five not-so-easy pieces
William Check, PhD
When the call
goes out to the clinical microbiology laboratory to "round up
the usual suspects," Bartonella, Cyclospora, Ehrlichia, Mycoplasma,
and Tropheryma are not typically the first names on people's
minds. So why was a whole symposium devoted to these microbes at
the 2001 Interscience Conference on Antimicrobial Agents and Chemotherapy?
"All these organisms fit into that unique category that we have
lumped with Haemophilus in the past as fastidious organisms,"
explains co-convener David Welch, PhD, national associate director
of microbiology at Laboratory Corp. of America, Dallas. "In the
subtitle for the session we called them recondite," he says. "Recondite
implies something hidden. That's appropriate—organisms like
Mycoplasma and Bartonella are at the far end of
the spectrum of fastidiousness and of culturability. On the other
hand, they are not uncommon causes of clinical syndromes."
Others agree. "Most people think these are rare organisms, but
they’re not if you know how to look for them," says David
Walker, MD, professor and chairman of the Department of Pathology
and director of the WHO Collaborating Center for Tropical Diseases
at the University of Texas Medical Branch, Galveston.
"If someone asked me how to detect these organisms, I would have
to go to a textbook," admits co-convener Bruce Hanna, PhD, associate
professor of pathology and microbiology at the New York University
School of Medicine and director of clinical microbiology at Bellevue
Hospital. For this reason, the symposium focused on methods of
detection. "These organisms are not easy to grow," Dr. Hanna says.
"Antibodies can sometimes be confusing and difficult to interpret.
And PCR is promising but still in progress."
Because of their occult nature, these five microbes have been
associated with mysterious maladies and have given rise to mistaken
identity, misattribution, and even an accusation of murder. Molecular
methods are now illuminating their identities. Use of nucleic
acid amplification assays for 16S rRNA sequences "has brought
about a new approach to the identification of microbial pathogens
that cannot be cultivated in the laboratory," wrote David Relman,
MD, and Stanley Falkow, PhD, of Stanford University, who have
worked on several such organisms. "These results suggest the existence
of a far greater microbial diversity among human pathogens than
has been so far appreciated with culture-dependent methods" (Infect
Agents Dis. 1992;1:245).
"From my perspective directing a large referral laboratory that
services the gamut of infectious diseases from community practice
to a major teaching hospital, it is an exciting time to be in
microbiology," says CAPMicrobiology Resource Committee member
Deirdre Church, MD, PhD. Dr. Church is division head of microbiology
in the Department of Pathology and Laboratory Medicine, Calgary
(Alberta) Laboratory Services. "With molecular technology coming
onboard, we can have a much better understanding of where a whole
host of organisms fits into disease patterns." Calgary Laboratory
Services tests for all of the microbes discussed except Ehrlichia,
whose tick vector is not found in its region.
Nothing illustrates more clearly the confusion that an
unidentified microbe can cause than what one review called the
"long and circuitous history" of Bartonella. Bartonellosis
was long thought to be a uniquely Peruvian illness called Carrion's
disease, after Peruvian medical student Daniel Carrion. In 1885,
Carrion inoculated himself with material from a child with a skin
disease called verruga peruana in an attempt to discover the natural
history of this illness. Surprisingly, Carrion became severely
ill and died six weeks later. His symptoms were those of another,
often-fatal Peruvian disease, Oroya fever. Carrion thus inadvertently
proved that these illnesses are two phases of infection with the
same organism, later determined to be Bartonella bacilliformis.
(A colleague who assisted with Carrion's self-inoculation was
briefly charged with homicide.)
Bartonellosis was synonymous with Carrion's disease for precisely
one century. In 1985, a technologist named Diane Hensel working
in a laboratory directed by Dr. Welch in Oklahoma City recovered
and worked up isolates from blood cultures of several HIV-infected
patients. Dr. Welch recalls that they saw one isolate of this
"Campylobacter-like" organism each year for the next few
In 1990, they published a detailed report on two cases in the
New England Journal of Medicine. In the same issue (vol.
