Analysing microbiological data: Tobit or not Tobit?

In this paper, methods used to collect microbiological data and the common statistical technique used to analyse such data are discussed. An alternative statistical approach, considered more appropriate for many microbial datasets is suggested. The effectiveness of this method is demonstrated using a simulation study and then, for a practical example, its application in a study on the effectiveness of a decontamination process for chicken carcases.

The use of femoral stems with exchangeable necks in primary total hip arthroplasty increases the rate of revision.

AIMS: Femoral stems with exchangeable (modular) necks were introduced to offer surgeons an increased choice when determining the version, offset and length of the femoral neck during total hip arthroplasty (THA). It was hoped that this would improve outcomes and reduce complications, particularly dislocation. In 2010, the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) first reported an increased rate of revision after primary THA using femoral stems with an exchangeable neck. The aim of this study was to provide a more comprehensive up-to-date analysis of primary THA using femoral stems with exchangeable and fixed necks. MATERIALS AND METHODS: The data included all primary THA procedures performed for osteoarthritis (OA), reported to the AOANJRR between 01 September 1999 and 31 December 2014. There were 9289 femoral stems with an exchangeable neck and 253 165 femoral stems with a fixed neck. The characteristics of the patients and prostheses including the bearing surface and stem/neck metal combinations were examined using Cox proportional hazard ratios (HRs) and Kaplan-Meier estimates of survivorship. RESULTS: It was found that prostheses with an exchangeable neck had a higher rate of revision and this was evident regardless of the bearing surface or the size of the femoral head. Exchangeable neck prostheses with a titanium stem and a cobalt-chromium neck had a significantly higher rate of revision compared with titanium stem/titanium neck combinations (HR 1.83, 95% confidence interval 1.49 to 2.23, p < 0.001). Revisions were higher for these combinations compared with femoral stems with a fixed neck. CONCLUSION: There appears to be little evidence to support the continued use of prostheses with an exchangeable neck in primary THA undertaken for OA. Cite this article: Bone Joint J 2017;99-B:766-73.

The effect of peri-conception nutrition on embryo quality in the superovulated ewe.

Evidence indicates that oocyte/embryo quality in the sheep is affected by nutrient status during the cycle of conception. This study aimed to determine, in the superovulated ewe, if there are stages during the peri-conception period (-18 days to +6 days relative to the day of ovulation [Day 0]) when quality is more likely to be influenced by nutrition. In Experiment 1, ewes were provided with either a 0.5 x maintenance (L), 1.0 x maintenance (M) or 1.5 x maintenance (H) diet (in terms of daily energy requirements) during the peri-conception period. Diet did not affect the mean ovulation rate (range: 15.4+/-1.47 to 16.1+/-1.55) nor the mean number of embryos collected per ewe (range: 10.9+/-2.05 to 12.4+/-1.82) but there was an increase (P<0.05) in the mean number of cells per blastocyst in the L diet (74.7+/-1.45) compared with either the M (66.4+/-1.29) or H (62.0+/-0.84) diets. This increase was due to an increase in the number of trophectoderm (Tr) cells, resulting in a shift (P<0.05) in the Tr:inner cell mass (ICM) cell ratio (range 0.69+/-0.03 to 0.73+/-0.04). In Experiment 2, six diets (HHH, MHH, MHL, MLH, MLL and LLL) were imposed during three 6-day periods commencing 12 days before and continuing until 6 days after ovulation. Although diet had minimal effect on the superovulatory response, both the mean number of cells per blastocyst and the Tr:ICM ratio were increased (P<0.05) when the L diet was provided after Day 0 (diets MHL, MLL and LLL). It is concluded that the ewe is able to respond to acute changes in nutrition imposed immediately after ovulation, resulting in changes in embryo development including cell lineage differentiation. The significance of these findings, in terms of fetal development, embryo-maternal signalling and the nutritional management of the ewe is discussed.

Quantitative development of Paris-type arbuscular mycorrhizas formed between Asphodelus fistulosus and Glomus coronatum.

• Arum- and Paris-type symbioses are the two main morphological types of arbuscular mycorrhiza. Here, the developmental time-course of the Paris-type association formed from colonization of Asphodelus fistulosus (onion weed) by Glomus coronatum is presented. • Development was monitored over 27 d. Root colonization was assessed using a modification of the magnified intersects technique (MIT), for investigating the interdependence (thus IMIT) of structures. • Hyphal and arbusculate coils were found predominantly in the outer and inner cortex of the root, respectively. The interdependence of external hyphae, hyphal coils and arbusculate coils was determined during the relatively slow development of the symbiosis. • The time required for development of Paris-type arbuscular mycorrhizas is slower than for the Arum type, and both time and space influence the formation of hyphal coils. Use of IMIT for scoring colonization allows determination of the interdependence of different fungal structures, and thus the technique has potentially wide applications, such as in relating the presence of different structures to signals from molecular probes.

Cytological examination and physical characteristics of the anal sacs in 17 clinically normal dogs.

OBJECTIVE: To quantify numbers of leucocytes, keratinocytes and microorganisms in, as well as the turgidity, colour and consistency of, anal sac exudates in clinically normal dogs. DESIGN: Selection criteria were formed based on the absence of clinical signs associated with anal sac disease, and the absence of factors potentially affecting colonic flora. Anal sacs were palpated for turgidity then expressed onto a swab, where colour and consistency were noted. A squash preparation made from any exudate was heat fixed and stained with modified Wright's stain. Eight representative 1000x oil immersion fields from each were examined for leucocytes, erythrocytes, keratinocytes, bacteria and yeast. Results were summarised, and cytological counts grouped into quartiles (minimal, few, moderate, numerous). Due to the multivariate nature of the study and limited subject numbers, further significant statistical analysis could not be performed. RESULTS: Seventeen dogs satisfied the selection criteria. The physical characteristics of the exudate and sac varied, though 31/34 sacs were empty or soft, 22/27 exudates were light or dark brown and 19/27 exudates were a thin liquid. Total leucocyte, keratinocyte and bacilli counts were extremely variable. Yeasts were present in 26/208 microscopic fields examined cytologically. Only 5/208 fields showed numerous cocci. A single instance of intracellular bacteria and a single erythrocyte were noted following examination of all fields. CONCLUSION: In this study, the characteristics of normal anal sacs and their exudate varied but greater than 70% showed similar features. Exudate cytology was highly variable, though yeasts were uncommon, and intracellular cocci and erythrocytes extremely rare.