Colonization resistance against multi-drug-resistant bacteria: a narrative review

Colonization resistance by gut microbiota is a fundamental phenomenon in infection prevention and control. Hospitalized patients may be exposed to multi-drug-resistant bacteria when hand hygiene compliance among healthcare workers is not adequate. An additional layer of defence is provided by the healthy gut microbiota, which helps clear the exogenous bacteria and acts as a safety net when hand hygiene procedures are not followed. This narrative review focuses on the role of the gut microbiota in colonization resistance against multi-drug-resistant bacteria, and its implications for infection control. The review discusses the underlying mechanisms of colonization resistance (direct or indirect), the concept of resilience of the gut microbiota, the link between the antimicrobial spectrum and gut dysbiosis, and possible therapeutic strategies. Antimicrobial stewardship is crucial to maximize the effects of colonization resistance. Avoiding unnecessary antimicrobial therapy, shortening the antimicrobial duration as much as possible, and favouring antibiotics with low anti-anaerobe activity may decrease the acquisition and expansion of multi-drug-resistant bacteria. Even after antimicrobial therapy, the resilience of the gut microbiota often occurs spontaneously. Spontaneous resilience explains the existence of a window of opportunity for colonization of multi-drug-resistant bacteria during or just after antimicrobial therapy. Strategies favouring resilience of the gut microbiota, such as high-fibre diets or precision probiotics, should be evaluated.

S-adenosylhomocysteine hydrolase deficiency in a 26-year-old man

This paper reports the third proven human case of deficient S-adenosylhomocysteine (AdoHcy) hydrolase activity. The patient is similar to the only two previously reported cases with this disorder in having severe myopathy, developmental delay, elevated serum creatine kinase (CK) concentrations, and hypermethioninaemia. Although he has been followed from infancy, the basic enzyme deficiency was established only at age 26 years. The diagnosis was based on markedly elevated plasma concentrations of both AdoHcy and S-adenosylmethionine, some 20% of the mean control activity of AdoHcy hydrolase activity in haemolysates of his red-blood cells, and two missense mutations in his gene encoding AdoHcy hydrolase. He had low values of erythrocyte phosphatidylcholine and plasma free choline and marginally elevated excretion of guanidinoacetate, suggesting that the elevated AdoHcy may have been inhibiting methylation of phosphatidylethanolamine and guanidinoacetate. His leukocyte DNA was globally more methylated than the DNA's of his parents or the mean extent of methylation measured in age-matched control subjects.

Fibrinogen Denver: a dysfibrinogenemia associated with an abnormal Reptilase time and significant bleeding

This paper reports a new dysfibrinogenemia with an unusual pattern of laboratory assays. The patient, a 51-year-old female with a lifelong moderate bleeding history, was initially diagnosed with von Willebrand disease based on routine coagulation assays and the clinical bleeding presentation. During recent testing as part of a preoperative screen and without any current history of treatment, levels of von Willebrand factor (VWF) antigen, VWF activity, and factor VIII activity were all significantly elevated, which was unexpected given her previous diagnosis. Additional testing was performed looking for other heritable causes for her considerable bleeding tendency. Interestingly, the patient had a significantly prolonged Reptilase time, minimally short thrombin time, and an abnormal fibrinogen-crossed immunoelectrophoresis pattern. Clearly, this patient had a fibrinogen abnormality that had been missed when only routine coagulation screening assays were performed. A brief review of the fibrinogen literature revealed no other dysfibrinogenemias reported with a similar pattern of test results, and thus this defect was designated fibrinogen Denver.

S-Adenosylhomocysteine hydrolase deficiency: a second patient, the younger brother of the index patient, and outcomes during therapy

S-Adenosylhomocysteine (AdoHcy) hydrolase deficiency has been proven in a human only once, in a recently described Croatian boy. Here we report the clinical course and biochemical abnormalities of the younger brother of this proband. This younger brother has the same two mutations in the gene encoding AdoHcy hydrolase, and has been monitored since birth. We report, as well, outcomes during therapy for both patients. The information obtained suggests that the disease starts in utero and is characterized primarily by neuromuscular symptomatology (hypotonia, sluggishness, psychomotor delay, absent tendon reflexes, delayed myelination). The laboratory abnormalities are markedly increased creatine kinase and elevated aminotransferases, as well as specific amino acid aberrations that pinpoint the aetiology. The latter include, most importantly, markedly elevated plasma AdoHcy. Plasma S-adenosylmethionine (AdoMet) is also elevated, as is methionine (although the hypermethioninaemia may be absent or nonsignificant in the first weeks of life). The disease seems to be at least to some extent treatable, as shown by improved myelination and psychomotor development during dietary methionine restriction and supplementation with creatine and phosphatidylcholine.

