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The antimicrobial susceptibilities of 75 Aeromonas isolates were determined by agar dilution. Differences in resistance patterns were observed between strains isolated from different geographic locations and between A. sobria and A. hydrophila isolates. Multiple resistance was common; however, only one conjugative plasmid was detected. This 110-megadalton plasmid mediated resistance to eight antibiotics.The motile aeromonads are recognized both as causes of infection in immunocompromised patients and as enteric pathogens which may cause diarrhea in healthy individuals (4,9,20). In view of the increasing clinical importance of these organisms, and since little is known about the genetic basis for drug resistance in the genus (1,7,12,19), we wished to assess the plasmid content of hospital isolates of Aeromonas spp. Because previous studies on antimicrobial susceptibility and its genetic basis were performed before the recent division of the motile aeromonads into three species (16), our studies also aimed to examine any speciesassociated antimicrobial resistance patterns.A total of 75 Aeromonas isolates were tested. Thirty-one strains were from patients in metropolitan hospitals in Australia and were collected during 1980 and 1981. A total of 29 of these were fecal isolates, including 26 from patients with diarrhea and 2 from patients with an infected wound and septicemia, respectively. Forty-four strains were collected in 1982, forty from diarrheal patients in Jakarta, Indonesia, and four from patients in Vellore, India, comprising three fecal isolates from diarrheal patients and one isolate from an infected wound. In all cases, isolates were taken from individual patients without duplication. The isolates from infected wounds or septicemias were recovered in pure culture and were considered to be the primary pathogens, whereas the fecal isolates were recovered in mixed culture and their clinical significance remains undetermined. The isolates were identified by the criteria of Popoff (16).Antimicrobial susceptibility testing was performed using a standard agar dilution method (17). Strains were considered resistant if more than 100 colonies grew from an inoculum of approximately 104 CFU on Iso-Sensitest agar (Oxoid Ltd., Basingstoke, England) containing antimicrobial agents at the concentrations shown in Table 1. These concentrations were chosen on the basis of the MICs reported for Aeromonas spp. by Richardson et al. (17). In general, concentrations 10-fold higher than those required to kill at least 50% of the Aeromonas strains in that study were used.All isolates were found to be resistant to at least one of the 17 antimicrobial agents tested. Multiple resistance to 3, 4, or 5 agents was common (76% of isolates), and resistance to as many as 11 agents was observed.

Plasmid DNA was isolated from Staphylococcus aureus by a rapid method that depends on the precipitation of DNA from cleared lysates by cetyltrimethylammonium bromide at low salt concentrations. The method was validated by its ability to provide DNA for restriction analysis of a highly relaxable plasmid species that is not isolated by more traditional techniques. The DNA can be digested with restriction endonucleases and used for transformation without further purification. The method also provides the basis for analysing staphylococcal plasmids that display a high frequency of deletion after transfer. Simple modifications of the technique allow plasmid DNA to be isolated from other bacteria and the rapid purification of DNA samples before in vitro manipulation.

SUMMARY. Aminoglycoside-resistance determinants in staphylococci are borne on conjugative and non-conjugative plasmids. The conjugative plasmids were found in methicillin-resistant strains of Staphylococcus aureus isolated recently in Darwin and Sydney, Australia and in Houston, Texas, USA. These plasmids and the class-2 conjugative plasmid reported by Archer and Johnston (1 983) had similar patterns of EcoR 1 restriction-endonuclease fragments, encoded resistance to gentamicin, kanamycin and neomycin, transferred to a non-lysogenic recipient in conditions that promoted close cell-to-cell contact and mobilised a small, non-conjugative plasmid. A further plasmid, pWG 14, encoding resistance to kanamycin, neomycin, streptomycin, erythromycin and lincomycin, also displayed conjugative properties but did not mobilise the small, non-conjugative plasmid. The transfer frequency of all conjugative plasmids was stimulated by the addition of polyethylene glycol, particularly at concentrations above 20%, to mixtures of donor and recipient broth cultures. Polyethylene glycol appeared to promote close cell-to-cell contact between donor and recipient cells. A representative of the most common aminoglycoside-resistance plasmids in Australian isolates of methicillin-resistant S. aureus was non-conjugative and transferred by a bacteriophage-mediated system to a lysogenic recipient. With the exception of plasmid pWG 14, the conjugative plasmids were also transferred by a bacteriophage-mediated system. Furthermore, cultural conditions that favoured conjugative transfer of plasmids inhibited bacteriophage-mediated transfer and vice versa. The efficacy of the two transfer systems for analysing the plasmids of gentamicin-resistant, methicillin-resistant isolates of S. aureus has been compared.

Perkinsus marinus, a protozoan parasite of the Eastern oyster Crassostrea virginica, has severely impacted oyster populations from the Mid-Atlantic region to the Gulf of Mexico coast of North America for more than 30 yr. Although a chemotherapeutic treatment to reduce or eliminate P. marinus from infected oysters would be useful for research and hatchery operations, an effective and practical drug treatment does not currently exist. In this study, the antimicrobial drug triclosan 5-chloro-2-(2, 4 dichlorophenoxy) phenol, a specific inhibitor of Fab1 (enoyl-acyl-carrier-protein reductase), an enzyme in the Type II class of fatty acid synthetases, was tested for its effects on viability, proliferation and fatty acid synthesis of in vitro-cultured P. marinus meronts. Treatment of P. marinus meront cell cultures with concentrations of ≥2 µM triclosan at 28°C (a temperature favorable for parasite proliferation) for up to 6 d stopped proliferation of the parasite. Treatment at ≥5 µM at 28°C greatly reduced the viability and fatty acid synthesis of meront cells. Oyster hemocytes treated with ≥20 µM triclosan exhibited no significant (p < 0.05) reduction in viability relative to controls for up to 24 h at 13°C. P. marinus meronts exposed to ≥2 µM triclosan for 24 h at 13°C exhibited significantly (p < 0.05) lower viability relative to controls. Exposure of P. marinus meronts to triclosan concentrations of ≥20 µM resulted in > 50% mortality of P. marinus cells after 24 h. These results suggest that triclosan may be effective in treating P. marinus-infected oysters. KEY WORDS: Triclosan · Dermo disease · Perkinsus marinus · Eastern oyster · Fatty acid synthesis Resale or republication not permitted without written consent of the publisherDis Aquat Org 67: [217][218][219][220][221][222][223][224] 2005 To be practical for use in controlling Perkinsus marinus infection, a drug therapy needs to have several important features: (1) high specific action against the parasite; (2) low toxicity to the host; (3) application through direct addition to water in holding containers; (4) low/no toxicity to humans; (5) low cost and ready availability. Several studies evaluating potential chemotherapeutic agents for treatment of Dermo disease have been published, but the protocols so far developed to successfully treat P. marinus infection in oysters fail to meet several of these criteria (Ray 1966a,b, Calvo & Burreson 1994, Faisal et al. 1999, Delaney et al. 2003.Parasitic protozoans must either acquire lipids from their host or synthesize lipids de novo to produce the new cell membrane necessary for cell replication. Inhibiting the ability to synthesize new membrane prevents the parasite from increasing in surface area, thereby halting cell proliferation and disease progression.The antimicrobial drug triclosan, 5-chloro-2-(2, 4 dichlorophenoxy) phenol, has been used in a wide array of consumer products such as soaps, toothpastes and household plastics for the last 30 yr. Triclosan inhibits fatty acid synthesis and stops the...