In vivo selection of OmpK35-deficient mutant after cefuroxime therapy for primary liver abscess caused by Klebsiella pneumoniae

Cefmetazole for extended-spectrum β-lactamase-producing Enterobacteriaceae in pediatric pyelonephritis

BACKGROUND

Pyelonephritis caused by extended-spectrum β-lactamase (ESBL)-producing Enterobacteriaceae is an urgent problem in pediatrics. Although carbapenem is the standard therapy for infections caused by ESBL-producing Enterobacteriaceae, some cephamycins, including cefmetazole, are stable against hydrolysis by ESBL. There are few reports, however, on the use of cefmetazole in children. The aim of this study was to evaluate the therapeutic effect of cefmetazole in pediatric pyelonephritis caused by ESBL-producing Enterobacteriaceae.

METHODS

Children with pyelonephritis caused by ESBL-producing Enterobacteriaceae were enrolled between April 2010 and November 2016 at Tokyo Metropolitan Children's Medical Center. Presence of ESBL was tested for using the disk diffusion method. Medical records were reviewed for a past history of bacterial infection. The outcomes were clinical cure rate at 4 weeks and the duration of therapy in the cefmetazole and non-cefmetazole groups.

RESULTS

Fifty-five patients met the criteria for pyelonephritis caused by ESBL-producing Enterobacteriaceae. The most common causative organisms were Escherichia coli (n = 51; 92.7%), Klebsiella pneumoniae (n = 3; 5.5%), and K. oxytoca (n = 1; 1.8%). Thirty-six and 19 patients were treated with cefmetazole and with other antibiotics as definitive therapy, respectively. There was no difference in the clinical cure rate (86.1% vs 89.5%; P = 0.72) or duration of therapy (median, 7.0 vs 7.0 days; P = 0.73) between the cefmetazole and non-cefmetazole groups.

CONCLUSIONS

Cefmetazole was not inferior to the other antibiotics in the treatment of pyelonephritis caused by ESBL-producing Enterobacteriaceae in children. Cefmetazole is a valuable therapeutic alternative to carbapenems for treating pyelonephritis caused by ESBL-producing Enterobacteriaceae.

Detection of Plasmid-Mediated β-Lactamase Genes and Emergence of a Novel AmpC (CMH-1) in Enterobacter cloacae at a Medical Center in Southern Taiwan

The plasmid-mediated extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases in Enterobacter spp. have increasingly been reported. In this study, we investigated the prevalence of the plasmid-mediated β-lactamases in Enterobacter cloacae from bloodstream isolates at a medical center in southern Taiwan. ESBL and ampC genes were detected by PCRs and DNA sequencing. Conjugation experiments were conducted to confirm the transferability of the genetic resistance trait. Among 41 non-repetitive blood isolates of cefuroxime-resistant E. cloacae, eight isolates exhibited ESBL phenotype confirmed by double-disk synergistic tests. Nearly all the strains were susceptible to carbapenems. The prevalence rate of the plasmid-mediated bla_ampC genes was 73% (30/41), including one bla_DHA-1, one bla_MIR-6, two novel bla_CMH-1 genes and other bla_ACT-like genes. Coexistence of plasmid-mediated bla_ACT and ESBL genes (10 with bla_SHV-12 and one with bla_CTX-M-3) was observed. Successful transmissions of the bla_ACT and bla_CMH-1 were demonstrated in some transconjugants. The inducible or derepressed CMH-1 had expanded activity of isolates versus ceftazidime. Enterobacterial repetitive intergenic consensus (ERIC)-PCR analysis and pulsotype showed distinct patterns suggesting non-clonal relationship. In conclusion, plasmid-mediated bla_ACT-likeampC genes in E. cloacae isolates have been highly prevalent in southern Taiwan and may continue genetic evolution, contributing to the complexities in antibiotic-resistant mechanisms.

The Use of Noncarbapenem β-Lactams for the Treatment of Extended-Spectrum β-Lactamase Infections

The continued rise in infections caused by extended-spectrum β-lactamase (ESBL)-producing pathogens is recognized globally as one of the most pressing concerns facing the healthcare community. Carbapenems are widely regarded as the antibiotics of choice for the treatment of ESBL-producing infections, even when in vitro activity to other β-lactams has been demonstrated. However, indiscriminant carbapenem use is not without consequence, and carbapenem overuse has contributed to the emergence of carbapenem-resistant Enterobacteriaceae. The use of non-carbapenem β-lactams for the treatment of ESBL infections has yielded conflicting results. In this review, we discuss the available data for the use of cephamycins, cefepime, piperacillin-tazobactam, ceftolozane-tazobactam, and ceftazidime-avibactam for the treatment of ESBL infections.

