Growth of Clostridium perfringens in cooked chili during cooling

U.S. Department of Agriculture regulations require that brick chili be cooled from 48.9 degrees C to 4.4 degrees C within 2 h of cooking, but processors may not always be able to comply. Studies were conducted to evaluate the extent of bacterial multiplication resulting from outgrowth of germinated Clostridium perfringens spores experimentally inoculated into chili and incubated at various temperatures. Inoculated samples were heated (75 degrees C for 20 min) to activate spores, quickly equilibrated, and held at one of five desired temperatures for 6 h. No growth was observed for C. perfringens in samples held at 26.7 degrees C and below for 6 h, but growth was observed by 6 h in samples held at 32.2 degrees C and after 2 h in samples held at temperatures between 37.8 degrees C and 48.9 degrees C. Using isothermal growth data, we developed a simple model for predicting the growth of bacteria with time under exponential cooling conditions. The model predicts both the lag phase and the numbers of bacteria at specific times during the growth phase. It was developed by using isothermal growth data and tested by using temperature-varying growth data from experiments with spores of C. perfringens in chili. Actual data agreed closely with predicted results. The results should be useful for evaluating the hazard potential for growth of C. perfringens in chili.     

Enhancement of squamous cell development in cultured skin by cyclic adenine nucleotide and prostaglandins

The present study tests the hypothesis that agents known to elevate the level of intracellular cyclic adenine nucleotide may direct different epithelial cells onto a pathway of epidermoid (squamous) development and differentiation. We report here that the mixture of dibutyryl cyclic AMP (dbcAMP), prostaglandins E1, E2 and B1 (PG E1, E2, B1), and papaverine (pap) enhances the rate of normal squamous cell development in organ-cultured skin of chick embryos. The three components may act synergistically to elevate the level of intracellular cyclic adenine nucleotide. We recently reported that the same group of agents induces abnormal development (squamous metaplasia) and aberrant differentiation (keratin production) in the normally cuboidal epithelium of cultured whole mammary glands of mice [1]. Thus, dbcAMP, PG E1, E2, B1, and pap are effective in enhancing normal squamous cell development and also in inducing squamous metaplasia de novo in the epithelial components of two different organs of embryonic and adult animals of two classes of vertebrates. The combined findings are suggestive that cyclic adenine nucleotide together with the prostaglandins may act generally on diverse types of epithelia to bring about squamous cell development and a differentiation marked by keratin production.     

Chemical sympathectomy decreases alveolar hypoxic vasoconstriction in lambs but not in sheep

We studied the role of the sympathetic nervous system in the augmented vasoconstrictor response of the newborn lamb, compared with the adult sheep, by producing a chemical sympathectomy with 6-hydroxydopamine (6-OHDA). Seven lambs, age 4-16 days, and five sheep, age 2 yr, were anesthetized and intubated with a double-lumen endotracheal tube, allowing ventilation of one lung with O2 to maintain systemic oxygenation while the contralateral lung was ventilated with N2 as a hypoxic challenge. Distribution of perfusion to each lung was evaluated using positron scintigraphy after inferior vena caval injections of 13N, a positron-emitting isotope. In the lambs, prior to 6-OHDA, distribution of perfusion to the test lung was 43 +/- 3% of total lung perfusion during bilateral O2 ventilation and fell with hypoxia to 24 +/- 2%, a reduction of 44 +/- 3% during N2 ventilation as compared with O2 ventilation. After 6-OHDA, hypoxic challenge reduced perfusion by only 22 +/- 2% (P less than 0.01 compared with pre-6-OHDA). In the adult sheep, hypoxic vasoconstriction reduced perfusion to the test lung by 28 +/- 2% but was unaffected by 6-OHDA. Absence of rise in pulmonary vascular resistance (PVR) or femoral artery pressure (Pfa) in response to Tyramine infusions after 6-OHDA confirmed complete sympathectomy in lambs and sheep. Persistent increases in PVR and Pfa to infusions of prostaglandin F2 alpha before and after 6-OHDA showed that the loss of alveolar hypoxic vasoconstriction in the lamb was specific. Thus sympathetic innervation may contribute to the greater strength of alveolar hypoxic vasoconstriction found in lambs than in sheep.     

Induction of squamous metaplasia: requirement for cell multiplication, and competition with lobuloalveolar development in cultured mammary glands

Mouse mammary glands were previously shown to undergo either of two courses of development and differentiation in whole organ culture. The combination of insulin, prolactin, aldosterone, and hydrocortisone induces a structural development of lobuloalveoli, followed by casein production. In the second course, the mixture of dibutyryl cyclic AMP, prostaglandins E1, E2 and B1, and papaverine brings about an extensive squamous metaplasia and excessive keratinization. In the present study, the foci of the metaplastic squamous cells appeared to originate from single or very few cells. A preferential stimulation of squamous cell multiplication was involved in the induction process. Twice the relative number of nuclei incorporated 3H-thymidine in the squamous metaplastic cells than in the surrounding cuboidal epithelium, according to autoradiography. The necessity for cell multiplication was indicated by the reversible and complete inhibitions of both the metaplastic squamous development and 3H-thymidine incorporation by 1 mM hydroxyurea in the culture medium. Simultaneous inductions of both courses of development and differentiation revealed a competitive and reciprocal relationship between the two pathways. The concurrent expressions of both courses were considerably less than those achieved when either pathway was induced alone. Only the combination of the three types of inducers of squamous metaplasia was able to compete effectively with the hormonal induction of lobuloalveolar development and differentiation. The findings suggest that individual metaplastic squamous foci may originate as clones of cells by processes that require cell multiplication, rather than through a direct non- replicative conversion of pre-existent cells of the cuboidal epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mitosis in hepatocytes is generally associated with elevated levels of the target polypeptide of a liver carcinogen

It has been suggested that, during odontoblast differentiation, the extracellular matrix present at the epitheliomesenchymal junction modulates the activity of the cytoskeleton by means of membrane constituents (proteins, proteoglycans or gangliosides). To investigate this, we studied the interaction of iodinated fibronectin and type-I collagen with dissociated dental tissues and with membrane proteins prepared from these tissues. Isolated dental papillae and enamel organs were cultured for increasing periods of time in the presence of iodinated proteins. Fibronectin and type-I collagen were preferentially bound to dental papillae; however, after 6 h of incubation, fibronectin no longer interacted with the dental papillae, and the bound radioactivity was released. In the meantime, de novo synthesized fibronectin was deposited in the extracellular matrix of the dental papillae. Membrane proteins were prepared from isolated enamel organs and dental papillae. After sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis, these proteins were transferred to nitrocellulose by electroblotting and then incubated in the presence of either 125I-labelled fibronectin or 125I-labelled type-I collagen. Autoradiography confirmed the preferential interaction of fibronectin with the dental papilla. Fibronectin interacted with three high-molecular-weight proteins (Mr, 145,000, 154,000 and 185,000), which were not detected when membranes were prepared from enamel organs. Under the same conditions, type-I collagen did not interact with membrane proteins. The known interaction of type-I collagen with the plasma membrane of dental-papilla cells might be mediated either by another constituent of the extracellular matrix or by cell-surface-associated proteoglycans.