The Changing Epidemiology and Antimicrobial Susceptibility of Staphylococcus aureus Isolated from Blood Cultures in a University Hospital from Argentina

Staphylococcus aureus bacteremia (SAB) is one of the most common serious bacterial infections worldwide. In this study, we demonstrated changes in SAB epidemiology in an Argentinean University Hospital during an 8-year period (2009-2016). A total of 326 S. aureus clinical isolates were recovered in three periods: P1: 2009-2010, P2: 2012-2014, and P3: 2015-2016. Among these, 127 were methicillin-resistant S. aureus (MRSA) and were characterized by phenotypic and molecular methods. We hereby report a significant decline in multiple drug resistance among MRSA isolates associated with an increase in SCCmec IV between the three periods. A diversity of MRSA-IV clones (mainly ST30-MRSA-IV, ST5-MRSA-IV, and ST8-MRSA-IV) replaced between 2009 and 2016 the previous prevalent MRSA clone causing bloodstream infections at this hospital (ST5-MRSA-I). MRSA population structure continued to diversify between P2 and P3. Notably, ST8-MRSA-IV-t008 related to USA300 was first detected during P2, and ST8-MRSA-IV together with ST30-MRSA-IV related to the Southwest Pacific clone were the more prevalent MRSA genotypes circulating during P3.

Genomic epidemiology of Staphylococcus aureus isolated from bloodstream infections in South America during 2019 supports regional surveillance

Staphylococcus aureus remains one of the leading causes of infections worldwide and a common cause of bacteraemia. However, studies documenting the epidemiology of S. aureus in South America using genomics are scarce. We hereby report on the largest genomic epidemiology study to date of both methicillin-resistant S. aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) in South America, conducted by the StaphNET-SA network. We characterised 404 genomes recovered from a prospective observational study of S. aureus bacteraemia in 58 hospitals from Argentina, Bolivia, Brazil, Paraguay and Uruguay between April and October 2019. We show that a minority of S. aureus isolates are phenotypically multi-drug resistant (5.2%), but more than a quarter are resistant to macrolide-lincosamide-streptogramin B (MLSb). MSSA were more genetically diverse than MRSA. Lower rates of associated antimicrobial resistance in community-associated(CA)-MRSA versus hospital-associated (HA)-MRSA were found in association with three S. aureus genotypes dominating the MRSA population: CC30-MRSA-IVc-t019-lukS/F-PV+, CC5-MRSA-IV-t002-lukS/F-PV- and CC8-MRSA-IVc-t008-lukS/F-PV+-COMER+. These are historically from a CA origin, carry on average fewer antimicrobial resistance determinants, and often lack key virulence genes. Surprisingly, CC398-MSSA-t1451-lukS/F-PV- related to the CC398 human-associated lineage is widely disseminated throughout the region, and is described here for the first time as the most prevalent MSSA lineage in South America. Moreover, CC398 strains carrying ermT (largely responsible for the MLSb resistance rates of MSSA strains: inducible iMLSb phenotype) and sh_fabI (related to triclosan resistance) were recovered from both CA and HA origin. The frequency of MRSA and MSSA lineages differed between countries but the most prevalent S. aureus genotypes are high-risk clones widely distributed in the South American region without a clear country-specific phylogeographical structure. Therefore, our findings underline the need for continuous genomic surveillance by regional networks such as StaphNET-SA. This article contains data hosted by Microreact.

Epidemiology of Invasive Infections Caused by Streptococcus agalactiae in Argentina

In recent years, an increase in the number of cases of invasive infections due to Streptococcus agalactiae (group B Streptococcus [GBS]) in adults has been reported. During 2014 and 2015, a multicentric, observational, and prospective study, including 40 health centers, was developed to describe the phenotypic and genotypic characteristics of GBS isolates circulating in Argentina and to analyze the clinical and demographic characteristics of patients with invasive infections. We recovered 162 invasive (GBSi) isolates from adult patients (n = 130, 80.2%), neonates (n = 24, 15%), and children below 18 years of age (n = 8, 4.8%), and colonizing (GBSc) isolates were recovered in prenatal GBS screening. GBS infection in adults was associated with underlying diseases, mainly diabetes mellitus. All isolates were penicillin susceptible. Resistance rates to erythromycin (25%) and clindamycin (26%) among the GBSc isolates were significantly higher than those from GBSi strains (17.3% and 16.1%, respectively); by contrast, levofloxacin resistance was significantly higher in GBSi isolates (14.8% vs. 7%). Serotype Ia was the most frequent in neonates and Ib was most frequent in adults. Serotypes Ia and III were prevalent in GBSc isolates. The increase of levofloxacin resistance was associated with the presence of a serotype Ib clone. This work emphasizes the need for GBS infection surveillance studies to implement correct treatments and adequate prevention strategies.

Antimicrobial resistance studies in staphylococci and streptococci isolated from cows with mastitis in Argentina

BACKGROUND

Staphylococcus aureus and Streptococcus agalactiae are the main cause of clinical mastitis in dairy cattle in Argentina, whereas coagulase-negative staphylococci (CNS) and environmental streptococci are the main cause of subclinical mastitis. Bacteria isolated from infected animals show increasing antimicrobial resistance.

