Gram negatives Flashcards
(33 cards)
gram negative cell
lipopolysaccharide
what is the primary driver for sepsis in gram negatives
lipopolysaccharide layer
features of a gram negative cells?
The Gram negative cell envelope contains an additional outer membrane composed by phospholipids and lipopolysaccharides which face the external environment.
• The highly charged nature of lipopolysaccharides confer an overall negative charge to the Gram negative cell wall.
• The chemical structure of the outer membrane lipopolysaccharides is often unique to specific bacterial strains (i.e. sub-species)
• It is responsible for many of the antigenic properties of these strains. Many species of Gram-negative bacteria are pathogenic.
• This pathogenicity is often associated with the lipopolysaccharide (LPS) layer of the Gram-negative cell envelope
diagnosing infection?
History (with differential diagnoses)
• Examination (review differential diagnoses)
• Investigations (radiology, biochemistry, immunology etc) review differential diagnoses even further
•Microbiology: Blood, stool, urine, wound, tissue cultures
•Microscopy: stool, urine, CSF, sputum •Serology
•Antigen detection
•PCR/ molecular studies
antibiotics that may be active against gram negatives
- Beta lactams ( and monobactam )
- Aminoglycosides
- Macrolides
- Tetracyclines
- Chloramphenicol
- Co-trimoxazole
- polymixins
ciproflaxacins
have been associated with seizures ruptures of aortic aneurysm epilepsy achilles tendon rupture tendonitis
HAP vs CAP?
hospitalized > 48hrs
context in pneumonia?
Time of year/ season
• Type of immunosuppression (CD4 in HIV, chemotherapy, steroid dose changes, immunotherapy, chemotherapy)
• Chronic lung disease (bronchiectasis, Cystic fibrosis (CF), COPD etc)
• Epidemiological exposures (mycoplasma 4 yearly peaks, Coxiella,
psittacosis , PWID, vaccine status)
• Travel (resistant gram negs, MERS Co-V, MDR –TB, XDR- TB, Legionella)
aztreonams
purely active against gram negative
instead of gentamicin in a niche set of people
aminoglycosides
IV therapy
don’t have Myasthenia graves
narrow therapeutic window
workforce for gram negatives in tayside
not against anaerobes
- gentamicin
most gram negatives
gram negative bacili
H. influenza
gram negative coccobacillus
aerobic but can be facultative anaerobe
In vitro growth requires accessory growth factors, including “X” factor (hemin) and “V” factor (nicotinamide adenine dinucleotide [NAD]).
how does H. influenza react to chocolate agar media?
Chocolate agar media. (will generally not grow on blood agar, which lacks NAD /V factor/ nicotinamide adenine dinucleotide
antibiotic of choice for H. influenza?
amoxicillin - in the UK and also covers strep. pneumonia
doxycycline also active
atypical pneumonia is not
strep pneumonia
atypical pneumonia causes?
Mycoplasma pneumoniae , acute Coxiella burnetii , Chlamydophila psittaci, Legionella pneumophila
treating atypical pneumonia?
Most respond to doxycycline (a tetracycline) – NOT so much Legionella
• Clarithromycin (a macrolide) also works
• Quinolones (levofloxacin) in penicillin allergic severe pneumonia. NOTE Cdiff risk)
mortality of atypical pneumonia?
varies with pathogen, but generally lower than classical bacterial pneumonia
Legionella has a higher mortality. Look out for risk factors
where do you get legionella?
Lukewarm aerosolised water ( showers, air conditioning , taps)
• More common in smokers, males, COPD, immunosuppressed, malignancy, diabetes, dialysis, hot tubs
• There is a milder disease caused by Legionella pneumophila called Pontiac disease
• In water,
• multiplies within amoebae and ciliated protozoa, which are small one-celled organisms.
• These provide nutrients and shelter from adverse environmental conditions, such as extreme temperatures and chemicals like chlorine.
• Human immune cells called alveolar macrophages look very similar to protozoa. Legionella invades and grows within alveolar macrophages, mistaking them for their natural host and causing disease
what is the most common form of legionella?
serogroup 1 but not all
important causes of gram negative sepsis?
Escherichia coli, Klebsiella, Pseudomonas, Serratia, Acinetobacter, Enterobacter (not to be confused with the gram positive Enterococcus), Citrobacter, and Neisseria meningitidis
• Neisseria meningitidis will be covered in the CNS
• Gram negs are also covered in GI infections and in Renal
what treats pseudomonas
ciproflaxacin - the only oral drug which will treat pseudomonas
what are coliforms?
E. coli and similar organisms • Gram negative rods • Biochemical tests to differentiate • Klebsiella sp., Proteus sp., Enterobacter sp., Serratia sp. etc.
antibiotic resistance?
antibiotics are only able to kill certain strains of bacteria
bacteria with certain traits survive
these bacteria are now able to multiply and colonise
