Microindentation of fresh soft biological tissue: A rapid tissue sectioning and mounting protocol

Microindentation of fresh biological tissues is necessary for the creation of 3D biomimetic models that accurately represent the native extracellular matrix microenvironment. However, tissue must first be precisely sectioned into slices. Challenges exist in the preparation of fresh tissue slices, as they can tear easily and must be processed rapidly in order to mitigate tissue degradation. In this study, we propose an optimised mounting condition for microindentation and demonstrate that embedding tissue in a mixture of 2.5% agarose and 1.5% gelatin is the most favourable method of tissue slice mounting for microindentation. This protocol allows for rapid processing of fresh biological tissue and is applicable to a variety of tissue types.

A retrospective cohort study of the characteristics of unsuccessful operative vaginal deliveries

INTRODUCTION

Unsuccessful operative vaginal delivery (OVD) is associated with high rates of materno-fetal morbidity. We aimed to examine institutional rates of unsuccessful OVDs (uOVD) and compare them with successful OVD (sOVD) in order to identify factors to aid patient selection and education.

METHODS

A 6-month retrospective cohort study was performed on all unsuccessful and successful OVDs in a tertiary level maternity hospital in the Republic of Ireland. Maternal demographics and obstetric factors were assessed to evaluate potential underlying risk factors for unsuccessful operative vaginal delivery versus successful vaginal delivery.

RESULTS

There were 4,191 births during the study period with an OVD rate of 14.2% (n = 595) with 28 (4.7% of OVDs) being unsuccessful. Unsuccessful OVD were predominately nulliparous (25; 89.2%) with a mean maternal age of 30.1 years (range 20-42), with more than half (n = 15, 53.5%) being induced. The most common indication for induction was prolonged rupture of membranes (PROM) (n = 7, 25%) which was significantly different from the successful OVD group. A senior obstetrician was significantly more likely to be the primary operator in uOVD when compared to sOVD. (82.1 % V 54.1% p < 0.01). The majority of unsuccessful OVD were vacuum deliveries (n = 17; 60.7%), with a significantly higher mean birthweight when compared to successful OVD (3.695 kg V 3.483 kg; p < 0.01). Following an unsuccessful OVD, women were more likely to have a postpartum haemorrhage (64.2 % V 31.5% p < 0.01) and their infant was more likely to require admission to the neonatal intensive care unit (NICU) (32.1 % V 5.8% p < 0.01) when compared with successful OVD.

CONCLUSION

Risk factors for unsuccessful OVD were higher birth weight and induction of labour. There was a higher incidence of postpartum haemorrhage and NICU admission when compared with successful OVD.

Comparison of macroscale and microscale mechanical properties of fresh and fixed-frozen porcine colonic tissue

Mechanical changes to the microenvironment of the extracellular matrix (ECM) in tissue have been hypothesised to elicit a pathogenic response in the surrounding cells. Hence, 3D scaffolds are a popular method of studying cellular behaviour under conditions that mimic in vivo microenvironment. To create a 3D biomimetic scaffold that captures the in vivo ECM microenvironment a robust mechanical characterisation of the whole ECM at the microscale is necessary. This study examined the multiscale methods of characterising the ECM microenvironment using porcine colon tissue. To facilitate fresh tissue microscale mechanical characterisation, a protocol for sectioning fresh, unfixed, soft biological tissue was developed. Four experiments examined both the microscale and macroscale mechanics of both fresh (Fr) and fixed-frozen (FF) porcine colonic tissue using microindentation for microscale testing and uniaxial compression testing for macroscale testing. The results obtained in this study show a significant difference in elastic modulus between Fr and FF tissue at both the macroscale and microscale. There was an order of magnitude difference between the Fr and FF tissue at the microscale between each of the three layers of the colon tested i.e. the muscularis propria (MP), the submucosa (SM) and the mucosa (M). Macroscale testing cannot capture these regional differences. The findings in this study suggest that the most appropriate method for mechanically characterising the ECM is fresh microscale mechanical microindentation. These methods can be used on a range of biological tissues to create 3D biomimetic scaffolds that are more representative of the in vivo ECM, allowing for a more in-depth characterisation of the disease process.