OBJECTIVES

This study aims to determine the antimicrobial resistance of staphylococci and streptococci isolated from milk with mastitis, and to genotypically characterize the methicillin-resistant (MR) staphylococci.

METHODS

Isolation was performed on blood agar and identification was based on biochemical reactions. Antimicrobial susceptibility was according to the Clinical and Laboratory Standards Institute guidelines. The antimicrobial resistance genes, SCCmec type and spa type were detected by the polymerase chain reaction method.

RESULTS

We isolated a total of 185 staphylococci and 28 streptococci from 148 milk samples. Among the staphylococcal isolates, 154 were identified as CNS and 31 as S. aureus. Among the 154 CNS, 24.6% (n = 38) were resistant to penicillin, 14.9% (n = 23) to erythromycin, 17.5% (n = 27) to clindamycin, 6.5% (n = 10) to cefoxitin and oxacillin. Among the S. aureus isolates, 16.1% (n = 5) were resistant to penicillin, 3.2% (n = 1) to cefoxitin and oxacillin (MRSA). Six MR isolates (5 CNS and 1 MRSA) were positive to the mecA gene, and presented the SCCmec IVa. The MRSA strain presented the sequence type 83 and the spa type 002. Among the 28 streptococcal isolates, 14.3% (n = 4) were resistant to penicillin, 10.7% (n = 3) to erythromycin and 14.3% (n = 4) to clindamycin.

CONCLUSIONS

The present findings of this study indicate a development of antimicrobial resistance in main bacteria isolated from cows with mastitis in Argentina.

Genomic Epidemiology of CC30 Methicillin-Resistant Staphylococcus aureus Strains from Argentina Reveals Four Major Clades with Distinctive Genetic Features

Staphylococcus aureus clonal complex 30 (CC30) has given rise to epidemics worldwide and is one of the most prevalent lineages in Argentina, represented by sequence type 30 methicillin-resistant S. aureus SCCmec type IV (ST30-MRSA-IV). ST30-MRSA-IV has displaced previous prevalent clones in the country and demonstrated increased virulence. Despite the burden of infections caused by ST30-MRSA-IV both in hospitals and in communities in Argentina, no detailed genome-based characterization of this clone is available to date. In this study, we used whole-genome sequencing (WGS) to evaluate the genetic diversity, population structure, and genomic characteristics of 190 CC30-MRSA strains circulating in Argentina between 2004 and 2015. Phylogenetic analysis revealed the existence of 4 major clades: ARG-1 (CC30-MRSA-IVc-spa t012), ARG-2 (ST30-MRSA-IVc-spa t021 related), ARG-3 (ST30-MRSA-IVh/j-spa t021 and related), and ARG-4 (CC30-MRSA-IVc-spa t019 and related). The clades were characterized by different distributions of antimicrobial resistance determinants, virulence genes, and mobile genetic elements (MGEs). While ARG-1 and ARG-4 were related to global epidemic MRSA-16 (EMRSA-16) and South West Pacific (SWP) clones, respectively, ARG-3 was phylogenetically distinct from previously defined CC30 epidemic clones. ARG-4, the most prevalent and geographically disseminated in the collection (N = 164), was characterized by specific MGEs and chromosomal mutations that might have contributed to its virulence and success. To our knowledge, this is the first genomic epidemiology study of CC30-MRSA in Argentina, which will serve as baseline genomic data going forward to inform public health measures for infection prevention and control.IMPORTANCE The rise in prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is of public health concern. In Argentina, several studies documented a shift in the epidemiology of CA-MRSA since 2009, with clonal complex 30 (CC30) and, in particular, sequence type 30 MRSA SCCmec type IV (ST30-MRSA-IV) replacing other clones both in communities and in hospitals and possibly displaying increased virulence. By sequencing the whole genomes of 190 CC30 MRSA isolates recovered from Argentina between 2005 and 2015, we showed that they represented a diverse population composed of 4 major clades. The predominant clade evolved from the South West Pacific clone but has acquired a distinct repertoire of mobile genetic elements, virulence genes, and chromosomal mutations that might play a role in its success. Our work is the first extensive genomic study of CC30 S. aureus in Argentina and will contribute not only to the development of genomic surveillance in the region but also to our understanding of the global epidemiology of this pathogen.

