A nosocomial epidemic of antibiotic-resistant Serratia marcescens urinary tract infections

Development and Evaluation of a Core Genome Multilocus Sequencing Typing (cgMLST) Scheme for Serratia marcescens Molecular Surveillance and Outbreak Investigations

Serratia marcescens can cause a range of severe infections and contributes to nosocomial outbreaks. Although whole-genome sequencing (WGS)-based typing is the standard method for molecular surveillance and outbreak investigation, there is no standardized analytic scheme for S. marcescens core genome multilocus sequence typing (cgMLST). Here, the development and evaluation of a S. marcescens cgMLST scheme is reported with the goal of enabling a standardized methodology and typing nomenclature. Four hundred ninety-one high-quality S. marcescens WGS data sets were extracted from public databases and-using the genomic sequence of NCBI reference strain S. marcescens Db11 (NZ_HG326223.1) as a starting point-all Db11 genes present in ≥97% data sets used to create a cgMLST scheme. The novel scheme was evaluated using WGS data from 24 outbreak investigations (n = 175 isolates) distributed over three continents. Analysis of Db11 genes within the 491 data sets identified 2,692 target genes present in ≥97% of genomes (mean, 99.1%; median, 99.9%). These genes formed the novel cgMLST scheme, covering 47.8% of nucleotides in the Db11 genome. Analyzing 175 isolates from 24 outbreaks using the novel scheme gave comparable results to previous typing efforts for both general groupings and allelic distances within clusters. In summary, a novel cgMLST scheme for S. marcescens was developed and evaluated. The scheme and its associated nomenclature will improve standardization of typing efforts for molecular surveillance and outbreak investigation, allowing better understanding of S. marcescens genomic epidemiology and facilitating interlaboratory comparisons.

Molecular and Epidemiologic Study of Multiresistant Serratia marcescens Infections in a Spinal Cord Injury Rehabilitation Unit

Between March 1984 and February 1986, ten patients admitted to a spinal cord injury/stroke rehabilitation unit became bacteriuric with a strain of Serratia marcescens resistant to ampicillin, cephalothin, cefoxitin, ticarcillin, cotrimoxazole, gentamicin, and tobramycin. All the patients were catheterized, and in most, bacteriuria was asymptomatic. The organism was also recovered from their hospital environment (sinks, toilets, urine-collecting basins). Analysis of total plasmid content of multiresistant isolates revealed the presence of two plasmids (7 kilobase, 25.5 kilobase), not found in aminoglycoside susceptible strains ofSerratia marcescens. Restriction endonuclease analysis and Southern hybridization (DNA probe: 25.5 kilobase plasmid) verified that these plasmids were identical. The 25.5 kilobase plasmid was purified, introduced by transformation into anEscherichia colistrain C recipient, and was found to mediate resistance to gentamicin and tobramycin. The emergence of multiresistantSerratia marcescenscoincided with an increase in antibiotic usage on the ward. The reservoir seemed to be the urinary tracts of asymptomatic catheterized patients and their contaminated hospital environment.

Serratia infections: from military experiments to current practice

Serratia species, in particular Serratia marcescens, are significant human pathogens. S. marcescens has a long and interesting taxonomic, medical experimentation, military experimentation, and human clinical infection history. The organisms in this genus, particularly S. marcescens, were long thought to be nonpathogenic. Because S. marcescens was thought to be a nonpathogen and is usually red pigmented, the U.S. military conducted experiments that attempted to ascertain the spread of this organism released over large areas. In the process, members of both the public and the military were exposed to S. marcescens, and this was uncovered by the press in the 1970s, leading to U.S. congressional hearings. S. marcescens was found to be a certain human pathogen by the mid-1960s. S. marcescens and S. liquefaciens have been isolated as causative agents of numerous outbreaks and opportunistic infections, and the association of these organisms with point sources such as medical devices and various solutions given to hospitalized patients is striking. Serratia species appear to be common environmental organisms, and this helps to explain the large number of nosocomial infections due to these bacteria. Since many nosocomial infections are caused by multiply antibiotic-resistant strains of S. marcescens, this increases the danger to hospitalized patients, and hospital personnel should be vigilant in preventing nosocomial outbreaks due to this organism. S. marcescens, and probably other species in the genus, carries several antibiotic resistance determinants and is also capable of acquiring resistance genes. S. marcescens and S. liquefaciens are usually identified well in the clinical laboratory, but the other species are rare enough that laboratory technologists may not recognize them. 16S rRNA gene sequencing may enable better identification of some of the less common Serratia species.

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.

An outbreak of carbapenem-resistant Pseudomonas aeruginosa in a urology ward

OBJECTIVE

To investigate an outbreak of carbapenem-resistant Pseudomonas aeruginosa (CRPA) in a urology ward.

METHODS

Patients infected or colonized with CRPA were prospectively identified by daily laboratory surveillance. Routine infection-control measures were reinforced, disinfection protocols were revised, and a surveillance program was set up, analyzing cross-transmission in the nursing ward and environment cultures from urology wards and the operating theater. CRPA isolates from clinical and environment samples were studied by pulsed-field gel electrophoresis (PFGE), following XbaI and SpeI restriction.

RESULTS

From February 1998 to September 2000, 59 adult urology patients were colonized or infected by CRPA. All patients had been operated on prior to identification of the CRPA isolate and 79% of these procedures were performed in the same cystoscopy room. No patients had received prior carbapenem therapy. No cross-transmission was detected, and environment cultures from the urology ward and theater were negative except for five samples collected in the cystoscopy room. PFGE identified a single clone in the isolates from different patients and the environment samples.

