Ingrid Kleber

Differences of two Borrelia burgdorferi strains in complement activation and serum resistance

Complement activation and serum resistance of the Borrelia burgdorferi strains B31 (American strain) and PKo (European strain) were compared. In 25% (v/v) normal human serum (NHS) free of B. burgdorferi-specific antibodies the cells of the PKo strain were high activators of complement as indicated by rapid and strong C9 consumption, by deposition of up to 336763 C9 molecules per cell and by the formation of the terminal complement complex on the cell surface. By comparison, complement activation by the B31 strain was low with 5.4-fold less C9 deposited per cell. The addition of B. burgdorferi-specific antibodies to NHS either as purified IgG or heat-inactivated patient sera, had no influence on the results with both strains. After an incubation period of 2h at 37 degrees C in 25% (v/v) NHS most cells of the PKo strain had lost their viability as indicated by cell immobilization and failure to multiply in subcultures. In addition, extensive cell fragmentation and bleb formation were observed in the electron microscope. In contrast, the B31 strain remained alive and morphologically intact after the same incubation with NHS. We conclude from our results that complement activation and serum resistance are properties which differ considerably between isolated strains of B. burgdorferi.

Ultrastructural Surface Alterations of Serratia marcescens after Exposure to Polymyxin B and/or Fresh Human Serum

Exposure of Serratia marcescens cells to 10, 5, and 2.5 mug/ml of polymyxin B resulted in outer cell surface alterations that consisted of coarse, pleomorphic projections which revealed a double-contoured membrane structure. In contrast, fresh, but not heat-inactivated human serum caused the deposition of very fine, thread-like aggregates on the outer cell surface of exposed cells. The combination of polymyxin B and fresh human serum caused clearly discernible ultrastructural changes of the polymyxin and the fresh serum type, respectively.

Selected and Spontaneous Variants of Serratia marcescens with Combined Resistance against Chloramphenicol, Nalidixic Acid, and Trimethoprim

Combined resistance against chloramphenicol (CHLOR), nalidixic acid (NA), and trimethoprim (TMP) was demonstrated in isolates and variants of a nosocomially significant, multiple-drug-resistant, nonconjugative strain of Serratia marcescens (bacteriocin type 18), either as a spontaneous event or after exposure of isolates and variants derived therefrom to increasing concentrations of CHLOR, NA, and TMP, respectively. This phenomenon was also noted among several selected mutants of two control strains of S. marcescens. The level of resistance was not absolute; the combined resistant mutants and variants were inhibited by 100–200 μg/ ml of CHLOR, 25–50 μg/ml of NA, and 12.5–25 μg/ml of TMP. However, the phenomenon of combined triple-resistance occurred irregularly with respect to the strain or variant of S. marcescens employed, and with regard to the selective drug utilized. Selection of mutants with CHLOR yielded a larger number of combined CHLOR-NA-TMP resistant mutants than selection with NA or TMP. Preliminary data obtained with spontaneously ‘cured’ variants of the multiple-drug-resistant strain of S. marcescens that had lost resistance against CHLOR, NA, TMP, penicillins, and aminoglycoside antibiotics, and which subsequently were shown to yield spontaneous mutants with combined triple-resistance against CHLOR, NA, and TMP, seem to indicate that this resistance phenomenon is not mediated extra-chromosomally, but rather chromosomally, and subject to phenotypic variation. The precise nature of this novel, unusual resistance mechanism against these three unrelated antimicrobial drugs remains to be elucidated.

In Vitro Additive Effect of Polymyxin B and Rifampin Against Serratia marcescens

The combination of polymyxin B and rifampin resulted in an additive effect against all 12 clinical isolates of Serratia marcescens examined, including multiple-drug-resistant isolates.

Detection of Fibrinolytic and Elastase Activity Among Clinical Isolates of Serratia Marcescens

Thirty-three of 35 clinical isolates of Serratia marcescens examined displayed fibrinolytic activity, whereas only 5 isolates elaborated a weakly active elastase. All strains liquef

Interpretation of Diffusion Susceptibility Data Obtained with 10-μg Fucidin (Sodium Fusidate) Disks against Clinical Isolates of Staphylococcus aureus

A total of 109 clinical isolates of Staphylococcus aureus as well as 2 isolates of S.epidermidis , 11 isolates of group A β -hemolytic streptococ