Comparative genomics of ST5 and ST30 methicillin-resistant Staphylococcus aureus sequential isolates recovered from paediatric patients with cystic fibrosis

Staphylococcus aureus chronic airway infection in patients with cystic fibrosis (CF) allows this pathogen to adapt over time in response to different selection pressures. We have previously shown that the main sequence types related to community-acquired methicillin-resistant S. aureus (MRSA) infections in Argentina - ST5 and ST30 - are also frequently isolated from the sputum of patients with CF, but in these patients they usually display multi-drug antimicrobial resistance. In this study, we sequenced the genomes of MRSA from four paediatric CF patients with the goal of identifying mutations among sequential isolates, especially those possibly related to antimicrobial resistance and virulence, which might contribute to the adaptation of the pathogen in the airways of patients with CF. Our results revealed genetic differences in sequential MRSA strains isolated from patients with CF in both their core and accessory genomes. Although the genetic adaptation of S. aureus was distinct in different hosts, we detected independent mutations in thyA, htrA, rpsJ and gyrA - which are known to have crucial roles in S. aureus virulence and antimicrobial resistance - in isolates recovered from multiple patients. Moreover, we identified allelic variants that were detected in all of the isolates recovered after a certain time point; these non-synonymous mutations were in genes associated with antimicrobial resistance, virulence, iron scavenging and oxidative stress resistance. In conclusion, our results provide evidence of genetic variability among sequential MRSA isolates that could be implicated in the adaptation of these strains during chronic CF airway infection.

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) clones from Paraguayan children

INTRODUCTION

Staphylococcus aureus is considered one of the most important human pathogens, and its levels of resistance to methicillin have increased even in strains isolated from people without nosocomial risk factors. Molecular analysis is essential for understanding the patterns of dissemination. The objective of this study was to identify community-acquired methicillin-resistant S. aureus (CA-MRSA) clones that infected Paraguayan children patients in two periods of time.

METHODOLOGY

An observational, descriptive study was designed to determine the genetic variability of 115 isolates of CA-MRSA recovered from children who attended four reference centers in Paraguay between 2009-2010 and 2012-2013.

RESULTS

The combined use of Pulsed Field Gel Electrophoresis (PFGE), Multi-Locus Sequencing Typing, Multi-Locus Variable Analysis (MLVA) and Spa typing techniques allowed the identification of two dominant clones: ST30-IV-t019 (77%) and ST5-IV-t311 (10%), and the establishment of the former as the leading cause of CA-MRSA infections in children during the study period.

CONCLUSIONS

This is the first study that provides epidemiological information as well as microbiological and molecular characteristics of CA-MRSA isolates recovered from children from Asunción and the Central Department of Paraguay.

Argentinian multicenter study on urinary tract infections due to Streptococcus agalactiae in adult patients

INTRODUCTION

Streptococcus agalactiae (group B streptococcus, GBS) is a recognized urinary pathogen both in males and pregnant or non-pregnant women. Data regarding GBS serotypes recovered from urinary tract infections (UTIs) are scarce. The aim of this study was to describe the clinical and microbiological characteristics of UTIs caused by GBS in adult patients in Argentina.

METHODOLOGY

A prospective multicenter study involving 86 centers was conducted in Argentina between July 1st, 2014 and June 30th, 2015. Antimicrobial susceptibility and serotype distribution of GBS isolated from the urinary tract of adult patients were determined. Susceptibility tests were performed by the disk diffusion and/or agar dilution methods. Epidemiological and clinical characteristics of the patients were considered to identify associated comorbilities.

RESULTS

Seven hundred and one GBS were sent to the reference laboratory in the above mentioned period, however, only 211 fulfilled our selection criteria (demographic data availability, underlying diseases reported, colony counts greater than 105 CFU/mL, single organism isolated from the urine sample). No penicillin-resistant GBS was found but fluoroquinolone resistance was high (12.8%), especially among GBS isolated from men and non-pregnant women. UTIs due to GBS were associated to underlying diseases in men and non-pregnant women, particularly diabetes mellitus. Most of the isolates showed serotypes Ia and III.

CONCLUSIONS

GBS are still susceptible to penicillin but fluoroquinolone resistance is a growing concern, at least in Argentina. There are underlying conditions that could be associated to urinary infections caused by GBS.

Fluoroquinolone-Resistant Streptococcus agalactiae Invasive Isolates Recovered in Argentina

Background: Streptococcus agalactiae or group B Streptococcus (GBS) is an important pathogen in neonates and nonpregnant individuals. Epidemiological studies of GBS resistance to fluoroquinolones (FQs) in Latin America are scarce. This study aimed to determine the local prevalence of FQ resistance in the frame of a national, prospective multicenter study of invasive GBS infections and to investigate mechanisms of resistance, serotype distribution, and clonal relationships among resistant isolates. Methods: From July 2014 to July 2015, 162 invasive GBS isolates were collected from 86 health care centers in 32 Argentinean cities. All isolates were screened for FQ nonsusceptibility using a five-disc scheme: levofloxacin (LVX), ciprofloxacin, norfloxacin (NOR), ofloxacin, and pefloxacin (PF). LVX minimal inhibitory concentration (MIC) was determined by the agar dilution method. Sequencing of internal regions of gyrA and parC genes was performed. Capsular typing and genetic characterization of nonsusceptible isolates were assessed by latex agglutination, pulsed-field gel electrophoresis (PFGE), and multilocus sequence typing. Results: Twenty-four of one hundred sixty-two GBS isolates exhibited no inhibition zones to all tested FQs with an MIC range of 16-32 mg/L for LVX, and one isolate with MIC = 1 mg/L showed no inhibition zones around NOR and PF discs. In all resistant isolates, point mutations were detected in both genes. Serotype Ib was prevalent (88%). One PFGE type accounted for 84% of the FQ-resistant isolates and belonged to serotype Ib, sequence type 10. Conclusions: The prevalence of FQ resistance was 14.8% likely to be associated with dissemination of an ST10/serotype Ib clone. The unexpected high rate of resistance emphasizes the relevance for continuous surveillance of GBS epidemiology and antibiotic susceptibility.

