Bacteremia in hospitalized patients with human immunodeficiency virus: A prospective, cohort study

Multi-Clinical Factors Combined with an Artificial Intelligence Algorithm Diagnosis Model for HIV-Infected People with Bloodstream Infection

Purpose

Although highly active antiretroviral therapy (HA-ART) can effectively suppress the disease process in patients with acquired immunodeficiency syndrome (AIDS), opportunistic infections, mainly bloodstream infections (BSI), are still the main cause of death in people living with HIV. There is no effective diagnostic strategy for HIV-infected people with BSI. This study aimed to develop an AI diagnostic model with high sensitivity to improve the early detection of HIV-infected people with BSI.

Patients and Methods

This study retrospectively analyzed the 40 clinical factors of 498 HIV-infected people (171 with BSI positive and 327 with BSI negative) who admitted to Wenzhou Central Hospital from September 2014 to July 2021. This study used the hospital information management system to collect the clinical characteristics, laboratory and imaging examination results, and clinical diagnosis of the two groups. The diagnostic results of all patients were in line with the diagnostic criteria of the Chinese Guidelines for the Diagnosis and Treatment of AIDS (2021 Edition), and the BSI diagnosis was in line with the diagnostic criteria of sepsis and bacteremia in Practical Internal Medicine (13th Edition). On this basis, various risk prediction models were established by combining 8 artificial intelligence (AI) algorithms in the training set and validating the diagnosis performance in the testing set. The model with the best diagnostic performance was selected as the final diagnostic model.

Results

The clinical characteristics of HIV-infected people with BSI are atypical, and the pathogens in this area are mainly fungi. Ten risk factors were selected: low level of hemoglobin, CD4+T cell and platelets, high level of lactate dehydrogenase and blood urea nitrogen, splenomegaly, without ART treatment, strip shadow, nodular shadow, and shock. The combination of the ten risk factors, age, gender and the "svmRadial" model can identify the HIV-infected people with BSI from the HIV-infected people without BSI with an area under the curve of 0.916 and a sensitivity and specificity of 0.824 and 0.855, respectively.

Conclusion

The model showed excellent performance in diagnosing HIV-infected people with BSI. Internal and external validation showed that the diagnosis model had high clinical application value.

Risk Factors and Outcomes of Bloodstream Infections Among People With Human Immunodeficiency Virus: A Longitudinal Cohort Study From 2000 to 2017

Background

Bloodstream infections (BSIs) among people with human immunodeficiency virus (PWH) remain a poorly studied source of morbidity and mortality. We characterize the epidemiology, microbiology, and clinical outcomes including reinfection, hospitalization, and mortality rates of both community-acquired and hospital-acquired BSI in PWH.

Methods

We identified all BSI, between January 1, 2000 and December 31, 2017 in PWH in care at Southern Alberta Clinic, by linking data from laboratory and clinical databases. Crude incidence rates per 1000 person-years for BSI and death were calculated. Cox proportional hazards models estimated crude and adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) to conduct a risk factor analysis of BSI in PWH. Logistic regression models with generalized estimating equations estimated crude and adjusted odds ratios (aORs) to identify characteristics associated with 1-year mortality after BSI.

Results

Among 2895 PWH, 396 BSI episodes occurred in 228 (8%) PWH. There were 278 (72%) Gram-positive and 109 (28%) Gram-negative BSI. People with human immunodeficiency virus with lower CD4 nadirs, higher Charlson comorbidity indices, and hepatitis C virus were at highest risk for BSI. Long-term all-cause mortality was greater in those experiencing BSI (HR, 5.25; 95% CI, 4.21-6.55). CD4 count <200 cells/mm³ measured closest to the time of BSI was associated with 1-year mortality after BSI (aOR, 3.88; 95% CI, 1.78-8.46). Repeat episodes (42%) and polymicrobial BSI (19%) were common.

Conclusions

Bloodstream infections continue to occur at an elevated rate among PWH with high reoccurrence rates and associated morbidity and mortality. To risk stratify and develop targeted interventions, we identified PWH at greatest risk for BSI. People with human immunodeficiency virus with low immunity at the time of BSI are at highest risk of poor outcomes.

