In vivo assessment of LV mass in mice using high-frequency cardiac ultrasound: necropsy validation

Left ventricular (LV) mass is an important descriptor of cardiac status that increases with normal aging and may be affected by a variety of disease processes. There are currently limited noninvasive techniques that permit accurate determination of in vivo LV mass in very small animals, such as the mouse, a frequently used model for cardiac research. We sought to evaluate the ability of high-frequency (7.0 or 7.5 MHz), two-dimensional (2-D) guided M-mode echocardiography to estimate in vivo LV mass in the mouse. Fifteen adult mice weighing 22-45 g were studied, including six young adult (2- to 3-mo-old), two adult (12- to 14-mo-old), and seven senescent (18- to 20-mo-old) animals. Resting heart rate varied up to 450 beats/min. Anterior wall, inferior wall, and end-diastolic dimensions were measured, and echocardiographic LV mass (LVMe) was calculated using an uncorrected cube approximation. Autopsy LV mass was determined within 4 h of echocardiographic examination. Autopsy LV mass ranged from 88 to 211 mg. LV chamber dimensions included anterior wall (1.0 +/- 0.2 mm), inferior wall (1.1 +/- 0.3 mm), and end-diastolic dimension (3.7 +/- 0.5 mm). There was a very good correlation between LVMe (x) and autopsy LV mass (y):y = 0.96x - 7, r = 0.94, standard error of the estimate = 18 mg, P < 0.001. This correlation was stronger than that for autopsy LV mass and body weight (r = 0.70) or age (r = 0.74), indexes which until now were the only noninvasive correlates available for this very small animal model. We conclude that, despite the rapid heart rate and small size of the mouse heart, these results demonstrate the potential of high-frequency 2-D guided M-mode transthoracic echocardiography for the in vivo assessment of LV dimensions and mass in the mouse and may prove useful for cardiac research on aging and cardiomyopathies.

Serial echocardiographic assessment of left ventricular geometry and function after large myocardial infarction in the rat

BACKGROUND

The development of heart failure after acute myocardial infarction (MI) may be related to alterations of left ventricular (LV) structure and function. Pathological LV remodeling may exacerbate systolic and diastolic dysfunction because increased cavity dimensions tend to increase LV wall stress. Unfortunately, many complicating factors have made it difficult to clearly define the time course of LV remodeling after myocardial infarction in patients, and the contribution of structural changes to altered function has not been fully explored.

METHODS AND RESULTS

To determine the type, magnitude, and time course of changes in LV geometry and function, we performed transthoracic Doppler echocardiographic examinations in rats before and 1 and 6 weeks after transmural MI induced by coronary ligation. LV internal diastolic dimension was greater in infarcted than in sham-operated rats at 1 and 6 weeks after MI (9.4 +/- 0.6 versus 8.0 +/- 0.5 and 10.1 +/- 0.9 versus 8.5 +/- 0.9 mm, respectively; P < .05 compared with sham-operated rats). There was significant thinning of the infarcted anterior wall at 1 and 6 weeks (0.99 +/- 0.2 versus 1.33 +/- 0.19 and 0.96 +/- 0.22 versus 1.51 +/- 0.18 mm, P < .05), while the thickness of the noninfarcted posterior wall increased but was not different from normal growth in sham-operated rats. Six weeks after surgery, fractional shortening was impaired (11 +/- 5% versus 35 +/- 5%, P < .05), and systolic thickening of the noninfarcted posterior wall was depressed (38 +/- 9% versus 67 +/- 18%, P < .05) in infarcted rats compared with shams. These changes in structure and systolic function were accompanied by progressive alterations in LV diastolic filling. Peak early filling velocity increased at 1 and 6 weeks in MI rats (91 +/- 9 versus 79 +/- 9 and 100 +/- 14 versus 74 +/- 11 cm/s, P < .05), and the deceleration rate of the early filling wave was more rapid in rats with MI (21.6 +/- 5.0 versus 15.6 +/- 3.1 and 26.1 +/- 9.8 versus 11.2 +/- 2.7 m/s2, P < .05). Late filling velocity was decreased (16 +/- 15 versus 33 +/- 7 and 15 +/- 18 versus 34 +/- 5 cm/s, P < .05), resulting in a marked increase in the ratio of early to late filling. The peak velocity and the velocity-time integral of LV outflow did not change after MI.

CONCLUSIONS

Postinfarction LV remodeling in the rat is characterized by progressive cavity dilatation, inadequate hypertrophy of the surviving myocardium, the gradual development of regional contractile dysfunction in noninfarcted segments, and marked abnormalities of diastolic filling. These changes can be tracked longitudinally with transthoracic echocardiography.

Echocardiographically detected myocardial infarction in the mouse

The ability to obtain high-quality echocardiographic images of the heart in a small mammal such as the mouse would enable investigators to noninvasively and serially assess cardiac function and identify focal lesions. We recently had the opportunity to perform noninvasive high-frequency M-mode echocardiography in a mouse that had a focal area of left ventricular hypokinesis involving the ventral wall. Postmortem histologic examination revealed lateral and ventrolateral wall infarction with fibrotic replacement of the ventricular wall and reactive hypertrophy of surrounding myocytes in noninfarcted zones. To our knowledge, this is the first reported case of noninvasive echocardiography identification of a myocardial infarction in the mouse and further high-lights the potential utility of this technique.

