Molecular mechanisms of tigecycline-resistance among Enterobacterales.

The global emergence of antimicrobial resistance to multiple antibiotics has recently become a significant concern. Gram-negative bacteria, known for their ability to acquire mobile genetic elements such as plasmids, represent one of the most hazardous microorganisms. This phenomenon poses a serious threat to public health. Notably, the significance of tigecycline, a member of the antibiotic group glycylcyclines and derivative of tetracyclines has increased. Tigecycline is one of the last-resort antimicrobial drugs used to treat complicated infections caused by multidrug-resistant (MDR) bacteria, extensively drug-resistant (XDR) bacteria or even pan-drug-resistant (PDR) bacteria. The primary mechanisms of tigecycline resistance include efflux pumps' overexpression, tet genes and outer membrane porins. Efflux pumps are crucial in conferring multi-drug resistance by expelling antibiotics (such as tigecycline by direct expelling) and decreasing their concentration to sub-toxic levels. This review discusses the problem of tigecycline resistance, and provides important information for understanding the existing molecular mechanisms of tigecycline resistance in Enterobacterales. The emergence and spread of pathogens resistant to last-resort therapeutic options stands as a major global healthcare concern, especially when microorganisms are already resistant to carbapenems and/or colistin.

New trends in application of the fumigation method in medical and non-medical fields.

INTRODUCTION: In the twentieth century, fumigation became a very popular method of disinfection, although in the same century many agents used as fumigants were withdrawn for ecological reasons. Fogging (fumigation) is a relatively new disinfection technology using dry fog, which behaves more like a gas and easily fills the sanitized space, reaching all surfaces in the room. The undoubted advantage of fumigation is the possibility of disinfecting difficult to clean areas. Fumigation has become particularly important in the twenty-first century due to procedures related to combating and preventing the spread of the coronavirus that causes COVID-19. OBJECTIVE: The aim of this review article is to summarize the current state of knowledge in the field of fumigation on the basis of past results of original research, taking into account new trends and possibilities of its application. BRIEF DESCRIPTION OF THE STATE OF KNOWLEDGE: Due to the fact that fumigation is safe for apparatus, equipment, and electronics, while simultaneously enabling the highest possible bactericidal and virucidal levels, this method is widely used in various areas, both medical and non-medical. Fogging technology is used in the medical, pharmaceutical, and food industries, as well as in transportation, for air fumigation or surface disinfection in closed spaces, such as hospital and laboratory rooms, incubators, refrigerators, ships, trucks, railway containers, and aircraft, to name only a few. The most common fumigants are hydrogen peroxide and peracetic acid, and their mechanism of action is related to their oxidizing properties. SUMMARY: Hydrogen peroxide and peracetic acid are highly effective and non-toxic fumigants that can be safely used for fogging laboratory and medical equipment, pharmaceutical facilities, hospital rooms, and animal breeding rooms.

Air Disinfection-From Medical Areas to Vehicle.

Cars with air conditioning systems have become the norm, but these systems can be dangerous for human health as a result of the accumulation of different microorganisms, including pathogenic ones, causing severe allergy or inflammation problems. The novel purpose of this study is 2-fold: on the one hand, to test different disinfection agents on a new area, that is, automobile cabins, and on the other, to compare activity in the gas phase of these agents for disinfection of car air conditioning and cabin surfaces. This study shown that tested disinfectant agents dedicated for decontamination medical areas (agent based on peracetic acid and an agent containing didecyldimethylammonium chloride, 2-phenoxyethanol with cinnamaldehyde) can be successfully used for disinfection car air conditioning and cabin surfaces. Both disinfectants were examined in comparison to a commercial "ready-to-use" spray from a local supermarket dedicated to car air conditioning disinfection. Our research found that very effective agents in this regard were acid stabilized by hydrogen peroxide applied by fumigator, and a combination of didecyldimethylammonium chloride, 2-phenoxyethanol, and cinnamaldehyde applied by atomizer. Tested disinfection procedures of car air conditioning significantly influence the quality of cabin air and surfaces by reducing the amount of microorganisms. The comparison of disinfection properties studied agents in the gas phase reveal statistically significant differences between it effect for disinfection car air conditioning and cabin surfaces. Our research found that very effective agents in this regard were acid stabilized by hydrogen peroxide applied by fumigator, and a combination of didecyldimethylammonium chloride, 2-phenoxyethanol, and cinnamaldehyde applied by atomizer. Tested disinfection procedures of car air conditioning significantly influence the quality of cabin air and surfaces by reducing the amount of microorganisms.

