Metallo-beta-lactamase-producing gram-negative bacilli: laboratory-based surveillance in cooperation with 13 clinical laboratories in the Kinki region of Japan

Epidemiology of Citrobacter spp. infections among hospitalized patients: a systematic review and meta-analysis

BACKGROUND

Infections due to Citrobacter species are increasingly observed in hospitalized patients and are often multidrug-resistant. Yet, the magnitude and burden of Citrobacter spp. resistance in the hospital setting have not been reported. We aimed to evaluate the epidemiology of Citrobacter spp. infections among hospitalized patients, their main resistance patterns and Citrobacter spp. involvement in hospital outbreaks.

METHODS

We conducted a systematic review and meta-analysis of published literature (PROSPERO registration Jan-2023, CRD42023390084). We searched Embase, Medline and grey literature for studies on hospitalized patients diagnosed with Citrobacter spp. infections, and nosocomial outbreaks due to Citrobacter spp. published during the years 2000-2022. We included observational, interventional, surveillance studies and outbreak reports. Outcomes of interest were the frequency of Citrobacter spp. infections among hospitalized patients and 3rd generation cephalosporin and/or carbapenem resistance percentages in these infections. We used random-effects models to generate pooled outcome estimates and evaluated risk of bias and quality of reporting of outbreaks.

RESULTS

We screened 1609 deduplicated publications, assessed 148 full-texts, and included 41 studies (15 observational, 13 surveillance and 13 outbreak studies). Citrobacter spp. urinary tract- and bloodstream infections were most frequently reported, with Citrobacter freundii being the main causative species. Hospital-acquired infection occurred in 85% (838/990) of hospitalized patients with Citrobacter infection. After 2010, an increasing number of patients with Citrobacter spp. infections was reported in observational studies. Pooled frequency estimates for Citrobacter spp. infections could not be generated due to lack of data. The pooled prevalence of ESBL and carbapenemase producers among Citrobacter isolates were 22% (95%CI 4-50%, 7 studies) and 18% (95%CI 0-63%, 4 studies), respectively. An increased frequency of reported Citrobacter outbreaks was observed after 2016, with an infection/colonization ratio of 1:3 and a case-fatality ratio of 7% (6/89 patients). Common outbreak sources were sinks, toilets, contaminated food and injection material. Implemented preventive measures included environmental cleaning, isolation of positive patients and reinforcement of hand hygiene. Only seven out of 13 outbreaks (54%) were definitively controlled.

CONCLUSION

This review highlights the clinical importance of endemic and epidemic Citrobacter spp. in healthcare settings. As an emerging, multidrug‑resistant nosocomial pathogen it requires heightened awareness and further dedicated surveillance efforts.

Identification of Providencia spp. clinical isolates co-producing carbapenemases IMP-27, OXA-24, and OXA-58 in Mexico

Providencia rettgeri, belonging to the genus Providencia, had gained significant interest due to its increasing prevalence as a common pathogen responsible for healthcare-associated infections in hospitals. P. rettgeri isolates producing carbapenemases have been reported to reduce the efficiency of carbapenems in clinical antimicrobial therapy. However, coexistence with other resistance determinants is rarely reported. The goal of this study was the molecular characterization of carbapenemase-producing Providencia spp. clinical isolates. Among 23 Providencia spp. resistant to imipenem, 21 were positive to blaNDM-1; one positive to blaNDM-1 and blaOXA-58 like; and one isolate co-producing blaIMP-27, blaOXA-24/40 like, and blaOXA-58 like were identified. We observed a low clonal relationship, and the incompatibility groups Col3M and ColRNAI were identified in the plasmid harboring blaNDM-1. We report for the first time a P. rettgeri strain co-producing blaIMP-27, blaOXA-24-like, and blaOXA-58 like. The analysis of these resistance mechanisms in carbapenemase co-producing clinical isolates reflects the increased resistance.

Alkyl gallates inhibit serine O-acetyltransferase in bacteria and enhance susceptibility of drug-resistant Gram-negative bacteria to antibiotics

A principal concept in developing antibacterial agents with selective toxicity is blocking metabolic pathways that are critical for bacterial growth but that mammalian cells lack. Serine O-acetyltransferase (CysE) is an enzyme in many bacteria that catalyzes the first step in l-cysteine biosynthesis by transferring an acetyl group from acetyl coenzyme A (acetyl-CoA) to l-serine to form O-acetylserine. Because mammalian cells lack this l-cysteine biosynthesis pathway, developing an inhibitor of CysE has been thought to be a way to establish a new class of antibacterial agents. Here, we demonstrated that alkyl gallates such as octyl gallate (OGA) could act as potent CysE inhibitors in vitro and in bacteria. Mass spectrometry analyses indicated that OGA treatment markedly reduced intrabacterial levels of l-cysteine and its metabolites including glutathione and glutathione persulfide in Escherichia coli to a level similar to that found in E. coli lacking the cysE gene. Consistent with the reduction of those antioxidant molecules in bacteria, E. coli became vulnerable to hydrogen peroxide-mediated bacterial killing in the presence of OGA. More important, OGA treatment intensified susceptibilities of metallo-β-lactamase-expressing Gram-negative bacteria (E. coli and Klebsiella pneumoniae) to carbapenem. Structural analyses showed that alkyl gallate bound to the binding site for acetyl-CoA that limits access of acetyl-CoA to the active site. Our data thus suggest that CysE inhibitors may be used to treat infectious diseases caused by drug-resistant Gram-negative bacteria not only via direct antibacterial activity but also by enhancing therapeutic potentials of existing antibiotics.

Screening for Metallo-Beta-Lactamases Using Non-Carbapenem Agents: Effective Detection of MBL-Producing Enterobacterales and Differentiation of Carbapenem-Resistant Enterobacterales

Metallo-beta-lactamases (MBLs) are enzymes that break down carbapenem antibiotics, leading to carbapenem-resistant organisms. Carbapenemase-resistant Enterobacterales (CRE) is one of them. Outbreaks of CRE infection can occur in healthcare facilities and lead to increased deaths, illness, and medical costs. This study was conducted to detect MBLs using non-carbapenem agents and exclude MBLs among CRE isolates. A total of 3776 non-duplicate sequential Enterobacterales isolates from a single facility were screened between January 2019 and December 2022 using non-carbapenem agents, ceftazidime and cefoperazone/sulbactam. Positive 153 isolates (4.0%) were further tested using carbapenemase-confirmation tests and verified through polymerase chain reaction (PCR) testing. Fifteen imipenemase (IMP)-type MBL-producing Enterobacterales (0.4%) including one susceptible to carbapenems were identified. Moreover, 160 isolates (4.2%) meeting the criteria for CRE were directly subjected to PCR testing. All fourteen CRE isolates with MBLs identified through PCR testing were found to be the same strains screened using ceftazidime and cefoperazone/sulbactam. Screening using ceftazidime and cefoperazone/sulbactam can effectively detect MBL-producing Enterobacterales strains. This screening method showed comparable results to screening with meropenem, potentially serving as a supplementary approach and contributing to differentiating between MBL- and non-MBL-producing CRE strains. Our findings support these screening methods, particularly in regions where IMP-type MBLs are prevalent.

A two-year retrospective study of multidrug-resistant Acinetobacter baumannii respiratory infections in critically Ill patients: Clinical and microbiological findings

BACKGROUND

Acinetobacter baumannii infection is a serious public health problem because it is highly resistant to antimicrobial therapy and causes a high fatality rate in critically ill patients. The aim of the study is to examine the demographics, microbiological findings, clinical presentation, and outcomes of multi-drug-resistant Acinetobacter baumannii respiratory infections in adult ICU intubated patients during COVID-19 pandemic.

