Biomedical subjects
M A Gaston
Publications and source records attributed to M A Gaston.
Health care for aging people with mental retardation.
The health practices and needs of two samples of older individuals with mental retardation were examined and contrasted over a period of 5 years. Their health status varied markedly, but most had poor health maintenance practices, and almost all had difficulty communicating with health care providers. Those who lived in community residential facilities or relatives' homes usually had adequate health care provided for them, whereas individuals who lived more independently had difficulty accessing health care. There is a pressing need for health care advocacy programs to help prevent chronic disability.
Survey of ethical issues in dental hygiene.
The purpose of this study was to determine the types and frequency of ethical problems encountered by dental hygienists, and to determine the type of instruction they have received in ethical theory and problem solving. A 40-item questionnaire mailed to 2,251 American Dental Hygienists' Association members resulted in a stratified random sample of 1,523 (68% response rate). The three ethical dilemmas most frequently encountered in dental hygiene practice are (1) observation of behavior in conflict with standard infection control procedures (66%); (2) failure to refer patients to a specialist such as a periodontist (60%); and (3) nondiagnosis of dental disease (58%). While almost 86% of the respondents received formal instruction in ethical theory, only 51% received formal instruction in methods for solving ethical problems. More hygienists (74%) felt their ethical principles were influenced by role models rather than by formal instruction (63%). This study indicates that serious ethical dilemmas are encountered by the majority of dental hygienists and that some modification of current entry-level education, as well as of continuing professional education, should be considered to prepare dental hygienists to recognize and resolve ethical problems.
Electrophoretic typing of Enterobacter cloacae with a limited set of enzyme stains.
Hospital isolates of Enterobacter cloacae were analysed by polyacrylamide gel electrophoresis for enzyme polymorphism and the results were compared with established serotyping, phage typing and biotyping techniques. Initially, the diversity of electromorphs of 13 enzymes was determined on a representative set of 62 distinct strains. Two broad clusters of strains were found in the species, and analysis by serotype suggested a limited diversity within the most frequent O serotypes. A subset of three enzymes, lactate dehydrogenase, 6-phosphogluconate dehydrogenase, glutamate dehydrogenase and an unidentified marker, were selected and used to type groups of hospital isolates. There was good general agreement between the two systems, although the enzyme method failed to distinguish between some strains with the same serotype. This method provided useful epidemiological information and, in the absence of established typing systems, it is a practical approach to subdividing the species.
Evaluation of numerical analysis of SDS-PAGE of protein patterns for typing Enterobacter cloacae.
Twenty cultures comprising 13 clinical isolates of Enterobacter cloacae from two hospitals, the type and another reference stain of E. cloacae and the type strains of four other Enterobacter sp. and of Escherichia coli, were characterized by one-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) of whole-cell proteins. The protein patterns were highly reproducible and were used as the basis of a numerical analysis which divided the clinical isolates into nine clearly defined protein types. Comparison with established typing methods indicated that the discrimination of SDS-PAGE was similar to that achieved with conventional typing methods and all strain groups recognized by combined sero/phage typing were also found by SDS-PAGE. In addition, protein typing sub-divided a group of four serotype O3 isolates that were difficult to distinguish by phage typing. We conclude that high-resolution SDS-PAGE of proteins provides an effective method of typing isolates of E. cloacae.
O-antigen specificities of the serotype strains of Serratia marcescens.
O antigens of the 24 O-serotype strains of Serratia marcescens were investigated in dot enzyme immunoassay with whole-cell antigens and by immunoblotting with lipopolysaccharide (LPS) antigens. Three pairs of strains, O2/O3, O6/O7, and O12/O14, had indistinguishable LPS antigens, despite having distinct specificities in agglutination tests with whole-cell antigens. Strong cross-reactions were also found in LPS antigens from strains O9/O15, O17/O19, O10/O22, and O16/O20. No high-molecular-weight LPS corresponding to O-side-chain material was detected in strain O11 or O13. A panel of absorbed antisera was prepared to facilitate the detection of a reduced set of LPS antigens in a dot enzyme immunoassay. We conclude that there are discrepancies between the existing serotypes as defined by agglutination tests and the antigenic composition of LPS antigens extracted from the serotype strains and that surface antigens other than LPS make a major contribution to the definition of serotype in the species.
Improved O-serotyping method for Serratia marcescens.
