Prevalence of aminoglycoside resistance in 20 European university hospitals participating in the European SENTRY Antimicrobial Surveillance Programme

The aim of this study was to analyse the current prevalence of aminoglycoside resistance in Europe and compare the in vitro activity of amikacin, gentamicin, and tobramycin against 7057 bacterial isolates from 20 university hospitals participating in the European SENTRY Antimicrobial Surveillance Programme. Amikacin exhibited better in vitro activity than tobramycin and gentamicin against most gram-negative bacilli in Europe. The resistance levels were 0.4-3% for amikacin, 2-13.1% for gentamicin, and 2.5-15.3% for tobramycin among different members of the family Enterobacteriaceae. Of the Staphylococcus aureus isolates tested, 75% were susceptible to gentamicin. Only 21% of all enterococcal strains tested were fully susceptible to gentamicin. Although intra-country variations in the prevalence of resistance phenotypes in Escherichia coli, Klebsiella spp., and Pseudomonas aeruginosa as well as in staphylococci and enterococci did occur, aminoglycoside resistance rates were generally higher in Italy, Portugal, Spain, Greece, France, the UK, and Poland than in Austria, Belgium, Germany, the Netherlands, and Switzerland. Compared with the 1987-88 data of the European Study Group on Antibiotic Resistance, gentamicin resistance has increased up to 5% in some gram-negative bacterial species. Furthermore, a greater than 10% increase in resistance to gentamicin has been seen in Staphylococcus aureus during the last decade. The reason for this observation is unclear, although changes in antibiotic prescribing patterns that result in increased selective pressure from gentamicin may have contributed to these increased rates of aminoglycoside resistance.

Sex-limited protein: in vitro and in vivo functions

Mouse complement component C4 exists in two isoforms, C4 and a protein with expression restricted to male animals called sex-limited protein (Slp). Although Slp is about 95% homologous to C4, it is generally believed to be non-functional, at least in conventional haemolytic complement assays. In a previous study, however, we showed that Slp is haemolytically active in a C1-inhibitor (C1INH)-regulated, EDTA-resistant mouse complement activation pathway. To study other possible implications of this finding, we generated constitutively expressing Slp-transgenic mice. The transgene was crossed into otherwise Slp-deficient C57Bl/6J and NZB mice. Members of the third backcross generation of C57Bl/6J mice were tested for functional Slp and classical and alternative complement pathway activities (CH50 and AP50 levels, respectively). Slp-transgenic C57Bl/6J mice showed enhanced CH50, but normal AP50 levels when compared with non-transgenic littermates. To discover a possible protective role for Slp in spontaneous systemic lupus erythematosus (SLE) in NZBxNZW (NZBxW) mice, the third backcross generation of Slp-transgenic NZB mice was mated with NZW mice and the development of SLE in the female offspring was followed. In these introductory experiments, Slp-transgenic NZBxW animals presented with a significantly extended life span. Our results imply that Slp is a mouse complement component with functions which partially resemble some of those of human C4A.

Comparative activity of 27 antimicrobial compounds against 698 Streptococcus pneumoniae isolates originating from 20 European university hospitals. SENTRY Participants Group

The purpose of this study was to compare the in vitro activity of 27 antimicrobial compounds against 698 clinical Streptococcus pneumoniae isolates collected at 20 European university hospitals. Of the isolates tested, 21.3% were intermediately resistant to penicillin and 6.2% displayed high-level resistance to penicillin. Resistance to different antibiotics was more common among intermediately penicillin-resistant strains than among penicillin-susceptible strains and was most common among high-level penicillin-resistant organisms. The results of the current surveillance study confirm the ongoing trend among European clinical pneumococcal isolates of decreased sensitivity to various antibiotics.

Frequency of occurrence and antimicrobial susceptibility of bacterial pathogens associated with skin and soft tissue infections during 1997 from an International Surveillance Programme. SENTRY Participants Group

The SENTRY Antimicrobial Surveillance Programme was established to provide a coordinated, standardised, international surveillance on antimicrobial resistance. In one part of the programme, isolates from skin and soft tissue infections sent from 20 hospitals in 12 different European countries were investigated in the European coordinating centre. Of 1013 isolates, Staphylococcus aureus and Pseudomonas aeruginosa were the most significant species, constituting almost 50% of the referred isolates. Methicillin resistance in Staphylococcus aureus averaged 22% across Europe, only slightly less than that in isolates derived from blood. Less than 5% of the enterococcal isolates were resistant to vancomycin. Piperacillin/tazobactam was the most active penicillin-derived beta-lactam compound against Pseudomonas aeruginosa, inhibiting 91.3% of the isolates, while ceftazidime and cefepime were the most active cephalosporins, inhibiting 85.8% and 80.3% of the isolates, respectively. Putative extended-spectrum beta-lactamase production was not detected in Escherichia coli and was found in only 5.1% of the Klebsiella pneumoniae isolates. In general, strains of the family Enterobacteriaceae remained mostly susceptible to carbapenems, cefepime, and amikacin.

Prevalence of resistance to MLS antibiotics in 20 European university hospitals participating in the European SENTRY surveillance programme. Sentry Participants Group

Macrolide, lincosamide and streptogramin (MLS) antibiotics are chemically distinct inhibitors of bacterial protein synthesis. Resistance to MLS antibiotics may be constitutive or inducible. The purpose of this study is to update our understanding of the prevalence of different forms of MLS resistance in Europe. The analysis of 3653 clinical pneumococcal, staphylococcal and enterococcal isolates exhibited an average percentage of 21.3% and 6.2% intermediate and high-level penicillin-resistant Streptococcus pneumoniae, 21.8% methicillin-resistant Staphylococcus aureus and 11% vancomycin-resistant Enterococcus faecium. Geographical differences in erythromycin and clindamycin resistance in isolates of S. pneumoniae and S. aureus strongly reflect geographical variations in susceptibility to penicillin and methicillin, respectively. A very narrow range of MICs was obtained with quinupristin/dalfopristin, with no S. pneumoniae, S. aureus and E. faecium isolate having an MIC of > 4 mg/L, indicating a possible role of quinupristin/dalfopristin in the treatment of infections by multi-resistant Gram-positive bacteria.

