Effect of beta-lactamase and salt on mecillinam susceptibility of enterobacterial strains

Abstract

Out of 15 selected enterobacterial strains resistant to ampicillin, 12 were able to transfer resistance to mecillinam to Escherichia coli K-12. This resistance to mecillinam was found to be coupled to the presence of beta-lactamase. One strain contained a beta-lactamase characterized as a class IV beta-lactamase, whereas the other 14 strains possessed a class HI (TEM-like) beta-lactamase. The specific activity of the class IV beta-lactamase against mecillinam was 55%, and those of the class III beta-lactamases were 180% of the specific activities against benzylpenicillin. In view of this high beta-lactamase sensitivity of mecillinam, the minimal inhibitory concentrations were lower than might be expected. However, after enzymatic hydrolysis of mecillinam, no antibacterial activity was found. At increasing salt or buffer concentrations the minimal inhibitory concentrations of mecillinam increase to a varying extent for all strains, independently of betalactamase production. This study indicates that the increase in miniimal inhibitory concentration is dependent on the salt concentration. The study also shows that this increase is not due to salt-mediated hydrolysis or to stimulation either of beta-lactamase activity or of beta-lactamase production. To explain the difference between ampicillin and mecillinam resistance in the beta-lactamase-positive strains, a hypothetical model is presented and discussed.Mecillinam (6-beta-amidinopenicillanic acid) shows a remarkably high activity against gramnegative bacteria, whereas its activity against staphylococci and streptococci is relatively low (6). At low concentrations of this antibiotic Escherichia coli becomes spherical; at higher concentrations (>10 ,tg/ml) cells tend to lyse (7). Previous studies of this antibiotic include antibacterial activity (2, 6), mechanism of action (4,7,8,12), and emergence of resistance (1,3,7).Three factors may contribute to bacterial resistance to beta-lactam antibiotics: (i) the specific antibiotic susceptibility of the target, (ii) the specific penetration barrier function of the cell wall, and (iii) the presence of a beta-lactamase (penicillin amido-beta-lactamhydrolase, EC 3.5.2.6). A combination of these factors may occur.In vitro Enterobacteriaceae may readily become resistant to mecillinam (2). During successive passages in media containing mecillinam, an Aerobacter aerogenes strain developed resistance to mecillinam more rapidly than against ampicillin, cloxacillin, or cephazolin (11). Crossresistance between mecillinam and ampicillin is minimal (1). These data and the fact that the spontaneous mutation frequency from mecillinam-susceptible to -resistant strains is quite high (10-5 to 10-4) for beta-lactamase-negative E. coli (3) strongly suggest that these kinds of mecillinam resistance are all due to chromosomal mutations of the mecillinam target or of other components of the cell wall.Richmond showed that a number ofpenicillins were impeded in penetrating the periplasmic space of E. coli UB 1005, whereas a penetration barrier...

Activity of Mecillinam and Clavulanic Acid on ESBL Producing and Non- ESBL Producing Escherichia Coli Isolated From UTI Cases

“…Further, few beta lactamases like type IIIa and IVc have activity against mecillinam causing hydrolysis of the agent. 10 These factors together results in mecillinam resistance in clinical practice. Addition of any compound that has inhibitory effect on these enzymes may improve the antibacterial activity of mecillinam.…”

Aminoglycoside phosphotransferase-II-mediated amikacin resistance in Escherichia coli

“…Conjugative plasmid transfer experiments were performed as described previously (2). After conjugation, the diluted washed suspensions were plated on brain heart infusion agar plates containing rifampin (100 ,tg/ml), nalidixic acid (80 jg/ml), and kanamycin (50 ug/ml) or amikacin (ranging from 2 to 128 ,ug/ml) as selective agents.…”

“…Cell-free sonicates were prepared as described previously (2). Cell-free osmotic shock extracts were prepared by the double osmotic shock procedure of Dankert and Woltjes (6).…”

Comparison of in vitro Activities of Eight New <i>β</i>-Lactam Compounds against Cephalothin-Resistant <i>Enterobacteriaceae</i> from Hospital Patients

“…Therefore, stability to /3-lactamase hydrolysis has considerable clinical importance. As has been shown by previ ous studies, cefotaxime, moxalactam, cef tazidime and ceftriaxone are either not hy drolyzed or hydrolyzed to a very small ex tent by /3-lactamases produced by aerobic gram-negative bacteria [4,7,20], Cefoxitin has also been proved considerably to resist destruction by bacterial /3-lactamases [7], In contrast to the afore-mentioned drugs, mecillinam, mezlocillin and piperacillin are hydrolyzed by /3-lactamases of Enterobacteriaceae, especially the most common type; the TEM enzymes [3,9,22], Our re sults are relevant to the above findings in the sense that the production of /3-lactamase(s) did not affect the activity of cefo taxime, moxalactam, ceftriaxone, ceftazi dime and cefoxitin whereas it did influ ence the activity of mecillinam mezlocillin and piperacillin.…”