Multi-institutional and multi-disciplinary care: A successfully managed aortic dissection in the third trimester of pregnancy

Multi-disciplinary collaborative care for pregnant women with complex and emergent conditions is essential. Logistical planning, clear communication and human factor awareness are all non-clinical skills which need to be utilised in order to maximise outcomes. We describe the case of a proximal aortic dissection in the late third trimester of pregnancy diagnosed in a peripheral hospital that was transferred to a cardiothoracic centre for successful operative management 160 km away. This required the time-sensitive mobilisation and liaison of a receiving cardiothoracic, anaesthesiology and perfusionist team in conjunction with obstetric and midwifery support from an affiliated maternity hospital, as well as the national neonatal transport team. We emphasise the importance of multidisciplinary team management in complex cases and how imperative good inter-disciplinary communication is to ensure safe inter-hospital transfer.

Induction of Labour: Reviewing the past to improve the future

BACKGROUND

Women undergoing induction of labor should be empowered with accurate information.

OBJECTIVE

This study aimed to examine the characteristics of and indications for induction of labor and delivery outcomes to help inform practice and counseling.

STUDY DESIGN

We conducted a retrospective cohort study of all singleton pregnancies undergoing induction of labor over a 3-month period in a tertiary-level hospital in the Republic of Ireland. Data were obtained from paper and electronic registries. Descriptive and inferential statistics were performed on data collected.

RESULTS

There were 1084 women delivered, with an induction rate of 46.0% (n=499). Primiparous women were more likely to be induced compared with multiparous women (51.4%; n=254/494 vs 41.5%; n=245/590; P<.001), and were more likely to be induced for postmaturity (30.7%; n=78/254 vs 23.6%; 58/245; P≤.001). More than half (50.3%; 251/399) were induced before 40 weeks’ gestation, irrespective of parity. Multiparous women and those induced for maternal medical indications had a shorter overall time to delivery interval (21.7 hours [standard deviation, 13.0] vs 13.8 hours [standard deviation, 11.2]; P<.001 and 18.3 hours [standard deviation, 12.7] vs 14.7 hours [standard deviation, 12.4]; P<.01).

CONCLUSION

Information on induction of labor can aid in the guidance and education of women undergoing the process, educate clinicians for appropriate counseling, and facilitate shared decision-making.

Medicine, media and the law: The effect on training in obstetrics and gynaecology

The inextricable link between medicine and the legal profession has flourished in the 21st century, with countless newspaper articles and social media content on medical cases visible at every juncture. This is particularly true in the speciality of obstetrics and gynaecology, with one of the highest rates of litigation of all medical specialities. We aimed to evaluate the influence of media and the legal environment on the career of trainees in obstetrics and gynaecology. Under the auspices of the Irish national training body, we distributed a 26-item questionnaire to doctors-in-training (DIT) working in obstetrics and gynaecology in the Republic of Ireland. Descriptive statistics and Chi-squared analyses were performed on the anonymised data. 151 DIT responded to the questionnaire, with a response rate of 86.2 % (sample size = 175). The majority were female (79.9 %, n = 121), Irish (85.5 %, n = 106) and had no children (67.0 %, n = 83). 86.7 % (n = 131) felt that the media did not have a positive impact on patients receiving care, and, further, unfairly represented the speciality (94.1 %; n = 142). Additionally, DIT felt that medico-legal issues had a negative impact on issues such as retention and recruitment. These two areas were implicated in over three quarters of DIT considering leaving the speciality. This study demonstrates that DIT perceive media scrutiny and litigation to have a negative effect on the speciality of obstetrics and gynaecology. Further support integrated into specialist training, is needed to ensure that trainees are adequately equipped to deal with both mainstream and social media as well as interactions they may have with the legal profession as they progress through their career.

The general populations' understanding of first trimester miscarriage: a cross sectional survey

OBJECTIVES

Miscarriage is a common, yet for many, devastating adverse pregnancy outcome. However, despite this the level of public knowledge on the topic is sub-optimal. We aimed to examine the general public's knowledge of miscarriage as well as their health information seeking behaviours associated with this topic.

STUDY DESIGN

We commissioned a national cross-sectional telephone survey of adults in the Republic of Ireland. 967 members of the general public consented to participate to this anonymised telephone survey. Sampling procedures ensured proportionality as per national standards. We examined respondents' definitions of miscarriage, its incidence and clinical findings, as well as the information seeking behaviours of the general population surrounding miscarriage.

RESULTS

699 (72%) of respondents provided an estimate of miscarriage frequency, with 28% of respondents correctly estimating that miscarriage occurs in 21-30% of pregnancies, with 61% under-estimating the incidence. Men were three times more likely than women to under-estimate (aOR3.5; 95% CI 2.4-4.9), as were those without children (aOR 1.7; 95% CI 1.2-2.6), or those living in urban areas (aOR 1.6; 95%CI 1.0-2.4. One third of respondents (33%) believed that the risk of miscarriage was higher following only one miscarriage. While 83% of respondents knew someone who had experienced a miscarriage, just over one third had discussed the topic of miscarriage with a family member/friend.

