Use of pulsed-field gel electrophoresis in the analysis of recurrent Staphylococcus aureus infections in patients on continuous ambulatory peritoneal dialysis

Prevalence and characterization of methicillin-resistant Staphylococcus aureus among healthy children in a city of Argentina

Community acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) is a major global problem. Healthy carriers of S. aureus strains have an important role in the dissemination of this bacterium. The aim of this study was to estimate the prevalence of S. aureus and methicillin-resistant S. aureus (MRSA) carriage among healthy children in a city of Buenos Aires province, Argentina, and to determine the potential risk factors for its acquisition. We also described the molecular features of MRSA strains circulating in this population. S. aureus carriage was investigated in all children attending the last year of kindergarten during the 2008 school- year period. Household contacts of MRSA carriers were also screened. Of 316 healthy children, 98 (31.0%) carried S. aureus, including 14 MRSA carriers (4.4%) and 84 methicillin susceptible S. aureus (MSSA) carriers (26.6%). All MRSA isolates carried the SCCmec type IV cassette. Eight of the fourteen isolates were closely related to the clone responsible for most severe community-acquired MRSA infections caused in our country (CAA: PFGE A, SCCmec IV, spa t311, ST5). Two subtypes (A(1) and A(2)) were distinguished in this group by PFGE. Both had agr type II and presented the same virulence determinants, except for PVL coding genes and sea that were only harbored by subtype A(1). Our results, based on the analysis of MRSA isolates recovered in the screening of healthy children, provide evidence of a community reservoir of the major CA-MRSA clone described in Argentina.

Molecular diagnostics of clinically important staphylococci

Bacterial species of the genus Staphylococcus known as important human and animal pathogens are the cause of a number of severe infectious diseases. Apart from the major pathogen Staphylococcus aureus, other species until recently considered to be nonpathogenic may also be involved in serious infections. Rapid and accurate identification of the disease-causing agent is therefore prerequisite for disease control and epidemiological surveillance. Modern methods for identification and typing of bacterial species are based on genome analysis and have many advantages compared to phenotypic methods. The genotypic methods currently used in molecular diagnostics of staphylococcal species, particularly of S. aureus, are reviewed. Attention is also paid to new molecular methods with the highest discriminatory power. Efforts made to achieve interlaboratory reproducibility of diagnostic methods are presented.

The Staphylococcus aureus Map protein is an immunomodulator that interferes with T cell-mediated responses

Staphylococcus aureus (SA) is an opportunistic pathogen that affects a variety of organ systems and is responsible for many diseases worldwide. SA express an MHC class II analog protein (Map), which may potentiate SA survival by modulating host immunity. We tested this hypothesis in mice by generating Map-deficient SA (Map(-)SA) and comparing disease outcome to wild-type Map(+)SA-infected mice. Map(-)SA-infected mice presented with significantly reduced levels of arthritis, osteomyelitis, and abscess formation compared with control animals. Furthermore, Map(-)SA-infected nude mice developed arthritis and osteomyelitis to a severity similar to Map(+)SA-infected controls, suggesting that T cells can affect disease outcome following SA infection and Map may attenuate cellular immunity against SA. The capacity of Map to alter T cell function was tested more specifically in vitro and in vivo using native and recombinant forms of Map. T cells or mice treated with recombinant Map had reduced T cell proliferative responses and a significantly reduced delayed-type hypersensitivity response to challenge antigen, respectively. These data suggest a role for Map as an immunomodulatory protein that may play a role in persistent SA infections by affecting protective cellular immunity.

Comparison of multilocus sequence typing and pulsed-field gel electrophoresis as tools for typing Staphylococcus aureus isolates in a microepidemiological setting

Multilocus sequence typing (MLST) of Staphylococcus aureus is well suited to the study of global or long-term epidemiology, but its role in local epidemiology has not been defined. The present study has compared MLST with pulsed-field gel electrophoresis (PFGE) by using S. aureus isolates associated with carriage and disease in a busy regional renal unit. One hundred forty-four patients were prospectively recruited, of whom 103 were receiving hemodialysis and 41 were on continuous ambulatory peritoneal dialysis. Three nasal swab specimens were obtained 1 month apart on entering the study. A nasal swab was positive for S. aureus on at least one occasion in 50 patients (35%). Typing of the 104 carriage isolates demonstrated 21 PFGE types and 21 sequence types (STs). Thirty-one carriers had two or more positive nasal swabs; of these, the isolates in all swabs from a given carrier had identical PFGE types for 29 carriers; the isolates in all of the same 29 swabs had identical STs. The carriage strain in two patients changed both PFGE type and STs during the period of swabbing. Eight patients (6%) had an episode of S. aureus bacteremia during the 12-month study period, and two of these were nasal carriers. One of these invasive isolates had the same PFGE type and ST as the carriage isolate. There were no differences between Simpson's index of diversity for PFGE and Simpson's index of diversity for MLST for both invasive and carriage isolates, suggesting that the two methods have very similar discriminatory abilities. We conclude that PFGE and MLST performed equally in this study.