Vertical Transmission at the Pathogen-Symbiont Interface: Serratia symbiotica and Aphids.

Many insects possess beneficial bacterial symbionts that occupy specialized host cells and are maternally transmitted. As a consequence of their host-restricted lifestyle, these symbionts often possess reduced genomes and cannot be cultured outside hosts, limiting their study. The bacterial species Serratia symbiotica was originally characterized as noncultured strains that live as mutualistic symbionts of aphids and are vertically transmitted through transovarial endocytosis within the mother's body. More recently, culturable strains of S. symbiotica were discovered that retain a larger set of ancestral Serratia genes, are gut pathogens in aphid hosts, and are principally transmitted via a fecal-oral route. We find that these culturable strains, when injected into pea aphids, replicate in the hemolymph and are pathogenic. Unexpectedly, they are also capable of maternal transmission via transovarial endocytosis: using green fluorescent protein (GFP)-tagged strains, we observe that pathogenic S. symbiotica strains, but not Escherichia coli, are endocytosed into early embryos. Furthermore, pathogenic S. symbiotica strains are compartmentalized into specialized aphid cells in a fashion similar to that of mutualistic S. symbiotica strains during later stages of embryonic development. However, infected embryos do not appear to develop properly, and offspring infected by a transovarial route are not observed. Thus, cultured pathogenic strains of S. symbiotica have the latent capacity to transition to lifestyles as mutualistic symbionts of aphid hosts, but persistent vertical transmission is blocked by their pathogenicity. To transition into stably inherited symbionts, culturable S. symbiotica strains may need to adapt to regulate their titer, limit their pathogenicity, and/or provide benefits to aphids that outweigh their cost.IMPORTANCE Insects have evolved various mechanisms to reliably transmit their beneficial bacterial symbionts to the next generation. Sap-sucking insects, including aphids, transmit symbionts by endocytosis of the symbiont into cells of the early embryo within the mother's body. Experimental studies of this process are hampered by the inability to culture or genetically manipulate host-restricted, symbiotic bacteria. Serratia symbiotica is a bacterial species that includes strains ranging from obligate, heritable symbionts to gut pathogens. We demonstrate that culturable S. symbiotica strains, which are aphid gut pathogens, can be maternally transmitted. Cultured S. symbiotica therefore possesses a latent capacity for evolving a host-restricted lifestyle and can be used to understand the transition from pathogenicity to beneficial symbiosis.

Sink traps as the source of transmission of OXA-48-producing Serratia marcescens in an intensive care unit.

BACKGROUND: Carbapenemase-producing Enterobacteriaceae (CPE) outbreaks are mostly attributed to patient-to-patient transmission via healthcare workers. OBJECTIVE: We describe successful containment of a prolonged OXA-48-producing S. marcescens outbreak after recognizing the sink traps as the source of transmission. METHODS: The Sheba Medical Center intensive care unit (ICU), contains 16 single-bed, semi-closed rooms. Active CPE surveillance includes twice-weekly rectal screening of all patients. A case was defined as a patient detected with OXA-48 CPE >72 hours after admission. A root-cause analysis was used to investigate the outbreak. All samples were inoculated on chrom-agar CRE, and carbapenemase genes were detected using commercial molecular Xpert-Carba-R. Environmental and patient S. marcescens isolates were characterized using PFGE. RESULTS: From January 2016 to May 2017, 32 OXA-48 CPE cases were detected, and 81% of these were S. marcescens. A single clone was the cause of all but the first 2 cases. The common factor in all cases was the use of relatively large amounts of tap water. The outbreak clone was detected in 2 sink outlets and 16 sink traps. In addition to routine strict infection control measures, measures taken to contain the outbreak included (1) various sink decontamination efforts, which eliminated the bacteria from the sink drains only temporarily and (2) educational intervention that engaged the ICU team and lead to high adherence to 'sink-contamination prevention guidelines.' No additional cases were detected for 12 months. CONCLUSIONS: Despite persistence of the outbreak clones in the environmental reservoir for 1 year, the outbreak was rapidly and successfully contained. Addressing sink traps as hidden reservoirs played a major role in the intervention.

Protracted Regional Dissemination of GIM-1-Producing Serratia marcescens in Western Germany.

