Meticillin-resistant Staphylococcus Aureus Isolates Research Articles

Nosocomial and community-acquired meticillin-resistant Staphylococcus aureus infections in hospitalized patients (Spain, 1993–2003)

A series of annual surveys on the prevalence of infections in hospitalized patients in Spain was undertaken from 1993 to 2003 to describe clinical and demographic characteristics, trends and geographical variations in the proportion of meticillin-resistant Staphylococcus aureus (MRSA). A total of 8312 S. aureus infections in patients from 296 acute care hospitals pertaining to 17 regions in Spain were observed during the study period. Overall, 23.8% of these organisms were reported as meticillin resistant. The proportion of MRSA varied widely across regions and during the study period. Patients with nosocomial infections (NIs) had a two-fold higher prevalence of MRSA (31%) than patients with community-acquired infections (CAIs) (14%; P<0.001). Nevertheless, there was an increasing trend in the prevalence of MRSA isolates, both in patients with NI (from 22% to 41%; P<0.001) and with CAI (from 7% to 28%; P<0.001) throughout the 11-year period. Geographical variations over the last three years (2001-2003) show a centripetal gradient, with the lowest MRSA prevalence in south-west Spain and the highest MRSA prevalence in the central regions. Almost five-fold differences in MRSA proportions were seen between regions (range 10.3-54.5%). Compared with bloodstream infections, infections in other sites were more likely to be caused by MRSA (adjusted odds ratios for surgical site, urinary tract, skin and respiratory infections of 1.2, 1.2, 1.5 and 2.1, respectively).

Epidemiological typing of MRSA isolates from blood cultures taken in Irish hospitals participating in the European Antimicrobial Resistance Surveillance System (1999–2003)

Between 1999 and 2003, meticillin-resistant Staphylococcus aureus (MRSA) isolates recovered from blood cultures in Irish hospitals that participate in the European Antimicrobial Resistance Surveillance System were investigated by epidemiological typing using antibiogram-resistogram (AR) typing, biotyping, and DNA macrorestriction digestion using SmaI followed by pulsed-field gel electrophoresis (PFGE). PFGE patterns were assigned five-digit pulsed-field type (PFT) numbers, and PFTs of apparently related patterns were abbreviated to two-digit PFT groups (PFGs). AR and PFGE typing results were combined to produce AR-PFG types. Representative isolates of each AR-PFG type recovered in 2002 were typed by multilocus sequence typing and staphylococcal cassette chromosome (SCC) mec analysis. Isolates from 1999 and 2000 were also typed by phage typing. The extent to which epidemiological types of MRSA from blood cultures could be extrapolated to the total MRSA population was investigated by comparing results obtained with isolates from the total MRSA population versus those obtained with blood cultures during three study periods. Over the 5 years from 1999 to 2003, 1,580 blood culture isolates from 1,495 patients were analysed. Typeability and discriminatory indices were as follows: AR typing, 1 and 0.97; phage typing, 0.29 and 0.89; PFGE, 0.99 and 0.95; AR-PFG typing, 1 and 0.95. The most frequently occurring AR-PFG types were 06-01, 07-02, 13-00, and 14-00 and were exhibited by 57, 7, 14, and 12% of isolates, respectively. During the study period, the distribution of AR-PFG type changed markedly, with the prevalence of one type (AR-PFG 06-01) increasing by 880%, from 22% (39/181) in 1999 to 80% (343/430) in 2003. Investigation of whether epidemiological types among blood culture isolates of MRSA were representative of the total MRSA population showed that there was no significant difference in most instances. MLST and SCCmec typing showed that AR-PFG types 06-01, 07-02, 13-00, and 14-00 were ST22-MRSA-IV, ST36-MRSA-II, ST8-MRSA-IID, and ST8-MRSA-IIE, respectively.

Linezolid resistance in a clinical isolate of Staphylococcus aureus

The new oxazolidinone antimicrobial, linezolid, has been approved for the treatment of infections caused by various gram-positive bacteria, including meticillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). Although instances of linezolid resistance in VRE have been reported, resistance has not been encountered among clinical isolates of S aureus. We have characterised an MRSA isolate resistant to linezolid that was recovered from a patient treated with this agent for dialysis-associated peritonitis.

Exanthematous disease induced by toxic shock syndrome toxin 1 in the early neonatal period

We have seen a number of patients who developed systemic exanthema and thrombocytopenia in the first week of life. Although nearly 100% of the patients were carriers of meticillin-resistant Staphylococcus aureus (MRSA), no clear link between MRSA and this exanthematous disease has yet been made. 20 neonates with exanthema and thrombocytopenia were selected for study. To see whether superantigenic exotoxins from MRSA are involved in the pathogensis of the exanthematous disease, we studied the production of these exotoxins by MRSA isolates from the neonates. We studied the expression of T-cell-receptor Vbeta and CD45RO in T cells taken from four of the neonates. We also analysed the DNA sequences of 16 cloned Vbeta2-positive T-cell-receptor-chain genes taken from two of the neonates. Although most of the patients recovered within 5 days of onset of the exanthematous disease without any active treatment, two preterm infants died in the recovery phase. All patients showed colonisation by MRSA. The MRSA produced toxic shock syndrome toxin-1 (TSST-1). The number of T cells positive for T-cell-receptor Vbeta2, reactive to TSST-1, was increased in the four patients studied (p<0.0001), and these T cells expressed CD45RO (p=0.0185). None of the Vbeta2 clones had the same junctional sequences. The polyclonal expansion of Vbeta2-positive T cells in patients colonised by TSST-1-producing MRSA suggests that the pathogenic micro-organism of this neonatal exanthematous disease is S aureus, mainly MRSA, and that in its pathogenesis it activates T cells by TSST-1. Although the pathogenesis of both this exanthematous disease and toxic shock syndrome are fundamentally the same, a diagnosis of toxic shock syndrome cannot be made in this case, based on the clinical criteria for toxic shock syndrome. We propose neonatal toxic-shock-syndrome-like exanthematous disease (NTED) as the name for this disease.

ResistantStaphylococcus aureus

Catalase. negative; Meticill resistance Summary The wide dissemination of a major epidemic meticillin-resistant Staphylococcus aureus (MRSA) clone in Brazilian hospitals (Brazilian clone) limits the value of molecular typing techniques such as pulsed-field gel elec- .in trophoresis (PFGE) for outbreak investigation. We report the first outbreak of a catalase-negative strain of MRSA, which was initially detected by the unusual result of this phenotypical test. The outbreak occurred in the Hospital Sanatorinhos de Carapicuiba, a 237-bed secondary hospital located in Sao Paulo, Brazil. From May to August 2002, a total of 11 MRSA isolates were recovered from four patients in the intensive care unit. A11 the isolates were catalase negative and susceptible only to vancomycin and linezolid. Three of the four patients eventually died. Molecular typing dernonstrated an indistinguishable PFGE pattern among the 11 isolates, with similarities to the Brazilian clone and the hospital's usual MRSA strain. This report empha- sizes the importance of an uncommon phenotypical result as a marker for initiating an outbreak investigation and should encourage clinical labora- tories to recognize and report such isolates. O 2006 The Hospital Infection Society. Published by Elsevier Ltd. All rights reserved