Epidemiology and infection control of vancomycin-resistant enterococci at a German university hospital: A three-year retrospective cohort study.

Vancomycin-resistant enterococci (VRE) occur in hospitalized patients, causing both infection and colonization. In recent years, there has been an increase in VRE in German and other hospitals, raising the question of how to control this epidemic best. To better understand the specific epidemiology and to guide infection control, we conducted a retrospective cohort study analyzing all patients with VRE at Hannover Medical School, a tertiary university clinic in Germany that specializes in solid organ transplantation. Epidemiologic and clinical characteristics of patients with VRE from 2015-2017 were collected. Basic epidemiologic parameters, including VRE incidence and incidence density, were calculated. Independent risk factors for nosocomial VRE infection compared to colonization were assessed using a logistic regression model. There were 1,492 VRE cases corresponding to 822 individual patients. The incidence was 0.8 VRE cases per 100 cases. A total of 536 (35.9%) of the 1,492 VRE cases were acquired nosocomially. Of the 1,492 cases, 912 cases had VRE-positive samples (894 Enterococcus (E.) faecium and 18 E. faecalis) in our hospital laboratory and the remaining cases were known VRE carriers. The vanB-phenotype was observed in 369 of the 894 (41.3%) E. faecium isolates and in 6 of the 18 (33.3%) E. faecalis isolates. There was an increase over time in the vanB-phenotype proportion in E. faecium (2015: 63 of 171, 36.8%, 2016: 115 of 322, 35.7% and 2017: 191 of 401, 47.6%). A total of 107 cases had a VRE infection (7.2% of all VRE cases) according to the criteria of the German National Reference Center for Surveillance of Nosocomial Infections. The remaining cases were only colonized. Among other factors, leukocytopenia (<1,000/µL), the use of a central venous catheter and the visceral surgery medical specialty were independently associated with nosocomial VRE infection. VRE imposed a relevant and increasing infection control burden at our hospital. Nosocomial VRE infection was predominantly found in certain medical specialties, such as hematology and oncology and visceral surgery. Infection control efforts should focus on these highly affected patient groups/specialties.

Epidemiology and infection control of Methicillin-resistant Staphylococcus aureus in a German tertiary neonatal intensive and intermediate care unit: A retrospective study (2013-2020).

In preterm and term infants who require intermediate or intensive care Methicillin-resistant Staphylococcus aureus (MRSA) infection can lead to significant morbidity. In this study MRSA colonization and infection were assessed in a mixed tertiary neonatal intensive and intermediate care unit in Germany over an 8-year period (2013-2020). We investigated patient-related factors, associated with nosocomial MRSA acquisition, and we discuss our infection control concept for MRSA. Of 3488 patients treated during the study period, 24 were MRSA positive patients, corresponding to 26 patient hospital stays. The incidence was 0.7 MRSA patients per 100 patients. The incidence density was 0.4 MRSA patient hospital stays per 1000 patient days. Twelve patients (50%) acquired MRSA in the hospital. One patient developed a hospital acquired MRSA bloodstream infection 9 days after birth (i.e., 0.03% of all patients on the ward during the study period). A total of 122 patients had to be screened to detect one MRSA positive patient. In a logistic regression model, the use of 3rd generation intravenous cephalosporin (cefotaxim) was associated with nosocomial MRSA acquisition compared with matched control patients who did not acquire MRSA. In sum, the burden of MRSA colonization and infection in the ward was low during the study period. A comprehensive infection control concept that included microbiologic colonization screening, prospective infection surveillance together with isolation and emphasis on basic hygiene measures is essential to handle MRSA in this specialized setting.

Target capture sequencing reveals a monoclonal outbreak of respiratory syncytial virus B infections among adult hematologic patients.

