Transcript Document

UNIVERSITY OF COLORADO
SCHOOL OF MEDICINE
DEPARTMENT OF PATHOLOGY
RESIDENCY TRAINING PROGRAM
MICROBIOLOGY
Alpha-hemolytic Streptococci and Enterococci
Topic 1: VRE Screening
CASE STUDIES AND TOPIC REVIEWS
As a point of departure from the case study format
presented before, the focus this week will be more
informational than self-assessment.
The purpose here is to introduce three topics as
related to the non-beta hemolytic streptococci based
on information presented either during past
CACMLE Teleconferences or during the 2006 “Micro
in the Mountains” conference.
The topic reviews will include:
• Screening for Vancomycin-Resistant Enterococci
•Emergence of penicillin-resistant pneumococci
•Clinical relevance of the viridans streptococci
ENTEROCOCCUS: VRE SCREEN
Presenter:
Claudia
Hinnenbusch,
MT(ASCP)
Clinical
Microbiology
UCLA Medical
Center, Los Angeles
CACMLE
Teleconference
Oct. 24, 2001
A 38-year-old female was admitted to the UCLA hospital for a liver
transplant. Following protocol, a rectal swab was collected to rule out
vancomycin-resistant Enterococcus sp. Colonies isolated on Columbia
colistin-naladixic acid modified agar containing 10ug of vancomycin were
transferred to sheep blood agar. Dull gray, opaque, alpha-hemolytic
colonies were isolated from the subculture after 24 (left) and 48 (right)
hours incubation. A Vitek Gram positive identification (GPITM) card gave a
profile number of 77367270530 = Enterococcus gallinarum/cassiloflavus.
The susceptibility result for vancomycin was 8 mcg/ml.
ENTEROCOCCUS: VRE SCREEN
Recapitulation
The increase in the numbers of vancomycin-resistant enterococci
has prompted the implementation of surveillance programs in
hospitals to monitor its incidence and spread. Enterococcus
faecium is most common vancomycin resistant strain, having
acquired either the Van- A or the Van-B gene. E. faecalis
possessing these vancomycin-resistant genes are less common.
Isolates of E. cassiloflavus and E. gallinarum, that have MIC levels
to vancomycin that are elevated (between 4 and 32 mcg/ml) are
also encountered. Since this low level resistance is intrinsic,
such isolates are not reported as VRE.
Automated bacterial identification systems are not always reliable
in identifying the enterococci to the species level. Thus, when
screening for VRE, one should accept results from these systems
only if they correlate with the colony morphology and the known
antimicrobial profile of the organism in question.
ENTEROCOCCUS: VRE SCREEN
Screening Protocol
VRE Screening Protocol used at the UCLA Medical Center
1. Patients being admitted for organ transplant have admission cultures, as
well as cultures when they are transferred to another ward, or released.
Cultures include a nasal swab to screen for MRSA, and a rectal swab to
screen for VRE.
2. Stool cultures from inpatients are only processed for VRE surveillance
when the Infection Control team has given prior approval. They are rarely
used to demonstrate clearance in patients previously found to have VRE.
3. Since a correlation has been made showing an increased incidence of
VRE in patients whose stool samples are positive for C. difficile toxin,
stool samples positive for C. difficile are screened quarterly for the
presence of VRE. In our institution, this has proven to be a cost-effective
and efficient way to screen for VRE.
NOTE: IS THERE ANY SUCH PROTOCOL IN EFFECT AT UCHSC?
UNIVERSITY OF COLORADO
SCHOOL OF MEDICINE
DEPARTMENT OF PATHOLOGY
RESIDENCY TRAINING PROGRAM
MICROBIOLOGY
Alpha-hemolytic Streptococci and Enterococci
Topic 2: Penicillin Resistant Pneumococci
Abbreviated Identification of Streptococcus pneumoniae
SUMMARY
Mucoid alpha-hemolytic colonies
on Blood agar
Lancet-shaped, gram-positive cocci
in pairs, with halo
Bile Soluble
Susceptible to Optochin (“P” Disk)
Streptococcus pneumoniae
Perform antimicrobial
susceptibility test
WHY IS THIS NECESSARY?
A respiratory isolate was
found to have no zone of
inhibition around the 1ug
oxacillin disk (6mm) in a
screening disk diffusion test.
It was reported out as
“penicillin resistant”.
As a follow up, a routine disk
antibiotic susceptibility test
panel was performed. As
illustrated in the photograph,
the isolate was found to be
susceptible to other
antibiotics (cefuroxime,
tetracycline, erythromycin,
chloramphenicol, and
ceftriaxone). The 15mm in
diameter zone around the disk
at the 1 o’clock position
indicates intermediate
resistance to SXT.
Antibiotic Resistant
Pneumococcus
Antibiotic Resistant Pneumococcus
Emergence of world-wide resistance to pneumococci
South Africa, Baraguanath Hospital, Johannesburg (Am J Dis Child
146:920-923, 1992) revealed resistance in 40% of community acquired
and 80% of hospital acquired isolates of S. pneumoniae recovered from
83 children with meningitis and/or bacteremia.
