Effects of Subinhibitory Concentrations of Antibiotics on Cross Walls of Cocci

Abstract

Cultures ofStaphylococcus aureus, Neisseria gonorrhoeae, and Streptococcus bovis were incubated on membrane filters on agar containing antibiotics at onethird to one-fourth the minimal inhibitory concentration for the particular bacterial strain. S. aureus was grown in the presence of oxacillin, cephaloridine, or lincomycin. N. gonorrhoeae and S. bovis were grown in the presence of penicillin. The membranes were then incubated in drug-free agar, after which viability was determined and the cells were examined by electron microscopy. S. aureus exposed to oxacillin and cephaloridine grew into cells two to seven times larger than normal that contained thick multiple cross walls. S. aureus exposed to lincomycin grew into cells 1.5 to 2 times larger than normal, with multiple thick cross walls and periheral cell walls twice the normal thickness. N. gonorrhoeae cells exposed to penicillin were slightly larger than normal and had cross walls that were up to eight times thicker than normal. After transfer to drugfree agar, cells became smaller, and some normal organisms could be seen. S. bovis incubated in the presence of penicillin grew into filaments that contained no cross walls. Two hours after the return to drug-free agar, filaments with cross walls as well as normal cells were observed. Exposure to subinhibitory concentrations of penicillin did not affect the growth of the peripheral cell wall of S. aureus, N. gonorrhoeae, or S. bovis, but appeared to inhibit lysis of cross walls in S. aureus and N. gonorrhoeae and to inhibit the synthesis of cross walls in S. bovis; that is, the rates of peripheral and cross wall formation differed in their susceptibility to penicillin. These facts suggest that peripheral growth and cross wall formation in cocci are separable processes.During bacterial growth there is an equilibrium between synthesis and lysis within the cell wall (24, 29). Cross wall growth at the equatorial plane is probably the only site of cell wall growth in gram-positive cocci (1, 5). During division, the cell wall of cocci grows inward and eventually forms a transverse cross wall (septum).Cross wall cleavage before cell separation is carried out by one or more autolytic enzymes (16,17,31,33). Subinhibitory concentrations of penicillin have appeared to inhibit cross wall lysis in Staphylococcus aureus (22). This paper reports changes in cross wall structure in three cocci species grown in the presence of subinhibitory concentrations of various antibiotics.MATERIALS AND METHODS Strain FDA 209P (ATCC 6538P) ofStaphylococcus aureus and a clinical isolate of Streptococcus bovis (8) were grown in Trypticase soy broth (BBL) for 20 h at 37 C. A clinical isolate ofNeisseria gonorrhoeae (21) was grown on brain heart agar (Difco) with 5% horse blood and IsoVitalex (BBL) (BHASI) for 24 h at 37 C in a 10% CO2 atmosphere.Trypticase soy agar (BBL) and BHASI plates with and without antibiotics were prepared. Penicillin G (Squibb), oxacillin (Bristol), cephaloridine (Lilly), and lincomycin (Upjohn) were used. Drug concentr...

Intermittent or Continuous Therapy of Experimental Meningitis Due to Streptococcus pneumoniae in Rabbits: Preliminary Observations on the Postantibiotic Effect in Vivo

“…The persistent effect of antibiotics on bacteria has been demonstrated in vitro for a number of different species: S. aureus [11][12][13], S. pneumoniae, Streptococcus [29], and E. coli [12]. The results are qualitatively similar for each of these organisms.…”

“…Some effects of subinhibitory concentrations of antibiotics on bacterial morphology in vitro are well known [13]. In our model, scanning electron microscopy of specimens of CSF aspirated 3 hr after exposure to ampicillin revealed large and aberrant pneumococcal forms.…”

“…The postantibiotic effect has been clarified further by in vitro studies [11,12], in which short-term exposure of Staphylococcus aureus or Escherichia coli to various antibiotics at or above the MIC produced a continued postantibiotic effect (decreased or stable bacterial counts) for various periods of time after removal of the antibiotic. Even subinhibitory levels of antibiotics can alter the growth rate and morphology of bacteria [13] and may modify important host defense mechanisms [14,15]. Previous exposure of E. coli to sub-MIC levels of chloramphenicol resulted in a prolonged decline in bacterial concentrations after exposure of the culture to leukocytes, antibody, and complement in vitro [12].…”

Protein antigens of encapsulated Klebsiella pneumoniae surface exposed after growth in the presence of subinhibitory concentrations of cephalosporins

“…1 and Fig. 2a (22,36). In a recent study we reported that cephalosporin antibiotics at a concentration as low as 1/10 of the MIC caused morphological alterations, reduced the production of enterochelin and capsular materials, and potentiated the agglutination by serum prepared against a nonencapsulated strain of K. pneumoniae (20).…”

Efeito de concentrações subinibitórias de penicilina sobre antígenos de estreptococos do grupo G

“…Sendo assim, não devemos atribuir o seu aumento a um desarranjo na parede celular que, porventura, possibilitasse a maior exposição dos determinantes antigênicos como as alterações causadas nos títulos aglutinantes conseguidos com o antíge-no O de salmonelas crescidas na presença de antibiótico 11 . Com estas salmonelas foi verificado que filamentos longos que possuem a mesma morfologia das células tratadas com antibióticos apresentam um aumento significante nos títulos aglutinantes e produzem aglutinação mais floculenta do que as bactérias de morfologia normal.…”