In a previous study, we found that some O serotypes of Serratia marcescens, as defined by agglutination tests, were not based on lipopolysaccharide (LPS) O antigens. We developed a dot enzyme immunoassay with a high degree of LPS specificity and tested 104 distinct clinical strains. Only 7 of the 24 existing O antigens were found in more than one strain: O12/O14 (30.8% of strains examined), O21 (12.5%), O8 (8.7%), O6/O7 (5.8%), O4 (3.8%), O18 (2.9%), and O9 (2.9%). Two new antigens, S1254 (13.5%) and S3255 (3.8%), were also found. Agglutination tests with O antisera identified the LPS antigen in only 36 strains. Prodigiosin production was restricted to serotypes O8, O6, and S3255 and strains with a rough or semirough LPS phenotype. Dot immunoassay appears to offer greater accuracy than agglutination tests for serotype identification in S. marcescens.
Epidemiological typing of Enterobacter aerogenes.
The applicability of Enterobacter cloacae and Klebsiella typing reagents for classifying clinical strains of Enterobacter aerogenes was evaluated. Of 75 strains, none were agglutinated by E. cloacae O antisera or were sensitive to E. cloacae bacteriophages. In contrast, 70 strains reacted with Klebsiella capsular antisera. Two-thirds of the strains were lysed by Klebsiella typing phages. A set of five E. aerogenes bacteriocin producers classified 92% of strains into 15 sensitivity types. In conclusion, E. aerogenes may be typed with Klebsiella reagents, and the simple bacteriocin test provides further discrimination between strains. The limited number of capsular antigens in the species and their apparent similarity to Klebsiella capsular antigens warrant further investigation.
Efficient selection of tests for bacteriological typing schemes.
To simplify the selection of tests for bacteriological typing methods, such as bacteriophage, bacteriocin, and biotyping, a computerised method was assessed. This uses a numerical index of discrimination (D) to facilitate the selection of an efficient typing set. The computer programs take the most discriminatory test as the initial test in the partial typing set, and then select the next test by combining each of the remaining candidates with the partial set and choosing the test which maximises D. This cycle is repeated until the remaining candidates do not increase the discriminatory power of the typing set. Options are provided for the investigator to pre-select certain tests for inclusion or exclusion from the typing set. It is concluded that the numerical index D is a simple means of test selection, but it must be emphasised that it is important to combine its use with data on the incidence of reaction in each test, on reproducibility, and on the similarity among tests.
Enterobacter: an emerging nosocomial pathogen.
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Evaluation of electrophoretic methods for typing methicillin-resistant Staphylococcus aureus.
Three electrophoretic methods of typing methicillin-resistant Staphylococcus aureus (MRSA) strains--plasmid profiles (PP), whole-cell protein profiles (WCPP) and immunoblotting profiles (IP)--were evaluated and compared with phage typing. The results obtained with isolates from 12 outbreaks were compared both within the outbreaks, to determine the consistency of results, and between outbreaks. There was generally good agreement between the typing methods but in only six outbreaks did all four methods indicate the same relationship between isolates. WCPP comprised more than 50 bands; when differences occurred, they were seen in only a few bands. In contrast, IP comprised only one or two major bands and the differences were much easier to interpret. The PPs of many of the isolates were similar; many isolates contained a plasmid of mol. wt (18-25) x 10(6). In several outbreaks both WCPP and IP showed minor differences between isolates that were not apparent with phage typing. When comparisons were made between the 12 index strains and an isolate representing the London epidemic MRSA strain, phage typing and WCPP were the most discriminatory methods; both gave nine distinct patterns, whereas there were eight IPs and only six PPs amongst the 13 strains. It was concluded that both WCPP and IP could provide valuable epidemiological data on MRSA and that IP was the easiest of the three methods to interpret.
Numerical index of the discriminatory ability of typing systems: an application of Simpson's index of diversity.
An index of discrimination for typing methods is described, based on the probability of two unrelated strains being characterized as the same type. This index may be used to compare typing methods and select the most discriminatory system.
Comparison of polyclonal rabbit antisera with monoclonal antibodies for serological typing of Pseudomonas aeruginosa.