South Africa: Witwaters-rand University: Of a study population of 4766
consecutive isolates of S. pneumoniae recovered from blood and CSF
during the period 1979-1986, the average penicillin resistance climbed
from 3.8% in 1979 to 14.2% in 1986. 92.2% of serogroups were 6 or 19.
Spain: Bellvitge Principes ‘Espanya Hospital, Barcelona: 23% rate of
resistance among 66 episodes of pneumococcal meningitis (Am J Med
84:839-846,1988).
Spain: Hospital General Gregorio Mara-nor, Madrid: 42.5% of strains
isolated from 139 patients were “non-susceptible” (Clin Infect Dis
14:427-425, 1992).
Emergence of world-wide resistance to pneumococci
Africa: Nairobi, Kenya. Study population—of 150 S. pneumoniae isolates
from HIV-positive patients, 19% were resistant with MIC’s ranging from 0.12
– 0.25ug/ml. Rare serotype 14 in 18% of cases.
Hungary, Heim Pal Children’s Hospital, Budapest. Epidemiologic study
revealed 58% of all S. pneumoniae isolates to be resistant to penicillin (70%;
of isolates recovered from children.) (J Infect Dis 163:542-548, 1991).
Houston, Baylor college of Medicine. Of 95 isolates of S. pneumoniae, 34
were susceptible at <0.1ug/ml, 42 were intermediate at 0.1 – 1.0 ug/ml; and,
19 were resistant at >2ug/ml (12.1% of all isolates). (Antimicrob Agents
Chemother 36:1703-1707. 1992).
Atlanta, Georgia, CDC. Pneumococcal Surveillance Working Group
(Facklam, et al. J Infect Dis 163:1273-1278, 1991): Study population—5,459
isolates of S. pneumoniae submitted from 35 hospitals during the period
1979 to 1987. Overall resistance was 5% at MIC’s >0.1ug/ml.
Emergence of world-wide resistance to pneumococci
These accounts were considered quite worrisome at the time. The high
prevalence of penicillin-resistant S. pneumoniae in certain locales
undoubtedly represents antibiotic pressure, where antibiotic therapy has
been administered virtually without restriction.
Recent studies reveal that resistance has increased in many parts
of the world to 15% - 35% depending on the geographic region.
(Whitney, et al. NEJM 343:1917-1924, 2000)
Thus it is currently recommended that S. pneumoniae isolates from
blood, CSF, and other closed body sites, and from treatment failures,
should be tested routinely for susceptibility to penicillin.
Guidelines:
Susceptible: MIC <0.06 ug/ml (oxacillin zones >20mm)
Relatively resistant: MIC 0.12 – 1.0 ug/ml (oxacillin zones <19mm)
Resistant: MIC >1.0 ug/ml (oxacillin testing cannot distinguish between
relatively resistant and resistant).
UNIVERSITY OF COLORADO
SCHOOL OF MEDICINE
DEPARTMENT OF PATHOLOGY
RESIDENCY TRAINING PROGRAM
MICROBIOLOGY
Alpha-hemolytic Streptococci and Enterococci
Topic 3: Viridans Streptococci
Case Study: Human Meningitis
The case is that of a 59 y.o. male
farmer with sudden onset of
fever, and confusion
Peripheral Blood count:
12,800 wbc’s/mm3 (73%
neutrophils; 12% bands)
Cerebrospinal Fluid:
– 3520 wbc’s/mm3 (100%
neutrophils)
– Glucose: <1 mg/deciliter
– Protein: 368 mg/deciliter
Case presented by:
William M. Janda, Ph.D. D(ABMM)
Assoc Prof Dept. Pathology
Director Clinical Microbiolog
Laboratory
University of Illinois Medical Center
Chicago, Illinois
“Micro in the Mountains” 2006
Illustration of gray white, alphahemolytic colonies recovered on
sheep blood agar from spinal fluid
sediment after 48 hours incubation.
The isolate was identified as:
Streptococcus suis
Case Study: Human Meningitis
Based on the clinical history and the laboratory findings,
the patient was empirically started on ceftriaxone and
vancomycin.
When the isolate was identified as Streptococcus suis, the
therpapy was switches to IV ampicillin.
The patient complained of lower back pain. MRI studies
revealed diskitis and osteomyelitis of L3 and L4.
The patient was discharged after 13 days to complete a 6week course of IV ampicillin and oral clindamycin.
This was the first reported case in the United States.
(NEJM 354:13-25, 2006)
Streptococcus suis: Characteristics
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α-hemolytic streptococcus
No growth at 10oC or 45oC
LAP-Positive
Esculin hydrolysis – Positive
Growth, 6.5% NaCl-Negative
Arginine Dihydrolase-Positive
Hippurate hydrolysis, urease, acetoin
production – Negative
• Acid from glucose, maltose, sucrose, and
lactose
• No acid from mannitol, sorbitol, or ribose
• Included in the API Strep data base
Streptococcus suis: Epidemiology
• Although found worldwide, there has never been a case
reported in the U.S. (until 2006!!!)
