Microbiology of Spiroplasma and Lactic Acid Bacteria

Spiroplasma

• Detection relies on molecular techniques (PCR) due to difficulty in culturing
• Recommended treatment: doxycycline pretreatment then azithromycin (or moxifloxacin)
• Antibiotic resistance is high

The Lactic Acid Bacteria

• Gram-positive bacteria
• Includes Streptococcus, Lactobacillus, and Enterococcus
• Produce lactic acid as a product of fermentation
• Non-spore forming, non-motile, and lack cytochromes
• Obtain energy by substrate level phosphorylation and not by electron transport and oxidative phosphorylation
• Normally obtain energy only from sugars
• Limited biosynthetic capability and require many vitamins, amino acids, purines, and pyrimidines
• Aerotolerant anaerobes, growth not affected by presence of air
• Tolerant of acid, and can produce and tolerate high concentrations of lactic acid
• Found in cultured buttermilk, sour cream, cottage cheese, and cheeses

Streptococcus

• Spherical cells divide only in one plane and form chains
• Require complex media for growth
• Unable to make haem group of cytochromes or catalase
• Grown on blood agar (good source of catalase)
• Grouping of Streptococci:
  • Hemolysis: β (complete hemolysis), α (incomplete hemolysis), and γ (no hemolysis)
  • Antigenically/Serologically (Lancefield Groups): A, B, C, D, etc. based on specific carbohydrate antigen extracted by heating cells up to 150°C
• Streptococcus pyogenes (Group A Strep):
  • β-hemolytic
  • Causes many streptococcal diseases in humans
  • Antigenicity of M-proteins in the cell wall provides sub-classification into over 100 sub-serotypes
  • Found in 5-30% of healthy people as carriers in their throat and nasopharynx
  • Bacitracin sensitivity test
• Streptococcal diseases:
  • Strep Throat
  • Impetigo
  • Scarlet Fever: caused by a pyrogenic toxin-producing organism, symptoms include fever, toxic shock, and erythematous rash
  • Cellulitis: infection of the deep layers of the skin
  • Necrotizing fasciitis: highly invasive, toxigenic, infection of soft tissues and fascia
  • Non-suppurative diseases:
    • Rheumatic fever: occurs in a small percentage of individuals, 2-3 weeks after an untreated pharyngeal infection
    • Glomerulonephritis: most cases occur about a week after group A Strep infection, leads to loss of protein through kidneys and hypertension
• Other Streptococci:
  • Group B Streptococci: S. agalactiae, found in vaginal flora of 25% of women, may cause serious infections in newborns
  • Group D Streptococci: faecal flora, enterococci, cause urinary and wound infections, and are a major problem of vancomycin-resistance
  • α-hemolytic Streptococci: Viridans group, includes many species that are normal inhabitants of throat and nasopharynx of humans
  • Streptococcus pneumoniae:
    • Lancet-shaped organism, usually arranged in pairs
    • Virulent organisms are encapsulated, resist phagocytosis
    • Subdivided into 90 types on the basis of antigenicity of capsular polysaccharide
    • Found in the normal commensal of the upper respiratory tract
    • Causes streptococcal pneumonia, accounts for about one million deaths per annum worldwide, and is the second most common cause of meningitis in adults

Lactic Acid Bacteria (LAB)

• LAB are used to eliminate competition in selective media
• They can be grouped by their fermentation patterns:
  • Homofermentative: produces a single fermentation product (lactic acid) using the Embden-Meyerhof (glycolytic) pathway
  • Heterofermentative: produces lactic acid and other products (CO2 and ethanol) using the pentose phosphate pathway
• Examples of LAB and their products:
  • Lactobacillus bulgaricus: Bulgarian buttermilk, yoghurt, kefir, koumiss, Swiss, Emmental, and Italian cheeses
  • Lactobacillus acidophilus: acidophilus buttermilk, Emmental, Cheddar, and Italian cheeses
  • Streptococcus thermophilus: acid, yoghurt, and Italian cheeses
  • Streptococcus diacetilactis: acid, sour cream, ripe cream, butter, cheese, buttermilk, and starter cultures

