La asistencia compartida, una forma distinta de organizar la colaboración con los servicios quirúrgicos / Shared-care, a different method for organising the collaboration with surgery departments

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La Medicina Interna y su futuro en los sistemas de salud. Posicionamiento de la Sociedad Española de Medicina Interna y de la Sociedad Portuguesa de Medicina Interna / Internal Medicine and its future in health systems. Positioning Statement of the Spanish Society of Internal Medicine and the Portuguese Society of Internal Medicine

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RAG Recombinase as a Selective Pressure for Genome Evolution.

The RAG recombinase is a domesticated transposable element co-opted in jawed vertebrates to drive the process of the so-called V(D)J recombination, which is the hallmark of the adaptive immune system to produce antigen receptors. RAG targets, namely, the Recombination Signal Sequences (RSS), are rather long and degenerated sequences, which highlights the ability of the recombinase to interact with a wide range of target sequences, including outside of antigen receptor loci. The recognition of such cryptic targets by the recombinase threatens genome integrity by promoting aberrant DNA recombination, as observed in lymphoid malignancies. Genomes evolution resulting from RAG acquisition is an ongoing discussion, in particular regarding the counter-selection of sequences resembling the RSS and the modifications of epigenetic regulation at these potential cryptic sites. Here, we describe a new bioinformatics tool to map potential RAG targets in all jawed vertebrates. We show that our REcombination Classifier (REC) outperforms the currently available tool and is suitable for full genomes scans from species other than human and mouse. Using the REC, we document a reduction in density of potential RAG targets at the transcription start sites of genes co-expressed with the rag genes and marked with high levels of the trimethylation of the lysine 4 of the histone 3 (H3K4me3), which correlates with the retention of functional RAG activity after the horizontal transfer.

Efecto analgésico del Lupinus mutabilis S (chocho) comparado con morfina / Analgesic effect of Lupinus mutabilis S (chocho) compared to morphine

El Lupinus mutabilis Sweet es una planta con alto contenido calórico y marcados efectos farmacológicos, por lo que pertenece al grupo de plantas nutracéuticas. Objetivo: Comparar la acción analgésica del Lupinus mutabilis S, con el de la Morfina, utilizando la técnica estandarizada de CYTED, del Plantar-test. Materiales y métodos: Utilizamos 50 ratones albinos, machos, de la cepa Holtzman, de aproximadamente 25 gramos de peso, obtenidos del bioterio del MINSA-Chorrillos, a los que previamente se les acondicionó en el bioterio de la Facultad de Medicina Humana de la Universidad San Martín de Porres y suministró alimento y agua. Se les distribuyó en cinco grupos, G1: Control negativo; G2: Lupinus mutabilis, 300 mg/kg; G3: Lupinus mutabilis, 300 mg/kg + Naloxona, 5 mg/kg; G4: Morfina, 10 mg/kg; y, G5: Morfina, 10 mg/kg + Naloxona, 5 mg/kg. Se determinó el umbral doloroso basal de cada uno de los animales en los diferentes grupos utilizando el test del Hot Plate, el mismo que se repitió a los 30, 60 y 90 ,imutos posteriores a la administración, vía intraperitoneal, de las sustancias correspondientes a cada grupo. Los resultados obtenidos fueron analizados estadisticamente con el programa Graph Pad Prism y Excel XP. Resultados: Apreciamos un efecto analgésico del Lupinus similar al de la Morfina, el mismo que fue bloqueado por Naloxona tanto en el grupo tratado con Morfina como en el tratado con Lupinus mutabilis, a la 1/2 hora. Conclusiones: El Lupinus mutabilis S, mostró un buen efecto analgésico, que al igual que la Morfina fue bloqueado por Naloxona.

