Heteroresistance to penicillin in Streptococcus pneumoniae
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Edited by Emil C. Gotschlich, The Rockefeller University, New York, NY, and approved July 13, 2007 (received for review March 14, 2007)
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Fig. 1.Characteristics of heteroresistant S. pneumoniae strains in the penicillin Etest. (A) Typical example of the zone phenomenon observed in the penicillin Etest for some S. pneumoniae strains with heteroresistance to penicillin (see also Table 2). The black arrow indicates the end of the bacterial lawn, and the white arrow points to the end of the hemolysis zone. (B) Satellite colonies observed in the penicillin Etest for some S. pneumoniae strains with heteroresistance to penicillin.
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Fig. 2.PAP for S. pneumoniae strains (Table 1). The x axis indicates the penicillin concentration in micrograms per milliliter used to select supopulations with higher penicillin-resistance levels, and on the y axis, the frequency of bacterial cells is given as the logarithm to the base 10 of cfu per milliliter. (A) PAP for S. pneumoniae strains collected in Switzerland and laboratory strains (see also Table 1). (B) PAP for S. pneumoniae strains representative of international clones (see also Table 1). (C) PAP for S. pneumoniae strains representative of international clones (see also Table 1).
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Fig. 3.PAP for the HOM* strains of three Swiss strains 208.39, 304.80, and 106.44 with heteroresistance to penicillin. HOM*1, HOM*2, and HOM*3 stands for derivatives of the respective strains obtained by selection of single colonies during successive PAP experiments. Colonies were selected from the plate with the highest or second-highest penicillin concentration showing bacterial growth. HOM*1p stands for a HOM1* strain that has been passaged 10 times on CSBA plates without antibiotics before repeating PAP. The x axis indicates the respective penicillin concentration in micrograms/milliliters used to select resistant subpopulations; on the y axis, the frequency of bacterial cells is given as the logarithm to the base 10 of cfu per milliliter.
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Fig. 4.S. pneumoniae strains with heteroresistance to penicillin exhibited visible heterogeneity of bacterial colony size when grown on CSBA plates with or without penicillin. This is demonstrated by comparing colony size diameters between the laboratory strain D39 and strain 304.80 grown on agar plates without antibiotics (A) and plates containing 0.02 μg/ml penicillin for strain D39 and 0.5 μg/ml penicillin for strain 304.80 (B). The x axis indicates the colony diameter in millimeters. The y axis gives the proportion of colonies with the respective colony diameter.
Footnotes
- †To whom correspondence should be addressed. E-mail: kathrin.muehlemann{at}ifik.unibe.ch
- © 2007 by The National Academy of Sciences of the USA
