PmrB mutations promote polymyxin resistance of Pseudomonas aeruginosa isolated from colistin-treated cystic fibrosis patients.

Pseudomonas aeruginosa can develop resistance to polymyxin and other cationic antimicrobial peptides. Previous work has shown that mutations in the PmrAB and PhoPQ regulatory systems can confer low to moderate levels of colistin (polymyxin E) resistance in laboratory strains and clinical isolates of this organism (MICs of 8 to 64 mg/liter). To explore the role of PmrAB in high-level clinical polymyxin resistance, P. aeruginosa isolates from chronically colistin-treated cystic fibrosis patients, most with colistin MICs of >512 mg/liter, were analyzed. These cystic fibrosis isolates contained probable gain-of-function pmrB alleles that conferred polymyxin resistance to strains with a wild-type or pmrAB deletion background. Double mutant pmrB alleles that contained mutations in both the periplasmic and dimerization-phosphotransferase domains markedly augmented polymyxin resistance. Expression of mutant pmrB alleles induced transcription from the promoter of the arnB operon and stimulated addition of 4-amino-l-arabinose to lipid A, consistent with the known role of this lipid A modification in polymyxin resistance. For some highly polymyxin-resistant clinical isolates, repeated passage without antibiotic selection pressure resulted in loss of resistance, suggesting that secondary suppressors occur at a relatively high frequency and account for the instability of this phenotype. These results indicate that pmrB gain-of-function mutations can contribute to high-level polymyxin resistance in clinical strains of P. aeruginosa.

Regimens for eradicating early Pseudomonas aeruginosa infection in children do not promote antibiotic resistance in this organism.

BACKGROUND: This study was designed to address the concern that intensive regimens to eradicate early Pseudomonas aeruginosa infection in patients with cystic fibrosis may lead to the emergence of antibiotic-resistant isolates. METHODS: Data was analysed retrospectively over a 10 year period at the Leeds Regional Paediatric Cystic Fibrosis Centre. All patients with first-ever isolation of P. aeruginosa who successfully completed an eradication regimen were included. Antibiotic sensitivities of P. aeruginosa were compared between initial and subsequent re-isolations in patients where eradication was successful and in those where treatment had failed. RESULTS: Forty one patients with first acquisitions for P. aeruginosa and who completed eradication treatment were identified. Eradication treatments consisted of oral, intravenous, nebulised antibiotics or a combination of these. The antibiotic sensitivity of P. aeruginosa in first growths was high and remained so on subsequent re-isolations. A repeated measures logistic model found no significant difference with time of isolation. There was no statistically significant difference in antibiotic sensitivity between P. aeruginosa isolated after successful and failed eradication. CONCLUSIONS: Repeated intensive regimens for P. aeruginosa eradication did not result in a significant increase in overall antibiotic resistance between initial and subsequent growths of this organism over the period of this study.

Clinical impact of reducing routine susceptibility testing in chronic Pseudomonas aeruginosa infections in cystic fibrosis.

BACKGROUND Susceptibility testing results are not predictive of clinical response to antibiotic therapy in chronic Pseudomonas aeruginosa infections in cystic fibrosis (CF). We assessed the impact of reducing the number of routine susceptibility tests performed on clinical outcome in these cases. METHODS In June 2006, we introduced a protocol whereby susceptibility tests of P. aeruginosa isolates obtained from respiratory samples of people with CF were limited to those taken at the commencement of antibiotic therapy, when there was evidence of clinical failure or routinely if not tested in the previous 3 months. At all other times, isolates were identified and reported as normal but P. aeruginosa isolates were not subjected to susceptibility testing. RESULTS Over a 6 month period, P. aeruginosa was isolated on at least one occasion from 193 patients attending the Adult Cystic Fibrosis Unit. In this period, we reduced the number of routine susceptibility tests by 56% (from a projected 2231 tests on 872 samples to an actual 972 tests on 427 samples). We assessed the response to courses of intravenous antibiotic treatment administered during the 6 month study period in 2006 and for courses administered in the same patients during the same calendar months in 2005. No significant differences in median change of FEV1, FVC, C-reactive protein (CRP), white cell count, weight or duration of intravenous antibiotics were observed. The projected savings of this intervention were 3500 euros in consumables and 170 h (costed at 6500 euros) of laboratory staff time per annum, a total annual saving of 10,000 euros (6500 pounds sterling). CONCLUSIONS For CF units sending regular, routine sputum samples, a reduction in the number of susceptibility tests performed in cases of chronic P. aeruginosa infection can be carried out without impacting on short-term clinical outcomes.

A laminar flow model of aerosol survival of epidemic and non-epidemic strains of Pseudomonas aeruginosa isolated from people with cystic fibrosis.

