Emergence in Taiwan of novel imipenem-resistant Acinetobacter baumannii ST455 causing bloodstream infection in critical patients

Molecular characterization & epidemiology of carbapenem-resistant Acinetobacter baumannii collected across India

Background & objectives

Acinetobacter baumannii is an opportunistic pathogen responsible for causing nosocomial infections. A. baumannii develops resistance to various antimicrobial agents including carbapenems, thereby complicating the treatment. This study was performed to characterize the isolates for the presence of various β-lactamases encoding genes and to type the isolates to compare our clones with the existing international clones across five centres in India.

Methods

A total 75 non-repetitive clinical isolates of A. baumannii from five different centres were included in this study. All the isolates were confirmed as A. baumannii by bl a_OXA-51-likePCR. Multiplex PCR was performed to identify the presence of extended spectrum β-lactamases (ESBL) and carbapenemases. Multilocus sequence typing was performed to find the sequence type (ST) of the isolates. e-BURST analysis was done to assign each ST into respective clonal complex.

Results

bla_OXA-51-likewas present in all the 75 isolates. The predominant Class D carbapenemase was bla_OXA-23-likefollowed by Class B carbapenemase, bla_NDM-like. Class A carbapenemase was not observed. bla_PER-likewas the predominant extended spectrum β-lactamase. ST-848, ST-451 and ST-195 were the most common STs. Eight-novel STs were identified. e-BURST analysis showed that the 75 A. baumannii isolates were clustered into seven clonal complexes and four singletons, of which, clonal complex 208 was the largest.

Interpretation & conclusions

Most of the isolates were grouped under clonal complex 208 which belongs to the international clonal lineage 2. High occurrence of ST-848 carrying bla_OXA-23-likegene suggested that ST-848 could be an emerging lineage spreading carbapenem resistance in India.

Carbapenem-Resistant Acinetobacter baumannii in Three Tertiary Care Hospitals in Mexico: Virulence Profiles, Innate Immune Response and Clonal Dissemination

Acinetobacter baumannii is one of the most important nosocomial pathogens distributed worldwide. Due to its multidrug-resistance and the propensity for the epidemic spread, the World Health Organization includes this bacterium as a priority health issue for development of new antibiotics. The aims of this study were to investigate the antimicrobial resistance profile, the clonal relatedness, the virulence profiles, the innate host immune response and the clonal dissemination of A. baumannii in Hospital Civil de Guadalajara (HCG), Hospital Regional General Ignacio Zaragoza (HRGIZ) and Pediatric ward of the Hospital General de México Eduardo Liceaga (HGM-P). A total of 252 A. baumannii clinical isolates were collected from patients with nosocomial infections in these hospitals between 2015 and 2016. These isolates showed a multidrug-resistant profile and most of them only susceptible to colistin. Furthermore, 83.3 and 36.9% of the isolates carried the bla_OXA–24 and bla_TEM–1 genes for resistance to carbapenems and β-lactam antibiotics, respectively. The clonal relatedness assessed by pulsed-field gel electrophoresis (PFGE) and by multi-locus sequence typing (MLST) demonstrated a genetic diversity. Remarkably, the ST136, ST208 and ST369 that belonged to the clonal complex CC92 and ST758 and ST1054 to the CC636 clonal complex were identified. The ST136 was a high-risk persistent clone involved in an outbreak at HCG and ST369 were related to the first carbapenem-resistant A. baumannii outbreak in HRGIZ. Up to 58% isolates were able to attach to A549 epithelial cells and 14.5% of them induced >50% of cytotoxicity. A549 cells infected with A. baumannii produced TNFα, IL-6 and IL-1β and the oxygen and nitrogen reactive species that contributes to the development of an inflammatory immune response. Up to 91.3% of clinical isolates were resistant to normal human serum activity. Finally, 98.5% of the clinical isolates were able to form biofilm over polystyrene tubes. In summary, these results demonstrate the increasingly dissemination of multidrug-resistant A. baumannii clones in three hospitals in Mexico carrying diverse bacterial virulence factors that could contribute to establishment of the innate immune response associated to the fatality risks in seriously ill patients.