METHODS

This study included 115 mechanically ventilated adult ICU patients who had multi-drug-resistant Acinetobacter baumannii retrieved from respiratory samples during the COVID-19 pandemic in Albaha, Saudi Arabia. The information was obtained from medical and laboratory files. Univariate analysis was used to compare gender, COVID-19 infection, and outcomes.

RESULTS

The rate of Acinetobacter baumanni respiratory infections among adult ICU patients was 6.2 %. Almost 93 % developed ventilator-associated pneumonia, and five of them developed bacteremia. The isolates had significant antibiotic resistance patterns, of which 3 % were pandrug-resistant bacteria. The death rate was 74 %, with major risk factors including sepsis, septic shock, VAP, liver diseases, and the use of inappropriate antibiotic therapy that lacked both colistin and tigecycline. Patients with COVID-19 coinfection had worse outcomes compared to non-COVID-19 patients.

CONCLUSIONS

The identification of MDR-AB as a threat highlights the importance of surveillance studies in this region.

Emergence and Evolution of Unique Plasmids Harboring blaIMP-70 and blaCTX-M-253 in Multidrug-Resistant Providencia rettgeri

Although the prevalence of carbapenem-resistant Enterobacterales remains low in Japan, these bacteria are a growing problem worldwide, owing to their multidrug resistance phenotype. We isolated a multidrug-resistant Providencia rettgeri strain, NR1418, harboring a rare bla_IMP variant, bla_IMP-70, a novel bla_CTX-M variant, designated bla_CTX-M-253, and bla_MOX-1. This strain is resistant to β-lactams, amikacin, levofloxacin, and colistin. Genomic analysis revealed that NR1418 carries two plasmids, designated pNR1418-1 and pNR1418-2. The pNR1418-1 plasmid harbors bla_CTX-M-253, bla_TEM-1, and bla_MOX-1, while the pNR1418-2 plasmid harbors bla_IMP-70, which is located in a class 1 integron. Both plasmids exhibit high similarities with the plasmid of the P. rettgeri isolate BML2526, which also harbors bla_IMP-70 and was identified in the same region of Japan as NR1418 at a different point in time. This indicates the possibility of the emergence and evolution of IMP-70-producing P. rettgeri and suggests that the plasmid of BML2526 may have occurred following recombination of the two plasmids harbored by NR1418. Further, bla_IMP-70 and bla_CTX-M-253 were found on unique plasmids, indicating that they likely evolved through mutations and recombination. IMPORTANCE Although Providencia rettgeri is an opportunistic pathogen, its intrinsic resistance to colistin and tigecycline makes the treatment of carbapenem-resistant P. rettgeri challenging. We isolated a multidrug-resistant P. rettgeri strain which harbored a rare bla_IMP variant, bla_IMP-70, a novel bla_CTX-M variant, bla_CTX-M-253, and bla_MOX-1 from a urinary sample obtained in Osaka, Japan. We investigated its genetic structure and evaluated the evolution of the plasmids carrying these genes. We show that bla_IMP-70, bla_CTX-M-253, and bla_MOX-1 are present on unique plasmids and that they have high similarities to the plasmid of another IMP-70-producing P. rettgeri isolate that was identified as being from the same location. The evolution of plasmids through mutations and recombination may play a role in the development and spread of multidrug resistance.

Emergence of Carbapenem-resistant Clinical Isolates of Providencia Species

Providencia is a genus of Gram-negative and non-spore forming bacteria belonging to the family Morganellaceae, which causes opportunistic infections in humans. Of the 10 Providencia species identified to date, three, P. alcalifaciens, P. rettgeri and P. stuartii, are clinically important. P. alcalifaciens causes diarrhea, including outbreaks arising from food-borne infections, and P. stuartii and P. rettgeri have been found to cause hospital acquired urinary tract infections. Four isolates of P. rettgeri and one isolate of P. stuartii were obtained from urine samples of five patients in Japan in 2018. All five isolates were highly resistant to carbapenems. Three isolates harbored bla IMP-70, encoding a variant of IMP-1 metallo-β-lactamase, with two amino acid substitutions (Val67Phe and Phe87Val), one isolate harbored two copies of bla IMP-1 and one isolate harbored bla IMP-11. Expression of bla IMP-70 conferred carbapenem resistance in Escherichia coli. Recombinant IMP-10, an IMP-1 variant with Val67Phe but without Phe87Val, had significant higher hydrolytic activities against meropenem than recombinant IMP-1, indicating that the Val67Phe amino acid substitution alters activities against meropenem in IMP-70. These results suggest that Providencia species. become more highly resistant to carbapenems by acquisition of two copies of bla IMP-1 or by mutations in bla IMP that result in amino acid substitutions, such as bla IMP-70.

Distribution of Carbapenemase Genes among Carbapenem-Non-Susceptible Acinetobacter baumanii Blood Isolates in Indonesia: A Multicenter Study

Carbapenem non-susceptible Acinetobacter baumannii (CNSAB) is an important pathogen that causes nosocomial bacteremia among critically ill patients worldwide. The magnitude of antibiotic resistance of A. baumanii in Indonesia is expected to be significant; however, the data available are limited. The aim of this study was to analyze the genetic profiles of CNSAB isolates from patients with bacteremia in Indonesia. CNSAB isolates from blood cultures of bacteremia patients in 12 hospitals in Indonesia were included. The blood cultures were conducted using the BacT/Alert or BACTEC automated system. The CNSAB were identified with either Vitek 2 system or Phoenix platform followed by a confirmation test using a multiplex polymerase chain reaction (PCR) assay, targeting the specific gyrB gene. The carbapenemase genes were detected by multiplex PCR. In total, 110 CNSAB isolates were collected and were mostly resistant to nearly all antibiotic classes. The majority of CNSAB isolates were susceptible to tigecycline and trimethoprim-sulfamethoxazole (TMP-SMX), 45.5% and 38.2%, respectively. The bla_OXA-51-like gene was identified in all CNSAB isolates. Out of the total, 83.6% of CNSAB isolates had bla_OXA-23-like gene, 37.3% bla_OXA-24-like gene, 4.5% bla_NDM-1 gene, 0.9% bla_IMP-1 gene, and 0.9% bla_VIM gene. No bla_OXA-48-like gene was identified. The bla_OXA-23-like gene was the predominant gene in all except two hospitals. The presence of the bla_OXA-24-like gene was associated with resistance to tigecycline, amikacin, TMP-SMX and cefoperazone-sulbactam, while bla_OXA-23-like gene was associated with resistance to TMP-SMX and cefoperazone-sulbactam. In conclusion, the bla_OXA-23-like gene was the predominant gene among CNSAB isolates throughout Indonesia. A continuous national surveillance system needs to be established to further monitor the genetic profiles of CNSAB in Indonesia.

Novel approach for rapid detection of extended spectrum β-lactamase and metalloid-β-lactamase using drug susceptibility testing microfluidic device (DSTM)

BACKGROUND/PURPOSE

Rapid detection of β-lactamases is important in a recent situation where resistant bacteria are increasing. By using the drug susceptibility testing microfluidic device (DSTM), rapid screening of extended spectrum β-lactamases (ESBLs) and metallo-β-lactamases (MBLs) has become possible.

METHODS

β-lactams and β-lactamase inhibitors were pre-fixed in the DSTM for use. A bacterial suspension in Mueller-Hinton broth (McF 0.25) was introduced into the device, and the effects of β-lactamase inhibitor on morphological changes caused by β-lactam were evaluated after 3 h incubation.

