N-Carboxybutyl chitosan, a modified chitin of crustacean origin, displayed inhibitory, bactericidal, and candidacidal activities when tested against 298 cultures of various pathogens. Examination by electron microscopy showed that microbial cells exposed to N-carboxybutyl chitosan underwent marked morphological alterations. The data are of importance in defining the suitability of N-carboxybutyl chitosan as a wound dressing.A number of polysaccharides, mainly cross-linked dextran, calcium alginate, carboxymethyl starch, modified agar, and carboxymethyl cellulose, are used in wound treatment (13,17). These polysaccharides, however, do not seem to combine favorable physical forms with functional properties; rather, besides the hemostatic action of oxycellulose, no functional property has been reported (17). The same is true for gelatin and collagen (15). On the other hand, chitin derivatives are not in widespread use as wound dressings, and relevant studies on wound healing have been confined to a few recent articles (1, 11). Interestingly, some antibacterial and antifungal activities have been described with chitosan and modified chitosans (5,8,9,18).N-Carboxybutyl chitosan is more versatile than any other polysaccharide currently used in wound management and lends itself to the manufacture of wound dressings with peculiar characteristics. Such dressings, in particular, can stimulate ordered regeneration (3) and vascularization (10) of tissue and allow gaseous exchange and turn into a gel form when they are in contact with body fluids (14), thus permitting dressing removal without disturbing the newly formed tissues. We undertook the present study to define the antimicrobial properties of N-carboxybutyl chitosan and to test it in different physical forms in view of its use in wound management. N-Carboxybutyl chitosan, which was prepared from crustacean chitosan (degree of deacetylation, 0.73) according to a proprietary procedure (R. Muzzarelli, U.S. patent 4,835,265, June 1986) and as described previously (12, 14), was tested against a variety of gram-positive and gramnegative pathogens and Candida spp. A total of 298 strains were used, all of which were freshly isolated from clinical material and identified according to conventional laboratory criteria.Two different methods were used to assess the antimicrobial activity of N-carboxybutyl chitosan. The first method was a quantitative assay based on conventional agar dilution tests (20), with final concentrations being 2, 4, 6, 8, and 9 mg/ml (concentrations above 9 mg/ml did not permit full solubilization of N-carboxybutyl chitosan into the test medium). The inoculum suspensions were prepared from fresh broth cultures and adjusted to obtain a concentration of approximately 107 CFU/ml. Test plates were inoculated by using an automatic replicating device (Titertek; Flow Labo-* Corresponding author. ratories, Inc., McLean, Va.) that delivered 1 1.l of bacterial suspension per spot. A control plate with no N-carboxybutyl chitosan was inoculated first, and a second co...

The Gram-negative opportunistic pathogen, Klebsiella pneumoniae, is responsible for causing a spectrum of community-acquired and nosocomial infections and typically infects patients with indwelling medical devices, especially urinary catheters, on which this microorganism is able to grow as a biofilm. The increasingly frequent acquisition of antibiotic resistance by K. pneumoniae strains has given rise to a global spread of this multidrug-resistant pathogen, mostly at the hospital level. This scenario is exacerbated when it is noted that intrinsic resistance to antimicrobial agents dramatically increases when K. pneumoniae strains grow as a biofilm. This review will summarize the findings about the antibiotic resistance related to biofilm formation in K. pneumoniae.

This study produces new findings that highlight a positive correlation between antibiotic resistance profile and biofilm-forming ability in XDR K. pneumoniae strains. These new evidences might contribute to the progress in selection of therapeutic treatments of infections caused by K. pneumoniae resistant also to the 'last line of defence' antibiotics, that is, carbapenems.

A novel resistance gene, named poxtA, encoding a protein of the antibiotic resistance (ARE) ABC-F lineage, was identified in the genome of an MRSA of clinical origin. PoxtA can confer decreased susceptibility to phenicols, oxazolidinones and tetracyclines and is associated with a putative mobile element that could contribute to its horizontal dissemination.

A total of 387 clinical strains of erythromycin-resistant (MIC, ≥1 μg/ml) Streptococcus pyogenes, all isolated in Italian laboratories from 1995 to 1998, were examined. By the erythromycin-clindamycin double-disk test, 203 (52.5%) strains were assigned to the recently described M phenotype, 120 (31.0%) were assigned to the inducible macrolide, lincosamide, and streptogramin B resistance (iMLS) phenotype, and 64 (16.5%) were assigned to the constitutive MLS resistance (cMLS) phenotype. The inducible character of the resistance of the iMLS strains was confirmed by comparing the clindamycin MICs determined under normal testing conditions and those determined after induction by pregrowth in 0.05 μg of erythromycin per ml. The MICs of erythromycin, clarithromycin, azithromycin, josamycin, spiramycin, and the ketolide HMR3004 were then determined and compared. Homogeneous susceptibility patterns were observed for the isolates of the cMLS phenotype (for all but one of the strains, HMR3004 MICs were 0.5 to 8 μg/ml and the MICs of the other drugs were >128 μg/ml) and those of the M phenotype (resistance only to the 14- and 15-membered macrolides was recorded, with MICs of 2 to 32 μg/ml). Conversely, heterogeneous susceptibility patterns were observed in the isolates of the iMLS phenotype, which were subdivided into three distinct subtypes designated iMLS-A, iMLS-B, and iMLS-C. The iMLS-A strains (n = 84) were highly resistant to the 14-, 15-, and 16-membered macrolides and demonstrated reduced susceptibility to low-level resistance to HMR3004. The iMLS-B strains (n = 12) were highly resistant to the 14- and 15-membered macrolides, susceptible to the 16-membered macrolides (but highly resistant to josamycin after induction), and susceptible to HMR3004 (but intermediate or resistant after induction). The iMLS-C strains (n = 24) had lower levels of resistance to the 14- and 15-membered macrolides (with erythromycin MICs increasing two to four times after induction), were susceptible to the 16-membered macrolides (but resistant to josamycin after induction), and remained susceptible to HMR3004, also after induction. The erythromycin resistance genes in 100 isolates of the different groups were investigated by PCR. All cMLS and iMLS-A isolates tested had theermAM (ermB) gene, whereas all iMLS-B and iMLS-C isolates had the ermTR gene (neither methylase gene was found in isolates of other groups). The M isolates had only the macrolide efflux (mefA) gene, which was also found in variable proportions of cMLS, iMLS-A, iMLS-B, and iMLS-C isolates. The three iMLS subtypes were easily differentiated by a triple-disk test set up by adding a josamycin disk to the erythromycin and clindamycin disks of the conventional double-disk test. Tetracycline resistance was not detected in any isolate of the iMLS-A subtype, whereas it was observed in over 90% of both iMLS-B and iMLS-C isolates.