Widespread dispersion of the resistance element tet(B)::ISCR2 in XDR Acinetobacter baumannii isolates.

Acinetobacter baumannii is a significant nosocomial pathogen often associated with extreme drug resistance (XDR). In Argentina, isolates of A. baumannii resistant to tetracyclines have accounted for more than 40% of drug-resistant isolates in some hospitals. We have previously reported the dispersion of the tet(B) resistance element associated with the ISCR2 transposase in epidemiologically unrelated A. baumannii isolates recovered from 1983 to 2011. This study extends this surveillance to 77 recent (2009-2013) XDR A. baumannii isolates with different levels of minocycline susceptibility. Isolates were examined by a pan-PCR assay, which showed six different amplification patterns, and specific PCRs were used for the confirmation of the the ΔISCR2-tet(B)-tet(R)-ISCR2 element. The tet(B) gene was present in 66 isolates and the ISCR2 element in 68 isolates; the tet(B) gene was associated with ISCR2 in all tet(B)-positive isolates. We conclude that this element is widespread in XDR A. baumannii isolates from Argentina and could be responsible for the emergence of tetracycline resistance in recent years.

Genetic Variability of AdeRS Two-Component System Associated with Tigecycline Resistance in XDR-Acinetobacter baumannii Isolates.

The emergence of tigecycline resistance has increased in the last years. Although tigecycline-resistant Acinetobacter baumannii isolates were described all over the world, few reports regarding the molecular basis of this resistance are available. It has been recognized that the overexpression of AdeABC efflux pump is related to the tigecycline-resistant phenotype. In 37 clinical A. baumannii isolates we first determined the tigecycline-resistant phenotype and then, within a selected group, we analyzed the sequence of the adeRS operon, which is involved in the expression of the AdeABC efflux pump. Nucleotide sequence analysis of adeR and adeS showed the presence of 5 and 16 alleles, respectively. These results expose a high genetic variability in both genes, the adeS gene being more susceptible to genetic variation. The presence of 2 AdeR and 2 AdeS new variants were reported. Two of the new AdeRS variants were present in the intermediate and the resistant tigecycline A. baumannii isolates, suggesting a putative role in the development of the observed phenotype. More studies need to be addressed to determine the role of the genetic variability observed in the adeRS operon.

Genotypic characterization of non-O157 Shiga toxin-producing Escherichia coli in beef abattoirs of Argentina.

The non-O157 Shiga toxin-producing Escherichia coli (STEC) contamination in carcasses and feces of 811 bovines in nine beef abattoirs from Argentina was analyzed during a period of 17 months. The feces of 181 (22.3%) bovines were positive for non-O157 STEC, while 73 (9.0%) of the carcasses showed non-O157 STEC contamination. Non-O157 STEC strains isolated from feces (227) and carcasses (80) were characterized. The main serotypes identified were O178:H19, O8:H19, O130:H11, and O113:H21, all of which have produced sporadic cases of hemolytic-uremic syndrome in Argentina and worldwide. Twenty-two (7.2%) strains carried a fully virulent stx/eae/ehxA genotype. Among them, strains of serotypes O103:[H2], O145:NM, and O111:NM represented 4.8% of the isolates. Xba I pulsed-field gel electrophoresis pattern analysis showed 234 different patterns, with 76 strains grouped in 30 clusters. Nine of the clusters grouped strains isolated from feces and from carcasses of the same or different bovines in a lot, while three clusters were comprised of strains distributed in more than one abattoir. Patterns AREXSX01.0157, AREXBX01.0015, and AREXPX01.0013 were identified as 100% compatible with the patterns of one strain isolated from a hemolytic-uremic syndrome case and two strains previously isolated from beef medallions, included in the Argentine PulseNet Database. In this survey, 4.8% (39 of 811) of the bovine carcasses appeared to be contaminated with nonO157 STEC strains potentially capable of producing sporadic human disease, and a lower proportion (0.25%) with strains able to produce outbreaks of severe disease.

Prevalence, characterization, and genotypic analysis of Escherichia coli O157:H7/NM from selected beef exporting abattoirs of Argentina.

In Argentina, Escherichia coli O157:H7/NM (STEC O157) is the prevalent serotype associated with hemolytic uremic syndrome (HUS), which is endemic in the country with more than 400 cases per year. In order to estimate the prevalence and characteristics of STEC O157 in beef cattle at slaughter, a survey of 1,622 fecal and carcass samples was conducted in nine beef exporting abattoirs from November 2006 to April 2008. A total of 54 samples were found positive for STEC O157, with an average prevalence of 4.1% in fecal content and 2.6% in carcasses. Calves and heifers presented higher percentages of prevalence in feces, 10.5 and 8.5%, respectively. All STEC O157 isolates harbored stx(2) (Shiga toxin 2), eae (intimin), ehxA (enterohemolysin), and fliC(H7) (H7 flagellin) genes, while stx(1) (Shiga toxin 1) was present in 16.7% of the strains. The prevalent (56%) stx genotype identified was stx(2) combined with variant stx(2c (vh-a)), the combination of which is also prevalent (>90%) in STEC O157 post-enteric HUS cases in Argentina. The clonal relatedness of STEC O157 strains was established by phage typing and pulsed-field gel electrophoresis (PFGE). The 54 STEC isolates were categorized into 12 different phage types and in 29 XbaI-PFGE patterns distributed in 27 different lots. STEC O157 strains isolated from 5 of 21 carcasses were identical by PFGE (100% similarity) to strains of the fecal content of the same or a contiguous bovine in the lot. Five phage type-PFGE-stx profiles of 10 strains isolated in this study matched with the profiles of the strains recovered from 18 of 122 HUS cases that occurred in the same period.