Mycoplasmas

• Mycoplasma genitalium has the smallest known genome of any self-replicating organism (580 kbp encoding 472 genes)
• Mycoplasma pneumoniae has a larger genome (816 kbp containing 679 putative genes)
• During evolution, mycoplasmas have undergone multiple reductions in genome size and have an unusually high rate of evolution
• Mollicutes (Mycoplasma-like organisms) are:
  • Mycoplasmas: require cholesterol, parasitic on animal mucous membranes, facultative anaerobes, and over 60 species recognized
  • Ureaplasma (T-Strain Mycoplasmas): microaerophilic, require cholesterol and urea for growth, and may be associated with nongonococcal urethritis
  • Acholeplasma: widely distributed animal parasites, facultative aerobes, able to grow in the absence of sterols
  • Anaeroplasma: strict anaerobes, inhabit bovine or ovine rumen
  • Spiroplasma: helical, motile, parasites on arthropods and plants, but a few cause disease in animals

Mycoplasma pneumoniae

• Causes primary atypical pneumonia in humans (PAP or "walking pneumonia")
• Affects individuals 5-20 years old
• Symptoms range from mild flu-like disease to severe pneumonia with fever, chills, and malaise
• Protracted course with gradual resolution (month)
• Transmitted through close personal contact via respiratory droplets
• May be a prevalence of infections occurring in autumn
• The bacterium settles on a respiratory epithelial cell, binds to it, and produces hydrogen peroxide, which is responsible for much of the initial cell disruption in the respiratory tract

Diagnosis and Treatment of Mycoplasma pneumoniae

• Diagnosis:
  • Clinical symptoms
  • Serological tests (Serum cold agglutination, Complement fixation test, ELISAs)
  • DNA test (PCR) is replacing serological tests
  • Microbiological detection: not that useful because culture is slow
• Treatment:
  • Erythromycin, doxycycline (not for children), azithromycin, and levofoxacin
  • Erythromycin is often used as it is also effective against legionella

GENITAL MYCOPLASMAS

• Mycoplasma genitalium:
  • Causes non-gonococcal (non-chlamydial) urethritis (NGU)
  • May be associated with infertility in men and women
  • Transmitted by direct venereal contact and vertically transmitted from mother to offspring
• Mycoplasma hominis and Ureaplasma urealyticum:
  • 50% of normal adults have antibodies
  • Causes of non-gonococcal urethritis (NGU)
  • May be associated with infertility in men and women

Streptococcus

• Spherical cells divide only in one plane and form chains
• Require complex media for growth
• Unable to make haem group of cytochromes or catalase
• Grown on blood agar (good source of catalase)

Grouping of Streptococci

• Hemolysis:
  • β - complete hemolysis -> clear zone
  • α - incomplete hemolysis of red blood cells -> greenish-brown zone
  • γ - hemolytic - no hemolysis
• Antigenically/Serologically:
  • Lancefield Groups of β-hemolytic Streps (A, B, C, D…H and K-W)
  • Group A - S. pyogenes
  • Group B - Cattle and humans (e.g. S. agalactiae)
  • Group D - Intestinal tract of man and animals (Enterococcus)

Group A Strep

• β hemolytic
• Causes many of the streptococcal diseases of humans
• Antigenicity of M-proteins in the cell wall provides sub-classification of group A into over 100 sub-serotypes
• Habitat: 5-30% of healthy people may be carriers of group A, beta hemolytic Streps in their throat and nasopharynx

Streptococcal Diseases

• Strep throat
• Impetigo
• Scarlet fever
• Cellulitis
• Necrotizing fasciitis
• Non-suppurative diseases:
  • Rheumatic fever
  • Rheumatic heart disease