In vitro susceptibility to β-lactam antibiotics and viability of Neisseria gonorrhoeae strains producing plasmid-mediated broad- and extended-spectrum β-lactamases

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N. gonorrhoeae strains producing plasmid-mediated broad- and extended-spectrum β-lactamases (ESBLs) have been obtained in vitro and studied for their viability and susceptibility to β-lactam antibiotics. The artificial p bla TEM-1 and p bla TEM-20 plasmids were constructed by site-directed mutagenesis from a p bla TEM-135 plasmid of the Toronto/Rio type, which was extracted from the clinical isolate. MIC values were determined for a series of β-lactam antibiotics, including benzylpenicillin, ampicillin, cefuroxime, ceftriaxone, cefixime, cefotaxime, cefepime, meropenem, imipenem, and doripenem. The N. gonorrhoeae strain carrying the p bla TEM-20 plasmid exhibited a high level of resistance to penicillins and II-IV generation cephalosporins (MIC ≥ 2 mg/L) but not to carbapenems (MIC ≤ 0.008 mg/L). However, this strain stopped growing after 6 hours of cultivation. The reduced viability was not associated with the plasmid loss but can be explained by the following factors: the presence of the plasmid itself, which requires additional costs for its reproduction, and the expression of ESBL, which can affect the structure of the peptidoglycan layer in the cell membrane. The cell growth was mathematically modeled using the generalized Verhulst equation. The parameter, characterizing the maximum possible number of cells grown under given conditions, decreased within the wild type (without plasmids) - p bla TEM-135 - p bla TEM-1 - p bla TEM-20 series, i.e. , the plasmid-bearing strains had reduced viability compared to that of the wild-type strain. The kinetics for the cell death of N. gonorrhoeae strains without the p bla TEM-20 plasmid in the presence of ceftriaxone can be described by a modified Chick-Watson law. For the N. gonorrhoeae strain that harbors the p bla TEM-20 plasmid, the kinetics for cell number changes with time reflected several processes: the hydrolysis of ceftriaxone by TEM-20 β-lactamase, growth and gradual death of cells. The demonstrated reduced viability of N. gonorrhoeae strains with the p bla TEM-20 plasmid probably explains the absence of clinical isolates of N. gonorrhoeae that produce ESBL.