High-level resistance to cefotaxime and ceftazidime in Klebsiella pneumoniae isolates from Cleveland, Ohio

Mechanisms of Resistance in Gram-Negative Urinary Pathogens: From Country-Specific Molecular Insights to Global Clinical Relevance

Urinary tract infections (UTIs) are the most frequent hospital infections and among the most commonly observed community acquired infections. Alongside their clinical importance, they are notorious because the pathogens that cause them are prone to acquiring various resistance determinants, including extended-spectrum beta-lactamases (ESBL); plasmid-encoded AmpC β-lactamases (p-AmpC); carbapenemases belonging to class A, B, and D; qnr genes encoding reduced susceptibility to fluoroquinolones; as well as genes encoding enzymes that hydrolyse aminoglycosides. In Escherichia coli and Klebsiella pneumoniae, the dominant resistance mechanisms are ESBLs belonging to the CTX-M, TEM, and SHV families; p-AmpC; and (more recently) carbapenemases belonging to classes A, B, and D. Urinary Pseudomonas aeruginosa isolates harbour metallo-beta-lactamases (MBLs) and ESBLs belonging to PER and GES families, while carbapenemases of class D are found in urinary Acinetobacter baumannii isolates. The identification of resistance mechanisms in routine diagnostic practice is primarily based on phenotypic tests for the detection of beta-lactamases, such as the double-disk synergy test or Hodge test, while polymerase chain reaction (PCR) for the detection of resistance genes is mostly pursued in reference laboratories for research purposes. As the emergence of drug-resistant bacterial strains poses serious challenges in the management of UTIs, this review aimed to appraise mechanisms of resistance in relevant Gram-negative urinary pathogens, to provide a detailed map of resistance determinants in Croatia and the world, and to discuss the implications of these resistance traits on diagnostic approaches. We summarized a sundry of different resistance mechanisms among urinary isolates and showed how their prevalence highly depends on the local epidemiological context, highlighting the need for tailored interventions in the field of antimicrobial stewardship.

Evaluation of the AID AmpC line probe assay for molecular detection of AmpC-producing Enterobacterales

OBJECTIVES

In this study, the commercially available AID AmpC line probe assay (LPA) was evaluated for detection of plasmid-mediatedbla_AmpC β-lactamase genes in Enterobacterales as well as chromosomal mutations in the bla_AmpC promoter/attenuator regions in Escherichia coli.

METHODS

Accuracy of the AID AmpC probes was assessed using Enterobacterales clinical isolates harbouring diverse plasmid-mediated AmpC enzymes (ACC, ACT, DHA, FOX, CMY and MOX) and E. coli clinical isolates with mutations in the chromosomal bla_AmpC promoter/attenuator regions. The diagnostic performance of the AID AmpC LPA for bla_AmpC detection directly from clinical specimens was determined using 99 clinical urine specimens with bacterial cell counts >10⁵CFU/mL and the results were compared with culture-based phenotypic drug susceptibility testing (DST).

RESULTS

Detection of bla_AmpC genes in Enterobacterales clinical isolates showed 100% congruence with phenotypic DST results. The AID AmpC LPA showed 100% specificity [95% confidence interval (CI) 96-100%] and 100% sensitivity (95% CI 75-100%) for detection of plasmid-meditated bla_AmpC and E. coli genomic bla_AmpC promoter/attenuator mutations directly from clinical urine specimens. The AID AmpC LPA detected three AmpC-producers in urine specimens with bacterial cell counts >10⁵CFU/mL that were missed by culture-based phenotypic DST, thereby displaying higher diagnostic sensitivity.

CONCLUSION

The AID AmpC LPA is an accurate, sensitive and easy-to-use test that can be readily implemented in any diagnostic laboratory for molecular detection of bla_AmpC genes in Enterobacterales.

