Static and dynamic properties of tissue cage fluid in rabbits

Neurophysiological assessment of animal welfare

Livestock industries such as the pork industry are striving to continuously improve the welfare of animals. Inherent to the success of this is the ability to rigorously assess the welfare of animals in the field. While much progress has been made towards the development of methodology to assess the welfare of animals, there have been major challenges to establishing practical and definitive procedures to assess the welfare of animals. These include, but are not limited to, establishing a universally accepted definition of animal welfare and the choice of measures that are taken from the animal to assess its welfare. Measures of biological functioning and affective (emotional) state of the animal have been common, but there have been many limitations in terms of practical application. Some of the reasons for this include the choice of physiological measures, which are often restrictive in providing information about welfare, affective measures being restricted to specific behavioural measures and the biological-functioning and affective-states approaches being undertaken in isolation. Biological and affective functioning are integrated and controlled by the brain. Many of the regions of the brain involved in the regulation of biological and emotional functioning have been identified. Furthermore, there is considerable knowledge about the roles and interactions among the neurophysiological systems in these brain regions. We propose a strategy to use this knowledge to develop procedures to assess animal welfare. The initial phase is to identify the neural pathways that regulate the physiological and emotional processes that allow animals to adapt and cope. The next phase is to determine the activity of these pathways in conscious animals in the field. This requires the identification of biomarkers of specific neuronal activity that can be measured in the conscious animal in the field. Emerging technologies are offering promise in the identification of such biomarkers and some of these are already applicable to the pig. There is now the opportunity to apply this strategy within the pork industry to assess the welfare of pigs throughout the value chain.

In vivo tumor secretion probing via ultrafiltration and tissue chamber: implication for anti-cancer drugs targeting secretome

Tumor secreted proteins/peptides (tumor secretome) act as mediators of tumor-host communication in the tumor microenvironment. Therefore, development of anti-cancer drugs targeting secretome may effectively control tumor progression. Novel techniques including a capillary ultrafiltration (CUF) probe and a dermis-based cell-trapped system (DBCTS) linked to a tissue chamber were utilized to sample in vivo secretome from tumor masses and microenvironments. The CUF probe and tissue chamber were evaluated in the context of in vivo secretome sampling. Both techniques have been successfully integrated with mass spectrometry for secretome identification. A secretome containing multiple proteins and peptides can be analyzed by NanoLC-LTQ mass spectrometry, which is specially suited to identifying proteins in a complex mixture. In the future, the establishment of comprehensive proteomes of various host and tumor cells, as well as plasma will help in distinguishing the cellular sources of secretome. Many detection methods have been patented regarding probes and peptide used for identification of tumors.

Penicillin pharmacodynamics in four experimental pneumococcal infection models

Clinical and animal studies indicate that with optimal dosing, penicillin may still be effective against penicillin-nonsusceptible pneumococci (PNSP). The present study examined whether the same strains of penicillin-susceptible pneumococci (PSP) and PNSP differed in their pharmacodynamic responses to penicillin by using comparable penicillin dosing regimens in four animal models: peritonitis, pneumonia, and thigh infection in mice and tissue cage infection in rabbits. Two multidrug-resistant isolates of Streptococcus pneumoniae type 6B were used, one for which the penicillin MIC was 0.016 microg/ml and the other for which the penicillin MIC was 1.0 microg/ml. Two additional strains of PNSP were studied in the rabbit. The animals were treated with five different penicillin regimens resulting in different maximum concentrations of drugs in serum (C(max)s) and times that the concentrations were greater than the MIC (T(>MIC)s). The endpoints were bacterial viability counts after 6 h of treatment in the mice and 24 h of treatment in the rabbits. Similar pharmacodynamic effects were observed in all models. In the mouse models bactericidal activity depended on the T(>MIC) and to a lesser extent on the Cmax/MIC and the generation time but not on the area under the concentration-time curve (AUC)/MIC. Maximal bactericidal activities were similar for both PSP and PNSP, being the highest in the peritoneum and blood (approximately 6 log10 CFU/ml), followed by the thigh (approximately 3 log10 CFU/thigh), and being the lowest in the lung (approximately 1 log10 CFU/lung). In the rabbit model the maximal effect was approximately 6 log10 CFU/ml after 24 h. In the mouse models bactericidal activity became marked when T(>MIC) was > or =65% of the experimental time and C(max) was > or =15 times the MIC, and in the rabbit model bactericidal activity became marked when T(>MIC) was > or =35%, Cmax was > or =5 times the MIC, and the AUC at 24 h/MIC exceeded 25. By optimization of the Cmax/MIC ratio and T(>MIC), the MIC of penicillin for pneumococci can be used to guide therapy and maximize therapeutic efficacy in nonmeningeal infections caused by PNSP.

