Resistencia a antibióticos de última línea en cocos Gram positivos: la era posterior a la vancomicina / Resistance to "last resort" antibiotics in Gram-positive cocci: The post-vancomycin era

En los últimos años se han desarrollado nuevas alternativas para el tratamiento de infecciones por patógenos Gram positivos multirresistentes, entre los cuales Staphylococcus aureus resistente a la meticilina (SARM) y los enterococos resistentes a la vancomicina (ERV) se consideran un verdadero reto terapéutico, y aunque el uso de la vancomicina en infecciones graves causadas por SARM ha generado serias dudas en los últimos años, continúa siendo escasa la información clínica de respaldo al uso de agentes terapéuticos que la superen en eficacia. El linezolid, la daptomicina y la tigeciclina son agentes que tienen actividad contra los cocos Gram positivos y que fueron aprobados e introducidos en la terapia clínica en la década pasada. Además, se han probado o están en las fases finales de desarrollo otros agentes como las cefalosporinas de última generación (ceftarolina y ceftobiprol). El propósito de esta revisión fue describir las nuevas alternativas terapéuticas, particularmente en la era posterior a la vancomicina, y repasar las características químicas más relevantes de los compuestos y su espectro de actividad, haciendo énfasis en sus mecanismos de acción y resistencia.

New therapeutic alternatives have been developed in the last years for the treatment of multidrug-resistant Gram-positive infections. Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) are considered a therapeutic challenge due to failures and lack of reliable antimicrobial options. Despite concerns related to the use of vancomycin in the treatment of severe MRSA infections in specific clinical scenarios, there is a paucity of solid clinical evidence that support the use of alternative agents (when compared to vancomycin). Linezolid, daptomycin and tigecycline are antibiotics approved in the last decade and newer cephalosporins (such as ceftaroline and ceftobiprole) and novel glycopeptides (dalvavancin, telavancin and oritavancin) have reached clinical approval or are in the late stages of clinical development. This review focuses on discussing these newer antibiotics used in the "post-vancomycin" era with emphasis on relevant chemical characteristics, spectrum of antimicrobial activity, mechanisms of action and resistance, as well as their clinical utility.

Genetic and physiological diversity of Tetragenococcus halophilus strains isolated from sugar- and salt-rich environments.

Tetragenococcus halophilus is known to flourish in extreme salt environments. Recently, this halophilic bacterium also appeared as the dominant microflora during storage of sugar thick juice, an intermediate product of beet sugar production. Although T. halophilus can cause degradation of thick juice, dominance of this bacterium does not always result in degradation. In this study T. halophilus strains from high-salt and high-sugar environments, and in particular from degraded and non-degraded thick juice, were compared in detail. Both physiological and genetic characterization using Biolog, repetitive PCR fingerprinting (rep-PCR) and random amplified polymorphic DNA (RAPD) technology, revealed clear differences between T. halophilus strains isolated from salt- and sugar-rich environments. However, no strain pattern could be specifically and systematically associated with degraded or non-degraded thick juice. Remarkably, halophilic T. halophilus strains were not able to grow in sugar thick juice. Irrespective of the differences between the strains from high-salt or high-sugar environments, DNA-DNA hybridization grouped all strains within the species T. halophilus, except one isolate from sugar thick juice that showed different physiological and genetic characteristics, and that may represent a new species of Tetragenococcus.

Frequencies of resistance to Melaleuca alternifolia (tea tree) oil and rifampicin in Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis.

This study was conducted to determine the frequencies at which single-step mutants resistant to tea tree oil and rifampicin occurred amongst the Gram-positive organisms Staphylococcus aureus, Staphylococcus epidermidis and Enterococcus faecalis. For tea tree oil, resistance frequencies were very low at <10(-9). Single-step mutants resistant to tea tree oil were undetectable at two times the minimum inhibitory concentration (MIC) for S. aureus RN4220 and derivative mutator strains or at 3 x MIC for the remaining S. aureus strains, including a clinical meticillin-resistant S. aureus isolate. Similarly, no mutants were recovered at 2x MIC for S. epidermidis or at 1x MIC for E. faecalis. Resistance frequencies determined in vitro for rifampicin (8 x MIC) ranged from 10(-7) to 10(-8) for all isolates, with the exception of the S. aureus mutator strains, which had slightly higher frequencies. These data suggest that Gram-positive organisms such as Staphylococcus and Enterococcus spp. have very low frequencies of resistance to tea tree oil.

Accuracy and potential usefulness of triplex real-time PCR for improving antibiotic treatment of patients with blood cultures showing clustered gram-positive cocci on direct smears.

Bacterial identification and antibiotic susceptibility testing currently require 48 h when a first blood culture (BC) is positive for clustered gram-positive cocci on direct smear examination (DSE). Meanwhile, antibiotic treatment is often inadequate, reducing the chances of effective treatment or creating unnecessary selective pressure. A new real-time PCR (RT-PCR) technique that differentiates Staphylococcus aureus from coagulase-negative staphylococci (CoNS) and detects methicillin resistance in 90 min in BC bottles could help solve these problems. BC bottles from 410 patients with gram-positive cocci on DSE were processed by current methods, and patients' treatments were prospectively recorded. The RT-PCR assay was performed on aliquots of these BCs, which had been kept frozen. For the 121 patients who had true bacteremia, we established whether the faster availability of RT-PCR results could have led to the initiation of treatments different from those actually given. RT-PCR sensitivity and specificity were 100% for differentiating between S. aureus and CoNS and detecting methicillin resistance with two manufacturers' BC bottles. For 31/86 (36%) of the S. aureus-infected patients and for 8/35 (23%) of the CoNS-infected patients who either had suboptimal or nonoptimal treatment or were untreated 48 h after positivity was detected, the early availability of RT-PCR results could have allowed more effective treatment. Unnecessary glycopeptide treatments could have been avoided for 28 additional patients. The use of RT-PCR would increase treatment effectiveness in patients with staphylococcal bacteremia and reduce the selective pressure created by glycopeptides.

