Clinical, microbiological, and genetic characteristics of heteroresistant vancomycin-intermediate Staphylococcus aureus bacteremia in a teaching hospital.

The emergence of vancomycin intermediate Staphylococcus aureus (VISA) and heterogeneous VISA (hVISA) is of major concern worldwide. Our objective was to investigate the prevalence, phenotypic and molecular features of hVISA strains isolated from bacteremic patients and to determine the clinical significance of the hVISA phenotype in patients with bacteremia. A total of 104 S. aureus blood isolates were collected from a teaching hospital of Argentina between August 2009 and November 2010. No VISA isolate was recovered, and 3 out of 92 patients (3.3%) were infected with hVISA, 2 of them methicillin-resistant S. aureus (MRSA) (4.5% of MRSA). Macro Etest and prediffusion method detected 3/3 and 2/3 hVISA respectively. Considering the type of bacteremia, the three cases were distributed as follows: two patients had suffered multiple episodes of bacteremia (both hVISA strains recovered in the second episode), while only one patient had suffered a single episode of bacteremia with hVISA infection. MRSA bloodstream isolates exhibiting the hVISA phenotype were related to HA-MRSA Cordobes clone (ST5-SCCmec I-spa t149) and MRSA Argentinean pediatric clone (ST100-SCCmec IVNV-spa t002), but not to CA-MRSA-ST30-SCCmec IV-spa t019 clone that was one of the most frequent in our country. Although still relatively infrequent in our hospital, hVISA strains were significantly associated with multiple episodes of bacteremia (p=0.037) and genetically unrelated.

Endocarditis caused by methicillin-susceptible Staphylococcus aureus with reduced susceptibility to vancomycin: a case report.

INTRODUCTION: Staphylococcus aureus is the most common cause of acute infective endocarditis.Recent reports have described heteroresistance to vancomycin associated with methicillin-resistant Staphylococcus aureus. We present the first case report in Argentina of the failure of treatment with vancomycin in endocarditis caused by methicillin-susceptible Staphylococcus aureus containing subpopulations with reduced susceptibility to vancomycin. CASE PRESENTATION: We report the case of a 66-year-old Hispanic man with infective endocarditis complicated by septic emboli in the lumbosacral spine and the left iliopsoas muscle. This disease was caused by methicillin-susceptible Staphylococcus aureus containing subpopulations with reduced susceptibility to vancomycin. He was initially treated with cephalothin and gentamicin but developed a rash caused by beta-lactams and interstitial nephritis. For that reason, the treatment was subsequently switched to vancomycin but he failed to respond. The infection resolved after administration of vancomycin in combination with gentamicin and rifampin. CONCLUSION: Our case report provides important evidence for the existence of subpopulations of methicillin-susceptible Staphylococcus aureus that have reduced susceptibility to vancomycin which would account for treatment failure. Our case raises an alert about the existence of these strains and highlights the need to determine the vancomycin minimum inhibitory concentration of Staphylococcus aureus to screen for the presence of strains that have reduced vancomycin susceptibility at different infection sites.

Congenital candidiasis: confirmation of mother-neonate transmission using molecular analysis techniques.

We describe a case of congenital acquired candidiasis in a preterm female delivered through Caesarean section due to the premature rupture of the amniotic membrane. The neonate presented with suspected chorioamnionitis and erythematous desquamative skin. Candida albicans was isolated from the placenta, mouth, groin, and periumbilical lesions. The infant developed candidemia due to Candida albicans and the same yeast was also isolated from a catheter. Culture inoculated with swabs from the mouth and vagina of the mother yielded C. albicans and C. krusei. All C. albicans isolates from the mother and the neonate were visually indistinguishable by molecular typing techniques which included chromosomal karyotyping and restriction endonuclease analysis followed by pulsed-field gel electrophoresis. These findings allowed the clinical condition to be confirmed as congenital acquisition of candidiasis in this case.

HLA-driven convergence of HIV-1 viral subtypes B and F toward the adaptation to immune responses in human populations.