Risk factors and outcomes of Clostridium difficile infection in hospitalized patients

BACKGROUND

The aim of this study was to identify risk factors for Clostridium difficile infection (CDI) and its attributable mortality and to propose methods to prevent CDI and improve patients' outcomes.

METHODS

CDI was defined as diarrheal patients with stool samples that were positive for C. difficile toxin. Clinical presentations of all patients with CDI and two times as many age- and sex-matched culture-negative controls at the Chang Gung Memorial Hospital in 2014 were identified and compared by multivariate, nonparametric, and Kaplan-Meier survival analysis.

RESULTS

There were no significant differences in ages, sex, or Charlson comorbidity indexes between the CDI group (n = 42) and the control group (n = 86). The multivariate analysis indicated that underlying peptic ulcer disease and previous use of gastric acid inhibitors or third-generation cephalosporins for at least 3 days were significantly more common in patients with CDI than in the controls. Charlson scores were associated with mortality due to CDI. Recommended treatment using oral vancomycin to treat patients with Charlson score ≥ 5 and oral metronidazole or vancomycin to treat those with moderate underlying disease (Charlson score ≥ 2 and ≤ 5) significantly increased survival in these patients (p = 0.001).

CONCLUSIONS

Oral vancomycin given to patients with high Charlson scores and oral metronidazole or vancomycin to patients with moderate Charlson scores decreased mortality due to CDI. Restricting the use of third-generation cephalosporins and gastric acid inhibitors is recommended to prevent CDI in hospitalized patients.

Virulence profiles and innate immune responses against highly lethal, multidrug-resistant nosocomial isolates of Acinetobacter baumannii from a tertiary care hospital in Mexico

Virulence profiles and innate immune responses were studied in Acinetobacter baumannii from nosocomial infections collected over one year in a tertiary care hospital in Mexico. A. baumannii were identified by VITEK 2 System followed by susceptibility tests. Carbapenemase genes, active efflux mechanism to imipenem and meropenem and outer membrane proteins profile were analyzed to evaluate their role on the activity of carbapenem resistance. All isolates were genotyped by pulsed field gel electrophoresis. The ability to form biofilm was determined on a polystyrene surface. The resistance to complement was determined with a pooled human normal serum and TNFα release by infected macrophages was determined by ELISA. The 112 isolates from this study were associated with a 52% of mortality. All were resistance to β-lactams, fluoroquinolones, and trimethroprim-sulfamethoxal, 96 and 90% were resistant to meropenem and imipenem, respectively, but with high susceptibility to polymyxin B, colistin and tigecyclin. Isolates were classified in 11 different clones. Most isolates, 88% (99/112), were metallo-β-lactamases and carbapenemases producers, associated in 95% with the presence of bla_OXA-72 gene. Only 4/99 and 1/99 of the carbapenem-resistant isolates were related to efflux mechanism to meropenem or imipenem resistance, respectively. The loss of expression of 22, 29, and/or 33-36-kDa proteins was detected in 8/11 of the clinical isolates with resistance to carbapenem. More than 96% (108/112) of the isolates were high producers of biofilms on biotic surfaces. Finally, all isolates showed variable resistance to normal human serum activity and were high inductors of TNFα release by macrophages. In summary, these results suggest that multidrug-resistant A. baumannii can persist in the hospital environment through its ability to form biofilms. The high mortality observed was due to their ability to survive normal human serum activity and capability to induce potent inflammatory immune response making this nosocomial pathogen a serious threat to hospitalized patients.

Molecular characterization and antimicrobial susceptibility of Acinetobacter baumannii isolates obtained from two hospital outbreaks in Los Angeles County, California, USA

BACKGROUND

Antibiotic resistant strains of Acinetobacter baumannii have been responsible for an increasing number of nosocomial infections including bacteremia and ventilator-associated pneumonia. In this study, we analyzed 38 isolates of A. baumannii obtained from two hospital outbreaks in Los Angeles County for the molecular epidemiology, antimicrobial susceptibility and resistance determinants.

METHODS

Pulsed field gel electrophoresis, tri-locus multiplex PCR and multi-locus sequence typing (Pasteur scheme) were used to examine clonal relationships of the outbreak isolates. Broth microdilution method was used to determine antimicrobial susceptibility of these isolates. PCR and subsequent DNA sequencing were employed to characterize antibiotic resistance genetic determinants.