Postantibiotic effect and postantibiotic sub-mic effect of dirithromycin and erythromycin against respiratory tract pathogenic bacteria

The postantibiotic effect (PAE) of dirithromycin and erythromycin against strains Streptococcus pyogenes group A M12, NCTC P1800, Streptococcus pneumoniae 23, Staphylococcus aureus Oxford strain 209, Moraxella catarrhalis 15616 and Haemophilus influenzae 5590 was investigated in vitro and in vivo by use of the tissue cage model in rabbits. By exposing strains to 2.5-5 x MIC levels for 6 h or 12 h, both compounds induced in vitro PAEs of 1-9 h, and in two cases >20 h. Cultures in the PAE-phase were then re-exposed to subinhibitory concentrations (0.25 x MIC and 0.5 x MIC) of antibiotic and prolonged suppression of regrowth was obtained for 2->20 h. Following i.v. antibiotic treatment of rabbits (10 mg/kg or 20 mg/kg dirithromycin and 20 mg/kg or 40 mg/kg erythromycin) and bacterial infection of the implanted tissue cages in the same rabbit, the tissue cage fluid (TCF) was sampled 6 h after infection and regrowth was monitored by sampling from new tissue cages in untreated rabbits. These i.v. single doses of both antibiotics induced in vivo PAEs of >6 h, but <20 h against S. pyogenes. Suppression of regrowth in TCF was also obtained for > or = 20 h on infection with exposed S. pyogenes in the PAE-phase in newly implanted tissue cages in rabbits that had been treated with low doses of antibiotic to produce subinhibitory concentrations in the TCE Dirithromycin was in general as active as erythromycin in inducing PAE and in prolonging suppression of bacterial regrowth in the PAE phase.

An experimental model for acute poststreptococcal glomerulonephritis in mice

A number of factors have been implicated in the pathogenesis of acute poststreptococcal glomerulonephritis (APSGN). The lack of a reliable animal model has made it difficult to further examine the role of these factors in the pathogenetic process. In this report, we present a tissue cage model in mice for the study of APSGN. Morphological and immunohistological changes in the kidney, resembling those of APSGN in man, were induced at high frequency in the experimental model after infection with group A streptococcal nephritis isolates. Nephritis-associated strain induced hypercellularity, occlusion of capillaries, and C3 deposition at high frequencies compared to the changes induced in animals infected with a non-nephritis-associated strain and non-infected controls. In animals infected with a nephritis isolate, hematuria and proteinuria were also detected. If penicillin treatment was initiated on the third day of infection, the development of the nephritis process was prevented. Streptokinase, as well as preabsorbing antigen and streptococcal pyrogenic exotoxin B (SpeB), have been implicated in the pathogenesis of APSGN. These proteins, as well as SpeA and SpeF, were detected in the fluids of the infectious focus, regardless of the origin of the strains and whether or not glomerulonephritis was seen. Antibodies to streptokinase were evoked in the majority of the infected animals. This immune response did not correlate with the nephritic process since hypercellularity was also seen in animals which lacked detectable streptokinase antibodies. The results show that the mouse tissue cage model can be used to study APSGN and to evaluate factors involved in the pathogenesis of the disease.

Postantibiotic effect of the penem FCE 22101 against selected gram-positive and gram-negative bacteria in vitro and in vivo by the use of a tissue cage model in rabbits

Isolates of Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae and Klebsiella pneumoniae were tested for their bactericidal activity and postantibiotic effect (PAE) with the new penem FCE 22101. The tissue cage model in rabbits was used to study PAE in vivo. The bactericidal activity against all four species was shown to be in the range of 0.05-4.0 mg/l. A 99.9% killing effect at MBC concentrations was reached within 2 hours with S. pneumoniae and K. pneumoniae and within 6-8 hours with S. aureus and H. influenzae. After in vitro exposure by FCE 22101 a PAE in vitro and in vivo was obtained against S. aureus, S. pneumoniae and H. influenzae strains but no PAE could be demonstrated against K. pneumoniae. FCE 22101 showed a good bactericidal activity and PAE against the strains investigated, except for K. pneumoniae.

The effect of zinc oxide on Staphylococcus aureus and polymorphonuclear cells in a tissue cage model

The effect of zinc oxide on S. aureus (209 P) was studied in steel net tissue cages implanted subcutaneously in guinea pigs and rabbits. Zinc oxide installed in the tissue cages created high, sustained concentrations of zinc in the cage fluid throughout the study. In a concentration of 22 mmol/l zinc oxide reduced viable counts in tissue cage fluid inoculated with S. aureus. No deleterious effect was observed on polymorphonuclear cell function.