BACKGROUND: Respiratory syncytial virus (RSV) causes community-acquired respiratory tract infections during winter. However, outbreaks in hospitals also occur repeatedly. In particular, patients with hematologic malignancies are at an increased risk for a severe and potentially fatal course of RSV infection. Here we present the investigation of an RSV outbreak in a hematology ward for adults following the ORION statement. METHODS: An epidemiologic and molecular outbreak analysis was performed. We developed and employed a minimal oligonucleotide probe set in target capture probe sequencing that allows cost-effective RSV-A or -B capturing to reconstruct RSV genomes from clinical samples. RESULTS: Four adult patients were involved in the outbreak caused by RSV-B in March 2019. The enforcement of the pre-existing infection control measures by effective training of hospital staff contributed to a successful containment. PCR-based RSV screening on the ward enabled early detection of new cases and rapid isolation measures. The molecular analysis demonstrated that the outbreak sequences were highly related and distinct to other RSV-B strains circulating at the same time. CONCLUSIONS: A multimodal infection control concept is essential for the timely detection and control of RSV outbreaks in patients with hematological disease. Among other measures, preventive screening for respiratory viruses is recommended. Furthermore, the integration of conventional and molecular epidemiology, such as whole-genome sequencing and variant calling, significantly contributes to the understanding of transmission pathways. Based on this, appropriate conclusions can be drawn for targeted prevention measures that have prepared us for the COVID-19 pandemic beyond the RSV approach described here.

Epidemiology and infection control of carbapenem resistant Acinetobacter baumannii and Klebsiella pneumoniae at a German university hospital: a retrospective study of 5 years (2015-2019).

BACKGROUND: Carbapenem resistant (CR) Klebsiella pneumoniae (Kp) and Acinetobacter baumannii (Ab) are emerging multidrug resistant bacteria with very limited treatment options in case of infection. Both are well-known causes of nosocomial infections and outbreaks in healthcare facilities. METHODS: A retrospective study was conducted to investigate the epidemiology of inpatients with CR Kp and CR Ab in a 1500-bed German university hospital from 2015 to 2019. We present our infection control concept including a weekly microbiologic screening for patients who shared the ward with a CR Kp or CR Ab index patient. RESULTS: Within 5 years, 141 CR Kp and 60 CR Ab cases were hospitalized corresponding to 118 unique patients (74 patients with CR Kp, 39 patients with CR Ab and 5 patients with both CR Ab and CR Kp). The mean incidence was 0.045 (CR Kp) and 0.019 (CR Ab) per 100 inpatient cases, respectively. Nosocomial acquisition occurred in 53 cases (37.6%) of the CR Kp group and in 12 cases (20.0%) of the CR Ab group. Clinical infection occurred in 24 cases (17.0%) of the CR Kp group and in 21 cases (35.0%) of the CR Ab group. 14 cases (9.9%) of the CR Kp group and 29 cases (48.3%) of the CR Ab group had a history of a hospital stay abroad within 12 months prior to admission to our hospital. The weekly microbiologic screening revealed 4 CR Kp cases caused by nosocomial transmission that would have been missed without repetitive screening. CONCLUSIONS: CR Kp and CR Ab cases occurred infrequently. A history of a hospital stay abroad, particularly in the CR Ab group, warrants pre-emptive infection control measures. The weekly microbiologic screening needs further evaluation in terms of its efficiency.

Detection of Serratia marcescens in neonatal intensive care units requires a rapid and comprehensive infection control response starting with the very first case.

Background: Serratia marcescens is a well-known and challenging pathogen in neonatal intensive care units. It is responsible for severe infections and can cause nosocomial outbreaks. Methods: We present the infection control response to a Serratia marcescens cluster which occurred in a tertiary neonatal intensive care unit. Results and conclusions: The presented comprehensive and decisive hygiene management response starting with the very first case aims especially at early detection and immediate interruption of nosocomial transmission. Frequent and sensitive microbiological screening, rigorous spatial isolation of colonized infants, and reinforcing adherence to hand hygiene are essential in this response, which comprises eight measures. It prevented a full-blown outbreak.

Epidemiologic and Molecular Investigation of a MRSA Outbreak Caused by a Contaminated Bathtub for Carbon Dioxide Hydrotherapy and Review of the Literature.

METHODS: We conducted an outbreak investigation and performed a molecular typing of the outbreak strains with pulsed-field gel electrophoresis (PFGE). In addition, we reviewed PubMed and the Outbreak Database for MRSA outbreaks related to hydrotherapy or other bathing activities. RESULTS: Four patients acquired nosocomial MRSA during the 4-week outbreak period. Environmental sampling revealed the presence of MRSA in the bathtub used for hydrotherapy. The environmental and the patients' isolates showed an indistinguishable restriction pattern in the PFGE. Subsequent discontinuation of bathing stopped the outbreak. The literature search found 9 MRSA outbreak reports related to bathing activities or hydrotherapy. CONCLUSION: The epidemiologic outbreak investigation together with the molecular findings suggests monoclonal spread of MRSA due to surface contamination of the bathtub. After enhancing the disinfection and cleaning process accompanied by staff training with respect to hand hygiene, no further cases occurred. Standardized and best practice cleaning and disinfection protocols are crucial, especially in critical facilities such as hydrotherapy units. Regular environmental sampling is helpful to monitor these processes and to detect potential contamination.

