Minimum inhibitory and lethal concentrations
The antimicrobial activities of chitosans and COS are depicted
in Fig. 1. It can be easily observed that MICs and MLCs depend on
the bacterium being studied, and on the MW of the active
compound tested. Growth of E. coli was markedly inhibited by COS
(Fig. 1a)—and the associated MICs were below 0.10% (w/v); this
threshold is lower than that reported elsewhere (Gerasimenko
et al., 2003)—1.0% (w/v) for a 5 kDa oligomer effect on growth, but
slightly higher than that associated with a 6 kDa oligomer—0.06%
(w/v). Furthermore, the inhibitory effect decreased slightly as MW
increased—0.25% (w/v) of high MW chitosan was required
to inhibit growth of E. coli. In the case of S. aureus (Fig. 1b),
chitosans showed a stronger antibacterial activity than COS;
apparently, chitosans exhibit a stronger bactericidal effect upon
Gram-positive than Gram-negative bacteria (No et al., 2002). The
MICs varied from 0.10% (in the case of high and medium MW
chitosan) to 0.23% (w/v) (in the case of o3 kDa COS); these values
are relatively high when compared with those obtained by Jeon
et al. (2001)—0.06% and 0.12% (w/v) for chitosan and COS,
respectively. In addition, the differences found between MICs and
MLCs for S. aureus were more substantial than those obtained for
E. coli: MLCs of COS for S. aureus, ca. 0.5% (w/v), were indeed more
than 3-fold those of high and mediumMWchitosans, ca. 0.15% (w/v).
Minimum inhibitory and lethal concentrationsThe antimicrobial activities of chitosans and COS are depictedin Fig. 1. It can be easily observed that MICs and MLCs depend onthe bacterium being studied, and on the MW of the activecompound tested. Growth of E. coli was markedly inhibited by COS(Fig. 1a)—and the associated MICs were below 0.10% (w/v); thisthreshold is lower than that reported elsewhere (Gerasimenkoet al., 2003)—1.0% (w/v) for a 5 kDa oligomer effect on growth, butslightly higher than that associated with a 6 kDa oligomer—0.06%(w/v). Furthermore, the inhibitory effect decreased slightly as MWincreased—0.25% (w/v) of high MW chitosan was requiredto inhibit growth of E. coli. In the case of S. aureus (Fig. 1b),chitosans showed a stronger antibacterial activity than COS;apparently, chitosans exhibit a stronger bactericidal effect uponGram-positive than Gram-negative bacteria (No et al., 2002). TheMICs varied from 0.10% (in the case of high and medium MWchitosan) to 0.23% (w/v) (in the case of o3 kDa COS); these valuesare relatively high when compared with those obtained by Jeonet al. (2001)—0.06% and 0.12% (w/v) for chitosan and COS,respectively. In addition, the differences found between MICs andMLCs for S. aureus were more substantial than those obtained forE. coli: MLCs of COS for S. aureus, ca. 0.5% (w/v), were indeed morethan 3-fold those of high and mediumMWchitosans, ca. 0.15% (w/v).
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