Prevalence of Extended Spectrum β-Lactamase and Antimicrobial Susceptibility Pattern of Clinical Isolates of Pseudomonas from Patients of Khyber Pakhtunkhwa, Pakistan

Majority of gram negative pathogenic bacteria are responsible for extended spectrum β-lactamases (ESBLs) production, which show resistance to some newer generation of antibiotics. The study was aimed at evaluating the prevalence of ESBL and antibiotic susceptibility pattern of Pseudomonas isolates collected during 2010 to 2014 from tertiary care hospitals of Peshawar, Pakistan. Out of 3450 samples, 334 Pseudomonas spp. isolates comprised of 232 indoor and 102 outdoor patients were obtained from different specimens and their susceptibility pattern was determined against 20 antibiotics. Antimicrobial susceptibility testing was carried out using the Kirby-Bauer agar diffusion method and ESBL production was detected by Synergy Disc Diffusion technique. The mean age group of the patients was 29.9 + 9.15 years. Meronem showed best activity (91.02%) from class carbapenem, β-lactam and β-lactamase inhibitors exhibited 69.16% activity, and doxycycline had a diminished activity (10.18%) to Pseudomonas spp. Outdoor isolates were more resistant than the indoor and during the course of the study the sensitivity rate of antibiotics was gradually reducing. ESBL production was observed in 44.32% while the remaining was non-ESBL. The moderate active antibiotics were amikacin (50.7%), SCF (51.4%), TZP (52.7%), and MXF (54.1%) among ESBL producing isolates. Lack of antibiotic policy, irrational uses (3GCs particularly), and the emergence of antibiotic resistant organisms in hospitals may be causes of high antibiotic resistance.

NmcA carbapenem-hydrolyzing enzyme in Enterobacter cloacae in North America

An imipenem-resistant Enterobacter cloacae isolate was recovered from the blood of a patient with a hematologic malignancy. Analytical isoelectric focusing, inhibitor studies, hydrolysis, induction assays, and molecular sequencing methods confirmed the presence of a NmcA carbapenem-hydrolyzing enzyme. This first report of NmcA detected in North America warrants further investigation into its distribution and clinical impact.

Expression of SHV-2 beta-lactamase and of reduced amounts of OmpK36 porin in Klebsiella pneumoniae results in increased resistance to cephalosporins and carbapenems

A Klebsiella pneumoniae clinical isolate was resistant to cefoxitin, cefotaxime, ceftazidime, ceftazidime-clavulanate, piperacillin-tazobactam (MICs, >256 micro g/ml in all cases), and meropenem (MIC, 16 micro g/ml) and was intermediate to imipenem (MIC, 8 micro g/ml). Decreased expression of the OmpK36 porin and expression of an SHV-2 beta-lactamase contributed to the observed resistance to these beta-lactam-containing agents.

Detection of plasmid-mediated AmpC beta-lactamase genes in clinical isolates by using multiplex PCR

Therapeutic options for infections caused by gram-negative organisms expressing plasmid-mediated AmpC beta-lactamases are limited because these organisms are usually resistant to all the beta-lactam antibiotics, except for cefepime, cefpirome, and the carbapenems. These organisms are a major concern in nosocomial infections and should therefore be monitored in surveillance studies. Six families of plasmid-mediated AmpC beta-lactamases have been identified, but no phenotypic test can differentiate among them, a fact which creates problems for surveillance and epidemiology studies. This report describes the development of a multiplex PCR for the purpose of identifying family-specific AmpC beta-lactamase genes within gram-negative pathogens. The PCR uses six sets of ampC-specific primers resulting in amplicons that range from 190 bp to 520 bp and that are easily distinguished by gel electrophoresis. ampC multiplex PCR differentiated the six plasmid-mediated ampC-specific families in organisms such as Klebsiella pneumoniae, Escherichia coli, Proteus mirabilis, and Salmonella enterica serovar Typhimurium. Family-specific primers did not amplify genes from the other families of ampC genes. Furthermore, this PCR-based assay differentiated multiple genes within one reaction. In addition, WAVE technology, a high-pressure liquid chromatography-based separation system, was used as a way of decreasing analysis time and increasing the sensitivity of multiple-gene assays. In conclusion, a multiplex PCR technique was developed for identifying family-specific ampC genes responsible for AmpC beta-lactamase expression in organisms with or without a chromosomal AmpC beta-lactamase gene.

Antimicrobial resistance in the chronically critically ill patient

Infection caused by organisms resistant to conventional antimicrobial therapy is an emerging problem of global proportions. This article describes the epidemiology of infections caused by resistant organisms in chronically critically ill patients and explores factors and mechanisms that lead to the development of resistance. Specific organisms and strategies for the treatment and control of these resistance organisms are discussed.

