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P F Wheat

Publications and source records attributed to P F Wheat.

At least 19 recordsLinked to original sources
PubMed2001

History and development of antimicrobial susceptibility testing methodology.

Antimicrobial susceptibility testing (AST) is performed daily on bacterial isolates in clinical laboratories. The techniques employed are often taken for granted. This paper traces the history and development of some methods still in common use for routine AST, e.g. disc diffusion and agar dilution. It was quickly recognized by early investigators that there were many variables affecting the results of these tests. Consequently, there was recognition (as early as the late 1950s) that standardization of these techniques was required. This need has led to many organizations producing standardized AST methodologies. Although some disc diffusion techniques that generated results within 4-6 h were described, most relied on 18-24 h incubation before a result was available. The clinical and economic pressures for rapid methods with low labour input led to the development of semi-automated and automated AST methodologies in the 1970s. Until 10 years ago, AST techniques relied on phenotypically testing the bacteria isolated. However, to increase the speed and reliability of resistance testing, the use of a genotypic approach has been advocated. The limitations and benefits of this new approach are discussed.

History, 19th Century↗
PubMed1995

Brucella melitensis: an unexpected isolate from cerebrospinal fluid.

A specimen of cerebrospinal fluid was initially handled with 'category 3' precautions because the patient came from Somalia, where tuberculosis and HIV infection are endemic. An isolate from the specimen, initially thought to be a Neisseria species, was subsequently handled on the open bench. It was later identified as Brucella melitensis. Laboratory procedures should allow for the possibility of brucella in such specimens until a positive identification has been made.

Brucella melitensis↗
PubMed1995

Quality assessment of Microbe Base antimicrobial susceptibility data.

AIMS: To assess the quality of centres contributing antimicrobial susceptibility data to a centralised database. METHODS: Twelve organisms were distributed to 31 regional microbiology laboratories contributing data to a centralised susceptibility database. Participants were asked to determine susceptibilities to certain antibiotics by their routine method and return the data to the Department of Microbiology, Royal Hallamshire Hospital, Sheffield, for analysis. RESULTS: Results for the overwhelming majority of organism/antibiotic combinations were in agreement with expected results. Reasons for discrepancies included the non-bimodal distribution of susceptibilities, the use of different content discs, and, more importantly, minimum inhibitory concentrations falling close to breakpoint values. CONCLUSIONS: It is inevitable that any large multicentre database will contain a degree of inaccurate data. This study has highlighted several areas where discrepant results have occurred and has enabled Glaxo Laboratories to approach individual laboratories to address this problem. This study emphasises the value and consistency of Microbe Base as the largest database, of its kind, nationally.

Databases, Factual↗
PubMed1993

Comparison of techniques for antimicrobial susceptibility testing of mycobacteria.

AIMS: To evaluate adenosine triphosphate (ATP) bioluminescence as a rapid technique for antimicrobial susceptibility testing of Mycobacterium spp by comparing it with conventional and radiometric methods, and to assess its potential for use in clinical microbiology laboratories. METHODS: 115 clinical isolates from a wide range of mycobacterial species and four control organisms of known susceptibility were tested against six antimicrobial agents. Minimum inhibitory concentrations (MICs) were determined after 4-6 weeks' incubation on Middlebrook 7H10 agar. Susceptibility was also determined radiometrically using a Bactec 460, and by bioluminescent assay of ATP using a 1250 luminometer (LKB-Wallac). RESULTS: Susceptibility results after 7 days showed excellent correlation with conventionally determined MICs. 714 susceptibility tests were performed by both techniques, with seven major discrepancies between the two systems. For pyrazinamide, agreement was 100%, but five strains of M tuberculosis, including one control, and 11 mycobacteria other than M tuberculosis (MOTT) failed to grow on Middlebrook agar at pH 5.5. 606 tests were performed by radiometry, with four major discrepancies between this technique and ATP bioluminescence. No particular species of Mycobacterium gave aberrant results. Contamination was a problem; 12 of the 119 strains tested were contaminated at day 1 and had to be repeated before results were obtained. Contamination of individual tests increased significantly after 7 days of incubation. CONCLUSIONS: ATP bioluminescence can be used to monitor mycobacterial growth in fluid culture media; the technique has considerable potential for rapid susceptibility testing. Advantages include lower initial cost of analytical equipment, lower reagent cost per test, and the use of non-radioactive substrates.

Adenosine Triphosphate↗
PubMed1993

Multipoint identification of Enterobacteriaceae: report of the British Society for Microbial Technology collaborative study.

AIMS: To evaluate the accuracy and reproducibility of multipoint identification schemes in a multicentre trial. METHODS: Forty two strains of Enterobacteriaceae were distributed to 22 laboratories for identification by routine multipoint methods. Analysis of results enabled inter- and intralaboratory reproducibility of a variety of tests, and the ability of laboratories to identify individual organisms to be determined. RESULTS: Interlaboratory reproducibility of most of the biochemical tests was acceptable. The least reproducible tests, both within and between laboratories, were citrate utilisation, production of urease and beta galactosidase, detection of motility, and decarboxylation of lysine and ornithine. Inconsistent results for these tests were often associated with misidentified strains. Most laboratories performed identifications satisfactorily. Most isolates (72.1%) were identified correctly to species level; 9.6% were incorrectly identified, and 6.4% could not be identified at all. The most difficult organisms to identify were Citrobacter freundii, Enterobacter cloacae, Hafnia alvei and Aeromonas hydrophila. Strains of Enterobacter, Serratia sp, and Providencia sp were difficult to speciate. Several laboratories could not identify organisms exhibiting at least one atypical biochemical reaction. CONCLUSION: This study emphasises the need for quality control of media and reagents for multipoint identification of Gram negative enteric bacilli.