323, no. 23) were articles on "the agent of bacillary angiomatosis
[BA]" from Stanford University and a report on bacillary peliosis
hepatis from the University of California, San Francisco. ("Peliosis"
is a histological term for cysts that become filled with red blood
cells.) Both Dr. Welch's paper and the one from Stanford suggested
that the unknown bacillus was related to Rochalimaea quintana.
Subsequent exchange of material among the laboratories and 16S
rRNA analysis showed that the three groups were working with the
same organism, which was first named Rochalimaea henselae
(after Dr. Welch's technologist) and then Bartonella henselae,
when sequencing revealed identity with that genus.
Soon after, polymerase chain reaction analysis showed the presence
of Bartonella henselae in lymph nodes of children with
cat-scratch disease, which had previously been misattributed to
Afipia felis. "Fifty years after the clinical entity cat-scratch
disease was described, we finally found the true cause," Dr. Welch
A third Bartonella species that causes human disease is
B. quintana, the agent of trench fever. B. quintana
has also been found to cause bacteremia in homeless people, possibly
transmitted by body lice and often leading to severe endocarditis.
Dr. Welch notes that B. henselae has also been found to
cause endocarditis, typically in patients who have had cat exposure.
"B. henselae as a cause of opportunistic infections in
HIV-infected persons is declining with the effective preventive
regimens currently employed," he says. "Now we are increasingly
seeing this pathogen as an agent of culture-negative endocarditis
in non-immunocompromised persons, many of them elderly. The majority
end up having cardiac valve replacement."
The most common reason to test for Bartonella is suspicion
in a child of apparent cat-scratch disease, of which there are
about 20,000 cases each year in the United States. It's "more
common than Lyme disease," says Dr. Welch. In 10 percent of cases,
"atypical" ocular or central nervous system complications occur.
Bartonella may also cause culture-negative endocarditis.
For identification, Dr. Welch says, "there are not many direct
detection methods worth pursuing." It is possible to visualize
B. bacilliformis in blood samples and B. henselae in tissue or
skin with Warthin-Starry silver stain.
"Cultures are not recommended, especially for cat-scratch disease,"
Dr. Welch says. "Efficiency of recovery is not good, even with
the shell vial technique." Cultures may be done for other manifestations
on blood- or chocolate-enriched medium with prolonged incubation
(up to 14 days). Recovery of Bartonella spp in cultures
is poor, partly because of broader dependence on continuous monitoring
systems that hold samples for less than seven days and that are
broth-based. "Bartonella does better on solid media," Dr.
He calls serology "the mainstay" of diagnosis. Immunofluorescent
antibody tests are 84 percent to 95 percent sensitive and 94 percent
to 98 percent specific. More recently, an IgG/IgM EIA showed 85
percent sensitivity and >98 percent specificity in PCR-proven
cases of cat-scratch disease (Clin Inf Dis. 2001;33:1852–1858).
Dr. Welch cautions that cross-reactions occur with Coxiella
burnetii and Chlamydia spp.
"Most laboratories are getting geared up to do molecular diagnostic
testing," he says. "If you have a molecular section in your microbiology
laboratory, it is certainly reasonable to consider PCR for Bartonella."
PCR, he says, "is no more of a homebrew method than serology,
since serology needs a source of antigen that is not commercially
available." PCR-based methods for B. henselae and other
Bartonella species have been published (Am J Clin Pathol.
2001;115:900–909). "As PCR methods become more refined,
they become more practical for the general microbiology laboratory
setting," Dr. Welch says.
While not all laboratories will set up testing for Bartonella,
Dr. Welch says, "infections due to Bartonella are common
enough that all laboratories should at least have a place to get
serology done routinely and a place for getting PCR-based assays
done if indicated." PCR can be helpful for suspected infective
endocarditis when tissue is available, for CNS disease, and possibly
when tissue is available from fine-needle aspirate of a lymph
node where serology is negative or equivocal.