Continuous intravenous infusion of a plasma-derived factor IX concentrate (Mononine) in haemophilia B

This prospective, multicentre, open-label study evaluated the efficacy and safety of a plasma-derived factor IX concentrate [Mononine, Coagulation Factor IX (Human) Monoclonal Antibody Purified] administered by continuous intravenous (CIV) infusion to patients with haemophilia B. Admission criteria included documented diagnosis of haemophilia B (mild, moderate, or severe). Twenty-eight patients (25 surgery, two trauma, one severe spontaneous haemorrhage) were enrolled to receive a therapeutic bolus dose followed by CIV infusion of factor IX (FIX) to maintain FIX:C plasma levels of 0.4-1.0 IU mL(-1) (i.e. 40-100%). A median intravenous bolus dose of 54.2 IU kg(-1) FIX was administered to a subset of 13 non-emergency patients 7-21 days prior to CIV infusion to determine pharmacokinetic parameters in order to guide the dosing for CIV. For treatment, a bolus injection (median FIX dose; 89.6 IU kg(-1)) (range, 12.4-108.3), followed by a median total CIV infusion dose of 396.4 IU kg(-1) (range, 44.9-785.5) was administered at a median rate of 3.84 IU kg(-1) h(-1) (range, 1.74-7.33) for 107.17 h (range, 31.75-144). Twenty-four patients completed 72-120 h of FIX CIV infusion. Overall, 'excellent' (i.e. achievement of normal haemostasis) efficacy was reported in 23 of 24 (96%) evaluable patients, and 'good' (i.e. slight oozing) efficacy was reported in one (4%) patient. Median FIX:C was 72-86% for all patients receiving FIX by CIV on all days. Nine patients reported 13 adverse events that were possibly related to study medication but were not deemed serious by the investigator and were mainly because of local irritation at the infusion site. FIX CIV infusion therapy is safe and effective in the treatment of haemophilia B patients undergoing surgery, exposed to trauma, or experiencing severe spontaneous haemorrhage.

Increasing homocysteine levels and diabetic autonomic neuropathy

OBJECTIVE

To determine if hyperhomocysteinemia is a risk factor for the development of diabetic sensorimotor peripheral neuropathy (DSPN) and diabetic autonomic neuropathy (DAN).

BACKGROUND

Hyperhomocysteinemia and non-insulin-dependent diabetes mellitus (NIDDM) are both associated with premature vascular disease. Microvascular ischemia may be a risk factor for DSPN and DAN; therefore, the relationship of hyperhomocysteinemia to DSPN and DAN was investigated.

METHODS

Baseline neurological tests and homocysteine levels were determined in patients from a large prospective study of diabetic complications, the Appropriate Blood Pressure Control in Diabetes (ABCD) Trial.

RESULTS

Total homocysteine (tHcy) was independently associated with DAN; for each 1 micromol/l increase in tHcy, there was a 7.1% increased risk of developing DAN (P<0.05). There was no association between tHcy and DSPN.

CONCLUSIONS

Hyperhomocysteinemia may be a risk factor for DAN but not for DSPN. This relationship may be related to differential small fiber injury. Further studies are needed to investigate this relationship between tHcy and DAN. specifically whether treatment of hyperhomocysteinemia may modify DAN.

Association of the APOE epsilon 4 allele with clinical subtypes of late life depression

The APOE genotypes of 45 elderly inpatients with major depression were determined to investigate the relationship of this disorder to irreversible dementia in late life. We specifically tested the hypothesis that the frequency of the APOE epsilon 4 allele is elevated in depressed elders with cognitive impairment or psychotic features, subtypes that have been reported to be at increased risk of developing Alzheimer's disease (AD). The frequency of epsilon 4 allele was not elevated in the overall group of 45 inpatients and, contrary to our expectation, was not associated with cognitive impairment in this group. In contrast, the epsilon 4 allele frequency for the patients with psychotic features was nearly four times that for the patients without psychotic features and nearly double that of elderly controls. These data suggest that elderly depressed inpatients with cognitive impairment are at risk for developing AD by an epsilon 4-independent pathway, while those with psychotic features are at risk for developing AD by an epsilon 4-dependent pathway. These findings suggest that subtypes of idiopathic major depression in late life may serve as landmarks that distinguish separable pathogenetic pathways to AD.

Association of the apolipoprotein E epsilon 4 allele with clinical subtypes of autopsy-confirmed Alzheimer's disease

Consistent with previous reports, we observed a significant association of the APOE epsilon 4 allele with Alzheimer's Disease (AD) in a series of 91 autopsy-confirmed cases. The epsilon 4 allele frequency was higher in cases with a family history of AD-like dementia (0.54 +/- 0.07), although the epsilon 4 allele frequency in the AD cases with a negative family history (0.38 +/- 0.05) remained significantly greater than that for the non-AD control group (0.13 +/- 0.03). A similar increase in epsilon 4 allele frequency (0.54 +/- 0.07) was observed in the AD cases with amyloid angiopathy, compared to those who did not have amyloid angiopathy (0.36 +/- 0.04). Contrary to previous reports, no effect of the dosage of the epsilon 4 allele was found on the age of onset of dementia among the AD cases and, contrary to reports suggesting an association of epsilon 4 and atherosclerosis, the epsilon 4 allele frequency was similar in cases with or without concurrent brain infarcts. Modest but consistent correlations were observed between the dosage of epsilon 4 alleles and the cortical density of senile plaques, but not neurofibrillary tangles. The last finding suggests that the pathogenic events mediated by the epsilon 4 allele may be more directly involved in the formation of senile plaques, the identifying lesions in AD, than neurofibrillary tangles. A robust association of both the presence of an epsilon 4 allele and a family history of AD-like dementia with concurrent amyloid angiopathy occurred within our sample of AD cases. This association arose from an interaction of the epsilon 4 allele with a separate familial factor for which a family history of dementia served as a surrogate. These results suggest that amyloid angiopathy may be a common or central feature of a form of familial AD that is associated with the transmission of the APOE epsilon 4 allele.