Unravelling the eco-specificity and pathophysiological properties of Cutibacterium species in the light of recent taxonomic changes.

In 2016, a new species name Cutibacterium acnes was coined for the well-documented species, Propionibacterium acnes, one of the most successful and clinically important skin commensals. The nomenclatural changes were brought about through creation of the genus Cutibacterium, when a group of propionibacteria isolates from the skin were transferred from the genus Propionibacterium and placed in the phylum Actinobacteria. Almost simultaneously, the discovery of two novel species of Cutibacterium occurred and the proposal of three subspecies of C. acnes were reported. These dramatic changes that occurred in a long-established taxon made it challenging for the non-specialist to correlate the huge volume of hitherto published work with current findings. In this review, we aim to correlate the eco-specificity and pathophysiological properties of these newly circumscribed taxa. We envisage that this information will shed light on the pathogenic potential of new isolates and enable better assessment of their clinical importance in the foreseeable future. Currently, five species are recognized within the genus: Cutibacterium acnes, Cutibacterium avidum, Cutibacterium granulosum, Cutibacterium modestum (previously, "Propionibacterium humerusii"), and Cutibacterium namnetense. These reside in different niches reflecting their uniqueness in their genetic makeup. Their pathogenicity includes acne inflammation, sarcoidosis, progressive macular hypomelanosis, prostate cancer, and infections (bone, lumbar disc, and heart). This is also the case for the three newly described subspecies of C. acnes, which are C. acnes subspecies acnes (C. acnes type I), subspecies defendens (C. acnes type II), and subspecies elongatum (C. acnes type III). C. acnes subspecies acnes is related to inflamed acne and sarcoidosis, while subspecies defendens to prostate cancer and subspecies elongatum to progressive macular hypomelanosis. Because the current nomenclature is based upon polyphasic analyses of the biochemical and pathogenic characteristics and comparative genomics, it provides a sound basis studying the pathophysiological roles of these species.

Dissecting the taxonomic heterogeneity within Propionibacterium acnes: proposal for Propionibacterium acnes subsp. acnes subsp. nov. and Propionibacterium acnes subsp. elongatum subsp. nov.

Propionibacterium acnes subsp. acnes subsp. nov. and Propionibacterium acnes subsp. elongatum subsp. nov. are described. These emanate from the three known phylotypes of P. acnes, designated types I, II and III. Electron microscopy confirmed the filamentous cell shape of type III, showing a striking difference from types I/II, which were short rods. Biochemical tests indicated that, in types I/II, either the pyruvate, l-pyrrolidonyl arylamidase or d-ribose 2 test was positive, whereas all of these were negative among type III strains. Matrix-assisted laser-desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) spectra, which profile mainly their ribosomal proteins, were different between these two groups. Surface-enhanced laser-desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS) spectra of all phylotypes revealed a specific protein biomarker that was overexpressed in type III strains compared with types I/II only when grown aerobically. Reference strains had high whole-genome similarity between types I (>91 %) and II (>75 %), but a considerably lower level of 72 % similarity with type III. recA and gyrB sequence dendrograms confirmed the distant relatedness of type III, indicating the presence of two distinct centres of variation within the species P. acnes. On the other hand, cellular fatty acid profiles and 16S rRNA gene sequence relatedness (>99.3 %) circumscribed the species. Thus, we propose two subspecies, Propionibacterium acnes subsp. acnes subsp. nov. for types I/II and Propionibacterium acnes subsp. elongatum subsp. nov. for type III. The type strain of Propionibacterium acnes subsp. acnes is NCTC 737T ( = ATCC 6919T = JCM 6425T = DSM 1897T = CCUG 1794T), while the type strain of Propionibacterium acnes subsp. elongatum is K124T ( = NCTC 13655T = JCM 18919T).

[Rhodococcus equi infection in AIDS patients: retrospective analysis of 13 patients in Argentina]. / Infección por Rhodococcus equi en pacientes con SIDA: Análisis retrospectivo de 13 pacientes en Argentina.