Whether typical cat-scratch disease needs treatment is "subject
to debate," Dr. Welch says. If an antibiotic is used, azithromycin
is the first choice. Other manifestations of B. henselae
or B. quintana can be treated with erythromycin or doxycycline.
Beta-lactams are largely ineffective. "In vitro tests don't predict
clinical response," Dr. Welch says.
Dr. Church agrees that testing for Bartonella is indicated
in cat-scratch disease with involved lymph nodes and for endocarditis
with multiple negative cultures. "We have worked hard to find
it in AIDS patients," she says. "But in retrospect, we are even
more likely to see it in a child with a cat or kitten at home
or in elderly or homeless people. It is probably a lot more prevalent
than we think."
Bartonella can be retrieved from an automated blood culture
system, in Dr. Church's experience. "One of the keys in blood
cultures is prolonged incubation," she says. "If we suspect Bartonella,
we incubate cultures for four weeks. If we get a positive signal,
we try to retrieve an organism on plated media." Dr. Church confirms
with molecular testing using an in-house PCR assay. She agrees
that Bartonella can be discovered via histopathological
examination of lymph node or heart valve using special stains
or PCR. "We don't do serology," she says, "but we could send that
to a reference laboratory. It takes a couple of weeks to get results."
The unmasking of Bartonella began in 1990, but the identification
and clinical importance of the "enigmatic parasite" Cyclospora
cayetanensis is even more recent, dating from 1993. In retrospect,
three 1977–1978 cases in New Guinea were caused by this
protozoan, but they were misattributed to a close relative, Isospora,
says Charles R. Sterling, PhD, professor of veterinary science
and microbiology at the University of Arizona, Tucson.
For some time Cyclospora was misidentified as an alga.
"People were confused by its autofluorescent properties, which
many algae have," Dr. Sterling explains. "Also, we could not make
out discrete structures inside the oocyst. We see many things
in the environment like that, including algae." In 1993, a student
of Dr. Sterling's confirmed Cyclospora's identity as a
coccidian parasite, like Cryptosporidium and Toxoplasma.
"The student was able to put the organism into culture and to
develop infected phases," Dr. Sterling says. The trick was to
incubate samples for two weeks at room temperature, inducing sporulation
into oocysts. (Typical coccidian parasites sporulate in 24 hours.)
After lysis with bile salts and trypsin, "out popped two sporocysts
with two sporozoites from each sporocyst, characterizing this
as Cyclospora," Dr. Sterling says. The organism is not
Waterborne outbreaks of Cyclospora have occurred in Nepal
and Guatemala. Multiple food source outbreaks occurred from 1995
to 1999 in North America from imported Guatemalan and Mexican
raspberries, basil, and leafy vegetables. Sequencing methods can
now link patients within an outbreak to each other and to the
implicated food. They can also link the outbreak organism to organisms
in humans working in the field where the raspberries were picked.
The FDA now blocks the importation of Guatemalan raspberries
during the spring and monitors compliance with preventive measures.
No outbreaks have been associated with Guatemalan raspberries
in the past two years.
Additional insight—and a new puzzle—arose from work
that Dr. Sterling's group did at a Lima clinic.
"We obtained permission to do endoscopy on patients infected
with Cyclospora," Dr. Sterling says. "This allowed us to
see where the parasite develops in the intestinal tract." Jejunal
biopsies revealed intestinal stages, implying that the parasite
completes its life cycle within the human host. The parasite causes
intestinal inflammation, which produces the prolonged watery diarrhea
characteristic of this illness. However, Dr. Sterling says, "We
may see only a few organisms, yet on biopsy see profound inflammation.
How is it caused? No one has isolated toxins from this group of
The parasite's development is a second puzzle. When shed in feces,
it is in a nonsporulated phase. But organisms found on fruit are
already sporulated. How and where do oocysts arise? Where do they
go? One "guess," Dr. Sterling says, is that they are dormant for
a portion of the year. "We can put Cryptosporidium in the
refrigerator for 18 months and still some organisms retain infectivity,"
he says. Perhaps oocysts get on fruit via an environmental source.
