V.P. Ackerman

Consumer survey on microbiology reports.

5 typical microbiology reports were circulated to the medical staff of a 900-bed teaching hospital and they were asked for their interpretations. Approximately 160 completed replies were received and it was clear that the reports were often misinterpreted; one report (isolation of a gram-negative rod from sputum) was misinterpreted by four doctors out of five. The reasons for this failure of communication seem to be the use of jargon and unfamiliar names of bacterial species, and use of ill-defined reporting conventions. The omission of a clear-cut conclusion from many reports also contributed to misunderstanding. These deficiencies in reporting practices result in unnecessary antibiotic therapy and unnecessary work for the laboratory, since clinicians are more likely to ask for a repeat of a test with a doubtful interpretation. Communications with clinicians would be more effective if microbiologists ensured that each report is free of jargon, states what conclusion can be drawn from the test, and makes recommendations, where appropriate, for antibiotic therapy.

Biochemical Identification of Bacteria by Replicator Methods on Agar Plates

&NA; Biochemical tests commonly used for the identification of bacteria were adapted to a replicator technique using agar plates. As many as 48 organisms could be tested on one 10 cm square Petri dish. A new indicator, 2‐(2,4‐dinitrophenylazo)‐1‐naphthol‐3,6‐disulphonic acid disodium salt made it possible to investigate Gram‐positive as well as Gram‐negative organisms. For certain tests, such as citrate, DNAase, gelatin or lipase, a standard method using agar was already available. For others the usual test in liquid medium had to be adapted to solid medium. All such tests were compared with the API 20E system or with a conventional test and the results of the replicator tests showed a high correlation with those of other systems. For Gram‐negative rods the corrected error rates (a measure of reproducibility) of 22 tests were 1% or less, for the remaining 9 tests the figure ranged between 1.5% and 4.8%. For Gram‐positive cocci the corrected error rates of 21 tests were 1% or less and for the remaining 10 the figure ranged between 2% and 11%. The plates could be kept at 4‐6 °C for 2 wk without appreciable loss of activity. The duration of incubation affected the results only marginally. This system has considerable advantages. Control organisms can be included in every run. As the cost in time and reagents for individual tests is much reduced, a larger number of tests can be carried out and this provides better identification. As Gram‐positive organisms will grow on these media, it would be possible to speciate them in a more detailed fashion than is usually done now.

In vitro studies of ciprofloxacin and survey of resistance patterns in current isolates

We studied the activity of ciprofloxacin and other antibiotics against both routine and multiresistant (multi-R) clinical isolates. Ciprofloxacin inhibited more than 98% of most species of Enterobacteriaceae at a concentration of 2 micrograms/ml. Only Acinetobacter calcoaceticus, and to a much lesser degree, Providencia and Serratia, were resistant. Most Pseudomonas aeruginosa isolates were susceptible. Only 1% of staphylococci were resistant; the test panel included 1200 MRSA. For most species of streptococci, the MIC90 was 1 microgram/ml; for enterococci, it was 2 micrograms/ml. We also surveyed resistance in our current isolates. Resistance to ciprofloxacin has increased in A. calcoaceticus and Providencia, and in Streptococcus pneumoniae and group B streptococci. Ciprofloxacin-resistant isolates tended to show increased resistance to other antibiotics, including aminoglycosides and, later, cephalosporins.

Reporting practices of microbiology laboratories.

Results of investigations on typical specimens were circulated to Australian microbiologists, who were asked to draft reports on the basis of the data provided. Many laboratories were found simply to report the results of their activities without explanations. This was true whether the finding was that of a Gram-negative rod in a postoperative sputum or an anaerobic diphtheroid in a blood culture. There was diversity of views as to what constituted probable contamination in a urine specimen. Often no clearcut verdict was given, nor did the report indicate when no conclusion was possible. Remedial measures are discussed.

In vitro Activity of A-56619 and A-56620 against Multi-Resistant and Routine Clinical Isolates

A-56619 and A-56620 are two new quinolone compounds that are currently being studied. They were found to be active against multi-resistant and routine isolates of Staphylococcus aureus, enterobacteria, aminoglycoside-sensitive and resistant strains of Pseudomonas aeruginosa. Most of the enterobacteria were inhibited by 0.5-1 mg/l of A-56620. A-56619 was less active, concentrations of 1-4 mg/l being needed for 90% inhibition. Both the compounds were active at concentrations of 0.5-1 mg/l against staphylococci, including multi-resistant S. aureus. The MIC90 for P. aeruginosa was 1-2 mg/l for A-56620 and 8 mg/l for A-56619.

