3-D histomorphometry of the normal and early glaucomatous monkey optic nerve head: prelaminar neural tissues and cupping

PURPOSE

To introduce a three-dimensional (3-D) histomorphometric strategy for characterizing the connective tissue (laminar) and prelaminar neural tissue (prelaminar) components of optic nerve head (ONH) cupping in one bilaterally normal monkey and three monkeys with early experimental glaucoma (EG) in one eye.

METHODS

Trephined ONH and peripapillary sclera from both eyes of four monkeys were serially sectioned at either 3-mum thickness (three EG monkeys) or 1.5-microm thickness (the bilaterally normal monkey) with the embedded tissue block face stained and imaged after each cut. Digital section images were aligned and stacked to create a 3-D reconstruction of each ONH. Within 40 digital radial sagittal sections of each reconstruction, Bruch's membrane opening (BMO), the neural canal wall, and the anterior laminar surface were delineated by two delineators. The 80 BMO points were used to establish a BMO-zero reference plane. The parameters prelaminar tissue volume, post-BMO cup (the estimate of the clinical cup), and post-BMO total prelaminar volume (a global measure of ONH connective tissue deformation) were calculated overall and within 15 degrees radial regions. The parameter prelaminar tissue thickness was calculated at each delineated anterior laminar surface point. For each monkey, an intra-animal difference map was generated for each parameter. Overall volume and thickness data were compared between normal and EG eyes by analysis of variance (ANOVA).

RESULTS

Regionally variable expansion of post-BMO cup volume and post-BMO total prelaminar volume were present in all three EG eyes and far exceeded the intra-animal, physiologic differences for these parameters in the bilaterally normal monkey. Prelaminar tissue thickness was increased in all three EG monkeys, with the greatest effects present within the peripheral regions of the canal.

CONCLUSIONS

These data suggest that in young adult monkeys with more compliant connective tissues, clinical cupping in early glaucoma is primarily due to fixed deformation of the ONH connective tissues and occurs in the setting of prelaminar tissues that are thickened rather than thinned.

3-D histomorphometry of the normal and early glaucomatous monkey optic nerve head: lamina cribrosa and peripapillary scleral position and thickness

PURPOSE

To delineate three-dimensionally the anterior and posterior surfaces of the lamina cribrosa, scleral flange, and peripapillary sclera, to determine the position and thickness of these structures within digital three-dimensional (3-D) reconstructions of the monkey optic nerve head (ONH).

METHODS

The trephinated ONH and peripapillary sclera from both eyes of three monkeys with early glaucoma (EG; one eye normal, one eye given laser-induced EG) were serially sectioned at 3-mum thickness, with the embedded tissue block's face stained and imaged after each cut. Images were aligned and stacked to create 3-D reconstructions, within which Bruch's membrane opening (BMO) and the anterior and posterior surfaces of the lamina cribrosa and peripapillary sclera were delineated in 40 serial radial (4.5 degrees interval) digital sagittal sections. For each eye, a BMO zero reference plane was fit to the 80 BMO points, which served as the reference from which all position measurements were made. Regional laminar, scleral flange, and peripapillary scleral position and thickness were compared between the normal and EG eyes of each monkey and between treatment groups by analysis of variance.

RESULTS

Laminar thickness varied substantially within the normal eyes and was profoundly thicker within the three EG eyes. Laminar position was permanently posteriorly deformed in all three EG eyes, with substantial differences in the magnitude and extent of deformation among them. Scleral flange and peripapillary scleral thickness varied regionally within each normal ONH with the scleral flange and peripapillary sclera being thinnest nasally. Overall, the scleral flange and peripapillary sclera immediately surrounding the ONH were posteriorly displaced relative to the more peripheral sclera.

CONCLUSIONS

Profound fixed posterior deformation and thickening of the lamina are accompanied by mild posterior deformation and thinning of the scleral flange and peripapillary sclera at the onset of confocal scanning laser tomography (CSLT)-detected ONH surface change in young adult monkey eyes with early experimental glaucoma.

Factors affecting long-term survival of tunnelled haemodialysis catheters--a prospective audit of 812 tunnelled catheters

BACKGROUND

In 2001, in the US, 23% of haemodialysis patients were dialysing through tunnelled venous catheters (TVCs), and in the UK (2006) there were 28% of prevalent patients using catheters. It is unlikely that numbers will significantly decrease. We present the results of a prospective audit of the survival of 812 TVCs placed in 492 patients at our institution over a 6-year period (comprising 212 048 patient catheter days or 7068 patient catheter months of follow-up). Four different designs of catheter were studied: Split-Cath III (Medcomp), HemoSplit (Bard), Tesio twin catheter (Medcomp) and Permcath (Quinton).