BACKGROUND: Cystic fibrosis (CF) is an inherited multi-system disorder characterised by chronic airway infection with pathogens such as Pseudomonas aeruginosa. Acquisition of P. aeruginosa by patients with CF is usually from the environment, but recent studies have demonstrated patient to patient transmission of certain epidemic strains, possibly via an airborne route. This study was designed to examine the survival of P. aeruginosa within artificially generated aerosols. RESULTS: Survival was effected by the solution used for aerosol generation. Within the aerosols it was adversely affected by an increase in air temperature. Both epidemic and non-epidemic strains of P. aeruginosa were able to survive within the aerosols, but strains expressing a mucoid phenotype had a survival advantage. CONCLUSION: This would suggest that segregating individuals free of P. aeruginosa from those with chronic P. aeruginosa infection who are more likely to be infected with mucoid strains may help reduce the risk of cross-infection. Environmental factors also appear to influence bacterial survival. Warming and drying the air within clinical areas and avoidance of humidification devices may also be beneficial in reducing the risk of cross-infection.

Serologic diagnosis of allergic bronchopulmonary aspergillosis in patients with cystic fibrosis through the detection of immunoglobulin G to Aspergillus fumigatus.

Allergic bronchopulmonary aspergillosis (ABPA) is seen in approximately 10% of patients with cystic fibrosis (CF) and can be difficult to diagnose. Consensus criteria require the presence of multiple elevated immunologic markers such as total immunoglobulin E (IgE), Aspergillus IgE and Aspergillus IgG, or precipitins for a robust diagnosis. There is some degree of standardization of total IgE and Aspergillus IgE levels, but there is no standardization in the measurement of IgG antibodies or precipitins to Aspergillus. The interpretation of results may, therefore, be confusing. Eighty-seven patients with CF were categorized as having ABPA or as controls, using the consensus criteria and an in-house enzyme immunoassay to measure IgG levels to Aspergillus. All sera from patients were then analyzed by commercial fluorescent immunoassay (FEIA) for the quantitative detection of anti-Aspergillus IgG. FEIA results were analyzed against the consensus conference minimum diagnostic criteria to ascertain a cutoff point, which could predict a diagnosis of ABPA in CF. Eighty patients with CF and with no or incomplete evidence of ABPA had a mean FEIA score of 51.1 mg/L, whereas 7 CF patients with ABPA had a mean FEIA score of 132.5 mg/L. Using receiver operator characteristic curve analysis of the ImmunoCAP (Phadia) IgG score on ABPA versus all other patients gave an area under the curve of 0.933 (estimated SE, 0.027). This analysis provisionally suggested that a score of 90 mg/L may be used as a cutoff point, which would give a sensitivity of 91% and specificity of 88.0% for the diagnosis of ABPA, though this requires further validation. This quantitative approach to Aspergillus IgG measurement in patients with CF along with the results of other tests will hopefully provide a more accurate approach to the diagnosis of ABPA.

Enterobacteriaceae.

This review summarises the changing epidemiology of resistance to cephalosporins and fluoroquinolones among the Enterobacteriaceae since the 1980s and its potential impact on prescribing choices now and in the immediate future. Whilst multiresistant Enterobacteriaceae are not a novel problem for high-risk hospital units, such as intensive care, the emergence of Escherichia coli co-expressing extended-spectrum beta-lactamases, such as CTX-M types, along with fluoroquinolone resistance in the community is starting to impact in situations where cephalosporins and ciprofloxacin were seen as reliable first-line choices. The reduction in effective options to treat these infections, particularly of the urinary tract and bacteraemia, is likely to result in increased prescribing of carbapenems, thus generating further selective pressure for carbapenemases and other mechanisms of carbapenem resistance in the future.

Adherence to infection prevention and control guidelines: A vignette-based study of decision-making and risk-taking in young adults with cystic fibrosis.

BACKGROUND: Balancing cystic fibrosis (CF) care with demands of normal life is associated with decreased adherence to infection prevention and control (IPC) guidelines. METHODS: Adults with CF, aged 18-25years, were invited to participate via UK CF Trust social media platforms. An online survey evaluated participants' decision-making in nine clinician-rated vignettes and assessed the perceived influence of infection-related information sources. RESULTS: Participants (n=87, mean 21.4years [SD=2.45]; 75% female) were less likely to engage in the high-risk scenarios, although demonstrated greater awareness of cross-infection than environmental risks. Associations between risk-perception and willingness to participate in five vignette-based hypothetical activities were significant (p<0.05). Thematic analysis emphasised influences of past experience and a need to achieve good quality of life. Knowledge gaps were evident. CONCLUSIONS: People with CF make decisions that discriminate between risk-levels but are not always based on robust knowledge. They also show some inclination towards engaging in risky behaviours.

Emergence and spread of a human-transmissible multidrug-resistant nontuberculous mycobacterium.