INTRODUCTION: Rhodococcus equi is a gram positive coccoid rod that causes pulmonary infections in immunosuppressed patients. METHODS: We retrospectively analyzed epidemiological, clinical, microbiological, radiological, and immunological features as well as the outcomes of 13 AIDS patients with R. equi infection. RESULTS: Between January 1994 and December 2012, 13 patients attending the AIDS department of the Infectious Diseases reference hospital in Buenos Aires were diagnosed with R. equi infection. All were men, the median age was 27 years. At the time of diagnosis, the median of CD4+ T cell counts was 11 cells/µl Twelve patients presented pulmonary disease with isolation of the microorganism from sputum or bronchoalveolar lavage; in the other patient the diagnosis was postmortem with positive culture of cerebrospinal fluid. The most frequent clinical manifestations were fever, haemoptysis, and weight loss. The predominant radiological finding was lobe consolidation with cavitation. Nine patients died after a median survival of 5.5 months. In all of them, cultures persisted positive until the last admission. The other 4 patients did continue clinical follow-ups. CONCLUSION: The insidious course of R. equi disease and the difficulties in the isolation of the microorganism contribute to the delay in the diagnosis and to the high mortality rate of this opportunistic infection.

Molecular signatures for Bacillus species: demarcation of the Bacillus subtilis and Bacillus cereus clades in molecular terms and proposal to limit the placement of new species into the genus Bacillus.

The genus Bacillus is a phylogenetically incoherent taxon with members of the group lacking a common evolutionary history. Comprising aerobic and anaerobic spore-forming bacteria, no characteristics are known that can distinguish species of this genus from other similar endospore-forming genera. With the availability of complete genomic data from over 30 different species from this group, we have constructed detailed phylogenetic trees to determine the relationships among Bacillus and other closely related taxa. Additionally, we have performed comparative genomic analysis for the determination of molecular markers, in the form of conserved signature indels (CSIs), to assist in the understanding of relationships among species of the genus Bacillus in molecular terms. Based on the analysis, we report here the identification of 11 and 6 CSIs that clearly differentiate a 'Bacillus subtilis clade' and a 'Bacillus cereus clade', respectively, from all other species of the genus Bacillus. No molecular markers were identified that supported a larger clade within this genus. The subtilis and the cereus clades were also the largest observed monophyletic groupings among species from the genus Bacillus in the phylogenetic trees based on 16S rRNA gene sequences and those based upon concatenated sequences for 20 conserved proteins. Thus, the relationships observed among these groups of species through CSIs are independently well supported by phylogenetic analysis. The molecular markers identified in this study provide a reliable means for the reorganization of the currently polyphyletic genus Bacillus into a more evolutionarily consistent set of groups. It is recommended that the genus Bacillus sensu stricto should comprise only the monophyletic subtilis clade that is demarcated by the identified CSIs, with B. subtilis as its type species. Members of the adjoining cereus clade (referred to as the Cereus clade of bacilli), although they are distinct from the subtilis clade, will also retain the Bacillus genus name as they contain several clinically important species, and their transfer into a new genus could have serious consequences. However, all other species that are currently part of the genus Bacillus and not part of these two clades should be eventually transferred to other genera. We also propose that all novel species of the genus Bacillus must meet minimal requirements, foremost among which is that the branching of the prospective species with the Bacillus sensu stricto clade or the Cereus clade of bacilli should be strongly supported by 16S rRNA gene sequence trees or trees based upon concatenated protein sequences. Additionally, the presence of one or more of the CSIs that are specific for these clades may be used to confirm molecularly the placement of the species into these clades. The identified CSIs, in addition to their usefulness for taxonomic and diagnostic purposes, also provide novel probes for genetic and biochemical studies of these bacteria.

Approaches to the study of the systematics of anaerobic, gram-negative, non-sporeforming rods: current status and perspectives.

The present article gives an overview of recent taxonomic changes among the Gram-negative, anaerobic rods, briefly highlighting areas where the biology and ecology have a bearing on recent nomenclatorial changes. The focus is among the genera Bacteroides, Prevotella, Porphyromonas, Leptotrichia, Dysgonomonas, Fusobacterium and the Synergistes group and additionally demonstrates the value of conserved indels and group-specific proteins for identifying and circumscribing many of these taxa and the Bacteroidetes-Chlorobi species in general.

Assessment of the stability of cell-surface components of microorganisms by MALDI-TOF-MS following preservation on lenticule discs.

Strains representing the species Campylobacter coli, Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella enterica, and Staphylococcus aureus were randomly selected to assess the consistency of cells preserved on lenticule discs to those archived in traditional freeze-dried ampoules. Each matched pair was cultured using identical conditions and analysed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MS) to profile the surface-associated molecules of the cells. In addition, the cytosolic/membrane-bound proteins of C. coli and S. aureus strains were further analysed by surface-enhanced laser desorption/ionization time-of-flight MS. The mass spectral profiles in all cases showed a high degree of concordance between cells preserved by both methods and suggest that the properties of cells preserved on lenticule disc are consistent with those archived by the traditional method of freeze-drying.

