Detection of extended-spectrum beta-lactamases in clinical isolates of Klebsiella pneumoniae and Escherichia coli

Mutations That Enhance the Ciprofloxacin Resistance of Escherichia coli with qnrA1

Plasmid-mediated qnr genes provide only a modest decrease in quinolone susceptibility but facilitate the selection of higher-level resistance. In Escherichia coli strain J53 without qnr, ciprofloxacin resistance often involves mutations in the GyrA subunit of DNA gyrase. Mutations in gyrA were absent, however, when 43 mutants with decreased ciprofloxacin susceptibility were selected from J53(pMG252) with qnrA1. Instead, in 13 mutants, individual and whole-genome sequencing identified mutations in marR and soxR associated with increased expression of marA and soxS and, through them, increased expression of the AcrAB pump, which effluxes quinolones. Nine mutants had increased expression of the MdtE efflux pump, and six demonstrated increased expression of the ydhE pump gene. Many efflux mutants also had increased resistance to novobiocin, another pump substrate, but other mutants were novobiocin hypersusceptible. Mutations in rfaD and rfaE in the pathway for inner core lipopolysaccharide (LPS) biosynthesis were identified in five such strains. Many of the pump and LPS mutants had decreased expression of OmpF, the major porin channel for ciprofloxacin entry. Three mutants had increased expression of qnrA that persisted when pMG252 from these strains was outcrossed. gyrA mutations were also rare when mutants with decreased ciprofloxacin susceptibility were selected from E. coli J53 with aac(6')-Ib-cr or qepA. We suggest that multiple genes conferring low-level resistance contribute to enhanced ciprofloxacin resistance selected from an E. coli strain carrying qnrA1, aac(6')-Ib-cr, or qepA because these determinants decrease the effective ciprofloxacin concentration and allow more common but lower-resistance mutations than those in gyrA to predominate.

Molecular epidemiology of carbapenem resistant Enterobacteriaceae in Valle d'Aosta region, Italy, shows the emergence of KPC-2 producing Klebsiella pneumoniae clonal complex 101 (ST101 and ST1789)

BACKGROUND

The spread of carbapenem resistant Enterobacteriaceae (CRE) is an emerging clinical problem, of great relevance in Europe and worldwide. The aim of this study was the molecular epidemiology of CRE isolates in Valle d'Aosta region, Italy, and the mechanism of carbapenem resistance.

RESULTS

Sixty consecutive CRE samples were isolated from 52 hospital inpatients and/or outpatients from November 2013 to August 2014. Genotyping of microbial isolates was done by pulsed-field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST), carbapenemases were identified by PCR and sequencing. Carbapenem resistance gene transfer was performed by filter mating, plasmids from parental and transconjugant strains were assigned to incompatibility groups by PCR-based replicon typing. Molecular characterization of CRE isolates assigned 25 Klebsiella pneumoniae isolates to PFGE types A1-A5 and sequencing type (ST) 101, 17 K. pneumoniae isolates to PFGE type A and ST1789 (a single locus variant of ST101), 7 K. pneumoniae isolates to PFGE types B or C and ST512, 2 K. pneumoniae isolates to PFGE type D and ST405, and 5 Escherichia coli isolates to PFGE type a and ST131. All K. pneumoniae ST101 and ST1789 isolates were extended-spectrum beta-lactamase (ESBL) producers and carried bla CTX-M-1 group gene; 4 K. pneumoniae ST101 isolates were resistant to colistin. Molecular analysis of beta-lactamase genes identified bla KPC-2 and bla CTX-M-group 1 into conjugative plasmid/s assigned to IncFII incompatibility group in ST101 and ST1789 K. pneumoniae isolates, bla KPC-3 into conjugative plasmid/s assigned to IncF incompatibility group in ST512 and ST405 K. pneumoniae isolates, bla VIM-1 into conjugative plasmid/s assigned to IncN incompatibility group in ST131 E. coli isolates.

CONCLUSIONS

The spread of CRE in Valle d'Aosta region was caused by the selection of KPC-2 producing K. pneumoniae ST101 and ST1789 epidemic clones belonging to clonal complex 101, KPC-3 producing K. pneumoniae epidemic clones assigned to ST512 and ST405, and VIM-1 producing E.coli ST131 epidemic clone. Carbapenem resistance, along with bla KPC-2, bla KPC-3 and bla VIM-1 carbapenemase genes, was transferred by conjugative plasmids assigned to IncFII, IncF, and IncN incompatibility groups, respectively, in filter mating experiments. The emergence of colistin resistance was observed in KPC-2 producing K. pneumoniae ST101 isolates.

Comparison of Antibiotic Resistance and Virulence Factors among Escherichia coli Isolated from Conventional and Free-Range Poultry

Microbiological contamination in commercial poultry production has caused concerns for human health because of both the presence of pathogenic microorganisms and the increase in antimicrobial resistance in bacterial strains that can cause treatment failure of human infections. The aim of our study was to analyze the profile of antimicrobial resistance and virulence factors of E. coli isolates from chicken carcasses obtained from different farming systems (conventional and free-range poultry). A total of 156 E. coli strains were isolated and characterized for genes encoding virulence factors described in extraintestinal pathogenic E. coli (ExPEC). Antimicrobial susceptibility testing was performed for 15 antimicrobials, and strains were confirmed as extended spectrum of β-lactamases- (ESBLs-) producing E. coli by phenotypic and genotypic tests. The results indicated that strains from free-range poultry have fewer virulence factors than strains from conventional poultry. Strains from conventionally raised chickens had a higher frequency of antimicrobial resistance for all antibiotics tested and also exhibited genes encoding ESBL and AmpC, unlike free-range poultry isolates, which did not. Group 2 CTX-M and CIT were the most prevalent ESBL and AmpC genes, respectively. The farming systems of poultries can be related with the frequency of virulence factors and resistance to antimicrobials in bacteria.

Genetic Contexts of blaNDM-1 in Patients Carrying Multiple NDM-Producing Strains

The carbapenem resistance determinant blaNDM-1 has been found in various Gram-negative bacteria and upon different plasmid replicon types (Inc). Here, we present four patients within two hospitals in Pakistan harboring between two and four NDM-1-producing Gram-negative bacilli of different species coresident in their stool samples. We characterize the blaNDM-1 genetic contexts of these 11 NDM-1-producing Gram-negative bacilli in addition to other antimicrobial resistance mechanisms, plasmid replicon profiles, and sequence types (STs) in order to understand the underlying acquisition mechanisms of carbapenem resistance within these bacteria. Two common plasmid types (IncN2 and IncA/C) were identified to carry blaNDM-1 among the six different bacterial species isolated from the four patients. Two of these strains were novel Citrobacter freundii ST 20 and ST 21. The same IncN2-type blaNDM-1 genetic context was found in all four patients and within four different species. The IncA/C-type blaNDM-1 genetic context was found in two different species and in two of the four patients. Combining genetic context characterization with other molecular epidemiology methods, we were able to establish the molecular epidemiological links between genetically unrelated bacterial species by linking their acquisition of an IncN2 or IncA/C plasmid carrying blaNDM-1 for carbapenem resistance. By combining plasmid characterization and in-depth genetic context assessment, this analysis highlights the importance of plasmids in antimicrobial resistance. It also provides a novel approach for investigating the underlying mechanisms of blaNDM-1-related spread between bacterial species and genera via plasmids.