Bacteriological Techniques↗
PubMed1991

Evaluation of a commercial automated system for the identification of gram-negative enteric bacilli.

A total of 908 distinct clinical isolates and 60 reference strains of aerobic gram-negative bacilli were identified by our own in-house biochemical identification system (RHH) and by a commercial automated system (Mastascan Colour). Overall, both systems performed well in the identification of routine isolates of aerobic gram-negative bacilli, with only six discrepancies between the two systems. These six organisms were species infrequently encountered in the clinical microbiology laboratory. Of the 60 reference strains, many of which were biochemically atypical, the RHH system was unable to identify one and mis-identified two others. The commercial system was unable to identify one strain and misidentified five others. Both systems were inexpensive in terms of consumable materials, and the commercial system was compatible with the routine work of the department.

Bacteriological Techniques↗
PubMed1991

Antimicrobial susceptibility testing of mycoplasmas by ATP bioluminescence.

The susceptibility of 72 mycoplasmas to a range of antimicrobial agents was assessed in a 6-h ATP bioluminescence system. ATP was assayed with the Amerlite Analyser. Correlation with conventionally determined MICs was excellent for erythromycin and tetracycline even at 3 h. However, for ciprofloxacin, correlation was poor unless incubation was extended to 6 h.

Adenosine Triphosphate↗
PubMed1990

A three year survey of clinical isolates in the United Kingdom and their antimicrobial susceptibility.

A United Kingdom national survey of clinical isolates and their antimicrobial susceptibility was performed, with 61 participating hospital laboratories, between 1986 and 1989. Each centre used Microbe Base, a commercial suite of micro-computer programs which can record and analyse antimicrobial susceptibility data Informative on 366,853 bacterial isolates and their antimicrobial susceptibility was received from hospital and domiciliary specimens; Candida spp. accounted for a further 9121 isolates. The sites of origin were urine 51%, skin and soft tissue 21%, lower respiratory tract 8%, genital tract 7%, ear, nose and throat 6%, eye 3%, blood 1.5% and faeces 1%. Gram-negative bacteria accounted for 242,307 isolates, the main species were Escherichia coli 48%, Proteus spp. 9%, Pseudomonas spp. 7%, Haemophilus influenzae 6% and Klebsiella spp. 4%. Gram-positive bacteria numbered 124,546 with a predominance of Staphylococcus aureus 42%, beta-haemolytic streptococci 20%, Enterococcus spp. 12%, coagulase negative staphylococci 10% and Streptococcus pneumoniae 5%. All pneumococci were sensitive to penicillin, and methicillin resistant in Staph. aureus was only 2%. Twelve per cent of H. influenzae strains were resistant to ampicillin. There were no significant levels of gentamicin resistance in Gram-negative bacilli.

Drug Resistance, Microbial↗
PubMed1989

A novel luminometer for rapid antimicrobial susceptibility tests on gram-positive cocci by ATP bioluminescence.

The susceptibility of 130 clinical isolates of gram-positive cocci to a wide range of antimicrobial agents was assessed by ATP bioluminescence in a 4-h test. ATP assays were performed on a novel luminometer, the Amerlite Analyser, which measures luminescence from microtitration trays. For most organisms tested, there was good correlation (greater than 90%) with conventional MIC values estimated on 18-h cultures. However, a problem was found with detection of penicillin resistance in Staphylococcus aureus by the ATP method, 13% of strains showing major disagreement. Methicillin resistance of S. aureus was shown reliably for most strains (94%) by ATP assay, provided they were incubated at 30 degrees C. The Amerlite Analyser offers the potential for the development of a semi-automated antimicrobial susceptibility test, with a significant reduction in reagent costs when compared with previously described bioluminescence protocols.

Adenosine Triphosphate↗
PubMed1989

Identification of Enterobacteriaceae: report of the British Society for Multipoint Technology collaborative study.

Under the auspices of the British Society for Multipoint Technology, 84 strains of Enterobacteriaceae were identified by multipoint inoculation techniques in eight laboratories. Results were compared to assess the inter-laboratory reproducibility and reliability of each test. Identity of the test strains was also determined by use of two commercially produced kits. Most test strains were identified by the multipoint inoculation systems, which were cost effective and generally accurate, although some laboratories performed better than others. Reproducibility of some test results was variable.

Bacteriological Techniques↗
PubMed1988

Rapid antibiotic susceptibility tests on Enterobacteriaceae by ATP bioluminescence.

The susceptibility of 76 clinical isolates of Enterobacteriaceae to ampicillin, piperacillin and gentamicin was assessed by ATP bioluminescence in a 4-h test. For most organisms tested (Escherichia, Klebsiella, Enterobacter and Serratia), there was good correlation with traditional MIC values estimated on 18-h cultures. However strains of Proteus mirabilis showed false resistance to the beta-lactam agents with the ATP method; and concordance was achieved only after manipulation of the growth conditions. Our method is simpler than those described previously, though currently it is still labour-intensive and expensive.

Adenosine Triphosphate↗