Risk factors for Klebsiella pneumoniae carbapenemase (KPC) gene acquisition and clinical outcomes across multiple bacterial species.

INTRODUCTION: Risk factors for carbapenemase-producing Enterobacterales (CPE) acquisition/infection and associated clinical outcomes have been evaluated in the context of clonal, species-specific outbreaks. Equivalent analyses for complex, multi-species outbreaks, which are increasingly common, are lacking. METHODS: Between December 2010 and January 2017, a case-control study of Klebsiella pneumoniae carbapenemase (KPC)-producing organism (KPCO) acquisition was undertaken using electronic health records from inpatients in a US academic medical centre and long-term acute care hospital (LTACH) with ongoing multi-species KPCO transmission despite a robust CPE screening programme. Cases had a first KPCO-positive culture >48 h after admission, and included colonizations and infections (defined by clinical records). Controls had at least two negative perirectal screens and no positive cultures. Risk factors for KPCO acquisition, first infection following acquisition, and 14-day mortality following each episode of infection were identified using multi-variable logistic regression. RESULTS: In 303 cases (89 with at least one infection) and 5929 controls, risk factors for KPCO acquisition included: longer inpatient stay, transfusion, complex thoracic pathology, mechanical ventilation, dialysis, and exposure to carbapenems and ß-lactam/ß-lactamase inhibitors. Exposure to other KPCO-colonized patients was only a risk factor for acquisition in a single unit, suggesting that direct patient-to-patient transmission did not play a major role. There were 15 species of KPCO; 61 (20%) cases were colonized/infected with more than one species. Fourteen-day mortality following non-urinary KPCO infection was 20% (20/97 episodes) and was associated with failure to achieve source control. CONCLUSIONS: Healthcare exposures, antimicrobials and invasive procedures increased the risk of KPCO colonization/infection, suggesting potential targets for infection control interventions in multi-species outbreaks. Evidence for patient-to-patient transmission was limited.

Comparison of risk factors and outcomes of daptomycin-susceptible and -nonsusceptible vancomycin-resistant Enterococcus faecium infections in liver transplant recipients.

BACKGROUND: Vancomycin-resistant Enterococcus faecium (VRE) infections are common in liver transplant recipients (LTRs). Daptomycin (DAP) is an important treatment for such infections; however, DAP-nonsusceptible VRE (DNS-VRE) are increasingly frequent. The purpose of this study was to compare clinical characteristics and outcomes of LTRs with infections due to DNS-VRE and DAP-susceptible VRE (DS-VRE). METHODS: A single center, retrospective review of patients who underwent liver transplantation between January 1, 2010 and December 31, 2015 and developed infections due to DS-VRE or DNS-VRE post transplant was performed. Patients with DNS-VRE and DS-VRE infections were compared using univariate and logistic regression analysis. RESULTS: Fourteen LTRs developed DNS-VRE and 20 LTRs developed DS-VRE infection post-transplantation. No significant differences were observed in demographics, model for end-stage liver disease (MELD) scores, causes of end-stage liver disease, or rate of pre-transplant perirectal VRE colonization between groups. Bleeding complications and renal replacement therapy were more common in the DNS-VRE group than in the DS-VRE group. The duration of transplant hospitalization and post-transplant intensive care unit (ICU) admission was longer in the DNS-VRE group than in the DS-VRE group. The 30-day and 6-month mortality rate associated with DNS-VRE infection was similar to that associated with DS-VRE infection. CONCLUSIONS: Liver transplant recipients who develop DNS-VRE infection have higher bleeding complications and longer, more complex hospitalizations compared to those who develop DS-VRE infection post transplantation; however, mortality at 30 days and 6 months is not significantly worse. Further study is needed to determine optimal strategies for the prevention and treatment of DNS-VRE infections in LTRs.

A single-center experience with infections due to daptomycin-nonsusceptible Enterococcus faecium in liver transplant recipients.

