Effects of quorum sensing signal molecules on the hydrogen peroxide resistance against planktonic Pseudomonas aeruginosa

The effects of quorum sensing signal molecules in Pseudomonas aeruginosa, N-butanoyl-L-homoserinelactone (C4-HSL) and N-(3-oxododecanoyl)-L-homoserinelactone (3-oxo-C12-HSL) on planktonic cell resistance against hydrogen peroxide were studied. In P. aeruginosa JP2 cells with the deletion of lasI and rhlI, the viable cell concentration decreased with time and was reduced by about 4 log after 2 h of 7.5 mM H2O2 treatment, while only a 2-log reduction was found for the wild type P. aeruginosa PAO1 cells. When cultured with 20% PAO1 spent medium, P. aeruginosa JP2 showed similar hydrogen peroxide resistance to that seen in P aeruginosa PAO1. Culturing with 20% JP2 spent medium or with 10 microM C4-HSL and 20 microM 3-oxo-C12-HSL did not affect P aeruginosa JP2 cell susceptibility to hydrogen peroxide. Although both 20% PAO1 and JP2 spent media reacted with H2O2 and reduced H2O2 to 50% of the strength of the original concentration, the remaining H2O2 was still sufficient to kill P. aeruginosa JP2. These results indicate that the difference in cell resistance against H2O2 between P. aeruginosa PAO1 and JP2 was related to the existence of gene products of the lasI and rhlI systems. However, adding synthetic homoserine lactones alone did not increase P. aeruginosa JP2 cell resistance to H2O2 as seen in the experiments adding PAO1 spent medium. Determination of the detailed relation between cascade regulation in P. aeruginosa and its cell resistance to H2O2 will require further investigation.

Parallel synthesis and evaluation of N-(1-phenylethyl)-5-phenyl-imidazole-2-amines as Na+/K+ ATPase inhibitors

A series of N-(1-phenylethyl)-5-phenyl-imidazole-2-amines was prepared using solution-phase, parallel synthesis and evaluated for Na+/K+ ATPase inhibition.

Superior mesenteric artery syndrome in traumatic paraplegia: a case report and literature review

Superior mesenteric artery syndrome (SMAS) is a relatively rare condition thought to be caused by the functional obstruction of the third part of the duodenum as it passes between the superior mesenteric artery and the aorta. The following case report describes a patient who developed SMAS in the setting of traumatic paraplegia. The patient began to exhibit symptoms consistent with SMAS (epigastric pain, postprandial epigastric fullness, nausea, emesis) shortly after his injury and during home therapies. On admission to an inpatient rehabilitation hospital, the patient's symptoms persisted and prevented participation in any therapies. When radiographic studies demonstrated the existence of SMAS, conservative and surgical management were discussed with the patient and the family. The patient was managed conservatively with positional changes during feeding and the administration of metoclopramide (10mg orally, three times a day) before meals and before sleep. The patient was able to meet or exceed all short-term physical and occupational therapy goals with one episode of postprandial nausea noted. The patient returned home 21 days after admission to the rehabilitation hospital with home therapies. The patient was able to perform transfer skills and most self-care tasks.

Geographic variation and environmental risk factors for the incidence of initial kidney stones in patients with spinal cord injury

PURPOSE

Although geographic variability in cases of kidney stones, primarily calcium stones, is reported in the general population, little is known about geographic variability in subjects with spinal cord injury, in whom struvite stones predominate. We examined regional variation in the incidence rate of initial kidney stones and clarified the contributing factors in a spinal cord injury cohort.

MATERIALS AND METHODS

We used data from the national spinal cord injury database between 1986 and 1999 on 7,784 participants from 21 spinal cord injury centers with 24,492 person-years of followup accumulated and 286 incident stone cases. A multilevel Poisson model was constructed to evaluate the ecological effects of latitude, air temperature, water hardness and sunlight index on stone formation while controlling for individual factors, including participant age, race, gender, severity of injury and bladder management.

RESULTS

The incidence rate was significantly greater in the southeast and tended to increase with decreasing latitude, similar to the geographic association with kidney stones in the general population. This finding was not explained by differences in individual risk factors. Decreasing water hardness had the strongest effect on stones during year 1 after injury (relative risk 0.6, p <0. 001), whereas average annual temperature had the strongest association with stones after year 1 (relative risk 1.1 per 1C increase, p = 0.03). The sunlight index had no association.

