# Preliminary Findings on Antibacterialativity of Selected Marine Invertebrates
## 4 Discussion  
This study provides the first comprehensive evaluation of antibacterial activity from extracts of marine invertebrates: limpets, snails, mussels and urchins, collected in the Adriatic Sea, revealing significant inhibitory effects on both environmental and reference bacterial strains. Furthermore, to our knowledge, this is the first study on the antibacterial activity of extracts from marine organisms against the members of soil-derived _Paenibacillus_ sp., _Bacillus_ sp. and _Geobacillus_ sp. as well as of seawater _Citrobacter_ sp. representatives (Table 1). The results show a very diverse sensitivity of the tested bacterial strains to combined solvent extracts from marine invertebrates, while those environmentally derived \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{5}{c}{**Marine Invertebrates**} \\ \hline
**Bacteria** & _Patella_ **sp.** & _Gibula_ **sp.** &
\begin{tabular}{c} _Mytitus_ \\ _galloproincialis_ \\ \end{tabular} & _Arbacia lixula_ \\ \hline _Paenibacillus cookii_ strain L1.2 & 0 & 0 & 0 & 0 \\ \hline _Bacillus licheniformis_ strain MA-42 & 2 & 2 & 3 & 1 \\ \hline _Geobacillus_ sp. HBB272 & 0 & 3 & 1 & 0 \\ \hline _Citrobacter_ sp. strain YB074 & 6 & 5 & 4 & 5 \\ \hline _Citrobacter freundii_ strain EF55 & 4 & 4 & 4 & 3 \\ \hline _Citrobacter_ sp. strain EB-C-4 & 4 & 5 & 3 & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Diameters of the inhibition zone (mm) of extracts from marine invertebrates against environmental bacteria. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{5}{c}{**Marine Invertebrates**} \\ \hline
**Bacteria** & _Patella_ **sp.** & _Gibula_ **sp.** &
\begin{tabular}{c} _Mytitus_ \\ _galloproincialis_ \\ \end{tabular} & _Arbacia lixula_ \\ \hline _Escherichia coli_ & 0 & 0 & 0 & 0 \\ \hline _Klebsiella aerogenes_ & 0 & 0 & 0 & 0 \\ \hline _Staphylococcus aureus_ & 0 & 0 & 0 & 0 \\ \hline _Staphylococcus aureus_ subsp. & 1 & 0 & 0 & 0 \\ _aureus_ Rosenbach & 1 & 2 & 1 & 0 \\ \hline _Salmonella enterica_ subsp. & 1 & 1 & 1 & 0 \\ _ enterica_ serovar Enteritidis & & 1 & 1 & 0 \\ \hline _Salmonella enterica_ subsp. _ enterica_ serotype Typhimurium & 1 & 1.5 & 1 & 0 \\ \hline _Listeria monocytogenes_ & 3 & 3.5 & 4 & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Diameters of the inhibition zone (mm) of extracts from marine invertebrates against reference bacteria. were more sensitive than the reference strains (Tables 2 and 3). All three strains of seawater _Citrobacter_ sp. were inhibited by all four extracts tested. The potent in vitro antibacterial activity could be due to the fact that all selected organisms have very limited mobility, which prevents their escape from predators, epiphyytes or pathogens, so it is possible that they possess some chemical defence mechanisms; in fact, marine invertebrates, living within very difficult, competitive, and hostile surroundings represent a great reservoir for compounds with improved bactericidal activity [11]. It is important to point out that some members of _Citrobacter_ sp. are multidrug-resistant [23] and are considered a growing threat to public health. They are frequently detected in neonatal illnesses, urinary tract infections and patients with severe underlying chronic diseases, including hypertension, diabetes, cancer and respiratory infections, or in immunocompromised patients [24]. The soil-associated _Bacillus_ and _Paenibacillus_ species are increasingly associated with various human diseases and are considered strains of increasing clinical relevance due to their virulence properties [25]. In addition, _B. licheniformis_ was identified as a cause of recurrent sepsis [26], while _Paenibacillus_ infections in infants are probably underestimated so effective treatments are urgently needed [27]. Unfortunately, the _P. cookii_ tested in this study was not inhibited at all, but it is noteworthy that _B. licheniformis_ was inhibited by all four extracts of marine invertebrates as members of _Citrobacter_ sp.