RESULTS

Clinical isolates genetically confirmed to produce β-lactamase were used. Of the 84 ESBL-producing strains, 80 strains (95%) turned to be ESBL positive, and five strains (6%) of them MBL were positive as well as ESBL. Four strains (5%) were negative for both ESBL and MBL. Of the 24 MBL-producing strains, 23 strains (96%) were positive for MBL. All the 43 AmpC-producing strains were negative for both ESBL and MBL. Of the 156 ESBL- and MBL-nonproducing strains, 155 strains (99%) were negative for both ESBL and MBL, and one strain was positive for ESBL. With this method, the detection sensitivity was 95% and the specificity was 100% for ESBL, whereas the detection sensitivity was 96% and the specificity was 98% for MBL. These results were not significantly different from the results of the disc diffusion method.

CONCLUSION

The DSTM method allows rapid detection of β-lactamases in 3 h and may be a useful replacement for the disc diffusion method.

Genomic Characterization of ESBL- and Carbapenemase-Positive Enterobacteriaceae Co-harboring mcr-9 in Japan

Worldwide spread of Enterobacteriaceae resistant to colistin, a polypeptide antibacterial drug for last-resort treatment of carbapenemase-producing Enterobacteriaceae (CPE) infections, is concerning. This study aimed to elucidate colistin MICs and molecular characteristics of mcr-1 to mcr-9 of ESBL-producing Escherichia coli (ESBL-Ec) and CPE in Japan and clarify the genomic structure of strains harboring mcr genes (especially mcr-9). This study included 168 ESBL-Ec and 126 CPE strains isolated at Japanese medical facilities. Colistin susceptibility testing and multiplex PCR targeting mcr-1 to mcr-9 were performed for all strains with S1-nuclease pulsed-field gel electrophoresis, Southern blot hybridization, and whole-genome sequencing (WGS) with hybrid assembly performed for mcr gene-carrying strains. Two CPE strains showed a MIC ≥ 4 μg/ml in colistin susceptibility testing, with no known resistance mechanism detected. However, PCR conducted on all target strains detected three mcr-9-carrying strains showing colistin susceptibility. The bla_CTX–M–62-positive E. coli THUN648 strain simultaneously carried bla_CTX–M–62 and mcr-9 on a 275-kbp plasmid. Besides, bla_IMP–6 + bla_CTX–M–2-positive Klebsiella pneumoniae THUN262 and bla_GES–24-positive Enterobacter kobei THUN627 had mcr-9 encoded on the chromosome. Only THUN627 encoded qseB/C, which is suggested to be a regulatory gene for mcr-9, downstream of mcr-9. However, this strain showed no increased expression of these genes in mRNA quantitative analysis under colistin exposure. Colistin MICs of ESBL-Ec and CPE in Japan were all below 2 μg/ml, which is below the epidemiological cutoff (ECOFF) value (https://eucast.org/) or clinical breakpoint (CB) (CLSI M100-S30) reported for colistin, indicating neither “microbiological” nor “clinical” resistance. Several colistin-susceptible Enterobacteriaceae carrying silent mcr-9 encoded on plasmids and chromosomes have already spread worldwide along with other antimicrobial resistance genes. However, the mechanism of colistin resistance by mcr-9 remains unclear.

Emergence of Enterobacter cloacae Complex Co-Producing IMP-10 and CTX-M, and Klebsiella pneumoniae Producing VIM-1 in Clinical Isolates in Japan

BACKGROUND

Carbapenemase-producing Enterobacteriaceae (CPE) are an emerging threat in healthcare settings worldwide.

OBJECTIVES

We evaluated the presence of carbapenemase genes in CPE in a tertiary care university hospital in Tokyo, Japan.

METHODS

Carbapenem-resistant clinical isolates were collected in 2018 at Teikyo University Hospital (Tokyo, Japan). Bacterial species were identified using MALDI-TOF MS. Carbapenemase production was evaluated using a carbapenemase inactivation method. The presence of carbapenemase genes was confirmed by multiplex PCR and DNA sequencing.

RESULTS

Four CPE isolates were identified: two Enterobacter cloacae complex strains and Klebsiella oxytoca and Klebsiella pneumoniae strains. Three of the isolates (E. cloacae complex and K. oxytoca) were IMP-1-type producers, including IMP-10 in their produced metallo-β-lactamase, and are epidemic in East Japan. The IMP-10-producing E. cloacae complex strain also produced CTX-M ESBL. The other CPE isolate (K. pneumoniae) is a VIM-1 producer. VIM-1-producing K. pneumoniae is epidemic in Europe, especially in Greece. Accordingly, the VIM-1 producer was isolated from a patient with a medical history in Greece.

CONCLUSIONS

This study revealed the emergence of E. cloacae complex co-producing IMP-1-type carbapenemase and CTX-M ESBL, and K. pneumoniae producing VIM-1 carbapenemase in clinical isolates in Japan. Metallo-β-lactamase was the most prevalent type of carbapenemase at Teikyo University Hospital, especially IMP-1-type carbapenemase. The detection of VIM-1-producing K. pneumoniae suggests that epidemic CPE from overseas can spread to countries with low CPE prevalence, such as Japan, highlighting the need for active surveillance.

Emergence of Carbapenem-Resistant Providencia rettgeri and Providencia stuartii Producing IMP-Type Metallo-β-Lactamase in Japan

Four Providencia rettgeri isolates and one Providencia stuartii isolate were obtained from urine samples of five patients in 2018 in Japan. All of the isolates were resistant to imipenem and meropenem, and three were highly resistant to both carbapenems, with MICs of 512 μg/ml. The three highly carbapenem-resistant isolates harbored bla_IMP-70, encoding a variant of IMP-1 metallo-β-lactamase with two amino acid substitutions (Val67Phe and Phe87Val), and the other two harbored bla_IMP-1 and bla_IMP-11, respectively. Whole-genome sequencing revealed that an isolate harbored two copies of bla_IMP-1 on the chromosome and that the other four harbored a copy of bla_IMP-11 or bla_IMP-70 in a plasmid. Expression of bla_IMP-70 conferred carbapenem resistance in Escherichia coli Recombinant IMP-70 and an IMP-1 variant with Val67Phe but without Phe87Val had significant higher hydrolytic activities against meropenem than recombinant IMP-1, indicating that an amino acid substitution of Val67Phe affects increased activities against meropenem in IMP-70. These results suggest that Providencia spp. become more highly resistant to carbapenems by acquisition of two copies of bla_IMP-1 or by mutation of bla_IMP genes with amino acid substitutions, such as bla_IMP-70.

Trends and molecular characteristics of carbapenemase-producing Enterobacteriaceae in Japanese hospital from 2006 to 2015

BACKGROUND

The increasing number of carbapenemase-producing Enterobacteriaceae (CPE) has become a global problem. Most carbapenemases detected in Japan are imipenemase, which is an imipenem-degrading enzyme with low ability; thus, CPE could have been overlooked. Therefore, this study aimed to detect and analyze CPE, without overlooking CPE showing the low minimum inhibitory concentration phenotype.

METHODS

CPE screening was conducted on 531 ceftazidime-resistant Enterobacteriaceae isolated from Kitasato University Hospital during 2006-2015. We confirmed the presence of the carbapenemase genes (bla_IMP, bla_VIM, bla_KPC, bla_NDM, and bla_OXA-48) by multiplex polymerase chain reaction. The detected CPE strains were analyzed by antimicrobial susceptibility testing, multilocus sequence typing, conjugal experiments, replicon typing, and plasmid profiling by restriction enzyme treatment.

RESULTS

The CPE detection rate in Kitasato University Hospital within the past 10 years was 0.0003% (nine CPE strains). These nine CPE strains were identified to harbor 8 bla_IMP-1 or 1 bla_NDM-5. The CPE strains consisted of five species including Klebsiella pneumoniae and Citrobacter freundii. Six of eight bla_IMP-1 were coded by IncHI2 plasmid, and the other two were coded by IncA/C plasmid. Plasmid profiling revealed that K. pneumoniae and C. freundii isolated from the same patient harbored the same plasmid.

