Staphylococcus aureus

Staphylococcus aureus

There are approximately 35 to 40 species in the genus Staphylococcus. Staphylococcus spp. (staphylococci) are GPC( Gram-positive cocci)  that may occur singly or in pairs (diplococci),  packets of four (tetrads), short chains, or irregular or grapelike clusters.The grapelike cluster is the morphologic arrangement most typical presentation of staphylococci.

Characterictics of  Staphylococcus spp. :

Staphyllococcus
  • They are Gram- positive facultative anaerobes, except for S. saccharolyticus and S. aureus subsp. aureus, which are anaerobic
  • Nonmotile
  • Do not form spores
  • Usually nonencapsulated
  • Catalase positive. This means that staphylococcus  produce the enzyme catalase; anaerobic Staphylococcus spp. are catalase negative
  • Modified oxidase negative, except for S. lentus, S. scuiri, and S. vitulus
Target tissues: Bone, Heart, Skin, Joint

I.Skin Infections

Cellulitis
Surgical Wound Infection (onset within 48 hours)
Impetigo
Furuncle or Carbuncle
Superficial Folliculitis
Toxic Shock Syndrome
Staphylococcal Scalded Skin Syndrome
Intravenous Catheter associated infection
Hydradenitis suppurativa
Mastitis

II. Cardiopulmonary infections

Staphylococcal Pneumonia ( risk of Empyema)
Infective Endocarditis

III. Musculoskeletal infections

Osteomyelitis
Septic Arthritis
Septic Bursitis

IV. CNS Infections

Meningitis
Brain Abscess
Epidural Abscess

V. Gastrointestinal infections

Staphylococcal Enterotoxin B Food Poisoning by unrefrigerated cold salads, meats, cream pastries. Onset is usually within  1 to 6 hours (duration to 24 to 48 hours).

IF – Sensitive staph (MSSA)
First line antibiotics
IV: Oxacillin/nafcillin, or cefazolin (first-generation cephalosporin)
Oral: Dicloxacillin or cephalexin(Keflex) (first-generation cephalosporin)

 

IF- Resistant staph (MRSA)

 

In case of  severe infection
First line antibiotics

Vancomycin, linezolid, daptomycin, ceftaroline, tigecycline, or telavancin.

Adverse reactions

Linezolid causes thrombocytopenia.
Daptomycin causes myopathy and a rising CPK.

In case of  minor infection

 

First line antibiotics

Trimethoprim/sulfamethoxazole (TMP/SMX), clindamycin, doxycycline

 

IF Penicillin allergy

 

  • Rash: Safe to use cephalosporins
  • Anaphylaxis: Macrolides (azithromycin, clarithromycin) or clindamycin
  • In the case of  severe infection:  Vancomycin, linezolid, daptomycin, telavancin
  • In the case of  minor infection: Macrolides (azithromycin, clarithromycin), clindamycin, or TMP/SMX

 

Good to know

Telavancin is a bactericidal lipopolysaccharide. It is a derivative of vancomycin derivative and has a similar efficacy. Telavancin inhibits bacterial cell wall synthesis by binding to the D-Ala-D-Ala terminus of the peptidoglycan in the growing cell wall. Ceftaroline inhibits cell wall growth by binding the penicillin-binding protein.

Linezolid inhibits protein synthesis.

TMP-SMX is a folate antagonist

Daptomycin is a lipopeptide antibiotic. It is a naturally occurring compound found in the soil saprotroph Streptomyces roseosporus.