Gonococcal resistance to beta-lactams and tetracycline involves mutation in loop 3 of the porin encoded at the penB locus.

penB is a chromosomal mutation that confers resistance to beta-lactams and tetracyclines and reduced susceptibility to quinolones in Neisseria gonorrhoeae. It is linked to the porin gene (por) and requires the increased expression of an efflux pump due to mtr. Transformation of a susceptible gonococcus (strain H1) with chromosomal DNA from strain FA140 (penA mtr penB; porin serovar IB1) and conjugal transfer of a beta-lactamase-expressing plasmid was used to produce isogenic strains for determination of equilibrium periplasmic penicillin concentrations by the method of Zimmermann and Rosselet (W. Zimmermann and A. Rosselet, Antimicrob. Agents Chemother. 12:368-372, 1977). In transformants with the Mtr and PenB phenotypes, equilibrium concentrations of penicillin were reduced. DNA sequence analysis of por from isogenic penB and penB+ transformants revealed 14 sequence differences; nine of these differences resulted in amino acid changes. Three amino acid changes were found in the putative gonococcal equivalent of the pore-constricting loop 3 of Escherichia coli OmpF. Two of these changes (Gly-101-Ala-102-->Asp-Asp) result in an increased negative charge at this position in por loop 3. PCR products comprising the complete por gene from strain FA140 were transformed into strain H1-2 (penA mtr; porin serovar IB-3), with the resulting transformants having the antibiotic susceptibility phenotype associated with penB. penB-like mutations were found in loop 3 of clinical isolates of gonococci with chromosomally mediated resistance to penicillin. We conclude that penB is a mutation in loop 3 of por that reduces porin permeability to hydrophilic antibiotics and plays an important role in the development of chromosomally mediated resistance to penicillin and tetracycline in gonococci.

Characteristics of gonococci isolated from men with urethritis in Dubai.

Neisseria gonorrhoeae were collected from men attending out-patient clinics in Dubai. The susceptibility to a range of therapeutic antibiotics and their auxotype and serotype was determined. The plasmid content of all penicillinase-producing strains was also analysed. Thirty-six strains of N. gonorrhoeae were isolated from specimens collected from 79 patients over a 24-day period. Of the 36 isolates, 9(25%) were penicillinase-producing N. gonorrhoeae (PPNG) and 15 (42%) were chromosomally resistant N. gonorrhoeae (CMRNG). CMRNG exhibited higher levels of resistance to cefuroxime, chloramphenicol, tetracycline and erythromycin than PPNG. All isolates were susceptible to ceftriaxone and spectinomycin. Three (8%) isolates showed reduced susceptibility (MIC, > or = 0.25 mg/l) to ciprofloxacin. Six isolates of PPNG carried the 4.4 MD and three the 3.2 MD penicillinase encoding plasmid. The total gonococcal population was phenotypically diverse, with 12 serovars, 6 auxotypes and 21 A/S classes. Gonorrhoea was found to be a major cause of urethritis in Dubai and the strains exhibited high levels of resistance to penicillin.