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Biomedical subjects

V Lorian

Publications and source records attributed to V Lorian.

At least 73 records · Page 4Linked to original sources
PubMed1978

Effect of serum on gram-positive cocci grown in the presence of penicillin.

Strains of Staphylococcus aureus, Streptococcus faecalis, Streptococcus bovis, and a strain of Streptococcus that produces filaments were grown on agar containing penicillin at concentrations of one-half to 1/10th the minimal inhibitory concentration. These penicillin-exposed organisms as well as untreated control organisms were incubated with human serum of plasma. Both serum and plasma produced a remarkable bactericidal effect on the filament-forming Streptococcus grown in the presence of penicillin, whereas the untreated control was only slightly affected. This response resembled that of gram-negative bacilli rather than that of gram-positive cocci. The growth of staphylococci exposed to penicillin was slightly inhibited in the presence of serum, whereas the growth of untreated staphylococci was stimulated. The streptococci, regardless of whether they were treated with penicillin or whether they were untreated, showed no change in growth pattern in the presence of serum.

Agar↗
PubMed1977

Comparison of the effects of mecillinam and 6-aminopenicillanic acid on Proteus mirabilis, Escherichia coli, and Staphylococcus aureus.

Single strains of Proteus mirabilis, Escherichia coli, and Staphylococcus aureus were grown on filter membranes placed on agar containing concentration series of mecillinam (FL 1060), 6-aminopenicillanic acid (6-APA), or ampicillin. P. mirabilis and E. coli were also exposed to combinations of mecillinam or 6-APA with ampicillin. Colony-forming units were counted, and cells were examined by interference phase-contrast and transmission electron microscopy. Mecillinam and 6-APA were very effective in reducing the viability of the two gram-negative species, but they were less effective against S. aureus. Combinations of mecillinam and 6-APA with ampicillin acted synergistically against the gram-negative bacilli. When the antibiotics were presented consecutively, their effects on viability were usually no greater than the effects of the individual antibiotics acting alone. When P. mirabilis and E. coli were exposed to mecillinam alone or in combination with ampicillin, the cells became rounded. 6-APA alone or in combination with ampicillin produced elongated polymorphic cells in these species. The most unusual morphological effects were ultrastructural. Mecillinam and, to a lesser extent, 6-APA produced inward growth of numerous pairs of trilamellar membranous structures within the cells. It is possible that these membranes represent the growth initiation of aberrant cross walls. Both mecillinam and 6-APA produced multiple, thick cross walls in S. aureus.

Ampicillin↗
PubMed1977

[Subinhibitory concentrations of antibiotics. Effects on morphology and growth (author's transl)].

Experiments with subinhibitory concentrations of antibiotics revealed certain effects that had not been observed at higher concentrations. Two different effects are described: morphological changer and inhibition of growth. The expression minimum antibiotic concentration (MAC) has been shown to be of both theoretical and practical value. It has served to make plain the differences between the effects of various antibodies that were not observed at the MIC. The ratio MAC/MIC could be be of importance to characterize the effect of antibiotics.

Ampicillin↗
PubMed1976

Agglutination with O antisera of salmonella exposed to antibiotics.

Five strains of Salmonella were grown on agar containing subinhibitory concentrations of ampicillin, gentamicin, tetracycline, or chloramphenicol, and on drug-free agar (control). Antigens were prepared by heating bacteria suspensions in saline solution at 100 C or by suspension in alcohol. Antigens were tested for agglutinability with somatic O antisera and fluorescent antibody staining. The alcohol-treated antigens prepared from organisms grown in the presence of antibiotics other than ampicillin had lower agglutination titers than did the control grown on drug-free agar. Heat-treated control antigens had lower agglutination titers than did the alcohol-treated control antigens. The agglutinability of heat-treated antigens prepared from organisms that had been exposed to antibiotics was preserved or enhanced. The agglutinated filaments produced a flocculent sediment, in contrast to the granular sediment of the controls. No significant morphologic abnormality in cell-wall structures of antibiotic-exposed cells could be detected by either electron microscopy or the fluorescent antibody staining.

Agglutination Tests↗
PubMed1976

Effects of subinhibitory concentrations of antibiotics on cross walls of cocci.