CONCLUSION

The CPE detection rate in this study was significantly lower than those previously reported in Japan. In one case, IncA/C plasmid transmission through different bacterial species within the body was speculated. Although the number of CPE detected was low, these results indicated that the resistance plasmid could spread to other bacterial species.

Genetics of Acquired Antibiotic Resistance Genes in Proteus spp

Proteus spp. are commensal Enterobacterales of the human digestive tract. At the same time, P. mirabilis is commonly involved in urinary tract infections (UTI). P. mirabilis is naturally resistant to several antibiotics including colistin and shows reduced susceptibility to imipenem. However higher levels of resistance to imipenem commonly occur in P. mirabilis isolates consecutively to the loss of porins, reduced expression of penicillin binding proteins (PBPs) PBP1a, PBP2, or acquisition of several antibiotic resistance genes, including carbapenemase genes. In addition, resistance to non-β-lactams is also frequently reported including molecules used for treating UTI infections (e.g., fluoroquinolones, nitrofurans). Emergence and spread of multidrug resistant P. mirabilis isolates, including those producing ESBLs, AmpC cephalosporinases and carbapenemases, are being more and more frequently reported. This review covers Proteus spp. with a focus on the different genetic mechanisms involved in the acquisition of resistance genes to multiple antibiotic classes turning P. mirabilis into a dreadful pandrug resistant bacteria and resulting in difficult to treat infections.

Tetrahymena promotes interactive transfer of carbapenemase gene encoded in plasmid between fecal Escherichia coli and environmental Aeromonas caviae

Tetrahymena can facilitate plasmid transfer among Escherichia coli or from E. coli to Salmonella Enteritidis via vesicle accumulation. In this study, whether ciliates promote the interactive transfer of plasmids encoding bla_IMP-1 between fecal E. coli and environmental Aeromonas caviae was investigated. Both bacteria were mixed with or without ciliates and incubated overnight at 30°C. The frequency of plasmid-acquired bacteria was estimated by colony counts using an agar plate containing ceftazidim (CAZ) followed by determination of the minimum inhibitory concentration (MIC). Cultures containing ciliates interactively transferred the plasmid between E. coli and Aeromonas with a frequency of 10^-4 to 10^-5 . All plasmid-acquired bacteria showed a MIC against CAZ of >128 μg/mL and the plasmid transfer was confirmed by PCR amplification of the bla_IMP-1 gene. Fluorescent observation showed that both bacteria accumulated in the same vesicle and that transwell sequestering significantly decreased the transfer frequency. Although ciliates preferentially ingested E. coli rather than A. caviae, both bacteria were co-localized into the same vesicles of ciliates, indicating that their meeting is associated with the gene transfer. Thus, ciliates interactively promote plasmid transfer between E. coli and A. caviae. The results of this study will facilitate control of the spread of multiple-antibiotic resistant bacteria.

Molecular characteristics of carbapenem-resistant Pseudomonas aeruginosa isolated from urine in Hyogo, Japan

OBJECTIVES

To investigate the molecular characteristics and epidemiology of metallo-β-lactamase-producing Pseudomonas aeruginosa from urine of urinary tract infection patients in Hyogo Prefecture, Japan.

METHODS

Carbapenem-resistant P. aeruginosa isolated from the urine of 21 urinary tract infection patients in three general hospitals in Hyogo Prefecture (Japan) were collected between 2007 and 2014. Their antibiotic susceptibilities, metallo-β-lactamase screening test, metallo-β-lactamase gene sequencing, multilocus sequence typing and repetitive-sequence-based polymerase chain reaction were determined for epidemiological analyses to investigate the genetic characteristics.

RESULTS

Out of 21 isolates, 13 (61.9%) were positive for metallo-β-lactamase. There were 11 (52.4%) isolates with IMP-1 in them, one (4.5%) isolate with IMP-7 and one (4.5%) isolate with VIM-1. Metallo-β-lactamase-positive isolates were mainly identified as ST235, and metallo-β-lactamase-negative isolates were STs 357, 277, 234, 439 and 639. Repetitive-sequence-based polymerase chain reaction showed metallo-β-lactamase-positive isolates were grouped in eight clusters, and ST235 isolates with IMP-1 from three hospitals belonging to the identical group I, the other ST235 isolates with IMP-7 and VIM-1 were from two hospitals belonging to group II.

CONCLUSIONS

Metallo-β-lactamase-positive P. aeruginosa of ST235 isolates with IPM-1 were mainly identified from the urine of urinary tract infection patients in Hyogo, Japan. A ST235 isolate with VIM-1 was found for the first time. Further investigation is necessary to follow the spread of metallo-β-lactamase-positive isolates.

Molecular and microbiological report of a hospital outbreak of NDM-1-carrying Enterobacteriaceae in Mexico

OBJECTIVES

To characterize the microbiological, molecular and epidemiological data of an outbreak of carbapenem-resistant Enterobacteriaceae (CRE) in a tertiary-care hospital in Mexico.

METHODS

From September 2014 to July 2015, all CRE clinical isolates recovered during an outbreak in the Hospital Civil "Fray Antonio Alcalde" in Jalisco, Mexico were screened for antimicrobial susceptibility, carbapenemase production, carbapenemase-encoding genes, and plasmid profiles. Horizontal transfer of imipenem resistance; and clonal diversity by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST); as well as biofilm production and the presence of 14 virulence genes were analyzed in selected isolates.

RESULTS

Fifty-two carbapenem-resistant isolates corresponding to 5 species were detected, i.e., Klebsiella pneumoniae (n = 46), Enterobacter cloacae (n = 3), Escherichia coli (n = 1), Providencia rettgeri (n = 1) and Citrobacter freundii (n = 1) with carbapenemase encoding genes blaNDM-1 (n = 48), blaVIM (n = 3), blaIMP (n = 1) and blaKPC (n = 1) detected in these isolates. The blaNDM-1 gene was detected in plasmids from 130- to 170-kb in K. pneumoniae (n = 46); E. cloacae (n = 3), E. coli (n = 1) and P. rettgeri (n = 1). The transfer of plasmids harboring the blaNDM-1 gene was obtained in eight transconjugants. One plasmid restriction pattern was detected, with the blaNDM-1 identified in different restriction fragments. Predominant clone A of K. pneumoniae isolates archived 28/46 (60%) isolates and belongs to ST392. Besides, ST307, ST309, ST846, ST2399, and ST2400 were detected for K. pneumoniae; as well as E. cloacae ST182 and E. coli ST10. The fimA and uge genes were more likely to be identified in K. pneumoniae carbapenem-susceptible isolates (p = <0.001) and biofilm production was more liable to be observed in carbapenem-resistant isolates (p = <0.05).

CONCLUSIONS

Four Enterobacteriaceae species harboring the blaNDM-1 gene were detected in a nosocomial outbreak in Mexico; horizontal transfer and strain transmission were demonstrated for the blaNDM-1 gene. Given the variation in the size of the plasmid harboring blaNDM-1, complex rearrangements must also be occurring.

Antimicrobial Resistance of Pseudomonas aeruginosa Isolated from Dogs and Cats in Primary Veterinary Hospitals in Japan

We collected 200 Pseudomonas aeruginosa isolates from dogs and cats in primary veterinary hospitals in Japan to investigate their antimicrobial resistance. Resistance rates against ciprofloxacin, cefotaxime, gentamicin, amikacin, and fosfomycin were 9%, 12.5%, 4.5%, 2.5%, and 35.5%, respectively. One strain displayed resistance (0.5%) to ceftazidime. We did not detect any imipenem-resistant or multidrug-resistant P. aeruginosa strains as defined by the Japanese Ministry of Health, Labour, and Welfare Law Concerning the Prevention of Infections and Medical Care for Patients with Infections. In addition, we did not find any P. aeruginosa isolates that produced metallo-β-lactamase, the aminoglycoside 6'-N-acetyltransferase AAC(6')-Iae, or the aminoglycoside acetyltransferase AAC(6')-Ib.