Lupinus mutabilis Sweet is a plant with high calorie content and many pharmacological effects; therefore, we consider it as a nutraceutic plant. Objective: The present investigation was made with the purpose of comparing the analgesic properties of Lupinus mutabilis S with Morphine, using the standardized technique of CYTED from Plantar Test. Materials and Method: We used fifty albino mice; male of Holtzman bred weighing 25 grams approximately and got from biotherius at MINSA, Chorrillos, to whom previous conditioning in the biotherius from Facultad de Medicina Humana at Universidad de San Martin de Porres and supply of food and water, distributed in the following five groups, G1: Negative control groups, G2: Lupinus mutabilis 300 mg/kg; G3: Lupinus mutabilis, 300 mg/kg+Naloxoma, 5 mg/kg; G4: Morphine, 10 mg/kg and G5: Morphine. 10 mg/kg+Naloxona, 5 mg/kg. It was determined the basal painful threshold to each one of the animals in different groups, using the test of the Hot Plate, the same thing was repeated at 30, 60 and 90 minutus after administration by intraperitoneal via of substances according to each group. The results were analyzed statistically with the program GraphPad Prism and Excel XP. Results: We appreciate an analgesic effect of Lupinus mutabilis Sweet similar to morphine, the same that was blocked by Naloxone in both group treated with Morphine and Lupinus mutabilis at the first 30 minutes. Conclusions: Lupinus mutabilis Sweet showed a good pharmacological action, which like to Morphine that was blockaded by Naloxone.

Eikenella corrodens and Porphyromonas asaccharolytica pleural empyema in a diabetic patient with obstructive sleep apnea syndrome on noninvasive ventilation.

Eikenella corrodens is a normal inhabitant of the human oral cavity and gastrointestinal and genitourinary tracts. Pleuropulmonary infections by this microorganism are uncommon. Pulmonary aspiration is a chief predisposing condition. Although the outcome is usually favorable, its distinctive antibiotic sensitivity pattern makes bacterial identification an important feature in dealing with this infection. The authors report a case of pleural empyema caused by co-infection with Eikenella corrodens and Porphyromonas asaccharolytica, in an immunocompetent diabetic patient with obstructive sleep apnea syndrome, followed by a discussion on the role of noninvasive ventilation in the development of this infection.

[99mTc-ceftizoxime scintigraphy in normal rats and abscess induced rats]. / Gammagrafía con 99mTc-ceftizoxima en ratas normales y en ratas con absceso inducido.

UNLABELLED: This study aimed to investigate the biodistribution of the 99mTc-ceftizoxime in normal rats and in rats bearing septic and sterile induced abscess. MATERIAL AND METHODS: Three groups of rats were studied. a) Six normal rats b) 15 rats with E. coli induced abscess and c) 15 rats with sterile zymosan induced abscess. Septic abscess was induced with 2 x 10(8) colony forming units of E. coli and sterile one with 0.1 mL of 5% sterile Zymosan. 24 h after the abscess induction, 12 MBq of 99mTc-CFT were injected iv. and whole body images were collected at 30 min, 1, 2, 4 and 6 h p.i. Areas of interest were drawn and lesion/background index was calculated. The 6 normal rats were scanned at the same times, killed at 6 h p.i and kidney, liver, spleen, lung, heart and muscle activity were measured. Each organ was weighed, cut and its activity measured. Parallelly, the biological activity of the labeled antibiotic and its binding to the E. coli and S. aureus bacteria were analyzed. RESULTS: High biliary excretion was seen in all rats. Organ measurement showed the maximal uptake in kidney and very low uptake in muscles. Mean +/- s.d abscess/background ratio at 30 min, 1, 2, 4 and 6 h were 2.60 +/- 0.36, 2.67 +/- 0.66, 2.6 0 +/- 0.58, 2.78 +/- 0.84, 3.24 +/- 1.00 for septic abscess and 2.37 +/- 0.39, 2.10 +/- 0.38, 1.97 +/- 0.34, 1.82 +/- 0.25, 1.65 +/- 0.23 for aseptic abscess. The 99mTc-CFT uptake was significantly higher in the septic abscess than in sterile one (p < 0.05). The 99mTc-CFT uptake in the septic abscess remains stable or increases until along the 6 h. The 99mTc-CFT uptake in the aseptic abscess decreases along the time. CONCLUSIONS: The scintigraphy with 99mTc-CFT seems able to differentiate sterile inflammation from infection. High biliary excretion limits its application in abdomen. Main application could be diagnosis of osteoarticular infection.