Many class I integrons comprise distinct stable structures occurring in different species of Enterobacteriaceae isolated from widespread geographic regions in Europe

Three sizes of inserted regions of DNA (800, 1,000, and 1,500 bp) were shown to be common among class I integrons in unrelated clinical isolates of Enterobacteriaceae from different European hospitals. Sequencing showed that 800-bp inserted regions comprised identical sequences including aacA4, that 1,000-bp inserted regions included aadA, and that 1,500-bp inserted regions included dfrI and aadA1, irrespective of host species and geographic origin. In addition promoter sequences were mostly identical for each size class. These data suggest that inserted gene cassettes and promoter regions of integrons are conserved and stable, with resistance genes transferred more often as part of the entire integron structure than as individual gene cassettes.

The prevalence of aminoglycoside resistance and corresponding resistance genes in clinical isolates of staphylococci from 19 European hospitals

Aminoglycosides still play an important role in antistaphylococcal therapies, although emerging resistance amongst staphylococci is widespread. To further our understanding of the prevalence of aminoglycoside resistance in Europe, we tested 699 and 249 consecutive unrelated clinical isolates of Staphylococcus aureus and coagulase-negative staphylococci (CNS), respectively, from the SENTRY Antimicrobial Surveillance Program, for susceptibility to gentamicin, tobramycin, kanamycin and streptomycin, and examined the relationship between susceptibility to these antimicrobials and susceptibility to methicillin. Three hundred and sixty-three staphylococcal isolates demonstrated resistance to at least one of the aminoglycosides tested; all of these isolates were screened for the presence of aac(6')-Ie + aph(2"), ant(4')-Ia and aph(3')-IIIa, the genes encoding the most clinically relevant aminoglycoside-modifying enzymes. S. aureus isolates derived from hospital-acquired pneumonia tended to be more resistant to aminoglycosides and methicillin than isolates from blood or wound infections. In S. aureus, resistance to aminoglycosides was closely associated with methicillin resistance. Susceptibility of S. aureus to gentamicin has decreased by 9% from previous European studies to a current level of 77%, while susceptibility of CNS, currently at 67%, has increased by 21%. Geographical variation occurred, correlating with methicillin resistance, although intra-country variation was considerable. aac(6')-Ie + aph(2"), ant(4')-Ia and aph(3')-IIIa were found throughout Europe in 68%, 48% and 14% respectively of staphylococci resistant to at least one aminoglycoside. aph(3')-IIIa was considerably more common in methicillin-susceptible S. aureus and CNS isolates; the reverse was true for the other two resistance genes. The prevalence of ant(4')-Ia and aph(3')-IIIa genes in aminoglycoside-resistant staphylococci was significantly greater than that reported in previous European studies.

Class I integrons in Gram-negative isolates from different European hospitals and association with decreased susceptibility to multiple antibiotic compounds

Class I integrons are associated with carriage of genes encoding resistance to antibiotics. Expression of inserted resistance genes within these structures can be poor and, as such, the clinical relevance in terms of the effect of integron carriage on susceptibility has not been investigated. Of 163 unrelated Gram-negative isolates randomly selected from the intensive care and surgical units of 14 different hospitals in nine European countries, 43.0% (70/163) of isolates were shown to be integron-positive, with inserted gene cassettes of various sizes. Integrons were detected in isolates from all hospitals with no particular geographical variations. Integron-positive isolates were statistically more likely to be resistant to aminoglycoside, quinolone and beta8-lactam compounds, including third-generation cephalosporins and monobactams, than integron-negative isolates. Integron-positive isolates were also more likely to be multi-resistant than integron-negative isolates. This association implicates integrons in multi-drug resistance either directly through carriage of specific resistance genes, or indirectly by virtue of linkage to other resistance determinants such as extended-spectrum beta-lactamase genes. As such their widespread presence is a cause for concern. There was no association between the presence of integrons and susceptibility to cefepime, amikacin and the carbapenems, to which at least 97% of isolates were fully susceptible.

The effect of reserpine, an inhibitor of multidrug efflux pumps, on the in-vitro activities of ciprofloxacin, sparfloxacin and moxifloxacin against clinical isolates of Staphylococcus aureus

In Staphylococcus aureus, in addition to mutations in the grl and gyr gene loci, multidrug efflux pumps like NorA contribute to decreased fluoroquinolone susceptibility. Efflux pumps can be inhibited by the plant alkaloid reserpine, which, at 20 mg/L, reduced sparfloxacin, moxifloxacin and ciprofloxacin IC50s and MICs by up to four-fold in 11, 21 and 48 of the 102 unrelated clinical isolates tested, respectively. The effect was less pronounced with the hydrophobic drugs sparfloxacin and moxifloxacin than with the hydrophilic drug ciprofloxacin and was stable in all 25 clonally related isolates tested.