Community spread of extended-spectrum β-lactamase-producing bacteria detected in social insurance hospitals throughout Japan

We surveyed the status of community-acquired infections involving four extended-spectrum β-lactamase (ESBL)-producing bacteria (Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Proteus mirabilis) isolated from clinical specimens from 11 social insurance hospitals in Japan in 2012. These are member hospitals of the Japan Community Healthcare Organization, an independent administrative hospital organization. The isolation rates for E. coli, K. pneumoniae, K. oxytoca, and P. mirabilis were 14.0% (165/1176), 3.3% (16/480), 3.1% (4/130), and 15.9% (17/107), respectively. The CTX-M-9 group, the most frequently detected genotype, was found in 77.0% (127/165) of E. coli and 43.8% (7/16) of K. pneumoniae isolates. Among K. oxytoca isolates, 75% (3/4) were the CTX-M-1 group, and all 17 P. mirabilis strains were the CTX-M-2 group. ESBL-producing bacteria isolation rates in each hospital ranged from 5.8% to 21.5% (median 9.5%), and the proportion of community-acquired infections among ESBL-producing bacteria isolates ranged from 1.6% to 30.8% (median 11.4%) in each hospital. Overall, the rates of ESBL-producing bacterial infection in all community-acquired infections and in all hospital infections were 10.6% (115/1081) and 10.7% (87/812), respectively. The ESBL-producing bacteria are not limited to certain regions or hospitals but are spreading in communities throughout Japan.

Isolation of Enterobacter aerogenes carrying blaTEM-1 and blaKPC-3 genes recovered from a hospital Intensive Care Unit

Enterobacter aerogenes has recently emerged as an important hospital pathogen. In this study, we showed the emergence of E. aerogenes isolates carrying the blaKPC gene in patients colonized by carbapenem-resistant Klebsiella pneumoniae strains. Two multiresistant E. aerogenes isolates were recovered from bronchial aspirates of two patients hospitalized in the Intensive Care Unit at the "Santa Maria della Scaletta" Hospital, Imola. The antimicrobial susceptibility test showed the high resistance to carbapenems and double-disk synergy test confirmed the phenotype of KPC and AmpC production. Other investigation revealed that ESBL and blaKPC genes were carried on the conjugative pKpQIL plasmid. This is a relevant report in Italy that describes a nosocomial infection due to the production of KPC beta-lactamases by an E. aerogenes isolate in patients previously colonized by K. pneumoniae carbapenem-resistant. In conclusion, it's necessary a continuous monitoring of multidrug-resistant strains for the detection of any KPC-producing bacteria that could expand the circulation of carbapenem-resistant pathogens.

Acquired metallo-β-lactamases and their genetic association with class 1 integrons and ISCR elements in Gram-negative bacteria

ABSTRACT 

Metallo-β-lactamases (MBLs) can hydrolyze almost all β-lactam antibiotics and are resistant to clinically available β-lactamase inhibitors. Numerous types of acquired MBLs have been identified, including IMP, VIM, NDM, SPM, GIM, SIM, DIM, KHM, TMB, FIM and AIM. IMPs and VIMs are the most frequent MBLs and disseminate in members of the family Enterobacteriaceae, Pseudomonas spp. and Acinetobacter spp. Acquired MBL genes are often embedded in integrons, and some are associated with insertion sequence (IS) elements. The class 1 integrons and IS common region (ISCR) elements are usually harbored in transposons and/or plasmids, forming so-called mobile vesicles for horizontal transfer of captured genes between bacteria. Here, we review the MBL superfamily identified in Gram-negative bacteria, with an emphasis on the phylogeny of acquired MBLs and their genetic association with class 1 integrons and IS common region elements.

Metallo-β-lactamase-producing Klebsiella pneumoniae infection in a non-hospital environment

Case

A 92-year-old female resident at a nursing home was transported to the emergency department unconscious, hypotensive, and febrile. Chest X-rays and computed tomography revealed a permeation shadow in the right lung. The patient was diagnosed with sepsis due to pneumonia. At the time of admission, she had not received antibiotics or treatment using medical devices over the past 6 months. Two sets of samples were taken for blood and sputum cultures, and Klebsiella pneumoniae was isolated from all cultures. The strain was identified as metallo-β-lactamase-producing K. pneumoniae, and the patient was successfully treated with tazobactam-piperacillin. This case indicates that metallo-β-lactamase-producing K. pneumoniae infection occurred in a non-hospital environment.

Outcome

After tazobactam-piperacillin treatment, the patient was transferred to another hospital.

Conclusion

Emergency physicians should be aware of multidrug-resistant bacterial infection even in a non-hospital setting.

Carbapenemase-producing Gram-negative bacteria: current epidemics, antimicrobial susceptibility and treatment options

ABSTRACT 

Carbapenemases, with versatile hydrolytic capacity against β-lactams, are now an important cause of resistance of Gram-negative bacteria. The genes encoding for the acquired carbapenemases are associated with a high potential for dissemination. In addition, infections due to Gram-negative bacteria with acquired carbapenemase production would lead to high clinical mortality rates. Of the acquired carbapenemases, Klebsiella pneumoniae carbapenemase (Ambler class A), Verona integron-encoded metallo-β-lactamase (Ambler class B), New Delhi metallo-β-lactamase (Ambler class B) and many OXA enzymes (OXA-23-like, OXA-24-like, OXA-48-like, OXA-58-like, class D) are considered to be responsible for the worldwide resistance epidemics. As compared with monotherapy with colistin or tigecycline, combination therapy has been shown to effectively lower case-fatality rates. However, development of new antibiotics is crucial in the present pandrug-resistant era.

Dual-tubed multiplex-PCR for molecular characterization of carbapenemases isolated among Acinetobacter spp. and Pseudomonas spp

AIM

To molecularly characterize clinical isolates of Acinetobacter spp. and Pseudomonas spp. from various clinical samples so as to identify the carbapenemases mechanisms harboured by them.

MATERIALS AND RESULTS

A total of 95 carbapenem-resistant, nonduplicate, multi-drug resistant Gram-negative clinical isolates (53 Acinetobacter spp. and 42 Pseudomonas spp.), were collected between July and December 2012. Modified Hodge test (MHT) for the detection of carbapenemases was performed. Inhibitor-based test, EDTA for the detection of metallo-β-lactamases (MBL) and phenyl boronic acid (PBA) for the detection of Klebsiella pneumoniae carbapenemase (KPC), were performed to distinguish between different classes of β-lactamases. Two-tubed multiplex-PCR was performed for genotypic characterization of different classes of carbapenemases ((blaNDM-1 , blaOXA-48 like , blaKPC , blaVIM , blaIMP ), (blaOXA-23 like , blaOXA-24 like , blaOXA-51 like , blaOXA-58 like )). Eighty-five per cent (81/95) isolates were carbapenemase producers. Among these, 56.7% (44) were multiple carbapenemase producers. Furthermore, 48.14% (39) were MBLs, 35.8% (29) were carbapenem hydrolyzing class D β-lactamases (CHDLs), 16% (13) had MBLs as well as CHDLs and 14.7% (14/95) had none of the targeted resistance mechanisms. The overall rate of concordance between phenotypic and genotypic test was 97% and 98% for the detection of carbapenemases and MBL, respectively.

CONCLUSION

This is the first study from Western India which highlights the presence of multiple carbapenemases in nonfermenters Gram-negative bacilli (NFGNB). Co-existence of multiple carbapenemases along with other resistance mechanisms might result in treatment failure. Molecular characterization of the resistance mechanisms of suspected pathogens would help provide appropriate antimicrobial treatment for good clinical outcome.