Plasmid Mediated mcr-1.1 Colistin-Resistance in Clinical Extraintestinal Escherichia coli Strains Isolated in Poland.

Objectives: The growing incidence of multidrug-resistant (MDR) bacteria is an inexorable and fatal challenge in modern medicine. Colistin is a cationic polypeptide considered a "last-resort" antimicrobial for treating infections caused by MDR Gram-negative bacterial pathogens. Plasmid-borne mcr colistin resistance emerged recently, and could potentially lead to essentially untreatable infections, particularly in hospital and veterinary (livestock farming) settings. In this study, we sought to establish the molecular basis of colistin-resistance in six extraintestinal Escherichia coli strains. Methods: Molecular investigation of colistin-resistance was performed in six extraintestinal E. coli strains isolated from patients hospitalized in Medical University Hospital, Bialystok, Poland. Complete structures of bacterial chromosomes and plasmids were recovered with use of both short- and long-read sequencing technologies and Unicycler hybrid assembly. Moreover, an electrotransformation assay was performed in order to confirm IncX4 plasmid influence on colistin-resistance phenotype in clinical E. coli strains. Results: Here we report on the emergence of six mcr-1.1-producing extraintestinal E. coli isolates with a number of virulence factors. Mobile pEtN transferase-encoding gene, mcr-1.1, has been proved to be encoded within a type IV secretion system (T4SS)-containing 33.3 kbp IncX4 plasmid pMUB-MCR, next to the PAP2-like membrane-associated lipid phosphatase gene. Conclusion: IncX4 mcr-containing plasmids are reported as increasingly disseminated among E. coli isolates, making it an "epidemic" plasmid, responsible for (i) dissemination of colistin-resistance determinants between different E. coli clones, and (ii) circulation between environmental, industrial, and clinical settings. Great effort needs to be taken to avoid further dissemination of plasmid-mediated colistin resistance among clinically relevant Gram-negative bacterial pathogens.

Expression of AraC/XylS stress response regulators in two distinct carbapenem-resistant Enterobacter cloacae ST89 biotypes.

BACKGROUND: The growing incidence of MDR Gram-negative bacteria is a rapidly emerging challenge in modern medicine. OBJECTIVES: We sought to establish the role of intrinsic drug-resistance regulators in combination with specific genetic mutations in 11 Enterobacter cloacae isolates obtained from a single patient within a 7 week period. METHODS: The molecular characterization of eight carbapenem-resistant and three carbapenem-susceptible E. cloacae ST89 isolates included expression-level analysis and WGS. Quantitative PCR included: (i) chromosomal cephalosporinase gene (ampC); (ii) membrane permeability factor genes, e.g. ompF, ompC, acrA, acrB and tolC; and (iii) intrinsic regulatory genes, e.g. ramA, ampR, rob, marA and soxS, which confer reductions in antibiotic susceptibility. RESULTS: In this study we describe the influence of the alterations in membrane permeability (ompF and ompC levels), intrinsic regulatory genes (ramA, marA, soxS) and intrinsic chromosomal cephalosporinase AmpC on reductions in carbapenem susceptibility of E. cloacae clinical isolates. Interestingly, only the first isolate possessed the acquired VIM-4 carbapenemase, which has been lost in subsequent isolates. The remaining XDR E. cloacae ST89 isolates presented complex carbapenem-resistance pathways, which included perturbations in permeability of bacterial membranes mediated by overexpression of ramA, encoding an AraC/XylS global regulator. Moreover, susceptible isolates differed significantly from other isolates in terms of marA down-regulation and soxS up-regulation. CONCLUSIONS: Molecular mechanisms of resistance among carbapenem-resistant E. cloacae included production of acquired VIM-4 carbapenemase, significant alterations in membrane permeability due to increased expression of ramA, encoding an AraC/XylS global regulator, and the overproduction of chromosomal AmpC cephalosporinase.