"One suggestion," Dr. Sterling says, "is that insecticide solutions
are made up with contaminated water."
He calls Cyclospora symptoms "classic" for enteric disease:
Profuse watery diarrhea (which may be intermittent for up to 40
days), with bloating and flatulence, is seen in nearly 100 percent
of patients, with weight loss and nausea in 80 percent.
For diagnosis, an acid-fast stain—found in many laboratories
because it is also used for Cryptosporidium—is used.
However, Cyclospora oocysts are acid-fast variable; some
don't pick up the stain at all. A modified safranin stain, which
is heated slightly in a microwave, was developed at the Centers
for Disease Control and Prevention. "It is important to have a
good ocular micrometer," Dr. Sterling adds, "since Cyclospora
oocysts are eight to 10 micrometers in diameter, whereas Cryptosporidium
oocysts are rarely more than six microns in diameter."
These are "relatively nonspecific techniques," Dr. Sterling acknowledges,
"yet that's what we use in the laboratory today." PCR is more
specific, but it hasn't found widespread application. "Everyone
agrees we need better primers before we have robust PCR testing
for this organism," Dr. Sterling says.
When Cyclospora infection is recognized, treatment with
trimethoprim/sulfamethoxazole for five to seven days is more effective
than ciprofloxacin, he says.
In the laboratory, Dr. Church says, the main diagnostic test
remains a stool sample for O&P examination and special stains,
such as modified Kinyoun acid fast, on concentrated stool specimens.
Cyclospora is structurally unlike any other parasite in
stool except for Cryptosporidium, she notes. Dr. Church
would not do a special stain on a stool specimen routinely; she
would do it only if the patient had a suspicious history. "These
are patients who come to a consultant, usually a gastroenterologist,
with unresolved disease," she says.
The story of human ehrlichioses has unfolded in three
chapters over the past 15 years, with an indispensable contribution
from molecular methods. Dr. Walker defines an Ehrlichia
as a "small, obligately intracellular, gram-negative bacterium
with characteristic dimorphic appearance and cell wall ultrastructure
that resides in cytoplasmic endosomes." In 1986, human patients
were first observed with mononuclear cells containing ehrlichia-like
organisms. In the second chapter, Dr. Walker and others described
in 1994 six patients with neutrophils or granulocytes containing
inclusions suggesting ehrlichial infection (J Clin Microbiol.
Human monocytic ehrlichiosis (HME) and human granulocytic ehrlichiosis
(HGE) have similar nonspecific presentations, with nearly ubiquitous
fever and malaise and less frequent nausea, cough, and confusion.
Arthralgias may occur. Leukopenia, lymphocytopenia, and thrombocytopenia
are present, and elevated liver enzymes are common. "Ehrlichioses
can be life-threatening," Dr. Walker says. Adult respiratory distress
syndrome and meningitis "are definitely not rare," he adds.
Analysis of 16S rRNA genes from the HME agent showed that it
was a new species, named Ehrlichia chaffeensis after the
town in Arkansas where the isolate originated. When the HGE agent
was found, Dr. Walker and his colleagues performed a serological
and PCR analysis comparing it to E. chaffeensis and two
nonpathogenic strains, E. phagocytophila and E. equi.