CONCLUSIONS

Our study implies that the increased stone risk in spinal cord injured subjects is potentially preventable by modifying environmental exposure. Etiological factors may be similar to those for kidney stones in the general population.

In vivo CD4+ T cell tolerance induction versus priming is independent of the rate and number of cell divisions

In vitro studies have suggested that tolerance induction (i.e., anergy) is associated with an inability of T cells to proliferate vigorously upon Ag recognition. In vivo, the relationship between T cell proliferation and tolerance induction is less clear. To clarify this issue, we have been studying a model system in which naive CD4+ T cells specific for the model Ag hemagluttinin (HA) are adoptively transferred into different transgenic founder lines of mice expressing HA as a peripheral self-Ag. When transferred into two lines whose HA expression differs by at least 1000-fold, HA-specific T cells undergo multiple rounds of cell division before reaching a nonresponsive (i.e., tolerant) state. While the proliferative response is more rapid in mice expressing higher levels of HA, the T cells become tolerant regardless of the level of peripheral HA expression. When the T cells encounter HA expressed as a viral Ag, they proliferate at a similar rate and undergo the same number of divisions as with self-HA, but they do not become tolerant. These results indicate that a tolerizing stimulus can induce similar T cell mitotic rates as a priming stimulus. Therefore, CD4+ T cell tolerance induction in vivo is not the result of an insufficient proliferative response elicited upon TCR engagement.

Quorum sensing in Pseudomonas aeruginosa controls expression of catalase and superoxide dismutase genes and mediates biofilm susceptibility to hydrogen peroxide

Quorum sensing (QS) governs the production of virulence factors and the architecture and sodium dodecyl sulphate (SDS) resistance of biofilm-grown Pseudomonas aeruginosa. P. aeruginosa QS requires two transcriptional activator proteins known as LasR and RhlR and their cognate autoinducers PAI-1 (N-(3-oxododecanoyl)-L-homoserine lactone) and PAI-2 (N-butyryl-L-homoserine lactone) respectively. This study provides evidence of QS control of genes essential for relieving oxidative stress. Mutants devoid of one or both autoinducers were more sensitive to hydrogen peroxide and phenazine methosulphate, and some PAI mutant strains also demonstrated decreased expression of two superoxide dismutases (SODs), Mn-SOD and Fe-SOD, and the major catalase, KatA. The expression of sodA (encoding Mn-SOD) was particularly dependent on PAI-1, whereas the influence of autoinducers on Fe-SOD and KatA levels was also apparent but not to the degree observed with Mn-SOD. beta-Galactosidase reporter fusion results were in agreement with these findings. Also, the addition of both PAIs to suspensions of the PAI-1/2-deficient double mutant partially restored KatA activity, while the addition of PAI-1 only was sufficient for full restoration of Mn-SOD activity. In biofilm studies, catalase activity in wild-type bacteria was significantly reduced relative to planktonic bacteria; catalase activity in the PAI mutants was reduced even further and consistent with relative differences observed between each strain grown planktonically. While wild-type and mutant biofilms contained less catalase activity, they were more resistant to hydrogen peroxide treatment than their respective planktonic counterparts. Also, while catalase was implicated as an important factor in biofilm resistance to hydrogen peroxide insult, other unknown factors seemed potentially important, as PAI mutant biofilm sensitivity appeared not to be incrementally correlated to catalase levels.

Simultaneous blood and biliary sampling of esculetin by microdialysis in the rat

Biliary excretion and intestinal reabsorption in enterohepatic circulation play major dispositional roles for some drugs. To circumvent multiple blood sampling and interruption of enterohepatic circulation in conventional biliary cannulation, the present study utilized the minimally invasive sampling technique of microdialysis in pharmacokinetics and biliary excretion studies. Microdialysis probes were inserted into the jugular vein and bile duct in the anesthetized rat for simultaneous and continuous sampling following intravenous administration of esculetin, a bioactive coumarin derivative. Placements of the microdialysis probes were designed to minimize obstruction to normal flows of the body fluids. Separation and quantitation of esculetin in the dialysates were achieved using high performance liquid chromatography (HPLC) coupled to UV detection. The results indicated higher drug concentrations in the bile than in the blood, suggesting active biliary excretion. The study also provided an example of successful application of in vivo microdialysis as an interesting and feasible alternative for pharmacokinetics and biliary drug excretion studies.