The metallo-beta-lactamase GIM-1 has been found in various bacterial host species nearly exclusively in western Germany. However, not much is known about the epidemiology of GIM-1-positive Serratia marcescens Here we report on a surprisingly protracted regional dissemination. In-hospital transmission was investigated by using conventional epidemiological tools to identify spatiotemporal links. Strain typing was performed using pulsed-field gel electrophoresis (PFGE) and whole-genome sequencing (WGS). Bayesian phylogeny was used to infer the time axis of the observed occurrence. Thirteen S. marcescens strains from 10 patients from 6 different German hospitals were investigated. Suspected in-hospital transmissions were confirmed by molecular typing at a higher resolution by WGS than by PFGE. A detailed sequence analysis demonstrated the spread of one predominant strain variant but also provided evidence for transfer of the blaGIM-1 gene cassette between different strains. A Bayesian phylogenetic analysis showed that the most recent common ancestor of the identified clonal cluster could be dated back to April 1993 (95% highest posterior density interval, January 1973 to March 2003) and that this strain might have already harbored the blaGIM-1 at that time and, therewith, years before the first detection of this resistance gene in clinical specimens. This study shows a long-standing clonal and plasmid-mediated expansion of GIM-1-producing S. marcescens that might have gone unnoticed in the absence of a standardized and effective molecular screening for carbapenemases. The systematic and early detection of resistance is thus highly advisable, especially for the prevention of potentially long-term dissemination that may progress beyond control.

Serratia marcescens outbreak due to contaminated 2% aqueous chlorhexidine. / Brote de Serratia marcescens producido por clorhexidina acuosa al 2% contaminada.

INTRODUCTION AND OBJECTIVE: An outbreak of Serratia marcescens infections outbreak is described, as well as the epidemiological study that linked the outbreak to the use of 2% aqueous chlorhexidine antiseptic. METHOD: In late November 2014 an increasing incidence of S. marcescens isolates was detected in patients treated in the emergency department. It was considered a possible outbreak, and an epidemiological investigation was started. RESULT: S. marcescens was isolated in 23 samples from 16 patients and in all new bottles of two lots of 2% aqueous chlorhexidine. The contaminated disinfectant was withdrawn, and the Spanish Drugs Agency was alerted (COS 2/2014). The epidemiological study showed that strains isolated from clinical samples and from chlorhexidine belonged to the same clone. No further isolates were obtained once the disinfectant was withdrawn. CONCLUSION: The suspicion of an outbreak and the epidemiological study were essential to control the incidence.

[Outbreak due to Serratia marcescens associated with intrinsic contamination of aqueous chlorhexidine]. / Brote de infección nosocomial por Serratia marcescens asociado a contaminación intrínseca de clorhexidina acuosa.

Serratia marcescens is a widely distributed gram-negative rod, often associated to nosocomial infections. Some outbreaks linked to contaminated antiseptic solutions have been reported. In this study we report a nosocomial outbreak of surgical site infection and catheter insertion site infection due to S. marcescens. 33 patients with positive cultures were studied after an index case was identified. Epidemiological, microbiological and molecular analysis demostrated an intrinsic contamination of alcohol free chlorhexidine solution as causal factor. Positive cultures were associated with 13 clinical infections, 9 colonized patients, 6 pseudobacteremia episodes and 5 patients without documented exposure. Hospital and national recall of contaminated chlorhexidine solution was performed after this study. Intrinsic contamination of antiseptic solutions is an infrequent cause of nosocomial infections with major epidemiological relevance.

Brote de infección nosocomial por Serratia marcescens asociado a contaminación intrínseca de clorhexidina acuosa / Outbreak due to Serratia marcescens associated with intrinsic contamination of aqueous chlorhexidine

Serratia marcescens is a widely distributed gram-negative rod, often associated to nosocomial infections. Some outbreaks linked to contaminated antiseptic solutions have been reported. In this study we report a nosocomial outbreak of surgical site infection and catheter insertion site infection due to S. marcescens. 33 patients with positive cultures were studied after an index case was identified. Epidemiological, microbiological and molecular analysis demostrated an intrinsic contamination of alcohol free chlorhexidine solution as causal factor. Positive cultures were associated with 13 clinical infections, 9 colonized patients, 6 pseudobacteremia episodes and 5 patients without documented exposure. Hospital and national recall of contaminated chlorhexidine solution was performed after this study. Intrinsic contamination of antiseptic solutions is an infrequent cause of nosocomial infections with major epidemiological relevance.