Mortality predictive factors of people living with human immunodeficiency virus and bloodstream infection

INTRODUCTION

Portugal has one of the highest mortality rates for people living with HIV (PLWHIV) in Europe. After antiretroviral therapy introduction, HIV-associated mortality declined, included the one associated with bloodstream infection (BSI). However it is still high, and European data are scarce . Therefore, characterizing BSI and defining prognostic factors may improve our approach.

METHODS

This was a 10-year retrospective study of predictive factors for 30-day and 3-year mortality in PLWHIV with BSI in a tertiary infectious diseases ward.

RESULTS

Of 2134 PLWHIV admissions, 145 (6.8%) had a BSI, mostly respiratory and catheter-related bacteremia and globally community-acquired. Nosocomial infections occurred in 42 (36%) cases, mostly caused by Enterococcus spp, Staphylococcus aureus, and Candida spp. PLWHIV with a BSI had higher 30-day mortality (27%) compared to those without a BSI (14%). APACHE II score, corticotherapy, and current intravenous drug use (IDU) had a prognostic impact on 30-day mortality. Three-year survival was 54% in PLWHIV with a BSI; a CD4 <200 cells, vascular or chronic pulmonary disease, and lymphoma were prognostic factors.

CONCLUSIONS

Patients with a BSI were more likely to present advanced HIV disease, have more comorbidities, a longer length of stay, and higher 30-day mortality. IDU and severity of infection determined the short-term prognosis. Three-year mortality was primarily influenced by lower CD4 cell counts, hematological tumor, and cardiopulmonary comorbidities. Systemic corticotherapy may influence nosocomial BSI and short-term prognosis.

Longitudinal evaluation of risk factors and outcomes of blood stream infections due to Staphylococcus species in persons with HIV: An observational cohort study

BACKGROUND

Staphylococcal blood stream infections (SBSI) are a significant cause of morbidity and mortality, however there is little data on such infections in persons with HIV (PWH) in the combination antiretroviral therapy era, particularly when divided by species; methicillin-sensitive (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) and coagulase-negative Staphylococcus (CoNS).

METHODS

Using linked longitudinal clinical and microbiologic databases, all cases of SBSI in PWH accessing care at Southern Alberta Clinic were identified and demographic features and outcomes characterized. We compared participants with SBSI to those with no SBSI and determined the 1-year all-cause mortality following SBSI and longitudinally over the study period.

FINDINGS

From 2000 to 2018, 130 SBSI occurred in 95 PWH over 21,526 patient-years follow-up. MSSA caused 38.4%, MRSA 26.1% and CoNS 35.3% of SBSI. Highest risks for SSBI were in Hepatitis C coinfection, low CD4 nadir, Indigenous/Metis ethnicity and in persons who use injection drugs (PWID). During follow-up, 423 deaths occurred in all PWH. Mortality rates for PWH with SBSI was 74.9/1000 patient-years (95% CI 59.2-94.9) compared with no SBSI 16.0/1000 patient-years (95% CI 14.4-17.7). The mortality Hazard Ratio was 2.61(95% CI 1.95-3.49, P= <0.001) for SBSI compared to no SBSI, following adjusting for confounding. Seventy deaths occurred in persons with SBSI with 40% in the first year. Higher 1-year mortality rates occurred in hospital-acquired infections.

INTERPRETATION

Incidence rates of SBSI are high in PWH, with identified characteristics that further increase this risk. PWH who experience SBSI have a significant mortality risk within the first year of follow-up, however they also have greater long-term all-cause mortality compared to those with no SBSI. Further investigation is needed in PWH evaluating host, environment and pathogen differences that lead to differing rates of SBSI and mortality seen here.

FUNDING

No funding was received for this work.

Antimicrobial Resistance Patterns of Bacterial Isolates from Blood Culture among HIV/AIDS Patients at Felege Hiwot Referral Hospital, Northwest Ethiopia

Background

The emergence and spread of antimicrobial resistance in bacteria is recognized as a global public health problem. Bloodstream infection with antimicrobial-resistant bacteria in HIV/AIDS patients makes the problem more challenging. So, regular and periodic diagnosis and use of the appropriate antimicrobial susceptibility pattern determination is the only option for decreasing the prevalence and development of drug-resistant bacteria.