Functions of a GyrBA fusion protein and its interaction with QnrB and quinolones

In order to study the interactions between Escherichia coli DNA gyrase and the gyrase interacting protein QnrB in vivo, we constructed a gyrB-gyrA fusion and validated its ability to correct the temperature-sensitive growth of gyrA and gyrB mutants. Like wild-type gyrA, the gyrB-gyrA fusion complemented a quinolone-resistant gyrA mutant to increase susceptibility. It functioned as an active type II topoisomerase, catalyzed negative supercoiling of DNA, was inhibited by quinolone, and was protected by QnrB.

Protective effect of Qnr on agents other than quinolones that target DNA gyrase

Qnr is a plasmid-encoded and chromosomally determined protein that protects DNA gyrase and topoisomerase IV from inhibition by quinolones. Despite its prevalence worldwide and existence prior to the discovery of quinolones, its native function is not known. Other synthetic compounds and natural products also target bacterial topoisomerases. A number were studied as molecular probes to gain insight into how Qnr acts. Qnr blocked inhibition by synthetic compounds with somewhat quinolone-like structure that target the GyrA subunit, such as the 2-pyridone ABT-719, the quinazoline-2,4-dione PD 0305970, and the spiropyrimidinetrione pyrazinyl-alkynyl-tetrahydroquinoline (PAT), indicating that Qnr is not strictly quinolone specific, but Qnr did not protect against GyrA-targeting simocyclinone D8 despite evidence that both simocyclinone D8 and Qnr affect DNA binding to gyrase. Qnr did not affect the activity of tricyclic pyrimidoindole or pyrazolopyridones, synthetic inhibitors of the GyrB subunit, or nonsynthetic GyrB inhibitors, such as coumermycin A1, novobiocin, gyramide A, or microcin B17.Thus, in this set of compounds the protective activity of Qnr was confined to those that, like quinolones, trap gyrase on DNA in cleaved complexes.

Molecular Analysis of Antibiotic Resistance Determinants and Plasmids in Malaysian Isolates of Multidrug Resistant Klebsiella pneumoniae

Infections caused by multidrug resistant Klebsiella pneumoniae have been increasingly reported in many parts of the world. A total of 93 Malaysian multidrug resistant K. pneumoniae isolated from patients attending to University of Malaya Medical Center, Kuala Lumpur, Malaysia from 2010-2012 were investigated for antibiotic resistance determinants including extended-spectrum beta-lactamases (ESBLs), aminoglycoside and trimethoprim/sulfamethoxazole resistance genes and plasmid replicons. CTX-M-15 (91.3%) was the predominant ESBL gene detected in this study. aacC2 gene (67.7%) was the most common gene detected in aminoglycoside-resistant isolates. Trimethoprim/sulfamethoxazole resistance (90.3%) was attributed to the presence of sul1 (53.8%) and dfrA (59.1%) genes in the isolates. Multiple plasmid replicons (1-4) were detected in 95.7% of the isolates. FIIK was the dominant replicon detected together with 13 other types of plasmid replicons. Conjugative plasmids (1-3 plasmids of ~3-100 kb) were obtained from 27 of 43 K. pneumoniae isolates. An ESBL gene (either CTX-M-15, CTX-M-3 or SHV-12) was detected from each transconjugant. Co-detection with at least one of other antibiotic resistance determinants [sul1, dfrA, aacC2, aac(6ˊ)-Ib, aac(6ˊ)-Ib-cr and qnrB] was noted in most conjugative plasmids. The transconjugants were resistant to multiple antibiotics including β-lactams, gentamicin and cotrimoxazole, but not ciprofloxacin. This is the first study describing the characterization of plasmids circulating in Malaysian multidrug resistant K. pneumoniae isolates. The results of this study suggest the diffusion of highly diverse plasmids with multiple antibiotic resistance determinants among the Malaysian isolates. Effective infection control measures and antibiotic stewardship programs should be adopted to limit the spread of the multidrug resistant bacteria in healthcare settings.

Clonal and horizontal spread of the blaOXA-232 gene among Enterobacteriaceae in a Korean hospital

All 16 Klebsiella pneumoniae isolates and both Escherichia coli isolates harbored the bla(OXA-232) and bla(CTX-M-15) genes. Furthermore, all 16 K. pneumoniae isolates belonged to a unique pulsed-field gel electrophoresis clone and were assigned to an identical sequence type (ST14). The 2 E. coli isolates were identified as ST131 and ST457. The bla(OXA-232) gene underwent horizontal transfer to E. coli isolates via a conjugative ColE-type plasmid. The introduction of this K. pneumoniae ST14 strain to the Korean hospital was attributed to an index patient who was likely colonized during a prior hospitalization in India.

Correlation of RAPD-PCR Profiles with ESBL Production in Clinical Isolates of Klebsiella pneumoniae in Tehran

BACKGROUND

Multidrug resistant K. pneumoniae, particularly the extended-spectrum β-lactamase (ESBL) producing strains, are often responsible for the failure of antibiotic treatment in nosocomial infections. Employing molecular methods to distinguish between ESBL and non-ESBL producing isolates can help quick identification of these multidrug resistant pathogens and thereby initiating appropriate antibiotic therapy. The aim of this study was to employ RAPD-PCR to distinguish the genetic fingerprints of ESBL producing clinical isolates of K. pneumoniae from ESBL negative strains.

MATERIALS AND METHODS

Antibacterial susceptibility of 104 K. pneumoniae clinical isolates was determined to 13 antibacterial agents by disc diffusion. ESBL production was measured by the double disc synergy test followed by phenotypic confirmatory tests. Genetic fingerprinting was carried out by RAPD-PCR.

RESULTS

All isolates were susceptible to imipenem. Antibiotic resistance rates were: piperacillin (100%), ceftazidime (62.5%), cefotaxime (57.6%), aztreonam (52.8%), cefepime (51.9%), kanamycin (50.9%), gentamicin (41.3%), ciprofloxacin (37.5%), nitrofurantoin (30.6%), nalidixic acid (22.1%), piperacillin/tazobactam (21.1%) and amikacin (9.6%). ESBL production was observed in 14 isolates (13.4%). Genetic fingerprinting performed on 43 isolates (14 ESBL positive and 29 ESBL negative) by RAPD-PCR, showed that 46.5% of the isolates belonged to a single profile (genotype 1), of which, the majority (62.1%) were non-ESBL producers.

CONCLUSION

RAPD-PCR results showed heterogeneity among the isolates. There was no association between ESBL production with any specific genetic fingerprint.