Cultures of Staphylococcus aureus, Neisseria gonorrhoeae, and Streptococcus bovis were incubated on membrane filters on agar containing antibiotics at one-third to one-fourth the minimal inhibitory concentration for the particular bacterial strain. S. aureus was grown in the presence of oxacillin, cephaloridine, or lincomycin. N. gonorrhoeae and S. bovis were grown in the presence of penicillin. The membranes were then incubated in drug-free agar, after which viability was determined and the cells were examined by electron microscopy. S. aureus exposed to oxacillin and cephaloridine grew into cells two to seven times larger than normal that contained thick multiple cross walls. S. aureus exposed to lincomycin grew into cells 1.5 to 2 times larger than normal, with multiple thick cross walls and periheral cell walls twice the normal thickness. N. gonorrhoeae cells exposed to penicillin were slightly larger than normal and had cross walls that were up to eight times thicker than normal. After transfer to drug-free agar, cells became smaller, and some normal organisms could be seen. S. bovis incubated in the presence of penicillin grew into filaments that contained no cross walls. Two hours after the return to drug-free agar, filaments with cross walls as well as normal cells were observed. Exposure to subinhibitory concentrations of penicillin did not affect the growth of the peripheral cell wall of S. aureus, N. gonorrhoeae, or S. bovis, but appeared to inhibit lysis of cross walls in S. aureus and N. gonorrhoeae and to inhibit the synthesis of cross walls in S. bovis; that is, the rates of peripheral and cross wall formation differed in their susceptibility to penicillin. These facts suggest that peripheral growth and cross wall formation in cocci are separable processes.

Anti-Bacterial Agents↗
PubMed1975

Abnormal forms of bacteria produced by antibiotics.

Subinhibitory concentrations of antibiotics can produce in vitro aberrant forms of bacteria that are similar to those observed in specimens and cultures from patients being treated with antibacterial agents. Eight species of bacteria were grown on membranes placed on agar containing subinhibitory concentrations of nine antibiotics. The resulting organisms were examined by Gram stain and electron microscopy. Gram stains showed filamentous and granular forms of enterobacteria with bipolar staining, giant staphylococci, and rodlike pneumococci. Electron micrographs showed changes in the number and distribution of ribosomes in enterobacteria and septum abnormalities in cocci. Such abnormal forms can occasionally simulate the appearance of quite different species, and they may indicate the presence of a subinhibitory antibiotic concentration at the site of infection as a result of prior antibacterial therapy.

Ampicillin↗
PubMed1975

Some effect of subinbilitory concentrations of penicillin on the structure and division of staphylococci.

A strain of Staphylococcus aureus was planted on filter membranes placed on Trypticase soy agar (BBL). After incubation, the membranes with growing staphylococci were transferred to Trypticase soy agar containing a subinhibitory concentration of penicillin (one-third minimal inhibitory concentration) and again incubated. The membranes were then returned to drug-free agar and incubated once more. Counts of the colony-forming units and electron microscopy were carried out at several time intervals. When grown on agar containing penicillin, the staphylococci formed what appeared to be abnormally large cells with multiple and unusually thick septa. Examination of a number of sections showed that these large cells were in reality clusters of staphylococci that had divided but failed to separate. When these large cells were subsequently grown on drug-free agar, smaller cells and normal staphylococci emerged. Subinhibitory concentrations of penicillin do not kill staphylococci; they seem to inhibit lysis of cross walls, preventing the separation of otherwise divided cells.

Cell Division↗
PubMed1975

Decrease in ribosomal density of Proteus mirabilis exposed to subinhibitory concentrations of ampicillin or cephalothin.

The finding of reduced ribosomal densities at lower concentrations than those required to stop growth or cause visible defects in the cell wall is in contrast to the current view that the initial lesion produced by penicillins or cephalosporins is a defect in murein synthesis (11). This reduction in ribosomal density could be a primary or secondary effect and might be due to a decreased rate of growth, which has been shown to be associated with a lower ribosome frequency (12, 13) or to less stable ribosomes which disintegrated either spontaneously or as a result of the fixation procedures. The possibility that the decrease in ribosomal frequency was due to dilution (influx of liquid through a defective cell wall and/or cytoplasmic membrane, or efflux of ribosomes) remains, but no gross defect in cell wall was seen in more than 50 sections of cells showing reductions in ribosomal frequency. These findings suggest that an effect on ribosomes may antecede an effect on the cell wall.

Ampicillin↗
PubMed1975

Susceptibility of newborn and adult guinea pigs to Mycobacterium intracellulare and M. kansasii.

