Veterinary Microbiology and Microbial Disease

P. J. Quinn, B. K. Markey, F. C. Leonard, P. Hartigan, S. Fanning, E. S. Fitzpatrick

• Editore: Wiley-Blackwell
• Anno: 2011
• ISBN:
  9781118251164
• Edizione: 2
• Argomento: Medicine
• Categoria: Veterinary Medicine

Microbiology is one of the core subjects for veterinary students, and since its first publication in 2002, Veterinary Microbiology and Microbial Disease has become an essential text for students of veterinary medicine. Fully revised and expanded, this new edition updates the subject for pre-clinical and clinical veterinary students in a comprehensive manner. Individual sections deal with bacteriology, mycology and virology. Written by an academic team with many years of teaching experience, the book provides concise descriptions of groups of microorganisms and the diseases which they cause. Microbial pathogens are discussed in separate chapters which provide information on the more important features of each microorganism and its role in the pathogenesis of diseases of animals. The international and public health significance of these pathogens are reviewed comprehensively. The final section is concerned with the host and is organized according to the body system affected.

Tables, boxes and flow diagrams provide information in an easily assimilated format. This edition contains new chapters on molecular diagnostics and on infectious conditions of the skin, cardiovascular system, urinary tract and musculoskeletal system. Many new colour diagrams are incorporated into this edition and each chapter has been updated.

Key features of this edition:

• Twelve new chapters included
• Numerous new illustrations
• Each chapter has been updated
• Completely re-designed in full colour
• Fulfils the needs of veterinary students and academics in veterinary microbiology
• Companion website with figures from the book as Powerpoints for viewing or downloading by chapter: www.wiley.com/go/quinn/veterinarymicrobiology

Veterinary Microbiology and Microbial Disease remains indispensable for all those studying and teaching this essential component of the veterinary curriculum.

Section III
Pathogenic Bacteria

Chapter 14

Staphylococcus species

Staphylococci are Gram-positive cocci, approximately 1 μm in diameter, that tend to occur in irregular clusters resembling bunches of grapes (Fig. 14.1). The name derives from the Greek words staphyle and kokkos for a ‘bunch of grapes’ and a ‘berry’, respectively. Staphylococcus species occur as commensals on skin and mucous membranes; some may act as opportunistic pathogens causing pyogenic infections.

Most staphylococci are facultative anaerobes and catalase-positive. They are non-motile and oxidase-negative and do not form spores. Two species, S. aureus subsp. anaerobius and S. saccharolyticus, are anaerobic and catalase-negative.

A total of 43 species of Staphylococcus have been described to date, seven of which are coagulase-positive or coagulase-variable species (Table 14.1). The coagulase-positive S. aureus subsp. aureus (referred to as S. aureus), S. pseudintermedius, and the coagulase- variable S. hyicus are important pathogens of domestic animals (Table 14.1). Staphylococcus intermedius was previously thought to be the major staphylococcal pathogen of dogs and cats but it is now considered that S. intermedius strains isolated from these hosts belong to the species S. pseudintermedius (Sasaki et al., 2007; Devriese et al., 2009). Coagulase production correlates with pathogenicity. Although coagulase- negative staphylococci are usually of low virulence, some occasionally cause disease in animals and humans (Table 14.2).

Usual habitat

Staphylococcal species occur worldwide as commensals on the skin of animals and humans. They are also found on mucous membranes of the upper respiratory tract and lower urogenital tract and as transients in the digestive tract. The carriage sites of the pathogenic staphylococci are usually the mucous membranes and moist areas of the skin such as the axillae or perineal area. The nares are a major site of carriage of S. aureus in animals and humans, and approximately 20% of humans are permanent nasal carriers of this organism. Staphylococcus sciuri and S. xylosus are the most common coagulase-negative staphylococci isolated from healthy domestic animals. Staphylococci are comparatively stable in the environment, and staphylococcal strains display a selective affinity for particular animal species. Transfer of staphylococcal strains between animal species and between animals and humans is limited but of importance. Transfer of methicillin-resistant S. aureus strains from humans to animals or animals to humans is of particular significance.

Key points

• Gram-positive cocci in clusters resembling bunches of grapes
• Grow on non-enriched media
• Moderately-sized white or golden colonies
• Colonies of S. aureus and S. pseudintermedius produce double haemolysis
• Facultative anaerobes, non-motile, catalase-positive
• Commensals on mucous membranes and skin
• Coagulase production correlates with pathogenicity
• Comparatively stable in the environment
• Cause pyogenic infections

Figure 14.1 Staphylococci in characteristic ‘bunches of grapes’ formations.

