Characterization of Acinetobacter baumannii genotypes recovered from patients with repeated colonization or infection

Repeat gram-negative hospital-acquired infections and antibiotic susceptibility: A systematic review

Repeat HAIs among frequently hospitalized patients may be contributing to the high rates of antibiotic resistance seen in gram-negative bacteria (GNB) in hospital settings. This systematic review examines the state of the literature assessing the association between repeat GNB HAIs and changes in antibiotic susceptibility patterns. A systematic search of English language published literature was conducted to identify studies in peer-reviewed journals from 2000 to 2015. Studies must have assessed drug resistance in repeat GNB infections longitudinally at the patient level. Two researchers independently reviewed search results for papers meeting inclusion criteria and extracted data. Risk of bias was assessed using a modified quality assessment tool based on the Checklist for Measuring Study Quality and the Quality Assessment Checklist for Cases Series. From 3385 articles identified in the search, seven met inclusion criteria. Five reported lower antibiotic susceptibility in repeated infections, one found a change but did not specify in which direction, and one reported no change. All studies were of low to average quality. Despite the dearth of studies examining repeat GNB infections, evidence suggests that repeat infections result in lower antibiotic susceptibility among hospitalized patients. Larger scale studies with strong methodology are warranted.

Risk of drug resistance in repeat gram-negative infections among patients with multiple hospitalizations

PURPOSE

Drug resistance in gram-negative bacterial hospital-acquired infections (GNB HAIs) has become ubiquitous in recent years. Patients who experience multiple hospitalizations are at high risk of developing repeat GNB HAIs. This study aims to evaluate the relationship between repeat GNB HAIs and antibiotic susceptibility patterns.

METHODS

Using electronic medical records from three hospitals, 4053 patients were identified with at least one HAI caused by K. pneumoniae or P. aeruginosa over multiple hospitalizations in a 9-year period. Modified Poisson regression was used to evaluate the risk of drug resistance with increasing number of prior susceptible infections. Drug resistance was defined as resistant to carbapenems for K. pneumoniae and resistant to levofloxacin for P. aeruginosa.

RESULTS

In patients with repeat infections, almost 15% of consecutive infections changed from susceptible to drug-resistant. Patients with K. pneumoniae infections had a 1.14 times increased risk of acquiring a drug-resistant HAI with each prior HAI, after adjusting for potential confounders and antibiotic use prior to infection. Patients with P. aeruginosa infections had a 1.23 times increased risk of a drug-resistant infection with each prior P. aeruginosa HAI.

CONCLUSIONS

Prevention of repeat infections in high healthcare utilizers may be important in reducing drug resistance in this population.

Frequency of Class 1 Integron and Genetic Diversity of Acinetobacter baumannii Isolated from Medical Centers in Kermanshah

BACKGROUND AND OBJECTIVE

Acinetobacter baumannii has emerged as an important pathogen in hospital and environment that can acquire transport element and antibiotic-resistant genes. The aim of this study was to determine the resistances to different antibiotics, frequency of Class 1 integron in A. baumannii and then molecular typing for A. baumannii isolated from Intensive Care Unit (ICU).

MATERIALS AND METHODS

A total of 100 isolates of A. baumannii were collected from patients admitted to hospitals in Kermanshah from April 2014 to September 2015. The isolates were identified using biochemical test. Antimicrobial susceptibility test for 20 antibiotics was determined by Kirby-Bauer antibiotic testing (or disc diffusion). The prevalence rate of class integrons among the isolates was determined using polymerase chain reaction and finally 80 isolates of A. baumannii obtained from the Intensive Care Unit were selected for molecular typing by pulsed-field gel electrophoresis (PFGE).

RESULTS

The maximum drug resistance was observed against cefotaxime, ceftriaxone, mezlocillin, imipenem, and ceftazidime and piperacillin. Twenty-nine isolates were multidrug resistant (MDR); about 21 isolates were extensively-drug resistant and none were pandrug resistance and 42 isolates (42%) contained Class 1 integrons. The results did not show a significant correlation between the presence of Class 1 integrons and incidence of MDR A. baumannii. Five clusters were obtained by PFGE.

CONCLUSION

This study did not show a significant correlation between the presence of Class 1 integrons and incidence of MDR A. baumannii. By PFGE analysis, the high level of similarity between some pulsotypes in A. baumannii strains showed genetic correlation between them.