Spread of ISCR1 elements containing blaDHA-₁ and multiple antimicrobial resistance genes leading to increase of flomoxef resistance in extended-spectrum-beta-lactamase-producing Klebsiella pneumoniae

Increasing resistance to quinolones, aminoglycosides, and/or cephamycins in extended-spectrum-β-lactamase (ESBL)-producing Enterobacteriaceae exacerbates the already limited antibiotic treatment options for infections due to these microbes. In this study, the presence of resistance determinants for these antimicrobial agents was examined by PCR among ESBL-producing Klebsiella pneumoniae (ESBL-KP) isolates that caused bacteremia. Pulsed-field gel electrophoresis was used to differentiate the clonal relationship among the isolates studied. Transferability and the location of the resistance genes were analyzed by conjugation experiments, followed by DNA-DNA hybridization. Among the 94 ESBL-KP isolates studied, 20 isolates of flomoxef-resistant ESBL-KP were identified. They all carried a DHA-1 gene and were genetically diverse. CTX-M genes were found in 18 of the isolates. Among these DHA-1/CTX-M-producing K. pneumoniae isolates, ISCR1 was detected in 13 (72%) isolates, qnr genes (1 qnrA and 17 qnrB genes) were detected in 18 (100%), aac(6')-Ib-cr was detected in 11 (61%), and 16S rRNA methylase (all armA genes) was detected in 14 (78%). Four transconjugants were available for further analysis, and qnrB4, aac(6')-Ib-cr, armA, and bla(DHA-1) were all identified on these self-transferable bla(CTX-M)-carrying plasmids. The genetic environments of ISCR1 associated with armA, bla(DHA-1), and qnrB4 genes in the four transconjugants were identical. Replicon-type analysis revealed a FIIA plasmid among the four self-transferable plasmids, although the other three were nontypeable. The cotransfer of multiple resistance genes with the ISCR1 element-carrying plasmids has a clinical impact and warrants close monitoring and further study.

Different culture medium formulations induce variant protein expression patterns of outer membrane porins in Klebsiella pneumoniae

Outer membrane porin (OMP) expression has been shown to play an important role in antimicrobial resistance. In this study, we observed that OmpK35 of Klebsiella pneumoniae had varied expression profiles in different nutrient broths. the potential factors that could influence protein expression were assessed. K. pneumoniae (ATCC 13883) was cultured into two commercial available nutrient broths and also into solutions of the individual ingredients. To ensure that OmpK35 was detected, an OmpK35 deficient mutant was generated as control. When OmpK protein expression profiles were analyzed by SDS-PAGE, OmpK35 exhibited two different isoforms. Expression of an additional isoform-like OmpK35 protein was identified in one of the broths. No OmpK35 isoforms were observed when the individual ingredients of beef extract, casein or gelatin were used as culture medium. OmpK35 isoform expression could be repressed by adding more beef extract. In summary, OmpK can exhibit varied protein expression profiles when growing in different nutrient broths. The isoform-like protein expression of OmpK35 may lead to confusion in OmpK protein analysis.

Klebsiella pneumoniae outer membrane porins OmpK35 and OmpK36 play roles in both antimicrobial resistance and virulence

OmpK35 and OmpK36 are the major outer membrane porins of Klebsiella pneumoniae. In this study, a virulent clinical isolate was selected to study the role of these two porins in antimicrobial resistance and virulence. The single deletion of ompK36 (ΔompK36) resulted in MIC shifts of cefazolin, cephalothin, and cefoxitin from susceptible to resistant, while the single deletion of ompK35 (ΔompK35) had no significant effect. A double deletion of ompK35 and ompK36 (ΔompK35/36) further increased these MICs to high-level resistance and led to 8- and 16-fold increases in the MICs of meropenem and cefepime, respectively. In contrast to the routine testing medium, which is of high osmolarity, susceptibility tests using low-osmolarity medium showed that the ΔompK35 mutation resulted in a significant (≥ 4-fold) increase in the MICs of cefazolin and ceftazidime, whereas a ΔompK36 deletion conferred a significantly (4-fold) lower increase in the MIC of cefazolin. In the virulence assays, a significant (P < 0.05) defect in the growth rate was found only in the ΔompK35/36 mutant, indicating the effect on metabolic fitness. A significant (P < 0.05) increase in susceptibility to neutrophil phagocytosis was observed in both ΔompK36 and ΔompK35/36 mutants. In a mouse peritonitis model, the ΔompK35 mutant showed no change in virulence, and the ΔompK36 mutant exhibited significantly (P < 0.01) lower virulence, whereas the ΔompK35/36 mutant presented the highest 50% lethal dose of these strains. In conclusion, porin deficiency in K. pneumoniae could increase antimicrobial resistance but decrease virulence at the same time.

