Low-virulence Citrobacter species encode resistance to multiple antimicrobials.

Citrobacter spp. are gram-negative commensal bacteria that infrequently cause serious nosocomial infections in compromised hosts. They are often resistant to cephalosporins due to overexpression of their chromosomal beta-lactamase. During a recent study of multidrug-resistant Enterobacteriaceae (MDRE) in solid-organ transplant patients, we found that almost half of patients colonized with MDRE carried one or more cefpodoxime-resistant Citrobacter freundii, Citrobacter braakii, or Citrobacter amalonaticus strains. Pulsed-field gel electrophoresis showed that 36 unique strains of Citrobacter were present among 32 patients. Genetic and phenotypic analysis of the resistance mechanisms of these bacteria showed that the extended-spectrum beta-lactamase (ESBL) SHV-5 or SHV-12 was encoded by 8 strains (26%) and expressed by 7 strains (19%). A number of strains were resistant to other drug classes, including aminoglycosides (28%), trimethoprim-sulfamethoxazole (31%), and fluoroquinolones (8%). PCR and DNA analysis of these multiresistant strains revealed the presence of class I integrons, including the first integrons reported for C. braakii and C. amalonaticus. The integrons encoded aminoglycoside resistance, trimethoprim resistance, or both. Despite the prevalence of MDR Citrobacter spp. in our solid-organ transplant patients, only a single infection with a colonizing strain was recorded over 18 months. Low-virulence Citrobacter spp., which can persist in the host for long periods, could influence pathogen evolution by accumulation of genes encoding resistance to multiple antimicrobial classes.

The HIV-positive dentist: balancing the rights of the health care worker and the patient.

We describe a hypothetical case of an HIV-positive dentist without cognitive impairment who uses proper infection control procedures. The dentist's physician notifies the medical officer of health without the dentist's consent. Although HIV-positive health care workers, including dentists, have been identified in the past, proven HIV transmission to patients is very rare. Most authorities recommend that an HIV-positive health care worker be monitored by an expert panel, which could then, if necessary, refer to the regulatory body to revoke or restrict the person's license to practice. Mandatory HIV testing is not required for health care workers because they generally do not pose a risk for infecting their patients; they are, however, ethically and legally obligated to report their HIV status to their profession's regulatory body.

A comparison of multifaceted versus Clostridium difficile-focused VRE surveillance strategies in a low-prevalence setting.

We compared our current screening strategy for vancomycin-resistant Enterococcus (VRE) with a focused strategy that screens all stool samples sent for Clostridium difficile toxin assay but limits rectal swab screening to wards with new VRE cases detected via C. difficile samples. The proposed strategy detects 72.7% of new VRE cases, with substantial cost savings.

Is methicillin-resistant Staphylococcus aureus an emerging community pathogen? A review of the literature.

OBJECTIVES: To discuss the historical epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) and review the literature suggesting that MRSA has become a community pathogen. DATA SOURCES: A search of the MEDLINE database was performed, encompassing all English or French language citations from 1966 to 1999 and containing the subjects and/or text words: 'Staphylococcus aureus', 'methicillin resistance', 'endocarditis', 'cellulites', 'pneumonia' and 'community-acquired'. Articles published in other languages that provided English or French abstracts were included. All relevant references cited in articles obtained from the MEDLINE database and book chapters were also included. DATA EXTRACTION: All articles obtained from the above sources were examined and were included in the review if a laboratory or epidemiological study of community-acquired MRSA was presented. DATA SYNTHESIS AND CONCLUSIONS: MRSA has emerged over the past 30 years to become a worldwide nosocomial pathogen and has recently been reported as a cause of community-acquired infections. The changing epidemiology of MRSA is likely because of two mechanisms: the movement of nosocomial MRSA strains into the community and the de novo appearance of community strains resulting from the transfer of genetic material from methicillin-resistant Gram-positive organisms to sensitive S aureus strains. The emergence of MRSA as a community pathogen has occurred at a slower rate than it did for penicillin-resistant S aureus (PRSA) in the 1950s and 1960s, possibly because the mechanism of methicillin resistance does not exhibit the same ease of transferability as that of penicillin resistance. Four case reports, seven case series, 10 case-control studies and two cohort studies on community-acquired MRSA were analyzed. Determining whether these reports involve new community-acquired strains rather than previously acquired nosocomial strains can be problematic. It appears, however, that MRSA strains of both nosocomial and community origin are now endemic in certain communities in different parts of the world. Few surveillance studies of nonhospitalized patient populations have been performed to date; thus, the true prevalence of MRSA in the community at large is essentially unknown, although it appears to be low. At present, the empirical treatment of community-acquired S aureus infections with a beta-lactamase-stable beta-lactam antibiotic is appropriate for most populations. However, empirical vancomycin therapy for serious S aureus infections should be strongly considered for patients with significant risk factors for previously-acquired nosocomial MRSA or for patients belonging to outpatient populations with a proven high prevalence of MRSA. Increasing vancomycin use will likely have a significant impact on the development of resistance in Gram-positive organisms.

Group B streptococcal necrotizing fasciitis and streptococcal toxic shock-like syndrome in adults.