BACKGROUND: Infections caused by vancomycin-resistant Enterococcus faecium (VRE) are a major cause of morbidity and mortality in the liver transplant population. Daptomycin (DAP) is often used to treat infections caused by VRE, but DAP nonsusceptibility in Enterococcus is increasing. METHOD: Patients with DAP-nonsusceptible Enterococcus (DNSE) infections who had undergone liver transplantation between January 1, 2010 and July 31, 2014 were retrospectively reviewed. A convenience sample of DNSE isolates was analyzed by pulsed-field gel electrophoresis (PFGE). RESULTS: We identified 14 liver transplant recipients (LTRs) who developed DNSE infections post transplantation. Postoperative complications were common, and most patients required repeat abdominal surgery within 90 days of transplantation. The initial DNSE culture was taken a median of 74.5 days post transplant and was secondary to an intra-abdominal infection in all but 1 patient. Half of patients were VRE colonized before or at the time of organ transplantation, and all those who were not VRE colonized at the time of transplantation later became colonized, a median of 27 days post transplant. Overall mortality in this cohort was 71%. PFGE did not demonstrate genetic relatedness among DNSE isolates. CONCLUSION: This study, the largest published series to our knowledge of DNSE infections in LTRs, demonstrates that these infections occur in patients with serious surgical complications and are associated with high morbidity and mortality. Established risk factors for VRE infection were common, as was DAP exposure. Although many risk factors for DNSE infection cannot be changed, this case series identifies several potentially modifiable variables. Further work is needed to identify interventions to decrease the risk of developing DNSE infections in this complex patient population.

Cryptosporidium enteritis in solid organ transplant recipients: multicenter retrospective evaluation of 10 cases reveals an association with elevated tacrolimus concentrations.

BACKGROUND: Cryptosporidial enteritis, a diarrheal infection of the small intestine caused by the apicomplexan protozoa Cryptosporidium, is infrequently recognized in transplant recipients from developed countries. METHODS: A retrospective review of all cases of cryptosporidiosis in solid organ transplant (SOT) recipients at 2 centers from January 2001 to October 2010 was performed and compared with transplant recipients with community-onset Clostridium difficile infection (CDI). A literature search was performed with regard to reported cases of cryptosporidiosis in SOT recipients. RESULTS: Eight renal, 1 liver, and 1 lung transplant recipient were diagnosed with cryptosporidiosis at median 46.0 months (interquartile range [IQR] 25.2-62.8) following SOT. Symptoms existed for a median 14 days (IQR 10.5-14.8) before diagnosis. For the 9 patients receiving tacrolimus (TAC), mean TAC levels increased from 6.3 ± 1.1 to 21.3 ± 9.2 ng/mL (P = 0.0007) and median serum creatinine increased temporarily from 1.3 (IQR 1.1-1.7) to 2.4 (IQR 2.0-4.6) mg/dL (P = 0.008). By comparison, 8 SOT recipients (6 kidney, 2 liver) hospitalized with community-onset CDI had a mean TAC level of 10.8 ± 2.8 ng/dL during disease compared with 9.2 ± 2.3 ng/mL at baseline (P = 0.07) and had no change in median creatinine. All patients recovered from Cryptosporidium enteritis after receiving various chemotherapeutic regimens. CONCLUSIONS: Cryptosporidiosis should be recognized as an important cause of diarrhea after SOT and is associated with elevated TAC levels and acute kidney injury. Increased TAC levels may reflect altered drug metabolism in the small intestine.

Fatal cross infection by carbapenem-resistant Klebsiella in two liver transplant recipients.

Members of the family Enterobacteriaceae including Klebsiella have re-emerged as major pathogens in solid organ transplantation. The recent appearance and dissemination of carbapenemase-producing Enterobacteriaceae in Europe and the northeastern United States represents a major challenge to the treatment of enteric gram-negative bacterial infections in immunocompromised patients; however, few reports have detailed the outcomes of such infections. Here we report 2 cases of Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella infections in orthotopic liver transplant recipients, which were the index case and initial secondary case for an outbreak of KPC-producing Enterobacteriaceae in our institution. In both instances, the pathogens were initially misidentified as being carbapenem sensitive, the infections recurred after cessation of directed therapy, and the patients ultimately succumbed to their infections.