The prevalence of low- and high-level mupirocin resistance in staphylococci from 19 European hospitals

The topical agent mupirocin plays a crucial role in strategies designed to control outbreaks of methicillin-resistant Staphylococcus aureus. The extent of high- or low-level mupirocin resistance amongst S. aureus from European hospitals is not known. Six hundred and ninety-nine S. aureus and 249 coagulase-negative staphylococci (CNS) derived from blood, hospital-acquired pneumonia or skin and soft tissue infections from 19 European hospitals were tested for susceptibility to mupirocin and oxacillin. Methicillin sensitivity was found in 72% and 32% of S. aureus and CNS, respectively. High-level mupirocin resistance was detected in 1.6% of S. aureus and 5.6% of CNS isolates, while low-level mupirocin resistance was detected in 2.3% of S. aureus and 7.2% of CNS isolates. Amongst S. aureus, methicillin-resistant isolates were twice as likely to have high- or low-level mupirocin resistance. This difference was less pronounced in CNS. No relationship was found between the site of infection and prevalence of mupirocin resistance. High- and low-level mupirocin resistance was detected amongst staphylococci from 10 and 16 of the hospitals studied, respectively. To maintain the relatively low prevalence of mupirocin resistance in Europe amongst both S. aureus and CNS, the prudent use of mupirocin restricted to defined infection control strategies should be emphasized.

The effect of culture conditions on the in-vitro adherence of methicillin-resistant Staphylococcus aureus

Methicillin-resistant isolates of Staphylococcus aureus (MRSA) were divided on the basis of their epidemiologic behaviour into two subgroups, epidemic MRSA (EMRSA) and sporadic MRSA (SMRSA) strains. An existing adherence assay was modified to determine differences in adherence properties between these two groups of MRSA, and the influence of culture conditions on the adherence of SMRSA and EMRSA strains to plastic, human collagen I (HuCol I) and pharyngeal carcinoma Detroit 562 cells (D562) was determined. In-vitro parameters, such as culture medium, growth temperature and growth phase of the bacterium, influenced the adherence of MRSA strains to plastic significantly. Even more pronounced differences in adherence due to changes in growth conditions and growth phase of the bacteria were found for the adherence of MRSA strains to HuCol I. Growth phase had a significant effect on the adherence of MRSA strains to the pharyngeal carcinoma cells D562. However, the study did not find conditions which made it possible to distinguish EMRSA from SMRSA strains. These data show that extrapolation of in-vitro data concerning adherence of MRSA strains to in-vivo conditions should be treated with caution.

Cloning and characterization of an accessory gene regulator (agr)-like locus from Staphylococcus epidermidis

The presence of sequences related to the agr of Staphylococcus aureus was demonstrated in Staphylococcus epidermidis by agr-specific PCR, and Southern blot. The agr-like locus of S. epidermidis A086 was cloned and sequenced. An overall homology of 68% was found between the agr locus from S. epidermidis and S. aureus. The agr locus from S. epidermidis was organized similar to those from S. aureus and S. lugdunensis. The putative RNAII molecule contains four open reading frames, agr A, B, C and D. AgrA was a response regulator. AgrB showed homology with transducer and translocase molecules. AgrC is expected to act as a histidine protein kinase in which a leucine zipper is present. AgrD is presumably processed into an autoinducer peptide. The putative RNAIII molecule contained an open reading frame encoding a putative 26 amino acid (aa) polypeptide, which differed in 3 aa from the RNAIII encoded delta-toxin of S. aureus. Kinetic studies showed that the production of this RNAIII was elevated during the post-exponential phase. delta-Toxin activity was demonstrated for 21 of 23 tested S. epidermidis strains. Kinetic studies of the production of delta-toxin showed that the toxin was produced during the post-exponential phase. Sequencing of S. epidermidis A097, which showed a delayed agr-response, revealed a truncated AgrC lacking the histidine kinase domain. These data indicate that an agr-like locus is active in S. epidermidis during the post-exponential phase.

Detection of staphylococcal genes directly from cerebrospinal and peritoneal fluid samples using a multiplex polymerase chain reaction

A multiplex polymerase chain reaction (PCR) that can simultaneously detect eubacterial isolates and the methicillin-susceptibility of staphylococcal isolates from cerebrospinal and peritoneal fluid samples was compared to conventional microbiological methods. Using conventional methods, bacteria were isolated from 8% (29/350) of the cerebrospinal fluid samples and from 5% (3/60) of the peritoneal fluid samples. All isolates except two Staphylococcus epidermidis isolates were also detected using the multiplex PCR. Coagulase-negative staphylococci and Staphylococcus aureus were correctly identified using both methods. The multiplex PCR can rapidly and simultaneously detect eubacteria, and the methicillin susceptibility of staphylococci from samples containing > or = 10(2) cfu/ml of bacteria.

Molecular identification of bacteria by fluorescence-based PCR-single-strand conformation polymorphism analysis of the 16S rRNA gene

PCR-single-strand conformation polymorphism (PCR-SSCP) analysis is a rapid and convenient technique for the detection of mutations and allelic variants. We have adapted this technique for the identification of bacteria by PCR with fluorescein-labeled primers chosen from the conserved regions of the 16S rRNA gene flanking a variable region. The PCR product was denatured, separated on a nondenaturing gel, and detected by an automated DNA sequencer. The mobility of the single-stranded DNA is sequence dependent and allows the identification of a broad panel of bacteria. A single nucleotide difference in the amplified region was sufficient to obtain different PCR-SSCP patterns. The simultaneous amplification of multiple polymorphic regions by multiplex PCR with subsequent multiplex SSCP increased the discriminatory power of PCR-SSCP. A broad range of gram-negative and gram-positive bacteria were tested by PCR-SSCP, including, e.g., Escherichia coli, Enterobacter spp., Klebsiella spp., Haemophilus spp., Neisseria spp., Staphylococcus spp, Streptococcus spp., Enterococcus spp., and Bacillus spp. In total, a panel of 178 strains of bacteria representing 51 species in 21 genera was examined. Although a limited number of strains from each species were tested, the strains tested gave species-specific patterns, with only one exception: Shigella species were indistinguishable from E. coli. PCR is a sensitive technique; as few as 10 CFU of E. coli was sufficient to produce PCR-SSCP patterns suitable for identification. The whole fluorescence PCR-SSCP procedure takes approximately 8 h for the detection and identification of low numbers of bacteria.2+ fluorescence PCR-SSCP seems to be a promising method for the differentiation of a broad range of pathogens found in usually sterile clinical sites, such as blood and cerebrospinal fluid.