Gammagrafía con 99mTc-ceftizoxima en ratas normales y en ratas con absceso inducido / 99mTc-ceftizoxzime scintigraphy in normal rats and abscess induced rats

El objetivo del trabajo fue analizar la biodistribución de la 99mTc-ceftizoxima (CFT) en ratas normales y en ratas con absceso inducido: séptico o estéril. Material y métodos: Se estudiaron 3 grupos de ratas. a) 6 ratas normales; b) 15 ratas en las que se indujo un absceso séptico con 2 x 10 8 unidades formadoras de colonias de Escherichia coli, y c) 15 ratas en las que se indujo un absceso estéril con 0,1 ml de 5 % zymosan estéril. A las 24 h de la inducción del absceso se inyectaron i.v. 12 MBq de 99mTc-CFT y se registraron imágenes de cuerpo entero a los 30 min y 1, 2, 4 y 6 h p.i. Se dibujaron áreas de interés y se calculó el índice lesión/fondo. En las 6 ratas normales se siguió el mismo procedimiento y además al finalizar las últimas imágenes se sacrificaron y se extrajeron riñones, hígado, bazo, corazón pulmones y un fragmento de músculo. Cada órgano, fue pesado, cortado y se midió la actividad que contenía. Paralelamente se analizó la actividad biológica del antibiótico marcado y la unión del mismo a las bacterias E. coli y Staphylococcus aureus. Resultados: Se observó eliminación biliar elevada en todos los animales. El contaje de los órganos mostró la mayor actividad en riñones y actividad muy baja en músculo. El índice medio de actividad lesión/fondo (Media ± d.e.) a los 30 min, 1, 2, 4 y 6 h fue 2,60 ± 0,36, 2,67 ± 0,66, 2,6 0 ± 0,58, 2,78 ± 0,84, 3,24 ± 1,00 en el absceso séptico y 2,37 ± 0,39, 2,10 ± 0,38, 1,97 ± 0,34, 1,82 ± 0,25, 1,65 ± 0,23 en el absceso estéril. La captación de 99mTc-CFT fue significativamente mayor en el absceso séptico que en el estéril (p < 0,05). La captación de 99mTc-CFT en el absceso séptico se incrementa con el tiempo hasta las 6h, mientras que en el estéril disminuye con el tiempo. Conclusión: La gammagrafía con 99mTc-CFT permite diferenciar la inflamación estéril de la infección y se podría aplicar al diagnóstico de la infección osteo-articular. La elevada eliminación renal y biliar limita su aplicación en abdomen

This study aimed to investigate the biodistribution of the 99mTc-ceftizoxime in normal rats and in rats bearing septic y sterile induced abscess. Material y methods: Three groups of rats were studied. a) Six normal rats b) 15 rats with E. coli induced abscess and c) 15 rats with sterile zymosan induced abscess. Septic abscess was induced with 2 x 10 8 colony forming units de E.Coli y sterile one with 0.1 mL de 5 % sterile Zymosan. 24 h after the abscess induction, 12 MBq de 99mTc-CFT were injected iv. and whole body images were collected at 30 min, 1, 2, 4 and 6 h p.i.. Areas of interest were drawn and lesion/background index was calculated. The 6 normal rats were scanned at the same times, killed at 6 h p.i. and kidney, liver, spleen, lung, heart and muscle activity were measured. Each organ was weighed, cut and its activity measured. Parallelly, the biological activity of the labeled antibiotic and its binding to the E. coli and S. aureus bacteria were analyzed. Results: High biliary excretion was seen in all rats. Organ measurement showed the maximal uptake in kidney and very low uptake in muscles. Mean ± s.d abscess/background ratio at 30 min, 1, 2, 4 and 6 h were 2.60 ± 0.36, 2.67 ± 0.66, 2.6 0 ± 0.58, 2.78 ± 0.84, 3.24 ± 1.00 for septic abscess and 2.37 ± 0.39, 2.10 ± 0.38, 1.97 ± 0.34, 1.82 ± 0.25, 1.65 ± 0.23 for aseptic abscess. The 99mTc-CFT uptake was significantly higher in the septic abscess than in sterile one (p < 0.05). The 99mTc-CFT uptake in the septic abscess remains stable or increases until along the 6 h. The 99mTc-CFT uptake in the aseptic abscess decreases along the time. Conclusions: The scintigraphy with 99mTc-CFT seems able to differentiate sterile inflammation from infection. High biliary excretion limits its application in abdomen. Main application could be diagnosis of osteoarticular infection

Early death and severe lymphopenia caused by ubiquitous expression of the Rag1 and Rag2 genes in mice.