First isolation of a methicillin-resistant Staphylococcus aureus from bovine mastitis in Argentina

This research communication describes the first isolation of a methicillin-resistant Staphylococcus aureus (MRSA) from cow's mastitic milk in Argentina. Bovine mastitis causes important economic losses in the dairy industry and the most commonly isolated bacteria from bovine mastitis are staphylococci. The mecA gene present in MRSA bacteria confers resistance to almost all β-lactam antibiotics, the most frequent drugs used in bovine mastitis therapy.

Resistance to β-lactams in enterococci

Enterococci are intrinsically resistant to several antimicrobial classes and show a great ability to acquire new mechanisms of resistance. Resistance to β-lactam antibiotics is a major concern because these drugs either alone or in combination are commonly used for the treatment of enterococcal infections. Ampicillin resistance, which is rare in Enterococcus faecalis, occurs in most of the hospital-associated Enterococcus faecium isolates. High-level resistance to ampicillin in E. faecium is mainly due to the enhanced production of PBP5 and/or by polymorphisms in the beta subunit of this protein. The dissemination of high-level ampicillin resistance can be the result of both clonal spread of strains with mutated pbp5 genes and horizontal gene transfer.

TNFR1 Signaling Contributes to T Cell Anergy During Staphylococcus aureus Sepsis

Early research on sepsis has focused on the initial hyper-inflammatory, cytokine mediated phase of the disorder whereas the events that govern the concomitant and subsequent anti-inflammatory compensatory response are not completely understood. In this context, the putative participation of TNFR1-mediated signaling in the immunosuppressive phase of Staphylococcus aureus sepsis has not been elucidated. The aim of this study was to determine the role of TNFR1 in directing the immune dysfunction during S. aureus sepsis and the potential contribution of MDSC to this process. Using a model of sepsis of peritoneal origin and tnfr1^−/− mice, we demonstrated that during staphylococcal sepsis CD4⁺ T cell anergy is significantly dependent on TNFR1 expression and that signaling through this receptor has an impact on bacterial clearance in the spleen. MDSC played a major role in the generation of anergic CD4⁺ T cells and their accumulation in the spleen during S. aureus sepsis correlated with IL-6 induction. Although TNFR1 signaling was not required for MDSC accumulation and expansion in the spleen, it determined the in vivo expression of Arginase 1 and iNOS, enzymes known to participate in the suppressive function of this population. Moreover, our data indicate that TNFR1-mediated IL-10 production may modulate MDSC function during staphylococcal sepsis. Taken together these results indicate that TNFR1 plays a critical role on T cell dysfunction during S. aureus sepsis by regulating immunomodulatory mediators in MDSC. The role of TNFR1-mediated signaling during the immunosuppressive phase of staphylococcal sepsis should be considered when designing novel alternative therapeutic approaches.

[Susceptibility of Streptococcus pyogenes isolated from invasive infections to trimethoprim-sulfamethoxazole]

It is erroneously believed that group A streptococci (GAS) are universally resistant to trimethoprim-sulfamethoxazole (TMS). This is mainly because media commonly used for in vitro determination of susceptibility to antibiotics contain thymidine, a nucleoside that antagonizes the antibiotic effect of TMS. The objective of this work was to determine EGA sensitivity to TMS in the presence and absence of thymidine. To this aim, 95 GAS isolates obtained from clinical tissues with i nvasive infections were analyzed. Susceptibility tests were performed by diffusion with TMS discs in Mueller Hinton agar supplemented either with 5% sheep blood or with 5% lysed equine blood (MH-LEB). Lysed equine blood contains thymidine phosphorylase, which degrades this nucleoside. Epsilometry (Etest) was used as gold standard. Quality controls with Enterococcus faecalis strain ATCC 29212 were satisfactory with both media. A 100% sensitivity to TMS was found in MH-SEL whereas 6 isolates (6.3%) resulted resistant in MH-SC; only one of them was found to have intermediate susceptibility by Etest (MIC > 1.5/28 υg/ml). The genetic determinants most frequently associated to TMS resistant EGA were not found in this isolate. Probably, if more accurate GAS-specific cut-off points were established for diffusion, the correlation with dilution methods or with the Etest could be improved, even employing MH-SB.

