bla OXA-23-like and bla TEM rather than bla OXA-51-like contributed to a high level of carbapenem resistance in Acinetobacter baumannii strains from a teaching hospital in Xi’an, China

Abstract

Acinetobacter baumannii is one of the major threats in clinical infections due to its antibiotic resistance ability. It shows increasing resistance to carbapenems, mainly due to β-lactamase mediated mechanisms. The aim of this study was to investigate carbapenem resistance (CR) profiles and analyze β-lactamases genes composition of clinical A. baumannii strains from a teaching hospital in Xi’an. The resistance patterns to imipenem and meropenem were checked for 51 clinical A. baumannii strains. The existence of 15 β-lactamases genes was detected by polymerase chain reaction (PCR), and the positive genes were sequenced. The correlation between PCR-positive genes and CR phenotype was analyzed using Chi-square test and contingency coefficient. The expressions of PCR-positive genes were investigated. Forty-five out of 51 strains were resistant to imipenem and meropenem. blaTEM, blaOXA-23-like, and blaOXA-51-like were positive among 15 β-lactamases genes, and TEM-1, OXA-23, and OXA-66/69 were their subtypes. TEM and OXA-23-like only showed up in CR isolates, with the occurrence rate of 91.1% and 97.8%, respectively, whereas OXA-51-like appeared in all strains. ISAba1 was present in the upstream of OXA-23-like, but absent from that of OXA-51-like in our strains. OXA-23-like had highest relationship with CR, followed by TEM, but OXA-51-like had no correlation. This was verified by RT-qPCR that the expression was positive for OXA-23 and TEM-1, but negative for OXA-66/-69. A high rate of CR A. baumannii was detected in this study. Coexistence of TEM, OXA-23-like, and OXA-51-like was the primary resistance profile. The expressions of OXA-23-like and TEM genes were closely related with CR, while OXA-51-like had no contribution to the CR phenotype.

Lysin LysMK34 ofAcinetobacter baumanniiBacteriophage PMK34 Has a Turgor Pressure-Dependent Intrinsic Antibacterial Activity and Reverts Colistin Resistance

“…Only A. baumannii MK60, MK22, O3, and A2 lack the bla OXA-23-like gene. The presence of this gene has been reported as having the strongest correlation with high resistance levels against carbapenems such as meropenem and imipenem (20). Accordingly, strains O3 and A2, which lack the bla OXA-23-like gene, are susceptible to meropenem and imipenem.…”

“…Exponentially grown bacterial cells were suspended in high tonicity, corresponding to a low intracellular turgor pressure (20 mM HEPES-NaOH, 150 mM NaCl [pH 7.4]) and then treated with 500 g/ml LysMK34 for 2 h at room temperature. The treated cells were washed twice using high-tonicity buffer and then either diluted prior to plating in high-tonicity (20 turgor pressure. Thus, also under conditions of low intracellular turgor pressure, LysMK34 can penetrate the outer membrane and then reach the peptidoglycan layer.…”

“…Exponentially grown bacterial cells were suspended in high tonicity, corresponding to a low intracellular turgor pressure (20 mM HEPES-NaOH, 150 mM NaCl [pH 7.4]) and then treated with 500 g/ml LysMK34 for 2 h at room temperature. The treated cells were washed twice using high-tonicity buffer and then either diluted prior to plating in high-tonicity(20 mM HEPES-NaOH, 150 mM NaCl [pH 7.4]; black bar) or low-tonicity (20 mM HEPES-NaOH [pH 7.4]; white bars) buffer, the latter condition causing an osmotic shock. The antibacterial activity was calculated as the ratio of reduction in log units [log 10 (N 0 /N i )], where N 0 is the number of LysMK34 untreated cells, and N i is the number of cells after treatment.…”

Epidemiological Analysis of Multidrug-Resistant Acinetobacter baumannii Isolates in a Tertiary Hospital Over a 12-Year Period in China

“…Recently, Yang et al collected 2,197 A. baumannii isolates from 27 provinces in China, found that the resistance rate for cefoperazone-sulbactam was 39.7%, and demonstrated that bla TEM−1 with four tandem copies structure played a key role in this resistance phenomenon (18). Meanwhile, Han et al proved that bla OXA−23 and bla TEM−1 genes were more conducive to resistance to carbapenems in A. baumannii (19). In the current study, bla TEM−1 gene had been detected in all isolates since 2012, and the overall positive rate of this resistance gene was 75.3% (222/295), meanwhile, the cefoperazone-sulbactam resistance rate of the 295 MDR A. baumannii isolates was up to 94.5%, and both had a certain correlation relationship.…”

Susceptibility to Imipenem/Relebactam of Pseudomonas aeruginosa and Acinetobacter baumannii Isolates from Chinese Intra-Abdominal, Respiratory and Urinary Tract Infections: SMART 2015 to 2018

“…The results from the 2015 SMART surveillance program, involving 17 European countries, revealed that the overall susceptibility of A. baumannii to imipenem was only 10.1% 27 and somewhat lower than found in the present study (21.0%). However, in both studies the imipenem non-susceptibilities could not be restored by relebactam in imipenem non-susceptible A. baumannii isolates, which has also been reported in the USA 15 and has been attributed to certain resistance mechanisms of A. baumannii strains, 28,29 since a main mechanism of carbapenem resistance in A. baumannii is expression of OXAs. 30 The A. baumannii percent susceptibilities to imipenem and imipenem/relebactam were virtually identical (both about 20%), whereas for amikacin they were 16.5-32.7%, indicating amikacin resistance, which has been attributed to aminoglycoside-modifying enzyme expressions in A. baumannii.…”