– Two cases reported in Canada
• Majority of human disease reported in Asia (Thailand,
China, and Hong Kong)
– Third most common agent of bacterial meningitis in
Hong Kong
– Human cases reported from the Netherlnds, Denmark,
Great Britain, France, Belgium, Germany, and Sweden
• Human infections most common in those who work
directly with swine or in the manufacture of pork products
– Abattoir and slaughterhouse workers, pig farmers,
meat inspectors, veterinarians
Streptococcus suis: The Pigs’
“Group B Streptococcus”
• Pathogen of swine
– Transmitted from aymptomatic sows to their
newborn
– Rapidly fatal disease in piglets (sepsis, meningitis,
pneumonia)
• Sporadic disease in humans
– Meningitis is the most serious manifestation
– Human fatality rate of 5-10%
– Serotype 2 (of 35 serotypes) responsible for vast
majority of human disease
Streptococcus suis: Clinical Disease
• Human infections enter through breaks in skin, the
nasopharynx, or the gastrointestinal tract
• “Influenza-like” prodrome with rapid development of
bacteremia and meningitis
• High rate of cochlear-vestibular involvement
resulting in ataxia, dizziness
– Cranial nerve involvement leads to hearing loss
• Complications associated with bacteremic
dissemination
– Arthritis, spondylodiscitis, endophthalmitis,
peritonitis, pneumonia, and endocarditis
Sichuan, China Outbreak:
July-August, 2005
• 215 human cases reported among farmers
exposed during the slaughter of pigs
– 28% developed toxic shock syndrome
– Sepsis (24%), meningitis (48%) or both
– 62% mortality
• Ribotyping revealed that the same strain was
reponsible for all cases
Streptococcus suis
Viridans Streptococcal Groups
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Group II: Sanguis Group
– S. sanguinis (3 biotypes), S. parasanguinis, S. gordonii, S. sinensis
Group III: Mitis Group
– S. mitis, S. oralis, S. cristatus, S. peroris, S. infantis, S. australis, S.
oligofermentans
Group IV: Mutans Group
– S. mutans, S. sobrinus, S. cricetus, S. downei, S. ratti, S. macacae,
S. ferus
Group V: Salivarius Group
– S. salivarius, S. vestibularis, S. infantarius, S. thermophilus, S.
hyointestinalis
Group VI: Anginosus Group (also included in beta-hemolyic group)
– S. constellatus subspecies, S. anginosus, S. intermedius
Group VII: Bovis Group
– S. bovis sensu stricto, S. gallolyticus, S. infantarius, S. suis.
Viridans Group Streptococci
• Found in the upper respiratory tract and the
urogenital tract
• Endocarditis
– 30-40% of cases due to viridans streptococci
– Usually isolated from multiple blood cultures
– Occur in patients with pre-existing valvular disease
– Also associated with infection of prosthetic valves
– Complications may include multi-valve infection,
mitral valve aneurysms, paravalvular abscesses,
and glomerulonephritis
– S. mitis, S. sanguis, S. oralis, S. gordonii, S. mutans,
S. salivarius, S. vestibularis, and S. sinensis
Viridans Streptococcal Bacteremia
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Prolonged bacteremia with viridans streptococci in neutropenic
pediatric and adult patients now recognized as a distinct clinical entity
•
Associated with aggressive cytotoxic chemotherapy given for
treatment of leukemias, lymphomas, solid tumors, and bone marrow
transplantation
•
Risk factors:
– Administration of high doses of cytotoxic agents (esp. cytarabine)
– Presence of mucosal ulcerations secondary to
chemotherapy/radiation (oral mucositis)
– Absence of previous antimicrobial therapy
– Severe neutropenia
•
May also be complicated by development of ARDS, hypotension,
shock, and endocarditis
Viridans Streptococcal Susceptibility Testing
In past years, the viridans streptococci were generally susceptible to
penicillin, ampicillin, and most other antimicrobial agents. More
recently, resistance has developed against penicillins, cephalosporins,
aminoglycosides, and other classes of antibiotics.
In a study of 211 viridans streptococci recovered from blood cultures,
38% were resistant to penicillin (MIC’s >0.25ug/ml) and 41% were
resistant to erythromycin (Potgeiter, et al. 1992. Eur J Clin Microbiol
Infect Dis 11:543-546). These strains remained susceptible to
cephalosporins, imipenem, and vancomycin.
In a second follow-up study (Antimicrob Agents Chemother 37:27402742, 1993) 4 strains of S. mitis were resistant to penicillin (MIC’s1632ug/ml), and two demonstrated high-level gentamicin resistance (MIC
>2000 ug/ml). These gentamicin resistant strains contained the same
structural gene that codes for gentamicin resistance in E. faecalis and
E. faecium, integrated into the chromosome and not the plasmid.
Abbreviated Identification of Viridans Streptococci
Small, dry, gray, alpha-hemolytic colonies on
sheep blood agar
Gram positive cocci in long chains
Optochin resistant; Bile insoluble
PYR Negative
VP Positive;
Acid from
mannitol/sorbitol
S. mutans
Arginine
dihydrolase
Positive
S. sanguius
VP Pos;
mannitol/sorbitol
Negative
S. salivarius
Chemically
inert
S. mitis