Molecular characterization of a multiply resistant Klebsiella pneumoniae encoding ESBLs and a plasmid-mediated AmpC

Organisms encoding multiple antibiotic resistance genes are becoming increasingly prevalent. In this report we describe a multiply resistant Klebsiella pneumoniae which possesses at least five different beta-lactamase genes. Isoelectric focusing, polymerase chain reaction and restriction fragment length polymorphism analysis identified TEM-1, multiple SHVs, OXA-9 and a plasmid-mediated ampC, beta-lactamase. Furthermore, Southern analysis and conjugation experiments established that most of the resistance genes were encoded on one large transferable plasmid. This report demonstrates the complexity of multiply resistant organisms.

Repeated epidemics caused by extended-spectrum beta-lactamase-producing Serratia marcescens strains

An outbreak of Serratia marcescens involving 42 patients admitted to the general intensive care unit of the Hospital of Varese, Italy, occurred from March 1994 to August 1995. The causative strains were resistant to oxyimino-cephalosporins and monobactams due to their production of an extended-spectrum beta-lactamase. Another outbreak caused by Serratia marcescens strains had occurred in the same unit a few months earlier, from February to October 1993, with the strains involved producing a novel TEM-derived extended-spectrum beta-lactamase. In order to verify whether there were any relationships between isolates from the two epidemics, the strains and their enzymes were characterized. Biochemical data and gene amplification experiments showed that the isolates of the second outbreak harbored a non-conjugative plasmid of approximately 48 kb, codifying for the production of an SHV-derived extended-spectrum beta-lactamase with pI 8.2. Restriction fragment length polymorphism analysis of total genomic DNA by pulsed-field gel electrophoresis of Serratia marcescens isolates unambiguously identified two different bacterial clones responsible for the two epidemics. Epidemiological and microbiological investigations demonstrated the long persistence of Serratia marcescens strains and their circulation in other hospital wards, thus suggesting their possible role as a long-term reservoir for further epidemic spread.

Detection and characterisation of extended spectrum beta-lactamases in Klebsiella pneumoniae causing nosocomial infection

One hundred and ninety-five multi-resistant strains of Klebsiella pneumoniae were isolated at Princess Alexandra Hospital (PAH) between December 1991 and June 1995. All these organisms produced extended spectrum beta-lactamases (ESBLs) as detected by the double disc synergy test (DDST). Between June 1994 and June 1995, a second population of 67 multi-resistant but DDST negative strains was isolated. Twenty multi-resistant Klebsiella pneumoniae strains (16 DDST positive and four DDST negative) and one susceptible strain were selected for further study. These were tested for production of ESBLs by two double disc synergy methods and agar dilution minimum inhibitory concentrations (MICs) with and without clavulanic acid. Detected ESBLs were further characterised by isoelectric focusing. The confirmed DDST positive K. pneumoniae strains all produced ESBLs that focused at an isoelectric point (pI) of 7.6, suggesting the presence of SHV-2, SHV-2a, SHV-6, SHV-7 or SHV-8 enzymes. The multi-resistant DDST negative strains showed no clavulanic acid synergy and thus no evidence of the presence of ESBLs.

Meropenem compared with ceftazidime in the empiric treatment of acute severe infections in hospitalized children. Italian Pediatric Meropenem Study Group

In a multicenter, randomized, open comparison of meropenem to ceftazidime as empiric treatment of severe acute infections, 185 children (1 mo-15 years old, mean 65.4 mo) were enrolled. Meropenem (20 mg/kg t.i.d. i.v.) was given to 98 and ceftazidime (10-30 mg/kg t.i.d. i.v.) to 87 children, generally for 5 to 10 days (mean: 6.9 for meropenem and 7.5 for ceftazidime). Clinical response was evaluated at the beginning and at the end of therapy and 4 weeks later (follow-up). Clinical response was deemed satisfactory at the end of therapy in 96.7% of the patients treated with meropenem and in 95.3% of those who received ceftazidime without any statistically significant difference. One relapse occurred in a meropenem-treated patient at the follow-up clinical assessment. The baseline infecting organism was eradicated or presumed eradicated at the end of therapy in 14/16 patients treated with meropenem and in 14/15 treated with ceftazidime. The incidence of drug-related adverse events (mostly a slight increase in liver enzymes) was 9.2% in the meropenem group and 4.6% in the ceftazidime group. Our data show that meropenem is as effective as ceftazidime in the empiric treatment of severe infections in infants and children.