The recombination activating proteins (RAG1 and RAG2) are essential for V(D)J recombination of immunoglobulin chains. Expression of both genes is lymphocyte-specific and RAG levels are tightly regulated throughout lymphopoiesis and cell cycle. To assess the significance of this pattern of expression, we generated transgenic mice expressing the Rag genes both continuously throughout lymphocyte development and constitutively in most non-lymphoid tissues. The transgenes partially complement an endogenous Rag2 null mutation and lead to a partial block in early B and T lymphopoiesis when introduced on a Rag2 sufficient background. The defect in thymocyte number is restricted to the alpha beta lineage leaving the gamma delta T cell pool intact, while neither IgH phenotypic allelic exclusion nor the kappa/lambda light chain ratio are altered. Finally, the ectopic expression of the Rag genes associates with growth retardation and early death of the animals, a phenotype reminiscent of those reported for mice deficient in double-strand break repair molecules.

Mice triallelic for the Ig heavy chain locus: implications for VHDJH recombination.

V(H)DJ(H) recombination has been extensively studied in mice carrying an Ig heavy chain rearranged transgene. In most models, inhibition of endogenous Ig rearrangement occurs, consistently with the feedback model of IgH recombination. Nonetheless, an incomplete IgH allelic exclusion is a recurrent observation in these animals. Furthermore, transgene expression in ontogeny is likely to start before somatic recombination, thus limiting the use of Ig-transgenic mice to access the dynamics of V(H)DJ(H) recombination. As an alternative approach, we challenged the regulation of somatic recombination with the introduction of an extra IgH locus in germline configuration. This was achieved by reconstitution of RAG2(-/-) mice with fetal liver cells trisomic for chromosome 12 (Ts12). We found that all three alleles can recombine and that the ratio of Ig allotype-expressing B cells follows the allotypic ratio in trisomic cells. Although these cells are able to rearrange the three alleles, the levels of Ig phenotypic allelic exclusion are not altered when compared with euploid cells. Likewise, we find that most VDJ rearrangements of the silenced allele are unable to encode a functional mu-chain, indicating that the majority of these cells are also genetically excluded. These results provide additional support for the feedback model of allelic exclusion.

Marcaje de ceftizoxima con 99mTc / Labelling of ceftizoxime with 99mTC

Se presenta un nuevo método de marcaje de antibióticos con 99mTc. Una cefalosporina de 3.ª generación de amplio espectro (ceftizoxima).Material y métodos: Se han utilizado 2,5 mg de ceftizoxima, 6,25 mg de ditionito sódico en una solución tampón (pH 11,4) como agente reductor y 300 MBq de 99mTc. El pH final se ajustó a 8,4 con NaOH 0,1N. La solución resultante fue hervida a 100ºC durante 5 min. La pureza radioquímica se valoró usando ITLC-SG/MEK, ITLC-SG/ 0,9 por ciento NaCl y HPLC fase reversa. La actividad biológica se valoró mediante la técnica de difusión en agar impregnadas con E. Coli de discos conteniendo 10,5 µg de antibiótico marcado y sin marcar. El mantenimiento de la actividad biológica fue evaluado por el diámetro de inhibición de los halos obtenidos tras 24 horas de incubación. Resultados: La eficiencia de marcaje fue de 94,9 ñ 2,4 por ciento (n = 20) y el compuesto mantuvo la estabilidad hasta 6 h. La cromatografía HPLC mostró 5 picos: dos a 1,7-2,0 min corresponden al compuesto derivado de la ceftizoxima (CDC) (82 por ciento-83 por ciento de la absorbancia y alrededor del 90 por ciento de la radioactividad), otro a los 4,7 min corresponde a la ceftizoxima intacta (6 por ciento de la absorbancia). Los dos picos restantes, aparecen a los 3,8 y 6,7 min y representan alrededor del 7-8 por ciento de la absorbancia. La actividad biológica del CDC respecto al antibiótico no marcado fue del 83 por ciento. Conclusiones: 1) El método de marcaje descrito da lugar a una modificación de la estructura de la ceftizoxima. 2) El 99m Tc se une a la nueva especie formada con un elevado rendimiento de marcaje y aceptable estabilidad. 3) El 99mTc-CDC mantiene 83 por ciento de la actividad antibiótica original y podría ser utilizado para la detección de infección in vivo (AU)

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Frequency and characterization of phenotypic Ig heavy chain allelically included IgM-expressing B cells in mice.

