Resistance of Aeromonas hydrophila to beta-lactam antibiotics

The activity of some beta-lactam antibiotics upon 20 strains of Aeromonas hydrophila and some properties of their beta-lactamases have been studied. High degree of resistance to benzylpenicillin and lower resistance to ampicillin and cephaloridine was observed. Clavulanic acid showed the highest activity. When clavulanic acid was assayed at subinhibitory concentrations in association with ampicillin. MICs of the latter decreased to two- to eight-fold. All strains produced inducible beta-lactamases with high activity upon ampicillin. A group of cephalosporinase-like enzymes was also found. Some beta-lactamases were inhibited by cloxacillin, and most of them were completely inhibited by 5 mg/l of clavulanic acid. Low impermeability of Aerom. hydrophila cells to beta-lactams was observed.