Biochemical characterization of the carbapenem-hydrolyzing beta-lactamase AsbM1 from Aeromonas sobria AER 14M: a member of a novel subgroup of metallo-beta-lactamases

AsbM1, a carbapenem-hydrolyzing beta-lactamase produced by Aeromonas sobria AER 14M, was purified chromatographically, with anion exchange chromatography performed in the absence of Zn2+. The molecular mass of AsbM1 was approximately 34,000; the isoelectric point was 9.1. AsbM1 had high hydrolytic specificity for carbapenems but low hydrolysis rates for penicillins and cephalosporins. AsbM1 was resistant to the commercially available beta-lactamase inhibitors but was inhibited by pCMB and the chelators EDTA and o-phenanthroline. Zinc, an activator for many metallo-beta-lactamases, inhibited AsbM1 with an IC50 of 8 microM. Analysis of the N-terminal sequence (27 amino acids) showed 26% similarity to the CphA metallo-beta-lactamase. Because of the high specificity for carbapenems and the sensitivity to inhibition by Zn2+, AsbM1 should be included in a new subgroup of metallo-beta-lactamases.

Sequential emergence of multi-resistant Klebsiella pneumoniae in Bahrain

During the mid-1980s, nosocomial infections due to aminoglycoside-resistant Klebsiella pneumonia were prevalent in the intensive care unit (ICU) of the Salamanya Medical Centre, Bahrain. In an attempt to control the spread of such organisms, the third-generation cephalosporins were introduced in early 1987. Subsequently there was a marked increase in the incidence of cephalosporin resistance among Klebsiella spp. isolated in the ICU. In 1990, over 60% of Klebsiella isolates were resistant to both cephalosporins and aminoglycosides. Cephalosporin resistance was due to production of extended-spectrum beta-lactamases encoded on the same plasmid as aminoglycoside resistance. The incidence of cephalosporin resistance declined during 1991-1992, which was coincident with severe restrictions on the use of third-generation cephalosporins and the preferential use of ciprofloxacin and imipenem for nosocomial klebsiella infections. Sequential overuse of aminoglycosides and cephalosporins for nosocomial klebsiella infection may select for organisms resistant to both classes of antibiotics.

Extended-spectrum beta-lactamases conferring resistance to monobactams and oxyimino-cephalosporins in clinical isolates of Serratia marcescens

We studied antibiotic resistance patterns and extended-spectrum beta-lactamases (ES beta Ls) production in Serratia marcescens strains isolated in our hospital during 1993. We examined 210 S. marcescens isolates. Of these, 172 were obtained from 49 patients admitted to an intensive care ward; 157 out of 172 were obtained from February to October and presented the same pattern of antibiotic resistance, including monobactams and oxyimino-cephalosporins. The remaining 15 out of 172 isolates (obtained from September to December) were susceptible to all drugs tested, with the exception of first generation cephalosporins. Thirty-eight additional isolates were recovered, during the same period, from 28 patients admitted to wards other than the intensive care unit; also these strains showed the high susceptibility pattern reported above. Epidemic strains of S. marcescens produced three different types of beta-lactamase with pI 5.4, 5.5, and 8.4. In contrast, non-epidemic strains produced only one type of beta-lactamase with pI 8.4. Conjugation experiments showed that the beta-lactamases having a pI of 5.4 and 5.5 (but not the one with pI 8.4) were plasmid-mediated. Since the beta-lactamase with pI 5.5 was capable of hydrolyzing monobactams and oxyimino-cephalosporins it was classified as ES beta L. Electrophoretic analysis showed that plasmids obtained from multiresistant strains were of about 54 kb; these plasmids appeared also to code for aminoglycoside resistance. Our data indicate that the plasmid-mediated production of ES beta Ls may contribute to the epidemic spread of Serratia marcescens in high-risk wards.

New variant of TEM-10 beta-lactamase gene produced by a clinical isolate of proteus mirabilis

A clinical isolate of Proteus mirabilis was found to produce a new variant of the TEM-10 beta-lactamase gene. This is the first report of TEM-10 production by P. mirabilis and the first report of extended-spectrum beta-lactamase production by an isolate of this species recovered in the United States.

