Gram âm

Bách khoa toàn thư mở Wikipedia

Gram âm là tên tập hợp các loại vi khuẩn không giữ được tinh thể tím khi cho phản ứng với hoá chất thử nghiệm theo tiêu chuẩn nhuộm Gram. Tiêu chuẩn này được dùng để phân dạng vi khuẩn làm hai loại Gram âmGram dương - dựa theo khác biệt của vỏ tế bào.

Trong khi vi khuẩn Gram dương giữ sắc xanh sau khi rửa qua rượu, vi khuẩn gram âm thì không - và hóa sắc đỏ hay hồng.



Many species of Gram-negative bacteria are pathogenic, meaning they can cause disease in a host organism. This pathogenic capability is usually associated with certain components of Gram-negative cell walls, in particular the lipopolysaccharide (also known as LPS or endotoxin) layer.

Mục lục

[sửa] Characteristics

The following characteristics are displayed by Gram-negative bacteria:

  1. Cell walls only contain a few layers of peptidoglycan (which is present in much higher levels in Gram-positive bacteria)
  2. Cells are surrounded by an outer membrane of lipopolysaccharide outside the peptidoglycan layer
  3. Porins exist in the outer membrane, which act like pores for particular molecules
  4. There is a space between the layers of peptidoglycan and the secondary cell membrane called the periplasmic space
  5. The S-layer is directly attached to the outer membrane, rather than the peptidoglycan
  6. If present, flagella have four supporting rings instead of two
  7. No teichoic acids are present
  8. Lipoproteins are attached to the polysaccharide backbone whereas in Gram-positive bacteria no lipoproteins are present

[sửa] Example species

The proteobacteria are a major group of Gram-negative bacteria, including Escherichia coli, Salmonella, and other Enterobacteriaceae, Pseudomonas, Moraxella, Helicobacter, Stenotrophomonas, Bdellovibrio, acetic acid bacteria, Legionella and many others. Other notable groups of Gram-negative bacteria include the cyanobacteria, spirochaetes, green sulfur and green non-sulfur bacteria.

Medically relevant Gram-negative cocci include three organisms, which cause a sexually transmitted disease (Neisseria gonorrhoeae), a meningitis (Neisseria meningitidis), and respiratory symptoms (Moraxella catarrhalis).

Medically relevant Gram-negative bacilli include a multitude of species. Some of them primarily cause respiratory problems (Hemophilus influenzae, Klebsiella pneumoniae, Legionella pneumophila, Pseudomonas aeruginosa), primarily urinary problems (Escherichia coli, Proteus mirabilis, Enterobacter cloacae, Serratia marcescens), and primarily gastrointestinal problems (Helicobacter pylori, Salmonella enteritidis, Salmonella typhi).

Nosocomial gram negative bacteria include Acinetobacter baumanii, which cause bacteremia, secondary meningitis, and ventilator-associated pneumonia in intensive care units of hospital establishments.

[sửa] Medical treatment

One of the several unique characteristics of Gram-negative bacteria is the outer membrane. This outer membrane is responsible for protecting the bacteria from several antibiotics, dyes, and detergents which would normally damage the inner membrane or cell wall (peptidoglycan). The outer membrane provides these bacteria with resistance to lysozyme and penicillin. Fortunately, alternative medicinal treatments such as lysozyme with EDTA, and the antibiotic ampicillin have been developed to combat the protective outer membrane of some pathogenic Gram-negative organisms.

[sửa] See also

  • Gram-positive

[sửa] References

  • Baron, Samuel (1996). Medical Microbiology, 4th ed., The University of Texas Medical Branch at Galveston. ISBN 0-9631172-1-1.
  • Madigan, Michael; Martinko, John (editors) (2005). Brock Biology of Microorganisms, 11th ed., Prentice Hall. ISBN 0-13-144329-1.
  • Bài viết này có sử dụng các nguyên liệu từ Science Primer phát hành tại NCBI, vì đây là một tác phẩm của chính quyền liên bang Hoa Kỳ nên nó thuộc bản quyền công cộng [1].

[sửa] External links