Serratia marcescens es un bacilo gramnegativo de amplia distribución, frecuentemente asociado a infecciones nosocomiales. Se han descrito brotes asociados a la contaminación de diversas soluciones antisépticas. Describimos a continuación un brote de infección de sitio operatorio (ISO) y de infección de sitio de inserción de catéter vascular (ISC) por S. marcescens. A raíz de un caso índice se estudió un total de 33 pacientes con cultivo positivo para S. marcescens. El análisis epidemiológico, microbiológico y molecular logró demostrar la contaminación intrínseca de un lote de clorhexidina acuosa, como fuente común de exposición. Las muestras positivas correspondieron a 13 infecciones clínicas, nueve colonizaciones, seis pseudo-bacteriemias y cinco pacientes sin exposición demostrada. Los resultados de este estudio determinaron el retiro del producto de la institución y posteriormente a nivel nacional. La contaminación intrínseca de antisépticos es una causa poco frecuente de brotes de infecciones nosocomiales cuya identificación posee un gran impacto epidemiológico.

Serratia marcescens strains implicated in adverse transfusion reactions form biofilms in platelet concentrates and demonstrate reduced detection by automated culture.

BACKGROUND AND OBJECTIVES: Serratia marcescens is a gram-negative bacterium that has been implicated in adverse transfusion reactions associated with contaminated platelet concentrates. The aim of this study was to investigate whether the ability of S. marcescens to form surface-attached aggregates (biofilms) could account for contaminated platelet units being missed during screening by the BacT/ALERT automated culture system. MATERIALS AND METHODS: Seven S. marcescens strains, including biofilm-positive and biofilm-negative control strains and five isolates recovered from contaminated platelet concentrates, were grown in enriched Luria-Bertani medium and in platelets. Biofilm formation was examined by staining assay, dislodging experiments and scanning electron microscopy. Clinical strains were also analysed for their ability to evade detection by the BacT/ALERT system. RESULTS: All strains exhibited similar growth in medium and platelets. While only the biofilm-positive control strain formed biofilms in medium, this strain and three clinical isolates associated with transfusion reactions formed biofilms in platelet concentrates. The other two clinical strains, which had been captured during platelet screening by BacT/ALERT, failed to form biofilms in platelets. Biofilm-forming clinical isolates were approximately three times (P<0·05) more likely to be missed by BacT/ALERT screening than biofilm-negative strains. CONCLUSION: S. marcescens strains associated with transfusion reactions form biofilms under platelet storage conditions, and initial biofilm formation correlates with missed detection of contaminated platelet concentrates by the BacT/ALERT system.

Outbreaks of Serratia marcescens in neonatal and pediatric intensive care units: clinical aspects, risk factors and management.

The following recommendations are derived from a systematic analysis of 34 Serratia marcescens outbreaks described in 27 publications from neonatal and pediatric intensive care units (NICU, PICU), in which genotyping methods were used to confirm or exclude clonality. The clinical observation of two or more temporally related cases of nosocomial S. marcescens infection should raise the suspicion of an outbreak, particularly in the NICU or PICU setting. Since colonized or infected patients represent the most important reservoir for cross transmission, hygienic barrier precautions (contact isolation/cohortation, the use of gloves and gowns in addition to strictly performed hand disinfection, enhanced environmental disinfection) should immediately be implemented and staff education given. Well-planned sampling of potential environmental sources should only be performed when these supervised barrier precautions do not result in containment of the outbreak. The current strategy of empiric antibiotic treatment should be reevaluated by a medical microbiologist or an infectious disease specialist. Empiric treatment of colonized children should use combination therapy informed by in vitro susceptibility data; in this context the high propensity of S. marcescens to cause meningitis and intracerebral abscess formation should be considered. In vitro susceptibility patterns do not reliably prove or exclude the clonality of the outbreak isolate. Genotyping of the isolates by pulse-field gel electrophoresis or PCR-based methods should be performed, but any interventions to interrupt further nosocomial spread should be carried out without waiting for the results.