Infection caused by Klebsiella pneumoniae ST11 in a patient after craniectomy.

Klebsiella pneumoniae infections have always been an important problem in public health, but today, the increasing resistance of these bacteria to antibiotics due to ß-lactamases production has renewed interest in K. pneumoniae infections. The aim of the study was to present a case of a neurosurgical patient with multidrug-resistant K. pneumoniae ST11 infection after craniectomy. Four K. pneumoniae isolates from various clinical materials of the patient undergone identification and susceptibility testing with the Vitek2 system. Tests for ß-lactamases production were performed according to EUCAST guidelines. Strains were analyzed for bla genes responsible for ß-lactamase production (blaTEM, blaSHV, blaCTX-M, blaVIM, blaIMP, blaNDM, blaKPC, blaOXA-48) using PCR. Moreover, the genetic relatedness of these isolates was determined by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). All tested strain presented multidrug resistance. The highest susceptibility was observed for imipenem, meropenem, and ertapenem. The strain isolated from the nervous system was ESBL-positive with blaSHV-11, blaTEM-1, and blaCTX-M-15 genes. Additionally, the strain from urine was blaKPC-3-positive. Molecular typing revealed that all strains belonged to the same clone and identified two PFGE profiles. The analysis of MLST allelic profile showed that tested K. pneumoniae strains belonged to ST11. Identification of ST11 K. pneumoniae as etiological factor of infection unfavorably impacts on prognosis among neurosurgical patient after craniectomy.

Activity of Ceftazidime-Avibactam Alone and in Combination with Ertapenem, Fosfomycin, and Tigecycline Against Carbapenemase-Producing Klebsiella pneumoniae.

The aim of this study was to investigate the synergy between ceftazidime-avibactam, ertapenem, fosfomycin, and tigecycline against carbapenemase-producing Klebsiella pneumoniae using the E test MIC:MIC (minimum inhibitory concentration) ratio synergy method. The results were interpreted using fractional inhibitory concentration index (FICI) to describe the effects of antimicrobial combinations in vitro. To assess the clinical significance of each antibiotic combination, the susceptible breakpoint index (SBPI) was calculated for each combination, and within each strain. The FICI method revealed that the most synergistic combinations against carbapenemase-producing K. pneumoniae were ceftazidime-avibactam with ertapenem and ceftazidime-avibactam with fosfomycin. This effect was demonstrated in 47% (9/19) of all tested clinical K. pneumoniae isolates. Considering the effects of all drug combinations in K. pneumoniae harboring blaKPC, blaNDM, and blaOXA-48 genes, we observed that the combination of ceftazidime-avibactam with fosfomycin was the most synergistic in New Delhi metallo-ß-lactamase (NDM)-producing K. pneumoniae, and the combination of ceftazidime-avibactam with ertapenem was the most synergistic in K. pneumoniae carbapenemase (KPC)-producing K. pneumoniae. In addition, all tested combinations were synergistic against oxacillinase (OXA)-48-producing K. pneumoniae, except the combination of ceftazidime-avibactam with tigecycline. The SBPI index showed that ceftazidime-avibactam in combination with fosfomycin reduced the MIC to less than the susceptibility breakpoint among all tested carbapenemase-producing K. pneumoniae. Moreover, the combinations of ceftazidime-avibactam with ertapenem, and ceftazidime-avibactam with tigecycline were able to reduce the MIC to less than the susceptibility breakpoint in all KPC- and OXA-48-producing K. pneumoniae.

Genetic basis of enzymatic resistance of E. coli to aminoglycosides.