BACKGROUND: Cytotoxic T-Lymphocyte (CTL) response drives the evolution of HIV-1 at a host-level by selecting HLA-restricted escape mutations. Dissecting the dynamics of these escape mutations at a population-level would help to understand how HLA-mediated selection drives the evolution of HIV-1. METHODOLOGY/PRINCIPAL FINDINGS: We undertook a study of the dynamics of HIV-1 CTL-escape mutations by analyzing through statistical approaches and phylogenetic methods the viral gene gag sequenced in plasma samples collected between the years 1987 and 2006 from 302 drug-naïve HIV-positive patients. By applying logistic regression models and after performing correction for multiple test, we identified 22 potential CTL-escape mutations (p-value<0.05; q-value<0.2); 10 of these associations were confirmed in samples biologically independent by a Bayesian Markov Chain Monte-Carlo method. Analyzing their prevalence back in time we found that escape mutations that are the consensus residue in samples collected after 2003 have actually significantly increased in time in one of either B or F subtype until becoming the most frequent residue, while dominating the other viral subtype. Their estimated prevalence in the viral subtype they did not dominate was lower than 30% for the majority of samples collected at the end of the 80's. In addition, when screening the entire viral region, we found that the 75% of positions significantly changing in time (p<0.05) were located within known CTL epitopes. CONCLUSIONS: Across HIV Gag protein, the rise of polymorphisms from independent origin during the last twenty years of epidemic in our setting was related to an association with an HLA allele. The fact that these mutations accumulated in one of either B or F subtypes have also dominated the other subtype shows how this selection might be causing a convergence of viral subtypes to variants which are more likely to evade the immune response of the population where they circulate.

[Candida albicans outbreak in a neonatal intensive care unit]. / Brote de candidemia por Candida albicans en neonatología.

The appearance of Candida albicans in three patients made physicians investigate an outbreak. Outbreak description and microbiologic screening: Case 1 developed C. albicans in the placenta culture and in the blood culture carried out on the 8th day of birth. Four days after this candidemia, C. albicans was recovered in a catheter tip of a second neonate (case 2) and finally five days later other newborn (case 3) developed C. albicans in the hemoculture. After that, the hands of all caregivers as well as case 3's incubator, case 1's mother, and from all nine neonates in the unit were studied with swabs. A wet mount was done to all swabs and then they were cultured in Chromagar Candida and SDA. All C. albicans were studied by RAPD. RAPD study showed that C. albicans recovered from placenta and blood cultures of case 1, the catheter tip of case 2 and the blood culture of case 3, resulted to be identical and these yeasts were related to the C. albicans from the mouth of case 1 mother and the mouth of another colonized newborn. C. albicans was not found in the others swabs. The isolations of identical C. albicans allowed to suppose the horizontal transmission from the case 1, that had acquired it congenitally. Not only isolation of unusual Candida species would be an alert. Despite patients' personal factors to justify a fungal infection, the recovery of C. albicans in a short period of time should warn physicians about the possibility of a horizontal transmission.

Salmonelosis extraintestinal: clínica, epidemiología y resistencia antimicrobiana / Salmonella extraintestinal infection: clinic features, epidemiology and antimicrobial resistance

Se evaluaron retrospectivamente las características clínicas de 59 pacientes con aislamientos extraintestinales de Salmonella enterica no Typhi y la resistencia antibiótica entre 1988 y 2004. En el 95% de los casos se conocieron las condiciones de base del huésped que consistieron en: enfermedad oncohematológica (15), lupus eritematoso sistémico (11), síndrome de inmuno deficiencia adquirida (10), pacientes internados en neonatología (8), colecistitis (4) y otras (7). Las formas clínicas halladas fueron: bacteriemias primarias (26), bacteriemias secundarias a gastroenteritis (15), artritis séptica (7), infección urinaria (12), infección intraabdominal (5), meningitis (1) y pericarditis (1). En 29 pacientes se aisló Salmonella enterica no Typhi en más de una localización. El 15,8% y el 21,0% de 59 aislamientos presentaron resistencia a cefalosporinas de 3ª generación y a ampicilina, respectivamente. Salmonella Agona causó un brote epidémico en la sala de cuidados intensivos de neonatología, aislándose de sangre en 5 pacientes y en uno también de LCR. Este serotipo fue multirresistente. Imipenem, trimetroprima-sulfometoxazol y ciprofloxacina fueron los antibióticos más activos (CIM 50: 0,5; 0,5 y 0,002 µg/mL, respectivamente).

The clinical and antimicrobial resistance of 59 patients with extraintestinal infection by nontyphi Salmonella was retrospectively evaluated from 1988 to 2004. In 95% of the patients there were underlying diseases, which included: oncohematologic disease (15), systemic lupus erythematosus (11), acquired immunodeficiency disease (AIDS) (10), patients of neonatal units (8), colecistitis (4), and other disorders (7). The clinical manifestation were primary bacteremias (26), bacteremias secondary to gastroenteritis (15), arthritis (7), urinary tract infections (12), abdominal infections (5), meningitis (1) and pericarditis (1). In 29 patients Salmonella enterica no Typhi was isolated in more than one site. Resistance to third generation cephalosporins was observed in 15,8 % of these isolates, and resistance to ampicillin in 21,0%. Salmonella Agona was isolated from an outbreak in neonatal ICU; the organism was recovered from blood samples of five neonates and in one patient also isolated from CSF. These isolates showed multiresistance. Imipenem, trimetoprim-sulfametoxazol and ciprofloxacin were the three most active antimicrobial agents (MIC 50: 0.5, 0.5 and 0.002 µg/mL, respectively).