Survey of laboratory-acquired infections around the world in biosafety level 3 and 4 laboratories

Laboratory-acquired infections due to a variety of bacteria, viruses, parasites, and fungi have been described over the last century, and laboratory workers are at risk of exposure to these infectious agents. However, reporting laboratory-associated infections has been largely voluntary, and there is no way to determine the real number of people involved or to know the precise risks for workers. In this study, an international survey based on volunteering was conducted in biosafety level 3 and 4 laboratories to determine the number of laboratory-acquired infections and the possible underlying causes of these contaminations. The analysis of the survey reveals that laboratory-acquired infections have been infrequent and even rare in recent years, and human errors represent a very high percentage of the cases. Today, most risks from biological hazards can be reduced through the use of appropriate procedures and techniques, containment devices and facilities, and the training of personnel.

Phylogeny of Rickettsia spp. inferred by comparing sequences of 'gene D', which encodes an intracytoplasmic protein

'Gene D' is the PS120-protein-encoding gene, first described in Rickettsia conorii and Rickettsia japonica. Sequence analysis of a 3030 bp fragment of 'gene D' in 24 representatives of the genus Rickettsia was carried out to complete phylogenetic analyses previously inferred by comparison of gene sequences encoding citrate synthase, 17 kDa antigen and rOmpA and rOmpB. The phylogenetic relationships between rickettsiae were inferred from the comparison of both the gene and the derived protein sequences, using the parsimony, neighbour-joining and maximum-likelihood methods. Five distinct groups of rickettsiae were identified. These were: the Rickettsia massiliae group, including R. massiliae, Bar 29, Rickettsia rhipicephali and Rickettsia aeschlimannii; the Rickettsia rickettsii group containing Rickettsia sibirica, 'Rickettsia mongolotimonae', Rickettsia parkeri, strain S, Rickettsia africae, the R. conorii complex, Rickettsia slovaca, Rickettsia honei, R. rickettsii, R. japonica and Rickettsia montanensis; the group currently containing only Rickettsia helvetica; the Rickettsia akari group including Rickettsia australis, R. akari and the ELB agent; Rickettsia prowazekii and Rickettsia typhi clustered in the typhus group. As significant bootstrap values were obtained for most of the nodes, sequence comparison of 'gene D' should be considered as a complementary approach in phylogenetic studies of rickettsiae.

Penetration of host cells by Rickettsia rickettsii appears to be mediated by a phospholipase of rickettsial origin

Internalization of obligate intracellular bacteria belonging to the genus Rickettsia by eukaryotic cells requires participation of both the parasitized host and the microorganism. The term "induced phagocytosis" has been used specifically to describe the entry of Rickettsia prowazekii, although a similar mechanism is likely for R. rickettsii. A role for a phospholipase in the internalization process has been proposed for both of these organisms, with the strongest supporting evidence provided for R. prowazekii. Despite general acceptance of the notion that phospholipase activity is involved in the internalization process of these bacteria, the origin of the enzyme is not known. The results of the study presented here, which used R. rickettsii and Vero cells, suggest that a rickettsial phospholipase, rather than a host cell phospholipase, mediates internalization of the organism. This conclusion is based upon results which show that pretreatment of R. rickettsii, but not of host cells, with a specific chemical inhibitor of phospholipase, and also antiserum to this enzyme, significantly reduces uptake of the organism and its ability to cause plaque formation.

Heparin protects human endothelial cells infected by Rickettsia rickettsii

Routine culture of endothelial cells currently includes the use of heparin, which significantly reduces cell doubling time and increases cell population size. Heparin protects cultured arterial endothelial cells from damage by toxic oxygen metabolites produced by the action of xanthine and xanthine oxidase. Because of our hypothesis implicating free radicals in cell injury caused by Rickettsia rickettsii, we have carried out a series of experiments to examine the effects of heparin on injury to endothelial cells infected by this microorganism. These studies showed that heparin does not inhibit replication of R. rickettsii in the cytoplasm of endothelial cells. Furthermore, heparin appears to exhibit a protective effect on the infected host cell as measured by (i) reduced plaque size, (ii) increased longevity of the cell monolayer, (iii) reduction in the amount of lactic dehydrogenase released from infected cells, and (iv) reduction in the levels of intracellular peroxides formed in infected cells. Electron microscopic studies also show a significant reduction in dilatation of the rough-surfaced endoplasmic reticulum of the infected cells in the presence of heparin. These observations appear to lend additional support to involvement of an oxidative mechanism in human endothelial cell injury caused by R. rickettsii.

Induction of hyperreactivity to endotoxin in mice by Coxiella burnetii

Intraperitoneal inoculation of mice with live or killed Coxiella burnetii phase I or phase II cells induced a marked hyperreactivity to the lethal effect of bacterial endotoxin and was accompanied by a marked hepatosplenomegaly. The degree and duration of hyperreactivity depended on the dose of C. burnetii administered and were higher with phase I than with phase II cells. Sensitization to the lethal effects of endotoxin and induction of splenomegaly by phase I C. burnetii cells also proceeded in the endotoxin-resistant C3H/HeJ strain of mice. Preincubation of C. burnetii cells with the corresponding immune serum significantly diminished the ability of phase I but not phase II cells to induce hyperreactivity to endotoxin.