Solubility of antibiotics used in animal feeds in selected solvents

The solubility of antibiotics used in animal feeds in organic solvents was determined. The solubility data could be used in identification of classes and in some cases individual members of the same class of antibiotics, and in differential step(s) in the analysis of these antibiotics. A universal solvent was developed to extract all antibiotics from animal feeds.

Atrial ejection force: a noninvasive assessment of atrial systolic function

OBJECTIVES

The purpose of this study was to define atrial ejection force and to develop a method for its noninvasive measurement from echocardiographic data.

BACKGROUND

Assessment of diastolic function through measurement of the components of ventricular filling has largely neglected the vigor of atrial systole, in part because this has been difficult to quantify. However, atrial ejection force, defined as that force exerted by the left atrium to accelerate blood into the left ventricle during atrial systole, can be assessed noninvasively by combined two-dimensional imaging and Doppler echocardiography. This index of atrial function, based on classic newtonian mechanics, provides a physiologic assessment of atrial systolic function.

METHODS

To evaluate the usefulness of atrial ejection force, we studied the return of left atrial ejection force in 29 patients after elective cardioversion for atrial fibrillation. Transmitral Doppler inflow patterns at rest were assessed immediately after cardioversion and at 24 h, 1 week, 1 month and > 3 months later. A healthy adult group (n = 10) served as control subjects.

RESULTS

After successful cardioversion, atrial ejection force was significantly depressed compared with that in the control group (5.2 +/- 6.8 vs. 16.3 +/- 4.7 kdynes; p < 0.0001). Over successive weeks, atrial ejection force improved in the subgroup of patients who remained in sinus rhythm (n = 18), whereas no improvement was seen during the period of maintained sinus rhythm in the patients with subsequent reversion to atrial fibrillation (n = 11).

CONCLUSIONS

Atrial ejection force provides a physiologic assessment of atrial systolic function and is a potentially useful index for assessing atrial contribution to diastolic performance. In patients who successfully underwent cardioversion from atrial fibrillation, atrial ejection force improved over several weeks only in the subgroup in which sinus rhythm was maintained.

Rapid determination of Listeria monocytogenes in foods using a resuscitation/selection/kit system detection

A resuscitation medium consisting of a trypticase soy broth base supplemented with 0.5% yeast extract, 0.25% sodium pyruvate, 0.01% sodium thioglycollate, and 0.1% chicken fat was used in the resuscitation of heat-injured and freeze-injured cells of Listeria monocytogenes. After a resuscitation period of 4-h, the medium was made selective through the addition of nalidixic acid, acriflavin, and cycloheximide. The organisms were incubated in the selectivized medium at 35 degrees C for an additional 16 h. The numbers of resuscitated Listeria monocytogenes cells rose from 10(1) to 10(7) cells/mL in 20 h. Similar numbers of Staphylococcus aureus, Escherichia coli, and Salmonella bonn were grown together with Listeria monocytogenes; these organisms did not inhibit the growth of Listeria monocytogenes nor interfere with its detection by the Listeria-Tek kit system. The resuscitation/selection/kit system (RSK) was compared with the methodology in the Bacteriological Analytical Manual (BAM) for the detection of Listeria monocytogenes in 22 naturally contaminated cheese samples: 8 of these were positive by the BAM system and 12 were positive by the RSK system. The 8 Listeria positives found by the BAM system were positive by the RSK system. All 12 Listeria-presumptive positive samples by the RSK system were confirmed to be Listeria monocytogenes. The use of the RSK system enhanced the recovery of the pathogen, and detection was accomplished within 24 h.

Unified procedure for the determination of antibiotics in animal feeds

A new method was developed for the determination of antibiotics in animal feeds. This qualitative and quantitative method can be applied to 17 antibiotics currently accepted for use in animal feeds. A solvent prewash step is used to differentiate groups of antibiotics and individuals of the same class of antibiotics and to remove interfering substances. Agarose gel electrophoresis at pH 6.0 and 8.0 is used to further differentiate the individual antibiotics and as an agar diffusion assay. Minimum detectable concentrations of antibiotics currently accepted for use in animal feeds were determined against selected microorganisms.

Agarose gel electrophoresis system for the separation of antibiotics used in animal agriculture

A novel electrophoresis system using agarose gel has been developed for the separation and as an aid in the classification of antibiotics. This system utilizes Nunc cell factory disposable tissue culture dishes, which serve as bioassay dish and cooling chamber for agarose gel, in a custom designed electrophoresis unit. Tris(hydroxymethyl) methylamine-succinate buffer at pH 6.0 and 8.0 are employed as the electrolyte for electrophoresis. Bioautography was used as the indicator of mobility. Any agar diffusion assay can be modified to use this system. A suggested name for this system is Nunc cell factory agarose gel electrophoresis (NUAGE). Selected antibiotics, representative of the aminoglycoside, beta-lactam, macrolide, moenocinol, peptide, polyene, polyether, quinone and tetracycline classes, were separated with this system.