Biodegradation of benzene and its derivatives by a psychrotolerant and moderately haloalkaliphilic Planococcus sp. strain ZD22.

The potential for biodegradation of aromatic hydrocarbons simultaneously at low temperatures and under saline and alkaline conditions is not well understood, but such biodegradation would be useful for remediation of polluted sites. A psychrotolerant, moderately haloalkaliphilic pure culture using benzene as a sole source of carbon and energy was isolated by selective enrichment from alkaline and saline soils in the vicinity of the Daqing oil field in China. An analysis of the 16S rDNA gene sequence and morphological and physiological characteristics showed that this strain is a member of the genus Planococcus, and it was designated as strain ZD22. Strain ZD22 could grow at temperatures between 2 and 36 degrees C (pH 7.5-11) and salt concentrations from 0.5 to 25%. Its optimal conditions for biodegradation of benzene were 20 degrees C (pH 9.5) and 10% salt concentration. Strain ZD22 not only utilized benzene, toluene, ethylbenzene and o-xylene, but also degraded chlorobenzene, bromobenzene, iodobenzene and fluorobenzene. The kinetic model of strain ZD22 for benzene was solved to obtain mumax=0.34 h-1, Ks=0.041 mM, n=1.21, Sm=10.2 mM. To our knowledge, this is the first report of biodegradation of benzene and its derivatives simultaneously under multiple extreme conditions.

The arcABC gene cluster encoding the arginine deiminase pathway of Oenococcus oeni, and arginine induction of a CRP-like gene.

Oenococcus oeni, the main species which induces malolactic fermentation in wine, uses arginine via the arginine deiminase (ADI) pathway. Using degenerated primers, two specific probes, one for ornithine transcarbamoylase (OTC) and the other for carbamate kinase (CK), were synthesized. These made it possible to clone and sequence a cluster containing genes encoding ADI (arcA), OTC (arcB) and CK (arcC). In addition, sequence analysis upstream of the arcA gene revealed the presence of an open reading frame (orf229) whose 3'-end was only 101 bp-distant from the start codon of the arcA gene and showed similarity with members of the FNR (regulation for fumarate and nitrate reduction) and CRP (cAMP receptor protein) family of transcriptional regulators. Moreover, a putative binding site for such regulators lies in the promoter region of the arcA gene. Induction of the arc cluster by arginine was studied first at the enzymatic level. The activities of the three enzymes strongly increased when cells were grown in the presence of the amino acid. In addition, the influence of arginine on gene transcription was monitored by RT-PCR (reverse transcriptase-polymerase chain reaction). Expression of the three arc genes, and particularly that of arcA, was positively affected by arginine supplementation and thus confirmed the enzymatic results. Moreover, transcription of the putative CRP-like gene orf229 was also stimulated by arginine. These data suggest that the protein encoded by orf229 could be a CRP-like regulator involved in the metabolism of O. oeni.

Characterization of ear fluid isolates of Alloiococcus otitidis from patients with recurrent otitis media.

Nineteen isolates of Alloiococcus otitidis from ear fluid samples collected by tympanostomy from patients at four geographic locations were identified by phenotypic characterization and genetic relatedness. Initial growth of A. otitidis isolates occurred after 3 days at 37 degrees C on brain heart infusion (BHI) agar with 5% rabbit blood. Heavy growth occurred in BHI broth supplemented with 0.07% lecithin and 0.5% Tween 80 after 4 days of incubation. The isolates were gram-positive cocci that divided on an irregular plane and produced metabolic lactic acid, pyrrolidonyl arylamidase, and leucine aminopeptidase. These cocci grew sparsely in 6.5% NaCl-BHI broth, were asaccharolytic on both fermentative and oxidative bases, and were cytochrome negative by the iron-porphyrin test. The cellular fatty acid profile of A. otitidis was distinguished from those of related genera and characterized by major amounts ( > or = 14%) of 16:0, 18:2, 18:1 omega 9c, and 18:0 and smaller amounts of 14:0, 16:1 omega 7c, 17:0, and 18:1 omega 7c. Fifteen isolates demonstrated > 69% relatedness by DNA-DNA hybridization. Four isolates plus the original 15 were confirmed as A. otitidis by dot blot hybridization with a digoxigenin-labeled nucleotide probe specific for this species. The intergenic space between the genes coding for the 16S and 23S rRNAs of alloiococci was amplified by PCR, analyzed by restriction fragment length polymorphism, and determined to consist of three different genetic types. Although beta-lactamase negative, A. otitidis demonstrated intermediate levels of resistance to beta-lactams, including expanded-spectrum cephalosporins, and were resistant to trimethoprim-sulfamethoxazole and erythromycin.