Phosphatidylcholine-specific phospholipase C and sphingomyelinase activities in bacteria of the Bacillus cereus group.

Bacillus anthracis is nonhemolytic, even though it is closely related to the highly hemolytic Bacillus cereus. Hemolysis by B. cereus results largely from the action of phosphatidylcholine-specific phospholipase C (PC-PLC) and sphingomyelinase (SPH), encoded by the plc and sph genes, respectively. In B. cereus, these genes are organized in an operon regulated by the global regulator PlcR. B. anthracis contains a highly similar cereolysin operon, but it is transcriptionally silent because the B. anthracis PlcR is truncated at the C terminus. Here we report the cloning, expression, purification, and enzymatic characterization of PC-PLC and SPH from B. cereus and B. anthracis. We also investigated the effects of expressing PlcR on the expression of plc and sph. In B. cereus, PlcR was found to be a positive regulator of plc but a negative regulator of sph. Replacement of the B. cereus plcR gene by its truncated orthologue from B. anthracis eliminated the activities of both PC-PLC and SPH, whereas introduction into B. anthracis of the B. cereus plcR gene with its own promoter did not activate cereolysin expression. Hemolytic activity was detected in B. anthracis strains containing the B. cereus plcR gene on a multicopy plasmid under control of the strong B. anthracis protective antigen gene promoter or in a strain carrying a multicopy plasmid containing the entire B. cereus plc-sph operon. Slight hemolysis and PC-PLC activation were found when PlcR-producing B. anthracis strains were grown under anaerobic-plus-CO(2) or especially under aerobic-plus-CO(2) conditions. Unmodified parental B. anthracis strains did not demonstrate obvious hemolysis under the same conditions.

Genetic and molecular R-plasmid analysis of Enterobacteriaceae hospital strains at Children's Hospitals of the former USSR.

R-plasmids from Enterobacteriaceae clinical strains, mainly Klebsiella and Serratia, isolated at different neonatal and children's hospitals of different cities of the former USSR for 10 years, were studied for their possible influence on the bacterial host phenotype. Hospital R-plasmids of stable inheritance persisted in hospitals from 2 to 7 years and were disseminated among strains of different genera (Klebsiella, Serratia, Enterobacter) and among different units. The data showed a possibility of long-term molecular rearrangements of R-plasmids in the hospital settings and an acquisition of genetic determinants encoding enterotoxin production. A novel R-plasmid encoding cytotoxicity to HEp-2 cells involved in two nosocomial outbreaks due to K. pneumoniae strains was reported. K. pneumoniae population heterogeneity was evaluated by using the plasmid parameters of strains. Their heterogeneity of a bacterial population was significantly lower during nosocomial outbreaks than in interepidemic periods.

[The incidence of finding and characteristics of Klebsiella pneumoniae strains isolated in neonatal infections]. / Chastota vstrechaemosti i kharakteristika shtammov Klebsiella pneumoniae, vydelennykh pri infektsiiakh novorozhdennykh.

The clinical and laboratory study of 190 hospitalized children revealed that in 122 cases the course of the underlying disease was complicated by Klebsiella infection. From different pathological material obtained from 122 patients 158 K. pneumoniae cultures were isolated. These cultures were mostly isolated from the respiratory organs (69%), from patients with the generalized infection (21.6%), and less frequently from operative wounds and burn surfaces (5.8%), the gastrointestinal tract (1.4%) and the urinary system (1.4%). The isolated clinical strains were multiresistant to antibiotics and contained plasmid DNA with molecular weights of 70 and 105 MD (60.4%). K. pneumoniae were shown to produce an aggravating effect on the course and outcome of the underlying disease, mainly in preterm babies or those born asphyxiated or with congenital defects of development, as well as in patients with immunodeficient states. The probability of infection was directly related to the character and number of medical manipulations on an infant, mainly in connection with artificial ventilation of the lungs and transfusion therapy.

[The resistance plasmid of Klebsiella pneumoniae that controls its cytotoxic activity]. / Plazmida rezistentnosti Klebsiella pneumoniae, kontroliruiushchaia tsitotoksicheskuiu aktivnost'.

R-plasmid (40 MD) isolated from K. pneumoniae hospital strain makes Escherichia coli strain J62 capable of inducing a cytotoxic effect which can be detected in Hep-2 cell culture. In contrast to the initial E. coli strain J62 producing no changes in the monolayer, E. coli J62 cells containing P-plasmid induced pronounced cytotoxic changes and a sharp increase in the number of nonviable Hep-2 cells by hour 24 of interaction.

[A new site-specific endodeoxyribonuclease EcoHI]. / Novaia saitspetsificheskaia éndodezoksiribonukleaza EcoHI.

A new sitespecific endonuclease of the II class EcoHI has been isolated from Escherichia coli strain and characterized. Restriction endonuclease EcoHI recognises the nucleotide sequence C C (C/G) G G with the cleavage site between the fourth and fifth nucleotide. It is an isoshizomer of the restriction endonuclease CauII. The yield of enzyme is 2500 units of activity per 1 g of biomass. The producing strain Escherichia coli HI is nonpathogenic, easily grown with the antibiotic resistance markers permitting to cultivate the strain under selective conditions.

[The role of R plasmids in the resistance of bacteria in air]. / Rol' R-plazmid v rezistentnosti bakterii v vozdukhe.

The study of Escherichia coli J 53, used as a model, has revealed that some R plasmids isolated from Serratia marcescens and Klebsiella pneumoniae, found to be the cause of the outbreak of hospital infection, ensure, besides multiple drug resistance, also their viability in the air.