Beta lactam

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, cefotaximeCARBAPENEMS: 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).