SIGNIFICANCE AND IMPACT OF THE STUDY

Dual-tubed multiplex PCR decreases the time of amplification and thus the turnaround time which is crucial in clinical microbiology; this would be helpful in rapid characterization of CHDLs and MBLs.

Molecular and epidemiological characterization of IMP-type metallo-β-lactamase-producing Enterobacter cloacae in a Large tertiary care hospital in Japan

IMP-type metallo-β-lactamase enzymes have been reported in different geographical areas and in various Gram-negative bacteria. However, the risk factors and epidemiology pertaining to IMP-type metallo-β-lactamase-producing Enterobacter cloacae (IMP-producing E. cloacae) have not been systematically evaluated. We conducted a retrospective, matched case-control study of patients from whom IMP-producing E. cloacae isolates were obtained, in addition to performing thorough molecular analyses of the clinically obtained IMP-producing E. cloacae isolates. Unique cases with IMP-producing E. cloacae isolation were included. Patients with IMP-producing E. cloacae were matched to uninfected controls at a ratio of 1 to 3. Fifteen IMP-producing E. cloacae cases were identified, with five of the isolates being obtained from blood, and they were matched to 45 uninfected controls. All (100%) patients from whom IMP-producing E. cloacae isolates were obtained had indwelling devices at the time of isolation, compared with one (2.2%) uninfected control. Independent predictors for isolation of IMP-producing E. cloacae were identified as cephalosporin exposure and invasive procedures within 3 months. Although in-hospital mortality rates were similar between cases and controls (14.3% versus 13.3%), the in-hospital mortality of patients with IMP-producing E. cloacae-caused bacteremia was significantly higher (40%) than the rate in controls. IMP-producing E. cloacae isolates were frequently positive for other resistance determinants. The MICs of meropenem and imipenem were not elevated; 10 (67%) and 12 (80%) of the 15 IMP-producing E. cloacae isolates had a MIC of ≤ 1 μg/ml. A phylogenetic tree showed a close relationship among the IMP-producing E. cloacae samples. Indwelling devices, exposure to cephalosporin, and a history of invasive procedures were associated with isolation of IMP-producing E. cloacae. Screening for carbapenemase production is important in order to apply appropriate clinical management and infection control measures.

Distribution of carbapenem resistance determinants among epidemic and non-epidemic types of Acinetobacter species in Japan

We performed a comparative molecular analysis on three types of clinically isolated Acinetobacter spp.: epidemic sequence types (STs) of Acinetobacter baumannii (epidemic ST-AB), non-epidemic sequence types of A. baumannii (non-epidemic ST-AB) and non-baumannii Acinetobacter spp. A total of 87 isolates - 46 A. baumannii, 25 A. pittii and 16 A. nosocomialis - from 43 hospitals were analysed. Of these, 31 A. baumannii isolates were ST1 or ST2 according to the Pasteur Institute multilocus sequence typing scheme and were defined as epidemic ST-AB. The other 15 A. baumannii isolates were defined as non-epidemic ST-AB. The epidemic ST-AB isolates harboured the blaOXA-23-like gene or had an ISAba1 element upstream of blaOXA-51-like, or both, whereas non-epidemic ST-AB and non-baumannii Acinetobacter spp. isolates harboured blaOXA-58-like or metallo-β-lactamase genes, or both. The proportion of multidrug-resistant isolates was significantly higher in the epidemic ST-AB isolates (48 %) than that in the other types of Acinetobacter isolates (5 %) (P<0.05). In addition, epidemic ST-AB isolates exhibited a relatively higher proportion of fluoroquinolone resistance. We demonstrated that, in terms of genotypes and phenotypes of antimicrobial resistance, non-epidemic ST-AB isolates shared more similarity with non-baumannii Acinetobacter spp. isolates than with epidemic ST-AB isolates, regardless of bacterial species. In addition, this study revealed that, even in Japan, where IMP-type metallo-β-lactamase producers are endemic, epidemic ST-AB harbouring blaIMP have not yet emerged.

NDM-1 Metallo-β-Lactamase and ArmA 16S rRNA methylase producing Providencia rettgeri clinical isolates in Nepal

Background

Drug-resistant Providencia rettgeri producing metallo-β-lactamase and 16S rRNA methylase has been reported in several countries. We analyzed P. rettgeri clinical isolates with resistance to carbapenems and aminoglycosides in a hospital in Nepal.

Methods

Five clinical isolates of multidrug-resistant P. rettgeri were obtained in a hospital in Nepal. Antimicrobial susceptibilities were determined using the microdilution method and entire genomes were sequenced to determine drug-resistant genes. Epidemiological analysis was performed by pulsed-field gel electrophoresis.

Results

Four of the 5 isolates were resistant to carbapenems (imipenem and meropenem), with MICs ≥16 mg/L, with the remaining isolate showing intermediate resistance to imipenem, with an MIC of 2 mg/L and susceptibility to meropenem with an MIC ≤1 mg/L. All 5 isolates had bla_VEB-1. Of the 4 carbapenem-resistant strains, 3 had bla_NDM-1 and 1 had bla_OXA-72. All isolates were highly resistant to aminoglycosides (MICs ≥1,024 mg/L) and harbored armA. As the result of pulsed-field gel electrophoresis pattern analysis in the 5 P. rettgeri isolates, 4 had identical PFGE patterns and the fifth showed 95.7% similarity.

Conclusions

This is the first report describing multidrug-resistant P. rettgeri strains harboring bla_NDM-1 or bla_OXA-72 and armA isolated from patients in Nepal.

Molecular Characterization of Imipenem-ResistantPseudomonas aeruginosain Hiroshima, Japan

Pseudomonas aeruginosa showing resistance to imipenem were found in 100 of 1,058 strains (9.5%) from six hospitals (a-f) in Hiroshima City, Japan. Of the 100 strains, 14 (14%) were double disk synergy test positive using sodium mercaptoacetic acid disks, and 18 (18%) were bla(IMP-1) or bla(VIM-2) allele positive by polymerase chain reaction (PCR). Among 100 imipenem-resistant strains, 32 were categorized into multi-drug resistant strains, in which 13 were positive for the metallo-beta-lactamase gene. Fifty-one strains (51%) among the 100 imipenem-resistant strains had elevated RND efflux pump activity against levofloxacin. But only 6 of 51 strains were classified as multi-drug resistant strains. The pulsed field gel electrophoresis analysis of the Spe I-digested DNA from the 100 isolates suggested not only clonal spread but spread of heterogeneous clones started to contribute to the prevalence of metallo-beta-lactamase producing P. aeruginosa strains in Japanese hospitals.

Detection of IMP metallo-β-lactamase in carbapenem-nonsusceptible Enterobacteriaceae and non-glucose-fermenting Gram-negative rods by immunochromatography assay

Metallo-β-lactamases (MBLs) are transmissible carbapenemases of increasing prevalence in Gram-negative bacteria among health care facilities worldwide. Control of the further spread of these carbapenem-resistant bacteria relies on clinical microbiological laboratories correctly identifying and classifying the MBLs. In this study, we evaluated a simple and rapid method for detecting IMP, the most prevalent MBL in Japan. We used an immunochromatography (IC) assay for 181 carbapenem-nonsusceptible (CNS) (nonsusceptible to imipenem or meropenem) strains comprising 74 IMP-producing and 33 non-IMP-producing strains of non-glucose-fermenting Gram-negative rods (NFGNR), as well as 64 IMP-producing and 10 non-IMP-producing Enterobacteriaceae strains. The IC assay results were compared to those from the double-disk synergy test (DDST), the MBL Etest, and the modified Hodge test (MHT) (only for Enterobacteriaceae). The IMP type was confirmed by specific PCR and direct sequencing. The IC assay detected all of the IMP-type MBLs, including IMP-1, -2, -6, -7, -10, -11, -19, -20, and -22 and IMP-40, -41, and -42 (new types), with 100% specificity and sensitivity against all strains tested. Although the sensitivity and specificity values for the DDST and MHT were equivalent to those for the IC assay, the MBL Etest was positive for only 87% of NFGNR and 31% of Enterobacteriaceae due to the low MIC of imipenem, causing an indeterminate evaluation. These results indicated that the IC assay might be a useful alternative to PCR for IMP MBL detection screening.

