- One hundred and fourteen strains of Moraxella species isolated
from marine fishery sources were investigated to determine the cause
of this organism's predominance in seafood. The nutritional requirements,
effect of pH, NaCl concentration, and temperature on growth,
utilization of carbohydrates, protein, and lipid, resistance to 12
antibiotics, sensitivity to phenethyl alcohol (PEA), production of
PEA, and a study of the deoxyribonucleic acids (DNA) of the Moraxella
strains were performed.
Two strains of Moraxella had a requirement for biotin; most other
strains, however, had no requirement for growth factors. The majority
of strains had a multiple amino acid requirement which was satisfied
by seven amino acids: leucine, isoleucine, valine, alanine, glycine,
serine, and hydroxyproline.
All strains grew in broth in the pH range of 6.9 to 8.8, with pH limits for growth by any strain being 4.9 to 10.4. All strains grew
in the presence of 6% NaCl, with most strains tolerating up to 10%.
Ninety five percent of strains tested grew at 5°C and no strain grew
at 37°C or above.
Thirty percent of all Moraxella strains were able to produce acid
from glucose. Xylose and arabinose were oxidized by 17.5 and 1.7% of
strains, respectively. Sucrose, fructose, lactose, and galactose
were not oxidized. Seven percent of strains were weakly proteolytic
while lipolytic activity was not observed in any strain.
All Moraxella strains were sensitive to tetracycline (Tc), chlorotetracycline
(Ct), oxytetracycline (Ot), streptomycin (St), neomycin
(Nm), kanamycin (Km), and nalidixic acid (Na). Half of all strains
were resistant to chloramphenicol (Ch) and nitrofurazone (Nf), 36%
were resistant to ampicillin (Am), and 70% were resistant to sulfathiazole
(Su). Thirty one strains (27.2%) were resistant to 3 IU of
penicillin G (Pe), thus, being classified as atypical Moraxella.
Atypical Moraxella strains were significantly more resistant to Ch
Moraxella strains were more resistant to PEA than were other gram
negative bacteria of fishery origin. At a concentration of 0.82
mmoles PEA/1iter, Moraxella strains were not affected; however, an
Arthrobacter strain of marine origin was totally inhibited and marine
Pseudomonas strains showed an extended lag period.
Moraxella strains produced PEA in concentrations ranging from
undetectable to 3.25 mmoles per liter. PEA production was strain dependent and substrate dependent and was not the direct function of
the cell concentration.
Moraxella strains tested showed a guanine plus cytosine mole
percent (G+C mole %) between 42.8 to 44.4. No relationship was observed
between G+C mole % and other parameters: penicillin resistance,
proteolytic ability, PEA production, or acid production from glucose
Four factors appear to allow Moraxella to predominate in seafood:
NaCl tolerance, the ability to grow at low temperatures, a simple
nutritional requirement, and production of PEA.