Nonsocomial infections Flashcards
- Which diseases are caused by group A streptococci (GAS)?
The classification made is based on the polysaccharide-group antigens (C-substrate). GAS (S. pyogenes) causes a broad spectrum of diseases.
- Purulent: Pharyngitis, tonsillitis (Angina), Pyodermia, wound infections, abscesses, erysipel, Necrotizing fasciitis, Puerperal sepsis (Childbed fever)
- Toxin derived: scarlet fever and streptococcal toxic syndrome.
- Immune pathological: rheumatic fever, acute glomerulonephritis and endocarditis.
- What are the major pathomechanisms involved with GAS?
- The production of toxins such as erythrogenic toxin, or superantigens (SpeA, B, C). these toxins cause scarlet fever and schock syndrome.
- Fimbriae: binding to fibronectin in pharyngeal epithelium.
- Another important virulence factor is The M protein, which is important for attachment to keratinocytes in skin infections.
- The hyaluronic acid capsule is required for resistance to phagocytosis
- The streptokinases are a family of secreted streptococcal proteins with the common function of converting plasminogen to plasmin
- Induction of proinflammatory responses in keratinocytes is associated with adherence of streptococci and their production of streptolysin O.
- Various antigens produce immunological crossreaction with and destruction of cardiac myosin. Immunocomplexes are deposited in kidneys and joints, which causes acute rheumatic fever, acute endocarditis and acute glomerulonephritis.
- How can S. pneumoniae infections be prevented?
The best way to prevent S. pneumoniae infections are vaccines. There are two types of vaccines: pneumococcal polysaccharide vaccines protective against 23 serotypes, and pneumococcal conjugate vaccines (PPV7) against 7 serotypes, effective in infants and toddlers.
- Define the term „health care-associated infections“ (HCAI)?
Healthcare-associated infections are infections acquired by patients during their stay in a hospital or another healthcare setting. Although some of these infections can be treated easily, others may more seriously affect a patient’s health, increasing their stay in the hospital and hospital costs, and causing considerable distress to these patients.
A nosocomial infection is defined as a localized or systemic condition that results from
1) adverse reaction to the presence of an infectious agent or its toxin(s)
2) that was not present or incubating at the time of admission to the hospital
The major routes of transmission are:
- What are the most common bacteria causing HCAI?
- Staphylococci (MRSA & Coagulase-negative staphylococci)
- E. coli, Klebsiella sp. & other enterobacteria
- Pseudomonas aeruginosa
- Vancomycin-resistant Enterococci (in the US)
- How does S. aureus cause disease?
CORREGIR
- Describe the impact of biofilms on staphylococcal HCAI
A biofilm is a thin layer of microorganisms adhering to the surface of a structure, which may be organic or inorganic, together with the polymers that they secrete. The S. epidermis biofilm matrix is formed by PIA (polysaccharide intercellular adhesin), proteins and extracellular DNA.
Staphylococci are recognized as the most frequent causes of biofilm-associated infections. This exceptional status among biofilm-associated pathogens is due to the fact that staphylococci are frequent commensal bacteria on the human skin and mucous surfaces (and those of many other mammals). Thus, staphylococci are among the most likely germs to infect any medical device that penetrates those surfaces, such as when being inserted during surgery. S. aureus and S. epidermis are the most common bacteria which cause biofilm-associated infections. These biofilms are characterized for having simple diffusion barrier, for binding to positively charged antibiotic molecules rendering them inactive, for attenuation of host response
and for retention of host nutrients.
- What is the genetic and functional mechanism of methicillin resistance in staphylococci?
All MRSA strains carry a mobile genetic element called staphylococcal cassette chromosome (SCC) which harbours the mecA gene. This gene encodes penicillin-binding protein 2a that confers resistance to β-lactam antibiotics. The Pbp2a has a reduced binding affinity to beta-lactam antibiotics, which confers an intrinsic resistance to all β-lactams.
The mecA gene and (ii) site-specific staphylococcal cassette recombinases (Ccr) that promote integration into and excision from the att site located within an open reading frame (orfX) of the staphylococcal chromosome.
SCCmecs may carry other resistance genes as well and can be exchanged between staphylococcal strains and species.
- Discuss the recent trends in antibiotic resistance development
- The intensive use of antibiotics is directly correlated to the increase of antibiotic resistance as it applies a selective pressure.
- Animals in the USA consume more than twice as many medically important antibiotics as humans, which applies again a selective pressure outside of human medicine.
- In 2019 4,95 million deaths were reported due to antimicrobial resistance. Six leading pathogens caused 929.000 deaths
- • Most deadly pathogen-drug combination is methicillin-resistant S. aureus (MRSA) with 100.000 deaths.
- Extended spectrum beta-lactamases (ESBLs) on the rise in Gram-negatives which is conferring additional antibiotic resistance. This leads to more carbapenem use which leads to more selection pressure.
