For this reason Gram-positive bacteria are very susceptible to penicillin (as first evidenced by the discovery of penicillin in 1928).Penicillin, or any other molecule, enters Gram-negative bacteria in a different manner. The bacteria have thinner cell walls but the external surface is coated with an additional cell membrane, called the outer membrane. The outer membrane is a lipid layer (lipopolysaccharide chain) that blocks passage of water-soluble (hydrophilic) molecules like penicillin. It thus acts as the first line of defence against any toxic substance, which is the reason for relative resistance to antibiotics compared to Gram-positive species But penicillin can still enter Gram-negative species by diffusing through aqueous channels called porins (outer membrane proteins), which are dispersed among the fatty molecules and can transport nutrients and antibiotics into the bacteria. Porins are large enough to allow diffusion of most penicillins, but the rate of diffusion through them is determined by the specific size of the drug molecules. For instance, penicillin G is large and enters through porins slowly; while smaller ampicillin and amoxicillin diffuse much faster. In contrast, large vancomycin can not pass through porins and is thus ineffective for Gram-negative bacteria. The size and number of porins are different in different bacteria. As a result of the two factors—size of penicillin and porin—Gram-negative bacteria can be unsusceptible or have varying degree of susceptibility to specific penicillin. Mechanism of action
The chemical structure of penicillin is triggered with a very precise, pH-dependent directed mechanism, affected by a unique spatial assembly of molecular components, which can activate by protonation.
Perineal hernia is a hernia involving the perineum (pelvic floor). The hernia may contain fluid, fat, any part of the intestine, the rectum, or the bladder. It is known to occur in humans, dogs, and other mammals, and often appears as a sudden swelling to one side (sometimes both sides) of the anus. A common cause of perineal hernia is surgery involving the perineum. Perineal hernia can be caused also by excessive straining to defecate. Other causes include prostate or urinary disease, constipation, anal sac disease (in dogs), and diarrhea. Atrophy of the levator ani muscle and disease of the pudendal nerve may also contribute to a perineal hernia. In humans
In humans, a major cause of perineal hernia is perineal surgery without adequate reconstruction. In some cases, particularly surgeries to remove the coccyx and distal sacrum, adequate reconstruction is very difficult to achieve. The posterior perineum is a preferred point of access for surgery in the pelvic cavity, particularly in the presacral space. Surgeries here include repair of rectal prolapse and anterior meningocele, radical perineal prostatectomy, removal of tumors including sacrococcygeal teratoma, and coccygectomy. Perineal hernia is a common complication of coccygectomy in adults, but not in infants and children (see coccygectomy). The standard surgical technique for repair of perineal hernia uses a prosthetic mesh, but this technique has a high rate of failure due to insufficient anchoring.