A panel of 219 distinct strains of Pseudomonas aeruginosa were serotyped with a set of monoclonal antibodies prepared against the serotype strains of the Homma scheme (J. Y. Homma, Jpn. J. Exp. Med. 46:329-336, 1976). A total of 87.6% were typable, and there was very good agreement with the corresponding polyclonal serotype. A high proportion of strains that were polyagglutinating or nontypable with polyclonal antisera were agglutinated by antibody towards Homma group M.
Subdivision of O serotypes of Pseudomonas aeruginosa with monoclonal antibodies.
Sixteen murine monoclonal antibodies (MAbs) against serotypes O2, O5, and O16 (serogroup II) and subtypes O2b and O5d of Pseudomonas aeruginosa were evaluated by agglutination and enzyme-linked immunosorbent assay. Six MAbs that exhibited different specificities were compared with absorbed rabbit O-type antisera for the serotyping of 55 clinical isolates of serogroup II. There was good agreement between the antibodies for strains of serotypes O2 and O2b, but MAbs revealed reproducible differences between strains that were indistinguishable with rabbit antisera. The greater serotype specificity of MAbs was illustrated by the fact that only 5 of 20 strains which were agglutinated by rabbit antiserum O16 reacted with the MAb to that serotype. One antibody, M89, that reacted with 27 of 55 serogroup II strains, apparently bound to core lipopolysaccharide epitopes. Three MAbs to the frequent serotype O6 identified six subtypes, one of which accounted for over half of the clinical strains, while two subtypes were represented by single strains only. Overall, MAbs provided a greater discrimination between strains of P. aeruginosa of the same serotype than did absorbed polyclonal antisera.
Serotypes and biochemical profiles of British hospital strains of Enterobacter cloacae in relation to site of infection and antibiotic susceptibility.
Comparisons were made between the O-serotype, API 20E profile, site of isolation and antimicrobial resistance of clinical isolates of Enterobacter cloacae. Correlations were found between autoagglutinable strains and urinary-tract infection, and API 20E profile 3305573 and strains isolated from blood. The proportion of strains sensitive to amikacin, gentamicin, cefotaxime, cefuroxime and trimethoprim were 100%, 93%, 91%, 83% and 89%, respectively. No individual resistances or patterns of resistance were associated with O-serotype or biochemical profile. Strains isolated from urinary-tract infections were the most resistant, 40% being resistant to five or more antimicrobials compared to 18%, 12% and 4% for strains from blood, wounds and sputum, respectively. There were no readily identifiable phenotypes within E. cloacae that possessed unique characteristics that could contribute to infections in hospitals.
Patients' endogenous flora as the source of "nosocomial" Enterobacter in cardiac surgery.
We prospectively studied Enterobacter colonization in cardiac surgery patients receiving cefazolin prophylaxis. Fifty-eight (67%) of 87 patients became colonized, 28 by the time of admission to a Cardiac Surgery Intensive Care Unit. Enterobacter cloacae was four times more prevalent than Enterobacter aerogenes. We found increased Enterobacter colonization, after prophylaxis, in 45% of surgery patients. None of 25 control patients, who underwent coronary angioplasty and received no antibiotic prophylaxis, showed increased colonization (P = .001). Both groups had similar baseline rates of Enterobacter carriage. Typing showed 50 distinct strains of E. cloacae and 11 of E. aerogenes; 25% of patients carried greater than or equal to 2 strains simultaneously. In the nine cases of horizontal transmission, source patients were intubated for greater than or equal to 5 days and had heavy throat carriage of Enterobacter. No environmental sources of transmission were found. Clinical Enterobacter infection developed in 12 patients; at least nine of these were infected with a strain that had been isolated by surveillance culture. We conclude that Enterobacter, part of the patients' endogenous flora, becomes an important pathogen when amplified by prophylactic antibiotics and is less often transmitted horizontally.
Isolation and selection of a bacteriophage-typing set for Enterobacter cloacae.
Seventy-six phages active against Enterobacter cloacae were isolated from sewage and other sources. They were tested at RTD on 92 selected strains of E. cloacae and their lytic reactions were used to select phages for a typing set. Numerical analysis by the Jaccard coefficient was used to assess the similarity between the phages. A computer-based test selection procedure selected sub-sets of phages to discriminate between all 92 E. cloacae strains and within the most frequent serological groups. A subjective analysis of the candidate phages based on similarity, clarity of plaque and frequency of lysis was combined with the computer selected sub-sets to produce a final set of 25 phages that gave a good theoretical discrimination of clinical isolates of E. cloacae.