Results showed that the HGE agent differed from E. chaffeensis
and was identical to the other two species. A more detailed evolutionary
analysis published in 2001 by Dr. Walker‘s former student,
J. Stephen Dumler, MD, of Johns Hopkins Medical Institutions,
and coworkers resulted in a major reorganization of this group
of organisms, as well as a new name for the HGE agent—Anaplasma
HME is transmitted by the lone star tick Amblyomma americanum;
HGEis transmitted by Ixodes ticks. In true evolutionary fashion,
these two microbes seem to have found complementary geographic
niches. HME occurs primarily in the southeastern and south central
regions of the United States, with an incidence in rural Missouri
of 11 to 100 cases per 100,000 people. HGE's distribution is similar
to that of Lyme disease (not surprising, since they share a vector):
more prevalent in the upper midwest and northeast U.S., with an
incidence in Connecticut of 51 cases per 100,000 people. HGE complicates
workup of Lyme disease. The Deer-Associated Infection Study Group
recently published an approach to differentiating Lyme disease,
HGE, and babesiosis (Clin Infect Dis. 2002; 34: 1184–
1191). HGE also occurs widely in Europe.
Most recently, in chapter three of the human ehrlichiosis saga,
human disease due to Ehrlichia ewingii has been reported
in a few patients in Missouri, Oklahoma, and Tennessee, about
70 percent of whom were immunocompromised because of HIV infection,
transplantation, or therapy for Crohn's disease.
Still under investigation are reports from Perm, Russia of patients
possibly infected with an E. muris-like organism.
To avoid the difficulty that has attended diagnosis of Lyme disease,
those working on human ehrlichioses formed the Consensus Approach
for Ehrlichiosis (CAFE) Society. CAFE has met for several years
with the goal of establishing criteria for diagnosing ehrlichioses,
as well as sharing samples in a de facto proficiency program.
"There has not been a big change in the last couple of meetings,"
Dr. Walker says, "which speaks to the slowness of getting recommended
serology tests to market."
Diagnostic criteria for the ehrlichioses are "still emerging,"
Dr. Walker says. He lists several "arbitrary criteria" for diagnosing
Candidate criteria for HGE are similar.
- Seroconversion—a fourfold increase in titer or an anti-E.
chaffeensis IFA >256.
- Isolation of E. chaffeensis.
- PCR detection of E. chaffeensis for two target genes.
- Positive serology (IFA >64).
- Identification of morulae on peripheral smear inside cells.
None of these criteria are ideal. "IFA is somewhat subjective,"
Dr. Walker says. Moreover, there is about 15 percent serological
cross-reactivity between E. chaffeensis and Anaplasma
"PCR is a dangerous tool in the hands of some people because
of contamination," he says. "Probing for two genes is desirable
because you are less likely to screw up twice."Even with positive
PCR, he says, "we like to have some additional confirmation, such
as seeing morulae or a single supportive titer of 64 or greater.
"We all would like to see a test that is more precise and could
be automated," Dr. Walker continues. "A few companies are interested,
but right now this disease has not got priority. People think
of it as a rare disease and as boutique testing, but in my opinion
that is not correct. These diseases are quite common; they are
just difficult to diagnose." Without good diagnostic methods,
however, establishing their true incidence is difficult.
In the absence of definitive diagnostic criteria, Dr. Walker
says, "I am definitely an advocate of treating patients empirically."
The preferred agent is doxycycline, given for more than one week.
Dr. Walker calls chloramphenicol "controversial," saying, "It
probably doesn't work." Nor do quinolones or macrolides.
The first direct evidence for a bacterial etiology of
Whipple's disease did not appear until 1991, when PCR was used
to identify a partial 16S rRNA gene sequence. In 1992 Drs. Relman
and Falkow confirmed this work, and the organism was recognized
as an actinomycete and assigned the name Tropheryma whippelii.
A highly accurate PCR test for diagnosis and monitoring was described
in 1997 (Ann Intern Med. 1236: 520–527).
Didier Raoult, MD, professor of clinical microbiology and director
of the rickettsial unit at the University of the Mediterranean
in Marseilles, reported in 2000 the first cultivation of T.
whippelii, from a 42-year-old man with blood culture-negative
endocarditis (N Engl J Med. 342: 620–625). In the
following year, Dr. Raoult isolated a second strain of T. whippelii
from an intestinal biopsy of a patient with typical relapsing
Whipple's disease. Almost 95 years after this condition was first
described, the etiologic agent was reliably cultivable.