Pneumonia in solid organ recipients: spectrum of pathogens in 217 episodes.

BACKGROUND: Lower respiratory tract infection (LRTI) remains a leading cause of morbidity and mortality after solid organ transplantation (SOT). PATIENTS AND METHODS: We performed a retrospective analysis of 217 episodes of LRTI in 143 SOT patients from a single center. RESULTS: There were 94 men and 49 women (85% Caucasian) of median age of 51 (range 17-79) years, including 50 renal, 86 liver, 6 pancreas, and 1 lung recipient. Forty patients experienced multiple episodes of LRTI. Median APACHE II score was 17 (range 5-40), median temperature was 38 degrees C (range 35.3 degrees C-40.2 degrees C), and median white blood cell count was 12000 (range 100-106,000). Pneumonia developed at a median of 11 (range 2-191) days after the last surgical intervention. Of the 217 LRTIs, 163 were nosocomial infections (60 ventilator-associated). Overall crude mortality of 21% was increased in patients with multiple episodes of LRTI (25%) and after liver transplantation (33%). In 40 cases, treatment was initiated without identification of a specific pathogen. Overall, 202 microorganisms were found (41 mixed infections): Staphylococcus aureus (n = 32) of which 81% were MRSA; Escherichia coli (n = 9); Klebsiella spp (n = 7); Enterobacter spp (n = 11); Serratia spp (n = 12); Pseudomonas aeruginosa (n = 15); Stenotrophomonas maltophila (n = 15); Acinetobacter spp (n = 9); fungi (n = 18), and viruses (n = 17). CONCLUSION: LRTI remains one of the most common, dangerous infections in transplant recipients with higher mortality than in other populations. MRSA is a particular problem. As a significant number of SOT patients develop multiple episodes of LRTI, a thorough reevaluation of the current guidelines for the treatment of pneumonia is urgently needed.

Group Milleri Streptococci in paediatric infections.

BACKGROUND: Group Milleri Streptococci (GMS), a subgroup of viridans streptococci, are commensals of the human respiratory, gastrointestinal and urogenital tracts. GMS tend to cause purulent infections often resulting in abscess formation. Little is known about the significance of these organisms in children. PATIENTS AND METHODS: For this retrospective study, a collection of 636 GMS positive isolates from 475 patients was used to identify 39 (8.2 %) paediatric patients (age < 18 years) with GMS infections (46 isolates) during a four-year period. RESULTS: There were 19 intra-abdominal, eleven dental/oropharyngeal, seven soft tissue and two central nervous system infections. Thirty-five patients (95 %) underwent primary surgical interventions. Furthermore, two patients - one with GMS meningitis that progressed to cerebral empyema and another with a liver abscess - initially treated with antibiotic agents alone eventually required surgical intervention to cure the infection. Only two children were treated with antibiotics alone. Polymicrobial infection was found in 22 (48 %) isolates; polymicrobial infection was most common in patients with intra-abdominal infection with 74 % and lowest in dental/oropharyngeal patients with 9 % (p = 0.001); Escherichia coli (n = 9) and Bacteroides fragilis (n = 9) were the most common secondary pathogens. Complications due to GMS infections were found in five cases (13 %). No patient died from GMS infection. Preferred antibiotics were penicillins (56 %) and cephalosporins (37 %). GMS tested susceptible to penicillin, cephalosporins, carbapenems in 100 % and clindamycin in 93 %. CONCLUSIONS: GMS infections in paediatric patients usually require both antibiotic therapy and surgical drainage. These infections may become life-threatening if not diagnosed in a timely fashion and treated aggressively.

A simple model host for identifying Gram-positive virulence factors.