PURPOSE: Over the past years, an increase in resistance to aminoglycosides has been observed among Enterobacteriaceae rods. This resistance development reduces therapeutic options for infections caused by multidrug-resistance organisms. Because of the changing epidemiology of extended-spectrum ß-lactamases (ESBLs) and resistance to aminoglycosides, we investigated the prevalence of the aac(3)-Ia, aac(6')-Ib, ant(4')-IIa, ant(2")-Ia, and aph(3")-Ib genes encoding aminoglycoside-modifying enzymes (AMEs) in ESBL-producing Escherichia coli as well as ESBL-non-producing isolates. To understand bacterial resistance to aminoglycoside antibiotics, we estimated resistance phenotypes and the presence of genes responsible for this resistance. MATERIALS AND METHODS: The study was conducted on 44 E.coli strains originated from patients hospitalized at University Hospital of Bialystok. MIC values were obtained for gentamicin, amikacin, netilmicin, and tobramycin. Isolates were tested for the presence of the aac(3)-Ia, aac(6')-Ib, ant(4')-IIa, ant(2")-Ia, and aph(3")-Ib genes with the use of the PCR technique. RESULTS: Resistance to aminoglycosides was found in 79.5% of the isolates. The highest percentages of resistance were observed for tobramycin (70,5%) and gentamicin (59%), followed by netilmicin (43.2%) and amikacin (11.4%). PCR assays revealed the presence of aac(6')-Ib among 26 (59.2%) strains, aph(3")-Ib among 16 (36.2%), aac(3)-Ia among 7 (15.9%), and ant(2")-Ia among 2 (4.6%) strains. CONCLUSIONS: The enzymatic resistance against aminoglycosides in northeastern Poland among clinical isolates of E. coli is predominantly caused by aac(6')-Ib and aph(3")-Ib. Amikacin may be used for therapy of infections caused by ESBL-producing E. coli, because of the low rates of resistance.

Emergence of Pseudomonas aeruginosa with class 1 integron carrying blaVIM-2 and blaVIM-4 in the University Clinical Hospital of Bialystok (northeastern Poland).

The effectiveness of carbapenems, considered as last-resort antimicrobials in severe infections, becomes compromised by bacterial resistance. The production of metallo-ß-lactamases (MBLs) is the most significant threat to carbapenems activity among Pseudomonas aeruginosa. The aim of this study was to assess the presence and type of MBLs genes in carbapenem-resistant P. aeruginosa clinical strains, to identify the location of MBLs genes and to determine genetic relatedness between MBL-producers using pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). The first identified MBL-positive (with blaVIM genes) P. aeruginosa strains were isolated from patients hospitalized in the University Clinical Hospital of Bialystok in the period from September 2012 to December 2013. Variants of MBLs genes and variable integron regions were characterized by PCR and sequencing. PFGE was performed after digesting of bacterial genomes by XbaI enzyme. By MLST seven housekeeping genes were analyzed for the determination of sequence type (ST). Three strains carried the blaVIM-2 gene and one harbored the blaVIM-4 gene. The blaVIM genes resided within class 1 integrons. PCR mapping of integrons revealed the presence of four different cassette arrays. Genetic relatedness analysis by PFGE classified VIM-positive strains into four unrelated pulsotypes (A-D). MLST demonstrated the presence of four (ST 111, ST27, and ST17) different sequence type including one previously undescribed new type of ST 2342. Antimicrobial susceptibility testing showed that VIM-positive strains were resistant to carbapenems, cephalosporins, aminoglycosides, and quinolones, intermediate to aztreonam, and susceptible only to colistin. Integrons mapping, PFGE, and MLST results may point to different origin of these strains and independent introduction into hospitalized patients.

Emergence of a multidrug-resistant Citrobacter freundii ST8 harboring an unusual VIM-4 gene cassette in Poland.

