Presented at 2013 Arkansas Association for Food Protection annual conference. Mark E. Hart, Ph.D. Division of Microbiology National Center for Toxicological Research Food and Drug Administration

1. Mark E. Hart, Ph.D.
Division of Microbiology
National Center for Toxicological Research
Food and Drug Administration
Current Issues in Foodborne Illness Caused
by Staphylococcus aureus
The views presented in this presentation do not necessarily reflect
those of the United States Food and Drug Administration.

2. Presentation Outline
 Introduce you to Staphylococcus aureus
 General characteristics
 Clinical picture
 Antibiotic resistance
 Virulence factors
 Staphylococcus and foodborne illness
 Is it a problem and why?
 Is it an infection or an intoxication?

3. Staphylococcus
 Gram-positive coccus (0.7 - 1.2
µm, dia.) with a marked tendency
to form clusters (Gk., staphyle -
“bunch of grapes”)
 Staphylococcus are among the
hardiest of the non-sporeforming
bacteria
Heat resistant (80°C for 1
hour)
Salt tolerant (NaCl @ 2.5 M)

4. Staphylococcus
Catalase test
Coagulase test
There are greater than 50
recognized species and
subspecies of
Staphylococcus but three
are of major importance
with respect to human
infections;
S. aureus (Coag+
)
S. epidermidis (Coag-
)
S. saprophyticus (Coag-
)
There are greater than 50
recognized species and
subspecies of
Staphylococcus but three
are of major importance
with respect to human
infections;
S. aureus (Coag+
)
S. epidermidis (Coag-
)
S. saprophyticus (Coag-
)

5. Too close for comfort!Too close for comfort!
 Estimates suggest thatEstimates suggest that
30 - 40%30 - 40% of the humanof the human
population arepopulation are
asymptomaticallyasymptomatically
colonized at any givencolonized at any given
time on one or more oftime on one or more of
their mucosal surfacestheir mucosal surfaces
 Up toUp to 70%70% of people mayof people may
be transiently colonizedbe transiently colonized
 Anterior nares are theAnterior nares are the
most common site ofmost common site of
colonizationcolonization
 Approximately 90% of
health-care workers
carry the organism
People who are colonized have a higher risk of infection than noncolonized persons.

6. Predisposing Conditions
 The very young and the very old
 Persons with traumatic or operative
wounds, burns, or other serious skin
lesions
 Persons with chronic debilitating
disorders such as diabetes mellitus,
cancer, or cystic fibrosis
It is therefore, not surprising that serious staphylococcal
disease is most often the result of hospital-acquired
infections.

7. Staph – pathogen extraordinaire!
 Each year an estimated 500,000 patients in
American hospitals contract staphylococci
infections
 Most common cause of
endocarditis
nosocomial infection
skin and soft tissues
cellulitis, osteomyelitis, and septic arthritis
 Common cause of bacteremia, nosocomial
pneumonia, foodborne disease, implant infection,
abscess, etc
 Causes illnesses that range from minor skin
infections and abscesses to life-threatening
diseases such as pneumonia, meningitis, bone and
joint infections and infections of the heart and
bloodstream.
 Toxemias such as food poisoning, scalded skin
syndrome, and toxic shock syndrome.

8. Toxic epidermal necrolysisBullous impetigo
Folliculitis Impetigo circinate
Clinical manifestations include —

9. Necrosis of the gum tissue
in an AIDS patient
Toxic shock syndrome - Fatal infection with
cutaneous and soft tissue involvement
Clinical manifestations include —

10. Bacterial endocarditis with
characteristic vegetations
caused by growth of S.
aureus on the heart valves.
Clinical manifestations include —

11. Osteomyelitis
Staphylococcal
Pneumonia
Clinical manifestations include —

12. So…what makes S. aureus such a
“good” pathogen?
Antibiotic resistance
Hospital-acquired (HA) methicillin resistant
Staphylococcus aureus (MRSA) endemic in most
hospitals
The emergence of a community-associated (CA)
MRSA not seen before 2000
The emergence of livestock-associated (LA) MRSA
Capacity to produce a wide variety of virulence
factors (up to 40 and still growing!)

13. Evolution of Drug Resistance inEvolution of Drug Resistance in
Staphylococcus aureusStaphylococcus aureus
S. aureusS. aureus Penicillin-resistant
S. aureus
Penicillin-resistant
S. aureus
1950s 1960s
Methicillin (1959)Penicillin (1941)
1997
2002
Vancomycin-resistant
S. aureus
(VRSA)
Vancomycin-resistant
S. aureus
(VRSA)
Methicillin-resistant
S. aureus (MRSA)
Methicillin-resistant
S. aureus (MRSA)
Vancomycin
intermediate-resistant
S. aureus (VISA or GISA)
Vancomycin (1957)
MRSA first reported in UK (1961) followed by US (1968)