Outbreak of extended-spectrum beta-lactamase producing Serratia marcescens in an intensive care unit

Serratia marcescens has recently been identified as an important etiological agent in nosocomial infections, and is considered to be an opportunistic pathogen agent in immunosuppressed patients undergoing long periods of intensive care. Research carried out in 1991 and 1992 showed that it was of epidemiological relevance in only 1-2% of clinical isolates at the Ospedale di Circolo, Varese, Italy. However, between 7 February and 11 October 1993, the incidence of cases attributable to S. marcescens had increased to 5%; 157 strains of Serratia marcescens were isolated from clinical specimens of 43 patients admitted to an intensive care unit; these strains, characterized by epidemic spread, showed the same pattern of multiresistance to antibiotics including monobactams and oxyimino-cephalosporins. During the same period 23 isolates were also recovered from 18 patients admitted to wards other than the intensive care unit; these strains, characterized by a wide range of antibiotic susceptibility, were also sensitive to beta-lactam antibiotics with the exception of first generation cephalosporins. The production of extended-spectrum beta-lactamases (ES beta Ls) and their genetic determinism were studied. All the epidemic strains of S. marcescens resistant to ceftazidime, cefotaxime, ceftriaxone and aztreonam produced three different beta-lactamases with pI 5.4, 5.5 and 8.4 respectively. In contrast, non-epidemic strains produced only a beta-lactamase with pI 8.4. The beta-lactamase with pI 5.5 was plasmid-mediated, hydrolizing ceftazidime and aztreonam, showing it to be an ES beta L; while the beta-lactamase with pI 5.4, although plasmid-mediated, did not hydrolize monobactams or oxyimino-cephalosporins.(ABSTRACT TRUNCATED AT 250 WORDS)

Extended-spectrum beta-lactamases from Klebsiella pneumoniae strains isolated at an Italian hospital

Eighteen strains of Klebsiella pneumoniae recently isolated from hospitalized patients were resistant or moderately resistant to oxyimino-cephalosporins (ceftazidime and/or cefotaxime), aztreonam, cefoxitin and all but one were susceptible to imipenem. Analysis of enzymes produced by these clinical isolates revealed a wide pattern of extended-spectrum beta-lactamases. All isolates produced one or more beta-lactamases that were characterized preliminarily by their isoelectric point. Strains isolated early were from patients in the Intensive Care Unit and produced an ES beta-lactamase with an apparent pI of 7.6, whereas the later isolates were from surgical and medical wards of the same hospital and produced ES beta-lactamases with apparent pI of 8.2 and 8.4, respectively. This suggests the emergence of SHV-5 and MIR-1 beta-lactamases in our hospital. Agarose gel electrophoresis of plasmid DNA revealed the presence of a similar plasmid of approximate size 60 Kb in all isolates.

Characterization of an SHV-5 related extended broad-spectrum beta-lactamase in Enterobacteriaceae from Western Australia

Among 209 isolates of aminoglycoside resistant Enterobacteriaceae isolated from patients attending the Sir Charles Gairdner Hospital in Perth, Western Australia between January 1985 and June 1991, 41 strains demonstrated additional resistance to cefotaxime, ceftriaxone, ceftazidime and aztreonam. Significant synergy was demonstrable between these beta-lactams and clavulanic acid against resistant strains. The beta-lactamase was mediated by a 170 Kb self-transferring plasmid and identified as the SHV-5 type in isoelectric focusing (pl 8.2) and substrate hydrolysis kinetic studies. The findings record the introduction of extended broad-spectrum beta-lactamases to Australia.

Detection of extended-spectrum beta-lactamases in members of the family Enterobacteriaceae: comparison of the double-disk and three-dimensional tests

The three-dimensional and clavulanate double-disk potentiation tests were compared as procedures for the detection of extended-spectrum beta-lactamase production in 32 strains of Escherichia coli and Klebsiella pneumoniae, 31 of which produced TEM-1, TEM-2, TEM-3, TEM-4, TEM-5, TEM-7, TEM-8, TEM-9, TEM-10, TEM-12, TEM-101, SHV-1, SHV-2, SHV-3, SHV-4, SHV-5, CAZ-2, MIR-1, or an unidentified extended-spectrum beta-lactamase with a pI of 5.95, with some strains producing multiple beta-lactamases. The three-dimensional test, which was performed in conjunction with a routine disk diffusion test, detected extended-spectrum beta-lactamase production in 26 of 28 (93%) of the strains that produced extended-spectrum beta-lactamases. The clavulanate double-disk potentiation test detected extended-spectrum beta-lactamases in only 22 of the 28 strains (79%) when it was performed as currently recommended. The three-dimensional test, when performed in conjunction with the disk diffusion test, offered the advantages of providing simultaneous information about both antibiotic susceptibility and extended-spectrum beta-lactamase production, coupled with a greater sensitivity and earlier detection of extended-spectrum beta-lactamases.