posiews

Posiews, in microbiology, refer to cultures of microorganisms grown on or in a nutrient medium under controlled conditions. The term comes from the Polish word posiew, meaning inoculation or sowing. Posiews are used to isolate, identify, and study organisms; to determine antimicrobial susceptibility; and to monitor contamination or quality in clinical, industrial, and environmental settings.

Process: A specimen is inoculated onto solid media (such as agar plates) or into liquid media (broths). The cultures are incubated at defined temperatures for a specified period. On solid media, growth typically appears as discrete colonies that may be isolated to obtain a pure culture. Enrichment steps or selective/differential media can favor certain organisms or reveal characteristic traits.

Types: Pure cultures contain a single organism; mixed cultures contain more than one. Clinical posiews aim to identify pathogens, while environmental and industrial posiews assess microbial communities or production strains. Media types include selective media that inhibit competitors and differential media that reveal metabolic properties.

Analysis and storage: Identification uses colony morphology, staining, biochemical tests, and increasingly matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) or sequencing. Antibiotic susceptibility is tested by methods such as disk diffusion or broth microdilution. Cultures are stored short-term at refrigeration temperatures or long-term in glycerol stocks at –80°C, sometimes after lyophilization.

Safety and limitations: Proper aseptic technique and biosafety practices are essential. Not all microorganisms grow readily in culture; some are fastidious or non-cultivable, which limits posiew-based work. Culture-independent methods (e.g., molecular assays) complement posiews in comprehensive investigations.