Methods

An institution-based cross-sectional study was conducted among 384 HIV/AIDS patients. Sociodemographic data of patients were recorded using structured questionnaires. Blood cultures were collected with BACTEC aerobic blood culture bottles. A pair of samples was collected from each patient aseptically and incubated at 37°. If samples are positive for bacterial agents, they were subcultured to solid media such as blood agar plate, chocolate agar plate, and MacConkey agar plates. Identification was performed using colony characteristics and standard biochemical techniques. The antimicrobial susceptibility test was determined by the Kirby–Bauer disc diffusion method. Data entry and analysis were performed while using SPSS version 20. Descriptive statistics were performed to calculate frequencies.

Results

Altogether, 384 patients were included, and 123 blood cultures were positive, so that the yield was thus 32%. About 46 (37.4%) of Gram-negative and 77 (62.6%) of Gram-positive bacterial species were identified. Among Gram-negative bacterial isolates, K. pneumoniae was the leading pathogen, 19 (41.3%), whereas S. aureus, 38 (49.4%), was predominant among Gram-positive isolates. In his study, the majority of Gram-positive isolates showed high level of resistance to penicillin, 72 (95.5%), tetracycline, 55 (71.4%), and cotrimoxazole, 45 (58.4%). About 28 (73.6%) of S. aureus isolates were also methicillin-resistant. Gram-negative bacterial isolates also showed a high resistance to ampicillin (91.3%), tetracycline (91.3%), and gentamicin (47.8%). Overall, about 78% of multidrug resistance was observed.

Conclusion

Several pathogens were resistant to greater than five antimicrobial agents, so that proper management of patients with bacteremia is needed, and a careful selection of effective antibiotics should be practiced.

Epidemiology and Outcomes of Bloodstream Infections in HIV-Patients during a 13-Year Period

No data on antibiotic resistance in bloodstream infection (BSI) in people living with HIV (PLWH) exist. The objective of this study was to describe BSI epidemiology in PLWH focusing on multidrug resistant (MDR) organisms. A retrospective, single-center, observational study was conducted including all positive blood isolates in PLWH from 2004 to 2017. Univariable and multivariable GEE models using binomial distribution family were created to evaluate the association between MDR and mortality risk. In total, 263 episodes (299 isolates) from 164 patients were analyzed; 126 (48%) BSI were community-acquired, 137 (52%) hospital-acquired. At diagnosis, 34.7% of the patients had virological failure, median CD4 count was 207/μL. Thirty- and 90-day mortality rates were 24.2% and 32.4%, respectively. Thirty- and 90-day mortality rates for MDR isolates were 33.3% and 46.9%, respectively (p < 0.05). Enterobacteriaceae were the most prevalent microorganisms (29.8%), followed by Coagulase-negative staphylococci (21.4%), and S. aureus (12.7%). In BSI due to MDR organisms, carbapenem-resistant K. pneumoniae and methicillin-resistant S. aureus were associated with mortality after adjustment for age, although this correlation was not confirmed after further adjustment for CD4 < 200/μL. In conclusion, BSI in PLWH is still a major problem in the combination antiretroviral treatment era and it is related to a poor viro-immunological status, posing the question of whether it should be considered as an AIDS-defining event.

Treating bacterial pneumonia in people living with HIV

Introduction: Bacterial pneumonia remains an important cause of morbidity and mortality in people living with HIV (PLWH) in the antiretroviral therapy (ART) era. In addition to being immunocompromised, as reflected by low CD4 cell counts and elevated HIV viral loads, PLWH often have other behaviors associated with an increased risk of pneumonia including smoking and injected drug use. As PLWH are aging, comorbid conditions such as chronic obstructive pulmonary disease (COPD), cancers, and cardiovascular, renal and liver diseases are emerging as additional risk factors for pneumonia. Pathogens are often similar to those in HIV-uninfected individuals; however, PLWH are at risk for unusual and/or multi-drug resistant organisms causing bacterial pneumonia based, in part, on their CD4 cell counts and other exposures. Areas covered: In this review, we focus on the recognition and management of bacterial community-acquired pneumonia (CAP) in PLWH. Along with antimicrobial treatment, we discuss prevention strategies such as vaccination and smoking cessation. Expert opinion: Early initiation of ART after HIV infection can decrease the risk of pneumonia. Improved efforts at vaccination, smoking cessation, and reduction of other substance use are urgently needed in PLWH to decrease the risk for bacterial pneumonia. As PLWH are aging, comorbidities are additional risk factors for bacterial CAP.