OBJECTIVES: The growing incidence of multidrug-resistant (MDR) bacteria is an emerging challenge in modern medicine. The utility of carbapenems, which are considered 'last-line' agents, is being diminished by the growing incidence of various resistance mechanisms in Gram-negative bacteria. A molecular investigation was performed of an MDR carbapenem-resistant Citrobacter freundii of sequence type 8 (ST8) isolated from a hematology patient with acute myeloid leukemia. METHODS: Multilocus sequence typing and analysis of the nucleotide sequence of the class I integron were performed using PCR and Sanger sequencing. Transformation of the resistance plasmid isolated following the alkaline lysis method was performed using chemically competent E. coli TOP10. RESULTS: Molecular analysis of the carbapenem-resistant C. freundii revealed the presence of the VIM-4 isoenzyme located on the ∼55-kb transferable resistance plasmid. Interestingly, the blaVIM-4 gene was inserted into an unusual gene cassette containing a 169-bp direct repeat of the 3' segment of the blaVIM-4 gene. CONCLUSIONS: All unusual gene cassettes containing VIM-DR (direct repeat) described thus far have been harbored by non-fermenters, i.e., Acinetobacter and Pseudomonas, underscoring the importance of resistance determinant mobility, which may go even beyond genus, family, and order boundaries. Great efforts need to be taken to explore pathways of resistance to 'last-resort' antimicrobials, especially among clinically relevant pathogens.

Altered Outer Membrane Transcriptome Balance with AmpC Overexpression in Carbapenem-Resistant Enterobacter cloacae.

The growing incidence of multidrug-resistant (MDR) bacteria is an emerging challenge in modern medicine. The utility of carbapenems, considered "last-line" agents in therapy of infections caused by MDR pathogens, is being diminished by the growing incidence of various resistance mechanisms. Enterobacter cloacae have lately begun to emerge as an important pathogen prone to exhibiting multiple drug resistance. We aimed to investigate the molecular basis of carbapenem-resistance in 44 E. cloacae clinical strains resistant to at least one carbapenem, and 21 susceptible strains. Molecular investigation of 65 E. cloacae clinical strains was based on quantitative polymerase chain reaction (qPCR) allowing for amplification of ampC, ompF, and ompC transcripts, and analysis of nucleotide sequences of alleles included in MLST scheme. Co-operation of three distinct carbapenem resistance mechanisms has been reported-production of OXA-48 (5%), AmpC overproduction (97.7%), and alterations in outer membrane (OM) transcriptome balance. Carbapenem-resistant E. cloacae were characterized by (1.) downregulation of ompF gene (53.4%), which encodes protein with extensive transmembrane channels, and (2.) the polarization of OM transcriptome-balance (79.1%), which was sloped toward ompC gene, encoding proteins recently reported to possess restrictive transmembrane channels. Subpopulations of carbapenem-susceptible strains showed relatively high degrees of sequence diversity without predominant types. ST-89 clearly dominates among carbapenem-resistant strains (88.6%) suggesting clonal spread of resistant strains. The growing prevalence of pathogens resistant to all currently available antimicrobial agents heralds the potential risk of a future "post-antibiotic era." Great efforts need to be taken to explore the background of resistance to "last resort" antimicrobials.

First Report of Klebsiella pneumoniae-Carbapenemase-3-Producing Escherichia coli ST479 in Poland.

An increase in the antibiotic resistance among members of the Enterobacteriaceae family has been observed worldwide. Multidrug-resistant Gram-negative rods are increasingly reported. The treatment of infections caused by Escherichia coli and other Enterobacteriaceae has become an important clinical problem associated with reduced therapeutic possibilities. Antimicrobial carbapenems are considered the last line of defense against multidrug-resistant Gram-negative bacteria. Unfortunately, an increase of carbapenem resistance due to the production of Klebsiella pneumoniae carbapenemase (KPC) enzymes has been observed. In this study we describe the ability of E. coli to produce carbapenemase enzymes based on the results of the combination disc assay with boronic acid performed according to guidelines established by the European Community on Antimicrobial Susceptibility Testing (EUCAST) and the biochemical Carba NP test. Moreover, we evaluated the presence of genes responsible for the production of carbapenemases (bla KPC, bla VIM, bla IMP, bla OXA-48) and genes encoding other ß-lactamases (bla SHV, bla TEM, bla CTX-M) among E. coli isolate. The tested isolate of E. coli that possessed the bla KPC-3 and bla TEM-34 genes was identified. The tested strain exhibited susceptibility to colistin (0.38 µg/mL) and tigecycline (1 µg/mL). This is the first detection of bla KPC-3 in an E. coli ST479 in Poland.

