Joe E. Coward

Properties of Silver Sulfadiazine-Resistant Enterobacter cloacae

Two silver sulfadiazine-resistant isolates of Enterobacter cloacae obtained in a burns unit where the drug was in use were studied. These strains were resistant to elevated levels of the drug, and they were cross-resistant to silver benzoate, but not to silver nitrate. Growth of the strains in nutritionally poor defined media sensitized them to the inhibitory action of the drug. Exposure of the bacteria to penicillins rendered them susceptible to silver sulfadiazine. The resistant bacteria harbored episomes for resistance to carbenicillin and kanamycin; however, resistance to silver sulfadiazine could not be transferred by these episomes. Twenty-three strains of E. cloacae isolated in a general hospital were sensitive to much lower levels of the drug (≤50 μg/ml).

Electron microscopic observations of visna virus-infected cell cultures.

Abstract Electron microscopic observations of three cell lines infected with visna virus revealed two types of extracellular particles. The smaller of these was 65–110 mμ in diameter and contained a 20–30 mμ electron-dense core. Ordered arrays of the latter type of particle occurred rarely in the cytoplasm. After cesium chloride density gradient centrifugation of the virus, the band that contained maximal infectivity was composed of numerous particles with osmiophilic cores similar to those found in infected cell cultures. This finding suggests that such particles represent the infective agent. The second type of extracellular particle was larger (100–140 mμ in diameter), lacked an electron-dense core, and contained material similar in appearance to cellular cytoplasm. This form appeared to develop by budding from the cell surface.

Silver Sulfadiazine: Effect on the Ultrastructure of Pseudomonas aeruginosa

Pseudomonas aeruginosa exposed to silver sulfadiazine (AgSu) were examined in an electron microscope. The treated cells were distorted in shape, and structures (blebs) protruded from the cell surface. These “blebs” appeared to arise from the cell wall. A strain of P. aeruginosa resistant to AgSu did not display these changes. Upon exposure of P. aeruginosa to silver nitrate, none of these changes was seen; rather, such cells are characterized by large, central aggregations of nuclear material. The results are consistent with previous findings which suggested that AgSu acted at the cell surface. Images

Silver Sulfadiazine: Effect on the Growth and Ultrastructure of Staphylococci

Clinical isolates of Staphylococcus aureus and S. epidermidis were sensitive to levels of silver sulfadiazine (AgSu) that can readily be achieved topically. As a

Electron microscopic study of the development of herpesvirus saimiri

Abstract Electron microscopic study of herpesvirus saimiri in thin sections of infected OMK and Vero cells showed the apparent intranuclear envelopment of capsids by membranes of vesicles. Clusters of filaments were also encountered. Numerous unenveloped intracytoplasmic capsids were observed in cells devoid of nuclear changes, raising the possibility that differentiation can occur within the cytoplasm.

Electron Microscopic Appearance of Silver Sulfadiazine-Treated Enterobacter cloacae

Upon exposure of Enterobacter cloacae silver sulfadiazine, a number of ultrastructural changes involving the cell envelope take place. Foremost among these is a modification of the cell wall from an undulating structure to one which is smooth and has become enlarged. Strains of E. cloacae resistant to silver sulfadiazine do not exhibit these changes.

Effect of Hydroxyurea on Staphylococcus epidermidis and Micrococcus lysodeikticus: Thickening of the Cell Wall

Hydroxyurea-sensitive strains of Staphylococcus epidermidis and Micrococcus lysodeikticus showed marked thickening of cell walls and reduction in deoxyribonucleic acid synthesis when grown in the presence of hydroxyurea. Images

An Effect of Hydroxyurea on Staphylococcus epidermidis: Temporary Loss of Viability

Although hydroxyurea (HU) is recognized as a specific inhibitor of deoxyribonucleic acid (DNA) synthesis, it did not have this effect in a strain of Staphylococcus epidermidis. In this case, HU caused a loss of colony-forming ability but did not prevent cell division in liquid medium. DNA synthesis apparently was affected only secondarily. About 10% of the population recovered colony-forming ability during the latter part of the growth cycle or when growth was slowed by chloramphenicol. Recovery also occurred when HU was removed from the medium. HU prevented cellular autolysis.

More on mutants with altered DNA's

Abstract A “DNA-base composition mutant” (No. 170) of Bacterium paracoli 5099 is identified as a member of the genes Bacillus. This suggests that the “mutant” is in reality a contaminant.