Lung infections with Mycobacterium abscessus, a species of multidrug-resistant nontuberculous mycobacteria, are emerging as an important global threat to individuals with cystic fibrosis (CF), in whom M. abscessus accelerates inflammatory lung damage, leading to increased morbidity and mortality. Previously, M. abscessus was thought to be independently acquired by susceptible individuals from the environment. However, using whole-genome analysis of a global collection of clinical isolates, we show that the majority of M. abscessus infections are acquired through transmission, potentially via fomites and aerosols, of recently emerged dominant circulating clones that have spread globally. We demonstrate that these clones are associated with worse clinical outcomes, show increased virulence in cell-based and mouse infection models, and thus represent an urgent international infection challenge.

Risk factors for acquisition of methicillin-resistant Staphylococcus aureus (MRSA) by patients with cystic fibrosis.

Methicillin-resistant Staphylococcus aureus (MRSA) is an increasing problem for patients with cystic fibrosis (CF). It has been associated with clinical deterioration in some patients with CF, creates additional infection control problems, and may affect acceptance onto transplant waiting lists. Recent attempts to eradicate the organism have met with only moderate success. An understanding of those factors which increase the risk of acquisition of MRSA by CF patients will aid the development of effective preventative strategies. We conducted a retrospective case-control study comparing a variety of risk factors for 15 MRSA-positive patients and 30 age-sex-matched MRSA-negative controls who attended the Regional Paediatric or Regional Adult Cystic Fibrosis Units in Leeds. During the year prior to initial isolation, MRSA-positive CF patients spent more days in hospital (mean 19.8 days versus 5.5 days, p=0.0003), received more treatment days of oral ciprofloxacin (43.5 days versus 13.9 days, p=0.03) more treatment days of oral/intravenous cephalosporins (42.7 days versus 15.4 days, p=0.04) and were more likely to be chronically infected with Aspergillus fumigatus (40% versus 10%, p=0.04) than the age-sex-matched MRSA-negative controls. There were no significant differences in observed clinical parameters (clinical and X-ray scores) with between the two groups. Minimising the number and length of hospital admissions and judicious use of antibiotics, particularly ciprofloxacin, should be the key components of any strategies designed to reduce the risk of MRSA acquisition by patients with CF.

Clostridium botulinum: an increasing complication of heroin misuse.

Wound botulism is a rare infectious disease due to neurotoxin release from the anaerobic, spore-forming bacterium Clostridium botulinum that is becoming an ever more frequent complication of parenteral drug abuse in the Western world. Before the year 2000, no such cases had been reported in the UK and Ireland, but since then the number of proven and suspected cases of wound botulism occurring in parenteral drug users has increased markedly. The diagnosis is often difficult, based on a high degree of clinical suspicion and if not considered in the initial differential diagnosis, then considerable delays in treatment may result. This is the case report of a male heroin user who presented three times to an Emergency Department in the UK before a diagnosis of wound botulism was made and treatment commenced. It is important that emergency clinicians are aware of the possibility of wound botulism in parenteral drug users that present with unusual neurological or respiratory symptomatology.

Evaluation of a new definition for chronic Pseudomonas aeruginosa infection in cystic fibrosis patients.

BACKGROUND: Patients were defined each successive month as either 'chronic' when more than 50% of the preceding 12 months were PA culture positive, 'intermittent' when < or =50% of the preceding 12 months were PA culture positive, 'free of PA', with no growth of PA for the previous 12 months, having previously been PA culture positive, or 'never infected', when PA had never been cultured. METHODS: Cross-sectional analysis of 146 children attending the Leeds Regional Cystic Fibrosis Centre was performed to assess relationship between the new definition and clinical scores and investigations. The response variable was regressed on age and sex and the residuals analysed using the Kruskal-Wallis test. RESULTS: The 'chronic' group (18% of patients) had significantly worse Shwachman-Kulczycki (SK) and Northern chest X-ray scores, and % predicted FEV(1) values than the 'free' (28%) or 'never' (20%) categories (P<0.004). The 'intermittent' group (34%) had a significantly higher SK score than the 'chronic' group (P<0.0001), and a significantly lower % predicted FEV(1) value than the 'free' or 'never' groups (P<0.0003). 'Chronic' patients were significantly associated with a positive, and 'never' patients with a negative, PA antibody result (P<0.001). CONCLUSIONS: The validity and importance of identifying these four subgroups is demonstrated. Previous definitions may over-estimate the prevalence of chronic infection.

Reduction in prevalence of chronic Pseudomonas aeruginosa infection at a regional pediatric cystic fibrosis center.