In vitro susceptibility of characterized β-lactamase-producing strains tested with avibactam combinations

Avibactam, a broad-spectrum β-lactamase inhibitor, was tested with ceftazidime, ceftaroline, or aztreonam against 57 well-characterized Gram-negative strains producing β-lactamases from all molecular classes. Most strains were nonsusceptible to the β-lactams alone. Against AmpC-, extended-spectrum β-lactamase (ESBL)-, and KPC-producing Enterobacteriaceae or Pseudomonas aeruginosa, avibactam lowered ceftazidime, ceftaroline, or aztreonam MICs up to 2,048-fold, to ≤4 μg/ml. Aztreonam-avibactam MICs against a VIM-1 metallo-β-lactamase-producing Enterobacter cloacae and a VIM-1/KPC-3-producing Escherichia coli isolate were 0.12 and 8 μg/ml, respectively.

Characterization of fosA5, a new plasmid-mediated fosfomycin resistance gene in Escherichia coli

A clinical strain of extended-spectrum β-lactamase-producing Escherichia coli E265, with a fosfomycin MIC of 512 μg ml(-1), was isolated from an inpatient with hospital-acquired pneumonia. This strain was negative for known fos genes, had no mutation in the target enzyme by polymerase chain reaction amplification and had functional transport systems for fosfomycin uptake. Fosfomycin resistance could be transferred from strain E265 to E. coli J53 azide(R) by conjugation. The DNA fragment containing fosfomycin resistance determinants was cloned into E. coli TOP10. The minimal inhibitory concentrations of fosfomycin for the transconjugant and transformant were 512 and 1024 μg ml(-1). By sequencing, a plasmid-mediated fosA subtype, designated fosA5, was found and characterized. The fosA5 gene was 420 bp in length and encoded a 139-amino-acid protein that shared 69 to 80% identity with FosA, FosA2, FosA3 and FosA4, and 31, 14 and 25% identity with FosB, FosC and FosX, respectively. The analysis of genetic environment of fosA5 suggested that a strain such as Klebsiella pneumoniae CG4 might be the origin of plasmid-mediated fosA5, with IS10 playing an important role in its mobilization.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study aimed to clone and characterize a plasmid-mediated fosA subtype gene, fosA5, in a clinical strain of ESBL-producing Escherichia coli, which confers fosfomycin resistance. Detection of the fosA5 gene clarified the mechanism of fosfomycin resistance in a strain that was negative for known fosfomycin resistance genes. Monitoring and surveillance will be important to follow the changes in fosfomycin resistance and prevent further dissemination of fos genes.

Prevalence and impact of extended-spectrum β-lactamase production on clinical outcomes in cancer patients with Enterobacter species bacteremia

BACKGROUND/AIMS

We examined the prevalence of extended-spectrum β-lactamase (ESBL) production and the impact of ESBL on clinical outcomes in cancer patients with Enterobacter spp. bacteremia.

METHODS

Using prospective cohort data on Enterobacter bacteremia obtained between January 2005 and November 2008 from a tertiary care center, the prevalence and clinical impact of ESBL production were evaluated.

RESULTS

Two-hundred and three episodes of Enterobacter spp. bacteremia were identified. Thirty-one blood isolates (15.3%, 31/203) scored positive by the double-disk synergy test. Among 17 isolates in which ESBL genes were detected by polymerase chain reaction and sequencing, CTX-M (n = 12), SHV-12 (n = 11), and TEM (n = 4) were the most prevalent ESBL types. Prior usage of antimicrobial agents (77.4% vs. 54.0%, p = 0.02) and inappropriate empirical antimicrobial therapy (22.6% vs. 3.0%, p < 0.001) were more commonly encountered in the ESBL-positive group than in the extended-spectrum cephalosporin-susceptible ESBL-negative group, respectively. Clinical outcomes did not differ significantly between the two groups (30-day mortality rate, 19.4% vs. 17.0%, p = 0.76; median length of hospital stay, 24.0 days vs. 30.5 days, p = 0.97). Initial presentation of severe sepsis/septic shock, pneumonia, and intra-abdominal infection were independently associated with 30-day mortality.

CONCLUSIONS

The prevalence of ESBL-producing isolates was 15.3% in cancer patients with Enterobacter bacteremia. Although inappropriate empirical therapy was more common in the ESBL-positive group, ESBL production was not associated with poorer outcomes.

Prevalence and characterization of antimicrobial-resistant Escherichia coli isolated from conventional and organic vegetables

To compare the characteristics and to identify the epidemiological relationships of Escherichia coli isolated from organic and conventional vegetables, the antimicrobial resistance and genetic properties of E. coli were investigated from 2010 to 2011. E. coli was isolated from 1 of 111 (0.9%) organic vegetables and from 20 of 225 (8.9%) conventional vegetables. The majority of strains were isolated from the surrounding farming environment (n=27/150 vs. 49/97 in organic vs. conventional samples). The majority of the vegetable strains were isolated from the surrounding farming environments. E. coli isolated from organic vegetables showed very low antimicrobial resistance rates except for cephalothin, ranging from 0% to 17.9%, while the resistance rates to cephalothin (71%) were extremely high in both groups. E. coli isolates expressed various resistance genes, which most commonly included blaTEM, tet(A), strA, strB, and qnrS. However, none of the isolates harbored tet(D), tet(E), tet(K), tet(L), tet(M), or qnrA. The transferability of tet gene, tet(A), and tet(B) was identified in tetracycline-resistant E. coli, and the genetic relationship was confirmed in a few cases from different sources. With regard to the lower antimicrobial resistance found in organic produce, this production mode seems able to considerably reduce the selection of antimicrobial-resistant bacteria on vegetables.

Co-production of ESBL and AmpC β-Lactamases in Clinical Isolates of A. baumannii and A. lwoffii in a Tertiary Care Hospital From Northern India

BACKGROUND

Acinetobacter baumannii is an important cause of health care associated infections which are difficult to control and treat, because of widespread antimicrobial resistance which is possessed by this organism.

AIMS

The aim of the present study was to know the prevalence of ESBLs and AmpC β-lactamases in clinical isolates of Acinetobacter spp. which were cultured from various clinical specimens by using different phenotypic methods.

SETTINGS AND DESIGN

Study was conducted over a period of one year at the Microbiology Department of a tertiary care teaching hospital. A total of 100 consecutive, non-duplicate strains of Acinetobacter species which were isolated from various clinical samples were included.

MATERIALS AND METHODS

All the isolates were identified by standard microbiological procedures and antimicrobial susceptibility testing was done by Kirby-Bauer disc diffusion technique. Isolates which showed reduced susceptibilities to third generation cephalosporins were tested for ESBL production by CLSI double disc synergy method and also by using sulbactam as an inhibitory agent. Isolates which showed reduced susceptibilities to cefoxitin were tested for AmpC detection by doing AmpC disc test.

STATISTICAL ANALYSIS

SPSS, version 17 was used to calculate p-value. If the p-value was <0.05, it was considered to be significant.

RESULTS

Out of 100 isolates, 82 were Acinetobacter baumannii and 18 were Acinetobacter lwoffii. ESBL were mentioned in 4% of the Acinetobacter isolates and in 77% of the isolates by using clavulanic acid and sulbactam as inhibitory agents respectively. AmpC β-lactamase production was detected in 60% isolates of Acinetobacter spp. Co-production of both ESBL and AmpC enzymes were seen in 29% of the Acinetobacter strains.