Six groups of guinea pigs, each consisting of 30 3-month-old and 20 7-day-old animals, received intraperitoneal inoculations with one of four strains of Mycobacterium intracellulare or one of two strains of M. kansasii. Three similar control groups received either an intraperitoneal injection of M. tuberculosis, no injection, or a sterile injection. Guinea pigs were sacrificed at 3, 5, 10, 20, 30, and 90 days. Lungs, spleen, liver and peritoneal fluid were cultured. Lungs were also examined histologically for inflammatory response. All the guinea pigs sacrificed within 20 days after inoculation showed positive cultures at nearly all sites. Thirty days after inoculation significantly more of the young guinea pigs had positive cultures, and the distribution of mycobacteria in their tissues was wider than was observed with the adult animals. At 90 days, the bacteriological results were similar for both groups. This histological findings were generally similar for both age groups, although acute reactions persisted longer in the young animals. All guinea pigs injected with M. tuberculosis died spontaneously within 90 days after inoculation and showed positive cultures at all sites. The results of the present study indicate that young guinea pigs are more susceptible to M. intracellulare and M. kansasii than are adult animals and should be preferred to old animals for diagnostic inoculations.

Age Factors↗
PubMed1974

Technique for determining the bactericidal effect of drug combinations.

Two paper strips, each containing different antimicrobial agents, were placed on plates on Mueller-Hinton agar to permit antibiotic to enter the agar. A filter membrane was placed on this plate, and the microorganisms were planted on the membrane. After 6 h of incubation at 37 C, the membrane was transferred to antibiotic-free Mueller-Hinton agar containing triphenyltetrazolium hydrochloride and incubated for 18 h at 37 C. Specific growth patterns were indicative of additive (indifferent), synergistic, or antagonistic effects of the drug combination used. Trimethoprim and sulfamethoxazole proved to act synergistically against 85% of Escherichia coli, 86% of Klebsiella, and 89% of Proteus mirabilis strains tested. A few strains resistant to either drug were susceptible to their combination. The technique was useful against organisms with widely differing susceptibilities to the two antimicrobial agents tested.

Anti-Bacterial Agents↗
PubMed1973

Pneumococcal beta hemolysin produced under the effect of antibiotics.

The relationship between exposure of pneumococci to antibiotics and appearance of beta hemolysis (rather than the usual alpha hemolysis) was studied in 100 isolates. All strains were capable of producing beta hemolysis. This occurred at the edge of inhibition zones produced by methicillin and other antibiotics, but only if grown anaerobically and subsequently exposed to air at reduced temperatures. Autolysis of the pneumococci was necessary for the beta hemolysis to be produced. Beta hemolysis was optimal at pH 6.8; none occurred at pH 7.4. The concentration of red cells influenced the reaction: at 4% the extent of beta hemolysis was drastically reduced, which suggests that the lysin is not an enzyme.

Agar↗
PubMed1973

Disk test for the differentiation of pneumococci from other alpha-hemolytic streptococci.

One hundred twenty-five strains of Diplococcus pneumoniae and one hundred twenty-five strains of other alpha-hemolytic streptococci were planted on horse red cell-Brucella agar, and a disk of methicillin was placed on each inoculated plate. All strains were incubated anaerobically at 37 C for 24 h and then exposed to air at 6 C for 48 h. All strains of pneumococci produced a ring of beta-hemolysis surrounding the zone of inhibition produced with the methicillin disk, whereas no strain of alpha-hemolytic streptococci produced beta-hemolysis. It is suggested that this new criterion is useful for the differentiation of pneumococci from other alpha-hemolytic streptococci in those cases where other characteristics were insufficient for an unequivocal identification.

Aerobiosis↗
PubMed1972

Pneumococci producing beta hemolysis on agar.

Fifty-six strains of pneumococci were studied for hemolysis on blood-agar Twenty-two (39%) of these strains produced beta hemolysis on agar containing horse red cells, six (11%) were beta hemolytic for sheep cells, and none lysed human or rabbit red cells. The substance producing beta hemolysis appeared after 24 hr of anaerobic incubation. Subsequent exposure to air at low temperature (6 to 20 C) for 48 hr was needed to activate it. There was no relation between serological type and beta hemolysis production. This substance appears to be different from the pneumococcal hemolysin previously described.

Agar↗