Bloodstream infections in patients living with HIV in the modern cART era

Retrospective multicentre study aiming at analysing the etiology, characteristics and outcome of bloodstream infections (BSI) in people living with HIV (PLWHIV) in an era of modern antiretroviral therapy. Between 2008 and 2015, 79 PLWHIV had at least 1 BSI, for a total of 119 pathogens isolated. Patients were mainly male (72.1%), previous intravenous drug users (55.7%), co-infected with HCV or HBV (58.2%) and in CDC stage C (60.8%). Gram-positive (G+) pathogens caused 44.5% of BSI, followed by Gram-negative (G−), 40.3%, fungi, 10.9%, and mycobacteria, 4.2%. Candida spp. and coagulase-negative staphylococci were the most frequent pathogens found in nosocomial BSI (17% each), while E.coli was prevalent in community-acquired BSI (25%). At the last available follow-up, (mean 3.2 ± 2.7 years) the overall crude mortality was 40.5%. Factors associated with mortality in the final multivariate analysis were older age, (p = 0.02; HR 3.8, 95%CI 1.2–11.7) CDC stage C (p = 0.02; HR 3.3, 95%CI 1.2–9.1), malignancies, (p = 0.004; HR 3.2, 95%CI 1.4–7.0) and end stage liver disease (p = 0.006; HR 3.4, 95%CI 1.4–8.0). In conclusion, the study found high mortality following BSI in PLWHIV. Older age, neoplastic comorbidities, end stage liver disease and advanced HIV stage were the main factors correlated to mortality.

Serum albumin and osmolality inhibit Bdellovibrio bacteriovorus predation in human serum

We evaluated the bactericidal activity of Bdellovibrio bacteriovorus, strain HD100, within blood sera against bacterial strains commonly associated with bacteremic infections, including E. coli, Klebsiella pneumoniae and Salmonella enterica. Tests show that B. bacteriovorus HD100 is not susceptible to serum complement or its bactericidal activity. After a two hour exposure to human sera, the prey populations decreased 15- to 7,300-fold due to the serum complement activity while, in contrast, the B. bacteriovorus HD100 population showed a loss of only 33%. Dot blot analyses showed that this is not due to the absence of antibodies against this predator. Predation in human serum was inhibited, though, by both the osmolality and serum albumin. The activity of B. bacteriovorus HD100 showed a sharp transition between 200 and 250 mOsm/kg, and was progressively reduced as the osmolality increased. Serum albumin also acted to inhibit predation by binding to and coating the predatory cells. This was confirmed via dot blot analyses and confocal microscopy. The results from both the osmolality and serum albumin tests were incorporated into a numerical model describing bacterial predation of pathogens. In conclusion, both of these factors inhibit predation and, as such, they limit its effectiveness against pathogenic prey located within sera.

Bloodstream infections in HIV-infected patients

In the combined antiretroviral therapy era, HIV-infected patients remain a vulnerable population for the onset of bloodstream infections (BSI). Worldwide, nontyphoid salmonellae, Streptococcus pneumoniae, Escherichia coli, Staphylococcus aureus and coagulase negative staphylococci are the most important pathogens. Intravenous catheter associated infection, skin-soft tissue infection and endocarditis are associated with Gram-positive bacteremia. Among the Gram-negative, nontyphoidal Salmonella have been previously correlated to sepsis. Other causes of BSI in HIV-infected patients are mycobacteria and fungi. Mycobacteria constitute a major cause of BSI in limited resource countries. Fungal BSI are not frequent and among them Cryptococcus neoformans is the most common life-threatening infection. The degree of immunosuppression remains the key prognostic factor leading to the development of BSI.

Characteristics, causes, and outcome of 54 episodes of bloodstream infections in a cohort of HIV patients

BACKGROUND

Patients infected with human immunodeficiency virus (HIV) have an increased risk for bloodstream infections (BSIs). Published recent data on characteristics, etiology, and outcome of BSIs in HIV patients in high income countries are scarce.