CONCLUSION

Failure in detecting β-lactamases contributes to their uncontrolled spread and therapeutic failures. Hence, these β-lactamases should be detected routinely and they should be reported to clinicians in time, so that inappropriate use of antibiotics can be stopped in time.

Development of ceftriaxone resistance in Salmonella enterica serotype Oranienburg during therapy for bacteremia

BACKGROUND

The majority of nontyphoid Salmonella infection is identified in children. When an invasive or severe Salmonella infection is encountered, ceftriaxone is recommended for such patients. A 2-year-old girl was hospitalized for the treatment of Salmonella bacteremia and discharged with standard ceftriaxone treatment. She was readmitted to the hospital after 2 days due to the recurrence of the Salmonella bacteremia. The study aimed to unveil the mechanism for the relapse.

METHODS

Six isolates (4 blood and 2 stool) were recovered from the patient, with the last two blood isolates being ceftriaxone-resistant. Pulsed-field gel electrophoresis was used for genotyping. Ceftriaxone resistance genes and transferability of the resistance plasmid were examined by molecular methods.

RESULTS

All isolates were identified as Salmonella enterica serotype Oranienburg. Five isolates demonstrated almost identical electrophoresis patterns, except that in the two ceftriaxone-resistant isolates an extra band (>100 kb) was noted. A blaCMY-2 gene, carried by a 120-kb conjugative IncI1 plasmid of the sequence type 53, was identified in the two ceftriaxone-resistant isolates. Transfer of the resistance plasmid from one blood isolate to Escherichia coli J53 resulted in the increase of ceftriaxone minimum inhibitory concentration from 0.125 μg/mL to 32 μg/mL in the recipient.

CONCLUSION

Ceftriaxone is the standard therapeutic choice for invasive or serious Salmonella infections in children. Pediatricians should be aware of the possibility of resistance development during therapy, especially in areas with a widespread of ceftriaxone resistance genes that are carried by a self-transferrable plasmid, such as the blaCMY-2-carrying IncI1 plasmid identified herein.

Risk factors and molecular epidemiology of community-onset extended-spectrum β-lactamase-producing Escherichia coli bacteremia

PURPOSE

Inadequate empirical therapy for severe infections caused by extended-spectrum β-lactamase-producing Escherichia coli (ESBLEC) is associated with poor outcomes. This study was designed to investigate risk factors for community-onset ESBLEC bacteremia at admission to a tertiary care hospital.

MATERIALS AND METHODS

A case-control study was performed that included all episodes of ESBLEC bacteremia in the outpatient department or within 48 hours of admission from January 2005 to March 2009. Data on predisposing factors were collected. The molecular epidemiology of ESBLEC clinical isolates was also determined.

RESULTS

Among 25281 blood cultures, 60 episodes of ESBLEC bacteremia were studied, which accounted for 7% of all E. coli bacteremia at admission. Healthcare-associated infection [odds ratio (OR), 8.3; 95% confidence interval (CI), 2.4-28.7; p=0.001], malignancy (OR, 4.6; 95% CI, 1.3-16.3; p=0.018), urinary tract infection (OR, 139.1; 95% CI, 24.6-788.2; p<0.001), hepatobiliary infection (OR, 79.1; 95% CI, 13.5-463.8; p<0.001), third generation cephalosporin usage during preceding 3 months (OR, 16.4; 95% CI, 2.0-131.8; p=0.008), and severe sepsis/septic shock (OR, 73.7; 95% CI, 12.4-438.5; p<0.001) were determined as independent risk factors for community-onset ESBLEC bacteremia. The most common extended-spectrum β-lactamase (ESBL) gene identified was blaCTX-M-15 (n=31) followed by blaCTX-M-14 (n=23).

CONCLUSION

The most common types of ESBLs in E. coli causing community-onset bacteremia were CTX-M-15 and CTX-M-14 in Korea. By result of decision tree analysis, the empirical use of carbapenems is suggested only for patients with severe sepsis/septic shock, hepatobiliary infection, or healthcare-associated urinary tract infection.

Molecular epidemiology of colonizing and disease-causing Klebsiella pneumoniae in paediatric patients

Klebsiella pneumoniae causes a range of clinical disease in paediatric patients and is of increasing concern due to growing antibiotic resistance, yet little is known about the relative distribution of commensal and pathogens throughout the population structure of K. pneumoniae. We conducted a prospective, observational study of 92 isolates from Seattle Children's Hospital, including 49 disease isolates from blood and urine (13 and 36 isolates, respectively) and 43 colonization isolates from stool. Susceptibility to 20 antimicrobials was evaluated using disc diffusion, VITEK 2 and Etest. Strain relatedness was investigated using multilocus sequence typing (MLST). Demographic and clinical characteristics were largely similar between disease and colonization cohorts, with 85.7 and 74.4 % of disease and colonization cohort patients, respectively, having an underlying medical condition; the sole exception was a relative abundance of patients with urologic or renal abnormalities in the disease cohort, consistent with the predominance of urine specimens among the disease isolates. With regard to antibiotic susceptibility properties, no significant differences were noted between the disease and colonization cohorts. Using molecular analysis, 71 unique sequence types (STs) were distinguished, with novel MLST findings evident in both cohorts; 43 (46.7 %) isolates represented novel STs, including 22 with a novel allele sequence. Thirteen STs contained multiple isolates and all seven isolates with resistance to three or more antibiotic classes were within one of four multirepresentative STs. This study demonstrates that nearly half of paediatric Klebsiella isolates represent novel STs, with clustering of multidrug resistance within specific STs. These findings expand our understanding of the intersection of bacterial population structure, human colonization ecology and multidrug resistance in K. pneumoniae.

The Epidemiology of Alcohol Abuse and Pneumonia

The association between alcohol abuse and pneumonia has been recognized for more than two centuries and represents an enormous health burden worldwide. The first published notation of alcohol as a clinical risk factor for the development of pneumonia is now over 200 years old, and since then there have been over a 1,000 references in the medical literature confirming these observations. Even in this modern era of medicine pneumonia remains a common infection that afflicts over 450 million persons worldwide annually and causes 7 % of all deaths. When one considers that alcohol is the most commonly abused substance in the world, the enormous excessive burden that alcohol contributes to the morbidity and mortality of pneumonia represents a major public health consideration. In this chapter we review the foundational literature that has chronicled the evolution of our understanding of the association between pneumonia and alcohol abuse over the past century. In addition, we discuss some of the specific pathogens that are particularly associated with serious lung infections in individuals with alcohol use disorders. Finally, we consider some of the specific guidelines for the treatment and prevention of pneumonia in the setting of alcohol abuse.

Antimicrobial Resistance Patterns and Prevalence of blaPER-1 and blaVEB-1 Genes Among ESBL-producing Pseudomonas aeruginosa Isolates in West of Iran

BACKGROUND

Pseudomonas aeruginosa is a leading cause of nosocomial infections worldwide. Resistance of P. aeruginosa strains to the broad-spectrum cephalosporins may be caused by extended-spectrum β-lactamases (ESBLs).