Drug residue analysis using immunoaffinity chromatography

The background and applicability of immunoaffinity chromatographic separations and clean-up to drug residue analysis of agricultural commodities is discussed. The uses of antibody specificity for separation and concentration of drug residues are presented. Examples of immunoaffinity chromatography for the determination of residues of (1) nortestosterone and methyl testosterone in swine muscle, urine and bile; (2) chloramphenicol in swine tissue, eggs and milk; (3) clenbuterol in calf urine; (4) zeranol and beta-zearalanolin in calf urine: (5) diethylstilbestrol, dienestrol and hexestrol in calf urine are presented. Further, examples of the successful coupling of immunoaffinity separations with other chromatographic techniques such as gas chromatography and high-performance liquid chromatography are presented.

Intracardiac echocardiography during simulated aortic and mitral balloon valvuloplasty: in vivo experimental studies

The feasibility of intracardiac echocardiography with a low-frequency transducer to assess catheter position and detect complications during experimental aortic and mitral balloon valvuloplasty was studied in 10 dogs. Intracardiac echocardiography was performed with a transesophageal echocardiographic probe placed in the right atrium. In all instances high-quality images of cardiac structures were obtained. The guide wire and balloon catheter were clearly seen as they crossed the valves. With inflation the balloon was seen as a hyperechoic structure. Doppler echocardiography documented aortic regurgitation after inflations. Acute pericardial effusion was instantly detected. It is concluded that intracardiac echocardiography is a potentially useful technique for cardiac imaging, assessing wire and balloon catheter position, evaluating valvular regurgitation, and instantly detecting acute pericardial effusion. Further research in humans with low-frequency, catheter-based transducers needs to be performed.

Competitive direct enzyme-linked immunosorbent screening assay for the detection of sulfamethazine contamination of animal feeds

A sensitive screening method has been developed for detecting sulfamethazine (SMZ) contamination of feeds by using either polyclonal or monoclonal antibodies and a direct competitive enzyme-linked immunosorbent screening assay (ELISA). Feed samples of 25.0 g are extracted with 0.5N HCl and centrifuged. The extract is adjusted to pH 7.0 with 3.0N NaOH and recentrifuged. This pH-adjusted extract is used in the ELISA. Levels as low as 0.004 micrograms SMZ/g feed were detected in supplemented extracts by polyclonal antibodies; levels of 0.4 micrograms SMZ/g feed were detected by a monoclonal antibody.

Real-time, intracardiac, two-dimensional echocardiography: enhanced depth of field with a low-frequency (12.5 mhz) ultrasound catheter

Advances in catheter-based ultrasound imaging technology allow for a unique opportunity to develop two-dimensional intracardiac echocardiography, an imaging method that could have significant clinical applications. In this study, we evaluated the potential of a new, percutaneous, 9-Fr prototype intracardiac echocardiographic catheter with a 12.5-MHz rotating crystal in 13 dogs. In all dogs, we were able to easily advance the intracardiac echocardiographic catheter into the right and left hearts percutaneously and obtain dynamic images of cardiac structures in various imaging planes. With the intracardiac echocardiographic catheter in the right atrium, the whole chamber could be visualized. Minor manipulation allowed visualization of the right atrium, right ventricle, and tricuspid valve in a two-chamber view; further maneuvering yielded four-chamber views. With advancement of the catheter into the right ventricle and pulmonary artery, the right ventricular cavity, right ventricular outflow tract, and pulmonary artery could be imaged. The intracardiac echocardiographic catheter in the aortic root allowed visualization of the pulmonary artery and its bifurcation, superior portions of the atria, interatrial septum, aortic valve, and the proximal left coronary artery. With the intracardiac echocardiographic catheter in the left ventricle, short-axis images of the whole left ventricle were obtained. Manipulating the catheter tip within the left ventricle, we could visualize the left ventricle, left atrium (LA), and the mitral valve in the long axis. We were also able to visualize and identify experimentally-induced ischemic regional left ventricular dyskinesis (four of of five dogs), aortic valvular tear (five out of five dogs), and pericardial effusion with right atrial collapse (two out of two dogs). Intracardiac echocardiography was not associated with any complications. We conclude that percutaneous, low-frequency intracardiac echocardiography with a 12.5-MHz, 9-Fr catheter yields cardiac images in many imaging planes with a good depth of field, allows identification of valvular, myocardial, and pericardial abnormalities, and has excellent clinical potential in the assessment of many cardiovascular disorders.