14. Dancer, S. J. J. Antimicrob. Chemother. 2008 61:246-253;
doi:10.1093/jac/dkm465
Mortality rates of staphylococcal
bacteraemia over time
(1941) (1959)
Vancomycin (1957)

15. Objective: To describe the
incidence and distribution
of invasive MRSA disease in
9 US communities and to
estimate the burden of
invasive MRSA infection in
the United States in 2005.
Conclusions: It is
estimated after adjusting
for age, race, and sex to the
US population, that 18,650
in-hospital deaths occurred
in 2005 as a result of
invasive MRSA infections.
By comparison, that same
year, roughly 16,000 people
in the US died from AIDS.
How serious are MRSA infections?
JAMA, October 17, 2007 - Vol. 298, No. 15

16. A new “kid in town,”
community-associated (CA) MRSA

17. Outbreaks of CA-MRSA have occurred among:
Athletic teams - football, wrestling, rugby,
fencing
Correctional facilities
Military barracks
Daycares and schools
Dormitories

18. Year Sport
No. infected
(attack rate)
Infection and
transmission factors
19941
High School
Wrestling
6 (19%) Close contact
20002
College
Football
10 (14%)
Close contact, shared
items, skin trauma
20033
College
Football
10 (10%)
Close contact, skin
trauma, poor hygiene
20034
Pro Football 5 (9%)
Close contact, skin
trauma, poor hygiene
20035
College
Football
11 (10%)
Close contact, shared
items, skin trauma
1
Lindenmayer JM, et al. Arch Intern Med 1998;158:895-9.
2
Kainer MA. MRSA among college football team. (CDC unpublished)
3
Begier EM, et al. Clin Infect Dis. 2004;39:1446-53.
4
Kazakova SV, et al. New Engl J Med. 2005;352:468-75.
5
Nguyen DM, et al.Emerg Infect Dis. 2005;11:526-532.
MRSA Outbreaks among U.S. Sports Teams
(1994-2004)

19. A new “kid in town,”
community-associated (CA) MRSA

20.  Survey of 11 EDs throughout US in Aug 2004Survey of 11 EDs throughout US in Aug 2004
 422 patients with skin & soft tissue infections422 patients with skin & soft tissue infections
 75% (320/422) caused by75% (320/422) caused by S. aureusS. aureus
 59% were MRSA (15% - 74%) and of these 97% were59% were MRSA (15% - 74%) and of these 97% were
pulse-field type USA-300pulse-field type USA-300
KC -KC - 74%74%
Atlanta - 72%Atlanta - 72%
Charlotte, NC - 68%Charlotte, NC - 68%
New Orleans - 67%New Orleans - 67%
Albuquerque - 60%Albuquerque - 60%
Phoenix - 60%Phoenix - 60%
 Philadelphia - 55%Philadelphia - 55%
 Portland, OR - 54%Portland, OR - 54%
 Los Angeles - 51%Los Angeles - 51%
 Minneapolis - 39%Minneapolis - 39%
 New York -New York - 15%15%
Prevalence of CA-MRSAPrevalence of CA-MRSA

21. Clinical Presentation of CA-MRSAClinical Presentation of CA-MRSA
Cellulitis
75 - 80% of CA-MRSA infections are of the skin and soft tissues

22. A new “kid in town,”
community-associated (CA) MRSA
• Numerous community outbreaks by predominantly two PFGE
types - USA300 and USA400
• Most notably in
 health care settings in Canada, Native Americans, children in day
care, and a maternity ward in New York (USA400)
 children, correctional facility inmates, participants in sports teams,
men who have sex with men, and military recruits (USA300)
• CA-MRSA is not an archetype to HA-MRSA
• Fatal infections in otherwise healthy individuals (USA400)
 Four pediatric deaths – Minnesota and North Dakota, 1997-1999.
MMWR 1999, 48:707-710
• These isolates all produced Panton-Valentine leukocidin (PVL)
• Genomic analysis of one of these isolates (MW2) revealed 19
novel genes for virulence factors as compared to 5 hospital
strains
• Carry the SCCmec type IVa mobile element
• Susceptible to non β-lactam antibiotics other than
erythromycin

23. Extracellular Proteins of S. aureus
(toxins, enzymes, and cell wall-associated proteins)
• Coagulase
• Enterotoxins
• Hemolysins (α-δ)
• Lipase
• Toxic shock syndrome
toxin
• Leukocidin
• Collagenase
• Hyaluronidase
• Acid phosphatase
• Endopeptidase
• Metalloprotease
• Penicillinase
• Microbial surface
components recognizing
adhesive matrix
molecules (MSCRAMMs)
• Nuclease
• Exfoliative toxins (A, B)
• Staphylokinase
• Phospholipase
• Pyrogenic exotoxin
• Fibrinolysin
• Elastase
• Protein A
• Alkaline phosphatase
• Serine protease
• Thiol protease
• Capsule and biofilm
formation
Includes cell wall-associated
binding proteins for collagen,
fibrinogen, fibronectin, and
bone-sialo protein

