Amoxicillin-clavulanate Breakpoints Against Enterobacterales: Rationale for Revision by the Clinical and Laboratory Standards Institute

Amoxicillin-clavulanate (AMC) is among the most frequently prescribed antibiotics globally. It has broad antibacterial activity against gram-positive, gram-negative, and anaerobic bacteria, and has been utilized to treat infections caused by a broad range of pathogens. AMC breakpoints against Enterobacterales were initially set in the 1980s but since then increases in antibiotic resistance, advances in pharmacokinetic (PK)/pharmacodynamic (PD) analyses, and publication of additional clinical data prompted a reassessment by the Clinical and Laboratory Standards Institute (CLSI) Subcommittee on Antimicrobial Susceptibility Testing. Based on this contemporary reappraisal, the CLSI retained the Enterobacterales breakpoints but revised comments regarding dosing associated with use of the AMC breakpoints in the 2022 supplement of M100. This viewpoint provides insight into the CLSI breakpoint reevaluation process and summarizes the data and rationale used to support these revisions to the AMC Enterobacterales breakpoint.

A Dose-Finding Study to Guide Use of Verapamil as an Adjunctive Therapy in Tuberculosis

Induction of mycobacterial efflux pumps is a cause of Mycobacterium tuberculosis (Mtb) drug tolerance, a barrier to shortening antitubercular treatment. Verapamil inhibits Mtb efflux pumps that mediate tolerance to rifampin, a cornerstone of tuberculosis (TB) treatment. Verapamil's mycobacterial efflux pump inhibition also limits Mtb growth in macrophages in the absence of antibiotic treatment. These findings suggest that verapamil could be used as an adjunctive therapy for TB treatment shortening. However, verapamil is rapidly and substantially metabolized when co-administered with rifampin. We determined in a dose-escalation clinical trial of persons with pulmonary TB that rifampin-induced clearance of verapamil can be countered without toxicity by the administration of larger than usual doses of verapamil. An oral dosage of 360 mg sustained-release (SR) verapamil given every 12 hours concomitantly with rifampin achieved median verapamil exposures of 903.1 ng.h/mL (area under the curve (AUC)0-12 h ) in the 18 participants receiving this highest studied verapamil dose; these AUC findings are similar to those in persons receiving daily doses of 240 mg verapamil SR but not rifampin. Moreover, norverapamil:verapamil, R:S verapamil, and R:S norverapamil AUC ratios were all significantly greater than those of historical controls receiving SR verapamil in the absence of rifampin. Thus, rifampin administration favors the less-cardioactive verapamil metabolites and enantiomers that retain similar Mtb efflux inhibitory activity to verapamil, increasing overall benefit. Finally, rifampin exposures were 50% greater after verapamil administration, which may also be advantageous. Our findings suggest that a higher dosage of verapamil can be safely used as adjunctive treatment in rifampin-containing treatment regimens.

A dose-finding study to guide use of verapamil as an adjunctive therapy in tuberculosis

Induction of mycobacterial efflux pumps is a cause of Mycobacterium tuberculosis (Mtb) drug tolerance, a barrier to shortening antitubercular treatment. Verapamil inhibits Mtb efflux pumps that mediate tolerance to rifampin, a cornerstone of tuberculosis treatment. Verapamil's mycobacterial efflux pump inhibition also limits Mtb growth in macrophages in the absence of antibiotic treatment. These findings suggest that verapamil could be used as an adjunctive therapy for TB treatment shortening. However, verapamil is rapidly and substantially metabolized when co-administered with rifampin. We determined in a dose-escalation clinical trial that rifampin-induced clearance of verapamil can be countered without toxicity by the administration of larger than usual doses of verapamil. An oral dosage of 360 mg sustained-release (SR) verapamil given every 12 hours concomitantly with rifampin achieved median verapamil exposures of 903.1 ng.h/ml (AUC 0-12h), similar to those in persons receiving daily doses of 240 mg verapamil SR but not rifampin. Norverapamil:verapamil, R:S verapamil and R:S norverapamil AUC ratios were all significantly greater than those of historical controls receiving SR verapamil in the absence of rifampin, suggesting that rifampin administration favors the less-cardioactive verapamil metabolites and enantiomers. Finally, rifampin exposures were significantly greater after verapamil administration. Our findings suggest that a higher dosage of verapamil can be safely used as adjunctive treatment in rifampin-containing treatment regimens.

The human proton pump inhibitors inhibit Mycobacterium tuberculosis rifampicin efflux and macrophage-induced rifampicin tolerance

Tuberculosis treatment requires months-long combination chemotherapy with multiple drugs, with shorter treatments leading to relapses. A major impediment to shortening treatment is that Mycobacterium tuberculosis becomes tolerant to the administered drugs, starting early after infection and within days of infecting macrophages. Multiple lines of evidence suggest that macrophage-induced drug tolerance is mediated by mycobacterial drug efflux pumps. Here, using assays to directly measure drug efflux, we find that M. tuberculosis transports the first-line antitubercular drug rifampicin through a proton gradient-dependent mechanism. We show that verapamil, a known efflux pump inhibitor, which inhibits macrophage-induced rifampicin tolerance, also inhibits M.tuberculosis rifampicin efflux. As with macrophage-induced tolerance, the calcium channel-inhibiting property of verapamil is not required for its inhibition of rifampicin efflux. By testing verapamil analogs, we show that verapamil directly inhibits M. tuberculosis drug efflux pumps through its human P-glycoprotein (PGP)-like inhibitory activity. Screening commonly used drugs with incidental PGP inhibitory activity, we find many inhibit rifampicin efflux, including the proton pump inhibitors (PPIs) such as omeprazole. Like verapamil, the PPIs inhibit macrophage-induced rifampicin tolerance as well as intramacrophage growth, which has also been linked to mycobacterial efflux pump activity. Our assays provide a facile screening platform for M. tuberculosis efflux pump inhibitors that inhibit in vivo drug tolerance and growth.

