Molecular Epidemiology of Acinetobacter calcoaceticus- Acinetobacter baumannii Complex Isolated From Children at the Hospital Infantil de México Federico Gómez

Abstract

The Acinetobacter calcoaceticus-baumannii (Acb) complex is regarded as a group of phenotypically indistinguishable opportunistic pathogens responsible for mainly causing hospital-acquired pneumonia and bacteremia. The aim of this study was to determine the frequency of isolation of the species that constitute the Acb complex, as well as their susceptibility to antibiotics, and their distribution at the Hospital Infantil de Mexico Federico Gomez (HIMFG). A total of 88 strains previously identified by Vitek 2®, 40 as Acinetobacter baumannii and 48 as Acb complex were isolated from 52 children from 07, January 2015 to 28, September 2017. A. baumannii accounted for 89.77% (79/88) of the strains; Acinetobacter pittii, 6.82% (6/88); and Acinetobacter nosocomialis, 3.40% (3/88). Most strains were recovered mainly from patients in the intensive care unit (ICU) and emergency wards. Blood cultures (BC) provided 44.32% (39/88) of strains. The 13.63% (12/88) of strains were associated with primary bacteremia, 3.4% (3/88) with secondary bacteremia, and 2.3% (2/88) with pneumonia. In addition, 44.32% (39/88) were multidrug-resistant (MDR) strains and, 11.36% (10/88) were extensively drug-resistant (XDR). All strains amplified the bla _OXA-51 gene; 51.13% (45/88), the bla _OXA-23 gene; 4.54% (4/88), the bla _OXA-24 gene; and 2.27% (2/88), the bla _OXA-58 gene. Plasmid profiles showed that the strains had 1-6 plasmids. The strains were distributed in 52 pulsotypes, and 24 showed identical restriction patterns, with a correlation coefficient of 1.0. Notably, some strains with the same pulsotype were isolated from different patients, wards, or years, suggesting the persistence of more than one clone. Twenty-seven sequence types (STs) were determined for the strains based on a Pasteur multilocus sequence typing (MLST) scheme using massive sequencing; the most prevalent was ST 156 (27.27%, 24/88). The Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas I-Fb system provided amplification in A. baumannii and A. pittii strains (22.73%, 20/88). This study identified an increased number of MDR strains and the relationship among strains through molecular typing. The data suggest that more than one strain could be causing an infection in some patient. The implementation of molecular epidemiology allowed the characterization of a set of strains and identification of different attributes associated with its distribution in a specific environment.

Keywords: Acinetobacter baumannii; Acinetobacter calcoaceticus-Acinetobacter baumannii complex; intensive care unit; molecular typing; resistance.

Figure 1

Frequency of isolation of the Acinetobacter baumannii, Acinetobacter pittii, and Acinetobacter nosocomialis strains. Percentage of patients from wards in which at least one of the strains was isolated in the period of study. BC, blood cultures; D, different samples; UC, urine cultures; SC, stool culture; A, autopsy; and CSF, cerebrospinal fluid.

Figure 2

Resistance profiles of the A. baumannii, A. pittii, and A. nosocomialis strains. Percentages of strains resistant to at least one antibiotic in the following groups: penicillins (piperacillin), β-lactam agents/beta-lactamase inhibitors (ampicillin-sulbactam and piperacillin-tazobactam), third- and fourth-generation cephalosporins (cefepime and ceftriaxone), carbapenems (imipenem), aminoglycosides (gentamicin), fluoroquinolones (ciprofloxacin), folates (trimethoprim/sulfamethoxazole), glycylcyclines (tigecycline), and lipopeptides (colistin). PIP, piperacillin; TZP, piperacillin/tazobactam; SAM, ampicillin-sulbactam; FEP, cefepime; CRO, ceftriaxone; IMP, imipenem; GEN, gentamicin; CIP, ciprofloxacin; SXT, trimethoprim/sulfamethoxazole; TGC, tigecycline; and CL, colistin.

Figure 3

Dendrogram profile of the A. baumannii, A. pittii, and A. nosocomialis complex strains. Dendrogram profile displaying the genetic relatedness among the 88 strains based on the pulsed-field gel electrophoresis (PFGE) pattern. The red line represents the strains with the same pulsotype. The species other than A. baumannii are shown with circles in gray (A. pittii) and black (A. nosocomialis). Internal data represent strain with the origin of isolation, followed by the patient and the ward of origin for each strain. The asterisk symbol shows the strains associated with HAIs (bacteremia and pneumonia). The first band represents the year of isolation, and the second represents the profile of resistance: Resistant (R), multidrug-resistant (MDR), and extensively drug-resistant (XDR). The strains with a R profile showed resistance to PIP, SAM, or TZP. The detection of bla_oxa genes is represented by clear blue clear squares and the amplification of the CRISPR-Cas system with dark blue squares. The number of plasmids associated with each strain is shown in the third band. The type sequences (ST) for each strain were added. The color codes for each analyzed characteristic are shown in the legends below the figure. The visualization was performed with the iTol program (Letunic and Bork, 2007).