CONCLUSIONS

The PFGE analysis indicated that the CRPA outbreak resulted from the contamination of the cystoscopy room via an unsealed drain. The outbreak ended when the drain was sealed.

Serratia marcescens infections

The recognition of serratia as an opportunistic human pathogen can be dated from 1959, when the microorganism entered the family ofEnterobacteriaceae,with features recognizable in the clinical laboratory and related to theKlebsiella/Enterobactergroup. Since then, physicians have been challenged to establish the significance of isolation of serratia from a clinical specimen.

Short-term versus prolonged systemic antibiotic prophylaxis in patients treated with indwelling catheters

Newly hospitalized patients with stroke treated by indwelling catheters were assigned randomly to 3 treatment groups. Group 1 (24 patients) received 3 gm. ampicillin intramuscularly in divided doses 1 hour before, at the time of and 6 hours after insertion of the catheter. Group 2 (28 patients) received daily 1 gm. ampicillin intramuscularly every 8 hours. Group 3 (26 patients) was not subjected to any antimicrobial prophylaxis. Within 1 week after catheter insertion significant bacteriuria developed in 12.5 per cent of the patients in group 1, 42.8 per cent in group 2 and 45.1 per cent in group 3. The difference in the incidence between group 1 and either group 2 or 3 was statistically significant (p less than 0.02 and p less than 0.01, respectively). The mean number of strains (plus or minus standard error of mean) isolated per case of bacteriuria in group 3 (1.25 plus or minus 0.18) was significantly lower (p less than 0.05) and antimicrobial resistant strains were fewer (4 of 15) than in group 2 (1.75 plus or minus 0.13 and 12 of 21, respectively).

Epidemiological and bacteriological investigation of Serratia marcescens epidemic in a nursery and in a neonatal intensive care unit

An epidemic caused by Serratia marcescens that involved 26 infants admitted to the Neonatal Intensive Care Unit (NICU) and 82 infants admitted to the Nursery of the 2nd Medical School of Naples is reported. Two different biotypes of S. marcescens with two completely different epidemiological patterns were identified. The prevalent biotype (A8b trigonelline-) was isolated in the delivery room, in the operating room, in the Nursery and in the NICU from items, healthy infant excreters and affected infants; the second biotype (A3a) was isolated only in the NICU from staff, two healthy infant excreters and two affected infants. Colonization of the throat and the gastrointestinal tract was frequent. Infected and colonized infants were the most important reservoir for serratia in the Nursery and in the NICU particularly for the type strain A3a. A mucus aspiration apparatus contaminated in the delivery room and the contamination of several instruments and items probably had a major role in the initiation and maintenance of the spread of the A8b strain. Mass contamination of the nursery has been related to overcrowding and a lack of the control measures; the transfer of high-risk colonized infants caused spread in the NICU. In the NICU the attack rate 26%; 69% of infants became ill; the case fatality ratio was 19%. Epidemiological investigation of the infants at risk showed some factors predisposing to infection with serratia. The hygienic measures failed to control the spread of serratia and it was necessary to refuse new admissions to pregnant women in order to decontaminate and re-organize the wards.

A nosocomial epidemic of Serratia liquefaciens urinary tract infection after cystometry

An epidemic involving 10 patients who developed a urinary tract infection within a few days after cystometry and/or cystoscopy is reported. A pure culture of Serratia liquefaciens was obtained from the fluid inside the disposable dome of the cystometer. The outbreak ceased when the dome was systematically changed after each examination as required.

Meningoencephalitis due to serratia marcescens infection in neonates

Six autopsy cases of Serratia meningoencephalitis were reported. The symptoms of this infection become apparent at an early stage in neonates; the meningoencephalitis in these six cases was severe, with or without inflammatory lesions in other organs. Serratia marcescens was originally described as a nonpathogenic organism; however, it is believed that after entering the blood stream of neonates, it becomes pathogenic, especially to the central nervous system. Meningoencephalitis due to Serratia marcescens is very severe and takes a rapid and progressive course against which no antibiotics have been found effective. Prevention of this infection is therefore considered of crucial importance.

Nosocomial urinary tract infections: secular trends, treatment and economics in a university hospital

During a 71-month interval 3,024 nosocomial urinary tract infections were identified by prospective surveillance at our hospital. The annual attack rate varied between 2.0 and 3.1 per 100 admissions. Gram-negative bacilli caused 74 per cent of all urinary infections and recurrent infections in the hospital accounted for only 1 per cent. The most frequent pathogens were Escherichia coli (24 per cent), Pseudomonas aeruginosa (8 per cent), Streptococcus faecalis (7 per cent), Klebsiella pneumoniae (6 per cent) and Proteus mirabilis (6 per cent). Candida species caused 10 per cent of the infections and may represent a hospital-acquired pathogen of increasing importance. The burn unit had a significantly higher proportion of Enterobacter infections (21 per cent) than any other service (p less than 0.05). The plastic surgery service had more Serratia infections (24 per cent), whereas obstetrics and gynecology had more Escherichia coli infections (47 per cent) relative to other hospital services. More than 99 per cent of the patients with nosocomial urinary tract infections received antimicrobial drugs; in 63 per cent the chart documented that drug therapy was prescribed specifically for treatment of the urinary infections. Hospital-acquired urinary infections added approximately 1 million dollars to hospital expenses during the study interval. Estimates were made of the economic benefits of successful control programs.