Gaucher disease protects against tuberculosis

Biallelic mutations in the glucocerebrosidase (GBA1) gene cause Gaucher disease, characterized by lysosomal accumulation of glucosylceramide and glucosylsphingosine in macrophages. Gaucher and other lysosomal diseases occur with high frequency in Ashkenazi Jews. It has been proposed that the underlying mutations confer a selective advantage, in particular conferring protection against tuberculosis. Here, using a zebrafish Gaucher disease model, we find that the mutation GBA1 N370S, predominant among Ashkenazi Jews, increases resistance to tuberculosis through the microbicidal activity of glucosylsphingosine in macrophage lysosomes. Consistent with lysosomal accumulation occurring only in homozygotes, heterozygotes remain susceptible to tuberculosis. Thus, our findings reveal a mechanistic basis for protection against tuberculosis by GBA1 N370S and provide biological plausibility for its selection if the relatively mild deleterious effects in homozygotes were offset by significant protection against tuberculosis, a rampant killer of the young in Europe through the Middle Ages into the 19th century.

Elevated cerebrospinal fluid cytokine levels in tuberculous meningitis predict survival in response to dexamethasone

Adjunctive treatment with antiinflammatory corticosteroids like dexamethasone increases survival in tuberculosis meningitis. Dexamethasone responsiveness associates with a C/T variant in Leukotriene A4 Hydrolase (LTA4H), which regulates expression of the proinflammatory mediator leukotriene B4 (LTB4). TT homozygotes, with increased expression of LTA4H, have the highest survival when treated with dexamethasone and the lowest survival without. While the T allele is present in only a minority of the world's population, corticosteroids confer modest survival benefit worldwide. Using Bayesian methods, we examined how pretreatment levels of cerebrospinal fluid proinflammatory cytokines affect survival in dexamethasone-treated tuberculous meningitis. LTA4H TT homozygosity was associated with global cytokine increases, including tumor necrosis factor. Association between higher cytokine levels and survival extended to non-TT patients, suggesting that other genetic variants may also induce dexamethasone-responsive pathological inflammation. These findings warrant studies that tailor dexamethasone therapy to pretreatment cerebrospinal fluid cytokine concentrations, while searching for additional genetic loci shaping the inflammatory milieu.

A Bayesian analysis of the association between Leukotriene A4 Hydrolase genotype and survival in tuberculous meningitis

Tuberculous meningitis has high mortality, linked to excessive inflammation. However, adjunctive anti-inflammatory corticosteroids reduce mortality by only 30%, suggesting that inflammatory pathophysiology causes only a subset of deaths. In Vietnam, the survival benefit of anti-inflammatory corticosteroids was most pronounced in patients with a C/T promoter variant in the leukotriene A₄ hydrolase (LTA4H) gene encoding an enzyme that regulates inflammatory eicosanoids. LTA4H TT patients with increased expression had increased survival, consistent with corticosteroids benefiting individuals with hyper-inflammatory responses. However, an Indonesia study did not find an LTA4H TT genotype survival benefit. Here using Bayesian methods to analyse both studies, we find that LTA4H TT genotype confers survival benefit that begins early and continues long-term in both populations. This benefit is nullified in the most severe cases with high early mortality. LTA4H genotyping together with disease severity assessment may target glucocorticoid therapy to patients most likely to benefit from it.

Tuberculous meningitis is a serious infection of the lining of the brain, which affects over 100,000 people a year. Without treatment, it is always fatal: even with proper antibiotics, about a quarter of patients do not survive and many will have permanent brain damage. Overactive inflammation is thought to contribute to this process. Corticosteroid drugs, which dampen the inflammatory process, are therefore often used during treatment. However, they merely reduce mortality by 30%, suggesting that only some people benefit from them.

Two recent studies have linked the genetic makeup of individuals who have tuberculous meningitis to how they respond to corticosteroids. There were, in particular, differences in the LTA4H gene that codes for an inflammation-causing protein. According to these results, only individuals carrying high-inflammation versions of the LTA4H gene would benefit from the treatment. Yet a third study did not find any effect of the genetic background of patients.

All three papers used frequentist statistics to draw their conclusions, only examining the percentage of people who survived in each group. Yet, this type of analysis can miss important details. It also does not work well when the number of patients is small, or when the effectiveness of a drug varies during the course of an illness.

Another method, called Bayesian statistics, can perform better under these limitations. In particular, it takes into account the probability of an event based on prior knowledge – for instance, that the risk of dying varies smoothly with time.

Here, Whitworth et al. used Bayesian statistics to reanalyse the data from these studies, demonstrating that death rates were correlated with the type of LTA4H gene carried by patients. In particular, corticosteroid treatment worked best for people with the high inflammation versions of the gene. However, regardless of genetic background, corticosteroids were not effective if patients were extremely sick before being treated.

The work by Whitworth et al. demonstrates the importance of using Bayesian statistics to examine the effectiveness of medical treatments. It could help to design better protocols for tuberculous meningitis treatment, tailored to the genetic makeup of patients.

Performance of the ImmuView and BinaxNOW assays for the detection of urine and cerebrospinal fluid Streptococcus pneumoniae and Legionella pneumophila serogroup 1 antigen in patients with Legionnaires' disease or pneumococcal pneumonia and meningitis

The performances of the ImmuView Streptococcus pneumoniae (Sp) and Legionella pneumophila (Lp) urinary antigen test were compared to that of the BinaxNOW Sp and Lp assays, using frozen urine from 166 patients with Legionnaires' disease (LD) and 59 patients with pneumococcal pneumonia. Thirty Sp-positive or contrived cerebrospinal fluids (CSF) were also tested. Test specimens were collected and tested at different sites, with each site testing unique specimens by technologists blinded to expected results. No significant differences in test concordances were detected for the ImmuView and BinaxNOW assays for the Sp or Lp targets for urine from patients with pneumococcal pneumonia or LD when performance from both sites were combined. At one of two test sites the ImmuView Lp assay was more sensitive than the BinaxNOW assay, with no correlation between test performance and Lp serogroup 1 monoclonal type. Urines from six of seven patients with LD caused by Legionella spp. bacteria other than Lp serogroup 1 were negative in both assays. Both tests had equivalent performance for Sp-positive CSF. The clinical sensitivities for pneumococcal pneumonia were 88.1 and 94.4% for the ImmuView and Binax assays, and 87.6 and 84.2% for the Lp assays, respectively. Test specificities for pneumococcal pneumonia were 96.2 and 97.0% for the ImmuView and Binax assays, and 99.6 and 99.1% for the Lp assays. Both assays were highly specific for Sp in pediatric urines from children with nasopharyngeal colonization by the bacterium. ImmuView and BinaxNOW assay performance was equivalent in these studies.