Detection of KPC-2 and qnrS1 in clinical isolates of Morganella morganii from China

Seven carbapenem-nonsusceptible Morganella morganii isolates, which have similar antibiotic susceptibility profiles, were isolated over a 5-month period. MICs of imipenem, meropenem, and ertapenem were 8, 1, and 0.25 to 0.5 μg/mL, respectively. Pulsed-field gel electrophoresis indicated that 6 isolates were indistinguishable or closely related. Carbapenem resistance can be transferred from M. morganii to Escherichia coli by conjugation. All M. morganii isolates and E. coli transconjugants produced KPC-2 and carried the qnrS1 gene. Production of KPC-2 mainly contributed to the carbapenem resistance in M. morganii. KPC-2-producing M. morganii clonally spread in a hospital in China.

Genotypes and infection sites in an outbreak of multidrug-resistant Pseudomonas aeruginosa

An outbreak of multidrug-resistant (MDR) Pseudomonas aeruginosa occurred in an acute care hospital in Japan, which lasted for more than three years. During January 2006 to June 2009, 59 hospitalised patients with MDR P. aeruginosa were mainly detected by urine culture in the first half, whereas isolation from respiratory tract samples became dominant in the latter half of the outbreak. Non-duplicate MDR P. aeruginosa isolates were available from 51 patients and all isolates were positive for bla(VIM-2). Pulsed-field gel electrophoresis (PFGE) analysis categorised the isolates into three major clusters; types A, B and C with eight, 19 and 21 isolates, respectively. The outbreak started with patients harbouring PFGE type A strains, followed by type B, and type C strains. Multivariate analysis demonstrated that patients with PFGE type C strains were more likely to be detected by respiratory tract samples (odds ratio: 11.87; 95% confidence interval: 1.21-116.86). Improved aseptic urethral catheter care controlled PFGE type A and type B strains and improvement in respiratory care procedures finally contained the transmission of PFGE type C strains.

Acinetobacter: a potential reservoir and dispenser for β-lactamases

Innate resistance and remarkable ability to acquire additional resistance determinants underline the clinical importance of Acinetobacter. Over 210 β-lactamases belonging to 16 families have been identified in the genus, mostly in clinical isolates of A. baumannii. In this review, we update the current taxonomy of the genus Acinetobacter and summarize the β-lactamases detected in Acinetobacter spp. with an emphasis on Acinetobacter-derived cephalosporinases (ADCs) and carbapenem-hydrolysing class D β-lactamases (CHDLs). We also discuss the roles of integrons and insertion sequence (IS) elements in the expression and dissemination of such resistance determinants.

Antimicrobial susceptibilities and bacteriological characteristics of bovine Pseudomonas aeruginosa and Serratia marcescens isolates from mastitis

The presence of metallo-β-lactamase (MBL)-producing and multidrug-resistant Pseudomonas aeruginosa (MDRP) strains among bovine isolates of Gram-negative bacilli, and O-serotypes of bovine Serratia marcescens and P. aeruginosa isolates have been reported rarely. The aims of this study were to (1) elucidate antimicrobial susceptibilities and O-serotypes of P. aeruginosa and S. marcescens isolates from bovine mastitis and the presence of MBL-producers and MDRP strains among them and (2) evaluate their relationships to human isolates. We investigated the MICs of 24 antimicrobials and O-serotypes for 116 P. aeruginosa and 55 S. marcescens isolates in Japan, primarily in 2006. A total of 171 isolates exhibited high antimicrobial susceptibilities with the exception of a partial drug. P. aeruginosa isolates exhibited high susceptibilities of ≥ 95.7% to ciprofloxacin, imipenem, meropenem, piperacillin, ceftazidime, cefepime, cefoperazone/sulbactam, amikacin, tobramycin, and gentamicin; however, they exhibited a susceptibility of only 69.8% to aztreonam. They exhibited substantial resistances to ceftriaxone, enrofloxacin, cefotaxime, and moxalactam. S. marcescens isolates exhibited high susceptibilities of ≥ 90.9% to kanamycin, ceftiofur, sulfamethoxazole-trimethoprim, and the 15 aforementioned drugs, but exhibited resistance to minocycline. Neither MBL-producers nor MDRP strains were detected among the 171 strains. The dominant serotypes of P. aeruginosa isolates were OG, OA, OB, OI, OF, OE, and OK; those of S. marcescens isolates were O6 and O5. Every S. marcescens isolate was pigmented. These findings suggest that bovine P. aeruginosa and S. marcescens isolates differ from human isolates from both antibiogram and phenotypic perspectives, and could help to evaluate differences in bacteriological characteristics between bovine and human isolates.

The inhibitory effect of Zingiber corallinum Hance essential oil on drug-resistant bacteria and evaluation of its acute toxicity

BACKGROUND

The excessive and irregular use of antibiotics could result in the generation and diffusion of drug-resistant bacteria. The aim of this study was to investigate the inhibitory effect of Zingiber corallinum Hance essential oil (ZCHO) on drug-resistant bacteria, especially on drug-resistant Acinetobacter baumannii.

MATERIAL/METHODS

Susceptibility testing was used to evaluate the effect of ZCHO on growth inhibition of drug-resistant bacteria by paper disk method. Mice orally administered with ZCHO were used to observe acute toxicity and to determine median lethal dose (LD₅₀) of ZCHO. Broth dilution method was used to determine minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of ZCHO on drug-resistant Acinetobacter baumannii.

RESULTS

ZCHO exhibited an obvious inhibitory effect not only on gram-negative drug-resistant bacteria including Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae and Acinetobacter baumannii, but also on gram-positive drug-resistant bacteria including Staphylococcus aureus, Staphylococcus epidermidis and Staphylococcus haemolyticus. The ZCHO containing 79% terpinen-4-ol revealed better bacteriostatic effect than ZCHO with 34% terpinen-4-ol. The LD₅₀ of ZCHO was 1790.427 mg/kg. The MIC and MBC of ZCHO on drug-resistant Acinetobacter baumannii were 1457.81 mg/L.

CONCLUSIONS

ZCHO has obvious bacteriostasis and bactericidal effects, especially against drug-resistant Acinetobacter baumannii. Therefore, ZCHO is a promising natural bioactive component with antibacterial effect and satisfactory safety due to its low toxicity.

IMP-type metallo-β-lactamases in Gram-negative bacilli: distribution, phylogeny, and association with integrons

Twenty-nine IMP-type β-lactamases (IMPs) have been identified in at least 26 species of clinically important Gram-negative bacilli from more than 24 countries/regions. Most of bla(IMP) genes are harbored by class 1 integrons that are usually embedded in transposons and/or plasmids, footnoting their horizontal transfer and worldwide distribution. bla(IMP) genes usually co-exist with other resistance genes, such as aacA, catB, and bla(OXA), resulting in multi-drug resistance. Compared to other gene cassettes, 76.3% of the bla(IMP) gene cassettes are located adjacent to Pc promoter of the class 1 integrons, indicating that the bla(IMP) genes are readily expressed in most of bacterial hosts.