Reduction of polysaccharide production in Pseudomonas aeruginosa biofilms by bismuth dimercaprol (BisBAL) treatment

Microorganisms in biofilms, cells attached to a surface and embedded in secreted insoluble extracellular polymers, are recalcitrant to chemical biocides and antibiotics. When Pseudomonas aeruginosa ERC1 biofilms were treated continuously with 1 x MIC of bismuth dimercaprol (BisBAL), biofilm density determined by both total cell counts and viable cell counts increased during the first 30 h period then decreased thereafter. After 120 h of treatment there was an approximate 3-log reduction in viable cell areal density compared with the untreated control. Per-cell total polysaccharide production was significantly reduced in biofilms exposed to 12.5 microM BisBAL compared with the untreated control. In biofilm cultures, 1 x MIC of BisBAL did not initially kill attached cells but was enough to reduce polysaccharide production. As treatment proceeded, the normalized polysaccharide content was reduced and those cells attached became susceptible to 1 x MIC of BisBAL.

Genetic characterization of the hemagglutinin of two strains of influenza B virus co-circulated in Taiwan

Two isolates of influenza B virus were obtained in the spring of 1997. One strain, B/Taiwan/21706/97, was isolated from a patient who had acute tonsillitis. The other, B/Taiwan/3143/97, was isolated from a patient who was diagnosed with meningoencephalitis. This implies that the influenza B viruses not only cause respiratory symptoms but may also cause inflammation of the nervous system. Sequence analysis of the hemagglutinin (HA) gene, HA1 domain, indicated that there were remarkable amino acid changes in the strain B/Taiwan/3143/97 compared to B/Victoria/2/87, B/Yamagata/16/88, and B/Taiwan/7/88. The changes in the positions 116, 200, 238, 242, and 271 were correlated with receptor binding. Furthermore, a potential glycosylation site at position 233 was lost. In total, 30 amino acid changes were noted at positions ranging from 116 to 295. These changes may affect the antigenicity of the virus. Phylogenetic analyses also showed that the B/Taiwan/3143/97 was located in an independent lineage, when compared to the reference strains belonging to B/Victoria/2/87 and B/Yamagata/16/88 lineages. This supports the hypothesis that influenza B viruses with distinct genetic characteristic were co-circulated in Taiwan.

Pharmacokinetics of granisetron in rat blood and brain by microdialysis

To characterize the pharmacokinetics of protein-free granisetron in blood and brain we implanted microdialysis probes into the jugular vein and cerebral frontal cortex of the rat. Granisetron (3 or 6 mg/kg, i.v., n=6) was then administered, and microdialysates from blood and brain were collected from both sites and assayed by a validated high-performance liquid chromatographic method. Pharmacokinetics parameters were calculated from the corrected dialysate concentrations of granisetron versus time data. The elimination half-lives of granisetron in blood and brain were 51.3+/-5.5 and 69.7+/-6.3 min for 6 mg/kg, and 50.7+/-4.3 and 74.3+/-12.5 min for 3 mg/kg, respectively. Granisetron rapidly entered the extracellular fluid of cerebral frontal cortex at Tmax of 24 min. The results suggest that simultaneous microdialysis in blood and brain can be usefully applied to study the pharmacokinetics of granisetron in the periphery and the central nervous system.

Measurement and pharmacokinetic study of unbound tropisetron in rat blood by microdialysis with high-performance liquid chromatography

A microdialysis system coupled with liquid chromatography was applied for the measurement of unbound tropisetron in rat blood. The microdialysis probe was inserted into a jugular vein/right atrium of male Sprague-Dawley rats. Tropisetron (5 or 10 mg/kg, i.v.) was then administered via a femoral vein of rat. Samples were eluted with a mobile phase containing acetonitrile-100 mM monosodium phosphate (pH 5.0, 26:74, v/v). The UV detector wavelength was set at 284 nm. The detection limit of tropisetron was 20 ng/ml. The in vivo recovery of microdialysis probe in rat jugular vein/atrium for tropisetron at 1, 2, and 5 microg/ml were between 49 and 53% (n=5). Intra- and inter-assay accuracy and precision of the analyses were <10% in the range of 0.1-1 microg/ml. The method has been applied to pharmacokinetic analysis of unbound tropisetron in rat intravenous administration. Rapid distribution followed by a slower elimination phase was observed from the blood concentration-time curve. The disposition of tropisetron at each dose fitted well to a two-compartment model.