Estandarización del análisis multi-locus de número variable de repeticiones en tándem para el estudio de Staphylococcus aureus resistentes a meticilina aislados de la comunidad en Paraguay

 Staphylococcus aureus es un patógeno capaz de causar infecciones con amplio rango de severidad y adaptarse a diferentes tejidos. Su epidemiología es compleja, por circulación de cientos de clones a nivel mundial, lo que requiere de métodos moleculares reproducibles y de alto poder discriminatorio para la identificación de los mismos. El presente estudio tuvo como objetivo principal la estandarización del análisis multi-locus de número variable de repeticiones en tándem (MLVA) para análisis de variabilidad genética de aislados de S. aureus previamente tipificados por electroforesis en gel de campo pulsado (PFGE), gold standard para tipificación de aislados. La MLVA se realizó por amplificación de 7 locus VNTR (clfA, clfB, sdrC, sdrD, sdrE, sspA y spA) por PCR. Se alcanzó un alto nivel de reproducibilidad. El empleo de cepas previamente tipificadas por análisis de secuencias multi-locus (MLST), PFGE, locus spa y cassette SCCmec, permitió validar de forma comparativa el agrupamiento generado por MLVA. Los aislados que fueron agrupados como idénticos por MLVA presentaron resultados congruentes con la totalidad de las otras técnicas moleculares y ésta demostró ser más sensible que PFGE para distinguir entre aislados que presentaron patrones PFGE idénticos. La MLVA cumple todos los criterios de un método de tipificación útil.

Screening assay for inhibitors of a recombinant Streptococcus pneumoniae UDP-glucose pyrophosphorylase

The UDP-glucose pyrophosphorylase of Streptococcus pneumoniae (GalU_Spn) is absolutely required for the biosynthesis of capsular polysaccharide, the sine qua non virulence factor of pneumococcus. Since the eukaryotic enzymes are completely unrelated to their prokaryotic counterparts, we propose that the GalU enzyme is a critical target to fight the pneumococcal disease. A recombinant GalU_Spn was overexpressed and purified. An enzymatic assay that is rapid, sensitive and easy to perform was developed. This assay was appropriate for screening chemical libraries for searching GalU inhibitors. This work represents a fundamental step in the exploration of novel antipneumococcal drugs.

Different Vancomycin-Intermediate Staphylococcus aureus Phenotypes Selected from the Same ST100-hVISA Parental Strain

The aim of this study is to characterize the factors related to peptidoglycan metabolism in isogenic hVISA/VISA ST100 strains. Recently, we reported the increase in IS256 transposition in invasive hVISA ST100 clinical strains isolated from the same patient (D1 and D2) before and after vancomycin treatment and two laboratory VISA mutants (D23C9 and D2P11) selected from D2 in independent experiments. High performance liquid chromatography-mass spectrometry (HPLC-MS) analysis of peptidoglycan muropeptides showed increased proportion of monomeric muropeptides and a concomitant decrease in the proportion of tetrameric muropeptide in D2 and derived mutants when compared to the original strain D1. In addition, strain D2 and its derived mutants showed an increase in cell wall thickness with increased pbp2 gene expression. The VISA phenotype was not stable in D2P11 and showed a reduced autolysis profile. On the other hand, the mutant D23C9 differentiates from D2 and D2P11 in the autolysis profile, and pbp4 transcription profile. D2-derived mutants exhibited differences in the susceptibility to other antimicrobials. Our results highlight the possibility of selection of different VISA phenotypes from a single hVISA-ST100 genetic background.

Increase in IS256 transposition in invasive vancomycin heteroresistant Staphylococcus aureus isolate belonging to ST100 and its derived VISA mutants

In Staphylococcus aureus, transposition of IS256 has been described to play an important role in biofilm formation and antibiotic resistance. This study describes the molecular characterization of two clinical heterogeneous vancomycin-intermediate S. aureus (hVISA) isolates recovered from the same patient (before and after antibiotic treatment) and two VISA derivatives obtained by serial passages in the presence of vancomycin. Our results showed that antibiotic treatment (in vivo and in vitro) could enhance IS256 transposition, being responsible for the eventual loss of agr function. As far as we know this is the first study that reports the increase of IS256 transposition in isogenic strains after antibiotic treatment in a clinical setting.

In vitro selection of Staphylococcus aureus mutants resistant to tigecycline with intermediate susceptibility to vancomycin

Background

Tigecycline (TIG) is an antibiotic belonging to the glycylcyclines class and appears to be a good choice to fight infections caused by Staphylococcus aureus. To date, TIG exhibits good activity against this microorganism. The aim of this work was to obtain in vitro mutants of S. aureus resistant to TIG and evaluate possible changes in their susceptibility patterns to other antibiotics.

Results

Two mutants of S. aureus resistant to TIG (MIC = 16 µg/mL) were selected in vitro from clinical isolates of methicillin-resistant S. aureus. In both mutants, corresponding to different lineage (ST5 and ST239), an increase of efflux activity against TIG was detected. One mutant also showed a reduced susceptibility to vancomycin, corresponding to the VISA phenotype (MIC = 4 µg/mL), with a loss of functionality of the agr locus. The emergence of the VISA phenotype was accompanied by an increase in oxacillin and cefoxitin MICs.

Conclusions

This study demonstrates that, under selective pressure, the increase of efflux activity in S. aureus is one of the mechanisms that may be involved in the emergence of tigecycline resistance. The emergence of this phenotype may eventually be associated to changes in susceptibility to other antibiotics such oxacillin and vancomycin.