METHODS

We used Kaplan-Meier survival analysis with log-rank test, to compare the effect of different parameters on catheter survival. The relative importance of significant parameters was determined by Cox regression analysis.

RESULTS

We have shown a significant catheter survival advantage of first catheters over second and subsequent insertions, of right internal jugular site over left internal jugular and thereafter over femoral site, and of non-diabetic over diabetic patients. Patient age, sex and operator (physician in ward-based procedure room under ultrasound control or surgeon in operating theatre under fluoroscopic assistance) did not significantly affect survival. The Permcath design demonstrated inferior survival in all but first catheter insertions in catheter-naïve patients. The HemoSplit and Tesio twin catheter designs demonstrated best survival overall. By Cox proportional hazard modelling the design and the position of the TVC seemed to be the most significant independent survival factors.

CONCLUSIONS

Clinicians need accurate data regarding catheter survival, mode of insertion and design, to inform practice.

Three-dimensional histomorphometry of the normal and early glaucomatous monkey optic nerve head: neural canal and subarachnoid space architecture

PURPOSE

To delineate three dimensionally the neural canal landmarks-Bruch's membrane opening (BMO), anterior sclera canal opening (ASCO), anterior laminar insertion (ALI), posterior laminar insertion (PLI), and posterior scleral canal opening (PSCO)-and the anterior-most aspect of the subarachnoid space (ASAS), within digital three-dimensional (3-D) reconstructions of the monkey optic nerve head (ONH).

METHODS

The trephinated ONH and peripapillary sclera from both eyes of three early glaucoma (EG) monkeys (one eye normal, one eye with laser-induced EG) were serial sectioned at 3-microm thickness, with the embedded tissue block face stained and imaged after each cut. The images were aligned and stacked in a 3-D volume, within which the BMO, ASCO, ALI, PLI, PSCO, and ASAS were delineated in 40 digital, radial, and sagittal sections. An ellipse was fitted to the 80 BMO points to establish a BMO zero reference plane, on which all other points were projected. The distance from each projected point to the BMO centroid (offset) and BMO zero reference plane (depth) were calculated and compared regionally between normal and EG eyes, both overall and within each monkey, by analysis of variance.

RESULTS

BMO was the clinically visible optic disc margin in all six eyes. The neural canal architecture was highly variable in the three normal eyes. Radial expansion of the neural canal was greatest posteriorly in the EG eyes. Axial elongation of the canal was less pronounced overall but was regionally present within all three EG eyes. ASAS was regionally radially expanded and anteriorly displaced within two of the three EG eyes.

CONCLUSIONS

Profound deformation of the neural canal and ASAS architecture are present in young adult monkey eyes at the onset of ONH surface change in early experimental glaucoma.

Prevalence and breed distribution of chronic pancreatitis at post-mortem examination in first-opinion dogs

OBJECTIVES

To assess the prevalence of canine chronic pancreatitis in first-opinion practice and identify breed associations or other risk factors.

METHODS

Three sections of pancreas were taken from 200 unselected canine post-mortem examinations from first-opinion practices. Sections were graded for inflammation, fibrosis and other lesions. Prevalence and relative risks of chronic pancreatitis and other pancreatic diseases were calculated.

RESULTS

The prevalence of chronic pancreatitis was 34 per cent omitting the autolysed cases. Cavalier King Charles spaniels, collies and boxers had increased relative risks of chronic pancreatitis; cocker spaniels had an increased relative risks of acute and chronic pancreatitis combined. Fifty-seven per cent of cases of chronic pancreatitis were classified histologically as moderate or marked. Forty-one per cent of cases involved all three sections. Dogs with chronic pancreatitis were more commonly female and overweight, but neither factor increased the relative risk of chronic pancreatitis. There were breed differences in histological appearances and 24.5 per cent of cases were too autolysed to interpret with an increased relative risk of autolysis in a number of large breeds.

CLINICAL SIGNIFICANCE

Chronic pancreatitis is a common, under-estimated disease in the first-opinion dog population with distinctive breed risks and histological appearances.