Is Mycobacterium tuberculosis infection life long?

People with immunoreactivity to tuberculosis are thought to have lifelong asymptomatic infection and remain at risk for active tuberculosis. Marcel A Behr and colleagues argue that most of these people are no longer infected

Revisiting the timetable of tuberculosis

Tuberculosis has a much shorter incubation period than is widely thought, say Marcel A Behr and colleagues, and this has implications for prioritising research and public health strategies

Bacteremia caused by the photosynthetic environmental bacterium Rhodopseudomonas

We report a case of persistent Rhodopseudomonas bacteremia in a patient two months after an allogeneic bone marrow transplant for acute myeloid leukemia. The bacteremia persisted until IV catheter removal. To our knowledge, this is the first report of Rhodopseudomonas causing infection in humans.

Legionella jamestowniensis fatal pneumonia in an immunosuppressed man

A fatal case of Legionnaires' disease caused by Legionella jamestowniensis is reported in a severely immunocompromised patient with metastatic hepatocellular carcinoma, and liver and kidney transplants. L. jamestowniensis was cultured from two separate respiratory tract specimens and a PCR test for Legionella species was also positive from the same specimens. This is apparently the first reported case of human infection caused by L. jamestowniensis.

Nuclemeter: a reaction-diffusion based method for quantifying nucleic acids undergoing enzymatic amplification

Real-time amplification and quantification of specific nucleic acid sequences plays a major role in medical and biotechnological applications. In the case of infectious diseases, such as HIV, quantification of the pathogen-load in patient specimens is critical to assess disease progression and effectiveness of drug therapy. Typically, nucleic acid quantification requires expensive instruments, such as real-time PCR machines, which are not appropriate for on-site use and for low-resource settings. This paper describes a simple, low-cost, reaction-diffusion based method for end-point quantification of target nucleic acids undergoing enzymatic amplification. The number of target molecules is inferred from the position of the reaction-diffusion front, analogous to reading temperature in a mercury thermometer. The method was tested for HIV viral load monitoring and performed on par with conventional benchtop methods. The proposed method is suitable for nucleic acid quantification at point of care, compatible with multiplexing and high-throughput processing, and can function instrument-free.

Prevalence and detection of mixed-population enterococcal bacteremia

Mixed-population (heterogeneous) enterococcal bacteremia (MEB) is rarely reported. Based on one occasion in which Vitek2 missed a vancomycin-resistant subpopulation isolated from a patient, we developed a simple method to detect this subpopulation and determined MEB frequency. The four patients presented here had either Enterococcus faecium or Enterococcus faecalis bacteremia caused by both vancomycin-resistant enterococci (VRE) and vancomycin-susceptible enterococci (VSE). No prior common antibiotic therapy was observed, and bacteremia resolved with daptomycin, gentamicin, and/or linezolid treatment. In two cases, VRE presence was missed by Vitek2. To detect the VRE subpopulation, tryptic soy broth was inoculated from positive blood cultures and a saline suspension was inoculated to a vancomycin (6-μg/ml) (V6) plate. Two isolates from each patient were studied further. Relatedness was assessed by multilocus sequence typing, fitness was evaluated by growth curve and competition assays, and vanA presence was determined by PCR. MEB represented ∼5% of all enterococcal bacteremias. All VRE subpopulations grew on V6 plates but were missed in two instances by Vitek2. VRE and VSE isolates from each patient were closely related and did not differ in overall fitness. All four VRE isolates and 2/4 VSE isolates were vanA positive. MEBs occur regardless of prior antimicrobial therapy, are relatively common in our hospital, and are important to detect. As far as we know, this study is the first to report heterogeneous E. faecalis bacteremia. There is a simple method to detect VRE subpopulations that may be missed by Vitek2.

Membrane-based, sedimentation-assisted plasma separator for point-of-care applications

Often, high-sensitivity, point-of-care (POC) clinical tests, such as HIV viral load, require large volumes of plasma. Although centrifuges are ubiquitously used in clinical laboratories to separate plasma from whole blood, centrifugation is generally inappropriate for on-site testing. Suitable alternatives are not readily available to separate the relatively large volumes of plasma from milliliters of blood that may be needed to meet stringent limit-of-detection specifications for low-abundance target molecules. We report on a simple-to-use, low-cost, pump-free, membrane-based, sedimentation-assisted plasma separator capable of separating a relatively large volume of plasma from undiluted whole blood within minutes. This plasma separator consists of an asymmetric, porous, polysulfone membrane housed in a disposable chamber. The separation process takes advantage of both gravitational sedimentation of blood cells and size exclusion-based filtration. The plasma separator demonstrated a "blood in-plasma out" capability, consistently extracting 275 ± 33.5 μL of plasma from 1.8 mL of undiluted whole blood within less than 7 min. The device was used to separate plasma laden with HIV viruses from HIV virus-spiked whole blood with recovery efficiencies of 95.5% ± 3.5%, 88.0% ± 9.5%, and 81.5% ± 12.1% for viral loads of 35,000, 3500, and 350 copies/mL, respectively. The separation process is self-terminating to prevent excessive hemolysis. The HIV-laden plasma was then injected into our custom-made microfluidic chip for nucleic acid testing and was successfully subjected to reverse-transcriptase loop-mediated isothermal amplification (RT-LAMP), demonstrating that the plasma is sufficiently pure to support high-efficiency nucleic acid amplification.

The Guinea pig model of legionnaires' disease

The guinea pig pneumonia model mimics Legionnaires' disease as seen in immunocompromised humans, with high untreated fatality rates and as such lends itself to studies of experimental chemotherapy. Guinea pig infection is also used to assess relative virulence of different Legionella bacterial strains, and has also been used to study host immune defenses. Here I describe the method used to produce Legionella sp. pneumonia in the guinea pig using the intratracheal infection technique. This method uses directly observed intratracheal injection of a bacterial suspension, requiring surgical exposure of the trachea.