OBJECTIVES

The aim of this study was to determine the antimicrobial resistance patterns and prevalence of PER-1 and VEB-1 type genes among ESBL producing strains of P. aeruginosa.

MATERIAL AND METHODS

A total of 106 P. aeruginosa isolates were collected from two university hospitals in Hamadan, Iran, during a7-month study (2009). The antimicrobial susceptibility of isolates was determined by disc diffusion method and interpreted according to the clinical and laboratory standards institute (CLSI) recommendations. Production of ESBL was determined by combined disk test and presence of PER-1 and VEB-1 type ESBL genes was identified by PCR.

RESULTS

The resistance against broad-spectrum cephalosporins and monobactames were: cefepime (97%), cefotaxime (92.5%) ceftazidime (51%), and aztreonam (27%). Ciprofloxacin (91.5%), imipenem (84.9%) and meropenem (82.1%) were the most effective anti-pseudomonas agents in this study. The results revealed that 88.7% of the isolates were multidrug resistant, 58.25% of those were ESBL positive. Sixteen (26.6%), 9 (15%) and 3 (5%) strains among ESBL-producing strains contained blaPER-1, blaVEB and blaPER-1-blaVEB, respectively.

CONCLUSIONS

This study highlighted the need to establish antimicrobial resistance surveillance networks for P. aeruginosa to determine the appropriate empirical treatment regimens. The high prevalence of multidrug resistance and production of ESBLs in P. aeruginosa isolates confirms the necessity of protocols considering these issues in the hospitals.

Characterization of multidrug-resistant Klebsiella pneumoniae from Australia carrying blaNDM-1

blaNDM genes, encoding metallo-β-lactamases providing resistance to carbapenems, have been reported in many locations since the initial report in 2008, including in several Enterobacteriaceae isolates in Australia/New Zealand. Here, we compare 4 additional carbapenem-resistant Klebsiella pneumoniae carrying blaNDM-1 isolated in Australia. Two are sequence type ST147, previously associated with blaNDM in Australia and elsewhere. They carry blaNDM-1 and different 16S rRNA methylase genes (armA or rmtC) on different conjugative plasmids, in 1 case with an IncFIIY replicon. One isolate belongs to the globally important ST11 but did not transfer a plasmid to Escherichia coli. The fourth isolate belongs to the novel ST1068 and transferred blaNDM-1, armA, and an IncA/C plasmid. Amplification and sequencing of ompK porin genes suggest that, unlike the case for other carbapenemase genes, ompK36 defects may not be required for NDM to cause clinically relevant levels of carbapenem resistance.

Characterization and comparison of extended-spectrum β-lactamase (ESBL) resistance genotypes and population structure of Escherichia coli isolated from Franklin's gulls (Leucophaeus pipixcan) and humans in Chile

We investigated the general level of antibiotic resistance with further analysis of extended-spectrum beta-lactamase (ESBL) prevalence, as well as the population structure of E. coli in fecal flora of humans and Franklin’s gulls (Leucophaeus pipixcan) in central parts of Chile. We found a surprisingly high carriage rate of ESBL-producing E. coli among the gulls 112/372 (30.1%) as compared to the human population 6/49 (12.2%.) Several of the E. coli sequence types (STs) identified in birds have previously been reported as Multi Drug Resistant (MDR) human pathogens including the ability to produce ESBLs. This means that not only commensal flora is shared between birds and humans but also STs with pathogenic potential. Given the migratory behavior of Franklin’s gulls, they and other migratory species, may be a part of ESBL dissemination in the environment and over great geographic distances. Apart from keeping the antibiotic use low, breaking the transmission chains between the environment and humans must be a priority to hinder the dissemination of resistance.

Combination of essential oils and antibiotics reduce antibiotic resistance in plasmid-conferred multidrug resistant bacteria

In this study we investigated the relationship between several selected commercially available essential oils and beta-lactam antibiotics on their antibacterial effect against multidrug resistant bacteria. The antibacterial activity of essential oils and antibiotics was assessed using broth microdilution. The combined effects between essential oils of cinnamon bark, lavender, marjoram, tea tree, peppermint and ampicillin, piperacillin, cefazolin, cefuroxime, carbenicillin, ceftazidime, meropenem, were evaluated by means of the checkerboard method against beta-lactamase-producing Escherichia coli. In the latter assays, fractional inhibitory concentration (FIC) values were calculated to characterize interaction between the combinations. Substantial susceptibility of the bacteria toward natural antibiotics and a considerable reduction in the minimum inhibitory concentrations (MIC) of the antibiotics were noted in some paired combinations of antibiotics and essential oils. Out of 35 antibiotic-essential oil pairs tested, four of them showed synergistic effect (FIC≤0.5) and 31 pairs showed no interaction (FIC>0.5-4.0). The preliminary results obtained highlighted the occurrence of a pronounced synergistic relationship between piperacillin/cinnamon bark oil, piperacillin/lavender oil, piperacillin/peppermint oil as well as meropenem/peppermint oil against two of the three bacteria under study with a FIC index in the range 0.26-0.5. The finding highlighted the potential of peppermint, cinnamon bark and lavender essential oils being as antibiotic resistance modifying agent. Reduced usage of antibiotics could be employed as a treatment strategy to decrease the adverse effects and possibly to reverse the beta-lactam antibiotic resistance.

A Disposable Microfluidic Virus Concentration Device Based on Evaporation and Interfacial Tension

We report a disposable and highly effective polymeric microfluidic viral sample concentration device capable of increasing the concentration of virus in a human nasopharyngeal specimen more than one order of magnitude in less than 30 min without the use of a centrifuge. The device is fabricated using 3D maskless xurography method using commercially available polymeric materials, which require no cleanroom operations. The disposable components can be fabricated and assembled in five minutes. The device can concentrate a few milliliters (mL) of influenza virus in solution from tissue culture or clinical nasopharyngeal swab specimens, via reduction of the fluid volume, to tens of microliters μL). The performance of the device was evaluated by nucleic acid extraction from the concentrated samples, followed by a real-time quantitative polymerase chain reaction (qRT-PCR). The viral RNA concentration in each sample was increased on average over 10-fold for both cultured and patient specimens compared to the starting samples, with recovery efficiencies above 60% for all input concentrations. Highly concentrated samples in small fluid volumes can increase the downstream process speed of on-chip nucleic acid extraction, and result in improvements in the sensitivity of many diagnostic platforms that interrogate small sample volumes.

KPC-4 Is encoded within a truncated Tn4401 in an IncL/M plasmid, pNE1280, isolated from Enterobacter cloacae and Serratia marcescens

We describe the transfer of bla(KPC-4) from Enterobacter cloacae to Serratia marcescens in a single patient. DNA sequencing revealed that KPC-4 was encoded on an IncL/M plasmid, pNE1280, closely related to pCTX-M360. Further analysis found that KPC-4 was encoded within a novel Tn4401 element (Tn4401f) containing a truncated tnpA and lacking tnpR, ISKpn7 left, and Tn4401 IRL-1, which are conserved in other Tn4401 transposons. This study highlights the continued evolution of Tn4401 transposons and movement to multiple plasmid backbones that results in acquisition by multiple species of Gram-negative bacilli.

