Bacteria gram-positive, membranes

Although it would be out of place to give here an extensive account of the surface anatomy of bacteria, current interest in the exact location of compounds in the anatomical components of cells, for example, in membranes, granules, mitochondria, and ribosomes, requires a reasonably precise description of the location of teichoic acids. In its turn, this requires an understanding of the main features of the outer regions of bacteria. Gram-positive bacteria possess a rigid cell-wall which is responsible for... 

Bacillus subitilis Second best studied bacteria Gram positive—no outer membrane—excretes proteins Problem excreting some foreign proteins Makes large amounts and varieties of proteases (degrades proteins rapidly) More difficult to manipulate genetically owing to limited vectors and promoters Instability of plasmids more problematic than E. coli... 

Gram-negative bacteria Gram-positive bacteria Outer membrane No outer membrane peptidoglycan layer thicker peptidoglycan layer ... 

Nisin acts bactericidally primarily against gram-positive bacteria. It acts best at acid pH and is almost insoluble at physiological pH. Nisin and probably all lantibiotics appear to permeabilize the bacterial ceU membrane to release small molecules, resulting in an immediate coUapse of the membrane... 

Fig. 9.1 Schematic representation of possible mechanisms of resistance in Gram-negative and Gram-positive bacteria. 1, antibiotic-inactivating enzymes 2, antibiotic efflux proteins 3, alteration or duplication of intracellular targets 4, alteration of the cell membrane reducing antibiotic uptake 5, alterations in porins or lipopolysaccharide reducing antibiotic uptake or binding.

AGAC-modifying enzymes are active outside the cytoplasmic membrane, in the periplasmic space in Gram-negative bacteria and extracellularly in Gram-positives. Table 9.4 summarizes some of the enzymes involved in AGAC resistance and their spectrum of activity. 

Gram-negative bacteria are intrinsically resistant to low levels of fusidic acid (a steroid) due to exclusion by the outer membrane. Nevertheless, acquired resistance does occur which has the effect of increasing the level of resistance to the antibiotic. Acquired resistance also occurs in Gram-positive bacteria normally susceptible to fusidic acid. 

The operation of cytochrome P450 in alkane oxidation has been reported both in bacteria and in yeasts. It has been shown that alkane hydroxylases of CHYP 153 are widespread both in Gram-negative and Gram-positive bacteria that lack the integral membrane alkane hydroxylase (van Beilin et al. 2006). 

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