- Volume 49, Issue 5, 2000

Different aspects of the terms strain, clone and species are discussed. The term strain is commonly used to denote a pure culture – here called ‘the strain in the taxonomic sense’ – but does also refer to a natural concept closely related to the clone. The term clone on the other hand is used both in a general and in a more restricted sense, the latter indicating a low degree of genetic exchange. The important distinction between the definition of a species and the criteria for a species is emphasised and the main kinds of criteria are considered.

A multiplex PCR-immunoassay for the rapid diagnosis of bacterial meningitis from cerebrospinal fluid (CSF) or peripheral blood was compared with conventional microbiological techniques used in the routine diagnostic laboratory. The multiplex PCR was designed to detect simultaneously a universal conserved sequence coding for bacterial 16S rRNA and the Neisseria meningitidis porA gene. The PCR-immunoassay had a detection limit of (3–5) × 102 cfu/ml (equivalent to 1–3 cfu/PCR) with spiked CSF or blood samples, compared with (3–5) × 103 cfu/ml for PCR followed by conventional agarose gel electrophoresis for detection of PCR products. Of 294 CSF samples from patients suspected on clinical grounds of suffering from meningitis, the PCR-immunoassay detected bacterial DNA in 29 CSF samples, 15 of which were also positive for N. meningitidis DNA. The 29 positive CSF samples comprised 25 samples that were also reported positive and four that were reported negative by conventional methodology; the latter four were all positive for N. meningitidis by the PCR-immunoassay. Of 173 peripheral blood samples examined, the PCR-immunoassay detected bacterial DNA in 18 samples, 14 of which were also positive for N. meningitidis DNA. In comparison, only 10 samples were reported positive for N. meningitidis by conventional methodology. All negative PCR-immunoassay results correlated with those obtained by conventional methodology for both CSF and blood samples. The sensitivity and speed of the PCR-immunoassay system indicated that it could be used as a routine diagnostic test for meningococcal meningitis, enabling a diagnosis to be made within 4 h of receipt of the specimen.

Characteristic patterns of β-lactam susceptibility are associated with different biovars of Yersinia enterocolitica. In a previous study differences in β-lactam susceptibility among biovar 2, 4 and 5 strains were largely attributed to differences in expression of β-lactamase A (BlaA) and β-lactamase B (BlaB). The basis for differences in β-lactam susceptibility of strains of biovars 1A, 1B and 3 is now considered. All the strains examined had blaB; nine of 31 biovar 3 strains and two of 13 biovar 1B strains had blaA, but PCR did not amplify blaA from biovar 1A strains. Nevertheless, inhibition data indicated that the majority of uninduced biovar 1A strains expressed BlaA and BlaB in similar amounts. Strong inducibility was seen in all these strains. Biovar 1B strains (which were less inducible than strains of biovar 1A) predominantly produced BlaA without induction; ticarcillin-sensitive strains of biovar 3 produced only BlaB but were not inducible; without induction biovar 3 strains resistant to ticarcillin and amoxycillin/clavulanate produced either predominantly BlaA, predominantly BlaB or exclusively BlaB and induction was demonstrated except for strains producing BlaB alone; biovar 3 strains resistant to ticarcillin but sensitive to amoxycillin/clavulanate predominantly produced BlaA without induction and were inducible for β-lactamase activity. After induction, nearly all strains predominantly or exclusively produced BlaB. Although PCR amplification fragments with primers specific for blaA were obtained only from some strains, the induction and inhibition data suggest that all Y. enterocolitica strains possess enzymes related to BlaA- as well as BlaB. Nevertheless, expression of the β-lactamase is regulated differently in different biovars and varies within most biovars. Failure to predict β-lactamase expression profiles from MIC data indicates the presence of additional mechanisms contributing to differences in susceptibility.