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 IV_NV-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.

Community-associated methicillin-resistant Staphylococcus aureus skin and soft tissue infections in a pediatric hospital in Argentina

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) emerged at the Pediatric Hospital of Misiones Province, north Argentina, in 2003 as a cause of community-acquired (CA) infections, mostly associated with skin and soft tissue infections (SSTIs). This study aimed to assess the microbiological, epidemiological, and clinical features of CA-MRSA SSTIs treated at the hospital.

METHODOLOGY

From 2003 through 2006, a longitudinal study on CA-MRSA SSTIs was conducted. Clinical, bacteriological, and molecular data were collected and analyzed by multiple correspondences and cluster analysis (MCCA).

RESULTS

A total of 138 children were enrolled; 55.8% of the children required hospitalization. The main clinical presentation was abscesses (51%). Antibiotic therapy in the previous six months was registered in 41% of the patients, and 72% of the patients had relatives with similar symptoms. Resistance to non-b-lactam antibiotics was found in less than 12% of patients. All 44 isolates carried staphylococcal cassette chromosomemec (SCCmec) type IV, and 30/44 had Panton-Valentine leucocidin (PVL) coding genes. Six pulsed-field gel electrophoresis (PFGE) patterns were detected from 17 isolates. MCCA hierarchic classification resulted in four distinctive patient classes (new variable). No relationship could be observed regarding the PVL detection, as PVL (+) isolates were detected in all classes; the same lack of significance was observed concerning the distribution of resistance to non-β-lactam antibiotics.

CONCLUSIONS

This study increases the understanding and knowledge about CA-MRSA skin and soft tissue infections in pediatric patients. Continuous efforts should be made to control this significant public health problem.

Prospective multicenter study of community-associated skin and skin structure infections due to methicillin-resistant Staphylococcus aureus in Buenos Aires, Argentina

BACKGROUND

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is now the most common cause of skin and skin structure infections (SSSI) in several world regions. In Argentina prospective, multicenter clinical studies have only been conducted in pediatric populations.

OBJECTIVE

PRIMARY: describe the prevalence, clinical and demographic characteristics of adult patients with community acquired SSSI due to MRSA; secondary: molecular evaluation of CA-MRSA strains. Patients with MRSA were compared to those without MRSA.

MATERIALS AND METHODS

Prospective, observational, multicenter, epidemiologic study, with molecular analysis, conducted at 19 sites in Argentina (18 in Buenos Aires) between March 2010 and October 2011. Patients were included if they were ≥ 14 years, were diagnosed with SSSI, a culture was obtained, and there had no significant healthcare contact identified. A logistic regression model was used to identify factors associated with CA-MRSA. Pulse field types, SCCmec, and PVL status were also determined.

RESULTS

A total of 311 patients were included. CA-MRSA was isolated in 70% (218/311) of patients. Clinical variables independently associated with CA-MRSA were: presence of purulent lesion (OR 3.29; 95%CI 1.67, 6.49) and age <50 years (OR 2.39; 95%CI 1.22, 4.70). The vast majority of CA-MRSA strains causing SSSI carried PVL genes (95%) and were SCCmec type IV. The sequence type CA-MRSA ST30 spa t019 was the predominant clone.

CONCLUSIONS

CA-MRSA is now the most common cause of SSSI in our adult patients without healthcare contact. ST30, SCCmec IV, PVL+, spa t019 is the predominant clone in Buenos Aires, Argentina.

Methicillin-resistant Staphylococcus aureus ST30-SCCmec IVc clone as the major cause of community-acquired invasive infections in Argentina

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections have become a major concern worldwide. We conducted a prospective multicenter study of invasive CA-MRSA to evaluate clinical features and genotype of strains causing invasive infections in Argentina. A total of 55 patients with invasive CA-MRSA infections were included. Most patients (60%) had bloodstream infections, 42% required admission to intensive care unit and 16% died. No CA-MRSA isolates were multiresistant (resistant ⩾3 classes of antibiotics). All isolates carried Panton-Valentine leukocidin (PVL) genes and staphylococcal cassette chromosome (SCCmec) type IV. The majority CA-MRSA strains belonged to ST30 and had identical pulsed-field gel electrophoresis (PFGE) patterns, qualifying as a clonal dissemination of a highly transmissible strain. The main clone recovered from patients with CA-MRSA invasive infections was genotyped as pulsed-field gel electrophoresis type C-ST30, SCCmec type IVc-spa type 019, PVL positive. It has become predominant and replaced the previously described CA-MRSA clone (PFGE type A, ST5, SCCmec type IV, spa type 311).