24. What about StaphylococcalWhat about Staphylococcal
Food Poisoning?Food Poisoning?
Taken from Gladwin and Trattler,Taken from Gladwin and Trattler, Clinical microbiology madeClinical microbiology made
ridiculously simpleridiculously simple, Edition 2 (1999), MedMaster Inc., Miami, Edition 2 (1999), MedMaster Inc., Miami

25. It is estimated (Scallan et al., Emerg. Infect. Dis., 2011)It is estimated (Scallan et al., Emerg. Infect. Dis., 2011)
that of the 48 million foodborne illnesses (1 in 6that of the 48 million foodborne illnesses (1 in 6
Americans) that occur in the United States each year, 9.4Americans) that occur in the United States each year, 9.4
million are caused by known pathogens.million are caused by known pathogens.
Is staphylococcal foodborne illness a problem?Is staphylococcal foodborne illness a problem?
1998 – 2008 surveillance data recorded 6,795 outbreak-1998 – 2008 surveillance data recorded 6,795 outbreak-
associated illnesses resulting in 333 hospitalizations, and 3associated illnesses resulting in 333 hospitalizations, and 3
deaths rankingdeaths ranking S. aureusS. aureus 44thth
behind norovirus,behind norovirus, SalmonellaSalmonella,,
andand Clostridium perfringens.Clostridium perfringens.

26. Infection or intoxication?
 Staphylococcal food poisoning (SFP) is caused byStaphylococcal food poisoning (SFP) is caused by
preformed toxin, known aspreformed toxin, known as staphylococcal enterotoxinsstaphylococcal enterotoxins
(SE), production in improperly handled foods,(SE), production in improperly handled foods,
therefore, SFP is a toxemia!therefore, SFP is a toxemia!
 Utilizing the MMWR surveillance report (06/28/2013)Utilizing the MMWR surveillance report (06/28/2013)
for 1998 – 2008 which recorded 458 outbreaksfor 1998 – 2008 which recorded 458 outbreaks
consisting of 6,741 confirmed and suspected illnesses,consisting of 6,741 confirmed and suspected illnesses,
 illnesses most often occurred in persons ≥ 20 yearsillnesses most often occurred in persons ≥ 20 years
of age (85%)of age (85%)
 had a median incubation period of 4 hourshad a median incubation period of 4 hours
 diarrhea was commonly reported (≥ 86%)diarrhea was commonly reported (≥ 86%)
 abdominal cramps (median of ≥ 61%) and vomitingabdominal cramps (median of ≥ 61%) and vomiting
(median of 87%)were reported and(median of 87%)were reported and
 median duration of illness was 15 hoursmedian duration of illness was 15 hours
 How much toxin does it take?How much toxin does it take? In humans and
nonhuman primates, 24- to 48-h episodes of retching,
vomiting, and diarrhea every 15 to 30 minutes without
fever resulted when nanogram quantities of SEs were
ingested!

27.  Meat or poultry dishes were the most commonMeat or poultry dishes were the most common
foods reported accounting for 55% of allfoods reported accounting for 55% of all S. aureusS. aureus
outbreaks; primarily pork of the ham variety.outbreaks; primarily pork of the ham variety.
 Foods implicated were most often prepared in aFoods implicated were most often prepared in a
restaurant or deli (44%)restaurant or deli (44%)
 The most common factors contributing to theThe most common factors contributing to the
occurrence of an outbreak were errors in foodoccurrence of an outbreak were errors in food
processing and preparation and contamination by aprocessing and preparation and contamination by a
food workerfood worker
Infection or intoxication?
(cont)
Reported errors included –
allowing foods to remain at room or outdoor temperature for several
hours (58%)
insufficient time or temperature during reheating (57%)
slow cooling of prepared foods (44%)
insufficient time or temperature during the initial cooking process (40%)
preparing foods more than one-half day in advance of serving (33%)
insufficient time or temperature during hot holding (33%)
and inadequate cold holding temperature (22%)

28. Characteristics of
staphylococcal enterotoxins (SE)
Molecular sizes ranging from 22 – 29 kDa
Unusually resistant to heat (biologically active
despite boiling for 1 h)
Generally resistant to proteolysis (trypsin and
pepsin) and acids (such as stomach acid) and slightly
resistant to desiccation.
They are secreted by all human-pathogenic S. aureus
Currently S. aureus strains can secret from 1 to 23 of
at least 23 serologically distinct enterotoxins
SEs are defined by emetic activity when ingested by
humans or when given orally to nonhuman primates
Almost all of the SEs are encoded on variable genetic
DNA elements
Note: Schlievert et al., Clin. Infect. Dis. (2008) reports a
strain that expresses all 23!

29. Over half of theOver half of the
SEs are encodedSEs are encoded
on mobileon mobile
genetic elementsgenetic elements
(plasmid,(plasmid,
bacteriophages,bacteriophages,
transposons, andtransposons, and
pathogenicitypathogenicity
islands)islands)

30. Mom says, “Wash your hands!!!