Ig H chain (IgH) allelic exclusion remains a puzzling topic. Here, we address the following question: Do phenotypic IgH allelically included cells exist in normal mice and, if so, at what frequency? Sorted cells from heterozygous mice were evaluated for the expression of both IgM allotypes by double intracytoplasmic stainings. Dual expressors were found at a frequency of 1 in 104 splenic B cells. These data were confirmed by direct sequencing of IgH-rearranged alleles obtained after single cell (or clone) PCR on dual expressors. Typically, these cells have one rearranged J558 VH whereas, in the other allele, a D-proximal VH gene is used. Interestingly, dual expressors have rearranged IgH alleles with similar CDR3 lengths. These results show that, in contrast to the kappa L chain and the TCR beta-chain, IgH allelic exclusion is the result of an extremely stringent mechanism. We discuss two non-mutually exclusive scenarios for the origin of IgH dual expressors: 1) IgH allelically included cells arise when the first allele to rearrange productively is unable to form a pre-BCR; dual expressors could be a subset of this population in which, upon conventional L chain rearrangement, both IgH are expressed at the surface; and 2) synchronous rearrangement of the IgH alleles.

[Labelling of ceftizoxime with 99mTc]. / Marcaje de ceftizoxima con 99mTc.

AIM OF THE STUDY: A new method to label antibiotics with 99mTc, using a third generation, wide spectrum cephalosporine (ceftizoxime), is presented. MATERIAL AND METHODS: 2.5 mg of ceftizoxime, 6.25 mg sodium dithionite in sodium bicarbonate buffer (pH=11.4) as a reductor agent, and 300 MBq of 99mTc were used. The final pH was adjusted to 8.4 with NaOH 0.1N. Radiochemical purity was assessed using ITLC-SG/MEK, ITLC-SG/0.9% NaCl and reverse phase HPLC. Biologic activity was assessed with the agar diffusion technique soaked with E. Coli in disks containing 10.5 microg labelled and non-labelled antibiotic. The maintenance of antibiotic activity was assessed by the diameter of the inhibition halos measured after 24 hours of incubation at 37 degrees C. RESULTS: The labelling efficiency was 94.9 +/- 2.4% (n = 20) and the complex was stable up to 6 h post-labelling. The HPLC chromatography showed five peaks: two of them at 1.7-2.0 min, which corresponds to the ceftizoxime derived product (82%-83% of the absorbance and about 90% of the radioactivity) and a third one at 4.7 min which corresponds to the intact ceftizoxime (6% of absorbance). The remaining two peaks appeared at 3.8 and 6.7 min and represented about 7%-8% of the absorbance. The antibiotic activity of the ceftizoxime-derived compound (CDC) was 83% of the unlabelled one. CONCLUSIONS: 1) The labelling method of ceftizoxime described causes a modification in its structure. 2) The 99mTc binds to the newly formed compound with high labelling efficiency and an acceptable shelf life stability. 3) The 99mTc-CDC maintains 83% of the original antibiotic activity and could be used for the detection of in vivo infection.

[Validation of the preparation of individual doses of 51Cr-EDTA in syringes]. / Validación de la preparación de dosis individuales de 51Cr-EDTA en jeringas.

The 51Cr-EDTA is one of the radiopharmaceuticals more used in the glomerular filtration rate determination. The necessity to prepare a daily reference dose every time that are prepared the patient's doses can go to a poor exploitation of the multidose vial. One way of improving its use consists on the preparation of individual doses in ready syringes to inject, for several days, employing only one of them as a standard. The aim of this study was to evaluate the storing of 51Cr-EDTA individual doses at room temperature and at 4 degrees C during 4 weeks, analyzing the radiochemical purity, the sterility and the radiopharmaceutical retention into the syringe. The results obtained showed that the radiochemical purity remains stable, always been greater than the value recommended for its use (> 95%). Likewise, there were not microorganism contamination nor 51Cr-EDTA appreciable retention into the syringes. We concluded that the preparation of individual doses of 51Cr-EDTA in syringes and their conservation at room temperature, or at 4 degrees C, during a period of 4 weeks, neither influence in the radiopharmaceutical quality nor increase its retention into the syringe.

Fatal microcystin intoxication in haemodialysis unit in Caruaru, Brazil.