CONCLUSIONS

The general populations' knowledge of miscarriage, its incidence and associated factors is concerning, as are their health information seeking behaviours. Improving the level of knowledge of the general public could be achieved by adopting the topic into existing public health and education strategies. This will allow those experiencing miscarriage to frame their experience and expectations.

Recurrent hepatocellular carcinoma in pregnancy: A case report and literature review

The incidence of hepatocellular carcinoma in pregnancy is rare, and we present the first reported case of a pregnancy complicated by pre-existing advanced hepatocellular carcinoma. We describe the case of a 39-year-old woman in her second pregnancy, with a diagnosis of hepatocellular carcinoma. This was discovered in 2013 incidentally following hepato-splenectomy and pancreatectomy for a presumed hepatic adenoma in the context of multiple arterio-venous malformations. Recurrent hepatocellular carcinoma, in conjunction with co-existing pulmonary hypertension was successfully managed in a multi-disciplinary setting, resulting in a spontaneous vaginal delivery of a live female infant with maternal and neonatal survival six months following delivery.

Menorrhagia Outcomes of Minimally Invasive Treatments (MOMITS): A 2 to 5-year follow-up

We conducted a retrospective postal questionnaire-based study to assess the effectiveness and patient experience of minimally invasive treatments for menorrhagia by performing a two- to five-year follow up of patient symptoms. Questionnaires were distributed to 111 and 117 women following thermal balloon endometrial ablation (TBEA) and levonorgestrel intrauterine system (LNG-IUS), with response rates of 58.5% and 43.6% respectively. Sanitary pad use during the heaviest day of bleeding reduced by 8.4 and 5.2 pads in the TBEA and LNG-IUS groups respectively (p<0.05). An improvement in patients' quality of life (QOL) score exceeding 10 points was found in 79% and 61% in the TBEA and LNG-IUS groups respectively. Patient satisfaction (PS) improved in all areas, more so regarding participation in social activities in the TBEA group (p<0.05). Women undergoing TBEA would recommend the procedure to other women in 95%, and 93% in the LNG-IUS group. TBEA and LNG-IUS are highly acceptable management options for the treatment of menorrhagia, with improvement in QOL, PS and menstrual blood loss.

Metastatic gestational choriocarcinoma: a masquerader in obstetrics

We describe a case of a 36-year-old woman presenting with vaginal bleeding and suboptimally rising serum human chorionic gonadotropin levels, who was investigated for a pregnancy of unknown location. Ultrasonography, laparoscopy and dilatation and curettage failed to reveal signs of an intra-uterine or intra-abdominal pregnancy. Following computed tomography imaging, a mediastinal mass was histologically determined to be a gestational choriocarcinoma. Following surgical resection and chemotherapy, the patient recovered and proceeded to have a successful intra-uterine pregnancy. We describe this exceptionally rare case and emphasise the importance of follow-up of hCG levels in pregnancy of unknown location.

The use and success of cold coagulation for the treatment of high grade squamous cervical intra-epithelial neoplasia: a retrospective review

OBJECTIVE

Cold coagulation is recognised as a viable, cost-effective and successful treatment for cervical intraepithelial neoplasia (CIN), being used less frequently than excisional treatments for high grade lesions. We set out to demonstrate successful long term follow-up of patient with high grade CIN treated with cold coagulation.

STUDY DESIGN

We conducted a retrospective review over a one-year period of women with biopsy-proven CIN 2 and 3 who were treated with cold coagulation to the cervix, attending the colposcopy service of a large tertiary referral hospital. We examined follow-up cervical smear data for three years post treatment of low and high grade CIN, evaluated the success of treatment and re-treatment rates.

RESULTS

93 patients were included in our study, with 39 (41.9%) having CIN 1 and 54 (58.1%) diagnosed with CIN 2 or 3. Follow-up smears revealed low levels of recurrent high grade changes in both groups, with 31 (79.5%) of our CIN 1 group having a negative smear one year following treatment with cold coagulation, compared to 44 (81.1%) of patients with CIN 2 and 3. Successful primary treatment (i.e. no requirement for further treatment after 3 year follow-up) occurred in 33 (84.6%) of the CIN 1 group, and 42 (77.7%) of the CIN 2/3 group, demonstrating no statistical significance between re-treatment rates between both groups.