Turbidimetric assay for tetracyclines in feeds using a microtiter plate system

The microtiter plate system for turbidimetric assay of chlortetracycline (CTC) and oxytetracycline (OTC) levels in feeds uses a 96 well microtiter plate, a multichannel pipette, and an ELISA reader to measure turbidity. Feeds are extracted for both tetracyclines using AOAC extraction systems. For CTC, the range of the standard curve is 0.001-0.005 microgram CTC/mL; for OTC, the range is 0.004-0.016 microgram OTC/mL. Repeatability of CTC assays, as shown by the coefficient of variation (CV), ranged from 0.54 to 5.65% for same-day assays and from 2.01 to 9.39% for assays on different days. For OTC, CVs ranged from 2.69 to 10.01% for same-day assays and 3.24 to 9.08% for different-day assays. Average recoveries for CTC were 108.7% for same-day assays and 106.8% for different-day assays; for OTC, average recoveries were 112.4% and 106.5% for same-day and different-day assays, respectively.

Intracardiac echocardiography. Experimental observations on intracavitary imaging of cardiac structures with 20-MHz ultrasound catheters

Recently catheter-based ultrasound devices have become available for obtaining high-resolution images of blood vessels. In this study we evaluated the feasibility of imaging cardiac structures using 20-MHz ultrasound catheters. In 25 dogs, the ultrasound catheter was advanced into the right and left heart chambers percutaneously. The intravascular devices yielded images of the right atrial wall, right and left ventricular myocardia, tricuspid, pulmonic, and aortic valves, and the great vessels. Although the small depth of field inherent to the frequency range of 20 MHz limited the visualization to only portions of the cardiac chambers, the images obtained were of high resolution and allowed easy identification of the various cardiac structures. Intracardiac echocardiography was easy to perform and did not result in damage to the cardiac structures. We conclude that intracardiac echocardiography using ultrasound catheters provides a new approach to cardiac imaging and that the development of lower frequency catheters could aid in extending the potential utility of intracardiac echocardiography.

Problems and pitfalls in the performance and interpretation of color Doppler flow imaging: observations based on the influences of technical and physiological factors on the color Doppler examination of mitral regurgitation

Color Doppler flow imaging has become an integral part of the echocardiographic examination. By providing real-time, two-dimensional spatial maps of normal and abnormal cardiac blood flows, this technique provides important information that may be used to guide patient management. The acquisition and display of color Doppler flow information may be influenced by technical factors, by the physiological condition of the patient, by abnormalities of cardiac morphology, and, on occasion, by artifact. In this article, the results of a study performed to evaluate the influence of technical factors on the color Doppler assessment of mitral regurgitation are reported. Mitral regurgitation jet area size changed significantly with variation in the control settings for color gain, color process, color map, color image resolution, and sector width. A review of those factors that influence the performance and interpretation of the color Doppler flow examination is provided and their significance discussed.

High-performance immunoaffinity chromatography for drug residue analysis

High-performance immunoaffinity chromatography (IAC) is a potentially strong analytical tool for measurement of drug residues in various matrixes. Although the use of Immunoaffinity separations is not new, the application to drug residue analysis is in its infancy. The present paper discusses the production and purification of antibody, the preparation of columns, the theoretical basis of the analytical separation and elution, and variations of the analytical approach.

Intravascular and intracardiac ultrasound imaging: current research and future directions

Intravascular and intracardiac ultrasound imaging is a newly emerging catheter-based imaging modality with considerable promise. This review article presents the rationale behind attempts at developing intravascular imaging methods, the design features of intravascular instrumentation, the knowledge obtained with in vitro studies, the in vivo experience in humans, and the potential applications of intravascular imaging in arterial atherosclerosis. The feasibility of pulmonary artery imaging and the potential applications of intracardiac echocardiography are discussed. Finally, future directions in intravascular imaging are outlined.

Real-time intracardiac two-dimensional echocardiography: an experimental study of in vivo feasibility, imaging planes, and echocardiographic anatomy

The traditional transthoracic and transesophageal echocardiographic examination have proven to be useful imaging tools for studying cardiac morphology, pathology, and function. Recently, catheter-based ultrasound transducers have been available for intravascular ultrasonic imaging. We supposed that echocardiographic examination performed from within the heart itself can provide useful information about cardiac structure and function, especially in settings where transthoracic or transesophageal echocardiography may be technically difficult to perform or poorly tolerated by the patient. To explore this concept, we performed intracardiac echocardiography in vivo in 22 dogs using both 5-MHz and 20-MHz transducers. High-quality images were obtained in all animals. Using the higher frequency transducer, detailed images with only a limited depth of field were obtained. With the 5-MHz transducer, a comprehensive cardiac examination was feasible from within the right atrium and inferior vena cava. We were able to visualize the great vessels, all cardiac valves, and cardiac chambers in a multitude of imaging planes. Alterations in ventricular function were instantly recognized. Color Doppler capabilities allowed visualization of flow abnormalities as well. We conclude that intracardiac echocardiography is feasible and could be potentially useful in certain clinical situations. With further research and development, this technique may have an important clinical impact in cardiac therapy and diagnosis.