Genome sequence of Escherichia coli J53, a reference strain for genetic studies

Escherichia coli J53 (F(-) met pro Azi(r)) is a derivative of E. coli K-12 which is resistant to sodium azide. This strain has been widely used as a general recipient strain for various conjugation experiments. Here, we report the genome sequence of E. coli J53 (=KACC 16628).

Analysis of drug resistance determinants in Klebsiella pneumoniae isolates from a tertiary-care hospital in Beijing, China

Background

The rates of multidrug-resistant (MDR), extensively drug-resistant (XDR) and pandrug-resistant (PDR) isolates among Enterobacteriaceae isolates, particularly Klebsiella pneumoniae, have risen substantially worldwide.

Methodology/Principal Findings

To better understand the molecular mechanisms of drug resistance in K. pneumoniae, we analyzed the drug resistance determinants for K. pneumoniae isolates collected from the 306 Hospital, a tertiary-care hospital in Beijing, China, for the period of September 1, 2010-October 31, 2011. Drug susceptibility testing, PCR amplification and sequencing of the drug resistance determinants were performed. Conjugation experiments were conducted to examine the natural ability of drug resistance to disseminate among Enterobacteriaceae strains using a sodium azide-resistant Escherichia coli J53 strain as a recipient. Among the 223 consecutive non-repetitive K. pneumoniae isolates included in this study, 101 (45.3%) were extended-spectrum beta-lactamases (ESBLs) positive. The rates of MDR, XDR, and PDR isolates were 61.4% (n = 137), 22.0% (n = 49), and 1.8% (n = 4), respectively. Among the tested drug resistance-associated genes, the following ones were detected at relatively high rates bla_CTX-M-10 (80, 35.9%), aacC2 (73, 32.7%), dhfr (62, 27.8%), qnrS (58, 26.0%), aacA4 (57, 25.6%), aadA1 (56, 25.1%). Results from conjugation experiments indicate that many of the drug resistance genes were transmissible.

Conclusions/Significance

Our data give a “snapshot” of the complex genetic background responsible for drug resistance in K. pneumoniae in China and demonstrate that a high degree of awareness and monitoring of those drug resistance determinants are urgently needed in order to better control the emergence and transmission of drug-resistant K. pneumoniae isolates in hospital settings.

First description of Escherichia coli producing CTX-M-15- extended spectrum beta lactamase (ESBL) in out-patients from south eastern Nigeria

We studied the presence of extended spectrum beta lactamases (ESBLs) in 44 clinical isolates of Escherichia coli collected from out-patients in two university teaching hospitals in South-Eastern Nigeria. Species identification was performed by standard microbiology methods and re-confirmed by MALDI-TOF technology. Phenotypic characterization of ESBL enzymes was done by double disc synergy test and presence of ESBL genes was determined by specific PCR followed by sequencing. Transfer of plasmid DNA was carried out by transformation using E. coli DH5 as recipient strain. Phenotypic characterization identified all isolates to be ESBL positive. 77% of strains were from urine, 13.6% from vaginal swabs and 9.0% from wound swabs. 63.6% were from female patients, 68% were from outpatients and 95.5% from patients younger than 30 years. All ESBL producers were positive in a PCR for bla_CTX-M-1 cluster, in exemplary strains bla_CTX-M-15 was found by sequencing. In all strains ISEcp1 was found upstream and ORF477 downstream of bla_CTX-M. PCR for bla_TEM and bla_OXA-1 was positive in 93.1% of strains, whereas bla_SHV was not detected, aac(6′)-Ib-cr was found in 97.7% of strains. RAPD analysis revealed seven different clonal groups named A through G with the majority of the strains (65.9%) belonging to clone A. Transfer of an ESBL plasmid with co-resistance to gentamicin, kanamycin, tobramycin, doxycycline and trimethropim-sulfamethoxazole was successful in 19 (43.2%) strains. This study showed a high rate of CTX-M-1 cluster - ESBLs in South-Eastern Nigeria and further confirms the worldwide spread of CTX-M ESBL in clinical isolates.

Characterization of Antimicrobial Resistance of Escherichia coli Recovered from Foods of Animal and Fish Origin in Korea

Antimicrobial-resistant Escherichia coli is transferred from food-producing animals to humans through the food chain. We investigated the prevalence of antimicrobial resistance and resistance determinants and characterized the integrons of foodborne E. coli in Korea. In total, 162 E. coli isolates from commercial foods (raw meat, fish, and processed foods) were collected by the National Antimicrobial Resistance Management Program from 2004 to 2006. Susceptibility to 20 antibiotics was tested by disk diffusion, and resistance determinants were detected using PCR and genomic sequence analysis. The isolates were highly resistant to antibiotics commonly used in livestock farming. Resistance to tetracycline (74.7%) was the most frequently observed, followed by streptomycin (71%) and ampicillin (51.2%). Class 1 integrons were detected in 13 isolates (8%), and nine of these integrons were located on conjugative plasmids. None of the isolates produced extended-spectrum β-lactamase. One isolate (0.6%) harbored blaCMY-2, which was located on a conjugative plasmid. Although the qnr gene was not detected, aac(6′)-Ib-cr was present in two isolates (1.2%). This is the first report of aac(6′)-1b-cr in food isolates. Three or four amino acid substitutions at positions 83 and 87 in gyrA and at positions 80 and/or 84 in parC were found in six isolates, representing high resistance to ciprofloxacin (MIC ≥ 16 mg/liter). These results suggest that E. coli isolates carrying resistance genes and integrons are present in the Korean food chain.

Dissemination of multidrug-resistant Escherichia coli in Korean veterinary hospitals

This study was performed to investigate the prevalence of rectal colonization with multidrug-resistant Escherichia coli in dogs hospitalized at veterinary hospitals in Korea and to assess the molecular epidemiologic traits of this organism. A total of 63 unique E. coli isolates obtained from the rectal swabs of hospitalized dogs were analyzed. Genes encoding CTX-M extended-spectrum β-lactamases (ESBLs) and AmpC enzymes were detected in 21 (33.3%) and 15 (23.8%) canine E. coli isolates, respectively. Twelve canine E. coli isolates harbored both the genes encoding the CTX-M and AmpC enzymes. Six ESBL-producing E. coli isolates also carried the rmtB gene. All 24 E. coli isolates producing CTX-M ESBL and/or CMY-2 were resistant to ciprofloxacin. Furthermore, mutations were found in the gyrA and the parC genes. In most cases, the bla genes of the CTX-M ESBL and AmpC enzymes and the rmtB gene were localized to incompatibility group F (IncF) plasmids. Possible small clonal outbreaks are suggested because some E. coli isolates recovered in the same veterinary hospital were identified as identical sequence types and showed identical banding patterns in repetitive sequence-based polymerase chain reaction. The horizontal transfer of IncF plasmids and the clonal transfer of E. coli strains are suggested to play a role in the dissemination of antimicrobial resistance genes, and this transfer may occur across host species (i.e., between humans and dogs).

