Denise Drudy

Enterobacter sakazakii: An Emerging Pathogen in Powdered Infant Formula

Enterobacter sakazakii represents a significant risk to the health of neonates. This bacterium is an emerging opportunistic pathogen that is associated with rare but life-threatening cases of meningitis, necrotizing enterocolitis, and sepsis in premature and full-term infants. Infants aged <28 days are considered to be most at risk. Feeding with powdered infant formula (PIF) has been epidemiologically implicated in several clinical cases. Infants should be exclusively breast-fed for the first 6 months of life, and those who are not should be provided with a suitable breast-milk substitute. PIF is not a sterile product; to reduce the risk of infection, the reconstitution of powdered formula should be undertaken by caregivers using good hygienic measures and in accordance with the product manufacturers food safety guidelines.

Emergence and control of Fluoroquinolone Resistant Toxin A Negative Toxin B positive Clostridium difficile

BACKGROUND Clostridium difficile is a major cause of infectious diarrhea in hospitalized patients. Between August 2003 and January 2004, we experienced an increase in the incidence of C. difficile-associated disease. We describe the investigation into and management of the outbreak in this article. METHODS A total of 73 consecutive patients with nosocomial C. difficile-associated diarrhea were identified. C. difficile isolates were characterized using toxin-specific enzyme immunoassays, a tissue-culture fibroblast cytotoxicity assay, polymerase chain reaction (PCR), and antimicrobial susceptibility tests. Rates of recurrence and of C. difficile colitis were recorded. Changes in antibiotic use and infection control policies were documented. RESULTS The incidence of C. difficile-associated diarrhea peaked at 21 cases per 1,000 patient admissions. Of the C. difficile isolates recovered, 85 (95%) were identical toxin A-negative and toxin B-positive strains, corresponding to toxinotype VIII and PCR ribotype 017. All clonal isolates were resistant to multiple antibiotics, including ofloxacin, ciprofloxacin, levofloxacin, moxifloxacin, and gatifloxacin (minimum inhibitory concentrations [MICs] of greater than 32 micro g/mL) and erythromycin, clarithromycin, and clindamycin (MICs of greater than 256 micro g/mL). Recurrent C. difficile-associated disease occurred in 26 (36%) of the patients. At least 10 (14%) of the patients developed C. difficile colitis. Additional infection control measures introduced included the use of ward memos, a hand-hygiene awareness campaign, increased environmental cleaning, attention to prescribing practices for antibiotics, increased awareness of diarrheal illness, and early isolation of affected patients. Total use of fluoroquinolones did not change throughout the study period. Despite persistence of this toxin-variant strain, the incidence of C. difficile-associated disease in our institution decreased to fewer than 5 cases per 1,000 admissions. CONCLUSIONS We report on the emergence of a fluoroquinolone- and clindamycin-resistant, toxin A-negative, and toxin B-positive strain of C. difficile associated with an outbreak of C. difficile-associated disease in our institution during a 6-month period. We found that careful attention to improvement of infection control interventions was the most important means of controlling this nosocomial pathogen.

Immunoreactive cell wall proteins of Clostridium difficile identified by human sera.

Clostridium difficile is a leading cause of nosocomial infection in the developed world, causing antibiotic-associated disease in susceptible populations. The identity of immunogenic proteins is important in understanding the pathogenesis of disease and in the design of vaccines. This study analysed the sera of six patients infected during a hospital outbreak of a C. difficile ribotype 017 strain. Using a proteomics-based approach, cell wall proteins were separated by two-dimensional PAGE, and immunoreactive proteins were revealed by reaction with patient sera. The identity of immunoreactive proteins was established by MS. Forty-two different proteins were identified in total. All patient sera reacted with at least one component of the surface-layer protein (SLP), four reacted with both components (high- and low-molecular-mass SLPs), and five reacted with one other cell wall protein, suggesting that these are immunodominant antigens. The role of these proteins as potential vaccine candidates and their roles in pathogenesis deserve further study.

Flow cytometric analysis of Clostridium difficile adherence to human intestinal epithelial cells.

Clostridium difficile is the most common cause of diarrhoea in hospitalised patients. Bacterial adherence to gut epithelial cells is a likely prerequisite to infection and toxin production. A novel flow cytometric method was developed for detecting adherence of C. difficile to human colonic and small intestinal epithelial cells (EC) and human intestinal cell lines. Small intestinal and colonic EC were isolated from biopsy specimens with mucolytic and chelating agents. Adherence of fluorochrome-labelled C. difficile to EC was measured by flow cytometry and was calculated as increase in median fluorescent intensity (deltaMFI). Cells with bacteria attached could be distinguished easily from cells alone or cells with unlabelled bacteria attached. Toxin-positive C. difficile adhered to colonic and small intestinal EC (deltaMFI mean 21.2 SD 16.7, n = 33 and 16.5 SD 20.7, n = 19 respectively). The toxin-negative strain also adhered to both epithelial cell types (deltaMFI 26.1 SD 32.5, n = 17 and 18.3 SD 31.3, n = 16). Adherence of toxin-positive C. difficile to the intestinal cell lines Caco-2 (deltaMFI 9.4 SD 4.4, n = 14) and HT29 (deltaMFI 8.1 SD 3.1, n = 12) was quantifiable, although at a significantly lower level than with primary colonic epithelial cells. Adherence of the toxin-negative strain was slightly lower, deltaMFI 6.5 SD 1.8, n = 9 with Caco-2 cells and deltaMFI 6.0 SD 2.0, n = 10 with HT29 cells. Adherence of C. difficile to epithelial cell lines was blocked with C. difficile antiserum, confirming specificity of adherence. In conclusion, flow cytometry is a useful approach to quantifying adherence of C. difficile to human colonic and small intestinal epithelial cells. Binding of toxin-negative as well as toxin-positive bacteria was detectable by this approach. Analysis of C. difficile adherence to target cells may have important implications for the understanding of the pathogenesis of C. difficile-related disease.