Diagnosis and surgical treatment of a nasopharyngeal cyst in a dog

A 21-month-old boxer dog was presented with clinical signs caused by nasopharyngeal obstruction. A mineralised mass in the nasopharynx was identified by radiography. Computed tomography allowed accurate anatomical localisation of the cystic lesion and identification of an ossified wall. Surgical removal of the mass by a ventral approach resulted in complete resolution of clinical signs. Histopathological examination strongly suggested that the cyst was derived from remnants of Rathke's pouch.

Clinical and magnetic resonance imaging features of nasopharyngeal lymphoma in two cats with concurrent intracranial mass

Lymphoma is reported to be the most common nasal and second most common intracranial neoplasm in cats. Intracranial lymphoma may occur as a primary central nervous system lymphoma or as part of multi-centric disease. Two cats were presented with histopathologically confirmed nasopharyngeal lymphoma and concurrent mass within the middle fossa of the cranial cavity, with magnetic resonance imaging suggestive of direct communication. Both cats demonstrated evidence of bilateral oculomotor nerve deficits and upper respiratory tract noise. In one cat, bilateral optic nerve deficits were also present. The magnetic resonance imaging features were similar in both cases and demonstrated a contrast-enhancing intracranial mass on the ventral aspect of the middle fossa of the cranial cavity and an adjacent mass arising from the dorsal aspect of the nasopharynx. Lymphoma should be included as an important differential diagnosis in cats presented with middle cranial fossa syndrome (in particular ophthalmoplegia) and stertor.

Cohort study of COX-1 and COX-2 expression in canine rectal and bladder tumours

OBJECTIVES

To determine the role that cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) play in malignant transformation in canine transitional cell carcinoma and rectal tumours.

METHODS

Histological sections of 21 canine rectal adenocarcinomas and 18 canine transitional cell carcinomas were stained for COX-1 and COX-2. Mann-Whitney non-parametric tests were applied to determine if there was any relationship between the percentage of cells expressing COX-1 or COX-2, and between COX-1 and COX-2 staining intensity and age, breed or sex.

RESULTS

For rectal adenocarcinomas, 19.0 per cent of the sections were negative for COX-1 and COX-2. A further 38.1 per cent of the sections were negative for COX-2 but positive for COX-1, and 38.1 per cent of the sections had rare or occasional single cells positive for COX-2. No significant differences were found in COX staining when compared with age, breed or sex. For transitional cell carcinomas, all of the sections were positive for COX-1 and COX-2. For COX-2 staining, 16.7 per cent had more than 30 per cent positive cells. For COX-1 staining, 38.9 per cent had more than 30 per cent positive cells. There was a significant increase in the percentage of COX-1 positive cells in small breed dogs (P = 0.0337).

CLINICAL SIGNIFICANCE

The variations in COX expression reported in this study may explain the differences in the clinical response of transitional cell carcinomas and rectal adenocarcinomas following treatment with non-steroidal anti-inflammatory drugs.

Implications of radiation dosimetry of the mandible in patients with carcinomas of the oral cavity and nasopharynx treated with intensity modulated radiation therapy

Intensity modulated radiation therapy (IMRT) is a newer method of delivering highly conformal, salivary gland sparing radiation treatment that is finding increasing applications in head and neck malignancies. However, the radiation dose distribution to the mandible is rarely considered with IMRT, and the potential risks of osteoradionecrosis or osseointegrated implant failure are not well characterized for this modality. In a series of 10 patients with oral cavity and nasopharyngeal cancers who previously underwent IMRT, examination of the three-dimensional mandibular dose distribution was undertaken. The findings indicate a modest potential risk of osteoradionecrosis and osseointegrated implant failure in cases where IMRT optimization constraints are not specifically aimed at sparing the mandibular bone. Significantly higher mandibular doses (P < 0.04) were received in cases of oral cavity as opposed to nasopharyngeal cancers with IMRT. Efforts to optimize IMRT to further reduce doses to the mandible should be considered, and development of software tools to integrate three-dimensional dose distributions into planning of post-radiotherapy osseointegration would be beneficial.