Prospective infection surveillance and systematic screening for vancomycin-resistant enterococci in hematologic and oncologic patients - findings of a German tertiary care center.

INTRODUCTION: Vancomycin-resistant enterococci (VRE) are emerging multidrug-resistant bacteria. They can cause serious nosocomial infections, especially in immunocompromised patients. OBJECTIVES AND METHODS: In this study, we aimed to determine the burden of intestinal VRE colonization and clinically relevant infection in adult hematologic and oncologic patients at a tertiary care clinic in Germany based on prospective infection surveillance and an active screening program. RESULTS: In a 12 month period, 132 of 555 patients had intestinal VRE-colonization (23.8%) and four patients (0.7% of the entire cohort, and 3.0% of those colonized with VRE) developed a nosocomial infection with VRE. CONCLUSIONS: The prospective surveillance and active screening for VRE was very useful to determine the true ratio of intestinal colonization to infection and thus helps to shape infection control management.

Infection control management and surveillance of carbapenem-resistant Gram-negative bacteria in hematopoietic stem cell recipients.

Hematopoietic stem cell transplantation (HSCT) is a curative treatment option for selected diseases of the hematopoietic system. In the context of HSCT, bloodstream infections caused by Gram-negative bacteria (GNB) significantly contribute to morbidity and mortality. Antibiotic treatment of bloodstream infections with carbapenem-resistant (CR) GNB presents a particular challenge. As a part of our infection control management, the admission of a patient who was known to be colonized with a CR Acinetobacter baumannii triggered an active weekly screening of all patients to determine the prevalence and potential transmission of CR GNB and CR Acinetobacter baumannii in particular. Over a 3 month period a total of 71 patients were regularly screened for colonization with CR GNB. Including the index patient, a total of three patients showed CR GNB colonization representing a prevalence of 4.2%. Nosocomial transmission of CR Acinetobacter baumannii or other CR GNB was not observed. However, the index patient developed a subsequent bloodstream infection with the CR Acinetobacter baumannii, therefore empiric antibiotic therapy based on the known resistance profile was initiated. A weekly prevalence screening for CR GNB might be an effective monitoring tool for potential transmission, may enhance existing infection control management concepts and may support the decision making for empiric antibiotic therapy.

Influenza and respiratory syncytial virus screening for the detection of asymptomatically infected patients in hematology and oncology.

Introduction: Respiratory syncytial virus (RSV) and influenza virus infections are a significant healthcare risk for immunocompromised patients. In addition to community onset, nosocomial acquisition and transmission may also occur. Detection of asymptomatic shedders (e.g., patients in the incubation period or immunosuppressed long term shedders) facilitates control of nosocomial transmission. Methods: To strengthen the existing infection control concept, a PCR-based screening for RSV and influenza virus was implemented for all patients lacking respiratory symptoms (asymptomatic patients) who were hospitalized on an adult and a pediatric hemato-oncological ward. Laboratory results of this screening were analyzed retrospectively. Results: 665 respiratory specimens were obtained for screening from 251 patients (26% were 18 years and younger) from December 2016 to April 2017. In 23 patients without respiratory symptoms, either influenza virus or RSV infection was found, resulting in a detection rate of about 9%. In 6 patients, the infection was presumably detected during the incubation period, because an increase of viral load was observed in subsequent specimens. Positive screening results facilitated timely implementation of adequate infection control precautions. Nosocomial clusters of RSV or influenza were not detected during the screening period on the two wards. Conclusion: The seasonal screening program expanded our existing infection control concept in terms of patients lacking respiratory symptoms who shed influenza virus or RSV. It enabled us to identify 23 RSV or influenza infections in patients lacking respiratory symptoms in a 4-month period and thus to rapidly take isolation precautions.

Author Correction: Lactate oxidation facilitates growth of Mycobacterium tuberculosis in human macrophages.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

Molecular characteristics and successful management of a respiratory syncytial virus outbreak among pediatric patients with hemato-oncological disease.