Multi-drug resistance in Salmonella enterica: efflux mechanisms and their relationships with the development of chromosomal resistance gene clusters.

Bacterial drug resistance represents one of the most crucial problems in present day antibacterial chemotherapy. Of particular concern to public health is the continuing worldwide epidemic spread of Salmonella enterica serovar Typhimurium phage type DT104 harbouring a genomic island called Salmonella genomic island I (SGI-1). This island contains an antibiotic gene cluster conferring resistance to ampicillin, chloramphenicol, florfenicol, streptomycin, sulfonamides and tetracyclines. These resistance genes are assembled in a mosaic pattern, indicative of several independent recombinational events. The mobility of SGI-1 coupled with the ability of various antibiotic resistance genes to be integrated and lost from the chromosomal resistance locus allows for the transfer of stable antibiotic resistance to most of the commonly used antibiotics and adaptation to new antibiotic challenges. This, coupled with the incidence of increasing fluoroquinolone resistance in these strains increases the risk of therapeutic failure in cases of life-threatening salmonellosis. Fluoroquinolone resistance has largely been attributed to mutations occurring in the genes coding for intracellular targets of these drugs. However, efflux by the AcrAB-TolC multi-drug efflux pump has recently been shown to directly contribute to fluoroquinolone resistance. Furthermore, the resistance to chloramphenicol-florfenicol and tetracyclines in DT104 isolates, is due to interaction between specific transporters for these antibiotics encoded by genes mapping to the SGI-1 and the AcrAB-TolC tripartite efflux pump. The potential for the use of efflux pump inhibitors to restore therapeutic efficacy to fluoroquinolones and other antibiotics offers an exciting developmental area for drug discovery.

Detection of Enterobacter sakazakii in Dried Infant Milk Formula by Cationic-Magnetic-Bead Capture

ABSTRACT Enterobacter sakazakii has been associated with life-threatening infections in premature low-birth-weight infants. Contaminated infant milk formula (IMF) has been implicated in cases of E. sakazakii meningitis. Quick and sensitive methods to detect low-level contamination sporadically present in IMF preparations would positively contribute towards risk reduction across the infant formula food chain. Here we report on the development of a simple method, combining charged separation and growth on selective agar, to detect E. sakazakii in IMF. This protocol can reliably detect 1 to 5 CFU of E. sakazakii in 500 g of IMF in less than 24 h.

Laboratory diagnosis of Clostridium difficile-associated disease in the Republic of Ireland : a survey of Irish microbiology laboratories

The Health Protection Surveillance Centre (HPSC) established a group to produce national guidelines for Clostridium difficile in Ireland in 2006. A laboratory questionnaire was distributed to determine current C. difficile diagnostic practices. Twenty-nine out of 44 laboratories providing C. difficile diagnostic services to 34 hospitals responded. Twenty-five out of 29 (86%) laboratories processed specimens for C. difficile and four (13.8%) forwarded specimens to another laboratory. Sixteen laboratories (64%) processed specimens for other healthcare facilities. None routinely examined stool for C. difficile, seven (28%) examined specimens only when requested to do so and 18 (72%) used specific selection criteria, including testing all liquid stools (39%), all nosocomial diarrhoea (44%), specific clinical criteria (28%) and history of antibiotic therapy (22%). All tested stool directly for C. difficile toxin with a variety of enzyme immunoassays, with 24 (96%) detecting both toxin A and B and one detecting toxin A only. Three (12%) laboratories used cytotoxicity assays; none used polymerase chain reaction and six (24%) laboratories performed C. difficile culture but only under specific circumstances. Seven (28%) laboratories had isolates typed during outbreaks, but none had the facilities to do so on-site. The HPSC group will produce national recommendations for laboratory diagnosis, surveillance and management of C. difficile infection. Since there are marked differences in diagnostic practices throughout the country and no national reference laboratory, the implementation of these recommendations will have cost implications that will need to be addressed.

An Investigation of the Subtype Diversity of Clinical Isolates of Irish Clostridium Difficile Ribotypes 027 and 078 by Repetitive-Extragenic Palindromic PCR

A repetitive-extragenic palindromic PCR (rep-PCR) subtyping method (DiversiLab) in conjunction with ribotyping, toxinotyping and antimicrobial-susceptibility testing was used to detect subtypes within Clostridium difficile ribotypes 027 and 078. Clinical isolates of ribotypes 027 (toxinotype III) (n = 30) and 078 (toxinotype V) (n = 23) were provided by health-care facilities across the Republic of Ireland over 2 months in 2006 and 1 month in 2009. Ribotype 027 isolates were significantly more related to each other (9 different subtype profiles) when compared to ribotype 078 isolates (14 different profiles) (P = 0.001; cut-off >90 % similarity). Almost half of ribotype 078 isolates (45.5 %) showed no relationship to each other. The clonality of ribotype 027 isolates suggests effective adaptation to the human niche, whereas the considerable genetic diversity within ribotype 078 isolates suggests that they may have originated from a variety of sources. Subtyping correlated well with antimicrobial susceptibility, in particular clindamycin susceptibility for ribotype 027, but diverse antimicrobial-susceptibility profiles were seen in ribotype 078 isolates, even within a single health-care facility. Between 2006 and 2009, a change in the predominant subtype of ribotype 027 was seen, with the recent clone representing half of all ribotype 027 isolates studied. This strain exhibited 89 % similarity to a rep-PCR profile of the North American NAP-1 strain.