Staphylococcus hominis on Blood Agar

Staphylococcus hominis is a coagulase-negative staphylococcus (CoNS) commonly found on human skin and in the environment. When cultured on blood agar, it typically exhibits the following characteristics:
Colony Morphology: Colonies of Staphylococcus hominis on blood agar are generally small to medium in size, round, and smooth. They appear opaque and may have a slight creamy or white color. Some strains may produce pigmented colonies that can be yellowish or orange.
Hemolysis: Staphylococcus hominis is usually non-hemolytic on blood agar, meaning it does not cause hemolysis (the breakdown of red blood cells), so there will be no clear zones around the colonies. However, slight alpha hemolysis (partial hemolysis resulting in a greenish discoloration around the colonies) can sometimes be observed.
Growth Conditions: It grows well under aerobic conditions, and colonies typically appear within 24-48 hours of incubation at 35-37°C.
Laboratory Identification
To definitively identify Staphylococcus hominis, additional biochemical tests and molecular methods may be employed:
Catalase Test: Positive, as it is a characteristic of all staphylococci.
Coagulase Test: Negative, distinguishing it from Staphylococcus aureus.
Mannitol Fermentation: Typically negative (does not ferment mannitol).
Antibiotic Susceptibility: Testing for resistance patterns, particularly for methicillin resistance, as CoNS can be methicillin-resistant (MR-CoNS).
Clinical Significance
While Staphylococcus hominis is generally considered part of the normal flora, it can be an opportunistic pathogen, particularly in immunocompromised individuals or those with indwelling medical devices. It can cause infections such as bacteremia, endocarditis, and wound infections.
Appearance on Blood Agar
This image represents the typical appearance of Staphylococcus hominis colonies on blood agar. You can observe the colony morphology and the absence of hemolysis around the colonies.
Staphylococcus hominis, blood agar, colony morphology, non-hemolytic, coagulase-negative staphylococcus, CoNS, human skin flora, opaque colonies, creamy colonies, white colonies, small colonies, medium colonies, round colonies, smooth colonies, pigmented colonies, yellowish colonies, orange colonies, alpha hemolysis, aerobic growth, 24-48 hours incubation, 35-37°C, catalase positive, coagulase negative, mannitol fermentation negative, antibiotic susceptibility, methicillin resistance, opportunistic pathogen, bacteremia, endocarditis, wound infections.

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