BACKGROUND: After a drought in February, 1996, all 126 patients in a haemodialysis unit in Caruaru, north-east Brazil, developed signs and symptoms of acute neurotoxicity and subacute hepatotoxicity following the use of water from a lake with massive growth of cyanobacteria (blue-green algae). 60 patients died. METHODS: Besides recording clinical details and outcome at follow-up, we arranged laboratory, radiological, and histological investigations on the patients and toxicological studies of serum and haemodialysis water filters. FINDINGS: The acute presentation was with malaise, myalgia and weakness, nausea and vomiting, and tender hepatomegaly, with a range of neurological symptoms from tinnitus, vertigo, headaches, and deafness to blindness and convulsions. Liver injury ranged from abnormal liver-function test results to rapidly progressive and fatal hepatic failure. Biochemical investigations revealed gross hyperbilirubinaemia, abnormal liver enzyme activities, and hypertriglyceridaemia, but there was no evidence of haemolysis or microangiopathy. Histology revealed a novel acute toxic hepatitis with diffuse panlobular hepatocyte necrosis, neutrophil infiltration, canalicular cholestasis, and regenerative multinucleate hepatocytes. Samples of serum, dialysis filters, and water-treatment columns contained microcystins, the highly toxic low-molecular-weight hepatotoxins produced by cyanobacteria. INTERPRETATION: Cyanobacteria present water-borne hazards to health via drinking water and recreational water. Haemodialysis presents an additional high-risk exposure route: when they enter directly into the circulation, microcystins can lead to fatal clinical syndromes ranging from acute neurotoxic illness to subacute liver failure.

Liver failure and death after exposure to microcystins at a hemodialysis center in Brazil.

BACKGROUND: Hemodialysis is a common but potentially hazardous procedure. From February 17 to 20, 1996, 116 of 130 patients (89 percent) at a dialysis center (dialysis center A) in Caruaru, Brazil, had visual disturbances, nausea, and vomiting associated with hemodialysis. By March 24, 26 of the patients had died of acute liver failure. METHODS: A case patient was defined as any patient undergoing dialysis at dialysis center A or Caruaru's other dialysis center (dialysis center B) during February 1996 who had acute liver failure. To determine the risk factors for and the source of the outbreak, we conducted a cohort study of the 130 patients at dialysis center A and the 47 patients at dialysis center B, reviewed the centers' water supplies, and collected water, patients' serum, and postmortem liver tissue for microcystin assays. RESULTS: One hundred one patients (all at dialysis center A) met the case definition, and 50 died. Affected patients who died were older than those who survived (median age, 47 vs. 35 years, P<0.001). Furthermore, all 17 patients undergoing dialysis on the Tuesday-, Thursday-, and Saturday-night schedule became ill, and 13 of them (76 percent) died. Both centers received water from a nearby reservoir. However, the water supplied to dialysis center B was treated, filtered, and chlorinated, whereas the water supplied to dialysis center A was not. Microcystins produced by cyanobacteria were detected in water from the reservoir and from dialysis center A and in serum and liver tissue of case patients. CONCLUSIONS: Water used for hemodialysis can contain toxic materials, and its quality should therefore be carefully monitored.

Depresión en la adolescencia

La adolescencia constituye una etapa crítica en el desarrollo de cada individuo, en ella se dan una serie de procesos y transformaciones de gran imnportancia, tales conmo: la afirmación de la personalidad, el ejercicio pleno de la sexualidad y la función reproductora, el crecimiento espiritual, la concresión de los proyectos de vida productiva, la autoestima, etc., llevando todos ellos a la estructuración del perfíl psíquico del adulto. (1) Es un camino dificil enb el que se encuentran momentos de gran satisfacción y otros de frustración y derrota; período lleno de riesgos, de problemas, de conflictos que paulatinamente permiten al joven captar la realidad. (2) Entre los problemas más comunes de los adolescentes se encuentran los trastornos afectivos con sus distintas variantes clínicas, predominando entre ellos la depresión con sus variadas formas de presentación.

Phage-mediated transfer of tetracycline resistance in Staphylococcus aureus isolated from cattle in Brazil.

Tetracycline-resistant strains of Staphylococcus aureus isolated from cattle in Brazil, were used as prospective donors for the transfer of resistance to laboratory strains, using mixed-culture and filter-mating protocols. Three lysogenic donors transferred tetracycline resistance in both mixed culture and during filter mating. In contrast, when a non-lysogenic strain was used as prospective donor, transfer was not detected using either mating protocol. In order to evaluate the involvement of phage, successful transfer experiments were repeated with the addition of sodium citrate, which sequestered calcium ions. Mixed-culture and filter-mating protocols did not result in the transfer of resistance. These results support the notion that transfer of the resistance determinant under both sets of conditions described here involve the same bacteriophage-mediated mechanism. Although transfer of tetracycline resistance was detected, without any attempt to create specialized transduction agents or to extract phages, the co-transfer of additional resistance markers indicated that it could not be conventional transduction.