Changes in glutamate receptor function in synaptic input to the superficial superior colliculus (SSC) with aging and in retinal degeneration in the Royal College of Surgeons (RCS) rat

Ionotropic and metabotropic glutamate receptors mediate and modulate retinocollicular transmission. The Royal College of Surgeons (RCS) dystrophic strain of rats suffers from a progressive retinal degeneration with age and hence loss of visual function. We investigated whether this loss of function is accompanied by functional changes in a central target of retinal axons, the superficial superior colliculus (SSC). Field potential recordings were made in SSC slices from RCS rats aged either 4-7 weeks or 33-52 weeks. Blockade of GABAergic transmission revealed a field EPSP in response to optic tract stimulation which was sensitive to the NMDA antagonist AP5. In normal non-dystrophic rats the contribution of NMDA receptors to the fEPSP declined with age, whereas in dystrophic animals no such decline was seen. As mGluR8 may be located on terminals of retinal axons, we also assessed the function of this receptor. The mGluR8 agonist DCPG reduced fEPSPs in normal and dystrophic rats in both age groups to a similar extent, although the effect of DCPG declined with age. These findings indicate that the contribution of NMDA receptors to retinocollicular transmission declines with age in normal rats, but that such a decline is not seen in dystrophic rats which have severely reduced visual function. As NMDA receptors are associated with neural plasticity, it may be that this finding represents an increased residual potential for plasticity in dystrophic rats which may be functionally important.

The influence of dehydroepiandrosterone and 8-OH-DPAT on the caloric intake and hypothalamic neurotransmitters of lean and obese Zucker rats

The 5 HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)-tetraline (8-OH-DPAT) increases the food intake of satiated Zucker rats, both lean and obese. Associated with this increased intake are changes in the hypothalamic content of serotonin and its metabolite, 5-HIAA (5-hydroxyindole-3-acetic acid); serotonin is increased while the level of 5-HIAA is decreased. Analysis of individual 5-HIAA/5-hydroxytryptamine (5-HT) ratios, a measure of serotonin turnover indicate that 8-OH DPAT affected serotonin turnover equally and dramatically in both phenotypes. This would be an expected physiological action of an autofeedback mechanism by a 5-HT1A receptor agonist. Dehydroepiandrosterone (DHEA) at doses as low as 10 mg/kg blocks the 8-OH-DPAT-induced increase in food intake but does not alter food intake of control satiated Zucker rats. The mechanism of DHEA's action was investigated by monitoring the steroid's effect on hypothalamic neurotransmitters in this satiated model. DHEA by itself induced some change in 5-HIAA in the obese satiated model but not the lean. 8-OH-DPAT, by itself, dramatically decreased serotonin turnover in either lean or obese rats, and DHEA combined with 8-OH-DPAT did not further change serotonin turnover, suggesting DHEA may work through mechanisms other than monoamines to cause its inhibition of 8-OH-DPAT-induced behavioral effects at such low doses.

Predictors of Recurrent Hyperparathyroidism after Total Parathyroidectomy in Chronic Renal Failure

BACKGROUND/AIMS

Recurrent hyperparathyroidism (HPT) after total parathyroidectomy (TPTX) in chronic renal failure appears more common than might be anticipated.

METHODS

To study its predictors, we reviewed all 20 cases of TPTX performed at our hospital in a 10-year period.

RESULTS

During follow-up (median 46.8 months (range 9.3-120.3)), 15 patients had measurable PTH levels (>10 pg/ml), 7 had levels above the normal range (recurrent HPT), and 3 had PTH levels >300 pg/ml (severe recurrent HPT). Total follow-up post-TPTX was equal in those who developed recurrent HPT and others, but those with recurrent HPT had spent longer on dialysis post-TPTX (61.9 +/- 34.9 vs. 21.8 +/- 12.0 months; p = 0.001). Patients with recurrent HPT required less vitamin D supplementation during the 10 days post-TPTX (p = 0.025). Log [maximal PTH post-TPTX] correlated with duration of dialysis dependency post-TPTX (r = 0.591, p = 0.006), lowest serum calcium level during the first 30 days post-TPTX (r = 0.449, p = 0.047), and mean serum calcium during the first 30 days post-TPTX (r = 0.546, p = 0.013). Mean log [maximal PTH post-TPTX] was significantly lower in patients with ectopic calcification (p = 0.047). In multiple regression analysis, duration of dialysis post-TPTX and lowest serum calcium level during the first 30 days post-TPTX were the only independent predictors of log [maximal PTH post-TPTX].

CONCLUSION

Recurrent HPT is common following TPTX and predicted by duration of dialysis dependency post-TPTX, a measure of overall exposure to the uraemic stimulus to parathyroid hyperplasia, and the degree of early hypocalcaemia, possibly reflecting the adequacy of operative parathyroid ablation.

