Wilhelm Frederiksen

Importance of blood volume cultured in the detection of bacteremia

The influence of the volume of blood cultured on the rate of detection of bacteremia was evaluated in a routine 12-tube blood culture system using 1693 samples from 1502 patients. Blood samples were drawn simultaneously into two transport tubes. The blood volume cultured was the only varying parameter. Generally, 17 % more cultures with clinically significant microorganisms (bothEnterobacteriaceae and gram-positive cocci) were found when blood from two instead of one tube was used (in most cases comparing 13–16 ml of blood with 6.5–8 ml). Of the most prevalent species, the maximum average extra yield was observed forStaphylococcus aureus (26 %) followed byEscherichia coli (16 %) andStreptococcus pneumoniae (12 %). In adults most cases of bacteremia are low-grade. The grade of bacteremia in our patient population was on average as low as 0.25 CFU/ml blood. Therefore, all patients suspected of having bacteremia should have the benefit of a sufficient volume of blood cultured. Since the volume of blood cultured seems to be the single most important factor in the detection of bacteremia, it is imperative that the volume is the same in comparative studies of different blood culture systems.

Susceptibility testing of Danish isolates of Capnocytophaga and CDC group DF-2 bacteria

Twelve Capnocytophaga and seven DF‐2 strains were tested for their susceptibility to 14 antimicrobial agents using an agar dilution and an agar diffusion method. Twenty‐three other antibiotics were evaluated using the diffusion test only. All strains were fully susceptible to penicillin, ampicillin, cefuroxime, cefotaxime, erythromycin, clindamycin, chloramphenicol, doxycycline, rifamycin and ofloxacin using both methods. Clindamycin, rifamycin and cefotaxime were most active. Using agar dilution some strains were susceptible to gentamicin, but agar diffusion showed total resistance. One Capnocytophaga strain was susceptible and another moderately susceptible to metronidazole, other strains were resistant. The agar diffusion test showed that both Capnocytophaga and DF‐2 were resistant to most other aminoglycosides, to fosfomycin, polymyxin and trimethoprim. All strains of both taxa were fully susceptible to piperacillin, cefoxitin, imipenem and fusidic acid and showed different susceptibilities to the other agents. Susceptibility testing by means of agar diffusion using an enriched chocolate agar and 5% CO2 atmosphere could be used to test Capnocytophaga and DF‐2 strains and gives sufficient accuracy for routine use, when revised inhibition zone breakpoints are employed.

Phenotypical properties of Enterobacter agglomerans (Pantoea agglomerans) from human, animal and plant sources

Clinical, animal and plant isolates, representing different geographical areas, were identified as Enterobacter agglomerans (Pantoea agglomerans) using a quantitative bacterial dot method for DNA‐DNA hybridization. The phenotypical properties of the 65 strains were investigated by conventional test methods. No strain decarboxylated ornithine. Twenty‐two strains, mainly plant isolates, showed delayed acid production from α‐methyl‐glycoside, a trait which may have ecological significance. With regard to these two properties, our results differed from the description of Pantoea agglomerans given by Gavini et al. (6); further investigations will clarify these differences. Three non‐pigmented, maltose‐negative and salicin‐negative variants were derived from yellow pigmented, maltose‐positive, salicin‐positive strains.

Comparative analysis of two blood culture systems (Isolator® and a 12-tube system) by cumulative differences in detection power at different times during incubation

A lysis‐centrifugation blood culture system (Isolator®) and a conventional system (4 tubes of nutrient broth, 4 tubes of semisolid agar, and 4 tubes of thioglycollate agar) were compared after different lengths of incubation by cumulative scoring of differences in detection power. After the first half day of incubation, the Isolator® system was already significantly faster in detecting isolates of clinical significance (15 vs. 4, P = 0.02). Maximum difference in first or only detection system was seen after two days of incubation and was based on an overall superior detection of Staphylococcus aureus (11 vs. 0, P = 0.001), and an earlier detection of Enterobacteriaceae (30 vs. 13, P = 0.01) in the Isolator® system. On the contrary, the detection of Streptococcus pneumoniae was significantly inferior in the Isolator® system (0 vs. 10, P = 0.002). The earlier finding of clinically significant microorganisms in the Isolator® system certainly contributes to good patient‐care. A drawback of the Isolator® system was the finding of clinically insignificant coagulase‐negative staphylococci in 11%, compared with 1% in the conventional system. This led to a considerable waste of time and materials in the laboratory. The comparison of the two blood culture systems, based on statistical analysis of cumulative differences in detection power, expressed as the earliest or only findings, gives the optimal information, and is in our opinion the clinically most relevant comparison.

The 1997 list: proposed new bacterial taxa and proposed changes of bacterial names published during 1997 and considered to be of interest to medical or veterinary bacteriology

Abbreviations used: IJSB = International Journal of Systematic Bacteriology; LAM= Letters of Applied Microbiology; JCM = Journal of Clinical Microbiology; MML= Medical Microbiology Letters; ; FEMS ML=FEMS Microbiology Letters; JAB = Journal of Applied Bacteriology; ATCC=American Type Culture Collection; DSM=Deutsche Sammlung von Mikroorganismen; NCTC=National Collection of Type Cultures; LMG=Laboratorium Microbiologie Gent Culture Collection; NCIB =National Collection of Industrial Bacteria; CCUG= Culture Collection University Goteborg; CIP=Collection Institut Pasteur; PCM=Polish Collection of Microorganisms.

Fatal septicaemia with Selenomonas sputigena and Acinetobacter calcoaceticus

A 38‐year‐old man with a history of alcohol abuse developed rapidly fulminating septicaemia and died. Selenomonas sputigena and Acinetobacter calcoaceticus were isolated from a blood culture. Selenomonas sputigena is a motile anaerobic gram‐negative rod rarely associated with systemic disease. Difficulties in isolation and taxonomic identification are discussed.

Ornithine decarboxylating strains of Klebsiella pneumoniae demonstrated by DNA-DNA hybridization

Genotypic relatedness was assessed to clarify the taxonomic position of strains phenotypically behaving like K. pneumoniae, but for the ornithine reaction. Using DNA‐DNA hybridization it could be shown that 25 non‐motile ornithine decarboxylating strains showed high genotypic relatedness to the type strain of K. pneumoniae. Thus, it is proposed that they be considered as ornithine decarboxylating strains of the species K. pneumoniae. The API 20E system was used for phenotypic characterization, but the API code obtained by these strains was not registered in the API Profile Index. However, except for the ornithine reaction the isolates behaved as typical K. pneumoniae. Three ornithine negative strains of E. aerogenes were identified as K. pneumoniae by the API 20E System, but they showed high genotypic relatedness to the type strain of E. aerogenes.