The prevalence, antibiotic resistance and mecA characterization of coagulase negative staphylococci recovered from non-healthcare settings in London, UK.

Background: Coagulase negative staphylococci (CoNS) are important reservoirs of antibiotic resistance genes and associated mobile genetic elements and are believed to contribute to the emergence of successful methicillin resistant Staphylococcus aureus (MRSA) clones. Although, these bacteria have been linked to various ecological niches, little is known about the dissemination and genetic diversity of antibiotic resistant CoNS in general public settings. Methods: Four hundred seventy-nine samples were collected from different non-healthcare/general public settings in various locations (n = 355) and from the hands of volunteers (n = 124) in London UK between April 2013 and Nov 2014. Results: Six hundred forty-three staphylococcal isolates belonging to 19 staphylococcal species were identified. Five hundred seventy-two (94%) isolates were resistant to at least one antibiotic, and only 34 isolates were fully susceptible. Sixty-eight (11%) mecA positive staphylococcal isolates were determined in this study. SCCmec types were fully determined for forty-six isolates. Thirteen staphylococci (19%) carried SCCmec V, followed by 8 isolates carrying SCCmec type I (2%), 5 SCCmec type IV (7%), 4 SCCmec type II (6%), 1 SCCmec type III (2%), 1 SCCmec type VI (2%), and 1 SCCmec type VIII (2%). In addition, three isolates harboured a new SCCmec type 1A, which carried combination of class A mec complex and ccr type 1.MLST typing revealed that all S. epidermidis strains possess new MLST types and were assigned the following new sequence types: ST599, ST600, ST600, ST600, ST601, ST602, ST602, ST603, ST604, ST605, ST606, ST607 and ST608. Conclusions: The prevalence of antibiotic resistant staphylococci in general public settings demonstrates that antibiotics in the natural environments contribute to the selection of antibiotic resistant microorganisms. The finding of various SCCmec types in non-healthcare associated environments indicates the complexity of SCCmec. We also report on new MLST types that were assigned for all S. epidermidis isolates, which demonstrates the genetic variability of these isolates.

Proteome analysis of serovars Typhimurium and Pullorum of Salmonella enterica subspecies I.

BACKGROUND: Salmonella enterica subspecies I includes several closely related serovars which differ in host ranges and ability to cause disease. The basis for the diversity in host range and pathogenic potential of the serovars is not well understood, and it is not known how host-restricted variants appeared and what factors were lost or acquired during adaptations to a specific environment. Differences apparent from the genomic data do not necessarily correspond to functional proteins and more importantly differential regulation of otherwise identical gene content may play a role in the diverse phenotypes of the serovars of Salmonella. RESULTS: In this study a comparative analysis of the cytosolic proteins of serovars Typhimurium and Pullorum was performed using two-dimensional gel electrophoresis and the proteins of interest were identified using mass spectrometry. An annotated reference map was created for serovar Typhimurium containing 233 entries, which included many metabolic enzymes, ribosomal proteins, chaperones and many other proteins characteristic for the growing cell. The comparative analysis of the two serovars revealed a high degree of variation amongst isolates obtained from different sources and, in some cases, the variation was greater between isolates of the same serovar than between isolates with different sero-specificity. However, several serovar-specific proteins, including intermediates in sulphate utilisation and cysteine synthesis, were also found despite the fact that the genes encoding those proteins are present in the genomes of both serovars. CONCLUSION: Current microbial proteomics are generally based on the use of a single reference or type strain of a species. This study has shown the importance of incorporating a large number of strains of a species, as the diversity of the proteome in the microbial population appears to be significantly greater than expected. The characterisation of a diverse selection of strains revealed parts of the proteome of S. enterica that alter their expression while others remain stable and allowed for the identification of serovar-specific factors that have so far remained undetected by other methods.

Quantification of endotoxins in necrotic root canals from symptomatic and asymptomatic teeth.

