Differences between "classical" risk factors for infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and risk factors for nosocomial bloodstream infections caused by multiple clones of the staphylococcal cassette chromosome mec type IV MRSA strain.

OBJECTIVE: To identify risk factors associated with nosocomial bloodstream infections caused by multiple clones of the staphylococcal cassette chromosome mec (SCCmec) type IV strain of methicillin-resistant Staphylococcus aureus (MRSA). DESIGN: An unmatched case-control study (at a ratio of 1:2) performed during the period from October 2002 through September 2003. SETTING: A 2,000-bed tertiary care teaching hospital affiliated with the University of São Paulo in São Paulo, Brazil. METHODS: Case patients (n=30) were defined either as patients who had a bloodstream infection due to SCCmec type IV MRSA diagnosed at least 48 hours after hospital admission or as neonates with the infection who were born in the hospital. Control patients (n=60) were defined as patients with SCCmec type III MRSA infection diagnosed at least 48 hours after hospital admission. Genes encoding virulence factors were studied in the isolates recovered from case patients, and molecular typing of the SCCmec type IV MRSA isolates was also done by pulsed-field gel electrophoresis and multilocus sequence typing. RESULTS: In multivariate analysis, the following 3 variables were significantly associated with having a nosocomial bloodstream infection caused by SCCmec type IV strains of MRSA: an age of less than 1 year, less frequent use of a central venous catheter (odds ratio [OR], 0.07 [95% confidence interval {CI}, 0.02-0.28]; p= .025), and female sex. A second analysis was performed that excluded the case and control patients from the neonatal unit, and, in multivariate analysis, the following variables were significantly associated with having a nosocomial bloodstream infection caused by SCCmec type IV strains of MRSA: less frequent use of a central venous catheter (OR, 0.12 [95% CI, 0.03-0.55]; p= .007), lower Acute Physiology and Chronic Health Evaluation II score on admission (OR, 0.14 [95% CI, 0.03-0.61]; p= .009), less frequent surgery (OR, 0.21 [95% CI, 0.06-0.83]; p= .025), and female sex (OR, 5.70 [95% CI, 1.32-24.66]; p= .020). Of the 29 SCCmec type IV MRSA isolates recovered from case patients, none contained the Panton-Valentine leukocidin, gamma-hemolysin, enterotoxin B or C, or toxic shock syndrome toxin-1. All of the isolates contained genes for the LukE-LukD leukocidin and alpha-hemolysin. Genes for enterotoxin A were present in 1 isolate, and genes for beta-hemolysin were present in 3 isolates. CONCLUSIONS: "Classical" risk factors do not apply to patients infected with the SCCmec type IV strain of MRSA, which is an important cause of nosocomial bacteremia. This strain infects a patient population that is less ill and has had less frequent invasive procedures than a patient population infected with the multidrug-resistant strain of SCCmec type III MRSA. We found that virulence factors were rare and that Panton-Valentine leukocidin was absent. There were multiple clones of the SCCmec type IV strain in our hospital. Children under 1 year of age were at a higher risk. There was a predominant clone (sequence type 5) in this patient population.

Type IV SCCmec found in decade old Brazilian MRSA isolates.

Methicillin-resistant Staphylococcus aureus (MRSA) commonly causes infection in hospitalized patients. Since its appearance in the 1960s, the SCCmec has evolved throughout the years into 5 different types (I-V), each bearing a different set of genes. Infection with MRSA SCCmec types I, II or III is almost exclusively restricted to hospitalised patients. However, recently, community acquired MRSA (CA-MRSA) infections have been reported with increasing frequency, usually caused by a type IV SCCmec MRSA in nosocomial settings. We studied the prevalence of SCCmec types in 50 nosocomial strains collected from 1995 to 1999. The SCCmec complex type and presence of Panton-Valentine leukocidin (PVL) were determined by PCR. Strains had been previously typed by PFGE and were now typed by MLST. We found that 3 of the isolates studied bore a type IVc SCCmec all having different PFGE and MLST profiles (ST3, ST5 and ST88). All strains bearing a type III SCCmec belonged to MLST ST239 (Brazilian/Iberian clone). Only the strain which presented the ST5 profile bore the pvl gene. The type IVc SCCmec strains presented relatively lower levels of resistance to oxacillin in comparison to the type III SCCmec strains. The pattern of dissemination of the type IV SCCmec remains to be elucidated. The finding of strains carrying a type IV SCCmec in the present study among strains isolated at least 7 years ago indicates that clones bearing a type IV SCCmec have been present in Brazil for quite some time, and must have gone by undetected.

