Bo Söderquist

Classification of staphylococcal cassette chromosome mec (SCCmec) : guidelines for reporting novel SCCmec elements.

Classification of staphylococcal cassette chromosome mec (SCCmec) : guidelines for reporting novel SCCmec elements.

Differences in Potency of Intravenous Polyspecific Immunoglobulin G against Streptococcal and Staphylococcal Superantigens: Implications for Therapy of Toxic Shock Syndrome

Administration of intravenous polyspecific immunoglobulin G (IVIG) has been proposed as adjunctive therapy for toxic shock syndrome caused by Streptococcus pyogenes or Staphylococcus aureus. We investigated whether superantigen-containing culture supernatants prepared from streptococcal isolates (n=21) and staphylococcal isolates (n=20) from cases of severe sepsis were inhibited to an equal extent by IVIG in proliferation experiments that used human peripheral blood mononuclear cells. All 3 IVIG preparations tested were highly efficient in neutralizing the superantigens, and most supernatants were completely inhibited at concentrations ranging from 0.05 to 2.5 mg IVIG/mL. An important finding was that culture supernatants from S. pyogenes isolates were consistently inhibited to a greater extent than those of S. aureus isolates (P<.01). The findings demonstrate that staphylococcal superantigens are not inhibited as efficiently as streptococcal superantigens by IVIG, and, hence, a higher dose of IVIG may be required for therapy of staphylococcal toxic shock syndrome in order to achieve protective titers and clinical efficacy.

Biofilm formation by Propionibacterium acnes is a characteristic of invasive isolates

Propionibacterium acnes is a common and probably underestimated cause of delayed joint prosthesis infection. Bacterial biofilm formation is central in the pathogenesis of infections related to foreign material, and P. acnes has been shown to form biofilm both in vitro and in vivo. Here, biofilm formation by 93 P. acnes isolates, either from invasive infections (n = 45) or from the skin of healthy people (n = 48), was analysed. The majority of isolates from deep infections produced biofilm in a microtitre model of biofilm formation, whereas the skin isolates were poor biofilm producers (p <0.001 for a difference). This indicates a role for biofilm formation in P. acnes virulence. The type distribution, as determined by sequencing of recA, was similar among isolates isolated from skin and from deep infections, demonstrating that P. acnes isolates with different genetic backgrounds have pathogenic potential. The biofilm formed on plastic and on bone cement was analysed by scanning electron microscopy (EM) and by transmission EM. The biofilm was seen as a 10-mum-thick layer covering the bacteria and was composed of filamentous as well as more amorphous structures. Interestingly, the presence of human plasma in solution or at the plastic surface inhibits biofilm formation, which could explain why P. acnes primarily infect plasma-poor environments of, for example, joint prostheses and cerebrospinal shunts. This work underlines the importance of biofilm formation in P. acnes pathogenesis, and shows that biofilm formation should be considered in the diagnosis and treatment of invasive P. acnes infections.

Guidelines for Reporting Novel mecA Gene Homologues

Methicillin-resistant staphylococci are disseminated all over the world and are frequent causes of health care- and community-associated infections. Methicillin-resistant strains typically carry the acquired mecA gene that encodes a low-affinity penicillin-binding protein (PBP), designated PBP2a or

Bacterial or Crystal-associated Arthritis? Discriminating Ability of Serum Inflammatory Markers

A retrospective study of patients with culture-verified septic arthritis (n = 54) and polarizing microscopy verified crystal-associated arthritis (n = 34) was conducted with the objective to identify discriminating laboratory parameters in serum. Serum CRP levels (p = 0.002) and ESR (p = 0.03) were significantly higher on admission in patients with septic arthritis than in those with crystal-associated arthritis. The peripheral WBC counts did not differ between the two groups, nor did the lactoferrin or procalcitonin (PCT) levels. Serum TNFalpha concentrations on admission were higher in patients with septic arthritis than in those with crystal-associated arthritis (p = 0.0008). Significant differences were also found for IL-8 (p = 0.01) and G-CSF (p = 0.002), but not for IL-6 (p = 0.5). However, extensive overlap between the groups was present, resulting in low sensitivity, specificity and predictive value for each test. Determining serum levels of acute phase reactants, including cytokines, does not replace careful synovial fluid examination, including direct microscopy and cultivation.

The origin of a methicillin-resistant Staphylococcus aureus isolate at a neonatal ward in Sweden—possible horizontal transfer of a staphylococcal cassette chromosome mec between methicillin-resistant Staphylococcus haemolyticus and Staphylococcus aureus

The first methicillin-resistant Staphylococcus aureus (MRSA) strain originated when a staphylococcal cassette chromosome mec (SCCmec) with the gene mecA was integrated into the chromosome of a susceptible S. aureus cell. The SCCmec elements are common among the coagulase-negative staphylococci, e.g. Staphylococcus haemolyticus, and these are considered to be potential SCCmec donors when new clones of MRSA arise. An outbreak of MRSA occurred at a neonatal intensive-care unit, and the isolates were all of sequence type (ST) 45, as characterized by multilocus sequence typing, but were not typeable with respect to SCCmec types I, II, III or IV. During the same time period, methicillin-resistant S. haemolyticus (MRSH) isolates identified in blood cultures at the same ward were found to be genotypically homogenous by pulsed-field gel electrophoresis, and did not carry a type I, II, III or IV SCCmec either. Thus, the hypothesis was raised that an SCCmec of MRSH had been transferred to a methicillin-susceptible S. aureus strain and thereby created a new clone of MRSA that caused the outbreak. This study showed that MRSA from the outbreak carried a ccrC and a class C mec complex that was also found among MRSH isolates. Partial sequencing of the mec complexes showed more than 99% homology, indicative of a common type V SCCmec. This finding may provide evidence for a recent horizontal transfer of an SCCmec from MRSH to an identified potential recipient, an ST45 methicillin-susceptible S. aureus strain, thereby creating a new clone of MRSA that caused the outbreak.