Activation of Group II and Group III metabotropic glutamate receptors by endogenous ligand(s) and the modulation of synaptic transmission in the superficial superior colliculus

Previous work from this laboratory indicates that Group II/III metabotropic glutamate (mGlu) receptors modulate responses of SC neurones to visual stimuli in vivo. It is thought that tonic levels of glutamate may be sufficient to activate some mGlu receptors. We wished to investigate if these receptors are activated under ambient conditions in SC. Field excitatory postsynaptic potentials (fEPSPs) evoked by optic tract stimulation were recorded from 300 microm slices of the adult pigmented rat superior colliculus at 34 degrees C. The Group II receptor selective agonist LY354740 (100-300 nM) had no significant effect on the peak amplitude of the fEPSP, although it did enhance the late phase of the fEPSP. In order to test for activation of Group II receptors by endogenous ligand, the selective antagonists LY341495 (50 nM) or EGLU (200 microM) were applied: these either enhanced or reduced the fEPSP amplitude. In similar experiments carried out at 22 degrees C, no effect was seen. The fEPSP enhancements, but not the fEPSP reductions, could be occluded by GABA antagonists. Application of higher concentrations of LY341495 (300, 600 nM-known to also affect Group III receptors, particularly mGlu8), or co-application of 50 nM LY341495 and the Group III-selective antagonist CPPG (100 microM) produced enhancements of responses, or counteracted response reductions over those seen with 50 nM LY341495 alone. The predominant Group II receptor in SC is mGlu3. It is known that this can be located presynaptically on GABAergic and glutamatergic terminals, postsynaptically, and on glia. Our results indicate that such receptors are tonically activated by endogenous transmitter, have distinct effects, and influence retino-collicular transmission. Furthermore, there is a segregation of effects where receptors exert some of their effects via modulation of GABAergic circuitry.

Clinical and pathological features of dilated cardiomyopathy in Holstein-Friesian cattle

Dilated cardiomyopathy is a primary disease of the heart muscle that has been reported in Holstein-Friesian cattle worldwide in the past 20 years. Nine cases of the condition were compared in terms of their clinical and pathological characteristics with nine unaffected animals matched for age, sex and breed. Their clinical signs included right-sided heart failure with severe subcutaneous oedema, ascites and/or hydrothorax and distended jugular veins. There were no characteristic biochemical or haematological changes. Postmortem, the affected hearts were enlarged with all the chambers dilated and walls of variable thickness. In most cases the kidneys were pale with a pitted surface. Histologically there was marked perimysial and endomysial fibrosis, extensive loss of cardiomyocytes by coagulative or colliquative necrosis, increased variation in the cross-sectional area of the myocardial fibres, and multifocal disarray and vacuolation of myocytes. Scanning electron microscopy showed that in all cases there was a mild myocardial inflammatory infiltrate, either diffuse or multifocal, which was identified by immunohistochemical labelling as T cells.

Serum antibody titres to canine parvovirus, adenovirus and distemper virus in dogs in the UK which had not been vaccinated for at least three years

Antibody titres to canine distemper (CDV), canine parvovirus (CPV) and canine adenovirus (CAV) were measured in 144 adult dogs that had not been vaccinated for between three and 15 years. Protective antibodies to CPV were present in 95 per cent of the population, to CDV in 71.5 per cent and to CAV in 82 per cent. The prevalence of protective titres did not decrease with increasing time interval from the last vaccination for any of the three diseases studied. Booster vaccination increased the dogs CAV titres. For comparative purposes, 199 puppies were sampled at the time of their first and second vaccination. In the case of CPV and CAV a significantly higher proportion of the adult dogs were protected than of the puppies immediately after they were vaccinated. Natural CPV boosting was strongly suspected because the dogs had significantly higher titres three years after their primary vaccination than two weeks after it and three unvaccinated dogs had acquired protective antibody levels uneventfully. There was no evidence of natural exposure to CDV.