Various management strategies were introduced at the Leeds Regional Cystic Fibrosis (CF) Unit in an attempt to reduce the prevalence of chronic Pseudomonas aeruginosa respiratory infection, previously thought to be inevitable in most children with CF. These included neonatal screening (1975), regular microbiological monitoring (1975), early antibiotic treatment of first isolations of P. aeruginosa (1985), intensive intravenous antibiotic treatment where nebulized antibiotics failed to eradicate P. aeruginosa (1988), and separate clinics for patients chronically infected with P. aeruginosa and uninfected patients (1991). The aim of this study was to assess the impact of these interventions. All 232 patients receiving full-time care at the Leeds Paediatric CF Centre during the period January 1990-December 2000 were categorized into four groups: never grown P. aeruginosa; free of P. aeruginosa for at least 1 year; intermittent grower of P. aeruginosa with 50% of months with samples positive for P. aeruginosa over the previous 12 months. The yearly prevalence of patients having chronic P. aeruginosa infection fell significantly during the study, from 24.5% in 1990 to 18.1% in 2000 (P < 0.05), despite an increase in mean age of patients from 7.73 to 9.42 years. The number of patients aged less than 11 years who had chronic P. aeruginosa infection fell from 23.8% in January 1990 to only 4.3% by December 2000. The annual incidence and mean age of first acquisition of P. aeruginosa did not alter significantly. In conclusion, antipseudomonal management strategies were associated with both reduced prevalence, and an increase in the mean age of onset of chronic P. aeruginosa infection.

Decision Making about Risk of Infection by Young Adults with CF.

Young people with cystic fibrosis (CF) are asked to avoid a number of environments associated with increased infection risk, but in practice they need to balance this with competing priorities such as building and sustaining relationships with friends and family. This study explored the process by which young people make these decisions. Mixed methods were used: a vignette study presenting choices around engaging in activities involving a degree of infection risk and a thematic analysis of participant's accounts of their decision making. The eight participants chose to engage in high risk behaviours in 59% of the choices. All participants chose to engage in at least one risky behavior, though this was less likely when the risk was significant. Thematic analysis revealed large areas of misunderstanding and lack of knowledge, leading to some potentially worrying misconceptions about the nature of infections and risk. Young people with CF are not currently making informed decisions around activities that involve increased risk of infection, and there is an urgent need for CF teams to address this in information provision.

Bloodstream infections in cystic fibrosis: nine years of experience in both adults and children.

BACKGROUND: We report the aetiology and outcome of bloodstream infections (BSI) occurring at two regional cystic fibrosis (CF) centres (one adult, one paediatric) between 1998 and 2006. METHODS: A retrospective analysis of all positive blood cultures during the study period was performed. RESULTS: During the study period 1691 blood culture sets were taken. Fifty-seven clinically significant episodes of BSI in 48 people with CF (36 adult, 12 paediatric) were identified, along with 28 other episodes considered to be contamination or not clinically significant. The most common BSIs were caused by coagulase-negative staphylococci (13) Candida spp (10), and Stenotrophomonas maltophilia (8). The majority (82%) of significant BSIs were considered to originate from totally-implantable vascular access devices (TIVADs); only 9% were attributed to the lower respiratory tract. The TIVAD was removed in two-thirds of cases of TIVAD-associated BSI. There were three deaths (60% of cases) attributable to BSI originating from the lower respiratory tract but no deaths attributable to TIVAD-associated BSI. CONCLUSION: Most significant BSIs in patients with CF originate from TIVADs. Targeted antimicrobial therapy and appropriate early device removal is associated with good clinical outcome. BSI originating from the lower respiratory tract is associated with poor clinical outcome.

A simple prophylaxis regimen for MRSA: its impact on the incidence of infection in patients undergoing liver resection.

INTRODUCTION: Methicillin-resistant Staphylococcus aureus (MRSA) infection has increased at an alarming rate in the recent past and has major cost implications. The aim of this study is to assess the impact of a policy of pre-operative MRSA prophylaxis on the incidence of MRSA infection in patients undergoing liver resection. PATIENTS AND METHODS: A total of 585 patients underwent hepatectomy in a tertiary referral centre between January 2000 and September 2005. In September 2003, a policy of MRSA prophylaxis (nasal mupirocin and triclosan wash for 5 days) was introduced within this unit. Demographic, pathological and outcome data were compared between the pre- and post-MRSA prophylaxis cohorts. RESULTS: The prevalence of MRSA infection prior to initiating the prophylaxis protocol was 29 patients (8.3%) and this fell to 9 patients (3.8%; P = 0.029). Furthermore, patients who had MRSA-related infection had a higher incidence of additional complications compared to the rest of the cohort (P = 0.001). Total cost savings incurred as a result of this protocol over the past 2 years has been approximated at 28,893 pounds. CONCLUSIONS: Introduction of a simple MRSA prophylaxis policy has had a significant reduction on the incidence MRSA-related infection within our patient population, leading to reduced morbidity and cost saving to the UK National Health Service.