COMPARATIVE ANALYSIS OF PATHOGENS OF VIBRIOSES ISOLATED IN UKRAINE

Abstract

Vibrio are natural inhabitants of aquatic communities and their variability helps them to adapt to different biological systems, among them human body they have an ability to cause human vibrioses. Most attention is drawn by diarrheagenic vibrioses caused by V.cholerae O1 and V.cholerae non O1, which are responsible for cholera and acute enteric infections with various clinical symptoms.

World distribution of V.cholerae O1 pathogen caused a series of cases in Ukraine in 1991, 1994, 1995 and 2011. Periodic introduction of cholera vibrios from abroad and circulation of local strains had lead to radication of V.cholerae O1 in southern regions of Ukraine, which in turn increased the risk of cholera outbreak. Also, every year acute enteric infections caused by V.cholerae non O1 are reported in southern regions of Ukraine. In view of this, study and comparative analysis of biological properties of vibrioses pathogens V.cholerae O1 and V.cholerae non O1 which covers their pathogenic potential more thoroughly and ensures rapid response in case of escalation of the epidemiological situation becomes more important.

The purpose of this paper is to study biological properties of pathogens of vibrioses V.cholerae O1 and V.cholerae non O1 isolated from people in Ukraine in various years and to make their comparative analysis. We used 104 strains of V.cholerae O1 isolated in 1991-2012 and 100 strains of V.cholerae non O1 isolated in 2011–2013 from people in Ukraine. The results of the study have shown that pathogens of human vibrioses isolated from patients in Ukraine have more stable morphological, cultural and biochemical properties, but also manifest some noteworthy differences in other aspects.

Serological studies have shown that 97.1% of V.cholerae O1 strains agglutinated with О1–serum by slide agglutination which allows us to label them as О1–serogroup, but only 84.6% of the strains agglutinated in diagnostic working titer. In serotype-specific antisera tests by slide agglutination 88.5% of V.cholerae strains agglutinated with Ogawa antiserum and 38.5% agglutinated with Inaba. Taking into account the results of agglutination of these strains with diagnostic working titer, 78.8% V.cholerae О1 were labeled as Ogawa and 11.5% were labeled as Inaba. By slide agglutination with RO–serum 19.2% agglutinated, but only 3.8% which were agglutinated by serum in diagnostic working titer or half of diagnostic titer were labeled as R-variant. Studies have shown that 17 strains of V.cholerae which exhibited agglutination with RO-serum agglutinated in different combinations with diagnostic antisera – О1, Ogawa, and Inaba, which indicates variability of antigenic structure.

Study of sensitivity to cholera biovar-specific phages: classic “С”, El Tor and cholera diagnostic phages HDF-3, 4, 5 indicated that among studied strains of V.cholerae O1 lysability by biovar El Tor phage in pure culture was 77.9%, by “С” phage - 41.3%, but in diagnostic working titer lysability by El Tor phage was 57.7%, by “С” phage - 1.9%. Studies have shown that it is not always possible to establish the biovar of V.cholerae by its sensitivity to bacteriophages which indicates low diagnostic value of this test and such vibrios require additional methods of diagnostics.

Lysability of vibrios by phages confirmed that typically virulent vibrios exhibit lysability by HDF-5, avirulent vibrios – by HDF-3. Studies showed that 84.6% of the strains of V.cholerae O1 were lysable by HDF-5 in pure culture, 38.5% by HDF-4 and 66.3% by HDF-3, but in diagnostic working titer only 51.9% were lysable by  HDF-5, 3.8% – by HDF-4 and 17.3% by HDF-3. Although virulent variants of  V.cholerae O1 exhibited lysability by HDF-5, not all vibrios were lysable in diagnostic titer which made estimation of their pathogenic ability more difficult.

Studies have shown that in Ukraine there are generally isolated V.cholerae О1 of El Tor biovar, mostly of Ogawa serotype. It should be noted that among studied strains of V.cholerae О1 there were 66.3% virulent variants which were isolated from people during cholera outbreaks, 2.9% of strains were also virulent but isolated from people in non-outbreak period, as well as 30.8% avirulent strains isolated during the non-outbreak period.

Study of biological properties of V.cholerae non O1 strains have shown that they corresponded to V.cholerae non O1 serogroup, but did not agglutinate with О1– and RO–sera and did not exhibit lysability by El Tor bacteriophages, classic “С” and diagnostic phages HDF–3, 4, 5. Also, 12% of V.cholerae non O1 strains agglutinated with cholera diagnostic antisera and phages in different titers which is a warning sign for epidemiologists because it indicates V.cholerae О1 serogroup properties.

Therefore, in Ukraine V.cholerae O1 and V.cholerae non O1 are the diarrheagenic pathogens of human vibrioses, with phenotype traits that correspond to taxonomic criteria of Vibrio genus. But strains of V.cholerae О1/non O1 possess certain variability of biological properties and require modern testing methods for rapid response to emerging outbreaks.