Identification of plasmid OXA and other ß-lactamase genes among carbapenem-resistant isolates of Pseudomonas aeruginosa from the Clinical University Hospital in northeastern Poland.

The aim of the study was to evaluate the prevalence of OXA and other ß-lactamase genes, antibiotic susceptibility, and the genetic relatedness among clinical isolates of P. aeruginosa resistant to carbapenems. The presence of bla- OXA genes was demonstrated in 48% of isolates belonging to four PFGE profiles. Most of them contained the blaOXA-2 gene (88.3%). Other blaOXA genes (Ps1310 with blaOXA-30 and Ps1309 with blaOXA-10) were found in only two isolates. The tested isolates also contained other ß-lactamase genes such as blaVIM-2, blaVIM-4, blaSHV-5, and blaTEM-1. All isolates were susceptible only to colistin (100%).

Prevalence of resistance to aminoglycosides and fluoroquinolones among Pseudomonas aeruginosa strains in a University Hospital in Northeastern Poland

The present study was conducted to investigate the prevalence of genes encoding resistance to aminoglycosides and fluoroquinolones among twenty-five Pseudomonas aeruginosa isolated between 2002 and 2009. In PCR, following genes were detected: ant(2")-Ia in 9 (36.0%), aac(6')-Ib in 7 (28.0%), qnrB in 5 (20.0%), aph(3")-Ib in 2 (8.0%) of isolates.

Influence of unmodified and ß-glycerophosphate cross-linked chitosan on anti-Candida activity of clotrimazole in semi-solid delivery systems.

The combination of an antifungal agent and drug carrier with adjunctive antimicrobial properties represents novel strategy of complex therapy in pharmaceutical technology. The goal of this study was to investigate the unmodified and ion cross-linked chitosan's influence on anti-Candida activity of clotrimazole used as a model drug in hydrogels. It was particularly crucial to explore whether the chitosans' structure modification by ß-glycerophosphate altered its antifungal properties. Antifungal studies (performed by plate diffusion method according to CLSI reference protocol) revealed that hydrogels obtained with chitosan/ß-glycerophosphate displayed lower anti-Candida effect, probably as a result of weakened polycationic properties of chitosan in the presence of ion cross-linker. Designed chitosan hydrogels with clotrimazole were found to be more efficient against tested Candida strains and showed more favorable drug release profile compared to commercially available product. These observations indicate that novel chitosan formulations may be considered as promising semi-solid delivery system of clotrimazole.

Emergence of OXA-48 carbapenemase-producing Enterobacter cloacae ST89 infection in Poland.

BACKGROUND: The utility of carbapenems, which are considered 'last-line' agents, is being diminished by the growing incidence of various resistance mechanisms in bacteria. We aimed to investigate the molecular mechanism of carbapenem resistance in Enterobacter cloacae recovered from a 76-year-old patient who had undergone coronary artery bypass grafting and repair of the mitral and tricuspid valves. Interestingly, the patient had no prior history of hospital admission abroad. METHODS: The Carba-NP test II and synergy testing were performed to confirm carbapenemase activity. PCR was used to detect carbapenemase-encoding genes. Nucleotide and amino acid sequence analysis was performed to identify OXA-48 variants. Moreover, we performed multilocus sequence typing (MLST) of multidrug-resistant (MDR) E. cloacae. RESULTS: We detected no significant increase in zone diameter around disks with inhibitors. However, the Carba-NP test II revealed carbapenemase activity in all isolates. All isolates showed the presence of the exact OXA-48 carbapenemase variant. Furthermore, MLST analysis revealed that the MDR E. cloacae isolates belonged to ST89. CONCLUSIONS: We report a case of infection caused by a unique carbapenem-resistant E. cloacae ST89 producing OXA-48 carbapenemase. Interestingly, these pathogens developed resistance to other 'last-resort' agents, namely colistin and tigecycline. There is a crucial need for surveillance programs aimed at screening for carbapenemase-producing Gram-negative bacteria, especially in patients transferred from high-incidence areas.