Still unanswere is whether there are carriers for T. whippelii,
or whether it rarely occurs in intestinal mucosa that lacks histopathologic
evidence of Whipple's disease.
This year, Dr. Raoult reported immunohistochemical detection
of T. whippelii in lymph nodes. "Fifteen percent of circulating
monocytes were positive to antibodies," he says. "This will be
a good test. There is no serological test."
Right now PCR testing is too sensitive and nonspecific, Dr. Raoult
says. "There is a lot of confusion in PCR diagnosis," he says.
"Some researchers have reported PCR positivity in saliva of up
to 30 percent of patients without Whipple's disease. At this time
it is difficult to make the diagnosis on the basis of PCR alone."
Also, antibiotics other than TMP/SMX are being evaluated.
"Tropheryma whippelii is an interesting organism," says
Dr. Church. "We don't see it commonly. It manifests mostly in
middle-aged white males who are otherwise well and who present
with severe weight loss, diarrhea, and steatorrhea.
"One thing that has hampered our understanding of this organism
and our ability to devise good tests is that we couldn't cultivate
it until recently," Dr. Church continues. "Now it can be cultured
in special systems, which should lead to genetic sequences to
target." Dr. Church relates that a case of culture-negative endocarditis
was recently diagnosed in Toronto in which T. whippelii
was identified in heart valve tissue using the universal primer
approach followed by PCR with specific primers. "The clinical
laboratory only did the molecular testing because the histology
of the cardiac tissue was highly suggestive of Tropheryma whippelii,"
she says. To eradicate the pathogen, the valve must be excised
and replaced, and the patient must take antibiotics for weeks
Mycoplasmas are "the smallest of the small" and "the simplest"
of microbes, says George Kenny, PhD, professor of pathobiology
in the School of Public Health and Community Medicine at the University
of Washington, who has studied these organisms since the 1960s.
Mycoplasmas are "extraordinarily difficult to culture," he says.
"They have almost no synthetic abilities, so they require complex
media, but there is no quality control of these media." Dr. Kenny
discovered when he entered this field that it didn't matter whether
commercial media supported the growth of established cultures;
he needed to test it on patient isolates, since wild strains are
harder to grow than cultivated ones.
Mycoplasma pneumoniae, the prime mycoplasmal pathogen,
causes atypical, relatively mild "walking pneumonia." "Patients
can be quite sick, with lung infiltrates, but still up and around,
but feeling miserable," Dr. Kenny says. In a long-term (1963–1975)
study of patients hospitalized with M. pneumoniae pneumonia,
Dr. Kenny and his colleagues found that most eventually recovered.
Many associations of M. pneumoniae with neurological disease
have been reported. "Now that we have PCR, we should be able to
settle these claims," he says.
In 1981, M. genitalium was first identified. That isolate's
genome was sequenced and a PCR assay developed, which was used
to implicate the organism in nongonococcal urethritis (NGU). There
were no further isolates until 1996, when Danish workers developed
a method to grow M. genitalium in tissue culture. The genome
of M. genitalium appears to be a cut-down M. pneumoniae
genome; until recently it was the smallest bacterial genome known,
making it a subject for evolution research.
M. hominis causes mild systemic infections and possibly
postpartum infections in women with ruptured membranes. Ureaplasma
urealyticum was thought to be associated with NGU. "Now we
are quite certain this is not so," Dr. Kenny says, "since 60 percent
of healthy women carry it." He notes that U. urealyticum
could still be important in postpartum fever and when found outside
the urethra or vagina.
Dr. Kenny and his colleagues compared the rates of recovery of
M. genitalium and U. urealyticum from urethral swabs
of heterosexual men with NGU. M. genitalium was found in
22 percent of patients and four percent of controls, similar to
incidences of Chlamydia trachomatis, showing that M.
genitalium might play a major role in NGU. U. urealyticum,
on the other hand, was recovered from 42 percent of patients and
50 percent of controls. "So perhaps we can get rid of the idea
that we need to test for ureaplasmas in NGU," Dr. Kenny concludes
(J Infect Dis. 2001;183: 269–275).