Phenotypic characterization of epidemic versus sporadic strains of methicillin-resistant Staphylococcus aureus

Forty strains of methicillin-resistant Staphylococcus aureus (MRSA) were divided on the basis of their epidemiologic behavior into two subgroups, sporadic MRSA (SMRSA) and epidemic MRSA (EMRSA) strains. The strains were examined for binding of 125I-labelled fibronectin, vitronectin, collagen, Fc fragments of immunoglobulin G, and fibrinogen. A significant difference between EMRSA and SMRSA strains was found for binding of 125I-labelled fibrinogen and for Fc fragments of immunoglobulin G, (P < 0.05). No significant difference in the binding of 125I-labelled fibronectin and collagen was found between EMRSA and SMRSA strains. The binding of 125I-labelled vitronectin to MRSA strains was found to be aspecific. Capsular serotypes of the strains were determined with monoclonal antibodies against capsular types 5 and 8. Strains could be divided into the following four groups: types 5, 8, and 5/8 and nontypeable. More nontypeable strains were found in the EMRSA group (66.6%). Significantly more EMRSA strains (79%) than SMRSA strains (44%) produced alpha-toxin (P < 0.025). Logistic regression analysis using a combination of the parameters 125I-labelled immunoglobulin G binding, capsular type, and alpha-toxin production predicted the epidemic character with a sensitivity of 83% and a specificity of 75%.

Rapid identification of bacteria by PCR-single-strand conformation polymorphism

A new molecular biological approach for the identification of bacteria is described. This approach employs PCR of bacterial cell lysates with conserved primers located in the 16S rRNA sequence flanking a variable region, and analysis of the amplified product was based on the principle of single-strand conformation polymorphism (SSCP). The PCR product was denatured and separated on a nondenaturing polyacrylamide gel. SSCP patterns were detected by silver staining the nucleic acids. The mobility of the single-stranded DNA is sequence dependent and could be used to identify the unknown bacteria. Feasibility of the technique was demonstrated for a broad panel of gram-negative and gram-positive bacteria. We tested over 100 strains of bacteria representing 15 genera and 40 species. With the use of only two primer sets, P11P-P13P and ER10-ER11, we were capable to discriminate the tested species at the genus and species levels. Species-specific patterns were obtained for, e.g., Clostridium spp., Listeria spp., Pseudomonas spp., and Enterobacter spp. PCR-SSCP is a sensitive technique; e.g., the sensitivity obtained for Escherichia coli cells was 30 CFU. This technique is a simple and rapid method for the detection and identification of a wide spectrum of bacteria by whole-cell-based PCR amplification with the use of conserved primers and identification by nondenaturing gel electrophoresis.

Clinical significance of Clostridium difficile and its toxins in faeces of immunocompromised children

In this study, clinical and laboratory findings were tested for correlation with the presence of Clostridium difficile. The toxigenicity of the isolated strains and the toxins were determined in faecal samples of immunocompromised children admitted to a single room for protective isolation. Using the toxin assay as the gold standard, the culture sensitivity of toxigenic C difficile was 94.1%, the specificity 93.8%, the positive predictive value 62.8%, and the negative predictive value 99.3%. Correction for stools with a positive culture of toxigenic C difficile preceding detection of toxin, resulted in a positive prediction value of 78.4%. A statistically significant association was found between a positive faecal toxin assay and fever, and between a positive culture of toxigenic C difficile and abdominal pain: 42% of the patients with positive toxin assays had fever versus 21% with negative toxin assays, and 66% of the patients with a positive culture for toxigenic C difficile had abdominal pain, versus 22% with negative cultures. Further analysis of the cultures and toxin assays showed no statistically significant association with diarrhoea, fever, white blood cell count, C reactive protein concentrations, or abdominal pain. Based on these findings, it is suggested that immunocompromised children should be treated when toxigenic C difficile is cultured or when toxin is detected in stool samples.

Rapid detection of toxigenic Clostridium difficile in fecal samples by magnetic immuno PCR assay

Rapid detection of toxigenic Clostridium difficile in fecal samples was accomplished with the magnetic immuno PCR assay (MIPA). Elaborate DNA extraction techniques were unnecessary. First, we generated a mouse monoclonal antibody (MAb) reactive with only C. difficile, Clostridium sordellii, and Clostridium bifermentans. Then, magnetic beads were coated with the MAb, incubated with fecal samples to allow binding with C. difficile, extracted from the stool with a magnet, and processed in the PCR with primers specific for the toxin B gene. After optimizing MIPA by raising the number of PCR cycles from 35 to 40 and adding Chelex 100 to the PCR mixture, we found a sensitivity of 96.7%, a specificity of 100%, a positive predictive value of 100%, and a negative predictive value of 94.1% when compared with the culture of cytotoxic C. difficile from fecal samples. MIPA is a rapid, easy, and sensitive PCR method for demonstrating the presence of toxigenic C. difficile in stool samples and avoids the disadvantage of elaborate extraction of DNA from fecal samples.

