Enucleated L929 mouse fibroblasts support invasion and multiplication of Shigella flexneri 5a

Invasive bacteria can induce their own uptake and specify their intracellular localization; hence it is commonly assumed that proximate modulation of host cell transcription is not required for infection. However, bacteria can also modulate, directly or indirectly, the transcription of many host cell genes, whose role in the infection may be difficult to determine by global gene expression. Is the host cell nucleus proximately required for intracellular infection and, if so, for which pathogens and at what stages of infection? Enucleated cells were previously infected with Toxoplasma gondii, Chlamydia psittaci, C. trachomatis, or Rickettsia prowazekii. We enucleated L929 mouse fibroblasts by centrifugation in the presence of cytochalasin B, and compared the infection with Shigella flexneri M90T 5a of nucleated and enucleated cells. Percent infection and bacterial loads were estimated with a gentamicin suppression assay in cultures fixed and stained at different times after infection. Enucleation reduced by about half the percent of infected cells, a finding that may reflect the reduced endocytic ability of L929 cytoplasts. However, average numbers of bacteria and frequency distributions of bacterial numbers per cell at different times were similar in enucleated and nucleated cells. Bacteria with actin-rich tails were detected in both cytoplasts and nucleated cells. Lastly, cytoplasts were similarly infected 2 and 24 h after enucleation, suggesting that short-lived mRNAs were not involved in the infection. Productive S. flexneri infection could thus take place in cells unable to modulate gene transcription, RNA processing, or nucleus-dependent signaling cascades.

Bacterial endosymbiosis within the cytoplasm of Acanthamoeba lugdunensis isolated from a contact lens storage case

Transmission electron microscopy of an Acanthamoeba isolate (KA/L5) from a contact lens case revealed bacterial endosymbionts within cytoplasm of the amoebae. The Acanthamoeba isolate belonged to the morphological group II. Based on the polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) of 18S ribosomal RNA coding DNA (rDNA), the isolate was identified as A. lugdunensis. Strain typing by isoenzyme analysis using isoelectric focusing (IEF) and mitochondrial (Mt) DNA RFLP revealed that the isolate was closely related with KA/L1, the most predominant type of isolates from contact lens storage cases, KA/E2, a clinical isolate, KA/W4, previously reported to host endosymbionts, and L3a strains of A. lugdunensis. The endosymbionts were similar to those of KA/W4 in aspects that they were randomly distributed in both trophozoites and cysts, and were rod-shaped bacteria measuring approximately 1.38 x 0.50 microns. But the number of endosymbionts per amoeba was significantly lower than that of KA/W4. They were neither limited by phagosomal membranes nor included in lacunaelike structure.

Attachment and intracellular penetration of classic enteropathogenic Escherichia coli into HEP-2 cells

Com E. coli dos sorogrupos 0111:K58 e 055:K59 observa-se, através de microscopia eletrônica, penetraçäo e provável multiplicaçäo intracelular em células Hep-2. Foram detectadas alteraçöes significativas da membrana citoplasmática das células, sugerindo um processo ativo de endocitose