JOURNAL OF CLINICAL MICROBIOLOGY, Sept. 2005, p. 4877–4879
0095-1137/05/$08.00⫹0 doi:10.1128/JCM.43.9.4877–4879.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Vol. 43, No. 9
Nosocomial Spread of a Staphylococcus hominis subsp. novobiosepticus
Strain Causing Sepsis in a Neonatal Intensive Care Unit
Fernando Chaves,1* Mónica Garcı́a-Álvarez,1 Francisca Sanz,1 Concepción Alba,2 and
Joaquı́n R. Otero1
Servicio de Microbiologı́a1 and Servicio de Neonatologı́a,2 Hospital Universitario Doce de Octubre,
Avenida de Córdoba sn, 28041 Madrid, Spain
Received 24 May 2005/Accepted 30 May 2005
From 2002 to 2003, 32 isolates of Staphylococcus hominis subsp. novobiosepticus (SHN) were recovered from
21 patients, 18 of whom were neonates, with 13 considered to have late-onset SHN sepsis. All isolates from
neonates had an indistinguishable pulsed-field gel electrophoresis pattern. Our data support SHN as an
important nosocomial pathogen in neonates.
Coagulase-negative staphylococci (CoNS) are now recognized as a major cause of nosocomial infections in neonatal
intensive care units (NICUs) (8) and are responsible for 48%
of late-onset sepsis among very-low-birth-weight neonates
(20). Although Staphylococcus epidermidis causes 60 to 93% of
CoNS bloodstream infections, several other CoNS species are
reported to cause disease in infants (10, 11, 18). Recently, a
novel subspecies of Staphylococcus hominis, S. hominis subsp.
novobiosepticus (SHN), was isolated from blood cultures and
other clinical specimens (6, 12). The name derives from the
combination of novobio, pertaining to the property of novobiocin resistance, and septicus, pertaining to the ability to cause
sepsis. After isolating SHN from several blood cultures at the
NICU during 2002 and 2003, we undertook a retrospective
study in our 1,300-bed tertiary care institution to determine the
prevalence of this subspecies, the clinical significance of the
isolates, and whether the infections were clonal in origin.
Clinical records of patients from whom SHN had been isolated were reviewed. Diagnosis of sepsis was based on the
assessment of the attending physician. For NICU patients, true
infection was defined either by isolation of SHN from two
separate blood cultures or by a single SHN-positive blood
culture and an elevated serum level of C-reactive protein (ⱖ2
mg/dl). Blood samples were inoculated and processed in an
automated system (BacT/Alert [BioMérieux, Durham, NC] or
BACTEC 9240 [BD Diagnostics, Sparks, MD]). The type
strain of SHN (ATCC 700236) was used as a reference standard throughout the investigations. Identification and susceptibility testing were performed using conventional methods and
the Wider system (Soria Melguizo, Madrid, Spain) (3, 16). A
zone of inhibition measuring ⱕ15 mm in Mueller-Hinton agar
or ⱕ11 mm on Trypticase soy agar plates was considered
indicative of novobiocin resistance (12). All isolates of SHN
underwent confirmatory PCR analysis for the mecA gene (7).
To confirm the identification of SHN, broad-spectrum primers
were used for sequencing the 5⬘ ends of both strands of the 16S
rRNA gene (2, 6) using an ABI Prism 3100 genetic analyzer
(Applied Biosystems, Foster City, CA). Further molecular
characterization of SHN isolates was performed by pulsed-field
gel electrophoresis (PFGE) following digestion of DNA extracts with SmaI (5).
During 2002 and 2003, 32 isolates of SHN were recovered
from 21 patients. Twenty-three isolates were from blood cultures, six were from catheters, one was from cerebrospinal fluid
(CSF), one was from a wound, and one was from external ear
fluid. All 21 patients yielded an SHN-positive blood culture.
