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Biomedical subjects

M A Levin

Publications and source records attributed to M A Levin.

18 recordsLinked to original sources
PubMed1994

Pseudomonas aureofaciens in soil: survival and recovery efficiency.

Efficient methods for the recovery of genetically engineered organisms (GEM) added to soil are critical if the safety of potential releases is to be evaluated and the actual release is to be monitored. Pseudomonas aureofaciens strain 3732 RN-L11 (lacZY) was added to 10 g sieved soil microcosms and incubated for 5 and 28 days. Various diluents, shaking methods, and settling of soil were examined to determine the optimum method for recovery of the GEM from the soil. Of the diluents examined, 0.1% agar gave significantly lower numbers than distilled water, 1.0% sodium metaphosphate, 1% peptone, and phosphate-buffered water. After 5 days of incubation, shaking for 10 min with glass beads and shaking for 30 min without glass beads resulted in the highest recovery of the GEM from soil, while sonification resulted in the lowest recovery. After 28 days of incubation, sonification produced significantly lower numbers than any of the other treatments. The addition of 1% CaCl2 to enhance settling significantly increased recovery efficiency. Although the use of CaCl2 in distilled water and shaking for 10 min was an effective method for recovering P. aureofaciens from a Maryland soil, when the same extraction procedure was compared with a standard technique (dd H2O, shaking for 10 min) for eight divergent soils, neither extraction method was consistently better than the other. Statistical analysis of the data showed the need for log transformation of the raw data. Four microcosm and two plate replicates for each dilution provided the greatest ability to detect differences between treatment means while maximizing experimental efficiency.

Calcium Chloride↗
PubMed1982

Swimming-associated gastroenteritis and water quality.

A direct, linear relationship between swimming-associated gastrointestinal illness and the quality of the bathing water was obtained from a multi-year, multiple-location prospective epidemiologic-microbiologic research program conducted in New York City, 1973-1975, Lake Pontchartrain, Louisiana, 1977-1978, and Boston, Massachusetts, 1978. Several microbial indicators were used in attempting to define the quality of the water; and, of those examined, enterococci showed the best correlation to total and "highly credible" gastrointestinal symptoms. The frequency of gastrointestinal symptoms also had a high degree of association with distance from known sources of municipal wastewater. A striking feature of the relationship was the very low enterococcus and Escherichia coli densities in the water (10/100 ml) associated with appreciable attack rates (about 10/1000 persons) for "highly credible" gastrointestinal symptoms. Moreover, the ratio of the swimmer to nonswimmer symptom rates indicated that swimming in even marginally polluted marine bathing water is a significant route of transmission for the observed gastroenteritis.

Bacteria↗
PubMed1981

A histochemical and electron microscopic study of a fast- and a slow-twitch muscle in genetically spastic mice.

Fast and slow muscle fibers were studied in the flexor digitorum longus (FDL) and soleus (SOL) muscles, respectively, in control and spastic mice. HIstochemical and electron microscopic studies indicated an increased number of mitochondria, a decreased deposition of glycogen and a vesiculation and distension of the sarcoplasmic reticulum in many fast-twitch fibers of the spastic FDL. Similar findings were not evident in the slow-twitch fibers of the spastic SOL. Since the spastic condition causes increased muscular activity as a result of more rapid and prolonged nerve impulse firing, these findings reinforce the idea that a muscle fiber's oxidative capabilities are a function of its activity.

Adenosine Triphosphatases↗
PubMed1981

Quantitative procedure for enumeration of bifidobacteria.

A membrane filter technique has been developed for the enumeration of bifidobacteria in natural aquatic environments. The technique is quantitative, selective, and differential. The medium (YN-6) contains: yeast extract, 2.0 g; agar, 1.5 g; polypeptone peptone, 1.0 g; vitamin-free Casamino Acids, 0.8 g; sodium chloride, 0.32 g; and L-cysteine hydrochloride, 0.003 g; in 100 ml of deionized water. The medium is adjusted to pH 7.0 before autoclaving. Nalidixic acid (80 micrograms/ml), neomycin sulfate (2.5 micrograms/ml), and bromcresol green (300 micrograms/ml) are included as selective and differential agents. After incubation for 48 h at 37 degrees C in an anaerobic environment, Gram-stained smears from green, glistening, smooth entire colonies are examined microscopically for typical bifidobacterial morphology. No significant difference in recoveries was observed when YN-6 was compared with reinforced clostridial agar, using bifidobacteria freshly isolated from feces and raw sewage. Using this technique with aquatic and fecal samples, less than 9% false-positive and 8% false-negative isolates were observed. These results indicated that the medium was able to satisfactorily recover organisms from a variety of situations.

Actinomycetaceae↗
PubMed1981

Assessment of bifidobacteria as indicators of human fecal pollution.

The distribution of bifidobacteria in the environment has been examined by using YN-6 medium. Although feces of humans, chickens, cows, dogs, pigs, horses, cats, sheep, beavers, goats, and turkeys were examined, bifidobacteria were isolated only from the feces of humans and swine. The frequency and distribution of component species of human fecal isolates were as in isolates from raw sewage. Bifidobacterium longum and B. adolescentis were most often isolated and in the highest densities. The levels of bifidobacteria in raw sewage were in the range of 10(6) organisms/100 ml, and the effect of primary and secondary sewage treatment on the number of viable organisms present was not significant. High densities of bifidobacteria were found in all samples from septic tanks. It was found that bifidobacteria did not survive as well as Escherichia coli in either fresh or marine waters. The ratio of bifidobacteria to E. coli is an indication of the age and of the effectiveness of treatment of sewage effluent.