Reactivity of monoclonal antibodies to Pseudomonas aeruginosa isolates from hospitalized adults and patients with cystic fibrosis

To assess the potential therapeutic use of three human monoclonal antibodies (MAbs) and one murine MAb, we tested the reactivity of these MAbs toward 100 clinical isolates of Pseudomonas aeruginosa. Seventy-five isolates were from hospitalized patients, while 25 were recovered from patients with documented cystic fibrosis. Nine isolates showed autoagglutination. The three human MAbs and one murine MAb exhibited agglutination with 81% of the P. aeruginosa isolates obtained from hospitalized patients and with 72% of the isolates from patients with cystic fibrosis. Eight of the autoagglutinating isolates were reactive in whole-cell ELISAs with the MAbs. The isolates recovered from patients with cystic fibrosis were reactive mainly with a MAb that is directed to the outer core of lipopolysaccharide (LPS); they showed hardly any reaction with O antigen-specific MAbs or typing sera, a finding indicating that these isolates lacked the O antigen and that the outer core of the LPS was still present. The reactivity of the MAb specific for the outer core of LPS toward P. aeruginosa isolates from patients with cystic fibrosis has potential value in eradicating P. aeruginosa from these patients.

Toxins A and B of Clostridium difficile

The toxins produced by Clostridium difficile share several functional properties with other bacterial toxins, like the heat-labile enterotoxin of Escherichia coli and cholera toxin. However, functional and structural differences also exist. Like cholera toxin, their main target is the disruption of the microfilaments in the cell. However, since these effects are not reversible, as found with cholera toxin, additional mechanisms add to the cytotoxic potential of these toxins. Unlike most bacterial toxins, which are built from two structurally and functionally different small polypeptide chains, the functional and binding properties of the toxins of C. difficile are confined within one large polypeptide chain, making them the largest bacterial toxins known so far.

Multivalent binding of toxin A from Clostridium difficile to carbohydrate receptors

A specific monoclonal antibody against toxin A from Clostridium difficile was generated that did not show thermolabile binding. Nonspecific murine monoclonal antibodies bound toxin A at 4 degrees C, but less effectively at 37 degrees C. Nonspecific human monoclonal antibodies did not bind to toxin A at 4 degrees C. Cytotoxic properties of purified toxin A were not inhibited by Bandeiraea simplicifolia lectin. This points to a carbohydrate moiety on the cell surface and a multivalent nonspecific carbohydrate binding ligand on toxin A.

Comparison of immunomagnetic beads coated with protein A, protein G, or goat anti-mouse immunoglobulins. Applications in enzyme immunoassays and immunomagnetic separations

Immunomagnetic beads were prepared using either protein A (PA) or protein G (PG) coupled to magnetic beads for binding antibodies at their Fc region. The performance of these beads was compared with commercially available beads coated with goat anti-mouse (G alpha M) immunoglobulins. Both the PA- and PG-beads possessed a higher binding capacity than the G alpha M-beads for the monoclonal antibodies tested, although, PA bound weakly with some IgG1 antibodies. PA-beads were compared with G alpha M-beads in a magnetic enzyme immunoassay for the detection of mouse immunoglobulins as an alternative to a conventional capture ELISA. The magnetic enzyme immunoassay was characterized by a detection time of less than 60 min and a linear assay range from 5-10 to 500 ng/ml for G alpha M-beads and 5-10 to 1000 ng/ml for PA-beads. The capture ELISA was linear from 10 to 250 ng/ml. For immunomagnetic separation of Salmonella with immunomagnetic beads, PA-beads were superior to both PG- and G alpha M-beads. For specific isolation of bacteria from heterogeneous suspensions by immunomagnetic separation, PA- and PG-beads are preferable since G alpha M-beads crossreact with bacteria possessing proteins with Fc-binding activity.

Comparison of typing methods for Clostridium difficile isolates

A simple discriminative typing method for Clostridium difficile has been developed. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of whole-cell proteins and restriction enzyme analysis are relatively simple techniques but are difficult to evaluate, especially the restriction enzyme analysis. Immunoblotting and restriction fragment length polymorphism typing facilitate simple discrimination of patterns.

Monoclonal antibodies that react with live Listeria spp

Seven monoclonal antibodies (MAbs) against Listeria spp. that were reactive with live Listeria spp. were developed. Two of these MAbs (55-8 and 55-37) were members of the immunoglobulin M class, and all other MAbs were members of the immunoglobulin G class. MAb 55-23 reacted with 148 of 157 strains tested. MAb 34-51 reacted with serotype 1/2a, 1/2b, and 1/2c strains and exhibited a scattered reaction pattern with strains belonging to other serotypes. MAb 55-44 reacted with all of the strains belonging to serotype 4b tested. MAb 55-4 reacted with all of the serotype 1/2a isolates tested, although reactivity with other isolates also was observed. The other MAbs exhibited scattered reaction patterns. No correlation of reactivity pattern with serotype was found. Marked differences were observed between the reactivities of MAbs as determined by a magnetic immunoluminescence assay and a whole-cell enzyme-linked immunosorbent assay. Only MAb 55-23 exhibited minor reactivity with three Streptococcus spp. isolates, while no reactivity was observed with six Bacillus spp. strains, one Escherichia coli strain, and one Citrobacter sp. strain. In Western blots (immunoblots) MAbs 55-23, 55-44, and 34-9 exhibited reactivity; all other MAbs were negative in this assay.

