Peculiar features of the Mycobacterium tuberculosis population structure in Albania

Albania is a Balkan country with moderate to low incidence of tuberculosis (TB) and very low prevalence of drug resistant TB. Here, we analyzed a country-wide multi-year Mycobacterium tuberculosis collection in order to detect possible dynamic trends of TB in Albania, with a focus on drug resistance and endemic/epidemic clones. In total, 743 isolates collected in 2007 to 2011 were divided into 107 spoligotypes and 351 MIRU-types. Based on the MIRU-VNTR phylogenetic analysis, the isolates were assigned to the following lineages/families: animal ecotypes (5 M. bovis and 2 M. caprae isolates), Lineage 2 (5 Beijing isolates), Lineage 3 (1 CAS-Delhi isolate) and, mostly and overwhelmingly, Lineage 4 (Cameroon, Uganda, Ghana and related; NEW-1-related; Ural, Haarlem, LAM, S, TUR; and unclassified isolates). Most of the isolates (452/743) were intermediately located on the global VNTR tree and did not cluster with any reference profile; they were distantly related to different families within Lineage 4 and we designated them as "unclassified L4" isolates. The significantly higher proportion of drug resistance was observed in (i) Beijing genotype compared to all other isolates (60%, P = .008), (ii) "unclassified L4" compared to all other isolates (13.9%, P = .04) and (iii) SIT2936 compared to other "unclassified L4" (34.3%, P = .0006). Analysis of the yearly collections revealed (i) some decrease of the large heterogeneous "unclassified L4" from 65% to 57%; (ii) steadily increasing gradient of LAM from 3.4 to 13.3%; (iii) stable prevalence of Haarlem (15-20%); and (iv) decrease of TUR with only 1.1% in 2011. Most of the LAM (33/49) and Beijing (3/5) isolates belonged to the VNTR types specific for Russia and former Soviet Union countries. To conclude, our results highlight a peculiar nature of M. tuberculosis population in Albania that is dominated by local and unclassified genotypes within Lineage 4, and also features European genotypes and epidemically relevant clones originating from the former Soviet Union countries. At the same time, these imported clones remain drug susceptible and prevalence of drug resistance on a whole is low.