Table of Contents
In order to understand which antibiotics patients require, it is necessary to know which infective organisms you needs to cover (outlined on this page) and which antibiotics cover which organisms (outlined here).
Respiratory
Community-acquired pneumonia
- Streptococcus pneumoniae
- Haemophilus influenzae (if not vaccinated)
- Atypicals
If immunocompromised (e.g. malnourished, alcoholic, diabetic, on long-term steroids), also: Staphylococcus aureus, coliforms, TB
If severely immunosuppressed (e.g. HIV with CD4 <200, transplant recipient), also: Pneumocystis carinii, Cryptococcus, CMV, Varicella zoster virus, influenza, fungal infections
Hospital-acquired pneumonia
- Staphylococcus aureus (including MRSA)
- Anaerobes
- Coliforms
- Pseudomonas
Colonising bacteria in chronic respiratory diseases
- Streptococcus pneumoniae
- Haemophilus influenzae
- Moraxella catarrhalis
- Staphylococcus aureus
- Pseudomonas
In cystic fibrosis, also: Burkholderia cepacia
Upper respiratory tract infections
- Streptococcus pneumoniae
- Streptococcus pyogenes
- Haemophilus influenzae
- Moraxella catarrhalis
Cavitating pneumonia
- Streptococcus pneumoniae
- Staphylococcus aureus
- Klebsiella
- TB
- Anaerobes
Abdominal
Intra-abdominal (including biliary)
Normal bowel flora:
- Anaerobes, e.g. Bacteroides
- Coliforms
- Enterococcus
Gastroenteritis/diarrhoea
- Salmonella enteritidis
- Shigella
- Campylobacter
- Escherichia coli (enterotoxic)
Less common: Yersinia enterocolitica, Bacillus cereus, Staphylococcus aureus
If risk factors, also: Clostridium difficile, Vibrio cholerae, Salmonella typhi
If dysentery: Shigella, Vibrio cholerae, amoebiasis
Don’t forget viral, parasitic and non-infectious causes!
Skin/joints/bone
Skin/joints/bone
- Staphylococcus aureus
- Streptococcus pyogenes
For wound/ulcer infections or severe/necrotising cellulitis, also: anaerobes
For burns, also: anaerobes, Pseudomonas
For post-surgical wounds, also: Gram negative bacilli (e.g. E. coli, Klebsiella, Pseudomonas), Enterococci, MRSA, CONS
NB: wound-colonising bacteria (i.e. bacteria present in exudate without necessarily causing infection) include: coliforms, Enterococcus, anaerobes
Neurological
Meningitis
- Neisseria meningitidis (meningococcal)
- Streptococcus pneumoniae (pneumococcal)
- Haemophilus influenzae (if not vaccinated)
- Listeria (if >65 years or immunocompromised)
If neonatal: group B Streptococcus, E. coli/coliforms, Listeria (rare)
Urinary
Urine infections
- Escherichia coli
- Staphylococcus saprophyticus
- Non-E. Coli enterobacteriaceae (Klebsiella, Enterobacter, Proteus), Pseudomonas, Enterococci, Staphylococci (CONS/aureus)
Less common organisms (3) are associated with: catheters, hospitals, structural abnormalities and instrumentation
Cardiac
Infective endocarditis
- Viridans group Streptococci and other Streptococci (e.g. bovis)
- Enterococci
- Staphylococcus aureus and coagulase-negative Staphylococci (e.g. epidermidis)
- Coxiella burnetii
- HACEK organisms
Other
Surgical prophylaxis
- Need to cover skin ± intra-abdominal organisms
Sepsis of unknown origin
- Need to cover skin, chest, urine, intra-abdominal organisms
Test yourself!
Here are some syndromes associated with group A streptococcus (Streptococcus pyogenes). Outline the cause, timeframe and clinical features of each.
Scarlet fever
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Streptococcal toxic shock syndrome
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Post-streptococcal glomerulonephritis
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Rheumatic fever
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