METHODS

Blood cultures from 2001 to 2011 from adult HIV patients were retrieved. Blood cultures considered to be contamination based on isolates and clinical context were excluded. Clinical and microbiological characteristics of BSIs and patients were described, those of community-acquired and nosocomial episodes were compared, and risk factors for 6-month mortality were analyzed.

RESULTS

We found 54 episodes of true BSI in 46 patients. Demographics were similar to those of the source cohort of all patients followed between 2001 and 2011. In 63% there was prior AIDS, in 91% a CD4 nadir below 200/mm(3), and in 72% a latest CD4 count < 200/mm(3). In 13% of patients BSI preceded a new HIV diagnosis within 1 week. Main causative microorganisms were coagulase-negative staphylococci (26%), Streptococcus pneumoniae (20%), and Enterococcus spp. (13%). The most frequent diagnoses were pneumonia (28%) and catheter-related BSI (CRBSI) (28%); 56% of episodes were nosocomial. The 1-month mortality rate was 17%, with a cause of death apparently unrelated to the BSI in five of nine episodes. The 6-month mortality was 28%. Factors of co-morbidity or immunodeficiency other than HIV were significantly associated with 6-month mortality.

CONCLUSIONS

BSIs in HIV-infected patients occur predominantly in patients with advanced HIV infection. Community-acquired bacteremic pneumococcal pneumonia and nosocomial staphylococcal CRBSIs are the main causes. Mortality following BSI is high, and seems to be driven by underlying complicated HIV infection.

Community-acquired bacterial bloodstream infections in HIV-infected patients: a systematic review

Information on community-acquired bacterial bloodstream infections (BSIs) in individuals infected with human immunodeficiency virus (HIV) is limited. We conducted a systematic literature review. The case fraction of community-acquired bacterial BSIs in hospitalized patients is 20% and 30% in adults and children, respectively, compared to 9% in HIV-negative adults and children. Worldwide, the main pathogens of community-acquired BSI are nontyphoid salmonellae (NTS), Streptococcus pneumoniae, Escherichia coli, and Staphylococcus aureus, but regional differences are apparent, especially for S. pneumoniae. Compared to HIV-negative populations, HIV patients are particularly at risk to develop NTS bacteremia. Bacteremia incidence is related to immunosuppression, and antiretroviral therapy reduces the incidence of BSI in HIV patients (rate ratios, 0.63-0.02). Mortality rates varied between 7% and 46%. These results suggest that bacterial BSI is more likely to be found in HIV-positive than in HIV-negative patients upon hospitalization, and that causative pathogens vary by region.

AIDS Patients in the ICU

At the beginning of the AIDS epidemic, there were higher mortality rates in patients requiring admission to an intensive care unit (ICU) most likely due to acute respiratory failure. Whereas the use of prophylaxis and corticosteroids for Pneumocystisjiroveci pneumonia and highly active antiretroviral therapy has changed this outcome and has improved survival rate. However, respiratory failure has remained the most common indication for an ICU admission. When HIV-infected patients are admitted to the ICU, intensivists need to be knowledgeable about the manifestations of common diseases and the new manifestations related to antiretroviral therapy. Much HIV mortality has been linked directly to late diagnosis and late initiation of appropriate antiviral therapy. This l, the most important cause of ICU admission for AIDS patients. We analyzed the characteristics of P.jiroveci pneumonia, bacterial pneumonia, cytomegalovirus pneumonia, mycobacterial infections, pulmonary invasive fungal infections, Kaposi’s sarcoma, and the immune reconstitution inflammatory syndrome.

Bacterial bloodstream infections in HIV-infected adults attending a Lagos teaching hospital