CONCLUSIONS

This study demonstrates the effectiveness of cold coagulation for the treatment of high grade cervical intraepithelial neoplasia. High success rates, and low re-treatment rates confirm that this is an acceptable primary treatment for CIN 2 and 3.

Conjoined twins: experience in an Irish tertiary centre

Conjoined twins are rare, with a reported incidence of 0.19 per 10,000 pregnancies in Europe. We discuss four spontaneous conjoined twin pregnancies presenting to a tertiary referral centre from 2005 to 2011, diagnosed on antenatal dating ultrasound. The cases were monitored closely throughout pregnancy by a multidisciplinary team, with serial surveillance, including ultrasound, fetal echocardiography, magnetic resonance imaging, amniocentesis and further referral to cardiology and paediatric surgery specialists, where indicated. Three female sets were determined antenatally to be not surgically separable; these infants were managed palliatively following a live birth. The male set of conjoined twins was accepted for surgical separation at Great Ormond Street Hospital, London, which was successfully performed electively at 4 months. Of interest, all four parents reside within 20 km of each other, representing a possible cluster of cases. The incidence of conjoined twins in our local population is approximately 0.63 per 10,000 over an 8-year period from 2005 to 2012. This case series highlights a cluster of conjoined twins, managed to viability and delivered in a tertiary referral centre.

[Abdominal morbidity following TRAM flap breast reconstruction--patient-reported outcome measures]

PURPOSE/BACKGROUND

Excellent aesthetic outcomes have been demonstrated with TRAM flap breast reconstruction. However, abdominal wall morbidity after TRAM flap breast reconstruction has not been accurately evaluated in terms of patient symptoms or patient quality of life. To further examine this issue, we performed a cross-sectional survey of TRAM flap breast reconstruction patients utilising questions from a patient-related outcome measure questionnaire.

PATIENTS AND METHOD

The questions were posed to post-mastectomy breast reconstruction patients. Items pertaining to abdominal wall symptoms and satisfaction with the outcome were reported on a 5-point Linkert Scale (1=very satisfied/no symptoms to 5=very dissatisfied/frequent symptoms).

RESULTS

The study population consisted of 270 patients who underwent pedicled (n=183) or free (n=87) TRAM flap procedures. The frequency of abdominal wall symptoms reported on abdomen-specific questionnaire items was increased in the pedicled TRAM group relative to the free TRAM group. This included "tightness or pulling in abdomen" (2.34 vs. 2.01); "abdominal pain, bloating, or discomfort" (2.11 vs. 1.69); "difficulty doing everyday activities requiring the use of your abdominal muscles" (2.11 vs. 1.67); and "abdominal weakness" (2.36 vs. 1.8).

CONCLUSION

We found a relatively low frequency of abdominal symptoms in the TRAM flap patients as a whole. However, there was a tendency towards increased abdominal symptoms in the pedicled TRAM patients compared to the free TRAM patients. As the population sizes in this study are somewhat limited, future studies with increased patient numbers may find greater differences between pedicled and free TRAM patients. In addition, studies evaluating the patients' abdominal wall symptoms pre- and postoperatively may allow for a detailed analysis of abdominal wall morbidity in post-mastectomy TRAM patients.

Viability and Metabolic Features of Bacteria Indigenous to a Contaminated Deep Aquifer

The quantitation and characterization of indigenous bacteria of a deep aquifer, located in the southwestern United States and contaminated with halogenated aliphatic compounds, was undertaken. Water samples were obtained aseptically from depths of 45 to 151 m from four sites that ranged from 260 to 1,800 m in distance from the location of contaminant release. Sediment samples were also obtained from the proximal and distal sites for analyses. Results for aerobic and anaerobic colony-forming units were obtained on four agar media that were used to retrieve heterotrophs, oligotrophs, and pseudomonads. Most probable number estimates were obtained from a liquid medium favorable for oligotrophs. Representative isolates were tested against Biolog plates (Biolog, Inc., Hayward, Calif.) for patterns of carbon source utilization. Of 103 Gram-negative (GN) isolates, 48 could not be identified and the others were only tentatively identified via the Biolog database, and none of the 35 Gram-positive (GP) isolates were identifiable. However, the metabolic patterns were subjected to average cluster linkage analyses; the GN and GP bacteria were separable into eight and four groups, respectively. The oligotroph group comprised one-third of the GN and one-half of the GP isolates. The consensus carbon source utilization pattern for each group was determined and will be useful in future characterization of additional aquifer bacterial isolates. Although predominantly aerobic and oligotrophic, the microbial community of this aquifer was highly diverse with discernible viability and metabolic features of the microbiota distinctive to each of the four water and two sediment samples.