Differentiation of Staphylococcus species

In clinical specimens, Staphylococcus species must be differentiated from Streptococcus species and from Micrococcus species (Table 14.3). Staphylococci are generally catalase-positive and streptococci catalase- negative. Staphylococcus species are usually categorized by their colonial appearance, haemolytic pattern, biochemical profiles and ribosomal RNA gene restriction patterns (Thomson-Carter et al., 1989I. Some of the principal reactions of the coagulase-positive staphylococci are indicated in Table 14.4. It may be particularly important to distinguish S. aureus from S. pseudintermedius in certain clinical conditions, especially in dogs and cats.

Table 14.1 Coagulase-positive staphylococci and their clinical importance.

Species	Hosts	Clinical conditions
Staphylococcus aureus^a	Cattle	Mastitis, udder impetigo
	Sheep	Mastitis
		Tick pyaemia (lambs)
		Benign folliculitis (lambs)
		Dermatitis
	Goats	Mastitis
		Dermatitis
	Pigs	Botryomycosis of mammary glands
		Impetigo on mammary glands
	Horses	Scirrhous cord (botryomycosis of the spermatic cord), mastitis
	Dogs, cats	Suppurative conditions similar to those caused by S. pseudintermedius
	Poultry	Arthritis and septicaemia in turkeys
		Bumblefoot
		Omphalitis in chicks
S. pseudintermedius	Dogs	Pyoderma, endometritis, cystitis, otitis externa, and other suppurative conditions
	Cats	Various pyogenic conditions
	Horses	Rarely isolated
	Cows	Rarely isolated
S. hyicus^b	Pigs	Exudative epidermitis (greasy-pig disease)
		Arthritis
	Cattle	Mastitis (rare)
S. intermedius	Horses	Isolated from nares
	Pigeons	Isolated from upper respiratory tract
S. aureus subsp. anaerobius	Sheep	Lymphadenitis
S. delphini	Dolphins	Suppurative skin lesions
	Horses	Isolated from nares
	Pigeons	Isolated from upper respiratory tract
S. lutrae	Otters	Pathogenic significance uncertain
S. schleiferi subsp. coagulans	Dogs	Otitis externa

a, S. aureus can cause neonatal septicaemia and wound infections in many species.

b, 25–50% of S. hyicus strains are coagulase-positive.

In veterinary diagnostic laboratories, specific identification of the coagulase-negative staphylococci is ordinarily reserved for those organisms that are isolated in almost pure culture, or are recovered from sites that are normally sterile such as joints or cerebrospinal fluid.

Table 14.2 Coagulase-negative staphylococci isolated from animals.

Species	Host/Source
S. arlettae	Goats/Nares
	Poultry/Skin
S. capitis	Cattle/Milk
S. caprae	Goats/Skin
S. chromogenes	Cattle/Milk^a
	Pigs, poultry/Skin
S. cohnii	Cattle/Milk^a
S. epidermidis	Cattle/Milk^a
	Dogs, horses/Wound infections
S. equorum	Horses/Skin
S. felis^b	Cats/Otitis externa, skin infections
S. gallinarum	Poultry/Skin infections
S. haemolyticus	Cattle/Milk^a
S. hominis	Cattle/Milk
S. lentus	Pigs, sheep, goats/Skin infections
S. nepalensis	Goats/Respiratory tract
S. saprophyticus	Cats/Skin
	Cattle/Nostrils
S. sciuri	Cats and other animals/Skin infections
S. simiae	Squirrel monkeys/Gastrointestinal tract
S. simulans	Cattle/Milk^a
	Dogs, cats, pigs/Skin
S. vitulinus	Cattle, sheep, pigs/Skin
S. warneri	Cattle/Milk^a
S. xylosus	Cattle, sheep/Milk^a
	Cats, poultry, pigs, horses/Skin

a, occasionally isolated from cases of subclinical or clinical mastitis.

b, described by Igimi et al. (1989).

• Colonial characteristics: Staphylococcal colonies are usually white, opaque and up to 4 mm in diameter. The colonies of bovine and human strains of S. aureus are golden yellow. Colonies of some coagulase-negative staphylococci are also pigmented.
• Haemolysis in sheep or ox blood agar: Four staphylococcal haemolysins are recognized, alpha, beta, gamma and delta. Individual haemolysins differ antigenically, biochemically and in their effects on the red blood cells of different animal species. Strains vary in their haemolysin-producing ability, and animal strains of S. aureus and S. pseudintermedius usually produce both alpha-haemolysin and beta-haemolysin. On ruminant blood agar, the alpha-haemolysin causes a narrow zone of complete haemolysis immediately around the colony, and the beta-haemolysin produces a wider zone of partial or incomplete haemolysis. This is referred to as double haemolysis (Fig. 14.2). These haemolysins act as toxins in vivo. Coagulase-negative staphylococci exhibit variation in their ability to produce haemolysis which usually develops slowly. Isolates of S. hyicus are non-haemolytic.
• Slide and tube coagulase tests: In these tests, a suspension of staphylococci is mixed with rabbit plasma either on a slide or in a small tube. The fibrinogen in rabbit plasma i...