The effect of staphylococcal cassette chromosome mec (SCCmec) type on clinical outcomes in methicillin-resistant Staphylococcus aureus bacteremia

OBJECTIVES

The impact of staphylococcal cassette chromosome mec (SCCmec) type on mortality in methicillin-resistant Staphylococcus aureus (MRSA) infections remains unclear. The objective of this study was to determine the association between SCCmec type and mortality in MRSA bacteremia.

METHODS

A cohort study of patients who were hospitalized with MRSA bacteremia was conducted within a university health system. A multivariable logistic regression model was developed to evaluate the association of SCCmec type with 30-day in-hospital mortality.

RESULTS

Thirty-four of a total of 184 patients with MRSA bacteremia died, resulting in a mortality rate of 18.5%. Adjusted risk factors for 30-day mortality included APRDRG Risk of Mortality score (odds ratio [OR], 5.33; 95% confidence interval [CI], 2.28-12.4; P<0.001), white blood cell count (OR, 1.09; 95% CI, 1.03-1.15; P=0.002), and malignancy (OR, 3.25; 95% CI, 1.17-9.02; P=0.02). On multivariable analyses, SCCmec II was not significantly associated with mortality in patients with MRSA bacteremia (OR, 1.85; 95% CI, 0.69-4.92; P=0.22).

CONCLUSIONS

Mortality in MRSA bacteremia was independent of SCCmec type. SCCmec type II is most likely a marker for disease severity rather than a direct mediator of mortality. Further research is needed to elucidate the factors associated with poor clinical outcomes in MRSA infections.

Reduced vancomycin susceptibility and staphylococcal cassette chromosome mec (SCCmec) type distribution in methicillin-resistant Staphylococcus aureus bacteraemia

OBJECTIVES

Recent epidemiological evidence suggests that genotypic and phenotypic characteristics that have typically distinguished community-associated methicillin-resistant Staphylococcus aureus (MRSA) and healthcare-associated MRSA strains may be evolving. The objective of this study was to examine the association between reduced vancomycin susceptibility (RVS) and staphylococcal cassette chromosome mec (SCCmec) type in MRSA bloodstream isolates.

METHODS

A cohort study of patients who were hospitalized from 2007 to 2009 with S. aureus bacteraemia was conducted within a university health system. Bivariable analyses were conducted to determine the association between RVS and SCCmec type, as well as other microbiological characteristics including Panton-Valentine leucocidin, accessory gene regulator (agr) dysfunction and vancomycin heteroresistance.

RESULTS

A total of 188 patients with MRSA bacteraemia were identified: 116 (61.7%) and 72 (38.3%) patients had infections due to healthcare-associated MRSA and community-associated MRSA, respectively. As defined by a vancomycin Etest MIC > 1.0 mg/L, the prevalence of RVS was 40.4%. Isolates with RVS were significantly more likely to be associated with SCCmec II compared with isolates without RVS (74.7% and 47.3%, respectively, P < 0.001), but not with Panton-Valentine leucocidin (P = 0.10), agr dysfunction (P = 0.19) or healthcare-associated infection (P = 0.36).

CONCLUSIONS

The results of our study demonstrate important microbiological characteristics among MRSA isolates characterized by RVS, including a significant association between SCCmec II and elevated vancomycin MIC. It is clear that the clinical and molecular epidemiology of MRSA is evolving, and further understanding of factors determining virulence will be important for the elucidation of optimal treatment approaches for associated infections.

Potential for pet animals to harbour methicillin-resistant Staphylococcus aureus when residing with human MRSA patients

Colonization by methicillin-resistant Staphylococcus aureus (MRSA) may be persistent in people and is horizontally transmissible. The scientific literature suggests that domestic pets may also participate in cross-transmission of MRSA within households. The objectives of this study were to evaluate the prevalence of and risk factors for MRSA carriage by pets residing in households with an MRSA-infected person. From 66 households in which an MRSA-infected patient resided, we screened 47 dogs and 52 cats using a swab protocol. Isolates from pets and humans were genotyped using two techniques and compared for concordance. Human participants completed a 22-question survey of demographic and epidemiologic data relevant to staphylococcal transmission. Eleven of 99 pets (11.5%) representing 9 (13.6%) of households were MRSA-positive, but in only six of these households were the human and animal-source strains genetically concordant. Human infection by strain USA 100 was significantly associated with pet carriage [OR = 11.4 (95% CI 1.7, 76.9); P = 0.013]. Yet, for each day of delay in sampling the pet after the person's MRSA diagnosis, the odds of isolating any type of MRSA from the pet decreased by 13.9% [(95% CI 2.6, 23.8); P = 0.017)]. It may be concluded that pets can harbour pandemic strains of MRSA while residing in a household with an infected person. However, the source of MRSA to the pet cannot always be attributed to the human patient. Moreover, the rapid attrition of the odds of obtaining a positive culture from pets over time suggests that MRSA carriage may be fleeting.

Antimicrobial efflux pumps and Mycobacterium tuberculosis drug tolerance: evolutionary considerations

The need for lengthy treatment to cure tuberculosis stems from phenotypic drug resistance, also known as drug tolerance, which has been previously attributed to slowed bacterial growth in vivo. We discuss recent findings that challenge this model and instead implicate macrophage-induced mycobacterial efflux pumps in antimicrobial tolerance. Although mycobacterial efflux pumps may have originally served to protect against environmental toxins, in the pathogenic mycobacteria, they appear to have been repurposed for intracellular growth. In this light, we discuss the potential of efflux pump inhibitors such as verapamil to shorten tuberculosis treatment by their dual inhibition of tolerance and growth.

Prior vancomycin use is a risk factor for reduced vancomycin susceptibility in methicillin-susceptible but not methicillin-resistant Staphylococcus aureus bacteremia

OBJECTIVE

Staphylococcus aureus is a cause of community- and healthcare-acquired infections and is associated with substantial morbidity, mortality, and costs. Vancomycin minimum inhibitory concentrations (MICs) among S. aureus have increased, and reduced vancomycin susceptibility (RVS) may be associated with treatment failure. We aimed to identify clinical risk factors for RVS in S. aureus bacteremia.

DESIGN

Case-control.

SETTING

Academic tertiary care medical center and affiliated urban community hospital.

