Marta Mollerach

Novel Class 1 Integron (InS21) Carrying blaCTX-M-2 in Salmonella enterica Serovar Infantis

ABSTRACT The genetic organization of the region coding for CTX-M-2 in Salmonella enterica serovar Infantis was determined by PCR mapping. This gene seems to have been mobilized from the Kluyvera ascorbata chromosome to a complex sulI-type integron, similar to In6 and In7.

Current trends in capsular polysaccharide biosynthesis of Streptococcus pneumoniae

The capsular gene cluster (cap/cps) of 13 out of the 90 known pneumococcal types has been sequenced. The cap/cps operon, located between dexB and aliA in the Streptococcus pneumoniae chromosome, contains some of the genes responsible for the synthesis of the type-specific polysaccharide flanked by four conserved open reading frames. The biochemical function of only a few capsular genes has been established, whereas the role of the flanking regions is controversial. Remarkably, only one gene (tts) located outside the cap locus is required for the synthesis of type 37 capsule. Moreover, other genes not linked to the cap gene cluster are also needed for capsule synthesis in pneumococcus.

Community-associated methicillin-resistant Staphylococcus aureus, eastern Argentina

Sixty-nine community-associated methicillin-resistant Staphylococcus aureus recovered in 6 healthcare centers from northeastern and eastern Argentina were genotyped by pulsed-field gel electrophoresis. The predominant pulsotype was widely distributed harbored SCCmec type IV and Panton-Valentine leukocidin genes. Representative isolates were characterized by multilocus sequence typing and spa typing, demonstrating that this clone belonged to ST5 and spa type 311.

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.

Cefotaxime-Hydrolysing Beta Lactamases in Morganella morganii

Abstract The frequency of enterobacterial isolates with high resistance to expanded-spectrum β-lactam antibiotics (mainly cefotaxime or ceftriaxone) has increased notoriously in Argentina, mainly because of the spread of extended-spectrum β-lactamases. The aim of this work was the study of extended-spectrum β-lactamases in several Morganella morganii isolates with unusually high resistance to ceftriaxone. These strains produced at least two β-lactamases, of apparent pIs of 5.4 and 8.2, molecular weight 23 000, well inhibited by clavulanate, compatible with a broad-spectrum β-lactamase – perhaps TEM-1 – and an extended-spectrum β-lactamase, respectively. The extended-spectrum β-lactamase was identified as a CTX-M-type β-lactamase – probably CTX-M-2 – by polymerase chain reaction, restriction profile analysis and DNA-DNA hybridisation. The remaining isolates studied produced either the broad-spectrum β-lactamase plus the ubiquitous AmpC β-lactamase (13 strains), or the AmpC β-lactamase only (10 strains).

The galU gene of Streptococcus pneumoniae that codes for a UDP-glucose pyrophosphorylase is highly polymorphic and suitable for molecular typing and phylogenetic studies.

The enzyme UTP-glucose-1-phosphate uridylyltransferase (UDP-glucose pyrophosphorylase, UDPG:PP) is synthesized by practically all organisms, although prokaryotic UDPG:PPs are evolutionarily unrelated to the eukaryotic counterparts. The primary structure of prokaryotic UDPG:PPs is well conserved, although little information exists on the polymorphism of the genes coding for these enzymes. It has been reported that the galU gene encoding the Streptococcus pneumoniae UDPG:PP is absolutely required for the synthesis of the capsular polysaccharide, a sine qua non prerequisite for virulence. A 594 bp fragment covering 66% of the galU gene from 37 pneumococcal isolates and the type strains of Streptococcus mitis, Streptococcus oralis, Streptococcus gordonii, Streptococcus sanguinis, Streptococcus salivarius, and Streptococcus sobrinus has been amplified by PCR and sequenced. Up to 21 different alleles were found in S. pneumoniae. They possess a mosaic-like structure and belong to, at least, two evolutionarily distinct families that show a sequence divergence of 15-20%. In spite of its marked polymorphism, phylogenetic relationships among pneumococcal strains deduced from the galU gene matched those previously established by using alternative approaches. Comparison of the pneumococcal galU alleles with those from other streptococci indicated the existence of a complex network of genetic interchange. The galU gene represents an informative marker to be used alone or in conjunction with other molecular typing methods.

