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Streptococcus is a genus of gram-positive or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales (lactic acid bacteria), in the phylum Bacillota. [2] Cell division in streptococci occurs along a single axis , thus when growing they tend to form pairs or chains, which may appear bent or twisted.
Streptococcus agalactiae (also known as group B streptococcus or GBS) is a gram-positive coccus (round bacterium) with a tendency to form chains (as reflected by the genus name Streptococcus). It is a beta-hemolytic, catalase-negative, and facultative anaerobe. [1] [2]
Anaerobic gram-positive cocci such as Peptostreptococcus are the second most frequently recovered anaerobes and account for approximately one quarter of anaerobic isolates found. Most often anaerobic gram-positive cocci are usually recovered mixed in with other anaerobic or aerobic bacteria from various infections at different sites of the ...
Diplococci are pairs of cocci. Examples of gram-negative diplococci are Neisseria spp. and Moraxella catarrhalis. Examples of gram-positive diplococci are Streptococcus pneumoniae and Enterococcus spp. [10] [11] Presumably, diplococcus has been implicated in encephalitis lethargica. [12] The genus Neisseria belongs to the family Neisseriaceae.
As mentioned, S. agalactiae is a Gram-positive coccus with a tendency to form chains, beta-haemolytic, catalase-negative, and facultative anaerobe (anaerobic organism). GBS grows readily on blood agar plates as microbial colonies surrounded by a narrow zone of β-haemolysis.
Pneumococci are typically gram-positive cocci seen in pairs or chains. When cultured on blood agar plates with added optochin antibiotic disk they show alpha-hemolytic colonies and a clear zone of inhibition around the disk indicating sensitivity to the antibiotic. Pneumococci are also bile soluble.
Reagents used for Lancefield grouping. Lancefield grouping is a system of classification that classifies catalase-negative Gram-positive cocci based on the carbohydrate composition of bacterial antigens found on their cell walls. [1]
Enterococcus faecalis – formerly classified as part of the group D Streptococcus system – is a Gram-positive, commensal bacterium inhabiting the gastrointestinal tracts of humans. [ 1 ] [ 2 ] Like other species in the genus Enterococcus , E. faecalis is found in healthy humans and can be used as a probiotic.