Actinomycetaceae↗
PubMed1981

Quantitative method for enumeration of enterotoxigenic Escherichia coli.

A rapid method was developed to quantify toxigenic Escherichia coli, using a membrane filter procedure. After filtration of samples, the membrane filter was first incubated on a medium selective for E. coli (24 h, 44 degrees C) and then transferred to tryptic soy agar (3%; 6 h, 37 degrees C). To assay for labile toxin-producing colonies, the filter was then transferred to a monolayer of Y-1 cells, the E. coli colonies were marked on the bottom of the petri dish, and the filter was removed after 15 min. The monolayer was observed for a positive rounding effect after a 15- to 24-h incubation. The method has an upper limit of detecting 30 toxigenic colonies per plate and can detect as few as one toxigenic colony per plate. A preliminary screening for these enterotoxigenic strains in polluted waters and known positive fecal samples was performed, and positive results were obtained with fecal samples only.

Bacteriological Techniques↗
PubMed1979

Relationship of microbial indicators to health effects at marine bathing beaches.

Findings are described from the second year of an epidemiological-microbiological study conducted at New York City beaches as part of the U.S. Environmental Protection Agency program to develop health effects-recreational water quality criteria. Symptomatology rates among swimmers (defined as immersion of the head in the water) relative to nonswimming but beach-going controls at a "barely acceptable" (BA) beach and a "relatively unpolluted" (RU) beach were examined. Data were collected by contacting family groups at the beach on weekends, obtaining information on bathing activity, and then questioning them by phone some 8--10 days later. In addition measurements were made for a number of potential water quality indicators. It was observed that the symptom rates, categorized as gastrointestinal (GI), respiratory, "other", and "disabling" (stayed home, stayed in bed, consulted a physician), were higher among swimmers than nonswimmers. As in the pretest conducted the previous year, the rate of GI symptoms was significantly higher among swimmers relative to nonswimmers at the BA but not the RU beach. Children, Hispanic Americans, and the low-middle socioeconomic groups were identified as the most susceptible portions of the population.

Adolescent↗
PubMed1976

Neural-tube defects caused by 5-bromodeoxyuridine in chicks.

Chick embryos were explanted at HH stage 4 and cultured for 24 h on thin albumen with 10 mug/ml 5-bromodeoxyuridine (BrdU). BrdU inhibited closure of the neural tube in over 90% of the embryos. Mitotic figures were found throughout adversely effected neuroepithelium, suggesting that interkinetic nuclear migration had been inhibited. Electron microscopic studies of BrdU-treated neural-tube cells showed fewer and more amorphous cytoplasmic extensions, microfilaments, and demosomal (juctional) tonofibrils than in controls, but microtubules were unaffected.

Abnormalities, Drug-Induced↗
PubMed1975

Membrane filter technique for enumeration of enterococci in marine waters.

A membrane filter procedure is described for the enumeration of enterococci in marine waters. The procedure utilizes a highly selective and somewhat differential primary isolation medium followed by an in situ substrate test for identifying colonies of those organisms capable of hydrolyzing esculin. The procedure (mE) was evaluated with known streptococci strains and field samples with regard to its accuracy, sensitivity, selectivity, precision, and comparability to existing methods. Essentially quantitative recovery was obtained with seawater-stressed cells of Streptococcus faecalis and S. faecium. Neither S. bovis, S. equinus, S. mitis, nor S. salivarius grew on the medium. The selectivity of the medium was such that a 10,000-fold reduction in background organisms was obtained relative to a medium which contained no inhibitors and was incubated at 35 C. About 90% of those typical colonies designated as enterococci confirmed as such and about 12% of the colonies not so designated were, in fact, identified as enterococci. Plate to plate variability across samples approximated that expected by chance alone. Verified recoveries of enterococci from natural samples by the mE procedure, on the average, exceeded those by the KF method by one order of magnitude.

Cell Count↗
PubMed1974

Quantitative large-volume sampling technique.

A filtration technique for high-volume sampling of water has been developed that, when combined with the most probable number procedure, permits the quantitation of microorganisms present at very low densities.

Bacteriological Techniques↗
PubMed1972

Membrane filter technique for enumeration of Pseudomonas aeruginosa.

A membrane filter procedure for the quantitation of Pseudomonas aeruginosa (mPA procedure) has been developed. Through the use of inhibitors and an elevated incubation temperature, the level of background microbial flora was decreased approximately 10,000-fold. Using P. aeruginosa cells suspended in sea water and held for 24 hr, between 70 and 100% of the "viable" cells could be recovered by the mPA procedure. Assay variability was found to be insignificant. The recoveries of P. aeruginosa from surface (fresh and salt) waters, potable waters, and sewage by the mPA procedure exceeded those obtainable by current methods. Subsequent to its development and evaluation, the mPA procedure was used at three other laboratories for the enumeration of P. aeruginosa in potable and recreational waters and in sewage samples. It was found amenable to routine use, and confirmation of typical colonies approached 100%.

Bacteriological Techniques↗