Chapter 129. Staphylococcal Infections (Part 1)

Chia sẻ: Colgate Colgate | Ngày: | Loại File: PDF | Số trang:5

Thêm vào BST

Báo xấu

87
lượt xem 3
download

Download Vui lòng tải xuống để xem tài liệu đầy đủ

Harrison's Internal Medicine Chapter 129. Staphylococcal Infections Staphylococcal Infections: Introduction Staphylococcus aureus, the most virulent of the many staphylococcal species, has demonstrated its versatility by remaining a major cause of morbidity and mortality despite the availability of numerous effective antistaphylococcal antibiotics. S. aureus is a pluripotent pathogen, causing disease through both toxin-mediated and non-toxin-mediated mechanisms. This organism is responsible for both nosocomial and community-based infections that range from relatively minor skin and soft tissue infections to life-threatening systemic infections. ...

Chủ đề:

Bình luận(0) Đăng nhập để gửi bình luận!

Lưu

Nội dung Text: Chapter 129. Staphylococcal Infections (Part 1)

Chapter 129. Staphylococcal Infections (Part 1) Harrison's Internal Medicine > Chapter 129. Staphylococcal Infections Staphylococcal Infections: Introduction Staphylococcus aureus, the most virulent of the many staphylococcal species, has demonstrated its versatility by remaining a major cause of morbidity and mortality despite the availability of numerous effective antistaphylococcal antibiotics. S. aureus is a pluripotent pathogen, causing disease through both toxin-mediated and non-toxin-mediated mechanisms. This organism is responsible for both nosocomial and community-based infections that range from relatively minor skin and soft tissue infections to life-threatening systemic infections. The "other" staphylococci, collectively designated coagulase-negative staphylococci (CoNS), are considerably less virulent than S. aureus but remain important pathogens in infections associated with prosthetic devices Microbiology and Taxonomy
Staphylococci, gram-positive cocci in the family Micrococcaceae, form grapelike clusters on Gram's stain (Fig. 129-1). These organisms are catalase- positive (unlike streptococcal species), nonmotile, aerobic, and facultatively anaerobic. They are capable of prolonged survival on environmental surfaces in varying conditions. Figure 129-1 Gram's stain of S. aureus in a sputum sample with polymorphonuclear leukocytes. (Reprinted with permission from FD Lowy: Staphylococcus aureus
infections. N Engl J Med 339:520, 1998. © 1998 Massachusetts Medical Society. All rights reserved.) More than 30 staphylococcal species are pathogenic. A simple strategy for identification of the more clinically important species is outlined in Fig. 129-2. Automated diagnostic systems, kits for biochemical characterization, and DNA- based assays are available for distinguishing among species. With few exceptions, S. aureus is distinguished from other staphylococcal species by its production of coagulase, a surface enzyme that converts fibrinogen to fibrin. Latex kits designed to detect both protein A and clumping factor also distinguish S. aureus from other staphylococcal species. S. aureus ferments mannitol, is positive for protein A, and produces DNAse. On blood agar plates, S. aureus tends to form golden β- hemolytic colonies; in contrast, CoNS produce small white nonhemolytic colonies. Figure 129-2
Biochemical characterization of staphylococci: algorithm of biochemical tests used to discriminate among the clinically important staphylococci. Additional tests are necessary to identify all of the different species. Determining whether multiple isolates (especially of CoNS) from a particular patient are the same or different is often an important factor in distinguishing contaminants from genuine pathogens. Determining whether multiple isolates from different patients are the same or different is relevant when there is concern that a nosocomial outbreak may have been due to a common point source (e.g., a contaminated medical instrument). Biochemical tests, often performed in conjunction with antimicrobial susceptibility testing, have been used
as a relatively simple means of distinguishing among staphylococcal species or strains. More discriminating molecular typing methods, such as pulsed-field gel electrophoresis and sequence-based techniques, have also been used for this purpose