We demonstrate the use of the nematode Caenorhabditis elegans as a facile and inexpensive model host for several Gram-positive human bacterial pathogens. Enterococcus faecalis, Streptococcus pneumoniae, and Staphylococcus aureus, but not Bacillus subtilis, Enterococcus faecium, or Streptococcus pyogenes, kill adult C. elegans. Focusing our studies on the enterococcal species, we found that both E. faecalis and E. faecium kill C. elegans eggs and hatchlings, although only E. faecalis kills the adults. In the case of adults, a low inoculum of E. faecalis grows to a high titer in the C. elegans intestine, resulting in a persistent infection that cannot be eradicated by prolonged feeding on E. faecium. Interestingly, a high titer of E. faecium also accumulates in the nematode gut, but does not affect the longevity of the worms. Two E. faecalis virulence-related factors that play an important role in mammalian models of infection, fsr, a putative quorum-sensing system, and cytolysin, are also important for nematode killing. We exploit the apparent parallels between Gram-positive infection in simple and more complex organisms by using the nematode to identify an E. faecalis virulence factor, ScrB, which is relevant to mammalian pathogenesis.

Pyogenic liver abscesses.

Pyogenic liver abscess is a classic clinical entity whose presentation and management have evolved significantly with the advent of potent antimicrobials and the availability of improved diagnostic imaging. The classic triad of fever, upper right quadrant pain or fullness, and jaundice resulting from advanced pylephlebitis is now seldom seen. Despite these changes, pyogenic liver abscess remains an important clinical entity for which prompt recognition and treatment are essential to achieve a favorable outcome. This article discusses the presentation and diagnosis of and current therapy for liver abscesses.

Transfection of Plasmodium falciparum within human red blood cells.

Plasmodium falciparum malaria parasites within human red blood cells (RBCs) have been successfully transfected to produce chloramphenicol acetyltransferase (CAT). Electroporation of parasitized RBCs was used to introduce plasmids that have CAT-encoding DNA flanked by 5' and 3' untranslated sequences of the P. falciparum hsp86, hrp3, and hrp2 genes. These flanking sequences were required for expression as their excision abolished CAT activity in transfected parasites. Transfection signals from native CAT-encoding DNA compared well with those from a synthetic DNA sequence adapted to the P. falciparum major codon bias, demonstrating effective expression of the bacterial sequence despite its use of rare P. falciparum codons. Transfected ring-stage parasites produced CAT signals at least as strong as transfected schizont-stage parasites even though ring stages are surrounded by more RBC cytoplasm than schizonts. The transfection of erythrocyte-stage P. falciparum parasites advances our ability to pursue genetic analysis of this major pathogen.

Amplification of the inosinate dehydrogenase gene in Trypanosoma brucei gambiense due to an increase in chromosome copy number.

Drug resistance is a significant impediment to the therapy of African sleeping sickness in humans. To evaluate molecular mechanisms that contribute to drug resistance in African trypanosomes, a clonal strain of Trypanosoma brucei gambiense, MPA10, was selected in medium containing mycophenolic acid (MPA), an inhibitor of IMP dehydrogenase (IMPDH) activity. IMPDH activity in MPA10 cells was approximately 6-fold higher than that of wild type parental cells, although the enzymes in both strains were equally sensitive to inhibition by MPA. To evaluate the mechanism of IMPDH overexpression in MPA10 cells, the gene encoding IMPDH (impdh) was isolated from a T.b. brucei library by cross-hybridization to the Leishmania donovani impdh. Sequence analysis indicated that the T. brucei IMPDH was 76% identical with the L. donovani IMPDH. The T. brucei impdh hybridized to a 2.7-kb transcript that was expressed at approximately 10-fold greater levels in the MPA10 cells, and this impdh overexpression could be ascribed to an approximately 10-fold amplification of the impdh copy number. Pulsed field gel electrophoresis revealed that the extra impdh copies in MPA10 cells were localized to an approximately 6.0-Mb chromosome that comigrated with the wild type chromosome encompassing impdh. The amplification of impdh could be ascribed to an increased copy number of this 6.0-Mb chromosome, and a predicted augmented DNA content in MPA10 cells was confirmed by flow cytometry. This is the first demonstration that DNA amplification can serve as a molecular mechanism by which T. brucei become resistant to cytotoxic drugs, and the amplification of the 6.0-Mb chromosome represents a novel mechanism of drug resistance in parasitic protozoa.