Evaluate the frequency distribution of nonadhesive virulence factors in carbapenemase-producing Acinetobacter baumannii isolated from clinical samples in Kermanshah

Background:

Acinetobacter baumannii which is a Gram-negative bacterium can cause several different infections. The appearance of carbapenemase-producing A. baumannii in recent years has made the treatment process more difficult. The identification of virulence factors (VFs), such as nonadhesives in A. baumannii, helps to fight against related infections.

Materials and Methods:

A total of 104 samples from teaching hospitals in Kermanshah, Iran, were collected during a 24 months period (2011-2013). Sample identification was first carried out by biochemical tests, and then their susceptibility to carbapenems was determined using the Kirby–Bauer method. For confirmation of carbapenemase-producing A. baumannii, polymerase chain reaction (PCR) was done for carbapenemase-encoding genes. In addition, the frequency of nonadhesive VFs in carbapenemase-producing isolates was determined by PCR.

Results:

There were 50 isolates that were identified as carbapenemase-producing A. baumannii. The PCR results showed; 40 isolates (80%) for traT, 17 isolates (34%) for cvaC, and 8 isolates (16%) for iutA, and these encode serum resistance, colicin V and aerobactin, respectively. No significant correlation was observed between these three genes.

Conclusions:

The mechanism of A. baumannii virulence has always been in question. The role of VFs has also been recognized in other Gram-negative bacteria. According to the prevalence of traT, cvaC and iutA, as nonadhesive VFs, we can suggest that they could be the main mechanism of carbapenemase-producing A. baumannii pathogenesis.

Genetic Mechanisms of Antimicrobial Resistance of Acinetobacter baumannii

OBJECTIVE

To summarize published data identifying known genetic mechanisms of antibiotic resistance in Acinetobacter baumannii and the correlating phenotypic expression of antibiotic resistance.

DATA SOURCES

MEDLINE databases (1966-July 15, 2010) were searched to identify original reports of genetic mechanisms of antibiotic resistance in A. baumannii.

DATA SYNTHESIS

Numerous genetic mechanisms of resistance to multiple classes of antibiotics are known to exist in A. baumannii, a gram-negative bacterium increasingly implicated in nosocomial infections. Mechanisms may be constitutive or acquired via plasmids, integrons, and transposons. Methods of resistance include enzymatic modification of antibiotic molecules, modification of antibiotic target sites, expression of efflux pumps, and downregulation of cell membrane porin channel expression. Resistance to β-lactams appears to be primarily caused by β-lactamase production, including extended spectrum β-lactamases (b/aTEM, blaSHV, b/aTX-M,b/aKPC), metallo-β-lactamases (blaMP, blaVIM, bla, SIM), and most commonly, oxacillinases (blaOXA). Antibiotic target site alterations confer resistance to fluoroquinolones (gyrA, parC) and aminoglycosides (arm, rmt), and to a much lesser extent, β-lactams. Efflux pumps (tet, ade, abe) contribute to resistance against β-lactams, tetracyclines, fluoroquinolones, and aminoglycosides. Finally, porin channel deletion (carO, oprD) appears to contribute to β-lactam resistance and may contribute to rarely seen polymyxin resistance. Of note, efflux pumps and porin deletions as solitary mechanisms may not render clinical resistance to A. baumannii.

CONCLUSIONS

A. baumannii possesses copious genetic resistance mechanisms. Knowledge of local genotypes and expressed phenotypes for A. baumannii may aid clinicians more than phenotypic susceptibilities reported in large epidemiologic studies.

Pathogenicity of clinical Acinetobacter baumannii isolates in a Galleria mellonella host model according to bla(OXA-40) gene and epidemiological outbreak status

Clinical studies have suggested that blaOXA-40-positive Acinetobacter baumannii isolates are associated with poor patient outcomes; however, reasons for unfavorable outcomes are difficult to discern in clinical studies. The objective of this study was to assess the virulence of carbapenem-resistant A. baumannii according to blaOXA-40 and epidemiological outbreak status in a Galleria mellonella model. Eight isolates of A. baumannii were studied. Nonoutbreak isolates and blaOXA-40-negative isolates more rapidly killed infected G. mellonella (P < 0.01).