Comparative Antibacterial Activities of New β-Lactam Antibiotics against Pseudomonas aeruginosa

In vitro activity of nine new cephalosporins and penicillins was determined against 417 isolates of Pseudomonas aeruginosa. Carbenicillin, ticarcillin, gentamicin, tobramycin and netilmicin were also included in the study. Imipenem showed highest activity. More than 90% of the isolates were susceptible to ticarcillin, piperacillin, azlocillin, cefoperazone, cefsulodin and to tobramycin. 57 isolates included in the study were resistant to gentamicin (MIC greater than 4 mg/l); of these, none were resistant to imipenem, and more than 80% were susceptible to piperacillin, azlocillin, cefoperazone and cefsulodin.

External quality assurance in microbiology. The programme of the Royal College of Pathologists of Australasia.

Summary Since 1967 the Royal College of Pathologists of Australasia has been providing an external quality assurance programme in microbiology. The number of participants has risen from 70 to 222, and the samples distributed for investigation have increased in quantity, now totalling 35‐40 per annum, and in variety, so that most aspects of clinical microbiology are now touched on. In recent years clerical accuracy and the adequacy of reports have been examined. However, more emphasis is needed on the stability of the specimens (freeze‐drying will be introduced soon), the assessment of a laboratorys general performance, the standardization of methods and the educational aspects of external quality control.

Primary antibiotic sensitivities by a replicator method

&NA; A replicator method of carrying out primary sensitivity tests on urine specimens is described. The results are compared with conventional sensitivity tests. Of 438 specimens examined, the procedure indicated a suitable antibiotic in all but 7 and yielded an incorrect result likely to mislead in 14 instances, in each case accompanied by several correct sensitivity reports. Results are available within 24 hours.

Principles of interpretation and reporting in clinical microbiology

Clinical microbiology is evolving rapidly. New information is accumulating at a rate that would have been inconceivable even twenty years ago. This accumulation is highlighting problems that have always been with us, but have been little considered. These relate to the conceptual basis of this branch of pathology. The principles guiding us in some of these activities have not been codified. Laboratory manuals of microbiology devote little attention to the general rules by which the results of cultures are interpreted or according to which these results are reported. However, I consider that most microbiologists will agree on certain guidelines for interpretation and reporting which I shall attempt to set forth. I am prompted to do this by the results of a recent exercise in the Microbiology Quality Assurance Programme (item 5.1.4). The scenario was as follows. The patient had symptoms and signs consistent with acute meningitis in some form. From the cerebrospinal fluid two colonies of a coagulase-negative staphylococcus and one colony of Listeria monocytogenes were grown. Participants were asked to identify the two isolates and to issue their normal reports. In most cases (over 75%) both the identification and the report were satisfactory, but there were exceptions. Some of these are listed below, the report being indicated by ‘. . .’. Staphylococcus aureus, coryneform bacteria. ‘Insignificant growth. Skin organisms.’ S. aureus, Streptococcus species. ‘No significant growth. ’ S . aureus, Neisseria meningitidis. ‘Scanty growth of S . aureus and N . meningitidis . . . indicative of contamination. ’ Corynebacterium renale. ‘Probable skin flora.’ S. faeculis, Lancefield group D. ‘Of doubtful significance.’ It is deplorable that 33 out of 194 participants failed to identify L. monocytogenes in a quality assurance exercise, where it is safe to assume that they are performing above their usual level. The most disturbing feature, however, is that 12 participants were prepared to report ‘skin flora only present’, without indicating the organisms actually isolated, and that others were prepared to label Corynebacterium ulcerans, Streptococcus faecalk, Haemophilus influenzae, Neisseria meningitidis and Klebsiella rhinoscleromatis as ‘contaminants’, origin unspecified. In previous exercises S. pneumoniae and S. milleri have been discarded in this summary fashion, in defiance of what I would consider good laboratory practice and of the principles that are outlined below. The principles referred to in this article apply only to . specimens from normally sterile sites. When the site of origin of the specimen has a normal flora (gut, upper respiratory tract, vagina) or is easily contaminated by representatives of such a flora (sputum, urine, wound swab), interpretation of the results of examination rests on different principles and each type of specimen needs specific consideration.

In vitro antibacterial activity of enoxacin (CL-919)

&NA; Antibacterial activity of enoxacin was evaluated against more than 3,700 clinical isolates using the agar‐dilution method and an inoculum of 104‐105 cells per site. For comparison other antibiotics appropriate for each species were also included. For most enterobacteria and for Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa, the MIC90 of enoxacin was below 2 mg/l. Serratia marcescens was more resistant; the MIC90 being 4 mg/ml. Enoxacin also showed high activity against Campylobacter jejuni and Neisseria gonorrhoeae. Streptococci were comparatively resistant, 32 mg/l to 64 mg/l of the compound being required to inhibit 90% of strains.