An investigation was carried out during October 2005-September 2006 to determine the prevalence of bloodstream infections in patients attending the outpatient department of the HIV/AIDS clinic at the Lagos University Teaching Hospital in Nigeria. Two hundred and one patients--86 males and 115 females--aged 14-65 years were recruited for the study. Serological diagnosis was carried out on them to confirm their HIV status. Their CD4 counts were done using the micromagnetic bead method. Twenty mL of venous blood sample collected from each patient was inoculated into a pair of Oxoid Signal blood culture bottles for 2-14 days. Thereafter, 0.1 mL of the sample was plated in duplicates on MacConkey, blood and chocolate agar media and incubated at 37 degrees C for 18-24 hours. The CD4+ counts were generally low as 67% of 140 patients sampled had < 200 cells/microL of blood. Twenty-six bacterial isolates were obtained from the blood samples and comprised 15 (58%) coagulase-negative staphylococci as follows: Staphylococcus epidermidis (7), S. cohnii cohnii (1), S. cohnii urealyticum (2), S. chromogenes (1), S. warneri (2), S. scuri (1), and S. xylosus (1). Others were 6 (23%) Gram-negative non-typhoid Salmonella spp., S. Typhimurium (4), S. Enteritidis (2); Pseudomonas fluorescens (1), Escherichia coli (1), Ochrobactrum anthropi (1), Moraxella sp. (1), and Chryseobacterium meningosepticum. Results of antimicrobial susceptibility tests showed that coagulase-negative staphylococci had good sensitivities to vancomycin and most other antibiotics screened but were resistant mainly to ampicilin and tetracycline. The Gram-negative organisms isolated also showed resistance to ampicillin, tetracycline, chloramphenicol, and septrin. This study demonstrates that coagulase-negative staphylococci and non-typhoidal Salmonellae are the most common aetiological agents of bacteraemia among HIV-infected adults attending the Lagos University Teaching Hospital, Nigeria. The organisms were resistant to older-generation antibiotics often prescribed in this environment but were sensitive to vancomycin, cefotaxime, cefuroxime, and other new-generation antibiotics.

Benefit of antiretroviral therapy on survival of human immunodeficiency virus-infected patients admitted to an intensive care unit

OBJECTIVE

To evaluate the impact of antiretroviral therapy (ART) and the prognostic factors for in-intensive care unit (ICU) and 6-month mortality in human immunodeficiency virus (HIV)-infected patients.

DESIGN

A retrospective cohort study was conducted in patients admitted to the ICU from 1996 through 2006. The follow-up period extended for 6 months after ICU admission.

SETTING

The ICU of a tertiary-care teaching hospital at the Universidade de São Paulo, Brazil.

PARTICIPANTS

A total of 278 HIV-infected patients admitted to the ICU were selected. We excluded ICU readmissions (37), ICU admissions who stayed less than 24 hours (44), and patients with unavailable medical charts (36).

OUTCOME MEASURE

In-ICU and 6-month mortality.

MAIN RESULTS

Multivariate logistic regression analysis and Cox proportional hazards models demonstrated that the variables associated with in-ICU and 6-month mortality were sepsis as the cause of admission (odds ratio [OR] = 3.16 [95% confidence interval [CI] 1.65-6.06]); hazards ratio [HR] = 1.37 [95% CI 1.01-1.88]), an Acute Physiology and Chronic Health Evaluation II score >19 [OR = 2.81 (95% CI 1.57-5.04); HR = 2.18 (95% CI 1.62-2.94)], mechanical ventilation during the first 24 hours [OR = 3.92 (95% CI 2.20-6.96); HR = 2.25 (95% CI 1.65-3.07)], and year of ICU admission [OR = 0.90 (95% CI 0.81-0.99); HR = 0.92 [95% CI 0.87-0.97)]. CD4 T-cell count <50 cells/mm(3) was only associated with ICU mortality [OR = 2.10 (95% CI 1.17-3.76)]. The use of ART in the ICU was negatively predictive of 6-month mortality in the Cox model [HR = 0.50 (95% CI 0.35-0.71)], especially if this therapy was introduced during the first 4 days of admission to the ICU [HR = 0.58 (95% CI 0.41-0.83)]. Regarding HIV-infected patients admitted to ICU without using ART, those who have started this treatment during ICU stay presented a better prognosis when time and potential confounding factors were adjusted for [HR 0.55 (95% CI 0.31-0.98)].

CONCLUSIONS

The ICU outcome of HIV-infected patients seems to be dependent not only on acute illness severity, but also on the administration of antiretroviral treatment.