M. fermentans was claimed to be a co-pathogen in AIDS
by HIV co-discoverer Luc Montanier, MD, of the Institut Pasteur,
but this has been disproved. "It is commonly found in the genital
tract and bloodstream of healthy people," Dr. Kenny says.
M. pneumoniae is readily culturable. In patients with
X-ray-proven pneumonia and significant antibodies to this microbe,
isolation had sensitivity of 64 percent and specificity of 88
percent, which meets the clinical laboratory's need. "Many bacteria
have about that isolation rate," Dr. Kenny says. "You never get
100 percent—that's folly." Unfortunately, culture is not
practical for diagnosis, since it may take several weeks. "We
could only do this study because we could prove positivity by
serodiagnosis," Dr. Kenny adds.
M. genitalium is "essentially unculturable in the clinical
laboratory," he says. M. hominis requires a specialized
medium but grows in two to five days, as does U. urealyticum.
Available EIA kits for M. pneumoniae measure IgM and IgG,
since not everyone produces both types of antibody (J Clin
Microbiol. 1992; 30: 1198–1204). "These assays are reasonably
successful,"; Dr. Kenny says, "but I believe PCR would be more
successful." Identification following PCR still requires Southern
blot analysis, however, which is too time-consuming for routine
laboratory diagnosis. "I am sure it will be reduced to a kit with
a different indicator than Southern blot," Dr. Kenny says. "We
have made our own." Japanese workers have described a real-time
PCR assay (J Clin Microbiol. 2002;40: 3854– 3856).
Mycoplasmas have no cell wall, so they are not susceptible to
beta-lactam antibiotics. They are susceptible to tetracyclines,
quinolones, streptogramins, and aminglycosides. M. pneumoniae
and M. genitalium are highly susceptible to macrolides,
including erythromycin, but M. hominis is not. Acquired
resistance to tetracycline, quinolones, and macrolides has been
Dr. Church calls mycoplasmas "a confused area. M. pneumoniae
is the most important one for us," she says, "since it is the
most common atypical cause of community-acquired pneumonia." Of
the "genital mycoplasmas"—M. genitalium, M. hominis,
and U. urealyticum—she says, "Their role in clinical
disease is not always clear."
Culture is not feasible for diagnosis, Dr. Church agrees. She
finds serology not sensitive enough and nonspecific. "The best
way to detect M. pneumoniae is with PCR," Dr. Church says.
"There are a number of good in-house assays described, even a
multiplex assay with Legionella pneumophila and Chlamydia pneumonia—the
three major causes of atypical community-acquired pneumonia."
Dr. Church's colleagues have developed such a multiplex assay
Of other mycoplasmas, she says, "Most laboratories are not too
keen to spend a lot of time on the normal flora of the genital
tract, especially Ureaplasma in vaginal specimens. So we
need to look in defined clinical conditions." She refers cases
of suspected infections with these organisms to the public health
laboratory, which does culture.
In the near future, Dr. Church sees molecular technology
as providing broader value than just illuminating the shadows
around recondite microbes.
"Microbiology, particularly bacteriology, has been a heavily
culture-based discipline," she says. "Now as we adopt testing
with molecular technology, we are not just going to find new conditions."
Even in common conditions like outpatient urinary tract infection
and chronic prostatitis, molecular methods are likely to redefine
the epidemiology and microbiology of those diseases.
With their culture-based techniques, microbiologists probably
are not retrieving all of the organisms causing those syndromes,
she says. "It is going to be a stretch for smaller laboratories
to keep up," Dr. Church acknowledges.
"On behalf of their patients, they will have to be partnered
with a larger laboratory, though it won’t necessarily be
a reference laboratory," she says. "Molecular diagnosis will become
common in many clinical laboratories in various regions over the
next 10 years."
William Check is a medical writer in Wilmette, Ill.