Analysis of genotypic diversity data for populations of microorganisms

ABSTRACT Estimation of genotypic diversity is an important component of the analysis of the genetic structure of plant pathogen and microbial populations. Estimates of genotypic diversity are a function of both the number of genotypes observed in a sample (genotype richness) and the evenness of distribution of genotypes within the sample. Currently used measures of genotypic diversity have inherent problems that could lead to incorrect conclusions, particularly when diversity is low or sample sizes differ. The number of genotypes observed in a sample depends on the technique used to assay for genetic variation; each technique will affect the maximum number of genotypes that can be detected. We developed an approach to analysis of genotypic diversity in plant pathology that makes specific reference to the techniques used for identifying genotypes. Preferably, populations that are being compared should be very similar in sample size. In this case, the number of genotypes observed can be used directly for comparing richness. In most cases, sample sizes differ and use of the rarefaction method to calculate richness is more appropriate. In all cases, scaling either Stoddart and Taylor's G or Shannon and Wiener's H' by sample size should be avoided. Under those circumstances where it might be important to distinguish whether richness or evenness contribute more to diversity, a bootstrapping approach, where confidence intervals are calculated for indices of diversity and evenness, is recommended.     

Effect of medetomidine administration on bispectral index measurements in dogs during anesthesia with isoflurane

OBJECTIVE: To determine the relationship between bispectral index (BIS) and minimum alveolar concentration (MAC) multiples of isoflurane after IM injection of medetomidine or saline (0.9% NaCl) solution in anesthetized dogs. ANIMALS: 6 dogs. PROCEDURE: Each dog was anesthetized 3 times with isoflurane. First, the MAC of isoflurane for each dog was determined by use of the tail clamp method. Second, anesthetized dogs were randomly assigned to receive an IM injection of medetomidine (8 microg x kg(-1)) or an equal volume of isotonic saline (0.9% NaCl) solution 30 minutes prior to beginning BIS measurements. Last, anesthetized dogs received the remaining treatment (medetomidine or isotonic saline solution). Dogs were anesthetized at each of 4 MAC multiples of isoflurane. Ventilation was controlled and atracurium (0.2 mg/kg followed by 6 microg/kg/min as a continuous infusion, IV) administered. After a 20-minute equilibration period at each MAC multiple of isoflurane, BIS data were collected for 5 minutes and median values of BIS calculated. RESULTS: BIS significantly decreased with increasing MAC multiples of isoflurane over the range of 0.8 to 2.0 MAC. Mean (+/- SD) MAC of isoflurane was 1.3 +/- 0.2%. During isoflurane-saline anesthesia, mean BIS measurements at 0.8, 1.0, 1.5, and 2.0 MAC were 65 +/- 8, 60 +/- 7 52 +/- 3, and 31 +/- 28, respectively. During isoflurane-medetomidine anesthesia, mean BIS measurements at 0.8, 1.0, 1.5, and 2.0 MAC were 77 +/- 4, 53 +/- 7, 31 +/- 24, and 9 +/- 20, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: BIS monitoring in dogs anesthetized with isoflurane has a predictive value in regard to degree of CNS depression. During isoflurane anesthesia, our results support a MAC-reducing effect of medetomidine.     

Risk factors and prevalence of injuries in horses during various types of steeplechase races

OBJECTIVE: To identify the types of injuries sustained by horses that competed in steeplechase races and determine the prevalence of and risk factors for those injuries. DESIGN: Prospective study. ANIMALS: 2,680 horses that competed in various types of steeplechase races from 1996 through 2000. PROCEDURE: Data regarding races; environment; equipment problems; the number of horses that entered, started, and finished races; the number of riders that fell; and the number of horses that were slowed or stopped by the rider, ran off the course, fell, and sustained injuries or physical abnormalities during races were collected on a standard form by the official veterinarian who attended each meet. Data from all meets were not recorded; however, in recorded meets, data from every race were reported. RESULTS: Data for 197 hurdle, 65 timber, 76 flat, and 8 mixed races were recorded. Nine (3.4/1,000 horses that started in races) horses died or were euthanatized, and 7 of those were associated with catastrophic musculoskeletal injury. Seven fractures were recorded. Four fractures involved forelimbs, 1 involved a hind limb, and 2 involved the cervical portion of the vertebral column. All horses with fractures were euthanatized. Deep or hard course conditions were associated with an increased risk of breakdown injuries. CONCLUSIONS AND CLINICAL RELEVANCE: Successful development and implementation of strategies to prevent injuries and death in horses in steeplechase races depend on a clear understanding of the types and prevalence of injuries involved and risk factors associated with those injuries.     