Type IV SCCmec found in decade old Brazilian MRSA isolates

Methicillin-resistant Staphylococcus aureus (MRSA) commonly causes infection in hospitalized patients. Since its appearance in the 1960s, the SCCmec has evolved throughout the years into 5 different types (I-V), each bearing a different set of genes. Infection with MRSA SCCmec types I, II or III is almost exclusively restricted to hospitalised patients. However, recently, community acquired MRSA (CA-MRSA) infections have been reported with increasing frequency, usually caused by a type IV SCCmec MRSA in nosocomial settings. We studied the prevalence of SCCmec types in 50 nosocomial strains collected from 1995 to 1999. The SCCmec complex type and presence of Panton-Valentine leukocidin (PVL) were determined by PCR. Strains had been previously typed by PFGE and were now typed by MLST. We found that 3 of the isolates studied bore a type IVc SCCmec all having different PFGE and MLST profiles (ST3, ST5 and ST88). All strains bearing a type III SCCmec belonged to MLST ST239 (Brazilian/Iberian clone). Only the strain which presented the ST5 profile bore the pvl gene. The type IVc SCCmec strains presented relatively lower levels of resistance to oxacillin in comparison to the type III SCCmec strains. The pattern of dissemination of the type IV SCCmec remains to be elucidated. The finding of strains carrying a type IV SCCmec in the present study among strains isolated at least 7 years ago indicates that clones bearing a type IV SCCmec have been present in Brazil for quite some time, and must have gone by undetected.

Genes de virulência agr-dependentes em cepas de Staphylococcus aureus resistentes a oxacilina SCCmec tipo IV isoladas no Brasil / Agr-dependent virulence genes in SCCmec IV Oxacillin Resistant Staphylococcus aureus (ORSA) strains isolated in Brasil

O Staphylococcus aureus é um patógeno extremamente versátil tanto em termos de resistência a antimicrobianos quanto em virulência. O S.aureus resistente a oxacilina (ORSA) adquire a resistência a toda a classe de beta-lactâmicos através de um cassete cromossômico (SCCmec) que carrega o gene mecA, mas pode carregar outros genes de resistência. A soma desses genes de resistência e de virulência torna o S. aureus um grave problema para hospitais do mundo inteiro, que nos últimos vem se estendendo também à comunidade. Foram estudados 50 isolados de ORSA, dentre os quais 15 pertencentes ao clone endêmico brasileiro (CEB) e 3 cepas SCCmec tipo IV isoladas entre 1995 e 1999. Adicionalmente, 32 amstras ORSA SCCmec tipo IV isoladas no Hospital de Clínicas de São PAulo...

Staphylococcus aureus is an extremely successful pathogen for it is both highly resistant to antibiotics in addition to being virulent. Methicillin-resistant Staphylococcus aureus (MRSA) acquires resistance to the beta-Iactam antibiotics through the acquisition of a chromosomal cassette (SCCmec) which carries the mecA gene, and can carry other resistance genes. The presence of these genes in S. aureus makes it a serious problem in hospitaIs worldwide. In spite of usually being restricted to the nosocomial environment, over the last few years MRSA has been spreading throughout the community. Fifty nosocomial MRSA strains were studied, including 15 belonging to the Brazilian endemic clone (BEC), 3 type IV SCCmec strains isolated between 1995-1999, and 32 type N SCCmec isolates from the "Hospital de Clínicas (HC) de São Paulo". The isolates were analyzed as to their susceptibility profile, SCCmec type, virulence and expression profile (toxins and adhesins), agr group classification and functionality, PFGE and MLST profiles. BEC isolates proved to be multiresistant to antibiotics. Type IV SCCmec strains presented a susceptibility profile to a number of drugs of different antimicrobial classes. BEC and type N SCCmec strains did not present significant differences in their virulence profiles. Only the type IV SCCmec strains isolated in 1995-1999 presented a greater virulence profile than those isolated in the HC. Type IV SCCmec strains isolated in Brazil were not highly virulent as described in other countries. Brazilian isolates usually do not possess virulence factors such as the Panton-Valentine leukocidin, exfoliative toxins and enterotoxins. On the other hand, they usually possess alpha-hemolysin and the LukED leukocidin, which is still very poorly studied that have been presented in papers like cause of serious ocular lesions and post-antimicrobial therapy diarrhea. A relation between the agr type and the virulence profile was not established, for virulence profiles were very similar even between isolates belonging to different agr groups.

First isolation of metallo-beta-lactamase-producing multiresistant Klebsiella pneumoniae from a patient in Brazil.

A multiresistant Klebsiella pneumoniae isolate was taken from the blood of a 75-year-old patient with nosocomial pneumonia who developed septic shock and failed therapy with imipenem. The isolate presented an MIC of imipenem of 128 microg/ml, and the production of a metallo-beta-lactamase was confirmed by phenotypic and genotypic techniques. We here report, for the first time, the detection of a metalloenzyme (IMP-1)-producing K. pneumoniae clinical strain in Latin America. The gene responsible for this phenotype was found to be bla(IMP-1), carried in a class 1 integron.