Use of inflammatory markers for early detection of bacteraemia in patients with febrile neutropenia.

The aim of the study was to evaluate the ability of procalcitonin, C-reactive protein, serum amyloid A, interleukin-6 and interleukin-8 to predict bacteraemia during the 2 first d of fever in neutropenic patients. A total of 94 febrile neutropenic episodes in 60 patients were studied. Plasma samples were analysed at 10-h intervals from the onset of fever. Clinical events were categorized into 4 groups: 1) bacteraemia caused by other agents than coagulase-negative staphylococci (non-CNS bacteraemia) (n=21), 2) coagulase-negative staphylococci bacteraemia (n=15), 3) microbiologically or clinically documented infection without bacteraemia (n=26) and 4) fever of unknown origin (n=32). In non-CNS bacteraemia all markers, except for serum amyloid A, showed significantly higher levels compared to patients with fever of unknown origin (p<0.05). For non-CNS bacteraemia the highest negative predictive value was found for procalcitonin (94%), followed by interleukin-6 (89%), C-reactive protein (88%) and interleukin-8 (87%). Procalcitonin, with a cut-off level of 1.4 ng/ml during 10–20 h after fever onset, showed the highest positive predictive value (67%) for a non-CNS bacteraemia. In conclusion, the value of the analysed markers to predict a non-CNS bacteraemia in neutropenic patients was limited due to low sensitivity and positive predictive value. However, procalcitonin, interleukin-6, C-reactive protein, and interleukin-8 could give useful information for the clinician in excluding a non-CNS bacteraemia.

Novel Type of Staphylococcal Cassette Chromosome mec in a Methicillin-Resistant Staphylococcus aureus Strain Isolated in Sweden

ABSTRACT We identified a novel type of staphylococcal cassette chromosome mec (SCCmec) element carried by methicillin-resistant Staphylococcus aureus (MRSA) strain JCSC6082 isolated in Sweden. The SCCmec element was demarcated by characteristic nucleotide sequences at both ends and was integrated at the 3′ end of orfX. The element carried a novel combination of a type 5 ccr gene complex and class C1 mec gene complex. The J regions of the element were homologous to those of the SCCmercury element of S. aureus strain 85/2082, with nucleotide identity greater than 99%. However, the novel SCCmec element from JCSC6082 did not carry the mer operon nor Tn554, suggesting that evolution to SCCmec could have been from a common ancestor by acquisition of the class C1 mec gene complex. The novel SCCmec element from JCSC6082 was flanked by a novel SCC-like chromosome cassette (CC6082), which was demarcated by two direct repeats and could be excised from the chromosome independently of the SCCmec element. Our data suggest that novel SCCmec elements can be generated on the staphylococcal chromosome through the recombination between extant SCC elements and mec gene complexes.

Antibody Responses in Patients with Staphylococcal Septicemia against Two Staphylococcus aureus Fibrinogen Binding Proteins: Clumping Factor and an Extracellular Fibrinogen Binding Protein

ABSTRACT We analyzed the serum antibody responses against twoStaphylococcus aureus fibrinogen binding proteins, the cell-bound clumping factor (Clf) and an extracellular fibrinogen binding protein (Efb). The material consisted of 105 consecutive serum samples from 41 patients suffering from S. aureussepticemia and 72 serum samples from healthy individuals. An enzyme-linked immunosorbent assay (ELISA) was developed. Healthy individuals showed variable levels of antibodies against the studied antigens, and cutoff levels (upper 95th percentile) against these antigens were determined. No correlation was seen between serum antibody levels against Clf and Efb. In acute-phase samples 27% of patients showed positive antibody levels against Clf and 10% showed positive levels against Efb, while in convalescent-phase samples 63% (26 of 41) showed a positive serology against Clf and 49% (20 of 41) showed a positive serology against Efb. Antibody levels against Efb were significantly lower in the acute-phase sera than in sera from healthy individuals (P = 0.002). An antibody response against Clf was most frequent in patients suffering from osteitis plus septic arthritis and from endocarditis (80% positive). The antibody response against Efb appeared to develop later in the course of disease. A possible biological effect of measured antibodies was demonstrated with the help of an inhibition ELISA, in which both high-titer and low-titer sera inhibited the binding of bacteria to fibrinogen. In conclusion, we have demonstrated in vivo production ofS. aureus fibrinogen binding proteins during deep S. aureus infections and a possible diagnostic and prophylactic role of the corresponding serum antibodies in such infections.

Assessment of systemic inflammation markers to differentiate a stable from a deteriorating clinical course in patients with febrile neutropenia

In this study, we evaluated the predictive values of procalcitonin (PCT), C‐reactive protein (CRP), interleukin‐6 (IL‐6) and serum amyloid A (SAA) for determining the clinical course in febrile neutropenic patients. Daily plasma analyses during the fever course were performed in 101 episodes with fever and chemotherapy‐induced neutropenia (neutrophil count <0.5 × 109/L). Procalcitonin (PCT) and IL‐6 values were significantly higher in febrile episodes in patients who developed complications. Procalcitonin with a cut‐off value of ≤0.4 ng/mL or IL‐6 ≤50 pg/mL 3 d after fever onset indicated daily high negative predictive values (NPVs) (91–100%) for episodes with complications. No marker could predict deterioration; however, daily low plasma concentrations of PCT or IL‐6 during the first 8 d of fever were found to be a good predictor of no subsequent complications in neutropenic patients and therefore to be a helpful tool for limiting anti‐microbial therapy.