PATIENTS

Cases were patients with RVS S. aureus isolates (defined as vancomycin E-test MIC >1.0 μg/mL). Controls were patients with non-RVS S. aureus isolates.

RESULTS

Of 392 subjects, 134 (34.2%) had RVS. Fifty-eight of 202 patients (28.7%) with methicillin-susceptible S. aureus (MSSA) isolates had RVS, and 76 of 190 patients (40.0%) with methicillin-resistant S. aureus (MRSA) isolates had RVS (P = .02). In unadjusted analyses, prior vancomycin use was associated with RVS (odds ratio [OR], 2.08; 95% confidence interval [CI], 1.00-4.32; P = .046). In stratified analyses, there was significant effect modification by methicillin susceptibility on the association between vancomycin use and RVS (P =.04). In multivariable analyses, after hospital of admission and prior levofloxacin use were controlled for, the association between vancomycin use and RVS was significant for patients with MSSA infection (adjusted OR, 4.02; 95% CI, 1.11-14.50) but not MRSA infection (adjusted OR, 0.87; 95% CI, 0.36-2.13).

CONCLUSIONS

A substantial proportion of patients with S. aureus bacteremia had RVS. The association between prior vancomycin use and RVS was significant for patients with MSSA infection but not MRSA infection, suggesting a complex relationship between the clinical and molecular epidemiology of RVS in S. aureus.

Association of pharyngitis with oral antibiotic use for the treatment of acne: a cross-sectional and prospective cohort study

OBJECTIVE

To prospectively evaluate the association between antibiotics used to treat acne and pharyngitis.

DESIGN

Cross-sectional and 9-month prospective cohort.

SETTING

Urban university setting.

PARTICIPANTS

University students.

INTERVENTION

Participants were asked to fill out a survey form, were swabbed for culture, and had a visual examination for acne.

MAIN OUTCOME MEASURE

Report of pharyngitis.

RESULTS

In the cross-sectional study, 10 of the 15 students receiving oral antibiotics for acne reported an episode of pharyngitis in the previous 30 days, whereas 47 of the 130 students not receiving oral antibiotics, but who had acne, reported an episode of pharyngitis in the prior month. The unadjusted odds ratio (OR) (95% CI) associating current oral antibiotic use in acne patients with a self-reported episode of pharyngitis was 3.53 (95% CI, 1.14-10.95). In the cohort study, there were 358 female and 218 male participants; 36 (6.2%) received oral antibiotics for acne during the study, and 96 (16.6%) received topical antibiotics for acne. Using mixed model logistic regression, the OR was 4.34 (95% CI, 1.51-12.47) associating oral antibiotic use with pharyngitis. Less than 1% of participants were colonized by group A streptococcus, which was not associated with pharyngitis.

CONCLUSIONS

Our studies show that that the odds of reporting pharyngitis is more than 3 times baseline in patients receiving oral antibiotics for acne vs those who are not receiving oral antibiotics. The true clinical importance of these findings needs to be evaluated further by prospective studies, but this finding is not associated with group A streptococcus.

Legionella steelei sp. nov., isolated from human respiratory specimens in California, USA, and South Australia

Legionella-like bacteria were isolated from the respiratory tract of two patients in California, USA, and South Australia, but were not thought to cause disease. These bacteria, strains F2632 and IMVS-3376(T), were found to have identical Legionella macrophage infectivity potentiator (mip) gene sequences and were therefore further characterized to determine their genetic and phenotypic relatedness and properties. Both of these Gram-negative-staining bacterial strains grew on buffered charcoal yeast extract medium, were cysteine auxotrophs and made a characteristic diffusible bright yellow fluorescent pigment, with one strain making a late appearing colony-bound blue-white fluorescent pigment. The optimal in vitro growth temperature was 35 °C, with very poor growth at 37 °C in broth or on solid media. There was no growth in human A549 cells at either 35 or 37 °C, but excellent growth in Acanthamoeba castellani at 30 °C and poorer growth at 35 °C. Phylogenetic analysis of these bacteria was performed by sequence analysis of 16S rRNA, mip, ribonuclease P, ribosomal polymerase B and zinc metalloprotease genes. These studies confirmed that the new strains represented a single novel species of the genus Legionella for which the name Legionella steelei sp. nov. is proposed. The type strain is IMVS-3376(T) ( = IMVS 3113(T) = ATCC BAA-2169(T)).

Antibiotics, acne, and Staphylococcus aureus colonization

OBJECTIVES

To determine the frequency of Staphylococcus aureus colonization among patients with acne and to compare the susceptibility patterns between the patients who are using antibiotics and those who are not using antibiotics.

DESIGN

Survey (cross-sectional) study of patients treated for acne.

SETTING

Dermatology outpatient office practice

PARTICIPANTS

The study included 83 patients who were undergoing treatment and evaluation for acne.

MAIN OUTCOME

Measure Colonization of the nose or throat with S aureus.

RESULTS

A total of 36 of the 83 participants (43%) were colonized with S aureus. Two of the 36 patients (6%) had methicillin-resistant S aureus ; 20 (56%) had S aureus solely in their throat; 9 (25%) had S aureus solely in their nose; and 7 (19%) had S aureus in both their nose and their throat. When patients with acne who were antibiotic users were compared with nonusers, the prevalence odds ratio for the colonization of S aureus was 0.16 (95% confidence interval [CI], 0.08-1.37) after 1 to 2 months of exposure and increased to 0.52 (95% CI, 0.12-2.17) after 2 months of exposure (P = .31). Many of the S aureus isolates were resistant to treatment with clindamycin and erythromycin (40% and 44%, respectively), particularly the nasal isolates. Very few showed resistance rates (< 10%) to treatment with tetracycline antibiotics.

CONCLUSION

Unlike current dogma about the long-term use of antimicrobial agents, the prolonged use of tetracycline antibiotics commonly used to treat acne lowered the prevalence of colonization by S aureus and did not increase resistance to the tetracycline antibiotics.