Low temperature protocol for efficient transformation of Mycobacterium smegmatis spheroplasts

Spheroplasts of Mycobacterium smegmatis LM15, strain 607, were prepared by a combined treatment with glycine and lysozyme. The spheroplasts were tested for ability to take up and express purified mycobacteriophage DNA. Exposure of 1.0 x 10(8) to 1.0 x 10(9) spheroplasts to saturating DNA (1 microgram) for 15 min at 5 degrees C resulted in a transfection efficiency of approximately 0.009% . The transfer of the beta-lactamase marker with DNA purified from strain LM15 to spheroplasts of a beta-lactamase-negative mutant, strain LM144, was achieved. The DNA-treated cultures, after reversion to the bacillary form, contained 20-fold more penicillin-resistant cells than the nontreated control culture. Approximately 80% of the penicillin-resistant colonies from the DNA-treated cells were positive for beta-lactamase Cell-free extracts of penicillin-resistant transformants contained beta-lactamase activity that ranged from 0.046 to 0.134 micromol of benzylpenicillin hydrolyzed/min per mg protein. This low temperature procedure is recommended for high efficiency transformation of M. smegmatis.

Incorporation of 5-fluorouracil into RNA by Mycobacterium avium complex strain LM1

The incorporation of 5-fluorouracil (FUra) into RNA of Mycobacterium avium complex strain LM1 was evaluated. Cells were labeled with either [14C]FUra or [3H]uracil and the ribonucleosides were analyzed by high-performance liquid chromatography. The identification of the ribonucleosides was facilitated by the use of an isocratic system that provided unambiguous identification of the RNA pyrimidine components. Uracil was incorporated into RNA as uridine, but an equal amount was converted to cytidine. [14C]FUra was incorporated directly into RNA as 5-fluorouridine and there was no evidence of its conversion to other pyrimidines. The ratio of 5-fluorouridine:uridine was 2.8-fold greater for cells grown in 100 micrograms FUra/mL than for cells grown in 20 micrograms FUra/mL. Analysis of the RNA nucleotides was performed and deoxyribonucleotides were present; DNA contamination was estimated to range from about 2 to 8% of the RNA preparations.

Multilocus enzyme electrophoresis analysis of the Mycobacterium avium complex and other mycobacteria

Multilocus enzyme electrophoresis analysis was used to evaluate the Mycobacterium avium complex (MAC), M. paratuberculosis, and nine other mycobacterial species. The average number of alleles per locus was 2.8 for the 35 MAC and 2 M. paratuberculosis strains which represented 24 electrophoretic types (ETs) and two distinct groups. The M. avium group was resolved into 17 ETs and contained the M. paratuberculosis ET. The M. intracellulare group consisted of six ETs. There was complete agreement between Gen-Probe identification and group placement by multilocus enzyme electrophoresis. The mean genetic diversity per locus for the 24 MAC ETs was 0.38. This procedure subdivided some serovars and, if implemented, should prove to be a powerful epidemiologic tool for the MAC. Eleven additional ETs were formed after the data for the other mycobacterial species were pooled with those for the MAC.

The AHA's priorities for 1991

The next decade presents formidable challenges for hospitals and for American health care in general. Whatever emerges from the current health care reform debates, a fundamental shift is taking place toward outpatient and non-hospital site care. Carol M. McCarthy, J.D., Ph.D, AHA president, outlines the association's plans for the coming year.

The AHA's priorities for 1990

The American Hospital Association will confront a number of key issues in the coming year, writes Carol McCarthy, AHA president. The association expects to face unprecedented challenges in its efforts to promote an environment conducive to the continuation of high-quality health care services. In addition, a number of forces may combine to create a sense of urgency--inside and outside of government--for major reforms in our current system.

Sweet's syndrome, acute leukemia, and t(3;5)

We report herein the case of a 36-year-old woman who was diagnosed as having Sweet's syndrome 13 months prior to developing acute myeloid leukemia (FAB type M2). Her bone marrow karyotype was 46,XX,t(3;5)(q21;q31). Translocation t(3;5) has been reported in seven other cases of acute nonlymphocytic leukemia. None of these cases have been associated with Sweet's syndrome.