The purpose of this investigation was to quantify the concentration of endotoxin in necrotic root canals and investigate the possible relationship between the concentration of endotoxin and endodontic signs and symptoms. Samples were collected from root canals of 50 patients requiring endodontic treatment due to necrosis of the pulpal tissue. Anaerobic techniques were used to determine the number of c.f.u. in each sample. A quantitative chromogenic Limulus amoebocyte lysate assay was used to measure the concentration of endotoxin in each sample. The presence of c.f.u. was detected by culture in all samples (range 10(2)-5x10(6)). In samples from cases of patients with spontaneous pain, the mean c.f.u. was 1.43x10(6) while in asymptomatic cases it was 9.1x10(4). Endotoxin was present in all the samples studied [range 2390.0-22100.0 endotoxin units (EU) ml-1]. The mean concentration of endotoxin in samples from patients with spontaneous pain was 18540.0 EU ml-1 while in asymptomatic cases it was 12030.0 EU ml-1. Asymptomatic cases generally had lower levels of endotoxin (i.e. a negative association). A positive association was found between endotoxin and symptomatic cases (e.g. spontaneous pain, tenderness to percussion, pain on palpation, swelling and purulent exudates). This study showed that endotoxin is present in high concentrations in root canals of symptomatic teeth. There was a positive correlation between the concentration of endotoxin in the root canal and the presence of endodontic signs and symptoms.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and proteomics: a new era in anaerobic microbiology.

Genome sequence data provide a framework for predicting potential microbial activities; however, the proteome content of the cell dictates its response to its environment. Microbiology is witnessing a major initiative to elucidate the nature of the proteome of large numbers of species. The tool driving the proteomic revolution is matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. During the analysis process, proteins are ionized and separated on the basis of their mass-to-charge ratios, which results in a characteristic mass-spectral profile. Because of the dynamic nature of the cell and the large number of external parameters that could influence its mass-spectral profile, considerable work was needed initially to optimize sample analysis and obtain consistent and reproducible results. For many anaerobes that grow poorly or are nonreactive in most diagnostic systems, proteome analysis is likely to have a major impact on microbial diagnosis and the delineation of centers of diversity associated with infections.

Compilation of a MALDI-TOF mass spectral database for the rapid screening and characterisation of bacteria implicated in human infectious diseases.

A database of MALDI-TOF mass spectrometry (MS) profiles has been developed with the aim of establishing a high throughput system for the characterisation of microbes. Several parameters likely to affect the reproducibility of the mass spectrum of a taxon were exhaustively studied. These included such criteria as sample preparation, growth phase, culture conditions, sample storage, mass range of ions, reproducibility between instruments and the methodology prior to database entry. Replicates of 12 spectra per sample were analysed using a 96-well target plate containing central wells for peptide standards to correct against mass drift during analysis. The quality of the data was assessed statistically prior to database addition using root mean squared values of <3.0 as the criterion for rejection. Cluster analysis using a nearest neighbour algorithm also enabled subsets of data to be compared. This was achieved using the bespoke MicrobeLynx trade mark software. Columbia blood agar was used to standardise all procedures for the database, since it permitted the culture of most human pathogens and also produced spectra with a broad range of mass ions. In some instances, alternative media such as CLED were used in specific studies with greater success. Following standardisation of the procedure, a database was developed comprising ca. 3500 spectra with multiple strain entries for most species. The results to date show unequivocally that as the number of strains per species increased, so too did the success of species matching. The technique demonstrated unique mass spectral profiles for each genus/species, with the variation in mass ions among strains/species being dependent on the intra-specific diversity. The success of identification against the database for wild-type strains ranged between 33 and 100%; the lower percentage results being generally associated with poor representation of some species within the database. These findings provide a new dimension for the rapid and high throughput characterisation of human pathogens with potentially broad applications across the field of microbiology.

Correlation between phylogroups and intracellular proteomes of Propionibacterium acnes and differences in the protein expression profiles between anaerobically and aerobically grown cells.

Propionibacterium acnes is one of the dominant commensals on the human skin and also an opportunistic pathogen in relation to acne, sarcoidosis, prostate cancer, and various infections. Recent investigations using housekeeping and virulence genes have revealed that the species consists of three major evolutionary clades (types I, II, and III). In order to investigate protein expression differences between these phylogroups, proteomic profiles of 21 strains of P. acnes were investigated. The proteins extracted from cells cultured under anaerobic and aerobic conditions were analysed using a SELDI-TOF mass spectrometer, high-resolution capillary gel electrophoresis, and LC-MS/ MS. The SELDI spectral profiles were visualised as a heat map and a dendrogram, which resulted in four proteomic groups. Strains belonging to type I were represented in the proteome Group A, while Group B contained type III strains. Groups C and D contained mixtures of types I and II. Each of these groups was not influenced by differences in culture conditions. Under anoxic growth conditions, a type IB strain yielded high expressions of some proteins, such as methylmalonyl-CoA epimerase and the Christie-Atkins-Munch-Petersen (CAMP) factor. The present study revealed good congruence between genomic and proteomic data suggesting that the microenvironment of each subtype may influence protein expression.

