Imaging manifestations of neck masses in the immunocompromised host.

Human immunodeficiency virus (HIV) infection, haematological malignancy, and immunosuppression for transplantation and autoimmune disorders have led to a large increase in immunocompromised patients. Neck masses are relatively common in this patient group and include both opportunistic and severe manifestations of common infections, benign hyperplasia, and primary or secondary malignancies. Although biopsy may be necessary for definitive diagnosis, features on cross-sectional imaging may suggest a specific diagnosis or limit the differential diagnosis and facilitate optimal patient management. This article will review critical aspects of neck anatomy, illustrate the spectrum of imaging features, and discuss the interpretative pearls and pitfalls when evaluating neck masses in immunocompromised patients.

Evidence that sorbic acid does not inhibit yeast as a classic 'weak acid preservative'.

Weak-acid preservatives are widely used to maintain microbial stability in foods and beverages. Classical weak-acid theory proposes that undissociated acid molecules pass through the plasma membrane, dissociate in the neutral pH of the cytoplasm, release protons and inhibit growth through acidification of the cytoplasm. Inhibitory concentrations of sorbic acid are shown to liberate fewer protons than other weak-acid preservatives. Sorbic acid shows similar inhibition to other six-carbon acids, alcohols and aldehydes, the latter being unable to act as weak acids. A survey of 22 yeasts showed high correlation between sorbate resistance and ethanol tolerance. Inhibition by short-chain acids or alcohols showed strong correlation with lipophilicity. It is proposed that sorbic acid acts as a membrane-active substance rather than as a weak-acid preservative.

Comparison of the inhibitory action on Saccharomyces cerevisiae of weak-acid preservatives, uncouplers, and medium-chain fatty acids.

This study was initiated to establish whether inhibition of growth of yeasts by medium-chain fatty acids resembled that caused by weak-acid preservatives or uncouplers. Unlike sorbic acid and 2,4-dinitrophenol, decanoic acid caused rapid cell death at its inhibitory concentration. This suggested a mode of action by medium-chain fatty acids, distinct from both weak-acid preservatives and uncouplers. Sorbic acid and 2,4-dinitrophenol both increased lag and doubling times, reduced cell yields and inhibitory concentrations of both were highly pH sensitive. The possibility is discussed as to whether weak-acid preservatives and uncouplers share common modes of inhibition.

Association of atrophy of the medial temporal lobe with reduced blood flow in the posterior parietotemporal cortex in patients with a clinical and pathological diagnosis of Alzheimer's disease.

A combination of medial temporal lobe atrophy, shown by computed tomography, and reduced blood flow in the parietotemporal cortex, shown by single photon emission tomography, was found in 86% (44/51) of patients with a clinical diagnosis of senile dementia of the Alzheimer type (SDAT). The same combination of changes was found in four out of 10 patients with other clinical types of dementia and in two out of 18 with no evidence of cognitive deficit. Of the 12 patients who died, 10 fulfilled histopathological criteria for Alzheimer's disease, nine of them having a clinical diagnosis of SDAT, and one a clinical diagnosis of multi-infarct dementia. All 10 patients with histopathologically diagnosed Alzheimer's disease had shown a combination of hippocampal atrophy and reduced parietotemporal blood flow in life. In 10 patients (nine with SDAT) out of 12 in whom the hippocampal atrophy was more noticeable on one side of the brain than on the other the parietotemporal perfusion deficit was also asymmetrical, being greater on the side showing more hippocampal atrophy. These results suggest that the combination of atrophy of the hippocampal formation and reduced blood flow in the parietotemporal region is a feature of dementia of the Alzheimer type and that the functional change in the parietotemporal region might be related to the loss of the projection neurons in the parahippocampal gyrus that innervate this region of the neocortex.

Use of fungicides in plant tissue culture.

We have examined a number of antifungal agents which might prove useful in plant tissue culture. We find that carbendazim, fenbendazole and imazalil can be used relatively safely and also have a broad spectrum of antifungal activity. Fungicides in clinical use do not prove to be as effective.

Hazard analysis applied to microbial growth in foods: development of mathematical models describing the effect of water activity.

Mathematical models have been developed which describe the effect of lowering the water activity on the growth kinetics of Staphylococcus aureus and Salmonella typhimurium. By treating the lag phase and exponential phase kinetics separately predictions can be made on the extent of microbial growth over successive time/temperature cycles. Staph. aureus was far more tolerant than Salm. typhimurium to lowered water activity and under near growth limiting conditions of water activity and temperature was showing lag periods as long as ca 40 d. The maximum lag period observed for Salm. typhimurium was ca 5 d. Under these conditions the predicted generation times for Staph. aureus were 2-3 d and for Salm. typhimurium.