אתגרים באבחון מחלות זיהומיות במעבדה המיקרוביולוגית 134046

סיכום שיעור 10

Munthernash

Munthernash

פרטי הסיכום

קורס: אתגרים באבחון מחלות זיהומיות במעבדה המיקרוביולוגית 134046

מספר השיעור: 10

סיכום השיעור

Antibiotics

uAntibiotic: Chemical produced by a microorganism that kills or inhibits the growth of another microorganism

Bactericidal antibiotics kill bacteria; inhibit cell wall synthesis: the beta-lactam antibiotics (penicillin derivatives (penams), cephalosporins (cephems), monobactams, and carbapenems) and vancomycin.

No growth of bacteria due to interfering protein production, DNA replication, other cellular metabolism

Vancomycin

uMechanism of action

uInhibits cell wall synthesis by binding to the D-Ala-D-Ala terminus of of peptidoglycan pentapeptide, which as a result inhibits transglycosylase, preventing peptidoglycan elongation and cross-linking

AMINOGLYCOSIDE TRANSPORT

●Transport across the cell membrane is by active transport.

●Antimicrobial activity is reduced in an anaerobic environment and at low pH.

Disc diffusion

First developed in the 1950s, it was refined and by W. Kirby and A. Bauer, then standardized by the World Health Organization in 1961.

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Measuring Antimicrobial Sensitivity

uE Test

uMIC: Minimal inhibitory concentration

RESISTANCE

Intrinsic resistance: Bacterial species  naturally resistant to a certain antibiotics without the need for mutation or gain of further genes.

There are two types of bacterial resistance to antibiotics, acquired and intrinsic resistance

 

Acquired resistance arises through mutation or exchange of genetic material between bacteria. 

 

Intrinsic resistance is a natural insensitivity in bacteria that have never been susceptible to a particular antibiotic.

MRSA

•Several antibiotic-resistant bacteria are considered clinically dangerous.

MRSA Methicillin-Resistant Staph. aureus and VRSA (Vancomycin-resitant S.aureus are very virulent in humans and are referred as professional pathogens. MRSA and VRSA contain many resistance genes.

›Three or four resistance islands on the chromosome

›26-28 additional gene clusters on plasmids which can move to other bacterial cells.

Clindamycin antibiotic is drug of choice for treating patients infected with MRSA

The resistance to erythromycin and clindamycin occurs by one of two mechanisms.

1. Efflux: typically mediated by msrA gene.

                (methionine sulfoxide reductase msrA)

 

2. Ribosome alteration: occur through methylation of the ribosomal    

 

   target site, and this resistance is mediated by erm gene.

                (erm- erythromycin ribosome methylase)

D-test principle

D test is done to allow erythromycin induce production of methylase.

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