Genetic diversity of Propionibacterium acnes strains isolated from human skin in Japan and comparison with their distribution in Europe.

Propionibacterium acnes, a commensal of human skin, is also an opportunistic pathogen of common acne and certain infectious diseases. However, it is still not obvious which strain is pathogenic for a certain infectious disease, and investigations to characterize pathogenic strains using molecular typing methods such as MLST using several housekeeping genes have been undertaken. However, to date, such analysis has focused mainly on strains isolated from Europeans, and it is unclear whether the clonal distribution in other parts of the world is similar. Here, we analysed 50 strains of P. acnes from healthy humans and patients with atopic dermatitis (AD) in Japan and utilized MLST of seven housekeeping genes to study their clonal patterns. The MLST successfully typed the strains into five types, IA, IB1, IB2, II and III. Strains that belonged to types IA, IB and II were common on the human skin of both populations (Europe and Japan), but this study demonstrated what we believe to be the first association of type III strains with human skin, existing on the skin of both the AD and non-AD population. These results indicate the global existence of type III strains on human skin.

Identification of a Bacillus anthracis specific indel in the yeaC gene and development of a rapid pyrosequencing assay for distinguishing B. anthracis from the B. cereus group.

Bacillus anthracis, the causative agent of anthrax, is a potential source of bioterrorism. The existing assays for its identification lack specificity due to the close genetic relationship it exhibits to other members of the B. cereus group. Our comparative analyses of protein sequences from Bacillus species have identified a 24 amino acid deletion in a conserved region of the YeaC protein that is uniquely present in B. anthracis. PCR primers based on conserved regions flanking this indel in the Bacillus cereus group of species (viz. Bacillus cereus, B. anthracis, B. thuringiensis, B. mycoides, B. weihenstephnensis and B. pseudomycoides) specifically amplified a 282 bp fragment from all six reference B. anthracis strains, whereas a 354 bp fragment was amplified from 15 other B. cereus group of species/strains. These fragments, due to large size difference, are readily distinguished by means of agarose gel electrophoresis. In contrast to the B. cereus group, no PCR amplification was observed with any of the non-B. cereus group of species/strains. This indel was also used for developing a rapid pyrosequencing assay for the identification of B. anthracis. Its performance was evaluated by examining the presence or absence of this indel in a panel of 81 B. cereus-like isolates from various sources that included 39 B. anthracis strains. Based upon the sequence data from the pyrograms, the yeaC indel was found to be a distinctive characteristic of various B. anthracis strains tested and not found in any other species/strains from these samples. Therefore, this B. anthracis specific indel provides a robust and highly-specific chromosomal marker for the identification of this high-risk pathogen from other members of the B. cereus group independent of a strain's virulence. The pyrosequencing platform also allows for the rapid and simultaneous screening of multiple samples for the presence of this B. anthracis-specific marker.

Tracing the transition of methicillin resistance in sub-populations of Staphylococcus aureus, using SELDI-TOF Mass Spectrometry and Artificial Neural Network Analysis.

Strains (n=99) of Staphylococcus aureus isolated from a large number of clinical sources and tested for methicillin sensitivity were analysed by MALDI-TOF-MS using the Weak Cation Exchange (CM10) ProteinChip Array (designated SELDI-TOF-MS). The profile data generated was analysed using Artificial Neural Network (ANN) Analysis modelling techniques. Seven key ions identified by the ANNs that were predictive of MRSA and MSSA were validated by incorporation into a model. This model exhibited an area under the ROC curve value of 0.9147 indicating the potential application of this approach for rapidly characterising MRSA and MSSA isolates. Nearly all strains (n=97) were correctly assigned to the correct group, with only two aberrant MSSA strains being misclassified. However, approximately 21% of the strains appeared to be in a process of transition as resistance to methicillin was being acquired.

Proteomic analysis of the adaptive response of Salmonella enterica serovar Typhimurium to growth under anaerobic conditions.