Epidemiology and genetics of VIM-type metallo-β-lactamases in Gram-negative bacilli

Metallo-β-lactamases (MBLs) are a rapidly evolving group of β-lactamases, which hydrolyze most β-lactams including the carbapenems. Of the known MBLs, VIMs are one of the most common families, with 27 variants detected in at least 23 species of Gram-negative bacilli from more than 40 countries/regions. The amino acid similarities of VIM variants range from 72.9 to 99.6% with 1–72 different residues. Most of the bla VIMs are harbored by a class 1 integron, a genetic platform able to acquire and express gene cassettes. The integrons are usually embedded in transposons and, in turn, accommodated on plasmids, making them highly mobile. Integrons display considerable diversity, with at least 110 different structures associated with the gain and spread of the bla VIMs. In most instances, the bla VIMs co-exist with one or more other resistance genes. The processes for the identification of bacteria harboring bla VIMs are also discussed in this article.

Laboratory surveillance for prospective plasmid-mediated AmpC beta-lactamases in the Kinki region of Japan

Extended-spectrum beta-lactamases, plasmid-mediated AmpC beta-lactamases (PABLs), and plasmid-mediated metallo-beta-lactamases confer resistance to many beta-lactams. In Japan, although several reports exist on the prevalence of extended-spectrum beta-lactamases and metallo-beta-lactamases, the prevalence and characteristics of PABLs remain unknown. To investigate the production of PABLs, a total of 22,869 strains of 4 enterobacterial species, Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis, were collected during six 6-month periods from 17 clinical laboratories in the Kinki region of Japan. PABLs were detected in 29 (0.13%) of 22,869 isolates by the 3-dimensional test, PCR analysis, and DNA sequencing analysis. PABL-positive isolates were detected among isolates from 13 laboratories. Seventeen of 13,995 (0.12%) E. coli isolates, 8 of 5,970 (0.13%) K. pneumoniae isolates, 3 of 1,722 (0.17%) K. oxytoca isolates, and 1 of 1,182 (0.08%) P. mirabilis isolates were positive for PABLs. Of these 29 PABL-positive strains, 20 (69.0%), 6 (20.7%), 2 (6.9%), and 1 (3.4%) carried the genes for CMY-2, DHA-1, CMY-8, and MOX-1 PABLs, respectively. Pattern analysis of randomly amplified polymorphic DNA and pulsed-field gel electrophoretic analysis revealed that the prevalence of CMY-2-producing E. coli strains was not due to epidemic strains and that 3 DHA-1-producing K. pneumoniae strains were identical, suggesting their clonal relatedness. In conclusion, the DHA-1 PABLs were predominantly present in K. pneumoniae strains, but CMY-2 PABLs were predominantly present in E. coli strains. The present findings will provide significant information to assist in preventing the emergence and further spread of PABL-producing bacteria.

Monobactam and aminoglycoside combination therapy against metallo-beta-lactamase-producing multidrug-resistant Pseudomonas aeruginosa screened using a 'break-point checkerboard plate'

Metallo-beta-lactamase-producing multidrug-resistant Pseudomonas aeruginosa (MDR P. aeruginosa) is a cause of life-threatening infections. With parenteral colistin not available in Japan, we treated MDR P. aeruginosa sepsis with monobactam and aminoglycoside combination therapy, with screening using a 'break-point checkerboard plate'.

Correlation between meropenem and doripenem use density and the incidence of carbapenem-resistant Pseudomonas aeruginosa

Optimal use of carbapenems is an important issue in the prevention of resistance in Pseudomonas aeruginosa. In this study, we investigated the correlation between antimicrobial use density (AUD) of carbapenems and imipenem/cilastatin (IPM/CS) or meropenem (MEPM) susceptibility of P. aeruginosa strains. The AUD of five carbapenems [IPM/CS, panipenem/betamipron, biapenem, MEPM and doripenem (DRPM)] was examined every 6 months between 2006 and 2008. The AUD was calculated using the defined daily doses methodology developed by the World Health Organisation. A minimum inhibitory concentration of IPM/CS or MEPM of < or =4 mg/L was considered to be sensitive. There was a significant negative correlation between MEPM susceptibility and the total AUD of MEPM and DRPM [r=-0.823, 95% confidence interval (CI) -0.035 to -0.980; P=0.044]. Furthermore, there was a significant correlation between MEPM susceptibility and IPM/CS susceptibility (r=0.839, 95% CI 0.084 to 0.981; P=0.037). Cross-resistance was therefore investigated and only 5.6% of MEPM-insensitive strains were susceptible to IPM/CS, although 43.3% of IPM/CS-insensitive strains were susceptible to MEPM. These results suggest that curtailing the use of MEPM and DRPM may curb the emergence not only of MEPM-resistant strains but also IPM/CS-resistant strains.

Antibacterial effects of Iranian fennel essential oil on isolates of Acinetobacter baumannii

The aim of the present study was the evaluation of the antibacterial activity of Fennel essential oil on isolates of Acinetobacter baumannii. Forty eight isolates were collected from clinical specimens from burn wards of hospitals in Tehran, Iran between April and September, 2006. The susceptibility of isolates was determined using a broth microdilution method. Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of isolates to Fennel essential oil were determined. The susceptibilities of isolates to different antibiotics were tested using agar disk diffusion method. The rates of resistance were determined to antibiotics as follows: cefazolin 100%, ciprofloxacin 100%, ofloxacin 95.8%, kanamycin 95.8%, carbenicillin 93.7%, ticarcillin 93.7%, piperacillin 88.9%, co-trimoxazole 79.1%, ceftizoxime 75%, gentamicin 70.8%, cefalotin 60.4%, amikacin 52% and imipenem 14.6%. Fennel essential oil possessed antibacterial effect against all isolates of A. baumannii. These results suggest the potential use of the Fennel essential oil for the control of multi-drug resistant A. baumannii infections. However, more adequate studies must be carried out to verify the possibility of using it for fighting bacterial infections in human.

Doripenem in hospital infections: a focus on nosocomial pneumonia, complicated intra-abdominal infections, and complicated urinary tract infections

Doripenem is the latest carbapenem on the market to date. Although not an antibiotic in a new class, it offers a glimmer of hope in combating serious infections secondary to multidrug-resistant Gram-negative bacteria when we have not seen a new class of antibacterial, particularly for Gram-negative bacteria, for more than 10 years. In vitro, doripenem exhibits a broad spectrum of activity against Gram-positive and Gram-negative bacteria, including extended-spectrum β-lactamase (ESBL) and Amp-C β-lactamase producing Enterobacteriaceae and anaerobes. Doripenem also exhibits better in vitro activity against Pseudomonas aeruginosa compared to other anti-pseudomonal carbapenems. It combines the desirable activities of both imipenem and meropenem. It has similar activity to imipenem against Gram-positive pathogens and has the antimicrobial spectrum of meropenem against Gram-negative organisms. Several randomized clinical trials have demonstrated that doripenem is non-inferior to meropenem, imipenem, piperacillin/tazobactam, or levofloxacin in its efficacy and safety profile in treating a wide range of serious bacterial infections including intra-abdominal infection, complicated urinary tract infection, and nosocomial pneumonia. Due to its wide spectrum of activity and good safety profile it is susceptible to misuse leading to increasing rates of resistance. Judicious use should be considered when using doripenem as a first-line agent or drug of choice for serious infections. Doripenem is a well-tolerated drug with common adverse effects including headache, nausea and diarrhea. Caution should be used in patients with hypersensitivity to carbapenems and adverse reactions to β-lactam agents. Dosage adjustment is needed for patients with renal impairment. Doripenem has demonstrated economic and clinical benefits. It has been shown to reduce hospital length of stay and duration of mechanical ventilation for intensive care unit (ICU) patients. Therefore, doripenem is a welcome addition to our limited armamentarium of antibiotics available to treat serious bacterial infections in hospitalized patients.