K. L. McCarthy

Pseudomonas aeruginosa: evolution of antimicrobial resistance and implications for therapy

Pseudomonas aeruginosa is a formidable pathogen in the infection arena. It is able to easily adapt to the environment which it inhabits and can also colonize and invade the human host to cause serious infections. In 2011, it was responsible for 7.1% of all health care-associated infection in the United States. The morbidity and mortality of both blood stream infections and ventilator-associated pneumonia are significant. On a global scale, we have seen the development of not only multidrug resistance but also extensive and pan drug resistance in this organism. This is often associated with limited clonal types of which we now have epidemiological evidence of spread. With this has come reduced antibiotic treatment options. Consideration of antibiotic infusions, combination therapy, and inhalational therapy has occurred in an attempt to gain the upper ground. Gram-negative resistance has appropriately been described as a global emergency.

Molecular epidemiology of Pseudomonas aeruginosa bloodstream infection isolates in a non-outbreak setting

Purpose. The molecular epidemiology of Pseudomonas aeruginosa bloodstream infection (BSI) isolates has received limited attention. This study aims to characterize the molecular relationship of P. aeruginosa BSI isolates in the non‐outbreak setting at a single tertiary healthcare facility. Methodology. P. aeruginosa BSI isolates from patients who were admitted to the Royal Brisbane and Womens Hospital over a 13 month period from November 2009 were identified retrospectively from the Pathology Queensland Clinical and Scientific Information System. The isolates were typed by the iPLEX MassARRAY matrix assisted lazer desorption/isonisation time of flight (MALDI‐TOF) MS genotyping. The DiversiLab automated rapid strain typing platform (bioMérieux) was used to assess the genotypic relationships between study isolates that showed indistinguishable iPLEX20SNP profiles. Clinical data was also collected retrospectively from patient notes. Results. Fifty‐three P. aeruginosa BSI episodes were available for study. Thirty‐five different clones or clonal complexes were identified by the iPLEX MassARRAY MALDI‐TOF MS genotyping. Seventeen BSI isolates with indistinguishable iPLEX20SNP profiles underwent further DiversiLab genotyping and were found to belong to a further 13 different genotypes. There was no relationship between clonality and acquisition type, source of infection or length of stay in the setting of hospital‐acquired infection. Conclusion. The non‐clonal population structure suggests that there is ongoing environmental exposure of inpatients to P. aeruginosa. In clinical areas dealing with at‐risk patients, routine attention to mechanism of environmental colonization is important and should be addressed even in the non‐outbreak setting.The molecular epidemiology of Pseudomonas aeruginosa bloodstream infection (BSI) isolates has received limited attention. This study aims to characterise the molecular relationship of P. aeruginosa bloodstream infection isolates in the non-outbreak setting at a single tertiary healthcare facility. P. aeruginosa BSI isolates from patients who were admitted to the Royal Brisbane and Womens Hospital over a 13 month period from November 2009 were identified retrospectively from the Pathology Queensland Clinical and Scientific Information System. The isolates were typed by iPLEX MassARRAY MALDI-TOF MS genotyping. The Diversilab® automated rapid strain typing platform (bioMérieux Australia Pty Ltd) was used to assess the genotypic relationships between study isolates that showed indistinguishable iPLEX20SNP profiles. Clinical data was also collected retrospectively from patient notes. Fifty three P. aeruginosa BSI episodes were available for study. Thirty five different clones or clonal complexes were identified by iPLEX MassARRAY MALDI-TOF MS genotyping. Seventeen BSI isolates with indistinguishable iPLEX20SNP profiles underwent further Diversilab® genotyping and were found to belong to a further 13 different genotypes. There was no relationship between clonality and acquisition type, source of infection or length of stay in the setting of hospital acquired infection. The non-clonal population structure suggests that there is ongoing environmental exposure of inpatients to P. aeruginosa. In clinical areas dealing with the at risk patient, routine attention to mechanism of environmental colonisation is important and should be addressed even in the non-outbreak setting.

P. aeruginosa blood stream infection isolates: A “full house” of virulence genes in isolates associated with rapid patient death and patient survival

We have recently characterised the epidemiology of P. aeruginosa blood stream infection (BSI) in a large retrospective multicentre cohort study [1]. Utilising corresponding patient BSI isolates we aimed to characterise the genotypic virulence profile of the P. aeruginosa isolates that were associated with rapid death in the non-neutropenic host. Five P. aeruginosa BSI episodes were identified from a larger cohort of P. aeruginosa BSI episodes previously described by McCarthy et al. [1]. The genotypic profile of another 5 isolates from this cohort in whom the non-neutropenic host had survived one year post the BSI was also analysed for comparison. These isolates underwent Illumina whole genome sequencing, de novo assembly and annotation. A comprehensive suite of virulence genes was collated from the Pseudomonas Genome Database (http://www.pseudomonas.com/) and were searched by BLAST based analysis in assemblies of all BSI isolates [2]. There was extensive conservation of virulence genes across all of the BSI isolates studied. The exoU gene was found in two isolates from patients who died rapidly and in one isolate from a patient that survived one year post BSI. The higA and higB genes were detected in all isolates. The exlA gene was not detected in any of the isolates studied. These findings suggest that to cause a BSI that it is only the virulent P. aeruginosa isolate that succeeds. The virulence gene profile seen was independent of patient outcome. Further phenotypic correlation is required to determine if there is any difference in genotypic expression by the BSI isolates that were associated with rapid death of the host and those BSI isolates associated with host survival at one year.