Translocation of viable bacteria from gut to bloodstream and other sterile body sites during shock has been demonstrated in several experimental and clinical studies. The factors causing translocation and its incidence at different stages of shock are not known. The aim of the study was to evaluate the importance of several factors causing translocation of indigenous microflora in an experimental model of septic shock based on intraperitoneal Escherichia coli sepsis in rats. Counts of inoculated E. coli and translocated bacteria in different locations, gut morphology and haematological values were evaluated at different stages of sepsis. Sepsis developed in all animals and E. coli achieved the highest counts in blood 6 h after inoculation. Translocation was commonest at 6 and 12 h after inoculation. Frequently translocating bacteria were lactobacilli, bifidobacteria, bacteroides and peptostreptococci. In early sepsis, translocation was associated with high E. coli counts in blood, yet in late sepsis the opposite correlation was present. Low infiltration by neutrophils in the ileum and decreased mitotic activity in the colon were associated with a high translocation rate. In early sepsis, translocation was associated with low lymphocyte counts, but in late sepsis, with low neutrophil counts. Translocation of bacteria (including anaerobes) that colonise the gut in high counts takes place during sepsis. Putative influencing factors such as activity of the primary disease (bacterial counts in blood), gut morphology or haematological values seem to have different impacts on translocation, depending on the stage of the disease.

Five hundred clinical group A streptococcal (GAS) isolates were collected in Belgium during the period 1 Nov. 1993 to 31 Oct. 1994. Clinical and laboratory data were recorded and isolates were characterised. The presence of the genes encoding streptococcal pyrogenic exotoxin types A (speA), B (speB), C (speC), F (speF) and streptococcal superantigen (ssa) were determined by PCR to target specific sequences. These isolates were also emm-typed and analysed by pulsed-field gel electrophoresis (PFGE) of genomic macrorestriction fragments with the enzyme SmaI. In total, 136 unrelated GAS PFGE types were identified and genetic diversity was clearly demonstrated. Two GAS PFGE types predominated; a first PFGE type comprised 66 (13.2%) emm1 isolates characterised by speA +, speB +, speC −, speF + and ssa −; the second PFGE type comprised 44 (8.8%) emm12 isolates characterised by speA −, speB +, speC + (or speC −), speF + and ssa −. Indistinguishable PFGE types were observed among both invasive and non-invasive isolates. Ten different PFGE types were found among 11 streptococcal toxic shock syndrome (STSS) isolates, and five of these lacked speA. Twenty-five (34.7%) of 72 invasive isolates gave negative results for speA, speC and ssa. This retrospective study confirmed the observation that the dissemination of one specific clone cannot be associated with invasive GAS disease and posed a question regarding the role of SPE A as a major virulence factor. Other streptococcal virulence factors in conjunction with host factors may determine the outcome of invasive GAS infection.

Infection continues to be one of the major complications of cerebrospinal fluid (CSF) shunting procedures, and is caused mainly by skin-derived bacteria. Production of an extracellular biofilm plays an important role in the pathogenesis of shunt-associated infections by protecting bacteria from immune mechanisms and antibiotics. So far, removal of the original shunt and implantation of a new shunting device has been the only successful treatment for most patients. As an alternative strategy to prevent CSF infections, a rifampin-impregnated silicone catheter was designed to provide high initial and long-lasting (>60 days) release of bactericidal drug. To investigate the pathophysiological mechanism of its function, this new device was investigated both in vitro and in a rodent model of CSF infection by scanning electron microscopy (SEM) and bacterial culture. Staphylococcus epidermidis (108 cfu/ml) and S. aureus (104 cfu/ml) served as test strains. SEM demonstrated that, in contrast to the unloaded catheters, initial bacterial adherence on the catheter surface could be reduced to a few single cells, which did not show visible signs of proliferation. Bacterial cultures obtained simultaneously were all sterile, showing that adherent bacteria were killed immediately by the rifampin released from the catheter. Although rifampin incorporation into silicone polymers was not able to prevent initial bacterial adhesion completely, subsequent colonisation could be prevented.