Screening systems for antimicrobial compounds from microbial metabolites were conducted using silkworm larvae as an animal model of methicillin-resistant Staphylococcus aureus (MRSA) or Candida albicans infection. When MRSA (2.5 x 10⁷ CFU/larva) or C. albicans (2 x 10⁴ CFU/larva) was injected into the blood of silkworm larvae (5th instar), over 90% of the larvae died within 3 days. An injection of vancomycin (1 μg/larva) or miconazole (5 μg/larva) proved effective in MRSA or C. albicans infection, respectively, allowing the larvae to survive. Under the conditions, microbial culture broths (over 5,000) were screened for antimicrobial compounds. Known amphotericin B, tetramycin and echinocandin-related compounds were purified from culture broths of actinomycete and fungal strains in the C. albicans infection system. On the other hand, Streptomyces sp. K04-0144 was selected in the MRSA infection system. The strain was isolated from a soil sample collected at Ishigakijima Island, Japan. Solid phase extracts of the 6-day old culture broth of the strain were purified by ODS column chromatography and HPLC using ODS column, yielding four active compounds designated nosokomycins A to D. The structures of nosokomycins were elucidated by various NMR experiments and mass spectra. They possessed a common phosphoglicolipid structure. An injection of nosokomycin A or B (50 μg/larvae) was effective in silkworm larvae infected with MRSA for 5 days. Other biological properties of nosokomycins are also presented.