RESULTS

Trilocus multiplex PCR showed these isolates belong to Global Clones I and II, which were confirmed to ST1 and ST2, respectively, by multi-locus sequence typing. Pulsed field gel electrophoresis analysis identified two clonal clusters, one with 20 isolates (Global Clone I) and the other with nine (Global Clone II), which dominated the two outbreaks. Antimicrobial susceptibility testing using 14 antibiotics indicated that all isolates were resistant to antibiotics belonging to four or more categories of antimicrobial agents. In particular, over three fourth of 38 isolates were found to be resistant to both imipenem and meropenem. Additionally, all isolates were found to be resistant to piperacillin, four cephalosporin antibiotics, ciprofloxacin and levofloxacin. Resistance phenotypes of these strains to fluoroquinolones were correlated with point mutations in gyrA and parC genes that render reduced affinity to target proteins. ISAba1 was detected immediately upstream of the bla OXA-23 gene present in those isolates that were found to be resistant to both carbapenems. Class 1 integron-associated resistance gene cassettes appear to contribute to resistance to aminoglycoside antibiotics.

CONCLUSION

The two outbreaks were found to be dominated by two clonal clusters of A. baumannii belonging to MLST ST1 and ST2. All isolates were resistant to antibiotics of at least four categories of antimicrobial agents, and their antimicrobial susceptibility profiles correlate well with genetic determinants. The results of this study will facilitate our understanding of the molecular epidemiology, antimicrobial susceptibility and mechanisms of resistance of A. baumannii obtained from Los Angeles hospitals.

A glimpse into evolution and dissemination of multidrug-resistant Acinetobacter baumannii isolates in East Asia: a comparative genomics study

Clonal dissemination is characteristic of the important nosocomial pathogen Acinetobacter baumannii, as revealed by previous multi-locus sequence typing (MLST) studies. However, the disseminated phyletic unit is actually MLST sequence type instead of real bacterial clone. Here we sequenced the genomes of 13 multidrug-resistant (MDR) A. baumannii strains from Taiwan, and compared them with that of A. baumannii from other East Asian countries. Core-genome phylogenetic tree divided the analyzed strains into three major clades. Among them, one ST455 clade was a hybrid between the ST208 clade and the other ST455 clade. Several strains showed nearly identical genome sequence, but their isolation sources differed by over 2,500 km and 10 years apart, suggesting a wide dissemination of the phyletic units, which were much smaller than the sequence type. Frequent structural variation was detected even between the closely related strains in antimicrobial resistance elements such as AbaRI, class I integron, indicating strong selection pressure brought by antimicrobial use. In conclusion, wide clonal dissemination and frequent genomic variation simultaneously characterize the clinical MDR A. baumannii in East Asia.

Structure and context of Acinetobacter transposons carrying the oxa23 carbapenemase gene

Theoxa23gene encoding the OXA-23 carbapenemase (and several minor variants of it) is widespread inAcinetobacter baumanniiclinical isolates and compromises treatment with carbapenem antibiotics. The gene is derived from the chromosome ofAcinetobacter radioresistenswhere it is an intrinsic gene, here designatedoxaAr InA. baumanniiand otherAcinetobacterspecies,oxa23is usually preceded by an IS, ISAba1, which supplies the strong promoter required for the gene to confer clinically relevant levels of resistance. TheoxaArgene appears to have been mobilized twice creating Tn2008and Tn2008B, both of which consist of a single ISAba1 and anA. radioresistens-derived fragment. Tn2006and Tn2009are clearly derived from Tn2008Band are each made up of Tn2008Bwith an additional segment of unknown origin and an additional ISAba1, creating a compound transposon. Tn2006, Tn2008and possibly Tn2008Bare globally disseminated, while Tn2009has as yet only been found in China. Of the four ISAba1-associated transposons, Tn2006has been most frequently observed worldwide and Tn2006in Tn6022, known as AbaR4, appears to contribute significantly to the dissemination ofoxa23 Moreover, AbaR4, Tn2006, Tn2008and Tn2009have each been found in conjugative plasmids, further facilitating their spread.