Page 111 - Journal of Special Operations Medicine - Spring 2015

abbreviation) that confers resistance to the beta­lactam natural disasters) tend to redistribute indigenous popu­
class of antibiotics such as methicillin and penicillin. 6,19,20 lations, disperse human­associated insects and are often
Of note, mecA is the gene responsible for the antibiotic factors in the emergence and geographic dispersion of
resistance properties of methicillin­resistant S. aureus vector­borne disease. 25–27
(MRSA), a seemingly ubiquitous pathogen responsible
for a large portion of the antibiotic resistance encoun­ Entomological Case Study
tered in the healthcare setting. The transfer of this gene
19
from one bacterial species to another has been well docu­ During a routine survey of two cockroach species (Peri-
mented and the transfer of the mecA gene into S. aureus planeta americana [the American cockroach] and Blat-
from an as­yet­unidentified bacterial species might have tella germanica [the German cockroach]) on the island
been responsible for the emergence of MRSA in the early of Oahu in Hawaii, we sought to determine whether
1960s. Furthermore, multidrug resistant strains of S. these organisms were colonized by (and possibly serv­
20
sciuri have been isolated from cattle demonstrating a po­ ing as mechanical vectors for) pathogenic bacteria. To
tential for zoonotic transmission to humans who have this end, we attempted to isolate bacteria from the outer
frequent contact with livestock. cuticles of two German and two American cockroaches.
This was accomplished by placing each animal into sep­
S. sciuri can be highly pathogenic. However, the degree arate 15mL conical tubes and covering them with 10mL
of pathogenicity appears to be strain specific. Research­ of sterile saline. Each tube was then vortexed for 10
ers have identified strains of S. sciuri that carry the genes seconds and inverted 10 times to release any microor­
necessary for the elaboration of bacterial virulence fac­ ganisms loosely attached to the outer cuticle. From each
tors such as exfoliative toxin, which is responsible for resulting suspension, 100µL was used to inoculate a set
a condition known as staphylococcal scalded skin syn­ of blood agar plates. These plates were incubated over­
drome in cases of human infection. Indeed, an exfolia­ night at 37ºC (the average human body temperature) to
21
tive toxin producing an isolate known as HBXX06 was encourage the growth of potential human pathogens. 24
shown to be highly pathogenic in piglets and caused a
fatal condition known as exudative dermatitis. 22 The next day, one of the American cockroach samples
yielded two distinct colony types: a large flat colony
S. sciuri can be readily identified and distinguished from and small pinpoint colonies. Interestingly, upon Gram
other Staphylococcus species. These organisms produce staining, both were found to be gram positive. These
large distinctive colonies on blood agar, they are usually colonies were then subcultured to fresh blood agar
pigmented, they are resistant to novobiocin, are coagu­ plates and subjected to both phenotypic (biochemical)
lase negative (i.e., does not possess a blood coagulation analysis using the Vitek2 instrument and nucleic acid­
factor that is present in certain Staphylococcus species), based analysis (mass spectrometry–mediated base­count
and are oxidase positive (i.e., they possess cytochrome determination) using the PLEX­ID system by Abbott
oxidase for aerobic respiration). Definitive identifica­ Molecular Diagnostics (Abbott Laboratories; www.
4.8
tion can be accomplished using automated identification abbottmolecular.com). 23,24 The small pinpoint colony
systems such as the Vitek2 instrument from bioMeriux was identified as a member of the Enterococcus species
(bioMeriux SA; www.biomerieux.com) or by the ap­ by both methods and the large flat colony was identi­
plication of nucleic acid­based procedures such as the fied as S. sciuri by both methods (Figures 1 and 2). In
polymerase chain reaction and sequencing. 23,24 addition, the PLEX­ID analysis revealed the presence of
the mecA gene, which may confer resistance to the beta­
Interestingly, although S. sciuri is an environmental or­ lactam class of antibiotics. A search of the literature
1
ganism, vector­mediated transmission has not previously revealed that while there have been sporadic reports of
been reported. Here, we present a case study in which S. cockroaches being colonized with Enterococcus species,
sciuri was isolated from the outer cuticle (integument or there has never been a report describing the coloniza­
skin) of an American cockroach. While this finding does tion of a cockroach by S. sciuri. Although it is notable
not prove vector transmission or demonstrate the vector that only one of the four specimens analyzed during
potential of the American cockroach it is an intriguing this study was colonized by S. sciuri, the finding of this
finding that may have public health significance. Indeed, organism associated with the outer cuticle of a rapidly
it is tempting to speculate that occasional colonization mobile insect is significant given the role of S. sciuri in
of a highly mobile insect can serve as a means of bac­ the development and evolution of human disease and
terial dispersion in densely populated urban areas. 25–28 the ubiquity of cockroaches in human habitats. 1,4,26,27
This may be particularly true during times of resource Importantly, this finding suggests that it is possible for
limitation and lapses in sanitation. Furthermore, hu­ the American cockroach to serve as both a reservoir
25
man migratory patterns and overcrowded conditions and a vector for bacterial pathogens in the tropical
(such as those that might occur during urban warfare or environment.

Staphylococcus sciuri: Entomological Case Study and Brief Review 101