Detection of Extended Spectrum B-Lactamases in Urinary Isolates of Klebsiella pneumoniae in Relation to Bla, Bla and Bla Gene Carriage

BACKGROUND

Resistance to contemporary broad-spectrum β-lactam antibiotics mediated by extended-spectrum β-lactamases (ESBLs) is increasing worldwide. Klebsiella pneumoniae, an important cause of nosocomial and community acquired urinary tract infections has rapidly become the most common ESBL producing organism. We examined ESBL production in urinary isolates of K. pneumoniae in relation to the presence of bla(SHV), bla(TEM) and bla(CTX-M) genes.

METHODS

Antibiotic resistance of 51 clinical isolates of K. pneumoniae was determined to amoxicillin, amikacin, ceftazidime, cefotaxime, cefteriaxon, ceftizoxime, gentamicin, ciprofloxacin and nitrofurantoin by disc diffusion. Minimum inhibitory concentrations were also measured for ceftazidime, cefotaxime, cefteriaxon, ceftizoxime and ciprofloxacin. ESBL production was detected by the double disc synergy test and finally, presence of the bla(SHV), bla(TEM) and bla(CTX-M) genes were shown using specific primers and PCR.

RESULTS

Disc diffusion results showed that 96.08 % of the isolates were resistant to amoxicillin followed by 78.43 % resistance to nitrofurantoin, 49.02 % to amikacin and ceftazidime, 41.17 % to ceftriaxone, 37.25% resistance to cefotaxime and ceftizoxime, and 29.42 % to gentamicin and ciprofloxacin. Both resistant and intermediately resistant organisms were resistant in MIC determinations. Twenty two isolates (43.14%) carried bla(SHV), 18 (35.29%) had bla(TEM) and 16 (31.37%) harbored bla(CTX-M) genes. ESBL production was present in 14 isolates (27.45 %) of which, 3 did not harbor any of the 3 genes. Among the non-ESBL producers, 9 lacked all 3 genes and 2 carried them all.

CONCLUSION

No relation was found between gene presence and ESBL expression.

Antibiotic resistance patterns and extended-spectrum β-lactamase production among Acinetobacter spp. isolated from an intensive care Unit of a hospital in Kerman, Iran

BACKGROUND

The global increase in multidrug resistance of Acinetobacter spp. has created widespread problems in the treatment of patients in intensive care units (ICUs) of hospitals. To assess the sensitivity of Acinetobacter isolates to antibiotics routinely used in ICUs, we investigated antibiotic resistance patterns and extended-spectrum β-lactamase (ESBL) production among Acinetobacter spp. isolated from the ICU of a university hospital in Kerman, Iran.

METHODS

Fifteen isolates of Acinetobacter spp. were recovered from one hundred clinical specimens collected from the ICU of Afzalipoor Hospital in Kerman, Iran, from October 2010 to June 2011. Preliminary antibiotic sensitivity testing was carried out using the disk-diffusion breakpoint assay, and MICs of different antibiotics were determined using the E-test. ESBL production was detected by a double-disk synergy test and confirmed by a phenotypic confirmatory test. Substrate hydrolysis in the presence and absence of the following inhibitors was carried out using the rapid fixed-time method: para-chloromercuribenzoate (p-CMB), clavulanic acid, sulbactam, and NaCl.

RESULTS

Overall, 73.3% of the isolates were resistant to imipenem (MIC range 240-128 µg/mL) and 66% to ciprofloxacin (MIC range 240-64 ± 0.08 µg/mL). All of the isolates were fully resistant (MIC 240 µg/mL) to piperacillin, while 93.3%, 53.3%, and 93.3% were resistant to piperacillin + tazobactam (MIC 240 µg/mL), amikacin (MIC range 128-16 µg/mL), and cefepime (MIC range 240-60 µg/mL), respectively. The isolates were also resistant to chloramphenicol and tetracycline: MICs of these two agents were ≥ 240 µg/mL. The test for ESBL production was positive for only three isolates (nos. 1, 10, and 15). The rate of substrate hydrolysis was highest in the presence of p-CMB (80.2 ± 0.02) and lowest in the presence of NaCl (2.1 ± 0.01) (P ≤ 0.05).

CONCLUSIONS

Many isolates of Acinetobacter spp. are resistant to almost all antibiotics routinely used in the ICU of our hospital, including imipenem, ciprofloxacin, and piperacillin + tazobactam. Three isolates were ESBL producers. The other isolates exhibited high resistance to β-lactams, but they did not produce any ESBL enzymes.

Increasing ceftriaxone resistance in Salmonellae, Taiwan

In Taiwan, despite a substantial decline of Salmonella enterica serotype Choleraesuis infections, strains resistant to ciprofloxacin and ceftriaxone persist. A self-transferable bla(CMY-2)-harboring IncI1 plasmid was identified in S. enterica serotypes Choleraesuis, Typhimurium, Agona, and Enteritidis and contributed to the overall increase of ceftriaxone resistance in salmonellae.

Increasing ceftriaxone resistance in Salmonellae, Taiwan

In Taiwan, despite a substantial decline of Salmonella enterica serotype Choleraesuis infections, strains resistant to ciprofloxacin and ceftriaxone persist. A self-transferable bla_CMY-2-harboring IncI1 plasmid was identified in S. enterica serotypes Choleraesuis, Typhimurium, Agona, and Enteritidis and contributed to the overall increase of ceftriaxone resistance in salmonellae.

Citrobacter spp. as a source of qnrB Alleles

qnrB is the most common of the five qnr families and has the greatest number of allelic variants. Almost two-thirds of the qnrB alleles have been reported in Citrobacter spp., and several were shown to be located on the chromosome. In this study, PCR was used to investigate the prevalence of plasmid-mediated quinolone resistance genes in 71 clinical isolates belonging to the Citrobacter freundii complex. Thirty-seven percent contained qnrB alleles, including 7 (qnrB32 to qnrB38) that were novel and 1 pseudogene, while none contained qnrA, qnrC, qnrD, qnrS, or aac(6')-Ib-cr. When the strains were arrayed by related 16S rRNA sequence and further separated into subspecies by biochemical criteria, clustering of qnrB-positive strains was evident. In only two strains with qnrB2 and qnrB4 was quinolone resistance transferable by conjugation, and only these strains contained the ISCR1 sequence that is often associated with qnrB on plasmids. Five of 26 qnrB-positive strains contained integrase genes, but these included the strains with qnrB2 and qnrB4 as well as two strains with other transmissible plasmids. In a fully sequenced genome of Citrobacter youngae, a member of the C. freundii complex, another novel qnrB allele, qnrB39, occurs in a sequence of genes that is 90% identical to sequence surrounding integron-associated qnrB4 incorporated into plasmids. The chromosome of Citrobacter is the likely source of plasmid-mediated qnrB.