Utilization of nitrate or nitrite as single nitrogen source by Mycobacterium avium

Twenty L-amino acids and several inorganic compounds were tested individually, as a sole nitrogen source, for ability to support the growth of Mycobacterium avium LM1 serovar 1. Of the amino acids tested, only L-glutamine provided nutritional support comparable to that of ammonium chloride at 1 mM. With either 1 mM potassium nitrate or nitrite substituted for ammonium chloride, similar numbers of CFU were produced. M. avium cells were grown in potassium nitrate or nitrite concentrations of 0.25, 0.5, 1.0, and 2.0 mM, and the medium was assayed for remaining nitrogen compound at several times during growth. Rates of utilization were of first-order kinetics, with nitrite removed more rapidly than nitrate. The rates were approximately 10 times as rapid at 0.25 mM than at 2 mM for either nitrogen source. Nine clinical isolates that included M. avium serovars 1, 4, and 8 and Mycobacterium scrofulaceum serovar 43 were tested for rate of utilization of ammonia, nitrate, or nitrite. Ammonia and nitrite were utilized with first-order kinetics by all strains. Nitrate utilization occurred but was not at the same level for all strains. Clinical tests indicate that M. avium is negative for nitrate reductase; this is because of the rapid reduction of nitrite produced from nitrate.

Recovery of Mycobacterium avium after treatment with chemical decontaminants

Cell suspensions of a pathogenic strain of Mycobacterium avium, serovar 1, were tested for susceptibility to chemical disinfectants that are frequently used for decontamination of environmental samples. Kinetic data were obtained by determining the viability at 15-min intervals during 60 min of exposure at room temperature with aeration. After 60 min exposure to a combination of 0.094% Zephiran, and 10% trisodium phosphate, only 0.3% of the initial number of colony-forming units survived. Survival after 60 min treatment with 2% sodium hydroxide, 1% sodium hydroxide, or 0.04% hexadecylpyridinium chloride was 20, 46, and 57%, respectively. To assess the practical applications, the same agents were employed to extract M. avium that had been seeded into soil. Recovery of more than 25% of the initial number of colony-forming units was achieved with any of the treatments. Several combinations of chloramphenicol and antifungal drugs were tested for inhibition of soil microbiota that survived the decontamination procedures.

Influence of nitrogen source and growth status on glutamine synthetase and glutamate synthase activity in Mycobacterium avium

An investigation was made of the activity of glutamine synthetase and glutamate synthase from batch-cultured cells of Mycobacterium avium. The bacteria were grown in medium with ammonium chloride concentrations of 0, 0.1, 0.25, 1, 5, or 25 mumol/mL or with glutamine at 0.1 or 1 mumol/mL. The specific activity of the two enzymes was determined at 0, 22, 45, and 70 h of incubation. Regardless of the ammonia concentration in the medium, glutamate synthase specific activity was two to five times higher in extracts from elongating cells, incubated 22 h, than in those from shortened cells, incubated 45 or 70 h. In contrast, there was no apparent difference in glutamine synthetase specific activity with regard to culture age; however, glutamine synthetase specific activity varied inversely with the concentration of ammonium chloride in the medium. Cells grown in glutamine had high activity of glutamine synthetase.

Glutamine synthetase from Mycobacterium avium

Mycobacterium avium was previously shown to be dependent upon ammonia or glutamine as a nitrogen source. In an effort to assess the physiology of ammonia assimilation by M. avium, a characterization of its glutamine synthetase was performed. The enzyme from M. avium was purified by streptomycin sulfate treatment, ammonium sulfate precipitation, and affinity chromatography. The enzyme was unusual in that it had a pH optimum of 6.4 and maximum enzyme activity was obtained between 50 and 60 degrees C as shown by the transferase assay. The glutamine synthetase activity from batch-cultured cells decreased with increasing concentration of ammonium chloride in the range of 0.25-5 mumol/mL of medium, which demonstrated a response to environmental supply of a nitrogen source. The mycobacterial enzyme was similar to the other bacterial glutamine synthetases in terms of molecular weight and sedimentation coefficient which were 600 000 and 19.5 S, respectively, and enzyme activity was lost by treatment with a glutamate analog, methionine sulfoximine. The isoelectric point was, however, pH 4.5. Treatment of the enzyme with snake venom phosphodiesterase resulted in an increase in specific activity. AMP was released by the phosphodiesterase treatment, thus demonstrating that M. avium glutamine synthetase was regulated by adenylylation modification.