In order to survive in the host and initiate infection, Salmonella enterica needs to undergo a transition between aerobic and anaerobic growth by modulating its central metabolic pathways. In this study, a comparative analysis of the proteome of S. enterica serovar Typhimurium grown in the presence or absence of oxygen was performed. The most prominent changes in expression were measured in a semiquantitative manner using difference in-gel electrophoresis (DIGE) to reveal the main protein factors involved in the adaptive response to anaerobiosis. A total of 38 proteins were found to be induced anaerobically, while 42 were repressed. The proteins of interest were in-gel digested with trypsin and identified by MALDI TOF mass spectrometry using peptide mass fingerprinting. In the absence of oxygen, many fermentative enzymes catalysing reactions in the mixed-acid or arginine fermentations were overexpressed. In addition, the enzyme fumarate reductase, which is known to provide an alternative electron acceptor for the respiratory chains in the absence of oxygen, was shown to be induced. Increases in expression of several glycolytic and pentose phosphate pathway enzymes, as well as two malic enzymes, were detected, suggesting important roles for these in anaerobic metabolism. Substantial decreases in expression were observed for a large number of periplasmic transport proteins. The majority of these are involved in the uptake of amino acids and peptides, but permeases transporting iron, thiosulphate, glucose/galactose, glycerol 3-phosphate and dicarboxylic acids were also repressed. Decreases in expression were also observed for a superoxide dismutase, ATP synthase, inositol monophosphatase, and several chaperone and hypothetical proteins. The changes were monitored in two different isolates, and despite their very similar expression patterns, some variability in the adaptive response to anaerobiosis was also observed.

Infección por Rhodococcus equi en pacientes con SIDA: Análisis retrospectivo de 13 pacientes en Argentina / Rhodococcus equi infection in AIDS patients: Retrospective analysis of 13 patients in Argentina

Introduction: Rhodococcus equi is a gram positive coccoid rod that causes pulmonary infections in immunosuppressed patients. Methods: We retrospectively analyzed epidemiological, clinical, microbiological, radiological, and immunological features as well as the outcomes of 13 AIDS patients with R. equi infection. Results: Between January 1994 and December 2012, 13 patients attending the AIDS department of the Infectious Diseases reference hospital in Buenos Aires were diagnosed with R. equi infection. All were men, the median age was 27 years. At the time of diagnosis, the median of CD4+ T cell counts was 11 cells/μl Twelve patients presented pulmonary disease with isolation of the microorganism from sputum or bronchoalveolar lavage; in the other patient the diagnosis was postmortem with positive culture of cerebrospinal fluid. The most frequent clinical manifestations were fever, haemoptysis, and weight loss. The predominant radiological finding was lobe consolidation with cavitation. Nine patients died after a median survival of 5.5 months. In all of them, cultures persisted positive until the last admission. The other 4 patients did continue clinical follow-ups. Conclusion: The insidious course of R. equi disease and the difficulties in the isolation of the microorganism contribute to the delay in the diagnosis and to the high mortality rate of this opportunistic infection.

Introducción: Rhodococcus equi es un cocobacilo grampositivo que provoca compromiso pulmonar en pacientes inmunodeprimidos. Métodos: En el presente trabajo se analizaron de manera retrospectiva los hallazgos epidemiológicos, clínicos, microbiológicos, imagenológicos, inmunológicos y la evolución de 13 pacientes con SIDA y enfermedad por R. equi. Resultados: Entre enero de 1994 y diciembre de 2012, 13 pacientes internados en la División de VIH/SIDA del hospital de referencia para Enfermedades Infecciosas de la ciudad de Buenos Aires egresaron con diagnóstico de enfermedad por R. equi. Todos eran varones y la mediana de edad fue 27 años. La mediana de linfocitos T CD4+ fue de 11 céls/μl Doce pacientes presentaron enfermedad pulmonar con aislamiento del microorganismo del esputo o del lavado bronco-alveolar; en el restante se recibió post mortem el cultivo positivo de líquido cefalorraquídeo. Las manifestaciones clínicas más frecuentes fueron fiebre, hemoptisis y pérdida de peso. La imagen radiológica predominante fue la consolidación con cavitación. Nueve pacientes fallecieron, con una mediana de supervivencia de 5,5 meses. En todos ellos el cultivo persistió positivo hasta la última internación. Los cuatro restantes abandonaron los controles y no pudieron ser evaluados en el tiempo. Conclusión: El curso insidioso de la enfermedad por R. equi y las dificultades en la identificación del microorganismo, contribuyen al retardo en el diagnóstico y a la elevada mortalidad de esta infección oportunista en esta población de pacientes.