Resistance to carbapenems in sequence type 11 Klebsiella pneumoniae is related to DHA-1 and loss of OmpK35 and/or OmpK36

This study investigated the molecular mechanisms of carbapenem resistance in clinical isolates of Klebsiella pneumoniae from Korea and the clinical outcomes of resistant K. pneumoniae infection. Sixteen K. pneumoniae isolates showing resistance to carbapenems collected from a tertiary-care hospital were examined for the mechanisms of carbapenem resistance. PCR and sequencing experiments detected the bla(DHA-1) AmpC β-lactamase gene in all 16 clinical isolates, whilst the bla genes of extended-spectrum β-lactamases were detected in 12 of 16 isolates. SDS-PAGE experiments indicated that all the isolates lacked the 35 kDa and/or 36 kDa outer-membrane proteins (OMPs). Sequence analysis of the corresponding OMP genes revealed various alterations. PFGE analysis demonstrated that there were no major clonal relationships among the K. pneumoniae isolates. However, multilocus sequence typing experiments showed that all isolates shared the same sequence type (ST), ST11, except for one isolate of ST48. The crude mortality rate of infected patients was 81.8 %. Carbapenem resistance was mainly due to a combination of DHA-1 AmpC β-lactamase coupled with the loss of OmpK35 and/or OmpK36 and was associated with poor clinical outcome.

Quinolone induction of qnrVS1 in Vibrio splendidus and plasmid-carried qnrS1 in Escherichia coli, a mechanism independent of the SOS system

Plasmid-carried qnrS1 is derived from Vibrio splendidus chromosomal qnrVS1. qnrVS1 transcripts increased 21- to 34-fold with subinhibitory concentrations of ciprofloxacin but much less with mitomycin. No LexA binding sites were upstream of qnrS1 or qnrVS1, and similar induction levels were observed in lexA-positive and lexA-negative Escherichia coli strains with native qnrS1 plasmid pMG306 but not with pUC18-cloned qnrS1 or qnrVS1. Thus, qnrS1 induction by quinolones is independent of the SOS system and requires sequence besides that of the structural gene.

Comparison of disc diffusion methods for the detection of extended-spectrum Beta lactamase-producing enterobacteriaceae

Background:

Resistance to broad-spectrum β lactams, mediated by extended-spectrum β lactamases (ESBLs), is an increasing problem world wide. This resistance poses problems for in vitro testing and reporting. Increased prevalence of ESBLs among Enterobacteriaceae creates a great need for laboratory testing methods that will accurately identify their presence.

Materials and Methods:

During the study, the Enterobacteriaceae isolated were tested for the presence of ESBL by the National Committee for Clinical Laboratory Standards (NCCLS) screening test, Jarlier double disc synergy (approximation) test (DDST) and NCCLS phenotypic confirmatory test (PCT), and compared their efficiency in detection.

Results:

A total of 313 Enterobacteriaceae were isolated and tested for the presence of ESBL. NCCLS PCT identified 200 (63.89%) as ESBL producers and DDST identified 176 (56.23%), with a P-value of <0.001. Among the screening agents, ceftazidime had a better sensitivity (89.49%) and specificity (95.74%).

Conclusions:

Close monitoring of the susceptibility pattern of isolates and careful spacing with specific discs can identify many ESBL producers. Ceftazidime has a better sensitivity and specificity as a screening agent. A combination of different tests can be useful for accurate identification.

Chromosome-encoded AmpC and CTX-M extended-spectrum β-lactamases in clinical isolates of Proteus mirabilis from Korea

Among 222 Proteus mirabilis clinical isolates collected from 17 hospitals in Korea in 2008, 28 (12.6%) and 8 (3.6%) isolates exhibited extended-spectrum β-lactamase (ESBL) and AmpC phenotypes, respectively. The most common type of ESBL gene identified by PCR and sequencing experiments was bla(CTX-M-14a) (n = 12). The bla(CTX-M-90) (n = 4), bla(CTX-M-15) (n = 3), bla(CTX-M-12) (n = 3), bla(CTX-M-2) (n = 2), bla(CTX-M-14b) (n = 1), bla(TEM-52) (n = 5), and bla(SHV-12) (n = 1) genes were also detected. Eight isolates carried an AmpC β-lactamase gene, such as bla(CMY-2) (n = 6) or bla(DHA-1) (n = 2). All bla genes encoding CTX-M-1- and CTX-M-9-type enzymes and all bla(CMY-2) genes were preceded by ISEcp1-like elements. The bla(CTX-M-2) gene found in two isolates was located on a complex class 1 integron. The bla(DHA-1) gene was preceded by a transcriptional regulator gene and was followed by phage shock protein genes. The bla(CTX-M) genes were located on the chromosome in 21 isolates. A plasmid location for the bla(CTX-M) gene was found in only four isolates: the bla(CTX-M-14a) gene was located on ∼150-kbp IncA/C plasmids in three isolates and on a ∼50-kbp IncN plasmid in one isolate. The bla(TEM-52) gene was located on ∼50-kbp IncN plasmids in all five isolates. The AmpC β-lactamase genes were located on the chromosome in seven of eight isolates; one isolate carried the bla(CMY-2) gene on a ∼150-kbp IncA/C plasmid. Our results show that a chromosomal location of CTX-M ESBL and AmpC β-lactamase genes in P. mirabilis is no longer an unusual phenomenon in hospital environments.

Plasmid-mediated quinolone resistance in pseudomonas putida isolates from imported shrimp

Fourteen quinolone-resistant Pseudomonas putida isolates were recovered from imported frozen shrimp sold in the United States. Two isolates harbored plasmids with qnrA and qnrB genes. PCR and DNA sequencing of quinolone resistance-determining regions identified novel substitutions in GyrA (His139→Glu and Thr128→Ala) and GyrB (Thr442→Asn, Gly470→Ala, and Ile487→Pro) and previously reported substitutions in GyrB (Asp489→Glu) and ParC (Thr105→Pro).

Determinants of beta-lactam resistance in meningitis-causing Enterobacteriaceae in Brazil

This study analyzed resistance determinants in extended-spectrum beta-lactamase (ESBL)-producing enterobacteria and the epidemiology of 11 Escherichia coli isolates obtained from meningitis patients in a region of Brazil from 2000 to 2005. ESBL-encoding genes and their genetic environment were investigated by PCR and sequencing. The gene blaCTX-M-2 was identified in 3 different enterobacteria (E. coli, Serratia marcescens, and Proteus mirabilis) downstream of the insertion sequence ISCR1 (localized in class 1 integrons), but not as part of the resistance cassettes region. Multilocus sequence typing (MLST) was used to investigate genetic relationships between the 11 E. coli isolates in this study and strains associated with meningitis in the E. coli MLST database. MLST analysis indicated high genetic diversity among isolates, and no significant genetic relationship was identified with meningitis-causing E. coli in the database. The results in this report reinforce the need to be attentive to meningitis suspected to be due to ESBL-producing enterobacterial isolates, especially where ESBL epidemiology is well known.