Community-associated methicillin-resistant Staphylococcus aureus in children treated in Uruguay

Introduction: Staphylococcus aureus produces a variety of diseases among children, ranging from skin and soft tissue infections to invasive life-threatening diseases. Since 1990, an increasing number of diseases produced by community-associated methicillin-resistant S. aureus (CA-MRSA) isolates have been reported. The aim of this study was to describe the importance and the microbiological characteristics of S. aureus isolates recovered from children treated at the Hospital Pediátrico del Centro Hospitalario “Pereira Rossell” (HP-CHPR); focusing on invasive diseases caused by CA-MRSA isolates, as well as some clinical aspects of the diseases they have produced. Methodology: One hundred and twenty-five S. aureus isolates recovered from the HP-CHPR between 2003 and 2006 from children with invasive (n=89) and superficial diseases (n=36) were included. Genotypic and phenotypic characteristics of S. aureus isolates and relevant clinical aspects of each child were studied. Results: CA-MRSA isolates accounted for 73% of all S. aureus recovered from invasive (mainly bone and joint) infections, pneumonia and bacteraemia. The most common CA-MRSA strain recovered from invasive (n=65) and superficial (n=36) diseases had the following features: pulsotype A (type USA1100), SCCmec cassette type IV, Panton-Valentine Leukocidin genes positive, susceptibility to trimethoprim-sulfamethoxazole without the inducible macrolide-lincosamide-streptogramin B (iMLSB) resistance phenotype. No association between genotypic characteristics of invasive CA-MRSA isolates and clinical outcomes was found. Conclusions: CA-MRSA isolates produced a wide spectrum of invasive diseases in a public paediatric hospital between 2003 and 2006. Microbiologic characterization suggests the spread of an adapted CA-MRSA clone lacking erm genes.

The galU gene expression in Streptococcus pneumoniae

The polysaccharide capsule of Streptococcus pneumoniae is the main virulence factor making the bacterium resistant to phagocytosis. The galU gene of S. pneumoniae encodes a UDP-glucose pyrophosphorylase absolutely required for capsule biosynthesis. In silico analyses indicated that the galU gene is co-transcribed with the gpdA gene, and four putative promoter regions located upstream of gpdA were predicted. One of them behaved as a functional promoter in a promoter reporter system. It is conceivable that the sequence responsible for initiating transcription of gpdA-galU operon is an extended -10 site TATGATA(T/G)AAT. Semi-quantitative real-time reverse transcription PCR experiments indicated that galU was expressed mainly in the exponential phase of growth.

The length of the Staphylococcus aureus protein A polymorphic region regulates inflammation: impact on acute and chronic infection

Staphylococcus aureus protein A (SpA) plays a critical role in the induction of inflammation. This study was aimed to determine whether the number of short sequence repeats (SSRs) present in the polymorphic region modulates the inflammatory response induced by SpA. We demonstrated that there is a dose-response effect in the activation of interferon (IFN)-β signaling in airway epithelial and immune cells, depending on the number of SSRs, which leads to differences in neutrophil recruitment. We also determined that a significant proportion of isolates from patients with chronic infections such as osteomyelitis and cystic fibrosis carry fewer SSRs than do isolates from patients with acute infections or healthy carriers and that there was an inverse correlation between the number of SSRs and the length of disease course. Given the importance of IFN signaling in eradication of S. aureus, loss of SSRs may represent an advantageous mechanism to adapt to and persist in the host.

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.

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.

PorA types in Neisseria meningitidis serogroup B isolated in Argentina from 2001 to 2003: implications for the design of an outer membrane protein-based vaccine

Identification ofNeisseria meningitidisPorA types remains important, as the PorA protein is a major immunogenic component of several meningococcal vaccines under development. In this study, 191N. meningitidisserogroup B isolates collected in Argentina through active laboratory-based surveillance from 2001 to 2003 were serosubtyped. Nucleotide sequences of theporAvariable region 1 (VR1) and VR2 regions were determined in 52 non-serosubtypeable isolates. A substantial number of distinct VR types were identified, and a new VR2 variant from the P1.16 family was described. This is the first report describing PorA types inN. meningitidisserogroup B isolates in Argentina. Furthermore, the wide diversity of subtypes detected by serosubtyping and genosubtyping reveals the difficulty in designing a useful outer-membrane vaccine applicable in this country. A possible mechanism responsible for altered PorA expression was analysed in two PorA types.

[Community-acquired methicillin-resistant Staphylococcus aureus infections in a hospital for acute diseases]

Community-acquired methicillin-resistant Staphylococcus aureus infections in a hospital for acute diseases. Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most prevalent pathogens associated with nosocomial infections. However, most recently, MRSA has arisen as an emerging community pathogen, causing serious infections, mainly among young patients. We herein describe 33 cases of infections caused by community-acquired MRSA (C-MRSA), diagnosed between May 2005 and June 2006, at "Eva Perón" Hospital. The isolations were retrospectively studied. Methicillin resistance was confirmed by means of the detection of the mecA gene, and the genes for two virulence factors (Panton-Valentine Leucocidin -PVL- and gamma-haemolysin) as well as the cassette mec type were screened by PCR. All the patients were previously healthy. Four patients under 12, presented bacteremia, one had serious pneumonia, and the three remaining patients had osteoarticular infections; all the patients over 12, had skin and soft tissue infections without systemic damage. The C-MRSA strains harboured cassette mec type IV, and the PVL and gamma-haemolysin genes. They were methicillin-resistant, with no other associated resistances. It is important to consider the presence of these community- acquired strains in order to develop strategies for their correct treatment.

