Modes of Resistance to Benzylpenicillin and Ampicillin in Twelve Klebsiella Strains

Abstract

SUMMARYTube sensitivity tests show that, of twelve penicillins, ampicillin, benzylpenicillin and 6-aminopenicillanic acid were the most active when tested against medium-sized inocula ( 106 organisms) of twelve strains of penicillinase-producing Klebsiella ( 11 Klebsiella mrogems and 1 R. oxaenae), which had been isolated from clinical material and were resistant to both ampicillin and tetracycline. An inoculum size effect was consistently noted when ampicillin and benzylpenicillin were tested against different inocula ; the effect was significantly greater with ampicillin. The following parameters were measured for the strains, using both benzylpenicillin and ampicillin : magnitude of the inoculum size effect; inherent sensitivity (sensitivity of a small inoculum) ; rate of penicillin destruction; ability of penicillins to pass bacterial permeability barriers. From considerations of the relationships between these values, it has been concluded that penicillinase is primarily responsible for the observed resistance of only two of the twelve strains ; although penicillinase and the lack of ability of penicillins to obtain free access into the bacterial cells add to the over-all penicillin resistance of the other ten strains, the primary reason for their penicillin resistance is neither their possession of penicillinase nor their permeability barrier : such resistance presumably reflects an innate lack of sensitivity of the cell wall synthesizing complex to inhibition by penicillins.

Wild type variants of penicillinase from Klebsiella aerogenes

“…The /3-lactamase from K. ozaenae 61 [3] was also examined, and its properties were found to resemble closely those of the "majority" group of K. aerogenes…”

“…The affinities of methicillin, quinacillin and cloxacillin, relative to that of benzylpenicillin, and activation energies and pH optima for each of the penicillinase preparations were determined as previously described [5,6]. The eleven strains of K. aerogenes, used in previous studies [3] 3. Results Table 1 shows the rates of hydrolysis of the six substrates relative to that of benzylpenicillin; each figure is the mean of at least three determinations.…”

Synergism between -Lactam Antibiotics: A Test of Theoretical Predictions Made with Staphylococcus Aureus

“…= maximum rate of hydrolysis of penicillin by penicillinase; and S, = concentration of penicillin at which the organisms can start to grow. The parameter S, represents the intrinsic resistance of the strain (see Hamilton-Miller, 1965), and will be referred to hereafter as the maximum non-inhibitory concentration (MNIC).…”

“…= maximum rate of hydrolysis of penicillin by penicillinase; and S, = concentration of penicillin at which the organisms can start to grow. The parameter S, represents the intrinsic resistance of the strain (see Hamilton-Miller, 1965), and will be referred to hereafter as the maximum non-inhibitory concentration (MNIC).The lag phase of the culture will be further prolonged if a competitive inhibitor of penicillinase is present, as the rate of penicillin destruction will be thereby decreased. This prolongation of lag phase (At) can be expressed (Hamilton-Miller, 1971a) by where i = concentration of competitive inhibitor and Kt = dissociation constant of penicillinase-inhibitor complex.…”

Possible Mechanism of Decreased Susceptibility of Neisseria gonorrhoeae to Penicillin

“…Resistance to a f3-lactam antibiotic may be occasioned by a ,B-lactamase which converts penicillin G to the antibiotically inactive benzyl penicilloic acid, although there is not universal agreement that ,-lactamase is involved in resistance to penicillin in either gram-positive or gram-negative cells (10,12,23), or by an acylase which converts the penicillin to 6-amino penicillanic acid, a product exhibiting at best 1/1,000 the activity of the parent molecule. The acylase, though theoretically possible as an explanation of resistance to penicillin, is probably not a factor in decreased susceptibility to the antibiotics since bacterial acylases have low affinities for their substrates.…”