Factors influencing optimization of diffusion assays for antibiotics

Agar nutrient content, cylinder charge volume, thickness (volume) of the agar layer, and incubation temperature were 4 factors varied to determine their effect(s) on the optimization of the cylinder-plate diffusion assay. Chlortetracycline was the pilot antibiotic and Bacillus cereus was used as the assay organism. Zones of inhibition were larger when the incubation temperature was lower than that which was commonly used and/or when the nutrient level was decreased; the zones were smaller when the incubation temperature was raised and/or when an increased nutrient level was used. The thickness (volume) of the assay layer played the most important role; the thinner the layer the less the effect the cylinder charge volume had on the zone diameter. The slopes of the response lines were minimally affected by cylinder charge volume. For a 7 mL assay layer per standard Petri plate, cylinder charge volumes ranging from 150 to 250 microL had little effect on zone diameter. The linearity of the response line was unaffected by assay layer thickness (volume), nutrient level, temperature of incubation, or cylinder charge volume. As long as the conditions for the assay were standardized, there were no discernible effects on recoveries or potencies.

Direct competitive enzyme-linked immunosorbent assay for sulfamethazine residues in milk

A direct competitive enzyme-linked immunosorbent assay (ELISA) is described for the detection and estimation of sulfamethazine residues in milk. Samples are cleaned up rapidly by acidifying and centrifuging the milk, adjusting the supernatant liquid to pH 7.0, and centrifuging again. The supernate is then assayed using set points to estimate sulfamethazine levels in the sample in the range of 1 ppb to 1 ppm. Multiple samples of milk can be screened in 1.5-2 h by this ELISA method.

Competitive direct enzyme-linked immunosorbent assay for detection of sulfamethazine residues in swine urine and muscle tissue

A sensitive assay for the detection of sulfamethazine in swine urine and muscle tissue using a direct competitive enzyme-linked immunosorbent assay (ELISA) has been developed. Undiluted urine or a phosphate-buffered saline extract of pork muscle tissue is mixed with an enzyme-labeled conjugate of sulfamethazine and horseradish peroxidase. The mixture is added to wells of a microtiter plate coated with antibody to sulfamethazine. After the test system is incubated, washed, and re-incubated with substrate and the reaction is stopped, the absorbance is measured at 405 nm. Levels of sulfamethazine as low as 20 ng sulfamethazine/g muscle tissue and 10 ng sulfamethazine/mL swine urine were detected and estimated.

Electrophoretic methods for screening for antibiotics in animal feeds

A new system for screening antibiotics in animal feeds involves washing antibiotic-containing animal feeds with a series of organic solvents to eliminate interferences and partially separate the antibiotics. Antibiotics are then determined by using paper electrophoresis and thin-layer bioautography. This approach enables the separation and qualitative identification of 17 antibiotics currently used in animal feeds and provides the ability to detect low-level cross-contamination.

Microbial diffusion assay for antibiotics in feeds using a simplified design

Results are compared for the microbiological analysis of antibiotics in feeds using the AOAC plate diffusion assay and the simplified 2-plate assay. Five antibiotics, bacitracin, chlortetracycline, oxytetracycline, penicillin, and streptomycin, were used to supplement feed extracts at levels of 100 and 25 micrograms antibiotic/g feed (bacitracin at 100 micrograms/g only). For bacitracin at the one level and for penicillin at both levels, the 2-plate design yielded significantly more accurate results than those of the AOAC assay. The same was true for the 25 micrograms/g level of oxytetracycline and the 100 micrograms/g level of streptomycin. For streptomycin at the 25 micrograms/g supplementation, the AOAC assay results showed better accuracy. There was no significant difference in results between the 2 designs for oxytetracycline at 100 micrograms/g and chlortetracycline at either level. The accuracy and precision of the results for the 2-plate design are equivalent to or better than those obtained using the AOAC design; in addition, the 2-plate assay is less labor-intensive, is more cost-effective, and is able to determine reasonable conditions of similarity.

Cytosolic glucocorticoid receptors in the developing rat heart

Glucocorticoid hormones alter functional cardiac responses in the rat heart. In the neonatal rat heart, glucocorticoid treatment on post-natal day 2 alters heart function for up to 3 weeks post-injection, which suggests that cardiac glucocorticoid receptors mediate cardiac function in neonates. However, glucocorticoid receptors have not been identified in neonatal rat heart. Glucocorticoid receptor binding was measured in neonatal rat heart cytosol extract using [3H] dexamethasone as ligand, and characterized by competition assays and Scatchard analysis. Saturable, specific, high affinity glucocorticoid receptor binding was found in the cytosol of the neonatal rat heart. We then examined the effects of a single, post-natal day 2 injection of hydrocortisone acetate on glucocorticoid receptor binding in 12 to 14-day-old rat heart. While this injection paradigm results in altered cardiac function in 12-day-old rat hearts, cytosol glucocorticoid receptor binding in 12 to 14-day-old heart was not altered by treatment on post-natal day 2 with hydrocortisone acetate. It is postulated that exposure to elevated glucocorticoid levels on neonatal day 2 may alter cardiac function by producing permanent organizational effects on cardiac tissue.

