Plasmids and resistance to antimicrobial agents in Aeromonas sobria and Aeromonas hydrophila clinical isolates

Abstract

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.

Impact of an Urban Effluent on Antibiotic Resistance of Riverine Enterobacteriaceae and Aeromonas spp

“…Most of the tested strains carried several plasmids, including some with a high molecular weight. However, no correlation was found between the number of antibiotic resistance markers and the number of plasmid bands, as previously reported (15), suggesting that most of these plasmids either encoded characters other than antibiotic resistances or were cryptic (13). In enterobacteria, resistances which are known to be exclusively (quinolones) or mainly (fosfomycin) due to mutations were found to be chromosomally located.…”

Antibiotic resistance of Aeromonas hydrophila isolated from marketed fish and prawn of South India

“…Local selective pressures can influence the antibiotic resistance. Chang and Bolton (1987) found that more percentage of Asian isolates of A. hydrophila were resistant to tetracycline and rifampicin than Australian isolates. More than 50% of the A. hydrophila strains was resistant to tetracycline and occurrence of tetracycline resistant strains of A. hydrophila from different sources was reported (Ansary et al, 1992;Ramteke et al, 1993;Pettibone et al, 1996;Son et al, 1997;Kampfer et al, 1999).…”

Use of plasmid profiles in epidemiologic surveillance of disease outbreaks and in tracing the transmission of antibiotic resistance

“…(33,82) and Plesiomonas shigelloides (83). Plasmids have also been reported in Vibrio cholerae (160).…”