Expression of MexAB-OprM efflux pump system and susceptibility to antibiotics of different Pseudomonas aeruginosa clones isolated from patients hospitalized in two intensive care units at University Hospital in Bialystok (northeastern Poland) between January 2002 and December 2009.

We investigated the genetic similarities and expression of the MexAB-OprM efflux pump system in different clones of multiresistant Pseudomonas aeruginosa strains collected from 2002 to 2009 at two intensive care units (ICU). Regulatory and structural genes mexB, mexR, and mexA were found in 99%, 98%, and 94% of tested strains, respectively. The presence of class 1 integron was found in 90% of the strains, while class 2 integron in only one strain (Psa506). Class 3 integron was not found in any of the tested strains. Among the eleven clones identified, only two clones, I and D, exhibited higher levels of mexB gene expression than the other clones. Clone I had the highest expression (FC = 10.36, p < 0.05). The results of our study indicated a high level of MexAB-OprM pump expression in groups of strains isolated in the years 2008-2009 (FC = 12.92, p < 0.03) and 2002-2006 (FC = 5.14, p < 0.03). There were no statistically significant differences in resistance to all tested antibiotics among the various clones. The high level of antimicrobial resistance may have been due to the coexistence of different resistance mechanisms among the studied P. aeruginosa strains. However, this does not exclude the contribution of the MexAB-OprM pump, particularly in resistance to meropenem and ciprofloxacin.

In vitro activity of rifampicin alone and in combination with imipenem against multidrug-resistant Acinetobacter baumannii harboring the blaOXA-72 resistance gene.

BACKGROUND: The growing incidence of multidrug resistance (MDR) in bacteria is an emerging challenge in the treatment of infections. Acinetobacter baumannii is an opportunistic pathogen prone to exhibit MDR that contributes significantly to nosocomial infections, particularly in severely ill patients. Thus, we performed research on rifampicin activity against selected MDR OXA-72 carbapenemase-producing A. baumannii strains. Since it is widely accepted that rifampicin should not be used as monotherapy in order to avoid the rapid development of rifampicin resistance, we evaluated the efficacy of combination therapy with imipenem. METHODS: Minimal inhibitory concentrations (MICs) of both rifampicin and imipenem were determined by use of the broth microdilution method. Evaluations of the interactions between rifampicin and imipenem were performed by analysis of the fractional inhibitory concentration index (∑FIC), determined using the checkerboard titration method. RESULTS: All tested isolates showed full susceptibility to rifampicin. The checkerboard method revealed synergism in 5 isolates (29%) and an additive effect in another 5 isolates (29%); no difference was reported in the remaining 7 isolates (41%). Strains moderately resistant to imipenem (MIC ≤ 64 mg/l) tended to show synergy or additive interaction. CONCLUSIONS: We conclude that in vitro synergism or an additive interaction between rifampicin and imipenem most likely occurs in A. baumannii strains showing moderate resistance to imipenem (MIC ≤ 64 mg/l). Moreover, utilizing this combination in the therapy of infections caused by strains exhibiting higher levels of resistance (MIC > 64 mg/l) is not recommended since in this setting imipenem could not prevent the development of rifampicin resistance.

Prevalence of resistance to aminoglycosides and fluoroquinolones among Pseudomonas aeruginosa strains in a University Hospital in Northeastern Poland.

The present study was conducted to investigate the prevalence of genes encoding resistance to aminoglycosides and fluoroquinolones among twenty-five Pseudomonas aeruginosa isolated between 2002 and 2009. In PCR, following genes were detected: ant(2″)-Ia in 9 (36.0%), aac(6')-Ib in 7 (28.0%), qnrB in 5 (20.0%), aph(3″)-Ib in 2 (8.0%) of isolates.