Methicillin-resistant Staphylococcus aureus in community-acquired meningitis

Historically, infections caused by methicillin-resistant Staphylococcus aureus (MRSA) have been associated with healthcare settings. However, since the 1990s, community-acquired MRSA (CA-MRSA) infections have been increasingly recognized [1]. The microorganisms involved differ from those related to nosocomial infections in the presence of type IV staphylococcal cassette chromosome (SCC) mec elements, virulence genes encoding a toxin called Panton–Valentine leukocidin (PVL), which is not found in HA-MRSA isolates [2], and in the lack of the typical multiresistance pattern present in nosocomial staphylococci. Even though most infections caused by CA-MRSA in the community involve skin and soft tissues, and invasive CA-MRSA infections have been reported infrequently until now, their incidence is increasing [3]. Among the life-threatening community-acquired staphylococcal infections, meningitis has fortunately been reported only sporadically, accounting for less than 3% of cases diagnosed as bacterial in origin [4, 5]. Considering the rarity of staphylococcal meningitis cases, it is not surprising that the role of CA-MRSA remains obscure, at least in our region, since almost no data is available on the prevalence of these strains. Nevertheless, hospital-acquired MRSA infections progressing to meningitis or cerebral abscesses are significant [6, 7]. The lack of accompanying resistance in a large series of CNS infections reported by Jones et al. [7] is noteworthy and may suggest the introduction and dissemination of CA-MRSA in the participating hospitals. Here, we report on two children with acute bacterial meningitis due to community-acquired MRSA who were admitted to the Pediatric Hospital of Posadas, a 100-bed tertiary-care hospital located in a region of about 1.5-million inhabitants in northeastern Argentina. As a reference, MRSA accounted for one-third of SA isolates during 2004, and most of them did not exhibit the typical antimicrobial resistance profile associated with nosocomial MRSA. In December 2004 a 5-year-old girl was admitted with a 5-day history of sacral and lumbar pain, fever and a cough, which were being treated with amoxicillin-clavulanic acid. Diagnosis at admission was meningeal syndrome. Cerebrospinal fluid was purulent and direct Gram stain showed gram-positive cocci. Blood counts showed 15,400 leukocytes/mm and a hematocrit level of 29%. Her C-reactive protein level was 768 mg/l, and she was hematuric. A combined cefotaxime-vancomycin antibiotic treatment was administered immediately. Upon characterization of MRSA without any accompanying resistance, cefotaxime was replaced by rifampin. After treatment for 21 days, clinical evolution was excellent and there was no evidence of neurologic sequelae. In January 2005, a 6-year-old boy from Posadas City was brought to the hospital with fever and a diffuse petechial rash; the rash had been present for 48 h and he had a 24-h history of headache and urinary incontinence. The severity of symptoms led to an initial diagnosis of anaphylactic shock, and he was admitted directly to the emergency room; he was then transferred to the intensive care unit, where he was treated with diphenhydramine, noradrenaline and corticoids. After medical reanimation was required, the clinical diagnosis was changed to septic shock and meningitis, and he was treated with cefotaxime and acyclovir. Cerebrospinal fluid analysis showed a leukocyte count of 528/mm, a glucose level of 0.51 (serum glucose 0.86), and a protein level of 0.31 g/l. Blood analysis showed definite leukopenia (leukocyte count about 3,100/mm). From day 3 after admission, when cultures of both blood and cerebrospinal fluid grew MRSA M. von Specht . P. Tagliaferri Hospital Público Provincial de Pediatría de Autogestión, Avenida Mariano Moreno 110, 3300-Posadas, Provincia de Misiones, 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).

Multicenter Study for Defining the Breakpoint for Rifampin Resistance in Neisseria meningitidis by rpoB Sequencing

ABSTRACT Identification of clinical isolates of Neisseria meningitidis that are resistant to rifampin is important to avoid prophylaxis failure in contacts of patients, but it is hindered by the absence of a breakpoint for resistance, despite many efforts toward standardization. We examined a large number (n = 392) of clinical meningococcal isolates, spanning 25 years (1984 to 2009), that were collected in 11 European countries, Argentina, and the Central African Republic. The collection comprises all clinical isolates with MICs of ≥0.25 mg/liter (n = 161) received by the national reference laboratories for meningococci in the participating countries. Representative isolates displaying rifampin MICs of <0.25 mg/liter were also examined (n = 231). Typing of isolates was performed, and a 660-bp DNA fragment of the rpoB gene was sequenced. Sequences differing by at least one nucleotide were defined as unique rpoB alleles. The geometric mean of the MICs was calculated for isolates displaying the same allele. The clinical isolates displaying rifampin MICs of >1 mg/liter possessed rpoB alleles with nonsynonymous mutations at four critical amino acid residues, D542, H552, S548, and S557, that were absent in the alleles found in all isolates with MICs of ≤1 mg/liter. Rifampin-susceptible isolates could be defined as those with MICs of ≤1 mg/liter. The rpoB allele sequence and isolate data have been incorporated into the PubMLST Neisseria database (http://pubmlst.org/neisseria/ ). The rifampin-resistant isolates belonged to diverse genetic lineages and were associated with lower levels of bacteremia and inflammatory cytokines in mice. This biological cost may explain the lack of clonal expansion of these isolates.

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.