Sodium nitroprusside-induced deliberate hypotension to facilitate patent ductus arteriosus ligation in dogs

OBJECTIVE: To report the use of sodium nitroprusside to induce deliberate hypotension to reduce hemorrhage and facilitate surgical ligation of complicated patent ductus arteriosus (PDA) in dogs. STUDY DESIGN: Retrospective study. ANIMALS: Six dogs. METHODS: Hemorrhage occurred during surgical ligation of PDA in 5 dogs. Surgical dissection and isolation of the PDA were very difficult in a sixth dog that was considered to be at increased risk for ductus rupture. Sodium nitroprusside (5 to 25 microg/kg/min intravenously) was administered to these 6 dogs to induce hypotension to reduce blood loss and facilitate surgical ligation of the PDA. RESULTS: Sodium nitroprusside infusion reduced blood pressure (mean arterial pressure, 45 to 60 mm Hg) within 5 to 10 minutes and hemorrhage from the PDA, facilitating its surgical ligation. Recovery from surgery and anesthesia was uneventful in all 6 dogs. CONCLUSIONS: Sodium nitroprusside infusion can be used to induce deliberate hypotension in dogs to facilitate surgical ligation of PDA. CLINICAL RELEVANCE: Sodium nitroprusside infusion produces hypotension within 5 to 10 minutes and is easy to control, rapidly abates, and should help to facilitate surgical ligation of PDA.     

A recombinant vaccine expressing a mammalian Mycobacterium sp. antigen is immunostimulatory but not protective in striped bass

A recombinant vaccine was constructed for piscine mycobacteriosis utilizing a Brucella abortus strain RB51 vector expressing a mammalian Mycobacterium sp. 85A antigen. Juvenile striped bass were inoculated with the resulting construct at doses equivalent to 10(6), 10(7), 10(8), 10(9), and 10(10) colony-forming units/fish. Blood and tissue samples from these fish demonstrated significant specific humoral and cell-mediated immune responses towards the 85A antigen in a dose-dependent manner. However, survival studies determined that inoculated fish failed to demonstrate cross-protective responses after live Mycobacterium marinum challenge 70 days post-inoculation.     

Prevalence of cpb2, encoding beta2 toxin,in Clostridium perfringens field isolates: correlation of genotype with phenotype

Beta2 toxin, encoded by the cpb2 gene, has been implicated in the pathogenesis of porcine, equine and bovine enteritis by type A Clostridium perfringens. By incorporating primers to cpb2 into a multiplex genotyping PCR, we screened 3270 field isolates of C. perfringens. Of these, 37.2% were PCR positive for the cpb2 gene. The majority of isolates from cases of porcine enteritis were positive for cpb2 (>85%), and this was even more true for C. perfringens isolated from cases of porcine neonatal enteritis (91.8%). In contrast, isolates from normal pigs only contained cpb2 in 11.1% of cases. The correlation between enteritis in other animal species and the presence of cpb2 was not so strong. cpb2 was found in 21.4% of C. perfringens isolates from cattle with enteritis, and in 47.3% of isolates from calves with enteritis or abomastitis. The prevalence of cpb2 varied with genotype, with type A isolates being positive for this gene in 35.1% of cases. Furthermore, enterotoxigenic type D or type E strains almost always carried cpb2. We cloned a 6xHIS-tagged beta2 (HIS-beta2) and used this protein to raise antiserum against beta2. Culture supernatants from 68 cpb2-positive and 13 cpb2-negative strains were tested for the presence of beta2 by Western blotting. In cpb2-positive isolates of porcine origin, beta2 was almost always detected (96.9%). However, in cpb2-positive isolates from other animal species, only 50.0% expressed beta2 protein. The high rate of cpb2-positivity among strains from neonatal pigs with enteritis and the high correlation of genotype with phenotype, supports the contention that beta2 toxin plays a role in the pathogenesis of these infections. However, it may be important to consider the use of an additional method for the detection of beta2 toxin in non-porcine cpb2-positive isolates when making claims about the role of beta2 in enteritis in non-porcine species.     

Combined dorsolateral and intraoral approach for the resection of tumors of the maxilla in the dog

This paper describes in detail a combined dorsal and intraoral approach for maxillectomy for tumors involving tissues more caudal to the third premolar. The only intraoperative complication was that of blood loss, with six out of 20 dogs requiring a single unit of blood. Histopathologically clean margins were obtained in 14 of the 20 cases, with a recurrence rate of 50% in these dogs and a median time to recurrence of 24 months. This represents an improvement in outcome over previously reported studies, and the authors postulate this is due to the better exposure and access to the area afforded by the combined approach over the standard intraoral approach.