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Beta Lactam Antibiotics

 

Mode of action:

 

 

 

Inhibition of cell wall synthesis.  This particular group is characterized by its four-membered, nitrogen-containing beta-lactam ring at the core of their structure, which is key to the mode of action of this group of antibiotics.  Beta lactam antibiotics target the penicillin-binding proteins or PBPs - a group of enzymes found anchored in the cell membrane, which are involved in the cross-linking of the bacterial cell wall. The beta-lactam ring portion of this group of antibiotics binds to these different PBPs, rendering them unable to perform their role in cell wall synthesis.  This then leads to death of the bacterial cell due to osmotic instability or autolysis. 

 

Examples:

 

PENICLLINS: NATURAL: penicillin G, penicillin V; PENICILLINASE-RESISTANT PENICILLLIN: methicillin; oxacillin, nafcillin; EXTENDED SPECTRUM PENICILLIN: ampicillin, amoxicillin, carbenicillin

CEPHALOSPORINS: cephalothin; cefamandole, cefotaxime CARBAPENEMS: primaxin

MONOBACTAMS: aztreonam

 

Source:

Penicillin: Penicillum chrysogenum (syn: P. notatum), Aspergillus nidulans

Cephalosporin: Acremonium chrysogenum (syn: Cephalosporium acremonium), Paecilomyces persinicus, Streptomyces clavuligerus, Nocardia lactamdurans, Flavobacterium sp. Lysobacter lactamgenus

Spectrum of activity:

 

Broad-spectrum: carbapenems, 2nd, 3rd and 4th generation cephalosporins

Narrow spectrum: penicillin, 1st generation cephalosporins, monobactams

 

Effect on bacteria:

 

Generally bactericidal

Examples of applications in Veterinary Medicine:

Ruminants: Anthrax, listeriosis, leptospirosis, clostridial and corynebacterial infections; streptococcal mastitis, keratoconjunctivitis

Swine: erysipelas, streptococcal and clostridial infections

Horses: Tetanus, strangles, other strep and clostridial infections, foal pneumonia,

Dogs and cats: streptococcal and clostridial infections, UTI

Poultry: Necrotic enteritis, ulcerative enteritis, and intestinal spirochetosis

 

Miscellaneous:

 

Although beta – lactam antibiotics should theoretically work against all types of bacteria, this is not the case.  This is because different bacteria have varying PBP content and nature. Also, some bacteria have natural structural characteristics which does not favor this mode of action (e.g., Gram-negatives have an outer membrane layer which makes the PBPs more difficult to reach).

 

 

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