Sick of mating: sexual transmission of a pathogenic bacterium in Drosophila melanogaster.

Internal fertilization protects gametes from inhospitable environments and ensures sufficient proximity for gamete union. However, close contact between individuals during mating also increases the risk of pathogen transfer. We developed an approach to transfer the entomopathogenic bacterium Serratia marcescens from males to females during courtship and mating in Drosophila melanogaster. We then examined the frequency of contamination and bacterial loads of females copulating with males for varying durations, showing that while courtship is sufficient for bacterial transmission, mating significantly increases the bacterial load received in a time-independent manner. S. marcescens transmission from contaminated males during mating was sufficient to establish rapid, systemic infection and death in mated females.

Outbreak of multidrug-resistant Serratia marcescens infection in a neonatal intensive care unit.

BACKGROUND: Serratia marcescens causes healthcare-associated infections and significant morbidity and mortality in neonatal intensive care units (NICUs). We report the investigation and control of an outbreak of multidrug-resistant (MDR) S. marcescens infection at an NICU. METHODS: An outbreak investigation and a case-control study were undertaken at a 36-bed NICU in a tertiary care hospital in Baltimore, Maryland, for the period from October 2004 through February 2005. The outbreak investigation included case identification, review of medical records, environmental cultures, patient surveillance cultures, personnel hand cultures, and pulsed-field gel electrophoresis (PFGE). The case-control study included case identification and review of medical records. Infection control measures were implemented. Eighteen NICU neonates had cultures that grew MDR S. marcescens during the study period. The case-control study included 16 patients with the outbreak strain or an unidentified strain of MDR S. marcescens and 32 control patients not infected and/or colonized with MDR S. marcescens, treated in the NICU for at least 48 hours during the study period. RESULTS: PFGE analysis identified a single strain of MDR S. marcescens that infected or colonized 15 patients. Two patients had unique strains, and 1 patient's isolate could not be subtyped. An unrelated MDR S. marcescens isolate was recovered from a sink drain. Exposure to inhalational therapy was an independent risk factor for MDR S. marcescens acquisition after adjusting for birth weight. Extensive investigation failed to reveal a point source for the outbreak. CONCLUSION: A single epidemic strain of MDR S. marcescens spread rapidly and threatened to become endemic in this NICU. Transient carriage on the hands of healthcare personnel or on respiratory care equipment was the likely mode of transmission. Cohorting patients and staff, at the cost of bed closures and additional personnel, interrupted transmission and halted the outbreak.

A cluster of hemodialysis-related bacteremia linked to artificial fingernails.

We examined a cluster of 5 hemodialysis patients who contracted gram-negative bacteremia. A nurse who used an artificial fingernail to open a vial of heparin that was mixed to make a flush solution had a culture of an artificial fingernail specimen positive for Serratia marcescens. The typing of the S. marcescens strains isolated from the 5 patients and the nurse showed them to be identical. This finding provides strong support for policies prohibiting artificial nails for healthcare workers in all hemodialysis units.

Three-year follow-up of an outbreak of Serratia marcescens bacteriuria in a neurosurgical intensive care unit.

We report on the investigations and interventions conducted to contain an extended outbreak of Serratia marcescens bacteriuria that lasted for years in a neurosurgical intensive care unit (NSICU). A case-control study was performed to identify the risk factors for S. marcescens acquisition in urine. In case patients, urine sampling for tests and central venous catheterization were performed more frequently before the isolation of S. marcescens. Case patients were more frequently prescribed third-generation cephalosporins. Adherence to hand antisepsis was encouraged through in-service educational meetings and infection control measures, especially concerning the manipulation of indwelling urinary catheters, were intensified. The outbreak persisted despite the reinforcement of infection control measures. However, no patient has newly acquired the organism in the NSICU since December 2004. Multiple factors, including inadequate infection control practices and inappropriate antimicrobial usage, possibly contributed to the persistence of this S. marcescens outbreak. Healthcare workers should consistently follow infection control policies to ensure quality care.