Drug tolerance in replicating mycobacteria mediated by a macrophage-induced efflux mechanism

Treatment of tuberculosis, a complex granulomatous disease, requires long-term multidrug therapy to overcome tolerance, an epigenetic drug resistance that is widely attributed to nonreplicating bacterial subpopulations. Here, we deploy Mycobacterium marinum-infected zebrafish larvae for in vivo characterization of antitubercular drug activity and tolerance. We describe the existence of multidrug-tolerant organisms that arise within days of infection, are enriched in the replicating intracellular population, and are amplified and disseminated by the tuberculous granuloma. Bacterial efflux pumps that are required for intracellular growth mediate this macrophage-induced tolerance. This tolerant population also develops when Mycobacterium tuberculosis infects cultured macrophages, suggesting that it contributes to the burden of drug tolerance in human tuberculosis. Efflux pump inhibitors like verapamil reduce this tolerance. Thus, the addition of this currently approved drug or more specific efflux pump inhibitors to standard antitubercular therapy should shorten the duration of curative treatment.

Exposure to children as a risk factor for bacteremic pneumococcal disease: changes in the post-conjugate vaccine era

BACKGROUND

The introduction of a pneumococcal conjugate vaccine has been associated with a shift in the serotypes responsible for bacteremic pneumococcal disease. We examined recent trends in serotypes responsible for disease and current risk factors among adults.

METHODS

Data were obtained from 48 acute care hospitals in the 5-county region surrounding Philadelphia, Pennsylvania, from October 1, 2002, through September 30, 2008, on all hospitalized adult patients with community-acquired bacteremic pneumococcal disease. Isolates were serotyped and patient characteristics were compared with data from a household survey of the adult population in the region.

RESULTS

During the study period, the annual rate of disease due to vaccine serotypes declined by 29% per year, but the rate of disease due to nonvaccine serotypes increased 13% per year, yielding an overall 7% increase in the annual rate of disease among adults. Advanced age was a risk factor for infection with nonvaccine serotypes compared with vaccine serotypes. Comparing all patients with the source population, African Americans were at increased risk of infection, and the presence of additional children in the home was associated with decreased risk of disease. Smoking, advanced age, and diabetes mellitus remained important risk factors in adults.

CONCLUSIONS

New serotypes are replacing the serotypes covered in the conjugate vaccine. While some risk factors for pneumococcal disease remain unchanged, the observation that exposure to children in the home is associated with lower risk of disease suggests that the changing epidemiology of pneumococcal disease may be altering the dominant modes of transmission in the community.

Risk factors and clinical impact of Klebsiella pneumoniae carbapenemase-producing K. pneumoniae

BACKGROUND

Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae is an emerging pathogen with serious clinical and infection control implications. To our knowledge, no study has specifically examined risk factors for KPC-producing K. pneumoniae or its impact on mortality.

METHODS

To identify risk factors for infection or colonization with KPC-producing K. pneumoniae, a case-control study was performed. Case patients with KPC-producing K. pneumoniae were compared with control subjects with carbapenem-susceptible K. pneumoniae. A cohort study evaluated the association between KPC-producing K. pneumoniae and in-hospital mortality.

RESULTS

Fifty-six case patients and 863 control subjects were identified. In multivariable analysis, independent risk factors for KPC-producing K. pneumoniae were (1) severe illness (adjusted odds ratio [AOR], 4.31; 95% confidence interval [CI], 2.25-8.25), (2) prior fluoroquinolone use (AOR, 3.39; 95% CI, 1.50, 7.66), and (3) prior extended-spectrum cephalosporin use (AOR, 2.55; 95% CI, 1.18, 5.52). Compared with samples from other anatomic locations, K. pneumoniae isolates from blood samples were less likely to harbor KPC (AOR, 0.33; 95% CI, 0.12, 0.86). KPC-producing K. pneumoniae was independently associated with in-hospital mortality (AOR, 3.60; 95% CI, 1.87-6.91).

CONCLUSIONS

KPC-producing K. pneumoniae is an emerging pathogen associated with significant mortality. Our findings highlight the urgent need to develop strategies for prevention and infection control. Limiting use of certain antimicrobials, specifically fluoroquinolones and cephalosporins, use may be effective strategies.

Fluoroquinolone-resistant Pseudomonas aeruginosa in chronic rhinosinusitis

BACKGROUND

Pseudomonas aeruginosa is cultured in nearly 1 of 5 patients with chronic rhinosinusitis and a history of sinus surgery. Fluoroquinolones are the only enterally administered antibiotics with efficacy against P. aeruginosa, but their frequent empiric use in the community raises concern for a rise in resistance.

OBJECTIVE

It was the aim of this study to determine the prevalence of fluoroquinolone-resistant P. aeruginosa in a tertiary rhinology practice.

METHODS

All bacterial sinus culture results from the outpatient otolaryngology clinic that yielded P. aeruginosa over a 5-year period (2002-2007) were reviewed along with the medical records of a randomly selected subset of patients.

RESULTS

In total, 689 culture results of 324 patients were examined. Nearly all patients had a history of endoscopic sinus surgery. Of all P. aeruginosa cultured, 13% were resistant to levofloxacin and 5% were intermediately sensitive, while 5% were resistant to ciprofloxacin and 7% intermediately sensitive. Of the 324 patients in the study, 19 and 15% had a history of a P. aeruginosa culture resistant to levofloxacin or ciprofloxacin, respectively. Mucoid strains of P. aeruginosa were significantly more likely to be fluoroquinolone resistant. No patient comorbidities were associated with a higher rate of resistance. The prevalence of resistant cultures remained stable over the 5-year study period.

CONCLUSIONS

P. aeruginosa is cultured primarily in patients with previous sinus surgery. Nearly 20% of isolates are resistant to fluoroquinolones. Resistance to levofloxacin is more common than resistance to ciprofloxacin. This study supports the use of culture-directed therapy in the management of the postfunctional endoscopic sinus surgery patient and the avoidance of empiric use of fluoroquinolones.

