Resident

The resident flora of teat skin has been examined using scanning electron microscopy, discovering that the natural flora was not spread uniformly over the skin.

Only a very small part of the surface was covered with bacteria and some were present in small niches of the skin (FIRSTENBERG-EDEN et al. 1979).

A tape stripping technique was used to investigate the teat skin flora (ORR and TAYLOR 1968). The authors applied 15 tapes successively to the same area of teat skin and determined the total bacteria count. A gradual decline in the counts from successive tapes was noted, which reflected the numbers of bacteria within the different layers of the stratum corneum. These results show that the bacteria not only stick to the surface of the stratum corneum, but also can be recovered from as many as 15 cell layers of the stratum corneum.

Cows of different age and breed (kept on grass) were chosen to study their teat skin flora by swabbing twice a week before the afternoon milking. The teat canal and milk were also sampled on the same occasions (CULLEN and HERBERT 1967). All 13 cows were in the same stage of lactation. The following types of organisms were found, in descending order:

1. Coagulase-negative, non-haemolytic staphylococci 2. Coagulase-negative, slightly haemolytic staphylococci 3. Corynebacterium bovis (mainly in milk)

4. Aesculin-splitting streptococci 5. Staphylococcus aureus 6. Streptococcus uberis

7. Viridans streptococci (α-haemolytic, non-aesculin-splitting) 8. Bacillus spp.

9. Actinomyces spp.

10. Coliform organisms, mainly E. coli 11. Pseudomonas spp.

12. Proteus spp.

Only the first four groups could be included in the statistical analysis, because the rest did not occur in sufficient numbers.

Comparing the three different sampling locations, the authors found that the teat skin yielded significantly higher numbers of coagulase-negative, non-haemolytic staphylococci, coagulase-negative, slightly haemolytic staphylococci and aesculin-splitting streptococci than the teat canal or milk (CULLEN and HERBERT 1967).

Seasonal trends for staphylococci and streptococci could not be observed, only C.

bovis showed a significant decline during the season.

Marked differences in colony counts between quarters of the same cow were found.

Some quarters yielded higher bacteria counts than others, which was a steady tendency throughout the lactation.

Mastitis pathogens were not observed very frequently. Sc. uberis was isolated mostly on the teat skin and in milk, whilst S. aureus occurred mostly on the teat skin.

Between cows, differences in colony number and distribution of colonies were noted (CULLEN and HERBERT 1967). Other investigators (ORR and TAYLOR 1968) observed coagulase-negative staphylococci as the predominant group of bacteria present on teat skin. S. aureus was not isolated from the teat skin despite S. aureus infections existing in some of the cows.

The resident teat skin flora of 10 heifers was examined by WOODWARD et al.

(1987). Aerobic isolates from around the teat orifice of each teat were determined by swabbing. No information was given as to whether these cows were kept indoors or on grass. Most heifers had corynebacteria, staphylococci, bacilli and Acinetobacter spp. on at least three of four teats. Other genera were present on at least one or two teats per heifer. Table 7 demonstrates the teats colonised per heifer with each genus of normal flora.

Tab. 7: Teats colonised per heifer with each genus of normal flora (WOODWARD et al. 1987)

Number of teats per heifer colonised Normal flora isolates

a Heifer identification number

Four to eleven different colony types were found on teat skin and 23 - 32 different colony types per heifer, shown in Table 8 (WOODWARD et al. 1987).

Tab. 8: Distribution of normal flora (WOODWARD et al. 1987)

Number of colony types *

Range x (± sd)

Flora per teat 4 - 11 7 (± 2) Flora per heifer 23 - 32 28 (± 3)

* Colony types counted because some were identified to species, but others only to genus

In another experiment, the teat skin flora of eleven cows during the first four weeks of the dry period and of 17 neonatal calves during their first two to three months of life was investigated (WOODWARD et al. 1988). In cows, large Gram-positive rods typical of Bacillus spp. and Streptomyces spp., smaller coryneform Gram-positive rods, Gram-positive cocci and a few Gram-negative rods of several colony types were detected. The predominant bacteria were the large Gram-positive rods and Gram-positive cocci (WOODWARD et al. 1988).

The same authors followed the acquisition of resident flora on seven neonatal calves during a 44-day sampling period. No information is given about the bedding material or the environment of these calves. Large positive rods, coryneform Gram-positive rods, Gram-negative rods and Gram-Gram-positive cocci were detected as a mixture in the first two to three days of life, with the Gram-negative rods the predominant group. After two days, the Gram-positive cocci increased in numbers, until they predominated from Day 5 on. The dominant Gram-positive cocci were identified and biotyped. S. hominis (biotype a), S. epidermidis (biotypes b and c), and S. hyicus (biotype d) were the most common bacteria found in the normal flora of these calves (Table 9).

Tab. 9: Acquisition of resident flora: occurrence and distribution of 15 Gram-positive cocci biotypes found on teat skin of newborn calves (WOODWARD et al. 1988)

Species (biotype) Number of calves with

the same biotype Times biotype found (%) n = 48

It was concluded that coagulase-negative staphylococci represent the major resident flora on teat skin of calves (WOODWARD et al. 1988).

Investigations of the distribution of coagulase-negative staphylococci in milk samples and on teat skin of dairy cows showed a differing prevalence. S. xylosus, S. sciuri and S. haemolyticus predominated in the teat skin and teat apex samples. In milk samples with raised California Mastitis Test (CMT) scores, S. epidermidis, S. hyicus ssp. chromogenes and S. simulans were found. Strains like S. cohnii, S. capitis, S.

hyicus ssp. hyicus and a heterogenous collection of micrococci were isolated from teat swab samples, but not from milk samples (DEVRIESE and KEYSER 1980).

Some authors observed a consistency of either high or low populations of specific bacterial species on individual teats, but no specific information about type or amount of bacteria was given (ZARKOWER and SCHEUCHENZUBER 1977). Most cows have a characteristic level of staphylococci on teat skin. On some teats, a persistent low level of CNS could be obtained despite the fact that one or more quarters of these cows had a chronic S. aureus infection (ORR and TAYLOR 1968).

RENDOS et al. (1975) agreed with the results of CULLEN and HERBERT (1967) that, regardless of bedding type, staphylococci were most numerous and streptococci were also common on teat skin, but only a few coliforms could be found (RENDOS et al. 1975).