All isolates were distinguished from S. hominis subsp. hominis
on the basis of failure to produce acid aerobically from Dtrehalose and resistance to novobiocin. Partial DNA sequencing of the 16S rRNA gene from four clinical isolates, representing three different PFGE patterns (see below), and the
ATCC type strain demonstrated 100% homology (6). Overall,
of 21 isolates of SHN from blood (1 per patient), 21 (100%)
were resistant to penicillin, oxacillin, and erythromycin while
20 (95.2%) were resistant to clindamycin and gentamicin, 19
(90.5%) were resistant to tetracycline, 6 (28.6%) were resistant
to trimethoprim-sulfamethoxazole, 5 (23.8%) were resistant to
chloramphenicol, and 2 (9.5%) were resistant to ciprofloxacin.
All 21 isolates were resistant to nalidixic acid and susceptible to
vancomycin. PCR analysis confirmed that all strains possessed
a mecA gene homologue.
Of 21 patients with SHN bacteremia, 18 were neonates, 1
was a 13-year-old boy, and 2 were adults admitted to the
obstetric and internal medicine wards, respectively. All patients had single episodes of SHN bacteremia. The demographic and clinical characteristics of the neonates are summarized in Table 1. According to the definition of sepsis in
neonates, 13 of these episodes were considered definite cases
of SHN infection. All of these patients were hospitalized from
birth and were considered to have late-onset sepsis (occurring
at ⬎72 h of age), with a median age at presentation of 9 days
(range, 5 to 65 days). All the infants had received previous
antimicrobial therapy with ampicillin and gentamicin and had
intravascular catheters in place at the time of their bacteremia.
All but cases 4 and 20 received treatment with vancomycin and
amikacin. At the same time as the SHN infection, case 20 had
another clinical episode of bacteremia with an extended-spec-
* Corresponding author. Mailing address: Servicio de Microbiologı́a, Hospital Universitario Doce de Octubre, Avenida de Cordoba sn,
Madrid 28041, Spain. Phone: (34) 91-3908239. Fax: (34) 91-5652765.
E-mail: fchaves.hdoc@salud.madrid.org.
4877
4878
NOTES
J. CLIN. MICROBIOL.
TABLE 1. Demographic and clinical characteristics of neonates with SHN bacteremia
Case no.
Sex
Gestational
age (wk)
Birth wt (g)
Date of bacteremia
(mo/day/yr)
Age at
bacteremia
(days)
Other source(s) of
SHN isolation
Underlying condition(s)
Clinical
significancea
1
2
3
4
5
6
7
8
9
10
11
12
16
17
18
19
20
21
Male
Female
Male
Female
Male
Male
Female
Male
Female
Female
Male
Female
Male
Male
Female
Female
Male
Female
29
31
27
27
32
35
41
35
36
33
37
36
26
26
25
38
28
29
1,251
1,395
1,020
900
1,650
2,340
1,750
1,209
3,000
1,830
2,120
2,950
800
950
711
2,300
520
1,258
2/28/2002
3/8/2002
4/8/2002
7/2/2002
8/5/2002
8/8/2002
8/28/2002
9/6/2002
9/10/2002
9/30/2002
10/30/2002
10/30/2002
9/22/2003
9/29/2003
10/17/2003
10/17/2003
10/20/2003
10/20/2003
9
6
11
9
10
35
7
11
9
7
65
29
120
9
5
16
12
8
None
Catheter
None
None
None
Catheter
None
CSF
None
Catheter, wound
None
None
None
Catheter, ear fluid
Catheter
None
Catheter
None
RDSb
RDS
RDS
RDS
None
Necrotizing enterocolitis
None
Malformative syndrome
Omphalocele
RDS, pulmonary hypoplasia
Gastroschisis
Congenital heart disease
Bronchopulmonary dysplasia
RDS
RDS
Intestinal obstruction
RDS
RDS
No
Yes
No
Yes
Yes
Yes
Yes
Yes
No
Yes
Yes
No
No
Yes
Yes
Yes
Yes
Yes
a
b
Clinical significance was assessed as described in the text.