In vivo selection of imipenem-resistant Klebsiella pneumoniae producing extended-spectrum beta-lactamase CTX-M-15 and plasmid-encoded DHA-1 cephalosporinase

Four Klebsiella pneumoniae isolates (KP1-4) were recovered sequentially from an infected patient. Whilst KP1-3 were resistant to all beta-lactams except carbapenems, KP4 recovered after 24 days of imipenem-containing treatment showed additional resistance to carbapenems. No carbapenem hydrolysis could be identified in KP4. Molecular characterisation revealed that KP1-4 were indistinguishable by pulsed-field gel electrophoresis, contained a 95-kb self-transferable plasmid harbouring bla(CTXM-15) and bla(TEM-1) genes and a 65-kb plasmid that was not transferred by conjugation into Escherichia coli, and harboured the plasmid-mediated bla(DHA-1) AmpC beta-lactamase gene. In addition, KP4 failed to express OmpK36 owing to a point mutation leading to a premature stop of the protein. This study demonstrates development of carbapenem resistance related to loss of OmpK36 expression in a K. pneumoniae isolate harbouring extended-spectrum beta-lactamase and plasmid-mediated cephalosporinase genes following prolonged imipenem exposure.

Contribution of fucose-containing capsules in Klebsiella pneumoniae to bacterial virulence in mice

Bacterium Klebsiella pneumoniae (KP) contains a prominent capsule. Clinical infections usually are associated with pneumonia or urinary tract infection (UTI). Emerging evidence implicates KP in severe liver abscess especially in diabetic patients. The goal of this study was to investigate the capsular polysaccharides from KP of liver abscess (hepatic-KP) and of UTI-KP. The composition of capsular polysaccharides was analyzed by capillary high-performance liquid chromatography (HPLC, Dionex system). The terminal sugars were assayed by binding ability to lectins. The results showed that the capsule of a hepatic KP (KpL1) from a diabetic patient contained fucose, while the capsule from UTI-KP (KpU1) did not. The absence of fucose was verified by the absence of detectable polymerase chain reaction (PCR) fragment for fucose synthesis genes, gmd and wcaG in KpU1. Mice infected with the KpL1 showed high fatality, whereas those infected with the KpU1 showed high survival rate. The KpL1 capsule was reactive to lectins AAA and AAL, which detect fucose, while the KpU1 capsule was reactive to lectin GNA, which detects mannose. Phagocytosis experiment in mouse peritoneal cavity indicated that the peritoneal macrophages could interact with KpU1, while rare association of KpL1 with macrophages was observed. This study revealed that different polysaccharides were displayed on the bacterial capsules of virulent KpL1 as compared with the less virulent KpU1. Interaction of KpU1 with mice peritoneal macrophages was more prominent than that of KpL1. The possession of fucose might contribute to KpL1 virulence by avoiding phagocytosis since fucose on bacteria had been implicated in immune evasion.

Collateral damage of flomoxef therapy: in vivo development of porin deficiency and acquisition of blaDHA-1 leading to ertapenem resistance in a clinical isolate of Klebsiella pneumoniae producing CTX-M-3 and SHV-5 beta-lactamases

OBJECTIVES

The study aimed to characterize the genetic basis of flomoxef and collateral ertapenem resistance in a clinical isolate of extended-spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBL-KP) after flomoxef exposure.

METHODS

Four ESBL-KP isolates (Lkp11-14) were recovered sequentially from four episodes of bacteraemia in an elderly patient. Laboratory investigations included genotyping by PFGE, resistance gene analysis by PCR and sequencing, and outer membrane protein analysis by SDS-PAGE. Plasmid analysis by DNA-DNA hybridization, electroporation and conjugation was also performed.

RESULTS

Lkp14 was recovered after 21 days of flomoxef therapy. It demonstrated an indistinguishable PFGE pattern when compared with those produced by Lkp11-13. However, resistance to both flomoxef and ertapenem emerged in Lkp14. Molecular characterization revealed that, in addition to the pre-existing ESBL production (CTX-M-3 and SHV-5) and OmpK35 deficiency found in Lkp11-13, Lkp14 had acquired an extra plasmid-mediated AmpC beta-lactamase gene (blaDHA-1) and failed to express OmpK36, because of insertional inactivation by an insertion sequence IS5. Other resistance mechanisms, such as production of carbapenem-hydrolysing enzymes or expression of chromosomal efflux, were apparently not involved. Conjugational transfer of the plasmid-mediated blaDHA-1 gene into Lkp11 resulted in a significant increase in the MICs of cephamycins and beta-lactamase inhibitors, but not in those of carbapenems.

CONCLUSIONS

Lkp14 was apparently derived from the previously flomoxef-susceptible isolates, Lkp11-13. After flomoxef exposure, the in vivo acquisition of the plasmid-mediated blaDHA-1 gene has led to flomoxef resistance in Lkp14, and the concomitant depletion of OmpK36 expression has resulted in a collateral effect of ertapenem resistance and diminished susceptibilities to imipenem and meropenem.