Detection of toxigenic Clostridium difficile in fecal samples by colony blot hybridization

A hybridization assay for detection of toxigenic Clostridium difficile in fecal samples was developed and compared with the classical tissue culture cytotoxicity assay. A DNA fragment probe specific for the toxin B gene of Clostridium difficile was synthesized by the polymerase chain reaction and labelled with digoxigenin. Fecal samples were cultured for 24 hours, replica-plated and hybridized with the probe. The hybridization assay had a sensitivity of 100%, specificity of 96.7%, positive predictive value of 86.7% and negative predictive value of 100% compared with the cytotoxicity assay.

Detection of Listeria monocytogenes in cheese with the magnetic immuno-polymerase chain reaction assay

A new detection system, the magnetic immuno-polymerase chain reaction (PCR) assay (MIPA) has been developed to detect Listeria monocytogenes in food. This method separates Listeria cells from PCR-inhibitory factors present in enrichment broths containing food samples by using magnetic beads coated with specific monoclonal antibodies (MAbs). The separated bacteria were lysed, and the supernatant containing the bacterial DNA was subjected to the PCR. Detection of L. monocytogenes in three naturally contaminated cheese samples with two different MAbs and PCR primers specific for the gene encoding the delayed-hypersensitivity factor showed that with MAb 55 all three samples were positive whereas with MAb A two samples were positive. A further improvement of the method was obtained by using a PCR step based on the listeriolysin O gene. A MIPA employing MAb 55 and the listeriolysin O gene primer set detected L. monocytogenes after 24 h of culture in Listeria Enrichment Broth samples from Port Salut artificially contaminated with 40 CFU/25 g. We could detect 1 CFU of L. monocytogenes per g of cheese after a second enrichment for 24 h in Fraser broth. The analysis time including both enrichments is approximately 55 h.

Rapid detection of salmonellae in poultry with the magnetic immuno-polymerase chain reaction assay

Rapid detection of salmonellae in chicken meat was accomplished by using the magnetic immuno-polymerase chain reaction assay (MIPA). A direct polymerase chain reaction assay performed with chicken meat spiked with Salmonella typhimurium resulted in poor sensitivity (approximately 10(7) CFU/g of meat). The use of immunoseparation with a Salmonella serogroup B-specific monoclonal antibody improved the sensitivity, but enrichment was required for the detection of low levels of contamination. Enrichment for 6 h in either buffered peptone water, lactose broth containing tergitol-7, or selenite-cystine broth resulted in the detection of an initial inoculum of 100 CFU per g of meat. Enrichment of the salmonellae present on 25 g of spiked chicken meat for 24 h in either buffered peptone water or selenite-cystine broth before detection by the MIPA yielded a detection limit of approximately 0.1 CFU/g of meat. A detection limit of approximately 1 CFU/g of meat was obtained when the spiked meat was stored at -20 degrees C before enrichment for 24 h and analysis with the MIPA. Although the MIPA was developed for S. typhimurium, a MIPA in which a panel of six monoclonal antibodies specific for Salmonella serogroups A through E was used detected the presence of 0.1 CFU of Salmonella enteritidis per g of chicken meat. These data indicate that the method is applicable to other commonly isolated serotypes.

Detection of enterovirulent Escherichia coli associated with diarrhoea in Seville, southern Spain, with non-radioactive DNA probes

To assess the role of diarrhoeagenic Escherichia coli in Southern Spain, faecal samples from 135 patients with diarrhoea and 40 healthy subjects from Seville, Andalusia, were investigated. In this prospective study, enterovirulent E. coli were identified by hybridisation with five non-radioactive DNA probes specific for enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC) and verocytotoxin-producing E. coli (VTEC). Probe-positive strains were isolated from four patients (3%) with diarrhoea and from none of the healthy controls. Two patients harboured ETEC and two patients had EPEC probe-positive strains in their faeces. No VTEC were isolated during this study. Salmonella spp. were the most frequently identified enteric pathogens, accounting for 10% of the cases, followed by Campylobacter jejuni (3%) and diarrhoeagenic E. coli (3%). This study indicates that enterovirulent E. coli play a modest role in the aetiology of diarrhoea among the indigenous population of Southern Spain.

Frequency of enterovirulent Escherichia coli in diarrhoeal disease in The Netherlands

To assess the role of enterovirulent Escherichia coli in The Netherlands, faecal samples of 279 patients (108 children, 171 adults) with diarrhoea and 100 healthy controls were investigated in a prospective study. Enterovirulent Escherichia coli were identified by hybridization with five different non-radioactively labelled DNA probes specific for enteropathogenic Escherichia coli (EPEC), verocytotoxin producing Escherichia coli (VTEC) and enterotoxigenic Escherichia coli (ETEC). The rate of isolation of EPEC was 6.5% in patients with diarrhoea and 2.0% in asymptomatic persons. During the study period, no VTEC were isolated from patients with diarrhoea. ETEC were isolated from two persons, both of whom had experienced diarrhoea and had returned from travel in (sub)tropical areas. Our results suggest that diarrhoea is sporadically caused by ETEC among the indigenous population of The Netherlands, and is mainly associated with travel in endemic areas. Furthermore, the presence of EPEC probe-positive strains in the stool need not always be accompanied by symptoms of diarrhoea.

[Detection of diarrhea-causing Escherichia coli using DNA-probes]

To assess the role of enterovirulent Escherichia coli at home and abroad, faeces samples of patients with diarrhoea and of healthy controls in Tunisia, Seville (southern Spain) and the Netherlands were investigated. Enterovirulent E. coli were identified by hybridization with five different non-radioactively labelled DNA probes specific for enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC) and verocytotoxin producing E. coli (VTEC). ETEC was the main causative agent of travellers' diarrhoea in Tunisia. The isolation of ETEC in the Netherlands was shown to be related to travel in endemic areas. EPEC probe positive strains were isolated in children and in adults, but were not in all cases associated with intestinal disease. During this study no VTEC were detected. From an immunocompromised kidney transplantation patient with sepsis and diarrhoea ETEC were isolated from blood.