Nucleotide biosynthesis is critical for growth of bacteria in human blood

Proliferation of bacterial pathogens in blood represents one of the most dangerous stages of infection. Growth in blood serum depends on the ability of a pathogen to adjust metabolism to match the availability of nutrients. Although certain nutrients are scarce in blood and need to be de novo synthesized by proliferating bacteria, it is unclear which metabolic pathways are critical for bacterial growth in blood. In this study, we identified metabolic functions that are essential specifically for bacterial growth in the bloodstream. We used two principally different but complementing techniques to comprehensively identify genes that are required for the growth of Escherichia coli in human serum. A microarray-based and a dye-based mutant screening approach were independently used to screen a library of 3,985 single-gene deletion mutants in all non-essential genes of E. coli (Keio collection). A majority of the mutants identified consistently by both approaches carried a deletion of a gene involved in either the purine or pyrimidine nucleotide biosynthetic pathway and showed a 20- to 1,000-fold drop in viable cell counts as compared to wild-type E. coli after 24 h of growth in human serum. This suggests that the scarcity of nucleotide precursors, but not other nutrients, is the key limitation for bacterial growth in serum. Inactivation of nucleotide biosynthesis genes in another Gram-negative pathogen, Salmonella enterica, and in the Gram-positive pathogen Bacillus anthracis, prevented their growth in human serum. The growth of the mutants could be rescued by genetic complementation or by addition of appropriate nucleotide bases to human serum. Furthermore, the virulence of the B. anthracis purE mutant, defective in purine biosynthesis, was dramatically attenuated in a murine model of bacteremia. Our data indicate that de novo nucleotide biosynthesis represents the single most critical metabolic function for bacterial growth in blood and reveal the corresponding enzymes as putative antibiotic targets for the treatment of bloodstream infections.

Bacterial growth in the bloodstream is a common manifestation of a number of bacterial infections. When growing in blood, bacteria not only have to evade the host's immune response, but also adjust their metabolism to suit availability of nutrients. Although the concentrations of various metabolites in human blood are known, it is difficult to predict which nutrients are abundant and which are scarce. To proliferate in human blood, bacteria need to synthesize metabolites that are present in the limiting concentrations. For that, they need to produce specific enzymes that are, thus, critical for the bacterial growth in the bloodstream. We carried out a comprehensive, genome-wide search for Escherichia coli genes that are essential for growth in human serum. We found that inactivation of nucleotide biosynthesis genes leads to a significant growth defect in human serum not only for E. coli but also for two other pathogens, Salmonella Typhimurium and Bacillus anthracis. The results of this study demonstrate that the limiting amounts of the nucleotide bases in human serum force invading pathogens to rely on de novo nucleotide biosynthesis. Hence, our findings reveal nucleotide biosynthesis enzymes as a possible target for the treatment of bloodstream infections.

The evidence for using conjugate vaccines to protect HIV-infected children against pneumococcal disease

Pneumococcal conjugate vaccines (PCVs) are a potentially useful complement to existing treatment strategies in HIV-infected children, for whom pneumococcal infections are common and serious. This Review summarises available data on the burden of pneumococcal disease and the safety and efficacy of PCVs in HIV-infected children. The data demonstrate that children with HIV have significantly increased risk of pneumococcal disease compared with uninfected children; the serotypes included in currently licensed or near-licensure conjugate vaccines include most serotypes that cause invasive pneumococcal disease (IPD) in HIV-infected children and adults; PCVs provide substantial protection against IPD and clinical pneumonia when given to HIV-infected infants; and HIV-infected adults gain an indirect benefit when children in the community are vaccinated. PCV should be considered as an important intervention for improving the lives of HIV-infected children.

Antibacterial activity of a competence-stimulating peptide in experimental sepsis caused by Streptococcus pneumoniae

Streptococcus pneumoniae, a major cause of human disease, produces a 17-mer autoinducer peptide pheromone (competence-stimulating peptide [CSP]) for the control of competence for genetic transformation. Due to previous work linking CSP to stress phenotypes, we set up an in vivo sepsis model to assay its effect on virulence. Our data demonstrate a significant increase in the rates of survival of mice, reductions of blood S. pneumoniae counts, and prolonged times to death for mice treated with CSP. In vitro the dose of CSP used in the animal model produced a transitory inhibition of growth. When a mutant with a mutation in the CSP sensor histidine kinase was assayed, no bacteriostatic phenotype was detected in vitro and no change in disease outcome was observed in vivo. The data demonstrate that CSP, which induces in vitro a temporary growth arrest through stimulation of its cognate histidine kinase receptor, is able to block systemic disease in mice. This therapeutic effect is novel, in that the drug-like effect is obtained by stimulation, rather than inhibition, of a bacterial drug target.