Morphometry of Bovine Dilated Cardiomyopathy

Bovine dilated cardiomyopathy (BDCM) is a primary disease of the myocardium that has been described in Holstein-Friesian cattle worldwide in the last 20 years. The principal morphological changes in the myocardium are interstitial fibrosis and increased variability in cardiomyocyte size. Sections of heart muscle from nine cases of BDCM and nine unaffected controls matched for age, sex and breed were studied by means of a computer-assisted image analyser to measure the degree of fibrosis, and the cardiomyocyte cellular and nuclear cross-sectional area and length. The amount of connective tissue in the hearts of BDCM cases was increased by 6.7 times, the nuclear transverse cross-sectional area by 1.9 times, and the cardiomyocyte length and cross-sectional area by 1.7 and 1.6 times, respectively. This resulted in an estimated 2.5-fold increase in mean cardiomyocyte volume. Animals with clinical signs of BDCM showed a mean loss of 51% of the total number of cardiomyocytes as compared with controls. Of the five parameters studied, the percentage of fibrosis was found to be the most consistent discriminator for BDCM. It is possible that the degree of fibrosis could be used to distinguish BDCM from other cardiac diseases of cattle.

Thoracic high-resolution computed tomography in the diagnosis of metastatic carcinoma

Three dogs were presented for investigation of recurrent pyrexia of unknown origin, chronic vomiting and respiratory distress, respectively. One dog was markedly underweight and the other two were cachexic. Physical examination and initial diagnostic tests failed to establish the underlying cause of the presenting signs. Thoracic radiographs were within normal limits for the age of the dog. In each case there was a high index of suspicion for an occult neoplastic process in view of the profound unexplained weight loss present. High-resolution computed tomography (HRCT) of the thorax was performed. The lung fields were divided into three zones for analysis and a novel classification scheme was used to describe the HRCT findings in each zone. Postmortem examination and histopathology confirmed the presence of an infiltrating metastatic carcinoma in all three cases. The HRCT changes correlated closely with the pathological findings. The authors conclude that HRCT of the lung should be considered for pulmonary metastatic screening in the dog and introduce a classification system for HRCT findings, based on terminology used in human medicine.

Nicotine applied by transdermal patch induced HSV-1 reactivation and ocular shedding in latently infected rabbits

The identification of factors involved in herpes virus latency and reactivation is critical to a better understanding of the mechanisms essential to viral neuroinvasiveness and neurovirulence. Recurrent episodes of ocular herpes infections cause irreversible corneal scarring and are the primary cause of loss of vision due to an infectious agent in industrialized countries. In this study, we examined the ability of nicotine, a compound known to be involved in stress-associated immunomodulation and recognized as one of the most frequently used addictive agents, to induce ocular shedding in rabbits latently infected with herpes simplex virus type 1 (HSV-1) strain McKrae. New Zealand white rabbits latently infected with HSV-1 at 3-4 weeks post-inoculation were randomly divided into two groups. The corneas of all rabbits were free of lesions as verified by slit lamp biomicroscopy. One group received nicotine by transdermal patch (21 mg/day) for 20 days and the other group served as the control. Reactivation data were obtained by detection of virus in tear film collected by ocular swabbing performed concurrently with the administration of nicotine. Compilation of data from three separate experiments demonstrated that 16.5% (258/1560) of the swabs taken from rabbits treated with nicotine were positive for virus, compared with 8.3% (53/639) of swabs taken from controls. Rabbits receiving nicotine exhibited a significantly (P < 0.0001) higher rate of ocular shedding than controls. The concentration of nicotine in the serum was determined at various times (0-24 hrs) after new patch replacement. Peak (average) serum level of nicotine was obtained 8 hours after patch replacement and exhibited a broad range of values (0.233 microg/mL-6.21 microg/mL). These results suggest that an initial systemic exposure to nicotine significantly increases HSV-1 reactivation. Further studies are needed to reveal any effects of nicotine dependency and nicotine withdrawal on herpesvirus reactivation.

Preliminary investigations into possible resistance to oxytetracycline in Melissococcus plutonius, a pathogen of honeybee larvae

AIMS

To investigate the occurrence of oxytetracycline (OTC) resistance in Melissococcus plutonius, which causes European foulbrood in honeybee colonies.

METHODS AND RESULTS

Strains of M. plutonius were isolated from diseased colonies in England and Wales and tested for resistance to OTC. The minimum inhibitory concentration (MIC) of OTC was also determined for selected isolates. No resistance to the antibiotic was found in any isolate and the average MIC was found to be 3.9 microg ml-1. Melissococcus plutonius was found to be susceptible to both chlortetracycline and tetracycline.

CONCLUSIONS

No resistance to OTC was found in M. plutonius.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrated that OTC can continue to be used to treat European foulbrood and that resistance may not explain why some treatments fail.