Monoclonal antibodies that detect live salmonellae

Nine immunoglobulin G and nine immunoglobulin M murine monoclonal antibody-producing hybridomas reactive with live Salmonella bacteria were obtained from several fusions of immune spleen cells and Sp2/0 myeloma cells. The antibodies were selected by the magnetic immunoluminescence assay. The monoclonal antibodies were reactive with serogroups A, B, C1, C2, D, E, and K and Salmonella choleraesuis subsp. diarizonae. Each monoclonal antibody proved to be reactive with a distinct serotype. Clinical isolates belonging to these Salmonella serogroups could be detected. Reactivity with non-Salmonella bacteria proved to be minor.

The magnetic immuno polymerase chain reaction assay for direct detection of salmonellae in fecal samples

Direct polymerase chain reaction (PCR)-based detection with fecal specimens is hampered by inhibitory compounds, such as bilirubin and bile salts. These fecal compounds showed significant inhibition of PCR at low concentrations (10 to 50 micrograms/ml). For direct PCR analysis, fecal samples must be diluted 500-fold to overcome inhibition. Therefore, the magnetic immuno PCR assay (MIPA), which combines immunomagnetic separation by using specific monoclonal antibodies and PCR, was used to directly detect salmonellae in feces from humans. Immunomagnetically extracted stool samples needed to be diluted only 10-fold when 1 microgram of T4 gene 32 protein was added to the PCR. The MIPA sensitivity obtained was 10(5) CFU/ml of feces. A panel of monoclonal antibodies specific for Salmonella serogroups A to E was used to extract salmonellae from clinical samples. MIPA detection of salmonellae occurred with 11 out of 14 stool samples stored at 4 degrees C for 2 months. MIPA detection of salmonellae in stool samples is a promising, fast method for detection and identification.

Nontoxigenic strains of Clostridium difficile lack the genes for both toxin A and toxin B

A total of 39 toxigenic and 20 nontoxigenic strains of Clostridium difficile were tested for the presence of either toxin A or toxin B by the polymerase chain reaction (PCR). All toxigenic strains produced cytotoxin as assayed by using highly sensitive fetal lung fibroblasts and were positive for toxin A as well as toxin B in the PCR assay. All nontoxigenic strains failed to produce toxin and were negative in the PCR assay. This study shows that nontoxigenic strains of Clostridium difficile lack the toxin A as well as the toxin B gene.

Evaluation of the magnetic immuno PCR assay for rapid detection of Salmonella

A new technique, the Magnetic Immuno PCR Assay (MIPA), has been developed for the detection of Salmonella. The assay utilizes magnetic particles coated with monoclonal antibodies against Salmonella to extract these bacteria from the sample. Trapped bacteria are lysed, and the supernatant, which contains bacterial DNA, is then subjected to the polymerase chain reaction (PCR) using primers from the Salmonella typhimurium origin of DNA replication to amplify a 163 bp region. The specificity of the primer set was tested in the PCR; amplification occurred with all 25 Salmonella strains tested but not with 19 other species of Enterobacteriaceae tested. A sensitivity of 100 cfu Salmonella typhimurium was achieved for the MIPA by visualization of the amplified products by ethidiumbromide stained agarose gel electrophoresis. A ten-fold higher sensitivity was obtained by Southern blotting of the amplified products. The presence of 10(7) cfu Escherichia coli did not interfere with these detection levels. The MIPA thus specifically detected 100 cfu of Salmonella within 5 h and may be potentially useful for rapid detection of Salmonella in clinical specimens and food.

Uncoupling of oxidative and non-oxidative mechanisms in human granulocyte-mediated cytotoxicity: use of cytoplasts and cells from chronic granulomatous disease patient

Human polymorphonuclear leukocytes (PMN) and granule-free cytoplasts were compared for their cytotoxic capacities against red blood cells (RBC) and K562 tumor cells. Phorbol myristate acetate (PMA) stimulated PMN to efficient lysis of RBC targets, while cytotoxicity against the tumor cell line K562 was moderate. Activated cytoplasts also lysed RBC targets but were not able to kill K562 tumor cells, even at high cell numbers. Suppression of the glutathione redox cycle of the K562 tumor targets markedly increased their susceptibility to lysis by PMA-activated PMN. Despite the enhanced susceptibility of antioxidant-depleted K562 tumor cells to oxygen radical-induced damage, PMA-stimulated cytoplasts did not kill these targets. Addition of exogenous myeloperoxidase or lactoferrin to cytoplasts devoid of granule did not improve the lysis of RBC and K562 tumor cells. Coating K562 targets with specific antibodies induced efficient PMN-mediated killing in comparison to PMA-stimulated lysis of non-coated targets. Cytoplasts, however, did not kill antibody-coated K562 tumor cells; this was not improved by glutathione depletion but showed some lysis of antibody-coated RBC. PMN from a patient with chronic granulomatous disease (CGD) showed normal antibody-dependent cell-mediated cytotoxicity (ADCC) against K562 tumor cells but were not able to lyse these targets after PMA stimulation. The analysis of target cell killing by cytoplasts and PMN from a CGD patient indicated that granular constituents are important mediators in the killing of nucleated target cells and that PMN-mediated ADCC does not require the release of reactive oxygen species. Differences in the susceptibility of target cells to oxygen-mediated lysis indicates that target cell antioxidant mechanisms play an important role in the outcome of the cytotoxic response.

