904 Letters to the Editors References Barrett AE, Cameron SJ, Fraser CG, Penberthy LA, Shand KL. A clinical view of analytical goals in clinical biochemistry. J Clin Pathol 1979 ;32: 893-6. 'Fraser CG, Peake MJ, Calvert GD. Rapid cholesterol measurement: patient classification in heart risk evaluation clinics. Med J Aust 1979;1 :465-6. sBarnett RN. Medical significance of lab- oratory results. Am J Clin Pathol 1968; 50:671-6. 4 Cambell DG, Owen JA. The physician's view of laboratory performance. Aust Ann Med 1969;18:4-6. 5 College of American Pathologists. Goals in Clinical Chemistry: Proceedings of the 2nd Annual Aspen Conference. Colorado, Aspen, 1976;3. Proceedings of the Sub-Committee on Analytical Goals in Clinical Chemistry, WASP, CIBA Foundation, London, Eng- land, 1978. Analytical goals in clinical chemistry: their relationship to medical care. Am J Clin Pathol 1979;71:624-30. 7Buttner J, Borth R, Boutwell JH, Brough- ton PMG, Bowyer RC. Approved recommendation (1978) on quality control in clinical chemistry. Part 1. General principles and terminology. Clin Chim Acta 1979;98:129F-43F. 8Elion-Gerritzen WE. Analytical precision in clinical chemistry and medical deci- sions. Am J Clin Pathol 1980;73:183-90. Immunoperoxidase method for detection of immunoglobulins We have appreciated the letter by Sells and Burton in this Journal (1980;33 :98). We agree that the sections lift and are lost during the immunoperoxidase re- action in spite of the use of adhesives such as amilopectin, albumin, and chrome alum. Furthermore, in our experience, it is very difficult to keep the sections on the slides when an argyrophilic method is used after bleaching for melanin or employing Lee's method for oestrogen receptors (Cancer 1979;44:1). We have developed an adhesive which is very simple to prepare and is also resistant to proteolytic digestion. It con- sists of a polyurethane adhesive (Quick set, USM Chemical SpA, Milan) which is formed in two parts; 0.3 ml of each part (1+2) is diluted in separate tubes with 20 ml of acetone. The two solutions are mixed together when needed, and the slides are immersed in the freshly made solution. The adhesive dries immediately, and the sections stick without any further treatment. The mixed solution keeps for 2 hours at room temperature and for 4 hours at 4°C. All possible staining procedures can be performed on these sections without any obvious interference by the adhesive. A BONDI F FEDELI V EUSEBI G BUSSOLATI* Istituto Anatomia e Istologia Patologica, University of Bologna and Torino,* Italy ,B-lactamase production by Campylobacter jejuni There is very little information now available about the incidence of ,-lactam- ase producing strains of Campylobacter jejuni among human isolates. Severin1 in Holland reported ,-lactamase production by 57 (92%) of 62 human isolates by the chromogenic cephalosporin method. We therefore decided to undertake a retro- spective study of the incidence of ,B-lac- tamase production among strains of C. jejuni isolated over a 12-month period from human stools. Two simple laboratory methods were used, the starch-iodine paper2 and the chromogenic cephalosporin substrate.3 In addition, minimum inhibi- tory concentrations (MIC) of ampicillin for each of the strains were determined. Identical strains isolated from family outbreaks were included only once. A total of 76 strains of C. jejuni were studied, of which 73 (96 %) had been stored in liquid nitrogen for varying periods not exceeding one year. Strains were inoculated on to Oxoid blood agar base with 7% lysed horse blood and incubated under appro- priate conditions.4 Minimum inhibitory concentrations of ampicillin for all 76 strains were deter- mined by 2 ,ul spot-inoculation on Oxoid Diagnostic Sensitivity Test agar incor- porating doubling dilutions of ampicillin. These plates were then incubated for 48 hours under identical conditions. The inoculum was derived from an overnight culture of the test strain suspended in Bloodgrow (Medical Wire and Equipment Co (Bath) Ltd, Potley, Corsham, Wilts, UK) and incubated in 10% CO2 atmos- phere at 37°C and diluted so that there were 106 to 107 organisms/ml. Of the 76 strains of C. jejuni tested for P-lactamase production, four (5.3 %) gave positive results; identical results were obtained by both methods. The Figure shows the MIC of ampicillin of 72 strains was 25-0 ,ug/ml or less; all these strains were negative when tested for ,B-lactamase. The MIC of the four ,-lactamase produc- ing strains was 50-0 ,ug/ml or more. Our finding of an incidence of 5.3% from human stools differs markedly from the 92 % of Severin's study. There may thus be a much higher prevalence of f-lactamase producing strains of C. jejuni in Holland. Severin also reports that 30 (48 %) of 62 strains were sensitive to 5.0 ,ug ampicillin/ ml, this figure being similar to our own findings, but sensitivities to higher concentrations of ampicillin were not given. We noticed that it was difficult to interpret the colour change with the chromogenic cephalosporin substrate method because of the pigmented nature of the colonies when picked off agar 40. 43 lactamase producing strains C 20. Sensitivity of 76 strains of C. jejuni to ampicillin. E z 10 039 078 1:56 312 625 12-5 25 50 >50 Minimum irnhibitory concentration of ampicillin (,ig/ml ) group.bmj.com on July 13, 2011 - Published by jcp.bmj.com Downloaded from