Increased risk of death with recurrent Pseudomonas aeruginosa bacteremia

This study aimed to characterize recurrent Pseudomonas aeruginosa blood stream infection (BSI). Positive blood cultures for P. aeruginosa were identified over a 3-year period from seven tertiary care hospitals. Patients with recurrent BSI were identified. Extensive epidemiological, clinical and outcome data were obtained. BSI recurrence was found to be uncommon with 9% of patients having a first relapse of BSI. Fourteen percent of these patients went on to have a second relapse of BSI. Significant variables associated with recurrence were the presence of a hematological malignancy or receiving recent corticosteroid therapy. Exposure to anti-pseudomonal beta-lactam therapy in the 30days prior to the BSI was more likely in the patient with the recurrent BSI episode. Recurrence was associated with increased mortality when compared to the primary BSI episode. Knowledge of a patients prior antibiotic therapy may be useful in ensuring effective empirical therapy in the recurrent BSI episode.

Detection of carbapenemase activity in Enterobacteriaceae using LC-MS/MS in comparison with the neo-rapid CARB kit using direct visual assessment and colorimetry

It has been described that the sensitivity of the Carba NP test may be low in the case of OXA-48-like carbapenamases and mass spectrometry based methods as well as a colorimetry based method have been described as alternatives. We evaluated 84 Enterobacteriaceae isolates including 31 OXA-48-like producing isolates and 13 isolates that produced either an imipenemase (IMP; n=8), New Delhi metallo-β-lactamase (NDM; n=3), or Klebsiella pneumoniae carbapenemase (KPC; n=2), as well as 40 carbapenemase negative Enterobacteriaceae isolates. We used the Neo-Rapid CARB kit, assessing the results with the unaided eye and compared it with a colorimetric approach. Furthermore, we incubated the isolates in growth media with meropenem and measured the remaining meropenem after one and 2h of incubation, respectively, using liquid chromatography tandem mass spectrometry (LC-MS/MS). Whilst all carbapenemase producing isolates with the exception of the OXA-244 producer tested positive for both the Neo-rapid CARB test using the unaided eye or colorimetry, and the 13 isolates producing either IMP, NDM or KPC hydrolysed the meropenem in the media almost completely after 2h of incubation, the 31 OXA-48-like producing isolates exhibited very variable hydrolytic activity when incubated in growth media with meropenem. In our study, the Neo-Rapid CARB test yielded a sensitivity of 98% for both the traditional and the colorimetric approach with a specificity of 95% and 100% respectively. Our results indicate that the Neo-Rapid CARB test may have use for the detection of OXA-48 type carbapenemases and that it may be particularly important to ensure bacterial lysis for the detection of these weaker hydrolysers.

Draft genome sequences of two Pseudomonas aeruginosa bloodstream infection isolates associated with rapid patient death

ABSTRACT The morbidity and mortality associated with Pseudomonas aeruginosa bloodstream infections are significant. New strategies are required to treat such infections. We report here the draft genome sequences of two antibiotic-sensitive P. aeruginosa bloodstream infection isolates that were associated with rapid death in nonneutropenic patients.

Draft Genome Sequence of an IMP-7-Producing Pseudomonas aeruginosa Bloodstream Infection Isolate from Australia

ABSTRACT IMP-7 is one of the two IMP-type carbapenemases that in Pseudomonas aeruginosa are not limited to a geographic area, but it has not been previously reported in the Australian setting. We report here the draft genome sequence of an Australian P. aeruginosa bloodstream infection isolate that contains IMP-7.

Community-acquired Pseudomonas aeruginosa bloodstream infection: a classification that should not falsely reassure the clinician

Pseudomonas aeruginosa bloodstream infection (BSI) is predominantly acquired in the hospital setting. Community-onset infection is less common. Differences in epidemiology, clinical features, microbiological factors and BSI outcomes led to the separation of bacterial community-onset BSI into the categories of healthcare-associated infection (HCAI) and community-acquired infection (CAI). Community-acquired P. aeruginosa BSI epidemiology is not well defined in the literature. In addition, it is also not clear if the same factors separate CAI and HCAI BSI caused by P. aeruginosa alone. A retrospective multicentre cohort study was performed looking at P. aeruginosa BSI from January 2008 to January 2011. Strict definitions for HCAI and CAI were applied. Extensive epidemiological, clinical and outcome data were obtained. Thirty-four CAI episodes and 156 HCAI episodes were analysed. The CAI group could be characterised into seven distinct categories based on comorbidities and clinically suspected source of infection. A pre-morbidly healthy group could not be identified. On multivariate analysis, the presence of a rheumatological or a gastrointestinal comorbidity were significantly associated with CAI. There was no significant difference in length of stay or rates of mortality between HCAI or CAI. The clinician should not be falsely reassured regarding outcome by the diagnosis of a community-acquired P. aeruginosa BSI.

Pseudomonas aeruginosa blood stream infection isolates from patients with recurrent blood stream infection: is it the same genotype?

The type identity of strains of Pseudomonas aeruginosa from primary and recurrent blood stream infection (BSI) has not been widely studied. Twenty-eight patients were identified retrospectively from 2008 to 2013 from five different laboratories; available epidemiological, clinical and microbiological data were obtained for each patient. Isolates were genotyped by iPLEX MassARRAY MALDI-TOF MS and rep-PCR. This showed that recurrent P. aeruginosa BSI was more commonly due to the same genotypically related strain as that from the primary episode. Relapse due to a genotypically related strain occurred earlier in time than a relapsing infection from an unrelated strain (median time: 26 vs. 91 days, respectively). Line related infections were the most common source of suspected BSI and almost half of all BSI episodes were associated with neutropenia, possibly indicating translocation of the organism from the patients gut in this setting. Development of meropenem resistance occurred in two relapse isolates, which may suggest that prior antibiotic therapy for the primary BSI was a driver for the subsequent development of resistance in the recurrent isolate.