Method to determine effect of antibiotics at residue levels on R-factor transfer

An analytical system was developed which can assess the ability of antibiotic/antimicrobial residues (0.01-1.00 ppm) to affect the conjugal transfer of resistance among the Enterobacteriaceae. The donor strain, Escherichia coli RP-4 (Amr Tcr Nmr Kmr Lac+), and recipient strain, E. coli Sc-8632 (Smr Lac-), were incubated together in a 1:9 donor:recipient ratio for 18 h with gentle shaking (50 rpm) in brain heart infusion broth in the presence of residue levels of antibiotics. The mating cultures were serially diluted and spread-plated onto MacConkey agar containing 25 micrograms streptomycin/mL to select the total recipient population of sensitive E. coli Sc-8632 and transconjugants. After an 18 h incubation at 37 degrees C, the plates were replicated onto MacConkey agar containing 25 micrograms ampicillin/mL to select the ampicillin-resistant transconjugant population. Repeatability was good; the average transfer was 51.8%, with a coefficient of variation of 9.3%. Residue levels of tylosin (0.10 and 1.00 ppm) increased the transfer of the ampicillin marker beyond the 95% confidence limits. Oxytetracycline, bacitracin, streptomycin, penicillin, and virginiamycin did not increase the percent transfer. Oxytetracycline at 0.01 ppm decreased the percent transfer. In general, residue levels of antibiotics (0.01-1.00 ppm) did not affect the conjugal transfer of antibiotic resistance.

In vitro analytical system for determining the ability of antibiotics at residue levels to select for resistance in bacteria

An analytical procedure, based on the concept that exposure of bacteria to antibiotics will result in the selection of a resistant population, was developed. Two strains of enteric bacteria, Escherichia coli CS-1 and Enterobacter cloacae B520, which are sensitive to a wide variety of antibiotics, were used as the test organisms. E. coli CS-1 were exposed to 1.00 micrograms antibiotic or antimicrobial/mL; E. cloacae B520 were exposed to 0.01, 0.10, 0.50, 1.00, and 5.00 micrograms/mL. Both organisms developed increased resistance to other antibiotics after exposure to chlortetracycline and oxytetracycline, as measured by the minimum inhibitory concentration (MIC). E. cloacae B520 showed increased resistance to ampicillin, oxytetracycline, and chloramphenicol after exposure to levels as low as 0.10 microgram/mL. Exposure to streptomycin, sulfamethazine, tylosin, bacitracin, flavomycin, virginiamycin, and monensin at levels of 1.00 microgram/mL did not increase the MIC. Exposure to 5.00 micrograms streptomycin, sulfamethazine, tylosin, and monensin/mL increased the MIC of E. cloacae to one of the antibiotic markers. These increased MICs exceeded the 95% confidence limits of the MIC values of the unexposed organisms.

Antibiotic/Antimicrobial Residues in Milk 1

A qualitative receptor assay for antibiotic and antimicrobial residues in milk was used in a survey of commercial milk samples obtained in the eastern Pennsylvania, Central New Jersey, New York City area. Sixty-four milk samples were obtained over a 3-month period, representing different brands and bottling plants. Sixty-three percent of milk samples contained one or more residues; 27% contained 2 residues; 11% contained 3 or more residues. Tetracyclines and sulfonamides were the most predominant residues detected. A subsample of milk was used to confirm the qualitative presence of residues, using microbial assays. Of 9 presumptive tetracycline-positive samples, 9 were confirmed. Of 4 presumptive streptomycin-positive samples, 3 were confirmed.

The effect of epinephrine versus methoxamine on regional myocardial blood flow and defibrillation rates following a prolonged cardiorespiratory arrest in a swine model

Recent studies in swine have shown that larger doses of epinephrine than those currently employed for cardiopulmonary resuscitation (CPR) significantly improve regional myocardial blood flow following prolonged cardiac arrest. The dose-response effect of a pure alpha-adrenergic agonist, methoxamine, on regional myocardial blood flow has not been investigated in this setting. This study compared the effect of high-dose epinephrine with graded doses of methoxamine on regional myocardial blood flow, oxygen delivery/utilization, and defibrillation rates during CPR. Twenty swine were instrumented for regional myocardial blood flow measurements using radiolabeled tracer microspheres. Measurements of regional myocardial blood flow, oxygen delivery, and oxygen consumption were made during normal sinus rhythm. Ventricular fibrillation was then induced. Following 10 minutes of ventricular fibrillation, CPR was initiated with a pneumatic compressor. Regional myocardial blood flow, oxygen delivery, and oxygen consumption were then measured during CPR. Following 3 minutes of CPR, the swine were allocated to one of four treatment groups (five per group): group I, epinephrine 0.2 mg/kg; group II, methoxamine 0.1 mg/kg; group III, methoxamine 1.0 mg/kg; and group IV, methoxamine 10.0 mg/kg. One minute after drug administration, regional myocardial blood flow, oxygen delivery, and oxygen consumption measurements again were made. Three and one half minutes after drug administration, defibrillation was attempted. Regional myocardial blood flow following drug administration was compared using an analysis of covariance. Epinephrine (0.2 mg/kg) significantly improved myocardial blood flow (P less than .002) for all tissues examined compared with all doses of methoxamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of AOAC microbial diffusion procedure for analysis of chlortetracycline in high mineral feeds

The performance of the AOAC microbial diffusion assay procedure for the analysis of chlortetracycline was evaluated in mixed feeds and premixes as well as laboratory-prepared feeds, all with various mineral contents. In 100 mixed feeds with a calcium content ranging from less than 1 to greater than 22%, no relationship was shown between calcium content and incidence of chlortetracycline deficiency. In 106 premixes, a relationship was shown between chlortetracycline content and adherence to guarantee: below 10 g/lb, the incidence of deficiency was high; in premixes containing 20 g chlortetracycline and above, the incidences of deficiency were less than 5%. In laboratory-prepared feeds containing 12-15% calcium, grinding and storage at both 4 degrees C and at room temperature (20 degrees C) caused no decrease in the chlortetracycline concentration. Only storage of the ground feed at 37 degrees C caused a distinct loss of activity. The temperature-related loss was attributed to the epimerization of chlortetracycline.

