Inhibition of beta-lactam antibiotics at two different times in the cell cycle of Streptococcus faecium ATCC 9790

Abstract

Treatment of Streptococcus faecium ATCC 9790 with sublytic concentrations of beta-lactam antibiotics revealed two different division blocks in the cell division cycle. One block, induced by N-formimidoyl thienamycin and methicillin, occurred before the completion of chromosome replication, whereas the other, induced by cefoxitin and cephalothin, took place later in the cycle. In addition, these antibiotics gave rise to distinct morphological forms; the antibiotics acting at the earlier block point produced mainly "dumbbells," whereas those affecting the later time formed "lemons." When used in combination N-formimidoyl thienamycin and cefoxitin exerted synergistic killing on this strain. These data suggest that beta-lactam antibiotics have at least two sites of action in S. faecium.

Relationship of shape to initiation of new sites of envelope growth in Streptococcus faecium cells treated with beta-lactam antibiotics

“…According to this alternative explanation, the primary sites of the ampicillin-treated cells were required to reach larger sizes than were the cephalothin-treated cells because new secondary sites could not be initiated at the normal rate in the ampicillin-treated cells; therefore, the existing primary sites in the ampicillintreated cells had to grow to greater than normal sizes to accommodate the continued synthesis of macromolecules. The latter explanation is consistent with studies which indicated that antibiotics such as ampicillin that bind preferentially to PBP3 block a process in the cell cycle required for division about 40 min before cell separation, whereas drugs such as cephalothin which bind to PBP2 preferentially interfere with a step needed for division that occurs about 12 min before separation (12). At the growth rate used in the present studies, new sites would be initiated in untreated cells at about the time that ampicillin would disturb normal surface growth (i.e., about 40 min before division) (4,9); this could explain the greater inhibition of new sites observed in the presence of this drug.…”

“…were added to final concentrations of 80 and 2 ,ug/ml, respectively, to cultures containing the equivalent of about 43 ,ug (dry weight) of cells per ml. These drug concentrations were selected on the basis of the highest concentration that would not significantly affect increases in turbidity rather than on the basis of maximum yields of lemons and dumbbells (12). Cell numbers were determined by electronic particle analysis (Celloscope; Particle Data Co., Chicago, Ill.) as described before (6).…”

“…It is well known that many of these alterations in shape can be related to the affinity of a given drug for various penicillin-binding proteins (PBPs) (2,15). For example, recent studies on S. faecium have shown that addition of an antibiotic with a preferential affinity for PBP2 results in an enrichment of cells which have one elongated, tapered pole and which are termed lemons, whereas addition of those drugs that have a preferential affinity for PBP3 result in cylindrical nondividing sites of envelope growth which give rise to cells termed dumbbells (12).…”

“…The addition of P-lactam antibiotics to cultures is known to distort the morphology of bacteria, leading to cell elongation or various types of cell surface bulging, depending on the organism, the drug, the duration of treatment, and the drug concentration used (10)(11)(12)(13)18). It is well known that many of these alterations in shape can be related to the affinity of a given drug for various penicillin-binding proteins (PBPs) (2,15).…”

Synthesis and antibacterial activity of new antibiotics arising from cephalosporin-monobactam coupling

“…10 The chosen β-lactam moieties have been Cefotaxime 11 (see Table 2), well known for its antibacterial activity, and monobactams 11, (E) The anti and the syn isomers of the methoxyiminopyridin-3-ylacetic acids (E)-10 and (Z)-10 were obtained by treating oxopyridin-3-ylacetic acid 14 (synthesized by oxidation of 3-acetylpyridine 13 as reported in the literature 16 ) with O-methylhydroxylamine (Scheme 3). After esterification with diazomethane the two isomers were separated by flash chromatography and were subsequently hydrolyzed to the free acids (E)-10 and (Z)-10: The configuration was assigned on the basis of the relative rates of methyl ester hydrolysis.…”