In Vitro Testing of Antimicrobial Agents

Influence of dietary catechols on the growth of enteropathogenic bacteria

The dietary constituents that may act, in the broadest sense, as co-factors to enable bacterial enteropathogens to replicate in gastrointestinal environments are still largely unknown. Recent work has demonstrated that certain non-nutritional components of food, such as the catecholamines, can contribute to the ability of Gram-negative pathogens to replicate in iron-restrictive media that may be reflective of gastrointestinal environments. The present report examines whether other, non-catecholamine, dietary catechols, which occur widely in plant foods, can also influence enteropathogen growth in an iron-restrictive environment such as might be found in the gastrointestinal tract. In the present study, we have examined the ability of a range of catechol-rich foodstuffs, ranging from beverages (tea and coffee) to fruit and vegetable extracts, as well as purified preparations of commonly consumed dietary catechols (catechins, chlorogenic acid, caffeic acid and tannic acid), to modulate the growth of the Gram-negative enteric pathogens Escherichia coli O157:H7 and Salmonella enterica SV Enteriditis. Time-dependent growth in response to dietary catechols (0.05-5.0% v/v of beverage or fruit/vegetable extracts; 10-200 microM of purified catechols) was examined in an iron-replete, rich medium as well as in an iron-limited, basal medium designed to reflect the iron-restricted environment that is more characteristic of human and animal tissues. Results obtained in iron-replete, rich medium demonstrated dose-dependent bacteriostatic effects for certain catechols, consistent with previous studies. However, in iron-restricted medium, all of the dietary catechols produced marked growth stimulation of up to 4 logs greater than non-supplemented controls. Mechanistic studies measuring the uptake of radiolabelled (55)Fe from (55)Fe-labelled lactoferrin and transferrin in bacteria grown in the presence or absence of dietary catechols demonstrated that the ability of catechols to stimulate bacterial growth was dependent on the provision of iron from iron-sequestering glycoproteins. Urea gel analysis of transferrin incubated in the presence of the dietary catechols confirmed that these compounds were directly chelating and removing transferrin-complexed iron. Analysis using E. coli O157:H7 entA and tonB mutants further showed that a functional siderophore synthesis and uptake system was required for the growth-stimulatory response. In contrast to previous studies, which have reported the anti-microbial activity of dietary catechols, the present study demonstrates that these non-nutritional components of foods can, under iron-restrictive conditions, provide iron and enable the growth of enteric bacterial pathogens.

Principles of Antimicrobial Therapy

The most compelling reason for practicing judicious antimicrobial use is to facilitate therapeutic success. The definition of therapeutic success has changed in recent years, however; not only does success include eradication of infection, but it must now include avoidance of resistance. If the goal of antimicrobial therapy is to achieve sufficient concentrations at the site of infection such that the infecting organism is killed, therapy should be successful.

Empiric antibiotic treatment and the misuse of culture results and antibiotic sensitivities in patients with community-acquired bacteraemia due to urinary tract infection

Recent data suggests that culture isolations and susceptibility profiles are overlooked, misinterpreted and are not a major determinant in the process of selecting anti-bacterial therapy. Compliance with empiric antibiotic protocols, relationship between blood culture results, change and selection of secondary antibiotic regimens and effect on outcome and length of hospitalization were assessed prospectively in 134 episodes of community-acquired bacteraemia due to urinary tract infection in adults. Empiric antibiotic protocols were correct in 112 episodes (83.6%), excessive in 12 episodes (8.95%) and inappropriate in 10 (7.5%) episodes, with no significant difference in outcome or length of hospitalization. Excluding early deaths, the adequacy of the initial antibiotic therapy was clearly associated with mortality (four deaths out of eight episodes treated incorrectly vs. 21/117 treated appropriately [P = 0.029]), but not with length of hospitalization. Antibiotic change was theoretically required in 92/119 (77.3%) episodes (27 [29.3] incorrect regimen, 65 [70.65%] excessive regimen), but actual change was made in only 43 episodes, of which three protocols were changed from a correct to an incorrect regimen, and one patient continued to receive an incorrect regimen. Eighteen out of 34 changes in excessive protocols were still excessive. Adequacy of secondary antibiotic treatment was clearly associated with outcome (5/10 vs. 4/109 [P<0.001]). Excessive protocols were not associated with better outcome or shorter hospital stay. Change of antibiotic regimen was associated with the presence of background diseases (5.6-fold increase) and inversely with hospitalization on the urology ward (0.254), but no independent factors associated with correct or incorrect secondary regimens could be identified. Although the compliance rate with empiric protocols was satisfactory, in many bacteraemic episodes blood culture results and antibiotic sensitivity profiles are overlooked, leading to higher mortality and excessive, unjustified use of expensive and broad-spectrum antibiotics. We could not identify factors associated with this disregard of susceptibility profiles.

Patient medication costs as a therapeutic consideration

Don't neglect therapeutic considerations in selecting drugs, but take their cost into account. Sometimes, selecting an older, established drug or generic equivalent can represent a significant savings for the patient.

Prevention and Management of Infective Endocarditis

Infective endocarditis is an infection of the endocardial surface of the heart and usually involves one or more heart valves but may occur on septal defects or the heart wall. Its incidence is approximately 1 per 1,000 adults and 0.5 per 1,000 pediatric hospital admissions. Factors predisposing to infective endocarditis include degenerative heart disease, survivable congenital cardiac defects, use of invasive procedures, chronic immunosuppression, and intravenous drug abuse. This article discusses the pathophysiology, diagnosis, therapy, and prevention of infective endocarditis.