[The role of nurse anesthetist in Taiwan (questionnaire report)]

BACKGROUND

Anesthesia as a specialty was introduced to Taiwan for over 40 years. In early days, there were quite a number of nurse anesthetists who were trained to share the heavy burden of anesthetic work. However, due to the increasing demand for better anesthetic quality, the role of nurse anesthetists is open to discussion.

METHODS

Questionnaires were sent to anesthesiologists working in medical centers, regional hospitals, and district hospitals. We hoped to find out the present working condition of nurse anesthetists and what their future role would be.

RESULTS

Over one-half of the questionnaires collected agree that nurse anesthetists should not conduct anesthesia by their own, and that they should only help prepare patients and drugs for anesthesia.

CONCLUSIONS

Anesthesia as a highly specialized field of medicine should be conducted by qualified and well trained anesthesiologists only. Training for nurse anesthetists should be confined to preparation of drugs and care of patients only.

Spatial physiological heterogeneity in Pseudomonas aeruginosa biofilm is determined by oxygen availability

The role of oxygen availability in determining the local physiological activity of Pseudomonas aeruginosa growing in biofilms was investigated. Biofilms grown in an ambient-air environment expressed approximately 1/15th the alkaline phosphatase specific activity of planktonic bacteria subjected to the same phosphate limitation treatment. Biofilms grown in a gaseous environment of pure oxygen exhibited 1.9 times the amount of alkaline phosphatase specific activity of air-grown biofilms, whereas biofilms grown in an environment in which the air was replaced with pure nitrogen prior to the inducing treatment did not develop alkaline phosphatase activity. Frozen cross sections of biofilms stained for alkaline phosphatase activity with a fluorogenic stain demonstrated that alkaline phosphatase activity was concentrated in distinct bands adjacent to the gaseous interfaces. These bands were approximately 30 micron thick with biofilms grown in air, 2 micron thick with biofilms grown in pure nitrogen, and 46 micron thick with biofilms grown in pure oxygen. Overall biofilm thickness ranged from approximately 117 to approximately 151 micron. Measurements with an oxygen microelectrode indicated that oxygen was depleted locally within the biofilm and that the oxygen-replete zone was of a dimension similar to that of the biologically active zone, as indicated by alkaline phosphatase induction. These experiments revealed marked spatial physiological heterogeneity within P. aeruginosa biofilms in which active protein synthesis was restricted by oxygen availability to the upper 30 micron of the biofilm. Such physiological heterogeneity has implications for microbial ecology and for understanding the reduced susceptibilities of biofilms to antimicrobial agents.

Simultaneous measurement of blood and brain microdialysates of granisetron in rat by high-performance liquid chromatography with fluorescence detection

Simultaneous microdialysis probes in the blood and brain and sensitive high-performance liquid chromatography with fluorescence detection were used to examine the granisetron concentration in the jugular vein and frontal cortex of rats after drug administration. Two microdialysis probes were inserted into the right jugular vein and frontal cortex of male Sprague-Dawley rats to which granisetron (6 mg/kg, i.v.) had been administered. Dialysates were automatically collected using a microfraction collector. Samples were eluted with a mobile phase containing 25 mM acetate buffer (pH 4.8)-acetonitrile (72:28, v/v). Excitation and emission wavelengths were set at 305 and 360 nm, respectively, on a scanning fluorescence detector. The limit of quantification for granisetron was 0.5 ng/ml. The in vitro recovery of granisetron was 29.7+/-1.2% (n=6) for the jugular vein microdialysis probe and 6.1+/-0.5% (n=6) for the frontal cortex microdialysis probe. The increasing brain/blood concentration ratio of granisetron suggests that granisetron penetrates the blood-brain barrier.

Feasibility study of a mechanical suturing device for less invasive mitral operations

BACKGROUND

Because of smaller incisions and limited exposure, less invasive operations on the mitral valve can be arduous and time-consuming. This study examined the feasibility of a mechanical suturing device to facilitate less invasive mitral replacement.