In vivo chemotaxis evoked by Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus

The chemotaxis-evoking capacity of 5 Actinobacillus actinomycetemcomitans and 5 Haemophilus aphrophilus strains were studied in a tissue cage model in rabbits. A significant increase of the total number of polymorphonuclear leukocytes was induced in the tissue cage fluid by both viable and killed bacteria, reaching a maximum after 12-24 h. In parallel, the proportion of viable/non viable leukocytes increased. The leukocyte counts declined during the following 24-48 h in all chambers except in those inoculated with viable cells of H. aphrophilus. The H. aphrophilus strains survived the 72 h experiment while A. actinomycetemcomitans decreased to undetectable levels within 24-72 h. Lactate dehydrogenase and lysozyme activities in cage fluid increased in all but the uninoculated chambers. Viable bacteria induced higher activities of the enzymes than killed ones. It is concluded that both species of bacteria exhibit similar chemotaxis evoking properties. A strain dependent ability to induce release of leukocyte-associated enzymes exists.

A streptococcal plasminogen activator in the focus of infection and in the kidneys during the initial phase of experimental streptococcal glomerulonephritis

Strains of group A streptococci known to secrete the nephritis strain-associated protein (NSAP), a plasminogen activator, were studied for their ability to produce APSGN in rabbits. A tissue cage model was used to monitor the secretion of NSAP at the focus of infection and histopathological examination of kidney tissue was used to determine glomerular pathology. Animals infected with NSAP positive strains exhibited NSAP deposits in the glomerular tissue by day 7 in the absence of antibody to this molecule with progressive pathology indicative of APSGN three weeks later. Animals infected with the NSAP negative streptococcal strain exhibited no abnormal pathology. The ability of NSAP to bind to kidney tissue suggested that it has unique nephrotropic properties; and its ability to activate plasminogen to plasmin, possibly in situ, suggests that much of the pathological events associated with APSGN may be initiated by plasmin activity.

Properties of high and low density subpopulations of group B streptococci: enhanced virulence of the low density variant

From the group B streptococcus (GBS) reference strain 090 la Colindale two subpopulations, which differed markedly regarding their capacities for biosynthesis of type-specific polysaccharide, were obtained by separation on a hypotonic Percoll density gradient. In the original strain and the high and low density variants, there was a negative correlation between buoyant density and bio-synthesis of type-specific polysaccharide as determined by ultrastructure and quantitative assays. The invasiveness of these variants was investigated by infecting rabbits via subcutaneously implanted tissue cages. In the animals infected with highly encapsulated bacteria, heavy bacteremia was detected 8 h post-infection, whereas in the animals which received high density bacteria with small amount of capsule, heavy bacteremia was not detected until after five days. All isolates recovered from the blood or organs of these rabbits were of the capsule rich phenotype, indicating a phenotypic shift in the subpopulation of high density bacteria. An apparently similar phenotypic shift was noted in an isolate from a baby with early onset septicemia. There was a dominance of low density bacteria in the isolate obtained from the baby as compared with the colonizing population of bacteria isolated from the cervix of the mother. From these type III isolates, subpopulations with different density maxima were obtained. A reversed shifting towards dominance of less encapsulated, high density bacteria was observed during in vitro passage of these subpopulations.

Factors influencing the biological inactivation of high protein bound beta-lactam antibiotics in vitro

Unpredictable inactivation of antimicrobial agents may cause erratic results in pharmacokinetic studies. In this study we followed the inactivation of the high protein bound beta-lactams flucloxacillin, dicloxacillin and ceftriaxone in vitro. The antibiotics were added to pools of human and rabbit sera, ultrafiltrates of these pools, rabbit interstitial fluid, phosphate buffered saline (PBS), rabbit albumin in PBS and sodium dodecyl sulphate (SDS) treated preparations of human sera. Ceftriaxone was relatively stable but different serum pools varied significantly in their flucloxacillin and dicloxacillin inactivating capacity. The dominating inactivation took place within five minutes after the addition of antibiotics to serum. The inactivating factor was heat stable at 56 degrees C, 0.5 h, of relatively high molecular weight, and not related to albumin. The inactivating capacity could be diminished by SDS-treatment of serum suggesting a lipoprotein nature.