Background: Respiratory syncytial virus (RSV) is responsible for upper and lower respiratory tract infection in adults and children. Especially immunocompromised patients are at high risk for a severe course of infection, and mortality is increased. Moreover RSV can spread in healthcare settings and can cause outbreaks. Herein we demonstrate the successful control and characteristics of a RSV outbreak that included 8 patients in our Department of Pediatric Hematology and Oncology. Methods: We performed an epidemiologic investigation and a molecular analysis of the outbreak strains. Moreover we present the outbreak control bundle and our concept for RSV screening in the winter season. Results: RSV A and B strains caused the outbreak. RSV B strains affected 3 patients, 2 of whom were co-infected with RSV A. Exactly this RSV A strain was detected in another 5 patients. Our multimodal infection control bundle including prophylactic RSV screening was able to rapidly stop the outbreak. Conclusion: An infection control bundle in RSV outbreaks should address all potential transmission pathways. In pediatric settings the restriction of social activities might have a temporal negative impact on quality of life but helps to limit transmission opportunities. Molecular analysis allows better understanding of RSV outbreaks and, if done in a timely manner, might be helpful for guidance of infection control measures.

Economic burden of nosocomial infections caused by vancomycin-resistant enterococci.

Background: Nosocomial infections due to vancomycin-resistant enterococci (VRE) have become a major problem during the last years. The purpose of this study was to investigate the economic burden of nosocomial VRE infections in a European university hospital. Methods: A retrospective matched case-control study was performed including patients who acquired nosocomial infection with either VRE or vancomycin-susceptible enterococci (VSE) within a time period of 3 years. 42 cases with VRE infections and 42 controls with VSE infections were matched for age, gender, admission and discharge within the same year, time at risk for infection, Charlson comorbidity index (±1), stay on intensive care units and non-intensive care units as well as for the type of infection, using criteria of the Centers for Disease Control and Prevention. Results: The median overall costs per case were significantly higher than for controls (EUR 57,675 vs. EUR 38,344; p = 0.030). Costs were similar between cases and controls before onset of infection (EUR 17,893 vs. EUR 16,600; p = 0.386), but higher after onset of infection (EUR 37,971 vs. EUR 23,025; p = 0.049). The median attributable costs per case for vancomycin-resistance were EUR 13,157 (p = 0.036). The most significant differences in costs between cases and controls turned out to be for pharmaceuticals (EUR 6030 vs. EUR 2801; p = 0.008) followed by nursing staff (EUR 8956 vs. EUR 4621; p = 0.032), medical products (EUR 3312 vs. EUR 1838; p = 0.020), and for assistant medical technicians (EUR 3766 vs. EUR 2474; p = 0.023). Furthermore, multivariate analysis revealed that costs were driven independently by vancomycin-resistance (1.4 fold; p = 0.034). Conclusions: This analysis suggested that nosocomial VRE infections significantly increases hospital costs compared with VSE infections. Therefore, hospital personal should implement control measures to prevent VRE transmission.

Hematopoietic stem cell gene therapy for IFNγR1 deficiency protects mice from mycobacterial infections.

Mendelian susceptibility to mycobacterial disease is a rare primary immunodeficiency characterized by severe infections caused by weakly virulent mycobacteria. Biallelic null mutations in genes encoding interferon gamma receptor 1 or 2 (IFNGR1 or IFNGR2) result in a life-threatening disease phenotype in early childhood. Recombinant interferon γ (IFN-γ) therapy is inefficient, and hematopoietic stem cell transplantation has a poor prognosis. Thus, we developed a hematopoietic stem cell (HSC) gene therapy approach using lentiviral vectors that express Ifnγr1 either constitutively or myeloid specifically. Transduction of mouse Ifnγr1-/- HSCs led to stable IFNγR1 expression on macrophages, which rescued their cellular responses to IFN-γ. As a consequence, genetically corrected HSC-derived macrophages were able to suppress T-cell activation and showed restored antimycobacterial activity against Mycobacterium avium and Mycobacterium bovis Bacille Calmette-Guérin (BCG) in vitro. Transplantation of genetically corrected HSCs into Ifnγr1-/- mice before BCG infection prevented manifestations of severe BCG disease and maintained lung and spleen organ integrity, which was accompanied by a reduced mycobacterial burden in lung and spleen and a prolonged overall survival in animals that received a transplant. In summary, we demonstrate an HSC-based gene therapy approach for IFNγR1 deficiency, which protects mice from severe mycobacterial infections, thereby laying the foundation for a new therapeutic intervention in corresponding human patients.