METHODS

Five mongrel dogs underwent limited left thoracotomy. After conventional cardiopulmonary bypass and cardioplegia, the mitral valve was exposed through a left atriotomy. After excision of the anterior leaflet, subannular sutures were placed using a mechanical suturing device. This device simultaneously passes two ends of a pledgeted 2-0 braided suture through the valvular annulus, then mechanically grasps both needles on the atrial aspect. Hence, a mattress suture is accomplished one-handed in a single continuous motion. This procedure was repeated around the entire annulus. A mechanical valve was seated and the sutures were tied and cut.

RESULTS

All mechanical valves were implanted successfully. In the 4 animals in which it was attempted, cardiopulmonary bypass was successfully weaned. No evidence of perivalvular leak was observed by echocardiography.

CONCLUSIONS

These data establish the feasibility of a mechanical suturing device for operations on the mitral valve. The device is easily mastered, maintains precise spacing between sutures, and permits rapid placement of mattress sutures. We predict widespread application for both less invasive and conventional valve operations.

Spatial patterns of alkaline phosphatase expression within bacterial colonies and biofilms in response to phosphate starvation

The expression of alkaline phosphatase in response to phosphate starvation was shown to be spatially and temporally heterogeneous in bacterial biofilms and colonies. A commercial alkaline phosphatase substrate that generates a fluorescent, insoluble product was used in conjunction with frozen sectioning techniques to visualize spatial patterns of enzyme expression in both Klebsiella pneumoniae and Pseudomonas aeruginosa biofilms. Some of the expression patterns observed revealed alkaline phosphatase activity at the boundary of the biofilm opposite the place where the staining substrate was delivered, indicating that the enzyme substrate penetrated the biofilm fully. Alkaline phosphatase accumulated linearly with time in K. pneumoniae colonies transferred from high-phosphate medium to low-phosphate medium up to specific activities of 50 mumol per min per mg of protein after 24 h. In K. pneumoniae biofilms and colonies, alkaline phosphatase was initially expressed in the region of the biofilm immediately adjacent to the carbon and energy source (glucose). In time, the region of alkaline phosphatase expression expanded inward until it spanned most, but not all, of the biofilm or colony depth. In contrast, expression of alkaline phosphatase in P. aeruginosa biofilms occurred in a thin, sharply delineated band at the biofilm-bulk fluid interface. In this case, the band of activity never occupied more than approximately one-sixth of the biofilm. These results are consistent with the working hypothesis that alkaline phosphatase expression patterns are primarily controlled by the local availability of either the carbon and energy source or the electron acceptor.

Enhancement of analgesic effect of intrathecal neostigmine and clonidine on bupivacaine spinal anesthesia

BACKGROUND AND OBJECTIVES

Intrathecal administration of neostigmine has been shown to produce analgesia in both animals and humans. The concurrent administration of intrathecal neostigmine and clonidine has been reported to produce no neurotoxicity in sheep. The purpose of the present study was to evaluate the efficacy and safety of the combining intrathecal neostigmine and clonidine for the relief of pain in patients after cesarean delivery.

METHODS

After giving their consents, 80 parturients who were scheduled for cesarean delivery during spinal anesthesia were enrolled by a double-blind randomized design into four groups: bupivacaine group (n = 20) received intrathecal (i.t.) 10 mg bupivacaine; bupivacaine + neostigmine group (n = 19) received i.t. 10 mg bupivacaine + 50 microg neostigmine; bupivacaine + clonidine group (n = 20) received i.t. 10 mg bupivacaine + 150 microg clonidine; and bupivacaine + both (n = 21) received i.t. 10 mg bupivacaine + 50 microg neostigmine + 150 microg clonidine. The maximum spread of anesthesia, duration of analgesia and motor block, vital signs, and incidence of adverse effects were recorded for 14 hours postinjection. Fifty milligrams intramuscular meperidine was given as a rescue analgesic whenever patient's pain score was greater than 5/10 by the visual analog scale.

RESULTS

The demographic data were similar for all four groups. Bupivacaine + both group had a significantly higher maximum spread of anesthesia of 23.3 +/- 2.9 segments than bupivacaine group of 20.5 +/- 2.9 segment. Bupivacaine + both group showed a later onset of postsurgical pain of 6.5 +/- 1.5 hours as compared to bupivacaine group of 1.3 +/- 0.6 hours. The pain score in bupivacaine + both group was significantly lower than that of bupivacaine group during the first 10 hours. The 24-hour meperidine consumption also was lower in bupivacaine + both group than that of bupivacaine group. However, motor block was significantly prolonged from 3.5 +/- 1.1 hours in bupivacaine group to 7.1 +/- 1.6 hours in bupivacaine + both group. In addition, other side effects such as nausea and vomiting and dizziness were significantly increased in bupivacaine + both group.