A probe for the detection of methicillin-resistant Staphylococcus aureus

An approximately 300 base pair DNA fragment for use as a probe was isolated from methicillin-resistant Staphylococcus aureus DNA partially digested with Sau3AI. This probe hybridized with 25 methicillin-resistant clinical isolates of Staphylococcus aureus belonging to 18 different phage types, but not with 41 clinical isolates susceptible to methicillin.

Degradation of herpes simplex virions by human polymorphonuclear leukocytes and monocytes

The degradation of herpes simplex virus particles after uptake by phagocytes was studied, but, since lysis of the phagocyte also resulted in damage to the viral envelope, measurement of viral infectivity as a criterion of viral degradation after phagocytosis was not possible. Therefore we focused on later events in viral destruction, namely the degradation of macromolecules. We have demonstrated that polymorphonuclear leukocytes (PMN) and monocytes (MN) can rapidly degrade the membrane proteins of the phagocytosed herpes-virus virions. PMN and MN from a patient with chronic granulomatous disease showed a similar rate of degradation compared to PMN and MN from healthy donors, which excludes an important role for toxic oxygen species in viral protein degradation. Experiments using toxic oxygen species-generating systems supported this observation. In contrast to PMN, MN are also effective in the digestion of viral DNA. We conclude that PMN and MN are able to neutralize large amounts of phagocytosed HSV, so their role in antiviral defence has again been demonstrated.

The use of a hybridization assay for the study of host defences against herpes simplex virus

A rapid and simple hybridization assay was developed as an alternative for virus titration for the investigation of host resistance against HSV-1 infections in vitro. The probe which was constructed for this assay was shown to be HSV-1-specific. When a monolayer of fibroblasts was infected for 24 h before hybridization, 15 PFU were detected reliably. A plateau in hybridization levels was found when the multiplicity of infection reached 1. In order to demonstrate the applicability of the probe for the study of host defences against HSV in vitro, fibroblasts were infected with HSV in the presence of different numbers of adherent cells and different concentrations of serum containing high titres of anti-HSV antibodies and complement. After 20 h of incubation, samples were lysed, spotted on Zetaprobe filter paper and hybridized with a 32P-labelled RNA probe. Spots were counted for radioactivity. The radioactivity was taken as a measure of the success of infection. Results showed that at high (10%) concentrations of serum containing high titres of anti-HSV antibodies and complement neutralization plays an important role. At low (1%) concentrations of serum containing high titres of anti-HSV antibodies and complement the phagocytic role of adherent cells becomes the dominant factor in preventing infection of the fibroblasts. However, when the number of infectious particles is increased, the protection provided by adherent cells is overwhelmed.

Quantitation of conjugate formation between human polymorphonuclear leukocytes and antibody-coated target cells by flow cytometry: the role of Fc receptor and LFA-1 antigen

The specific binding of human polymorphonuclear leukocytes (PMN) to antibody-coated target cells was characterized by flow cytometry. PMN were labeled with phycoerythrin-E (PE) via a granulocyte-specific monoclonal antibody (leu-M1) and mixed with fluorescein isothiocyanate-labeled K562 tumor cells sensitized with rabbit antiserum. Specific conjugates were formed as analyzed by two-color fluorescence in a flow cytometer. The formation of stable conjugates was dependent on initiation of contact, temperature, time, and antiserum concentration. Studies with inhibitors implicate that microfilaments, but not microtubules, Ca2+, Mg2+, or energy-dependent processes were a prerequisite for binding of PMN to the antibody-coated target cells. No conjugates were formed when uncoated target cells were used or when the experiment was performed in the presence of protein A, indicating that binding was specifically mediated through Fc receptors (FcR). Monoclonal antibodies against the FcRII and FcRIII were used to address the role of these receptors in conjugation. One of the two anti-FcRIII antibodies and an anti-FcRII antibody effectively prevented conjugation. A monoclonal antibody directed against the common beta-chain of the adhesion molecule family and a combination of antibodies against the alpha-chain of LFA-1 and Mo-1 also blocked conjugation when target cells were sensitized under suboptimal conditions. The antibody against the beta-chain also diminished killing of antibody-coated K562, as measured by chromium release when included in the cytotoxicity assay. These results indicate that flow cytometry permits accurate quantitation and characterization of the binding between PMN and antibody-coated target cells, which in principle, can be prevented by monoclonal antibodies against surface receptors. Binding is primarily established by both the FcRII and FcRIII. Adhesion-associated molecules on the PMN surface contribute to optimal binding.

Phagocytosis of herpes simplex virus by human granulocytes and monocytes

Polymorphonuclear leukocytes (PMN) can mediate cytotoxic reactions against virus infected targets cells. We observed very efficient binding of PMN to HSV-infected fibroblasts when loaded with HSV-specific antibodies. Using electron microscopy, infected fibroblasts were found to be totally surrounded by PMN and the phagocytosis of virions and fragments of infected cells was demonstrated. To quantify and study this phenomenon, and to compare PMN with monocytes, we developed radiometric and fluorometric phagocytosis assays. Leukocytes were mixed with [3H]glucosamine- or FITC-labeled virus and incubated at 37 degrees C. PMN associated radioactivity or fluorescence per cell as measured by flow cytometry was determined. PMN phagocytosis was dependent on the presence of specific anti-HSV antibodies and could be enhanced by addition of complement. Monocytes were also able to phagocytize virions; however, the rate of uptake was less than that for PMN. Under optimal conditions the total amount of herpes simplex particles that could be associated with one PMN or monocyte was about 10,000. PMN and monocytes are capable of phagocytosis of HSV. This may be an important factor in preventing the spread of infection in vivo.