Antibiotic and heavy metal resistance of Aeromonas hydrophila isolated from charal (Chirostoma humboldtianum, Valenciannes, 1835)

Abstract

Antibiotic and heavy metal susceptibilities of twenty Aeromonas hydrophila strains, isolated from the gastrointestinal tract of the charal (Chirostoma humboldtianum), an autochthonous Mexican fish, were analyzed. All strains produced ?-lactamase and were resistant to penicillin and dicloxacillin, showing single peak for minimum inhibitory concentration (MIC) distributions at 2000-4000 µg/mL and 500-1000 µg/ml, respectively. Ampicillin MIC distribution was bimodal with 20% resistant strains (125-250 µg/ml) and 80% highly resistant ones (500-4000 µg/ml). All strains were susceptible to ceftriaxone (MIC= 3.9 µg/ml) and all but one were susceptible to cefuroxime (3.9 µg/ml and 62.5 µg/ml). All strains had a single MIC distribution pattern for lead (800-3200 µg/ml), and mercury (20 µg/ml) and were considered resistant and susceptible to these ions, respectively. Fifteen percent of the isolates were resistant to arsenite (MIC= 400-800 µg/ml) and all were susceptible to silver (MIC= 1.25-2.5µg/ml), chromate (MIC= 93.5-375 µg/ml), and zinc (MIC=21.25-42.5 µg/ml).