Simplified plate diffusion system for microbial assays of antibiotics

A protocol for microbial assays of antibiotics, using the plate diffusion system, is presented. The system is based on the concept that a complete standard curve and assay unknowns can be placed on an assay plate and that 2 plates can be a complete assay with an accuracy and precision essentially equivalent to the official AOAC diffusion procedure. Four antibiotics, bacitracin, chlortetracycline, oxytetracycline, and streptomycin, were used in the design and comparison studies with the AOAC protocol. The coefficients of variation (CVs) for the AOAC design, using 10 replicates, ranged from 1.4 to 10.3% with a mean of 4.5%. The CVs for the single-plate option of the simplified design ranged from 4.3 to 9.6% with a mean of 6.6%; the CVs for the 2-plate option ranged from 2.5 to 6.8% with a mean of 4.3%; the CVs for the 3-plate option ranged from 1.2 to 5.0% with a mean of 3.0%.

Microbiological assay for chloramphenicol residues

Procedures for the assay of chloramphenicol in milk, urine, serum, and muscle tissue are presented. The procedures specify an assay design with all standards as well as samples present on each plate, oxytetracycline in the buffer-diluent for greater sensitivity, a minimal medium to enhance the inhibitory effect of chloramphenicol on the assay organism, and a tetrazolium dye to improve the ability to measure the zones of inhibition. Recoveries of unbound chloramphenicol from bovine urine were 90.8%, from serum 88.3%, from milk 79.3%, from swine muscle 71.3%, and from beef and chicken muscle 61.0 and 61.4%, respectively. The lower levels of measurement in urine and serum were 0.25 microgram/mL, 0.025 microgram/mL in milk, and 0.10 microgram/g in muscle tissue.

Effects of antimicrobial agents fed to chickens on some gram-negative enteric bacilli

Total and antimicrobial agent-resistant aerobic and facultative anaerobic gram-negative enteric bacilli in fecal samples of broiler chickens fed growth-promotional levels of antimicrobial agents were determined quantitatively. Two 8-week studies were conducted utilizing groups of chickens fed antimicrobial-supplemented rations; the second study involved feed "pasteurization" as a means of minimizing colonization from the feed. Dilution/spread-plating/replica-plating techniques on selective media were used to obtain counts of total organisms and those resistant to tetracycline, chloramphenicol, streptomycin, ampicillin, or kanamycin. The predominant aerobic and facultative anaerobic gram-negative organism was Escherichia coli, which was detected in all samples at levels ranging from 10(5) to over 10(10) CFU/g of feces. Less common were Proteus mirabilis, Klebsiella pneumoniae, and Pseudomonas sp., which varied in occurrence and levels from group to group (range, less than 10(3) to 10(8) CFU/g). Resistance to all antimicrobials (except chloramphenicol in E. coli) was commonly observed at incidences exceeding 10(3) CFU/g in the total populations. Colonization of the chickens' intestinal tracts by susceptible and resistant strains of E. coli, K. pneumoniae, and Pseudomonas sp. appeared to result from their presence in the environment of the newly hatched chickens. Ration pasteurization did affect P. mirabilis, which appeared to colonize from the feed. The results suggest that colonization by, and proliferation of, antimicrobial-resistant aerobic and facultative anaerobic gram-negative enteric bacilli in chicken intestinal tracts may be less dependent on selection through antimicrobial supplementation of the ration than on their prevalence in environments from which they can colonize newborns.

Evaluation of the Escherichia coli K12 inductest for detection of potential chemical carcinogens

46 chemicals of diverse classes and structures, including 30 known animal carcinogens, were evaluated for prophage-inducing ability using the Escherichia coli inductest with lysogenic strain GY5027 envA - uvrB- and indicator strain GY4015 ampR . The inductest detected 9 of 30 known carcinogens as genotoxic agents, including 3 polycyclic hydrocarbons, 2 aflatoxins, and 2 antitumor antimicrobials. Among the 21 carcinogens ineffective as prophage inducers were 3 aromatic amines (other than 2-aminoanthracene), 3 azo-aminoazo compounds, 2 methanesulfonates, and 2 nitro aromatics. In contrast, 18 and 17 of the 30 animal carcinogens were detected as genotoxic agents in the Salmonella/Ames test and E. coli WP2/ WP100 rec assay, respectively. The threshold sensitivity of the inductest was less than that of the Salmonella/Ames test for chemicals genotoxic in both tests. The ineffectiveness of the inductest as a routine test for detecting potential chemical carcinogens may be related to the nature of the DNA damage lesions formed by various genotoxic agents.