Treatment and outcomes for patients with bacteremic pneumococcal pneumonia

Delayed time to antibiotic administration has been linked with higher mortality for patients with community-acquired pneumonia, but the impact of antibiotic resistance on clinical outcomes has been controversial. In the current study we assess the combined impact of antibiotic resistance and antibiotic timing on outcomes, including inhospital mortality, complications, length of stay, and time to stability, for patients hospitalized with community-acquired bacteremic pneumococcal pneumonia. We conducted a retrospective cohort study in 43 hospitals in the Southeastern Pennsylvania region from 2001 to 2004. Eligible adult patients had pneumococcal bacteremia and radiographic evidence of pneumonia. Outcomes were assessed based on medical record review. Multivariable regression was used to adjust for severity of illness and sequentially assess the impact of antibiotic resistance and time to active antibiotic therapy. The overall inhospital mortality was 10%. Overall, levels of macrolide, cephalosporin, and fluoroquinolone resistance were low and did not adversely impact the time to administration of active antibiotic therapy. Receipt of at least 1 active antibiotic within 4 hours was associated with reduced mortality (odds ratio [OR], 0.47; 95% confidence interval [CI], 0.2-1.0) and shortened length of stay (OR, 0.77; CI, 0.6-1.0) but did not reduce the risk of other adverse outcomes. We conclude that early antibiotic administration reduces the risks of mortality in patients with bacteremic pneumococcal pneumonia. Current patterns of drug resistance did not lead to delays in administration of active antimicrobial therapy.

Clinical and microbiological outcomes of serious infections with multidrug-resistant gram-negative organisms treated with tigecycline

Eighteen patients received tigecycline as treatment for infection due to multidrug-resistant gram-negative bacilli, including Acinetobacter baumannii and Klebsiella pneumoniae carbapenemase- and extended-spectrum beta-lactamase-producing Enterobacteriaceae. Pretherapy minimum inhibitory concentration values for tigecycline predicted clinical success. Observed evolution of resistance during therapy raises concern about routine use of tigecycline in treatment of such infections when other therapies are available.

Gr-1highPolymorphonuclear Leukocytes and NK Cells Act via IL-15 to Clear IntracellularHaemophilus influenzaein Experimental Murine Peritonitis and Pneumonia

Polymorphonuclear leukocytes (PMNs) can be divided into Gr-1(high) and Gr-1(low) subpopulations, but the differences in the functions of these cells in the host are unknown. This study investigated the roles of these two cell populations in the clearance of an intracellular pathogen (Haemophilus influenzae) causing murine peritonitis and pneumonia. Microarray analysis and quantitative real-time PCR analysis of proteose peptone-elicited peritoneal murine PMNs showed that IL-15 mRNA levels were significantly higher in Gr-1(high) PMNs than in Gr-1(low) PMNs. In addition, IL-15 was produced only by Gr-1-positive PMNs, especially Gr-1(high) PMNs. IL-15 was required for efficient clearance of experimental murine H. influenzae pneumonia, as 4 days postinfection lungs from IL-15 knockout mice contained 50- to 100-fold more bacteria than did wild-type mouse lungs. Gr-1 PMN-depleted C57BL/6 mice were more susceptible to H. influenzae pneumonia than were Gr-1 PMN replete C57BL/6 mice or C57BL/6 nude mice, demonstrating that Gr-1 PMNs are important in the clearance of intracellular bacteria. IL-15-activated NK cells killed H. influenzae in PMNs. Flow cytometry confirmed the expression of CD69 on the cell membrane of IL-15-activated NK cells. Our results show that Gr-1(high) PMNs produce more IL-15 than Gr-1(low) PMNs, and that IL-15-activated NK cells protect against early infection by H. influenzae.

Why is long-term therapy required to cure tuberculosis?

The authors argue that understanding and countering general bacterial mechanisms of phenotypic antibiotic resistance may hold the key to reducing the duration of treatment of all recalcitrant bacterial infections, including tuberculosis.

Macrolide resistance in adults with bacteremic pneumococcal pneumonia

We conducted a case-control study of adults with bacteremic pneumococcal pneumonia to identify factors associated with macrolide resistance. Study participants were identified through population-based surveillance in a 5-county region surrounding Philadelphia. Forty-three hospitals contributed 444 patients, who were interviewed by telephone regarding potential risk factors. In multivariable analyses, prior exposure to a macrolide antimicrobial agent (odds ratio [OR] 2.8), prior flu vaccination (OR 2.0), and Hispanic ethnicity (OR 4.1) were independently associated with an increased probability of macrolide resistance, and a history of stroke was independently associated with a decreased probability of macrolide resistance (OR 0.2). Fifty-five percent of patients with macrolide-resistant infections reported no antimicrobial drug exposure in the preceding 6 months. Among patients who reported taking antimicrobial agents in the 6 months preceding infection, failure to complete the course of prescribed drugs was associated with an increased probability of macrolide resistance (OR 3.4).

Macrolide resistance in adults with bacteremic pneumococcal pneumonia

We conducted a case-control study of adults with bacteremic pneumococcal pneumonia to identify factors associated with macrolide resistance. Study participants were identified through population-based surveillance in a 5-county region surrounding Philadelphia. Forty-three hospitals contributed 444 patients, who were interviewed by telephone regarding potential risk factors. In multivariable analyses, prior exposure to a macrolide antimicrobial agent (odds ratio [OR] 2.8), prior flu vaccination (OR 2.0), and Hispanic ethnicity (OR 4.1) were independently associated with an increased probability of macrolide resistance, and a history of stroke was independently associated with a decreased probability of macrolide resistance (OR 0.2). Fifty-five percent of patients with macrolide-resistant infections reported no antimicrobial drug exposure in the preceding 6 months. Among patients who reported taking antimicrobial agents in the 6 months preceding infection, failure to complete the course of prescribed drugs was associated with an increased probability of macrolide resistance (OR 3.4).

Association between Fluoroquinolone Resistance and Mortality in Escherichia coli and Klebsiella pneumoniae Infections: The Role of Inadequate Empirical Antimicrobial Therapy

BACKGROUND

The prevalence of fluoroquinolone (FQ) resistance among Escherichia coli and Klebsiella pneumoniae has increased markedly in recent years. However, the impact of FQ resistance on mortality remains unknown.

METHODS

To identify the association between FQ resistance and mortality, we conducted a retrospective cohort study of hospitalized patients with infections due to FQ-resistant strains and FQ-susceptible strains of E. coli and K. pneumoniae between 1 January 1998 and 30 June 1999.