Necrotizing fasciitis, which is a severe and uncommon infection involving the subcutaneous tissues, is usually caused by group A streptococci. To our knowledge, however, group B streptococci (Streptococcus agalactiae) have been reported to cause necrotizing fasciitis in only 4 instances (2 involving neonates) over the past 4 decades. We report 3 cases of group B streptococcal necrotizing fasciitis in adults that occurred in southern Ontario and Quebec within a 10-month period. All 3 patients had significant underlying illness, and all required surgical debridement in addition to antibiotic therapy. One of the cases fulfilled the criteria for streptococcal toxic shock-like syndrome. Group B streptococcus has been recognized as a frequent cause of serious disease in adults. It has become evident over the past decade that invasive streptococcal infections are on the increase. We speculate that group B streptococcus has recently acquired an increased ability to cause necrotizing fasciitis and suggest that this may represent the emergence of a new clinical syndrome in adults.

Overutilization of indwelling urinary catheters and the development of nosocomial urinary tract infections.

OBJECTIVE: To assess the impact of the overutilization of indwelling urinary catheters in the emergency department on the development of nosocomial urinary tract infection. DESIGN: Prospective cohort study. SETTING: 638-bed tertiary-care hospital. PATIENTS: 118 consecutive medical and surgical admissions from the emergency department collected over 3 weeks. INTERVENTION: Catheterized patients were assessed. The completeness of documentation relating to catheter insertion and two outcomes were measured: asymptomatic bacteriuria and urinary tract infection. RESULTS: 24 (20.3%) had catheters inserted, of whom 12 (50%) were catheterized for justifiable indications. Positive urine cultures were found in 10 of the catheterized patients (42%), 5 of whom fulfilled the definition for catheter-associated urinary tract infection. Three of the five infections occurred in patients for whom catheterization was not justifiable. An order was written for catheter insertion in 62.5% of charts, while the rationale for catheterization was documented in 16.7%. CONCLUSIONS: Many nosocomial urinary tract infections are due to the inappropriate placement of indwelling urinary catheters in the emergency department. The prevention of these infections should begin with restricting catheterization to those patients for whom it is appropriate.

Optochin revisited: defining the optimal type of blood agar for presumptive identification of Streptococcus pneumoniae.

To determine the optimal media for optochin susceptibility testing of Streptococcus pneumoniae, we measured inhibition zones for 72 S. pneumoniae and 22 Streptococcus viridans isolates on three blood-containing media. Because 15.3, 0, and 22.2% of S. pneumoniae organisms were misidentified on Columbia agar, Trypticase soy agar (TSA), and Mueller-Hinton agar, respectively, each containing sheep blood, we recommend that TSA-sheep blood agar be used.

Partitioning of exchangeable fluorescent phospholipids and sphingolipids between different lipid bilayer environments.

Exchangeable phospho- and sphingolipid probes (phosphatidylcholine, -ethanolamine, -serine, and -glycerol, phosphatidic acid, sphingomyelin, cerebroside, and sulfatide) have been synthesized in which one acyl chain is substituted with a fluorescent bimanyl, 7-(dimethylamino)coumarin-3-yl, or diphenyl-hexatrienyl group. The distribution of these probes between two different populations of lipid vesicles can be readily monitored by fluorescence intensity measurements, as described by Nichols and Pagano [Nichols, J. W., & Pagano, R. E. (1982) Biochemistry 21, 1720-1726], when one of the vesicle populations contains a low mole fraction of a nonexchangeable quencher, (12-DABS)-18-PC. The probes examined in this study exchange between phospholipid vesicles on a time scale of minutes, with kinetics indicating that the transfer process takes place by diffusion of probe monomers through the aqueous phase. As expected, lipid probes with different charges differ markedly in their equilibrium distributions between neutral and charged lipid vesicles. However, probes with different polar headgroups differ only modestly in their relative affinities for vesicles composed of "hydrogen-bonding" lipids (PE and PS) vs "non-hydrogen-bonding" lipids (PC and PG or O-methyl-PA). Probes with different headgroups also show modest, albeit reproducible, differences in their relative affinities for cholesterol-containing vs cholesterol-free PC/PG vesicles. Our results suggest that lipids with different headgroup structures may mix more nearly ideally in liquid-crystalline lipid bilayers than would be predicted from previous analyses of the phase diagrams for binary lipid mixtures.

The NADP-dependent trifunctional methylenetetrahydrofolate dehydrogenase purified from mouse liver is immunologically distinct from the mouse NAD-dependent [corrected] bifunctional enzyme.

Methylenetetrahydrofolate dehydrogenase - methenyltetrahydrofolate cyclohydrolase - formyltetrahydrofolate synthetase was purified to homogeneity from mouse liver, taking advantage of its very high affinity for 2',5'-ADP-Sepharose. Antibodies raised to this trifunctional enzyme and to the bifunctional NAD-dependent dehydrogenase-cyclohydrolase from mouse Ehrlich ascites tumour cells were found not to cross-react with the purified proteins on Western blots. Each of these polyclonal antibodies detects the appropriate protein in extracts of Ehrlich ascites tumour cells after sodium dodecyl sulfate - polyacrylamide gel electrophoresis and electrophoretic transfer of the proteins to nitrocellulose. The procedure has also been used to obtain a purified preparation of the trifunctional enzyme from human liver obtained at autopsy.