CONCLUSION

Our study showed that the combination of 150 microg i.t. clonidine and 50 microg neostigmine provided longer postsurgical analgesia than with either drug used alone. However, this combination also produced significantly more adverse effects of prolonged motor block and nausea and vomiting. A further study combining the two study drugs but using a lower dose of i.t. neostigmine (e.g., 25 microg) is recommended.

Central nervous system infection due to Clostridium septicum: a case report and review of the literature

A patient with end stage breast cancer was admitted to hospital due to fever, chills, multiply eroded discharging wounds, and sudden onset of left hemiparesis. Clostridium septicum bacteremia and brain abscess were diagnosed. The patient was treated successfully with intravenous penicillin and clindamycin and stereotactic aspiration of the abscess. Eleven cases of C. septicum central nervous system infection are reviewed. They showed an extremely fulminant course and high fatality. Nevertheless, some relationship seems to exist between outcome and type of brain lesion. Hemolytic-uremic syndrome associated with central nervous system infection is also discussed, because all these cases in the literature were due to this organism. Early diagnosis and aggressive treatment, including surgical drainage and appropriate antibiotics, are the key to improving the prognosis. A long-term prophylactic oral antimicrobial agent is suggested for patients who survive this infection.

Recurrent epistaxis following nasotracheal intubation--a case report

Epistaxis is one of the common complications of nasotracheal intubation. Clinical patterns of all nasal bleeding are mild and may stop spontaneously in most patients. Serious nasal bleeding requiring hospitalization are rare. Nasal bleeding occurs more frequently in children than in adults. Among adults, men have a higher incidence than women. Although numerous publications have reported the cases of initial epistaxis caused by nasotracheal intubation, recurrent epistaxis was reported rarely. We experienced a case of recurrent epistaxis occurring in the 6th, 8th, 15th and 18th day after nasotracheal intubation. Herein, we describe the clinical events and discuss the causes of epistaxis.

Increasing antibiotic resistance in clinical isolates of Aeromonas strains in Taiwan

A total of 234 clinical isolates of Aeromonas, primarily A. hydrophila, were collected for the present study. Most were isolates from blood. By the agar dilution method, more than 90% of the Aeromonas strains were found to be susceptible to moxalactam, ceftazidime, cefepime, aztreonam, imipenem, amikacin, and fluoroquinolones, but they were more resistant to tetracycline, trimethoprim-sulfamethoxazole, some extended-spectrum cephalosporins, and aminoglycosides than strains from the United States and Australia.

Spatial variations in growth rate within Klebsiella pneumoniae colonies and biofilm

The use of acridine orange to visualize and quantify spatial variations in growth rate within Klebsiella pneumoniae colonies and biofilm was investigated. Bacterial colonies supported on polycarbonate filter membranes were grown on R2A agar plates. Some colonies were sampled for cell enumeration, while others were cryoembedded, sectioned, and stained with the fluorescent nucleic acid stain acridine orange. Spatial patterns of fluorescent color and intensity with depth in the colony were quantified using confocal microscopy and image analysis of stained cross sections. Colonies sampled in the midexponential phase were thin (20 microns), had high average specific growth rates (> 1 h-1), and had all the cells stained bright orange. Colonies sampled after more than 24 h of growth were thick (> 200 microns) and were growing slowly (mu < 0.15 h-1). These older colonies were characterized by distinct bands of orange at the colony edges and a dark green center. Stained biofilm cross sections displayed a similar orange band at the biofilm-bulk fluid interface and a green interior. Colony-average specific growth rates, determined by calculating the local slope of the cell accumulation versus time data, were correlated with colony-average fluorescence intensities. There was no correlation between average specific growth rate and orange or green intensity individually, but growth rate did correlate with the orange:green intensity ratio (r2 = 0.57). The resulting regression was used to predict specific growth rate profiles within colonies. These profiles indicated that bacteria were growing rapidly near the air and agar interfaces and more slowly in the center of the colonies when thicker than about 30 microns. The dimension of the orange bands ranged from 10 to 30 microns, which may indicate the thickness of growing regions. The inherent variability associated with this technique suggests that it is best applied in single species systems and that the results should be regarded as qualitative in nature.