaluation is necessary, we have found single agent therapy with ticarcillin and clavulanate to be equivalent in safety and efficacy to standard combination therapy. Also discussed are the relative merits of immediate versus delayed primary closure of the abdominal wound after appendectomy.

Anti-Bacterial Agents↗
PubMed1990

Recurrent meningitis and Mondini dysplasia.

Three infants with cerebrospinal fluid otorrhea and recurrent meningitis due to Mondini dysplasia have been treated at Baylor College of Medicine, Houston, Tex; 39 other patients with this association have been described. This review highlights the characteristics and embryologic basis of the malformation. The clinical evaluation of an infant with recurrent meningitis is outlined, and the importance of brain-stem response audiometry and thin-cut computed tomography of the temporal bones is discussed. Surgical management depends on the functional status of the dysplastic ear; usually, a stapedectomy is performed and the vestibule is obliterated. Although the surgical failure rate is 30% after one procedure, early identification of the dysplasia and prompt surgical management diminish morbidity and mortality and permit early habilitation of the child with congenital hearing impairment.

Audiometry, Evoked Response↗
PubMed1990

Cerebrospinal fluid values in the very low birth weight infant.

The cerebrospinal fluid values obtained in the first 12 weeks of life from 43 infants with birth weights of 1500 gm or less were analyzed to determine the ranges for leukocyte count and chemistry values. All these neonates had birth weights appropriate for gestational age, negative cerebrospinal fluid culture for bacteria, and no evidence of intracranial bleeding by head ultrasound examination. The mean birth weight was 1002 gm (range 550 to 1500 gm), and mean gestational age was 27 weeks (range 24 to 33 weeks). The mean cerebrospinal fluid leukocyte count was 5 cells/mm3 (range 0 to 44 cells/mm3); leukocyte differential was 7% polymorphonuclear leukocytes (range up to 66%) and 85% mononuclear leukocytes (range 13% to 100%). Additional values included protein concentration, 142 mg/dl (range 45 to 370 mg/dl); and glucose, 60 mg/dl (range 29 to 217 mg/dl). Knowledge of these measurements should help in the interpretation of the cerebrospinal fluid values of the very low birth weight infant undergoing examination of a central nervous system disorder.

Birth Weight↗
PubMed1990

Pilus- and non-pilus-mediated interactions of Haemophilus influenzae type b with human erythrocytes and human nasopharyngeal mucosa.

The role of pili of Haemophilus influenzae type b (Hib) in binding to human erythrocytes and in colonization and invasion of human nasopharyngeal (NP) organ cultures has been evaluated. Hib strains 1009 and 1007, NP and cerebrospinal fluid isolates from the same child with Hib meningitis, were studied. Strain 1009 was piliated (P+), produced pilin of approximately 24 kDa, and was hemadsorption-positive (HA+); strain 1007 was nonpiliated (P-), did not produce pilin, and was hemadsorption-negative (HA-). The rate of transition from one hemadsorption phenotype to the other in broth cultures and NP organ culture supernatants was 3 x 10(-4) per bacterium per generation for HA+ to HA- and 7 x 10(-4) per bacterium per generation for HA- to HA+. Growth in human NP organ culture supernatants of the P+HA+ strain was greater than that of the P-HA- strain at 6 and 12 h after infection. No difference was noted when the strains were grown in nutrient broth. Strain 1009 (P+HA+) attached in large clusters to cellular debris and nonciliated cells, a phenomenon never noted with strain 1007 (P-HA-). NP organ cultures infected with strain 1007 showed greater mucosal invasion than those infected with the 1009 strain. While P+HA+ and P-HA- Hib both attached to NP mucosa, P+HA+ strains may have a selective advantage in mucosal colonization but P-HA- strains may be more invasive.

Bacterial Adhesion↗