Cloning and sequence analysis of a Drosophila melanogaster cDNA encoding IMP dehydrogenase.

A cDNA encoding the entire Drosophila melanogaster IMP dehydrogenase (IMPDH) protein was isolated and sequenced. Translation of the impdh cDNA nucleotide sequence indicated that the Drosophila IMPDH exhibited 48% and 65% amino acid identity to the Leishmania donovani and human isoform II counterparts, respectively. Northern analysis revealed that expression of the 2.4 kb impdh transcript was equivalent in adult Drosophila head and body and that impdh expression was developmentally regulated. In situ hybridization of the cloned impdh cDNA probe to Drosophila salivary gland chromosomes indicated that the impdh gene is located at position 9E1-4 on the X chromosome.

Molecular characterization of the ldmdr1 multidrug resistance gene from Leishmania donovani.

The ldmdr1 gene that confers resistance to multiple structurally dissimilar hydrophobic drugs in Leishmania donovani has been isolated within a 5.4-kb XmaI fragment from a genomic library of L. donovani DNA and its protein coding region sequenced. The longest open reading frame within ldmdr1 encodes a 146.5-kDa protein of 1341 amino acids, designated LDMDR1. The primary structure and predicted membrane topology of LDMDR1 indicates that it is a member of the P-glycoprotein superfamily with the greatest homology to the mammalian multidrug resistance P-glycoproteins. A 2.3-kb SalI fragment derived from a second ldmdr1 allele was also cloned from the L. donovani library. Nucleotide sequence analysis of a portion of the SalI insert revealed 5 single base differences from its counterpart within the 5.4-kb XmaI fragment, one of which created a PvuI restriction site polymorphism. Southern blots of PvuI-digested DNA divulged that the amplified ldmdr1 gene copies in a multidrug-resistant L. donovani strain were all derived from the single ldmdr1 allele whose protein coding segment was sequenced in its entirety.

Multidrug resistance in Leishmania donovani is conferred by amplification of a gene homologous to the mammalian mdr1 gene.

Drug resistance is a major impediment to the effective treatment of parasitic diseases. The role of multidrug resistance (mdr) genes and their products in this drug resistance phenomenon, however, remains controversial. In order to determine whether mdr gene amplification and overexpression can be connected to a multidrug resistance phenotype in parasitic protozoa, a mutant strain of Leishmania donovani was generated by virtue of its ability to proliferate in medium containing increasing concentrations of vinblastine. The vinblastine-resistant strain, VINB1000, displayed a cross-resistance to puromycin and the anthracyclines, a growth phenotype that could be attributed to an impaired ability to accumulate the toxic drugs. By using the polymerase chain reaction, two different DNA fragments, LEMDR06 and LEMDRF2, were amplified from leishmanial genomic DNA, and each amplified fragment encoded a product that was significantly homologous to parts of the mammalian P-glycoprotein. In the VINB1000 strain, the mdr gene recognized by the LEMDR06 probe was amplified approximately 50-fold in copy number, whereas the mdr genes that hybridized to LEMDRF2 or to a fragment of the previously characterized ltpgpA gene were not amplified. Moreover, the VINB1000 cell line expressed a LEMDR06 gene transcript of 12.5 kb in size that was not detected in the parental wild-type strain. To furnish a functional test for mdr gene amplification and expression in L. donovani, the L. donovani gene recognized by the LEMDR06 polymerase chain reaction product, ldmdr1, was isolated from a genomic library, transfected into wild-type cells, and amplified over 500-fold by selection in 0.5 mg of G418 per ml. The resulting transfectants were resistant to all drugs to which VINB1000 cells were resistant and sensitive to all drugs to which VINB1000 cells were sensitive. These studies demonstrate that amplification of the ldmdr1 gene either by direct selection or subsequent to transfection can confer a drug-resistant phenotype in parasitic protozoa similar to that observed for MDR mammalian cells.