[Resistance to azithromycin of Neisseria gonorrhoeae strains isolated in Poland in 2012-2013 years].

BACKGROUND

Azithromycin is one of the most commonly used macrolide antibiotics. As other macrolides it inhibits bacterial proteins synthesis by binding with V domene of bacterial 23S rRNA. Resistance to azithromycin can be related to: 1. Mutations in gene encoding 23S rRNA. Significant effect on azithromycin MIC (minimal inhibitory concentration) is not observed when the mutation occurs only in 1 allele. In case of mutations occurring in 4 alleles, more common mutation C2611T is associated with MIC 2-16 mg/L and the second mutation A2059T results in high level resistance to azithromycin MIC > 256 mg/l 2. Over- production of membrane pumps proteins MtrCDE and MacAB, that remove antibiotics from bacterial cells. The mechanism is not able to cause azithromycin resistance itself but coexisting with other mechanisms of resistance can additionally increase MIC. 3. Synthesis of 23S rRNA methylases ErmB, ErmF, ErmC, ErmA. These enzymes cause demethylation of adenine (A2058) in V domain of 23S rRNA. The mechanism was common in the past, but it has been replaced by mutations in in V domain of 23S rRNA. Nowadays 23S rRNA methylases are very rare in N. gonorhoeae.

METHODS

Sixty five Neisseria gonorrhoeae strains isolated from patients of the Department of Dermatology and Venereology in Warsaw in the second half of 2012 and first of 2013 were investigated. The strains were cultured on chocolate agar plates in a 5% CO2 atmosphere at 37 °C and identified by colony morphology, Gram staining and oxidase reaction, followed by carbohydrate utilization test. Azithromycin susceptibility was determined by E-Tests (bioMerieux). Bacteria were incubated at 37°C in 5% CO2 for 24 h on chocolate agar plates. Tests were performed according to producers recommendations. The results (sensitive or resistant) were interpreted according to EUCAST recommendations.

RESULTS

The MIC of azithromycin in investigated strains ranged from 0,064 to 4 mg/L, MIC50 = 0.5 mg/L, MIC90 = 2 mg/L. It was shown that only 38.5% of the strains were sensitive to azithromycin according to EUCAST criteria from 2014 year and 89.3% of the strains were sensitive to azithromycin according to CDC criteria from 2014 year.

CONCLUSIONS

The percentage of azithromycin resistant Neisseria gonorrhoeae strains is increasing in Poland and the antibiotic should not be used in monotherapy as gonorrhoea patients. It should only be used in combination with ceftriaxone or cefixime.