Acinetobacter baumannii has emerged as a major relevant global nosocomial pathogen in the last two decades, causing a variety of serious infections such as pneumonia and bacteraemia, often associated with high mortality [Reference Roca1]. In a CDC report published last year, A. baumannii was considered as a microorganism of serious concern, since about the 63% of the isolates are multidrug resistant with about 500 deaths each year attributed to its infections in the USA [2].

The accumulation of antibiotic resistance mechanisms occurs frequently in this species, underlining its genomic plasticity to evolve to extensive multidrug resistance in the nosocomial environment. Class 1 and 2 integrons have been frequently found in a variety of resistance determinants [Reference Ramirez3, Reference Turton4]. However, a clear differential distribution of both these integron classes in clinical isolates across continents has been reported by different groups with class 1 integrons being frequently identified from Europe, USA and Australia, while class 2 integrons are more common in several countries in South America [Reference Ramirez3–Reference Fonseca5].

This prompted us to investigate if there was a particular dissemination of integrons in different A. baumannii lineages. We therefore analysed the association between the circulating clones in South America and the presence of class 1 and 2 integrases in A. baumannii isolates recovered from 1982 to 2014 from 11 hospitals. Some isolates included in the present work, were from previously published studies (Table 1) [Reference Ramirez3, Reference Ramirez6–Reference Vilacoba8] but hitherto had not been investigated for association of strain lineages with the presence of class 1 and 2 integrons.

Table 1. Origin, clonal lineage and integron content of 60 isolates of Acinetobacter baumannii from 11 hospitals

CC, Clonal complex; PCR, polymerase chain reaction.

* ^B Bartual scheme; ^P Institut Pasteur scheme.

A total of 168 A. baumannii isolates was investigated by polymerase chain reaction (PCR) amplification of intI1 and intI2 genes using specific primers [Reference Ramirez3, Reference Nardelli9]. Sixty isolates were positive either for class 1 (n = 17) or class 2 integrases (n = 35) or both (n = 8). Confirmatory DNA sequencing was performed on 23 of the 43 intI2 amplicons, and one intI1 amplicon [Reference Ramirez3]. All intI2 amplicons possessed the typical internal stop codon [Reference Ramirez3, Reference Hansson10], and the intI1 amplicon harboured one of the most common alleles of intI1 [Reference Nardelli9]. Isolates with class 1, or class 2 integrons were identified respectively in 9 and 10 of the 11 hospitals studied. Coexistence of both classes of integrons in the same strain was found in five hospitals from two cities, Buenos Aires and Rosario. Overall these results evidence the widespread presence of these genetic elements in nosocomial settings in Argentina.

The lineages of these 60 intI-positive isolates were determined by a pan-PCR assay [Reference Yang11] and multilocus sequence typing [Reference Stietz12] which revealed the presence of six defined clonal complexes (CC) and at least nine singletons (Table 1) Statistical analysis was undertaken by the sign test which is a non-parametric test to confirm a zero median difference between continuous distributions of two random pairs. This showed high significant associations between intI2 and the CC113 lineage (P = 0·003) as well as between intI2 and the novel singletons (P = 0·01). In fact, 15/16 isolates of CC113^B/CC79^P and 15/17 isolates belonging to novel singletons harboured intI2.

Regarding class 1 integrons, 16 of the 25 intI1-positive isolates were assigned to lineage CC109^B/CC1^P. Only two isolates of CC113 harboured a class 1 integron and the other six intI1-positive isolates corresponded to singletons, and one to CC110. No statistical association between CC109^B/CC1^Pand class 1 integrons (P = 0·052345) was found. However, CC109 was infrequently reported in Argentinean isolates recovered during the period 1982–2010 [Reference Stietz12]. Interestingly, eight isolates possessed both integrons and belonged to different CCs or singletons; three were of lineage CC109^B/CC1^P, one of CC113^B/CC79^P, and five of different singletons (Table 1). These last results suggest that novel singletons may play a role in the double acquisition of integrons.

In conclusion, we describe a marked association between intI2 and CC113^B/CC79^P, which is the most frequently isolated lineage of A. baumannii in Argentinean isolates during the years 1992–2009 and this explains the hitherto high frequency of intI2 observed in isolates from Argentina [Reference Ramirez3, Reference Ramirez6, Reference Ramirez7, Reference Stietz12]. In addition, several novel singletons frequently containing intI2, some harbouring both classes of integrons, were evident.