Pad-plate diffusion assay for virginiamycin in mash-type feeds

An assay procedure has been developed for virginiamycin in mash-type feeds which includes removing fat interferences from the feeds by a rapid petroleum ether wash, a citric acid extraction, an acetone extraction, and the use of the pad-plate diffusion system. The procedure eliminates the need for compensatory curves prepared from feeds of the same or similar composition. Recoveries from 10 laboratory-prepared feeds containing 11.0 micrograms virginiamycin/g averaged 89.3% with a coefficient of variation (CV) of 5.76%. Recoveries from a laboratory-prepared feed containing 13.2 micrograms virginiamycin/g averaged 89.9% (CV 9.92%). The procedure is simple, reasonably accurate, and precise.

Rapid assay for tetracycline in premixes and mixed feeds

A rapid assay for tetracyclines in premixes and mixed feeds is described, which uses the extraction and dilution systems of AOAC methods, and a strain of Bacillus stearothermophilus ATCC 12980 selected to grow at 40 degrees C. The incubation period is 4.5 h. The rapid assay yields results similar to those obtained using the AOAC methods. For a 50 g chlortetracycline (CTC)/lb commercial premix, the rapid procedure averaged 109.2% of label vs 104.4% obtained using the AOAC method; for a 20 g CTC/lb premix, the rapid procedure averaged 89.2% vs 89.3% obtained with the AOAC method. In 2 commercial premixes containing 50 g oxytetracycline/lb, the rapid assay averaged 127.1 and 110.5% vs 134.7 and 113.5% obtained using the AOAC method. In feed extracts supplemented with CTC equivalent to 25-200 g/ton, rapid assay recoveries averaged 101.9%; recoveries using the AOAC method averaged 110.6%. For feed extracts supplemented with oxytetracycline at the same levels, recoveries by the rapid assay averaged 95.4%, and by the AOAC method, 106.0%.

Psychometric comparisons of trainees and consultants in anaesthesia and psychiatry

Two psychometric tests were taken by trainees in anaesthesia and psychiatry, and by consultant practitioners in these specialties. The Cattell 16 Personality Factor Questionnaire measured primary and secondary aspects of personality. The Strong-Campbell Interest Inventory assessed interests, and compared the results with those of the test's control subjects who worked satisfactorily in one of 162 occupations. All clinician groups scored highly in intelligence, innovation, self-sufficiency, and interests in the arts and medical science. Anaesthetic trainees were very similar to psychiatric trainees except in the quality, tender-mindedness, in which the psychiatrists' mean score was much higher. Trainee anaesthetists closely resembled consultants in that specialty, except that the younger group was more apprehensive and less conscientious. Consultant anaesthetists were more conscientious, realistic, conventional, and had more "tough-poise" than consultant psychiatrists, who were higher in social interests and tender-mindedness. These differences appear to be largely the result of the types of practice in these specialties, rather than reasons people chose their fields. It is unlikely that these tests would be useful in the process of trainee selection, but the possibility that psychometric tests could be devised for that purpose must be considered.

Achievement motivation in medical students

Medical students were assessed by questionnaire in their third and fourth years regarding attitudes about sex role, medical school, and career plans and in the third year about fear of success. Nine percent of each sex were judged to fear success. Stereotypical responses were reported by the students. Males, anticipating that they would work more than 60 hours per week, looked forward to academic careers, while females more often desired the sharing of financial and child care responsibilities with spouses. Attitudes toward chores were egalitarian, but in reality women performed most routine household activities. Both sexes agreed upon the characteristics that are necessary to be a good student as well as to succeed in later life. Women were more inclined toward artistic and domestic interests and helping others, while men were more interested in scientific investigation, athletics, and adventure. The implications of these similarities and differences for the students' future careers are discussed.

Down and out in the city: the homeless mentally ill

The plight of the homeless in New York City and other urban areas has become the focus of increasing attention. In an effort to clarify and understand the problems of the homeless, the authors studied the demographic characteristics, psychiatric diagnoses, histories, and dispositions of 100 homeless patients treated at Bellevue Psychiatric Hospital's emergency service. The most striking finding was that 96.6 percent of the sample had had a previous psychiatric hospitalization. Seventy-two percent of these homeless patients were diagnosed as suffering from schizophrenia; the second most common diagnosis was personality disorder, which accounted for 13.3 percent of the sample. The authors discuss other demographic findings of their study and explore the roots of the problem of homelessness, review the psychiatric literature on the subject, and delineate some of the unique treatment needs of this population.

Nephro colo cutaneous fistula: use of CT scan to aid diagnosis

Nephro colo cutaneous fistula is an uncommon complication of calculus disease of the urinary tract. A case is presented in which CT scan was helpful in the diagnosis. The treatment which must be individualized usually consists of nephrectomy and colonic repair via oversewing, exteriorization with secondary closure, or resection with primary anastomosis.