Horizontal acquisition of a hypoxia-responsive molybdenum cofactor biosynthesis pathway contributed to Mycobacterium tuberculosis pathoadaptation.

The unique ability of the tuberculosis (TB) bacillus, Mycobacterium tuberculosis, to persist for long periods of time in lung hypoxic lesions chiefly contributes to the global burden of latent TB. We and others previously reported that the M. tuberculosis ancestor underwent massive episodes of horizontal gene transfer (HGT), mostly from environmental species. Here, we sought to explore whether such ancient HGT played a part in M. tuberculosis evolution towards pathogenicity. We were interested by a HGT-acquired M. tuberculosis-specific gene set, namely moaA1-D1, which is involved in the biosynthesis of the molybdenum cofactor. Horizontal acquisition of this gene set was striking because homologues of these moa genes are present all across the Mycobacterium genus, including in M. tuberculosis. Here, we discovered that, unlike their paralogues, the moaA1-D1 genes are strongly induced under hypoxia. In vitro, a M. tuberculosis moaA1-D1-null mutant has an impaired ability to respire nitrate, to enter dormancy and to survive in oxygen-limiting conditions. Conversely, heterologous expression of moaA1-D1 in the phylogenetically closest non-TB mycobacterium, Mycobacterium kansasii, which lacks these genes, improves its capacity to respire nitrate and grants it with a marked ability to survive oxygen depletion. In vivo, the M. tuberculosis moaA1-D1-null mutant shows impaired survival in hypoxic granulomas in C3HeB/FeJ mice, but not in normoxic lesions in C57BL/6 animals. Collectively, our results identify a novel pathway required for M. tuberculosis resistance to host-imposed stress, namely hypoxia, and provide evidence that ancient HGT bolstered M. tuberculosis evolution from an environmental species towards a pervasive human-adapted pathogen.

The transcriptional regulator LysG (Rv1985c) of Mycobacterium tuberculosis activates lysE (Rv1986) in a lysine-dependent manner.

The Mycobacterium tuberculosis protein encoded by the Rv1986 gene is a target for memory T cells in patients with tuberculosis, and shows strong similarities to a lysine exporter LysE of Corynebacterium glutamicum. During infection, the pathogen Mycobacterium tuberculosis adapts its metabolism to environmental changes. In this study, we found that the expression of Rv1986 is controlled by Rv1985c. Rv1985c is located directly upstream of Rv1986 with an overlapping promoter region between both genes. Semiquantitative reverse transcription PCR using an isogenic mutant of Mycobacterium tuberculosis lacking Rv1985c showed that in the presence of lysine, Rv1985c protein positively upregulated the expression of Rv1986. RNA sequencing revealed the transcription start points for both transcripts and overlapping promoters. An inverted repeat in the center of the intergenic region was identified, and binding of Rv1985c protein to the intergenic region was confirmed by electrophoretic mobility shift assays. Whole transcriptome expression analysis and RNAsequencing showed downregulated transcription of ppsBCD in the Rv1985c-mutant compared to the wild type strain. Taken together, our findings characterize the regulatory network of Rv1985c in Mycobacterium tuberculosis. Due to their similarity of an orthologous gene pair in Corynebacterium glutamicum, we suggest to rename Rv1985c to lysG(Mt), and Rv1986 to lysE(Mt).

Lactate oxidation facilitates growth of Mycobacterium tuberculosis in human macrophages.

Mycobacterium tuberculosis (Mtb) uses alveolar macrophages as primary host cells during infection. In response to an infection, macrophages switch from pyruvate oxidation to reduction of pyruvate into lactate. Lactate might present an additional carbon substrate for Mtb. Here, we demonstrate that Mtb can utilize L-lactate as sole carbon source for in vitro growth. Lactate conversion is strictly dependent on one of two potential L-lactate dehydrogenases. A knock-out mutant lacking lldD2 (Rv1872c) was unable to utilize L-lactate. In contrast, the lldD1 (Rv0694) knock-out strain was not affected in growth on lactate and retained full enzymatic activity. On the basis of labelling experiments using [U-13C3]-L-lactate as a tracer the efficient uptake of lactate by Mtb and its conversion into pyruvate could be demonstrated. Moreover, carbon flux from lactate into the TCA cycle, and through gluconeogenesis was observed. Gluconeogenesis during lactate consumption depended on the phosphoenolpyruvate carboxykinase, a key enzyme for intracellular survival, showing that lactate utilization requires essential metabolic pathways. We observed that the ΔlldD2 mutant was impaired in replication in human macrophages, indicating a critical role for lactate oxidation during intracellular growth.

