In vitro antimicrobial activity of diethyldithiocarbamate and dimethyldithiocarbamate against methicillin-resistant Staphylococcus.

Staphylococcus aureus has appeared which is highly resistant to both methicillin and aminoglycosides. Current therapy involves long-term intravenous therapy of vancomycin. Since vancomycin is currently the only drug used to treat these patients, there is a need to develop additional antimicrobial therapy. The in vitro antimicrobial effect of the metal chelator, diethyldithiocarbamate (DDTC) and its structural analog dimethyldithiocarbamate (DMTC) were investigated. Both DDTC and DMTC were effective against S. aureus including methicillin-resistant S. aureus (MRSA). By agar diffusion, DDTC at 10 micrograms per disk produced zone sizes of 12 to 21 mm and at 100 micrograms per disk produced zone sizes of 26 to 34 mm against MRSA. The DMTC produced slightly greater zone sizes against MRSA of 16 to 24 mm and 24 to 37 mm for 10 micrograms per disk and 100 micrograms per disk, respectively. The minimum inhibitory concentration (MIC) for DMTC against MRSA was 6 micrograms per ml. Both DDTC and DMTC were also effective against enterococci, Proteus mirabilis, Klebsiella pneumoniae, Klebsiella oxytoca, Escherichia coli, Enterobacter cloacae, Enterobacter aerogenes, Salmonella species, Serratia marcescens and Citrobacter freundii at 100 micrograms per disk. The MICs of DMTC for Klebsiella pneumoniae, Klebsiella oxytoca, Escherichia coli, Salmonella and Citrobacter freundii were approximately 128 micrograms per ml while the MICs for Proteus vulgaris, Proteus mirabilis, Pseudomonas aeruginosa and Serratia marcescens was greater than or equal to 256 micrograms per ml. In addition, DMTC was synergistic with gentamicin against MRSA and coagulase-negative staphylococcus species, Enterobacter cloacae, Klebsiella pneumoniae and Pseudomonas aeruginosa. Additive and synergistic effects of DMTC were displayed with gentamicin against S. aureus including methicillin-resistant S. aureus.(ABSTRACT TRUNCATED AT 250 WORDS)