RDS, respiratory distress syndrome.
trum -lactamase-producing strain of Klebsiella pneumoniae
and received several regimens of antimicrobial treatment.
None of the patients died of causes related to their SHN sepsis.
Twenty-three isolates of SHN (21 from blood, 1 from CSF,
and 1 from a catheter), corresponding to 21 patients, and one
type culture (ATCC 700236) were available for PFGE typing
(data not shown). Twenty-one isolates from the 18 neonates
and 1 13-year-old boy (case 15) had an indistinguishable macrorestriction pattern (pattern A) that differed by three bands
from the patterns of the two adult patients (cases 13 and 14).
All isolates with PFGE pattern A were susceptible to ciprofloxacin and resistant to tetracycline. Most isolates of SHN
from the neonatology department were obtained during two
separate periods of time: eight cases between August and September, 2002, and six cases between September and October,
2003 (Table 1). The second period was coincidental with an
outbreak of infections in this department due to extendedspectrum -lactamase-producing K. pneumoniae.
After the initial description of SHN in 1998 (12), to our
knowledge, this is the first clinical report implicating this microorganism as the cause of bacteremia in hospitalized patients
and particularly among patients from a NICU. As in other
studies on neonatal CoNS infections that have demonstrated
significant morbidity but a low rate of mortality, there were no
deaths associated with SHN sepsis at our institution (15, 23).
The incidence and types of infection associated with SHN in
hospitalized patients are not known as, like others, our laboratory does not routinely identify CoNS to the species level.
Although there is no information on the prevalence of colonization with SHN, Kloos et al. (12) suggest that if SHN is a
resident on human skin, it probably persists in very small numbers and requires enrichment for detection. In our study, 6/13
(46%) neonates with clinically significant bacteremia had
proven catheter-related bloodstream infections. CoNS account
for a significant proportion of nosocomial bacteremia cases
related to the insertion and maintenance of intravascular cath-
eters (1, 22). It is likely that more cases of neonatal bacteremia
in our study were also catheter related, but catheters were not
processed for culture in all instances.
An important characteristic of SHN is its pattern of multidrug resistance, including resistance to oxacillin. This has important clinical implications because the alternative to oxacillin
for treatment of these patients is administration of vancomycin, the overuse of which has implications for the continued
emergence of vancomycin resistance in both CoNS and Staphylococcus aureus (4, 19, 21).
Molecular epidemiology showed that a single clone of SHN
caused sepsis in at least 13 neonates in the NICU during the
2-year study period. Surprisingly, following the first outbreak in
August 2002, after an interlude of about a year, the same strain
was associated with another outbreak in September 2003. Empirical antibiotic therapy with the combination of ampicillin
and gentamicin is likely to have favored selection of this
multidrug-resistant SHN clone, which subsequently became
endemic within our institution (14). Although we did not
investigate the reservoir and mode of transmission, it has
been postulated that the infants themselves are the reservoirs of endemic strains of staphylococci, with organism
transmission occurring through contact with the hands of
health care workers (4). Furthermore, other reports have
shown that CoNS isolates from the nasopharynges and
hands of health care workers are often genetically related to
the organisms that colonize and/or cause disease in neonates, confirming the importance of health care workers in
the nosocomial transmission of CoNS in the NICU setting
(9, 17).
In summary, our data support that SHN is a significant cause
of nosocomial bacteremia in the NICU and that, like other
species of CoNS (9, 13), isogenic clones can persist during long
periods of time and be transmitted between neonates.
Nucleotide sequence accession number. The partial 16S
rRNA sequence of the clinical isolate of SHN from blood
VOL. 43, 2005
NOTES
corresponding to case number 2 was deposited in GenBank
under accession number DQ056840.
D-glucosamine-negative,
13.
We thank Tobin Hellyer for his suggestions and comments and
Antonia Martı́n and Mar Aguilera for excellent technical assistance.
This study was supported by grant 02/0572 from the Fondo de
Investigaciones Sanitarias, Spain.
14.
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