Systemic complement activation and complement gene analysis in enterohaemorrhagic Escherichia coli-associated paediatric haemolytic uraemic syndrome.

BACKGROUND: In contrast to atypical haemolytic uraemic syndrome (aHUS), only single case reports and limited data have been published on systemic activation of the complement system and mutations in complement genes in paediatric enterohaemorrhagic Escherichia coli-induced HUS (EHEC-HUS). METHODS: Complement activation (CH50, APH50, C3d, sC5b-9) was analysed at four timepoints (Week 1, Week 2, Month 3 and Month 6 after primary diagnosis of HUS) in 25 children with EHEC-HUS. Seven patients received the complement C5 inhibitor eculizumab. Targeted next generation sequencing for a total of 89 genes involved in complement regulation and coagulation and haemostasis was performed in all patients. RESULTS: Activity of classical (CH50) and alternative (APH50) complement pathways was normal or even elevated throughout the observation time, except for patients under eculizumab treatment. In contrast, the mean concentration of the soluble terminal complement complex (sC5b-9) was significantly elevated at the first timepoint (mean 498 ng/mL), dropping to normal values after 2 weeks. Initially elevated (42 mU/L) median C3d concentration reached normal levels from Week 2. Levels of sC5b-9 >320 ng/mL at the time of HUS diagnosis were associated with arterial hypertension, oedema and lower platelet counts, but not with the duration of dialysis. Genetic analysis revealed various changes that may have had a modifying impact on the clinical course. CONCLUSIONS: Complement activation at the acute phase of EHEC-HUS, indicated by increased levels of sC5b-9, predicts a poor outcome. Complement alterations appear to be more frequent in patients with EHEC-HUS than previously thought and are suspected to have a role in the severity of the disease.

GenoType NTM-DR for Identifying Mycobacterium abscessus Subspecies and Determining Molecular Resistance.

We studied the performance of a new line probe assay for identifying the subspecies and determining the macrolide and aminoglycoside resistance levels of 50 Mycobacterium abscessus isolates. Agreement of GenoType NTM-DR results with sequencing and phenotypic resistance results was 92% for subspecies identification and 98% for determining molecular and phenotypic resistance.

Principal component analysis of MALDI TOF MS mass spectra separates M. abscessus (sensu stricto) from M. massiliense isolates.

BACKGROUND: The discrimination of the members of the Mycobacterium abscessus complex is of clinical interest because one of the subspecies, M. massiliense, exhibits higher rates of response to antibiotic treatment for lung infection than do the other members of that complex. M. abscessus complex contains three subspecies that are laborious to identify; therefore, a routine diagnostic tool would be worthwhile. RESULTS: We used principal component analysis, hierarchical cluster analysis, and single-peak analysis to examine peak lists derived from matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI TOF MS) mass spectra of 50 clinical M. abscessus complex isolates, including 28 M. abscessus (sensu stricto), 19 M. massiliense, and 3 M. bolletii isolates grown in mycobacterium growth indicator tube liquid medium and prepared with a bead-based protocol. Principal component analysis but not hierarchical cluster analysis separated M. abscessus (sensu stricto) isolates and M. massiliense isolates into two clusters. Furthermore, single-peak analysis displayed 4 discriminating peaks that separated M. abscessus (sensu stricto) from M. massiliense isolates. M. bolletii isolates did not exhibit specific peaks but resembled the M. abscessus (sensu stricto) peak profile and also grouped within this principal component analysis cluster. Principal component analysis of all peak lists with the exclusion of the four discriminating peaks again separated M. abscessus (sensu stricto) from M. massiliense isolates, thus relativizing the importance of these peaks for subspecies identification. CONCLUSIONS: Principal component analysis of peak lists derived from MALDI TOF mass spectra is a robust and convenient method of discriminating M. massiliense isolates from the other members of the M. abscessus complex.