Outbreak of Serratia marcescens colonization and infection traced to a healthcare worker with long-term carriage on the hands.

OBJECTIVE: To reveal the source of a nosocomial outbreak of colonization and infection with a strain of Serratia marcescens positive for Guiana extended-spectrum beta-lactamase 1 (GES-1) that occurred among patients in a neurosurgical intensive care unit (ICU) in a Dutch university medical center from May 2002 through March 2003. METHODS: Samples from the environment and from the hands of healthcare workers (HCWs) were cultured. A retrospective case-control study was carried out. RESULTS: Fifteen neurosurgical ICU patients who had 1 or more cultures that yielded the epidemic strain of S. marcescens from May 2002 through March 2003 were defined as case patients and matched with 30 control patients. Environmental cultures did not reveal a prominent source of S. marcescens. Cultures of specimens from the hands of 100 HCWs revealed colonization of a single HCW with the epidemic strain. Although this HCW instantly went on leave, serial cultures detected prolonged carriage of the epidemic strain on the hands of the HCW for 3 months. The skin of the HCW's hands was psoriatic. The epidemic abruptly ended after the colonized HCW went on leave. Retrospective case-control analysis showed that the patients colonized or infected with S. marcescens received significantly more nursing care from the colonized HCW than did control patients (P<.05). From February 2004 through October 2004, a second cluster of 3 patients was detected with the epidemic strain of S. marcescens. In October 2004, the formerly colonized HCW appeared to have carriage of the epidemic strain on the hands again. CONCLUSIONS: A single HCW with the epidemic strain of S. marcescens on the hands was considered the source of this outbreak.

Acquisition of multidrug-resistant Serratia marcescens by critically ill patients who consumed tap water during receipt of oral medication.

We describe an outbreak of multidrug-resistant Serratia marcescens infection and colonization involving adults admitted to a surgical intensive care unit. Examination of the outbreak revealed epidemiological evidence that consumption of tap water from a contaminated faucet during receipt of oral medication was the mechanism of S. marcescens acquisition.

The potential spread of infection caused by aerosol contamination of surfaces after flushing a domestic toilet.

AIMS: To determine the level of aerosol formation and fallout within a toilet cubicle after flushing a toilet contaminated with indicator organisms at levels required to mimic pathogen shedding during infectious diarrhoea. METHODS AND RESULTS: A semisolid agar carrier containing either Serratia marcesens or MS2 bacteriophage was used to contaminate the sidewalls and bowl water of a domestic toilet to mimic the effects of soiling after an episode of acute diarrhoea. Viable counts were used to compare the numbers of Serratia adhering to the porcelain surfaces and those present in the bowl water before and after flushing the toilet. Air sampling and settle plates were used to determine the presence of bacteria or virus-laden aerosols within the toilet cubicle. After seeding there was a high level of contamination on the porcelain surfaces both under the rim and on the sides of the bowl. After a single flush there was a reduction of 2.0-3.0 log cycles cm(-2) for surface attached organisms. The number of micro-organisms in the bowl water was reduced by 2.0-3.0 log cycles ml(-1) after the first flush and following a second flush, a further reduction of c. 2.0 log cycles ml(-1) was achieved. Micro-organisms in the air were at the highest level immediately after the first flush (mean values, 1370 CFU m(-3) for Serratia and 2420 PFU m(-3) for MS2 page). Sequential flushing resulted in further distribution of micro-organisms into the air although the numbers declined after each flush. Serratia adhering to the sidewalls, as well as free-floating organisms in the toilet water, were responsible for the formation of bacterial aerosols. CONCLUSIONS: Although a single flush reduced the level of micro-organisms in the toilet bowl water when contaminated at concentrations reflecting pathogen shedding, large numbers of micro-organisms persisted on the toilet bowl surface and in the bowl water which were disseminated into the air by further flushes. SIGNIFICANCE AND IMPACT OF THE STUDY: Many individuals may be unaware of the risk of air-borne dissemination of microbes when flushing the toilet and the consequent surface contamination that may spread infection within the household, via direct surface-to-hand-to mouth contact. Some enteric viruses could persist in the air after toilet flushing and infection may be acquired after inhalation and swallowing.