RESULTS

Of 123 patients with FQ-resistant infection, 16 (13.0%) died, compared with 4 (5.7%) of 70 patients with FQ-susceptible infection (odds ratio [OR], 2.47; 95% confidence interval [CI], 0.75-10.53). After adjustment for other significant risk factors and confounders, there remained an independent association between FQ-resistant infection and mortality (adjusted OR, 4.41; 95% CI, 1.03-18.81). Patients with FQ-resistant infection were significantly less likely to have received antimicrobial therapy with activity against the infecting pathogen within the first 24 h and 48 h of infection (P=.002 and P<.001, respectively). The association between FQ resistance and mortality was no longer significant, after adjusting for inadequate empirical therapy.

CONCLUSIONS

FQ resistance is an independent risk factor for mortality in patients with health care-acquired E. coli and K. pneumoniae infections. This may be explained, at least in part, by a delay in the initiation of appropriate antimicrobial therapy in patients with FQ-resistant infection. These results highlight the grave clinical consequences of FQ resistance and emphasize the importance of efforts designed to curb the increase in the prevalence of resistance to these agents.

Legionella pneumophila NudA Is a Nudix hydrolase and virulence factor

We studied the identity and function of the 528-bp gene immediately upstream of Legionella pneumophila F2310 ptsP (enzyme I(Ntr)). This gene, nudA, encoded for a Nudix hydrolase based on the inferred protein sequence. NudA had hydrolytic activity typical of other Nudix hydrolases, such as Escherichia coli YgdP, in that Ap(n)A's, in particular diadenosine pentaphosphate (Ap(5)A), were the preferred substrates. NudA hydrolyzed Ap(5)A to ATP plus ADP. Both ptsP and nudA were cotranscribed. Bacterial two-hybrid analysis showed no PtsP-NudA interactions. Gene nudA was present in 19 of 20 different L. pneumophila strains tested and in 5 of 10 different Legionella spp. other than L. pneumophila. An in-frame nudA mutation was made in L. pneumophila F2310 to determine the phenotype. The nudA mutant was an auxotroph that grew slowly in liquid and on solid media and had a smaller colony size than its parent. In addition, the mutant was more salt resistant than its parent and grew very poorly at 25 degrees C; all of these characteristics, as well as auxotrophy and slow-growth rate, were reversed by transcomplementation with nudA. The nudA mutant was outcompeted by about fourfold by the parent in competition studies in macrophages; transcomplementation almost completely restored this defect. Competition studies in guinea pigs with L. pneumophila pneumonia showed that the nudA mutant was outcompeted by its parent in both lung and spleen. NudA is of major importance for resisting stress in L. pneumophila and is a virulence factor.

Impact of pediatric vaccination with pneumococcal conjugate vaccine on the risk of bacteremic pneumococcal pneumonia in adults

Invasive pneumococcal disease in adults may be declining, reflecting a form of herd protection from a new pediatric pneumococcal conjugate vaccine. Our aim was to determine whether vaccination of children protects adults in the same home from bacteremic pneumococcal pneumonia. We conducted a case-control study with 43 participating hospitals across a five-county region in Pennsylvania. Eligible cases were adults with bacteremic pneumococcal pneumonia identified by the microbiology laboratories at participating hospitals. Controls were healthy adults from the region identified through random digit dialing. Cases and controls were interviewed by telephone. We analyzed vaccine protection in those adults who reported living in homes with at least one child < or =6 years of age. From April 2002 through June 2004, there was a significant decline in the proportion of adult pneumococcal bacteremia due to any of the seven serotypes in the conjugate vaccine (p=0.006). Within this time period, 17% of cases and controls reported living in homes with at least one child < or =6 years of age. In adjusted analysis, vaccination of the youngest child in the home was associated with an 80% reduction in the odds of bacteremic pneumococcal pneumonia among adults with children in the home (OR=0.2, 95% CI 0.1-0.8). We conclude that introduction of a pneumococcal conjugate vaccine for children has reduced the population rate of adult pneumococcal bacteremia due to vaccine serotypes and is associated with a reduced risk of bacteremic pneumococcal pneumonia for adults with children in the home.

In vitro and intracellular activities of LBM415 (NVP PDF-713) against Legionella pneumophila

LBM415 activity against extracellular and intracellular Legionella pneumophila was studied. The LBM415 MIC50 for 20 Legionella sp. strains was 4 microg/ml, versus 0.06, 0.25, and <or=0.03 microg/ml for azithromycin, erythromycin, and levofloxacin, respectively. LBM415 (0.5 and 16 microg/ml) reversibly prevented intracellular growth of two L. pneumophila strains and was less active than erythromycin.

Legionella maceachernii pneumonia in a patient with HIV infection

We report a case of fatal Legionella maceachernii pneumonia in a 49 year-old man with HIV infection and review the 3 previous reported cases, all of which occurred in individuals with underlying immune defects. Infection with L. maceachernii was attributable to the deaths of all cases. Issues related to the clinical aspects, laboratory identification of this unusual species, and detection of Legionnaires' diseases are discussed.

Pneumococcal Resistance to Macrolides, Lincosamides, Ketolides, and Streptogramin B Agents: Molecular Mechanisms and Resistance Phenotypes

The macrolides, lincosamides, ketolides, and streptogramin B agents (the MLKS(B) antimicrobial agents) have related chemical structures and share similar molecular targets on the 50S ribosomal subunit of Streptococcus pneumoniae. Mutations in rRNA or ribosomal proteins generate a variety of resistance phenotypes. The M phenotype of S. pneumoniae, which predominates in North America, affords low-level resistance to macrolides only (excluding macrolides with 16-member rings) by means of an efflux pump encoded by the mefA gene. The MLS(B) phenotype, which predominates in Europe, affords high-level resistance to macrolides, lincosamides, and streptogramin B agents and arises, in most cases, from dimethylation of adenine 2058 in the 23S rRNA of the 50S ribosomal subunit. Other, less common, phenotypes arise from other 23S rRNA modifications (ML and K phenotypes) or from amino acid substitution (MS(B) phenotype) or insertion (MKS(B) phenotype) into the 50S subunit ribosomal protein L4. In all cases, the decrease in susceptibility to ketolides (for example, telithromycin) is less than the decrease in susceptibility for other MLKS(B) agents.