Pharmacodynamics of beta-lactam antibiotics. Studies on the paradoxical and postantibiotic effects in vitro and in an animal model

The pharmacodynamics of antibiotics, i.e. the rate of killing and the time before regrowth of surviving bacteria, may be important factors for determination of the dosage interval. In the present study the effect of protein binding, antibiotic concentrations, bacterial growth phase and bacterial inoculum on the rate of bacterial killing was investigated. The postantibiotic effect (PAE) was also studied in vitro and in vivo. The killing rate of S. aureus did not differ when the bacteria were exposed to the same free concentrations of dicloxacillin in medium with and without albumin. Protein binding per se did thus not diminish the bactericidal activity. A paradoxically reduced bactericidal effect was noted when S. aureus was exposed to high concentrations of dicloxacillin, cloxacillin and benzylpenicillin. For determination of PAE of imipenem on Ps. aeruginosa, counts of viable bacteria were compared with assay of bacterial intracellular ATP. Both methods demonstrated a PAE for the strains tested at an inoculum of 10(6) cfu/ml. At an inoculum of 10(8) cfu/ml no PAE was found, which coincided with a lack of bactericidal effect. Both the PAE and the bactericidal effect were restored with aeration of the cultures, indicating insufficient penetration of imipenem to the target sites at low oxygen tension. An in vivo model in rabbits with implanted tissue cages was developed for evaluation of the PAE. Group A beta-hemolytic streptococci showed a PAE of approximately 2 h in vivo, which correlated well with the PAE found in vitro. Despite that streptococci in postantibiotic phase (PA-phase) were non-multiplying, such bacteria were killed as efficiently as previously untreated controls when exposed to 10xMIC of penicillin both in vitro and in vivo. However, streptococci in PA-phase were much more sensitive to the repeated challenge to subinhibitory concentrations of penicillin than previously untreated controls. In vivo, no difference in sensitivity to sub-MIC penicillin concentrations between streptococci in PA-phase and untreated controls was seen, probably due to the presence of host factors in the tissue cage fluid. It seems that for streptococci, subinhibitory antibiotic concentrations are more important for the sucess with intermittent dosing than the PAE, especially when a normal host defence is present.

An in vivo model for evaluation of the postantibiotic effect

A new experimental model to evaluate the postantibiotic effect (PAE) in vivo was developed using subcutaneously implanted tissue cages in rabbits with normal host defence mechanisms. The rabbits received benzylpenicillin i.v. in a dose giving a free penicillin concentration of 10 X MIC in the tissue cage fluid (TCF). A log-phase suspension of group A streptococci was injected into the tissue cages exposing them to penicillin in vivo. After 2 h bacterial samples were withdrawn, treated with penicillinase and transferred to 2 tissue cages in untreated rabbits. Simultaneously, unexposed streptococci were implanted in 2 other cages in the same animals. By repeated sampling of TCF, growth curves of the streptococci exposed to penicillin and the controls could be compared and a PAE of 1.6-2.4 h demonstrated. The PAE was of the same magnitude as that found in vitro. The model has several advantages for the demonstration of PAE in vivo: repeated samplings are easy to perform percutaneously, the effect of subinhibitory antibiotic concentrations are avoided, interindividual variations are eliminated since each animal is its own control, and the experiments can be performed in animals with undisturbed host defence mechanisms.

The effect of penicillin on bacterial interference in vivo

The study was designed to analyse the effect of penicillin on interference between alfa-streptococci and group A streptococci in vivo. Tissue cages were implanted subcutaneously in 9 rabbits and inoculated with 10(5) cfu of alfa- and beta-streptococci together as well as separately. Both streptococci were recovered 96 h after the inoculation in the untreated rabbits. Alfa-streptococci inhibiting the growth of beta-streptococci in vitro retained this capacity under the experimental in vivo conditions. Higher penicillin concentration did not increase the killing rate of beta-streptococci grown separately while a faster killing was observed with low penicillin levels in the presence of inhibiting alfa-streptococci, indicating synergistic effect.

The influence of penicillin on growth and morphology of Streptococcus pyogenes in vivo

The influence of penicillin (pc) on the growth, phagocytosis and killing of Streptococcus pyogenes was studied for an M protein positive (M+) and an M protein negative (M-) strain in vivo as well as in vitro. In vivo studies were based on a tissue cage model and the analyses were performed by CFU determinations and electron microscopic investigations. The M- strain was easily phagocytized with and without pc, but killing only occurred after pc treatment and thus the number of viable bacteria rapidly decreased under the influence of pc. M+ streptococci were not reduced in numbers by pc-treatment in vivo, but morphological changes and at high pc concentrations, phagocytosis could be seen. When this strain (M+) was cultivated in the absence of pc, the phagocytic cells were totally destroyed - a reaction that was prevented by penicillin. Variations in surface morphology of the two strains seem to influence the differences in sensitivity to penicillin, phagocytosis and killing.