[Surveillance of Neisseria meningitidis in Argentina, 1993-2005: distribution of serogroups, serotypes and serosubtypes isolated from invasive disease]

Neisseria meningitidis is an important cause of meningitis, bacteremia and septic shock syndrome. We herein present the distribution of serogroups, serotypes and serosubtypes of 2244 isolates of N. meningitidis from patients with meningitis or meningococcemia, received within the period 1993-2005, in the National Reference Laboratory, INEI-ANLIS "Dr. Carlos G. Malbrán", from 33 Argentine hospitals that are included in a National Network devoted to for the study of bacterial meningitis. Between 1993-1995, serogroup B was prevalent (66%) whereas in the period from 1995-2001, serogroup C prevailed (65%). However, following but after that period, the prevalence of serogroup B was recovered. In the last 5 years of the studied period, the serogroups Y and W135 represented as a whole a 15.6% as a whole whereas up to the year 2000 during the first 6 years they accounted for it was of 4.7%. Higher diversity in the distribution of serotypes and serosubtypes was observed within serogroup B. The nonsubtypable isolates throughout the period of study represented the 52.8%, this high percentage demonstrates the limited capacity of the serotyping for the determination of meningococcal/meningococcus subtypes. of meningococco.

Molecular characterization of InJR06, a class 1 integron located in a conjugative plasmid of Salmonella enterica ser. Typhimurium

The presence of class 1, 2, and 3 integrons was investigated in four pediatric isolates of Salmonella enterica ser. Typhimurium (S. Typhimurium). A class 1 integron was detected in one S. Typhimurium strain, the only one that also showed resistance to various aminoglycoside antibiotics. This integron, called InJR06, and the aminoglycoside resistance determinants were located in pS06, a large (> or = 55 kb) conjugative plasmid. A single mobile cassette (encoding the aminoglycoside adenylyltransferase ANT(3'')-Ia) was detected in the variable region of InJR06, while the architecture of the attI1 and attC sites was conserved.

[PCR-based capsular typing of Haemophilus influenzae isolates non-typeable by agglutination]

Haemophilus influenzae is recognized as a pathogenic agent responsible of localized and systemic infections. Six antigenically different capsular polysaccharide types have been described (a, b, c, d, e, and f ) which can be identified by slide agglutination with specific antisera. Besides there are non capsulated strains that cannot be typed by slide agglutination. The introduction of the conjugated vaccine produced an important reduction of invasive diseases caused by H. influenzae type b. Capsular typing by PCR is the most appropriated method for distinguishing non capsulated strains from capsule deficient type b mutants (b-) and for detecting strains of other serotypes that cannot be detected by slide agglutination. Capsular genotype was studied in 38 isolates of non-typeable Haemophilus influenzae received at INE-ANLIS "Dr. Carlos G. Malbrán" between 2002-2004. Of the isolates included in this study 78.9% of them were recovered from blood cultures and most of them were associated with a respiratory focus. By PCR technique 100% of the isolates were identified as non-capsulate H. influenzae and genotype b-was not detected.

Biochemical characterization of the pneumococcal glucose 1-phosphate uridylyltransferase (GalU) essential for capsule biosynthesis

The glucose 1-phosphate uridylyltransferase (GalU) is absolutely required for the biosynthesis of capsular polysaccharide, the sine qua non virulence factor of Streptococcus pneumoniae. The pneumococcal GalU protein was overexpressed in Escherichia coli, and purified. GalU showed a pI of 4.23, and catalyzed the reversible formation of UDP-glucose and pyrophosphate from UTP and glucose 1-phosphate with K(m) values of 0.4 mM: for UDP-glucose, 0.26 mM: for pyrophosphate, 0.19 mM: for glucose 1-phosphate, and 0.24 mM: for UTP. GalU has an optimum pH of 8-8.5, and requires Mg(2+) for activity. Neither ADP-glucose nor TDP-glucose is utilized as substrates in vitro. The purification of GalU represents a fundamental step to provide insights on drug design to control the biosynthesis of the main pneumococcal virulence factor.

Methicillin-resistant Staphylococcus aureus strains in Buenos Aires teaching hospitals: replacement of the multidrug resistant South American clone by another susceptible to rifampin, minocycline and trimethoprim-sulfamethoxazole

The aim of this study was to characterize methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered from different infectious sites of hospitalized patients at two university hospitals. Fourteen isolates were analyzed by repetitive sequence based PCR (Rep-PCR), randomly amplified polymorphic DNA assay (RAPD-PCR), and pulsed-field gel electrophoresis (PFGE). We found that a prevalent clone of MRSA, susceptible to rifampin, minocycline, and trimethoprim/sulfamethoxazole (RIF(s), MIN(s), TMS(s)) was present in both hospitals in replacement of the multiresistant MRSA South American clone, previously described in these hospitals. The staphylococcal chromosomal cassette (SCCmec) type I element was detected in this new clone.