A tailed bacteriophage, phi MR11 (siphovirus), was selected as a candidate therapeutic phage against Staphylococcus aureus infections. Gene 61, one of the 67 ORFs identified, is located in the morphogenic module. The gene product (gp61) has lytic domains homologous to CHAP (corresponding to an amidase function) at its N-terminus and lysozyme subfamily 2 (LYZ2) at its C-terminus. Each domain of gp61 was purified as a recombinant protein. Both the amidase [amino acids (aa) 1-150] and the lysozyme (aa 401-624) domains but not the linker domain (aa 151-400) caused efficient lysis of S. aureus. Immunoelectron microscopy localized gp61 to the tail tip of the phi MR11 phage. These data strongly suggest that gp61 is a tail-associated lytic factor involved in local cell-wall degradation, allowing the subsequent injection of phi MR11 DNA into the host cytoplasm. Staphylococcus aureus lysogenized with phi MR11 was also lysed by both proteins. Staphylococcus aureus strains on which phi MR11 phage can only produce spots but not plaques were also lysed by each protein, indicating that gp61 may be involved in 'lysis from without'. This is the first report of the presence of a tail-associated virion protein that acts as a lysin, in an S. aureus phage.

Increases in multidrug-resistant strains of Serratia marcescens are of great concern in pediatrics, especially in neonatal intensive care units. In the search for bacteriophages to control infectious diseases caused by multidrug-resistant S. marcescens, three phages (KSP20, KSP90, and KSP100) were isolated from environmental water and were characterized morphologically and genetically. KSP20 and KSP90 belonged to morphotype A1 of the family Myoviridae, and KSP100 belonged to morphotype C3 of the family Podoviridae. Analysis of the DNA region coding virion proteins, together with their morphological features, indicated that KSP20, KSP90, and KSP100 were related to the P2-like phage (temperate), T4-type phage (virulent), and phiEco32 phage (virulent), respectively. Based on amino acid sequences of the major capsid protein, KSP90 formed a new branch with a Stenotrophomonas maltophilia phage, Smp14, in the T4-type phage phylogeny. Both Smp14 and phiEco32 have been reported as potential therapeutic phages. These results suggest that KSP90 and KSP100 may be candidate therapeutic phages to control S. marcescens infection.

A novel bacteriophage, phiMR25, was isolated from a lysogenic Staphylococcus aureus strain by mitomycin C induction. Its biological features were analyzed in comparison with phiMR11, which was described previously as a prototype therapeutic phage. phiMR25 is morphologically similar to phiMR11 (morphotype B1 of family Myoviridae) but has a broader host range than phiMR11 on S. aureus strains. phiMR25 can also multiply on S. aureus lysogens of phiMR11. Its DNA is 44,342 bp in size, is predicted to include 70 open reading frames, and does not contain genes related to toxin or drug resistance. The lysogenic module and most of the putative virion protein genes are completely different from those of phiMR11. In spite of their genetic diversity, intraperitoneal administration of phiMR25 rescued mice inoculated with a lethal dose of S. aureus, as was the case for phiMR11. These results suggest that phiMR25 could be another candidate phage to treat S. aureus infection.

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Abstract. Developmental changes of horse testis were examined morphologically. Spermatogenesis initiated in the spring of 2-year-olds, and spermatogenic activity appeared to increase age dependently up to 9 years old. The characteristic feature of fetal testis is its large interstitial mass. The interstitial region revealed no proportionate change during the fetal period, but gradually decreased with age-dependency from birth to 9 years old. On the other hand, the area of seminiferous tubules showed no changes up to 1 year old. Most characteristic feature during development is the appearance/disappearance of pigmented cells. These cells first appeared in 3-day-old individuals and gradually increased in volume up to 1 year old (sampled in spring). The number of cells reached maximum at 2 months old, gradually decreased, and completely disappeared after 3 years old. The pigmented cells possessed large and small round bodies with various electron densities in the cytoplasm. Key words: Horse, Testis, Development.(J. Reprod. Dev. 44: [377][378][379][380][381][382][383] 1998) and sperm production has also been performed. The number of Leydig cells per testicular weight increases toward breeding season [7]. Daily sperm production shows the same tendency [5]. As for age-related changes, it is reported that serum gonadotropin levels and/or daily sperm production also increases with aging [5,8]. On the other hand, there is little information on the testicular morphology of horse testis during prenatal development. Cole et al. [9] found that the testis weight of the fetus reaches maximum (approximately 80 g) at 215 days of pregnancy. After that, its weight decreases to 10-20 g in newborn horses.easonal and/or age-related changes in reproduction of male horses have been described in S several reports. Spermatozoa in testes were seen one year after birth. It takes approximately two years to attain sexual maturation [1], and thereafter the serum concentrations of testosterone, luteinizing hormone, and prolactin are higher in breeding season than in non-breeding season [2][3][4][5][6][7]. Morphometric analysis on some parameters, such as the number of Leydig and Sertoli cells,