What bacteria are Gram-positive, occurring in clusters, specifically Staphylococcus (Staph) species?

From the Guidelines

Gram-positive bacteria that typically arrange in clusters include Staphylococcus species, with Staphylococcus aureus being the most clinically significant example, as evidenced by a systematic review and meta-analysis published in 2020 1.

Key Characteristics

• These bacteria appear purple when Gram stained due to their thick peptidoglycan cell wall that retains crystal violet dye.
• The cluster arrangement, often described as resembling bunches of grapes under microscopic examination, is a key identifying characteristic during laboratory diagnosis.
• This clustering occurs because these bacteria divide in multiple planes rather than a single axis.

Clinical Significance

• Staphylococcus aureus is particularly important clinically as it can cause various infections ranging from skin and soft tissue infections to more serious conditions like pneumonia, endocarditis, and toxic shock syndrome, with a pooled sensitivity and specificity of 68% (95%CI 49e83) and 95% (95%CI 86e98), respectively, in respiratory samples 1.
• The cluster arrangement helps distinguish these bacteria from streptococci, which typically form chains rather than clusters, representing an important diagnostic distinction in clinical microbiology.

Diagnostic Utility

• Gram staining morphology suggestive of Staphylococcus in respiratory samples of patients with VAP holds great potential for predicting VAP caused by S. aureus, with a high negative predictive value observed in the majority of scenarios 1.
• The use of Gram staining morphology could provide information during clinical decision-making processes as it concerns empirical antibiotic coverage for VAP, although randomized clinical trials with patient-centred outcomes are needed for strong recommendations in clinical practice 1.

From the FDA Drug Label

The in vitro spectrum of activity of linezolid also includes certain Gram-negative bacteria and anaerobic bacteria Linezolid has been shown to be active against most isolates of the following microorganisms, both in vitro and in clinical infections, as described in the INDICATIONS AND USAGE section Aerobic and facultative Gram-positive microorganisms Staphylococcus aureus (including methicillin-resistant strains) Staphylococcus epidermidis (including methicillin-resistant strains) Staphylococcus haemolyticus

• Gram-positive bacteria in clusters are likely Staphylococci, which include:
  • Staphylococcus aureus
  • Staphylococcus epidermidis
  • Staphylococcus haemolyticus 2

From the Research

Gram-Positive Bacteria in Clusters

• Staphylococcus aureus is a gram-positive coccus that forms grape-like clusters and is a major commensal bacterium and human pathogen 3, 4.
• It is a spherical-shaped bacterium that belongs to the family Staphylococcaceae and is often present asymptomatically on parts of the human body 4.
• Staphylococcus aureus is known to cause a wide range of clinical infections, including abscesses, pneumonia, osteomyelitis, endocarditis, arthritis, and sepsis 3, 5.

Characteristics of Staphylococcus aureus

• Most strains of S. aureus ferment mannitol and form characteristic golden yellow colonies 3.
• They produce catalase, coagulase, and extracellular cell clumping factor, and some strains can also produce capsules 3.
• S. aureus has an outstanding ability to acquire resistance to most classes of antimicrobial agents, making treatment and control of staphylococcal infections increasingly difficult 3.